JP2863977B2 - Optical disk drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device for recording and reproducing information by condensing a light spot on an optical disk which is an optical information recording medium.

[0002]

2. Description of the Related Art In an optical disk apparatus, when irradiating a light spot on an optical disk which is an optical information recording medium, the light spot should be focused on the optical disk and the optical axis should be perpendicular to the optical disk. It is especially important to In order to match the focal points of the light spots on the optical disk, reflected light of the irradiated light is received to detect the focal point position, and the lens position is adjusted based on the result.

FIG. 70 is a schematic view showing a part of a conventional optical disk device, and FIG. 71 is an enlarged conceptual diagram of an information track for showing a relationship between an information track of an optical disk and a defocus signal of each light spot in the conventional optical disk device. is there. In FIG. 70, 101 is an optical disk, 102 is a semiconductor laser as a light source, 103 is a light beam emitted from the semiconductor laser 102,
104 is a collimator lens for converting the light beam 103 into a parallel light beam, 105 is a beam splitter, 106 is an objective lens, 10
7 is a light spot focused on the optical disk 101, 108a,
108b is a focusing coil for driving the objective lens 106 in the optical axis direction, 109 is a converging lens, 110 is a defocus detecting optical element such as a cylindrical lens for detecting the defocus amount of the light spot 107 with respect to the optical disk 101. Reference numeral 111 denotes a photodetector and a differential amplifier for obtaining a defocus signal and an information signal. 112 is a semiconductor laser
102, objective lens 106, photodetector and differential amplifier 111
It is an optical head device section configured by the above. Reference numeral 113 denotes an output (a defocus signal) of the photodetector and the differential amplifier 111, and a defocus signal of the light spot 107 with respect to the optical disc 101 is output. Reference numeral 114 denotes a defocus control circuit.

In FIG. 71, reference numeral 115 denotes a land portion on which information is recorded, 116 denotes a groove portion, and 117 denotes a groove interference signal observed as a defocus signal when the light spot 107 is scanned in a direction crossing the information track. This signal is superimposed on the defocus signal 113. One cycle of the groove interference signal corresponds to the interval between the information tracks (this is equal to the interval between the land portions or the interval between the groove portions).

Next, the operation will be described. In FIG. 70, a light beam 103 emitted from a semiconductor laser 102 is converted by a collimator lens 104 into a parallel light beam. The light beam 103 transmitted through the beam splitter 105 is condensed as a light spot 107 on the optical disk 101 by the objective lens 106. Light beam 10 reflected from optical disk 101
3 is reflected by the beam splitter 105, passes through the defocus detecting optical element 110, and is
The light is received by 111 and converted into an electric signal.

Defocus correction of the light spot 107 with respect to the optical disk 101 is performed by correcting the light spot 10 with respect to the optical disk 101.
7 is detected by using a defocus detection optical element 110, a photodetector and a differential amplifier 111, and the output thereof is output to a focusing coil 10 via a defocus control circuit 114.
This is performed by controlling the driving of the objective lens 106 in the direction of its optical axis by applying the voltage to 8a and 108b.

FIG. 72 is disclosed, for example, in Japanese Patent Publication No. 62-18973 and G. Bouwhiis et al., "Principl
es of Optical Disk System
m, "Adam Hilger, pp. 77-79.
(1985) is a configuration diagram showing a conventional device used for a general focus error detection called a pupil occlusion method or a half-beam method described in (1985), showing a case where a shielding plate is used. Figures 73-78
Fig. 4 shows the relationship between the defocus state of the light spot on the optical disk and the shape of the light spot on the photodetector of the conventional device.

In FIG. 72, reference numeral 201 denotes a light emitting source such as a semiconductor laser which emits a recording / reproducing light beam. In the drawing, the luminous flux emitted from the semiconductor laser is shown as E. Reference numeral 202 denotes a beam splitter that transmits the outgoing light beam E and reflects a reflected light beam R from the optical disc 206 described later. Collimator lens, 205
Reference numeral denotes an objective lens which focuses the emitted light beam E on an optical disk 206 such as an optical disk and converts the reflected light beam R from the optical disk into a parallel light beam. Reference numeral 207 denotes a shielding plate that shields almost half of the light beam R reflected from the optical disk 206.

Reference numeral 209 denotes a two-segment photodetector for receiving the reflected light beam R1 part of which is removed by the shielding plate 207, and two light receiving surfaces 210 and 21 arranged in a plane perpendicular to the optical axis A
Consists of 1 The direction of the dividing line between the light receiving surfaces 210 and 211 substantially coincides with the tangential direction of the upper edge 208 of the shielding plate 207. Usually, this two-segment photodetector is constituted by a PIN photodiode. S1 and S2 are each light receiving surface
210 and 211, the difference between S1 and S2 output from the comparator 214 is the focus error signal F.
ES.

Next, the operation of the conventional apparatus shown in FIG. 72 will be described with reference to FIGS. 73 to 78. Outgoing light flux E emitted from light emitting source 201 when recording and reproducing information
Passes through the beam splitter 202 and passes through the collimator lens 20.
At 3, the light beam becomes a parallel light beam, is condensed by the objective lens 205, and is irradiated on the optical disk 206. Then, the reflected light beam R reflected by the optical disk 206 reaches the beam splitter 202 via the objective lens 205 and the collimator lens 203,
The light is reflected by the beam splitter 202. Next, after almost half of the reflected light beam R is shielded by the shielding plate 207, the remaining reflected light beam R1 is incident on the two-divided photodetector 209.

As shown in FIGS. 73 and 74, when the converging point of the outgoing light beam E is located on the optical disk 206, the converging point of the reflected light beam R1 is shifted to the light receiving surface of the two-part photodetector 209. It is adjusted so as to be located at the gap between 210 and 211, that is, on the dividing line 209a in the two-part photodetector 209. Therefore, when the converging point of the outgoing light beam E is located on the optical disk 206, the amounts of light incident on the light receiving surfaces 210 and 211 are equal, and the electric signals S1 and S2 from the light receiving surfaces 210 and 211 are also equal. In FIG. 74, P1 is a condensed spot of the reflected light beam R1 on the light receiving surface.

Next, when the optical disk 206 approaches the objective lens 205, as shown in FIG. 75, the reflected light flux R1 enters the two-divided photodetector 209 before being converged. Therefore, the figure
As shown at 76, most of the reflected light flux R1 enters the light receiving surface 210 and hardly enters the light receiving surface 211. P in FIG. 76
Reference numeral 3 denotes the shape of the reflected light beam R1 on the light receiving surface 210.

Conversely, if the distance between the optical disk 206 and the objective lens 205 becomes longer, the reflected light beam R1 is converged before the two-divided photodetector 209 as shown in FIG. Therefore, as shown in FIG. 78, most of the reflected light flux R1 enters the light receiving surface 211 and hardly enters the light receiving surface 210. P5 in FIG. 78 indicates the shape of the reflected light beam R1 on the light receiving surface 211.

The light receiving surfaces 210, 21 on which each reflected light beam R1 is incident
1 generates currents S1 and S2 proportional to the respective received light amounts, so that the focus error signal FES can be obtained by taking the difference between S1 and S2. 73 and 74
As shown in the figure, the distance between the optical disk 206 and the objective lens 205 is appropriate, and the focal point of the emitted light beam E is just
This is because the difference between S1 and S2 becomes zero when it is located on the upper side. Also, if the distance between the optical disk 206 and the objective lens 205 is too short as shown in FIGS.
If the distance between 6 and the objective lens 205 is too long, the distance becomes negative (or positive). The focus error signal FES obtained in this way is supplied to an objective lens actuator (not shown) through a phase corrector and an amplifier, and the emitted light beam E
Is always kept on the optical disk 206.

Here, the focus error signal FES is defocused Δ
The range that changes in proportion to x (the distance between the converging point of the emitted light beam E and the optical disk 206) is called a linear zone. The width of the linear zone according to the pupil occlusion method is 2-3 μm. Figure
FIG. 79 is an enlarged view of the vicinity of the converging spot P1 to show the relationship between the converging spot P1 on the two-part photodetector 209 and the dividing line 209a. FIG. 80 shows the relationship between the focus error signal FES and the defocus Δx. Here, as shown in FIG. 79, the width d ₂ of the division line 209a of the two-divided photodetector 209 is assumed to be sufficiently smaller than the spread of the focused spot P1. For details, see G. Bouwhuis et al., “Princ
iples of Optical Disc Sys
tem, "Adam Hiller, pp. 77-
79 (1985) Or Irie et al. “Focu
s Sensing Characteristics
of the Pupil Obscuration
Method for Continuously
Grooved Disks, "Jpn. J. Ap
pl. Phys. 26, p. p. 183-186
(1987).

FIG. 81 is a perspective view showing a configuration in which a roof-type prism is used to perform the pupil blocking method or the half light beam method described above. FIGS. 82 to 84 show the relationship between the defocus state of the light spot on the information recording surface and the position and shape of the light spot on the photodetector of the conventional device. In FIG. 81, reference numeral 301 denotes a light source such as a semiconductor laser which emits a light beam for recording / reproducing. The light beam emitted from the light source 301 is indicated by E. Reference numeral 302 denotes a collimator lens for converting the light beam E emitted from the light source 301 into a parallel light beam. Reference numeral 303 denotes a beam splitter that reflects a parallel light beam from the collimator lens 302 and transmits a reflected light beam R from an optical disk 305 described later.
5 on the information recording surface 323 and the optical disk 30
5 is an objective lens that converts the reflected light beam R from 5 into a parallel light beam.

Reference numeral 306 denotes a condensed spot formed on the information recording surface 323 of the optical disc 305. Reference numeral 307 denotes a guide groove, which is engraved in the x direction as shown in the figure.
Here, the y direction is a direction that is in a plane parallel to the optical disc 305 and orthogonal to the guide groove 307. Also, z
The direction is a direction perpendicular to the information recording surface 323. Reference numeral 308 denotes a converging lens for condensing the reflected light beam R on a two-divided photodetector 311, 315, which will be described later. . Reference numeral 310 denotes a ridge line of the roof prism 309, which faces the y direction. Reference numeral 311 denotes a two-segment photodetector for receiving the light beam R1, which is composed of two light receiving surfaces 312 and 313 arranged in a plane perpendicular to the optical axis A. 314 is a two-segment photodetector
The light spot on 311. Reference numeral 315 denotes a two-segment photodetector for receiving the light beam R2, which comprises two light receiving surfaces 316 and 317 arranged in a plane perpendicular to the optical axis A.
Reference numeral 318 denotes a light spot on the two-segment photodetector 315.

The direction of the dividing line which is the boundary between the light receiving surfaces 312 and 313 and the direction of the dividing line which is the boundary between the light receiving surfaces 316 and 317 substantially coincide with the direction (the y direction) of the ridge 310 of the roof type prism 309. ing. Usually, these two-split photodetectors are PI
It is composed of an N-type photodiode. Also, S
1 represents the sum of the output signals obtained from the light receiving surfaces 312 and 317, and S2 represents the sum of the output signals obtained from the light receiving surfaces 313 and 316. Then, the difference between S1 and S2 is taken out by the differential amplifier 319 and becomes the focus error signal FES. This focus error signal FES is used as a phase compensation circuit / amplifier.
It is supplied to the objective lens driving mechanisms 321 and 322 via 320.

Next, the operation of the conventional apparatus shown in FIG. 81 will be described with reference to FIGS. When recording and reproducing information, the emitted light flux E emitted from the light source 301 is used.
Is converted into a parallel light beam by the collimator lens 302, reflected by the beam splitter 303, and travels to the objective lens 304. Next, the emitted light beam E is condensed by the objective lens 304 and is radiated on the information recording surface 323 as a condensed spot 306. Then, the reflected light beam R reflected by the information recording surface 323 passes through the objective lens 304 and the beam splitter 303, and passes through the focusing lens 30.
After being converged by 8, it is split into two light beams R 1 and R 2 by a roof prism 309, and R 1 enters a two-segment photodetector 311 and R 2 enters a two-segment photodetector 315.

Incidentally, the condensing spot 306 of the emitted light beam E
82 is located on the information recording surface 323 of the optical disk 305, as shown in FIG. 82, the focused spot 314 of the light beam R1 is The position of the two-segment photodetector 311 is adjusted so as to be located on the line. At the same time, the focal spot 31 of the light beam R2
The position of the two-segment photodetector 315 is also adjusted so that 8 is located on the two-segment photodetector 315 and on the dividing line between the light receiving surfaces 316 and 317. Therefore, when the converging spot 306 of the outgoing light beam E is located on the information recording surface 323, the amount of light incident on the light receiving surfaces 312, 313 becomes equal, and the light receiving surfaces 316, 3
The output from 17 is also equal. Therefore, the light receiving surfaces 313 and 316
S1 which is the sum of the output signals obtained from the light receiving surfaces 312 and 31
S2, which is the sum of the output signals obtained from FIG.

Next, consider the case where the optical disk 305 approaches the objective lens 304 by Δz. As shown in FIG.
Before focusing, R1 and R2 enter the two-split photodetectors 311 and 315, respectively. Therefore, most of the light beam R1 enters the light receiving surface 313 and hardly enters the light receiving surface 312, and at the same time, most of the light beam R2 enters the light receiving surface 316 and the light receiving surface 317
Is hardly incident. Therefore, the light receiving surfaces 313 and 31
S1 which is the sum of the output signals obtained from 6 is
317, which is greater than S2, which is the sum of the output signals.

Conversely, if the distance between the optical disk 305 and the objective lens 304 becomes longer by Δz, as shown in FIG.
1 and R2 converge before each of the two split photodetectors 311 and 315. Therefore, most of the light flux R1 enters the light receiving surface 312 and hardly enters the light receiving surface 313.
Most of the light flux R2 enters the light receiving surface 317, and hardly enters the light receiving surface 316. Therefore, S1, which is the sum of the output signals obtained from the light receiving surfaces 313 and 316, is equal to the light receiving surfaces 312 and 317.
Is smaller than S2, which is the sum of the output signals obtained from.

As described above, the focus error signal FE
S can be obtained by taking the difference between S1 and S2. This is because, as shown in FIG. 82, the distance between the optical disc 305 and the objective
If 6 is located exactly on the information recording surface 323, S
This is because the difference between 1 and S2 becomes zero. 83 is negative (or positive) when the distance between the optical disc 305 and the objective lens 304 is too short as shown in FIG. 83, and when the distance between the optical disc 305 and the objective lens 304 is too long as shown in FIG. 84. Is positive (or negative).

FIG. 85 shows a defocus Δf (Δf is a focused spot)
306 and an information recording surface 323) and a focus error signal FES. The focus error signal FES obtained in this way is applied to the phase compensator / amplifier 320
Are supplied to the objective lens driving mechanisms 321 and 322 through the convergence spot, and the condensed spot 306 of the emitted light beam E is always kept on the information recording surface 323. Also, the ridgeline 31 of the roof prism 309
The direction of 0 is set substantially perpendicular to the tangential direction (x direction) of the guide groove 307 of the optical disc 305,
This is because the focusing spot 306 is located on the guide groove 307 of the optical disc 305.
This is to keep disturbance appearing in the focus error signal FES as small as possible. See “Irie et al., Focus Sensing Characteristics of the Pupil O
bscuration Method for Continuously Grooved Disks,
Japan Journal of Applied Phisics, vol.26, pp.183-18
6 (1987) ".

Next, referring to FIG. 86, parameters of optical components when this method is applied to a typical optical disk device will be described. When the distance between the guide grooves 307 is 1.6 μm and the optical disk 305 has a diameter of 90 mm or 130 mm, the numerical aperture NAobj of the objective lens 304 is usually 0.5.
Is set to 0.55. Now, this NAobj is 0.5
Assuming that the diameter φobj of the entrance pupil of the objective lens is 3 mm, the focal length fobj of the objective lens 304 is fobj = (φobj / 2) / NAobj = (3/2) /0.55=3.3 ( mm) (1) At this time, the focal spot 30 on the information recording surface 323
6 has a diameter of about 1 to 2 μm. Meanwhile, the focusing lens 30
The focal length fs of 8 is often set to be 10 to 20 times fobj so that the diameter of the condensed spots 314 and 318 on the photodetectors 311 and 315 can be increased from several tens of μm to 50 μm. In the following, fs is 33 mm, which is 10 times as large as fobj.
Consider the case where is set to

Incidentally, it is desirable that the optical distance d ₃ from the focusing lens 308 to the ridgeline 310 of the roof prism 309 be small. This is a roof type prism 309 is a focusing lens
The light flux diameter of the distance from 308 and (d ₃ is increased) at the position of the ridge 310 is reduced, the positional accuracy of the edge line 310 for splitting the reflected light beam R into two semicircular light beams R1, R2 are severely It is because it becomes. Further, since the shape of the ridgeline 310 is not a perfect acute angle, if the light beam diameter at this position is small, scattering at the ridgeline 310 increases, and the two-part photodetectors 311, 315
This is because the amount of light reaching the light source decreases. Here, the case where d ₃ is 1/3 of fs, that is, 11 mm is considered. Then, the diameter φ of the luminous flux at the position of the ridgeline 310 of the roof type prism 309
p is, φp = φobj * (fs -d 3) / fs = 3 3 *.. (33 - 11) / 33 = 2 2 (mm) ... (2) , and the positional accuracy in the x direction of the ridge 310 is the number This is a practical value of 100 μm.

Next, the deflection angle θ by the roof type prism 309
₃ is the distance s from the optical axis A of the dividing line between the light receiving surfaces 312 and 313 of the two-part light detector 311 (or the dividing line between the light receiving surfaces 316 and 317 of the two-part light detector 315). And d ₃ and f
By s, it can be expressed as θ ₃ = s / (fs−d ₃ ) (3). s cannot be increased because the two-part detectors 311 and 315 are usually contained in one package, and is generally in the range of 0.2 mm to 0.5 mm. Here, assuming that s is 0.3 mm, from the above equation, θ ₃ is as follows: θ ₃ = 0.3 / (33-11) = 13.6 (mrad) (4)

Finally, the vertex angle of the ridge 310 is 2φ, and θ ₃
Is sufficiently small, between θ ₃ and φ, θ ₃ = Arcsin {n * sin (π / 2−φ)} − (π / 2−φ) = n * (π / 2−φ) − (Π / 2−φ) = (n−1) * (π / 2−φ) (5) Therefore, the refractive index n of the glass constituting the roof prism 309 is set to a general value of 1.5. Then, φ becomes φ = π / 2− {θ ₃ /(n−1)}=π/2−{0.0136/0.5}=1.54359 (rad) = 88.44 (degrees) ... (6) Therefore, the vertical angle 2φ is 176.88 degrees.

Next, a mechanism for making the optical axis of the light applied to the optical disk perpendicular to the optical disk will be described.
FIG. 87 is an exploded perspective view showing a conventional optical disk device described in Japanese Patent Application Laid-Open No. 59-223953, and FIG. 88 is a schematic sectional view thereof. 87 and 88, 401 is an objective lens, 402 is an objective lens driving device, 410 is a convex spherical surface formed on the bottom of the base of the objective lens driving device 402, 403 is an optical block, and 411 is an optical block 403. 404a, 404b, 412a, 412b are coil springs, 405a, 405b, 405c, 405d are screw holes, 406a, 406
b, 406c, 406d are screws, 408 is the optical axis of the objective lens 401, 4
09 is the focus.

The convex spherical surface 410 is fitted into the concave spherical surface 411, and the objective lens driving device 402 is rotatable around the center of the convex spherical surface 410 and the concave spherical surface 411.
Attached to 3. The coil springs 412a and 412b are compressed by screws 406c and 406d screwed into the screw holes 405c and 405d, and pull the objective lens driving device 402 toward the optical block 403 with a constant force.

Next, the operation will be described. Coil spring 40
4a and 404b push up the objective lens driving device 402, and the spherical surface 410
And the spherical surface 411 move smoothly. Screw 406
a and 406b are screws for adjusting the tilt of the objective lens.
By turning the screw, the inclination of the objective lens 401 integrated with the objective lens driving device 402 is adjusted.

FIG. 89 is a perspective view of a main part of a conventional optical disk apparatus shown as a conventional example in Japanese Patent Publication No. 63-53618, and FIG. 90 is a sectional view taken along the line III-III of FIG. In the figure, reference numeral 531 denotes a base formed of a magnetic material, and a shaft 532 is fixed to the center of the upper surface. 533 is fitted and held on the shaft 532, and is fixed to the holding tube 534 by a bearing tube constituting a sliding bearing mechanism together with the shaft 532. 534a is the objective lens 53
Reference numeral 534b denotes a cylindrical portion having a focusing coil 536 and a tracking coil 537 fixed to its outer periphery. And the outer yokes 539a and 539b are outside the cylindrical portion 534b,
An inner yoke (not shown) is provided inside the cylindrical portion 534b, and the permanent magnet 540 is connected to the outer yokes 539a, 539b and the base.
It is adhesively fixed between 531.

Reference numeral 541 denotes a small shaft erected on the upper surface of the base 531, and a damper member 542 for setting a neutral position in the tracking direction formed of rubber or the like is provided between the small shaft and the bearing cylinder 533. Reference numeral 543 denotes a light passage hole for guiding light incident on the objective lens 535.

Next, the operation will be described. By controlling the energization of the focusing coil 536, the position of the holding cylinder 534 is driven in the Z-axis direction in FIG. 89 to perform the focusing control. Also, by controlling the energization of the tracking coil 537, the position of the holding cylinder 534 is driven in the Y-axis direction in FIG. 89 to perform tracking control.

FIG. 91 is a cross-sectional view of a main part showing a conventional optical disk apparatus disclosed in Japanese Patent Application Laid-Open No. 4-243221.
FIG. 91 is a model diagram showing a state in which the adhesive as the fixing means after angle adjustment becomes a spring element and a damping element in FIG. 91.

In the figure, an optical head 651 is composed of an objective lens assembly 652 and a carriage 653. The objective lens assembly 652 includes an objective lens 654, an objective lens actuator 655, and a mirror 656 for starting up a laser.
Spherical convex portion 65 composed of a part of a sphere having a radius R ₆ centered on 4
8

On the upper surface of the bottom plate 661 of the box portion 660 of the carriage 653, a mounting base 662 having a spherical concave portion is formed.

The objective lens assembly 652 is housed in the box 660 of the carriage 653. With the spherical convex portion 658 mounted on the mounting table 662, the spherical convex portion 658 is formed by a plurality of screws 663 from the bottom plate 657 side. The area around is fixed.

The angle adjustment so that the optical axis 664 of the objective lens 654 is perpendicular to the surface of the loaded optical disk 665 is performed by adjusting the chassis base 667 of the optical disk device main body 666.
Through the opening 668 formed in the chassis base 667
The screw 663 is tightened or loosened as appropriate using a screwdriver from the lower surface of the device. By operating the screw 663, the objective lens assembly 652 slides by a small amount in a state where the spherical projection 658 and the mounting base 662 are in contact with each other, and the angle of the optical axis 664 can be adjusted.

Reference numeral 670 denotes a spherical projection 658 of the bottom plate 657 and the mounting base 66
After adjusting the angle of the optical axis 664 with the adhesive applied between 2,
The bottom plate 657 is fixed to the mounting base 662. 670a and 670b are a spring element and a damping element respectively representing the mechanical properties of the adhesive 670.

[0041]

The defocus signal 11 which is the output from the differential amplifier 111 in the conventional device shown in FIG.
In 3, as shown in FIG. 93, the interference signal 117 from the groove section 116 shown in FIG. 71 is superimposed on the mechanical runout of the optical disc 101. Therefore, the objective lens 106 should originally only have to follow the mechanical runout component of the optical disk 101 only.
7, which causes a problem such as voltage saturation on the control circuit. In particular,
At the time of accessing the information track, the entire amplitude of the interference signal 117 from the groove portion is superimposed on the defocus signal 113 at a frequency determined by the access speed, which has the most adverse effect on the focus control system. FIG. 94 is a schematic diagram showing a defocus signal at the time of track access. As shown in FIG. 94, T1 and T at the time of tracking
T2 at the time of accessing the information track compared to the three areas
In the region, the groove interference signal 117 in the defocus signal 113
However, when the frequency of the groove interference signal 117 is high, the focus control system may be saturated or oscillated.

Since the conventional device shown in FIG. 72 is configured as described above, the range in which the focus error signal FES changes linearly with respect to defocus, that is, the width of the linear zone is 2
There was a problem that it was as narrow as ~ 3 µm. If the linear zone is too narrow, the servo for focus control is lost due to vibration or impact from the outside of the apparatus, and the phenomenon that the focal point of the emitted light beam E cannot be maintained on the optical disk 206 is likely to occur. Also, a slight displacement of the two-part photodetector 209 gives a large offset to the focus error signal FES.

As a method of enlarging the width of the linear zone for focus error detection in the pupil occlusion method, the dividing line 20 shown in FIG.
How to expand 9a width d ₂ of JP 63-131333
Publication or Irie et al. “Focus Sensi
ng Characteristics of the
Pupil Obsulation Method
for Continuously Grooved
Discs, "Jpn. J. Appl. Phys.
s. 26, p. p. 183-186 (1987). For example, one of the above documents (by Irie)
The width d ₂ of the dividing line 209a and the wavelength λ (=
0.78 μm), the numerical aperture NA ₁ (= 0.053) in front of the shielding plate 207 for the reflected light flux entering the two-divided photodetector 209.
_{Between, d 2 ≧ λ / NA 1} = 0. 78μm / 0. 053 = 14. 7μm ... if established relationship of (7), the linear zone has been shown to be capable of expanding. Actually, when the above d ₂ is set to 50 μm and the numerical aperture of the objective lens 205 is 0.5, d ₂ becomes 10 μm
The width of the linear zone is twice or more as compared with the two-segment photodetector. FIG. 95 shows that the width d _{2 of the} dividing line is 10 μm and 50 μm.
The relationship between the focus error signal FES and the defocus Δx is shown for each case of m.

FIG. 96 shows how the light receiving surfaces 210 and 211 of the two-part photodetector 209 used in this analysis have a sensitivity (output current per unit received light amount) distribution near the dividing line 209a. K1 indicates the sensitivity distribution of the light receiving surface 210, and K2 indicates the sensitivity distribution of the light receiving surface 211. In this figure, the coordinate origin (z = 0) is the z coordinate at the center of the dividing line 209a, and the light beam incident here causes an equal amount of current to flow on both of the light receiving surfaces 210 and 211 (that is, light reception at z = 0). The sensitivities K1 and K2 of the surfaces 210 and 211 are equal). Also, within the dividing line 209a, the sensitivity of each light receiving surface changes linearly and becomes zero at the end of the opposing light receiving surface.

However, such a two-segment photodetector 209
Is used, most of the reflected light beam R1 from the optical disk 206 is incident on the dividing line 209a. Normally, two split photodetector 20
9 is constituted by a PIN photodiode, when the width of the dividing line 209a is wide, a depletion layer is not easily formed in the region of the dividing line 209a, and the moving speed of electrons and holes generated by the incident light beam is reduced. This phenomenon occurs. Due to this phenomenon, if this two-segment photodetector 209 is also used for reproducing an information signal, the frequency characteristics of a two-segment photodetector having a wide dividing line 209a are deteriorated, and the reproduction output in a high frequency range is reduced. There was a problem of reduction.

Further, since the conventional apparatus shown in FIG. 81 is configured as described above, the roof prism 309 is formed despite the vertex angle 2φ of the ridge 310 being slightly smaller than 180 degrees (176 to 178 degrees). There is a problem that the ridge 310 must be polished so that the ridge 310 is not rounded and the positional accuracy of the ridge 310 is several hundreds μm or less. Usually, since such polishing requires time and precise work, the position accuracy of the ridgeline is strict and the price of the roof-type prism whose apex angle is close to 180 degrees is expensive.

On the other hand, in the conventional apparatus shown in FIGS. 87 and 88 for making the optical axis perpendicular to the optical disk, the tilt angle of the entire objective lens driving device is adjusted even though only the tilt of the objective lens is to be adjusted. Therefore, there is a problem that the apparatus is complicated and the number of parts is large, which is an obstacle to miniaturization and thinning. In addition, there is another problem that the degree of freedom of design is greatly restricted by providing a spherical surface. Also, an adhesive is often used as a fixing method after adjusting the tilt angle, but the weight of the portion held by the adhesive is large, and the entire objective lens driving device vibrates when accessing the optical disc, and the tracking pull-in after the access is performed. , It takes a long time, so that the access time cannot be reduced.

In the conventional device shown in FIGS. 89 and 90,
There were the following problems. That is, the shaft 532 and the bushing
Since the sliding bearing mechanism is composed of 533, frictional force is generated between the shaft 532 and the bearing cylinder 533 during focusing drive and tracking drive, and the frictional force acts as a non-linear element, making the control system unstable. There was a case.

In addition, wear particles are generated due to the relative contact movement between the shaft 532 and the bearing cylinder 533, and the scattering of the wear particles has an optically adverse effect on the objective lens and the optical disk. There was also a problem that it lowered.

Further, the conventional device shown in FIG.
The adjustment angle of 4 corresponds to the adjustment angle of the screw 663, but the rotation angle of the screw 663 is not exactly determined, so it is empirically determined how much the screw 663 should be turned In other words, considerable skill is required to increase the adjustment accuracy, and it has been difficult to accurately adjust the angle of the optical axis 664.

Further, since a screw is used for adjusting the angle, if another screw is used as a fixing means for the adjusted portion after the adjustment, the adjustment will be shifted, so that the adhesive is used as the fixing means. Therefore, there is a problem that the readjustment cannot be performed even if the readjustment is required after the fixing.

Further, since the reliability and fixing force of the adhesive are lower than those in the case of screw fixing, there is a problem that unnecessary resonance is generated in the focusing and tracking control system of the objective lens 654 with respect to the optical disk 665. there were. FIG. 97 is a frequency characteristic diagram in the focus direction of the optical disk device of FIG. In the focus control system for driving the lens 654 in the direction of arrow F in FIG. 92, since the adhesive 670 acts as a spring element 670a, the frequency f _{1 in} FIG.
Unnecessary resonance occurred.

The present invention has been made in order to solve the above-mentioned problems, and by enlarging the linear zone without increasing the width of the dividing line of the two-part photodetector used in the pupil occlusion method, While stabilizing the focus control operation,
It is an object of the present invention to provide an optical disk device capable of preventing the high frequency characteristics of the two-segment photodetector from deteriorating.

Another object of the present invention is to provide an efficient optical disk device that uses a low-cost diffraction grating instead of an expensive roof-type prism, has stable operation, and is efficient.

[0055]

According to a first aspect of the present invention, there is provided an optical disc apparatus wherein a shape of an end portion of a light receiving surface in a divided band in which two light receiving surfaces of a two-divided photodetector face each other is smaller than a diameter of a reflected light beam. In a substantially sawtooth shape, a substantially triangular wave shape, or a substantially sine wave shape, and the respective light receiving surface ends are configured to mesh with each other.

In the optical disk device according to the second aspect of the present invention, the dividing line for dividing the two light receiving surfaces is defined as p where the pitch of the substantially triangular wave portion at the end of the light receiving surface of the two-divided photodetector is smaller than the diameter of the reflected light beam. y = (p / d) z + 2npy y =-(p / d) z + (2n-1) p, where -d / 2 ≦ z ≦ d / 2, n: integer.

An optical disk device according to a third aspect of the present invention provides an optical disk device comprising: a substantially saw-toothed, substantially triangular or substantially sinusoidal portion at the light receiving surface end of the two-segment photodetector;
NA ₁ ≦ λ / 2p is established between the numerical aperture NA ₁ of the reflected light beam from the optical disk incident on the two-divided photodetector.

The optical disk apparatus according to the fourth invention is characterized in that the width d of the light receiving surface of the two-part photodetector in the direction crossing the divided band of the substantially sawtooth, substantially triangular or substantially sinusoidal portion, and the wavelength of the light source and lambda, between the aperture NA ₁ of the reflected light beam from the optical disk incident to the two-divided photodetector, as d ≧ λ / NA ₁ is satisfied, constitute the two-divided optical detector is there.

In the optical disk apparatus according to the fifth aspect of the invention, a large number of minute light receiving surfaces are formed in the divided band of the two-segment photodetector, and these minute light receiving surfaces are electrically connected to one of the two light receiving surfaces. Connection lines are provided at substantially equal intervals, the direction of the connection lines is set in a direction crossing the dividing band, connection lines extending from the respective light receiving surfaces are alternately arranged, and furthermore, the connection lines are connected by one connection line. The two-segment photodetector is configured such that the area of the minute light receiving surface decreases substantially in proportion to the distance from the electrically connected light receiving surface.

In the optical disc device according to the sixth aspect of the invention, a number of rectangular light receiving surfaces are arranged in the divided band of the two-segment photodetector, and adjacent rectangular light receiving surfaces are alternately connected to the left and right light receiving surfaces. The rectangular light-receiving surface connected to each light-receiving surface constitutes a two-divided photodetector such that the length of its short side is reduced substantially in proportion to the distance from the light-receiving surface.

In the optical disc apparatus according to the seventh aspect of the present invention, the means for dividing the reflected light beam into three light beams is constituted by a light beam splitting element whose substantially half surface of the incident surface is a diffraction grating portion. The boundary line with the non-diffraction grating portion is a straight line, and the direction of this straight line is projected in a direction substantially orthogonal to the tangential direction of the guide groove on the optical disk.

The optical disk device according to the eighth invention is characterized in that:
A means for splitting the reflected light beam into three light beams is a diffraction grating section in which a substantially half surface of the incident surface is formed with a transmission type or reflection type flat diffraction grating, and the remaining substantially half surface is a non-transmissive or reflective non-light surface. It is composed of a light beam splitting element that is a diffraction grating part, and
The boundary between the diffraction grating portion and the non-diffraction grating portion is a straight line,
The direction of the straight line is projected in a direction substantially perpendicular to the tangential direction of the guide groove on the optical disk.

The optical disc device according to the ninth aspect of the present invention
In the invention according to claim 7 or claim 8, the grating lines of the diffraction grating portion are straight and the grating period is constant,
In addition, the direction of the grating line is substantially orthogonal to the direction of the boundary between the diffraction grating portion and the non-diffraction grating portion.

The optical disk device according to the tenth aspect of the present invention
In the flat diffraction grating of the light beam splitting element, the flat diffraction grating has a binary phase depth, the duty of the phase modulation is approximately 50%, and the depth of the phase modulation is approximately 180 degrees. is there.

The optical disk device according to the eleventh aspect of the present invention
In the planar diffraction grating of the light beam splitting element, phase modulation is realized by irregularities on the surface or modulation of the refractive index.

The optical disk device according to the twelfth invention is characterized in that:
The plurality of two-divided photodetectors receive light beams obtained by the diffraction action of the diffraction grating portion of the light beam splitting element.
The split photodetector and the two split photodetectors that receive the light beam from the non-diffraction grating portion of the light beam splitting element are housed in one package.

An optical disc device according to a thirteenth aspect of the present invention comprises:
In the plurality of split photodetectors, the split line of each split photodetector is substantially linear, and all the split lines exist on one substantially straight line.

In the optical disc apparatus according to the fourteenth aspect, the light beam splitting means is constituted by an element having a diffraction grating portion on substantially half the surface, and the shape of the split line of the two-segment photodetector is smaller than the diameter of the reflected light beam. , A substantially triangular wave shape or a substantially sine wave shape.

[0069]

According to the first to sixth aspects of the present invention, the range in which the focus error detection signal changes linearly with respect to the defocus amount, that is, the linear zone is enlarged, and the high frequency characteristic is not deteriorated.
A split photodetector is obtained.

In the seventh to thirteenth aspects, the boundary between the diffraction grating portion and the non-diffraction grating portion of the light beam splitting element functions as a ridgeline of the conventional roof prism, and splits the light beam reflected from the optical disk. Further, the light beam incident on the diffraction grating portion is deflected by the diffraction grating and is condensed at a different position from the light beam passing through the non-diffraction grating portion. Is received at.

The planar diffraction grating generates diffracted light by spatially modulating the phase of the wavefront of the incident light beam.

In the fourteenth invention, the light beam splitting means is constituted by an element having a diffraction grating portion on substantially one half surface, and the shape of the split line of the two-segment light detector is substantially sawtooth having a pitch smaller than the diameter of the reflected light beam. Shape, a substantially triangular wave shape or a substantially sine wave shape, so that the range in which the focus error detection signal changes linearly with respect to the defocus amount, that is, the linear zone is expanded, and high-frequency characteristics are less deteriorated and the two-segment photodetector is small. Of the focus error signal due to the lateral displacement of the lens can be reduced.

[0073]

FIG. 1 is a schematic view showing a part of an optical disk apparatus according to the first embodiment, FIG. 2 is a detailed view of a photodetector section 124 in FIG. 1, and FIG. 3 is a light spot on an information track in the first embodiment. FIG. 4 is a schematic diagram showing an arrangement relationship, FIG. 4 is an enlarged conceptual diagram of an information track for showing a relationship between an information track of the optical disk device and a defocus signal of each light spot in the first embodiment, and FIG. FIG. 6 is a schematic diagram showing a defocus signal at the time of track access of the optical disc device in the first embodiment. In the figure, the same or corresponding parts as those of the conventional apparatus are denoted by the same reference numerals, and description thereof will be omitted.

In the figure, reference numeral 120 denotes two light beams 121a,
Semiconductor lasers 122a and 122b which emit light 121b are light spots in which light beams 121a and 121b are condensed by an objective lens 106, respectively, and as shown in FIG.
Are arranged at a distance of Pd / 2 which is half the track pitch Pd of the information track on the optical disk 101 as shown in FIG. Reference numeral 123 denotes a defocus detection optical element including a cylindrical lens for detecting the defocus amount of the light spots 122a and 122b with respect to the optical disc 101;
Reference numeral 4 denotes a photodetector pattern 124a, 124b and a differential amplifier 124 as shown in FIG.
c, 124d. An optical head unit 125 includes a semiconductor laser 120, an objective lens 106, a photodetector unit 124, and the like. 126 is the light detector 12
Adder for adding the defocus signal obtained from
127 is a focus control circuit.

Next, the operation will be described. First, it is assumed that the light spots 122a and 122b have the same intensity. As shown in FIG. 4, when the light spots 122a and 122b cross the information track, the groove interference signals 128a and 128b observed in the defocus signals obtained from the respective light spots 122a and 122b are:
On the time axis, they appear as waveforms having the same amplitude and 180 ° out of phase. This is because one period of the groove interference signal corresponds to the interval between the information tracks, and the light spots 122a and 122b
The relative position shift (tracking shift) in the direction perpendicular to the information track is half the information track pitch Pd. Therefore, the adder 126 adds the defocus signal obtained from the photodetector section 124 to the adder.
At the output of 126, as shown in FIG. 5, a defocus signal from which the groove interference signal has been removed is obtained. Therefore, as shown in FIG. 6, the groove interference signal is not superimposed on the defocus signal at the time of track access, and no noise appears in the defocus signal even in the T2 region at the time of information track access.

FIG. 7 is a schematic diagram showing a part of an optical disk device according to the second embodiment, and FIG. 8 is a schematic diagram showing an arrangement relationship of light spot arrays on information tracks in the second embodiment. The same reference numerals are given to the same or corresponding parts as those in the conventional apparatus or the first embodiment, and the description is omitted. In the figure, reference numeral 140 denotes a semiconductor laser emitting three or more light beams, and 141a, 141b, 141c, 141d, and 141e denote semiconductor lasers.
0, the light beams 142a, 142b, 142c, 142d,
Reference numeral 142e denotes light spots obtained by condensing the light beams 141a, 141b, 141c, 141d, and 141e by the objective lens 106 at a distance of Pd / 2, which is half the track pitch Pd of the information tracks on the optical disk 101. Are located. 14
3 is for separating the light beams 141a, 141b, 141c, 141d, 141e and for light spots 142a, 142
b, 142c, 142d, 142e, a defocus detection optical element including a cylindrical lens and the like for detecting the defocus amount of 144e, a photodetector unit 144, and light beams 141a, 141b, and 14e.
It is constituted by photodetector patterns 144a, 144b, 144c, 144d, 144e for receiving 1c, 141d, 141e and a differential amplifier (not shown).

In the second embodiment shown in FIGS. 7 and 8, the light spots 141a,
With 141c and 141e, parallel recording / reproduction of information can be performed. In the optical spots 141a, 141c and 141e focused on the lands of the information track and the optical spots 141b and 141d focused on the groove, the observed groove interference signal has a 180 ° phase difference. Therefore, the defocus signal output obtained from the light spot focused on the land portion and the defocus signal output obtained from the light spot focused on the groove portion are selectively operated by the arithmetic processing circuit 145. The groove interference signal can be removed from the defocus signal.

FIG. 9 is a schematic diagram showing a part of an optical disk device according to the third embodiment, and FIG. In the figure, the same reference numerals are given to the same or corresponding parts as those of the conventional apparatus and the above-described embodiment, and the description is omitted. FIG.
, 150 is a diffraction grating for dividing the light beam 103 emitted from the semiconductor laser 102 into a plurality of light beams 151a, 151b, 151c, and 152a, 152b, 152c are light beams 151a, 151b, 15c.
Numerals 1c denote light spots condensed by the objective lens 106, respectively, and are arranged at a distance of Pd / 2, which is half the track pitch Pd of information tracks on the optical disk 101, as shown in FIG. 153 is the light beam 151a, 151
b, 151c, and a defocus detecting optical element such as a cylindrical lens for detecting the defocus amount of the light spots 152a, 152b, 152c with respect to the optical disk 101. Reference numeral 154 denotes a photodetector unit, and a light beam , 151b,
154a, 15 which are photodetector patterns for receiving 151c
4b, 154c and a differential amplifier.

In the third embodiment shown in FIGS. 9 and 10, the light spot 152b focused on the land portion of the information track and the light spots 152a and 152c focused on the groove portion are:
The observed groove interference signals are 180 ° out of phase. Therefore, the photodetector unit 154 depends on the light amount ratio of each of the light spots 152a, 152b, and 152c determined by the shape of the diffraction grating.
Is output by the arithmetic processing circuit 145, and the groove interference signal can be removed from the defocus signal. The distance between the light spots 152a, 152b, 152c is set according to the shape of the diffraction grating. Also, a light spot for the information track
The relative arrangement of 152a, 152b, and 152c is finely adjusted by rotating and adjusting the diffraction grating.

FIG. 11 is a schematic diagram showing a part of an optical disk device according to the fourth embodiment, and FIG. 12 is a detailed diagram showing a photodetector section in FIG. In the figure, the same reference numerals are given to the same or corresponding parts as those of the conventional apparatus and the above-described embodiment, and the description is omitted. In FIG. 11, reference numeral 160 denotes a photodetector unit, which comprises three photodetectors 161, 162, 163 for receiving the light beams 151a, 151b, 151c, and a differential amplifier (not shown). . 161a-161d, 162a
To 162d, 163a to 163d are the photodetectors 161, 162, 163, respectively.
3 is a photodetector division pattern.

As shown in FIG. 12, the photodetectors 161, 162,
Each of the 163 photodetector division patterns is divided into four parts, 161a to 161a.
1d, 162a to 162d, and 163a to 163d, an appropriate coefficient G is selected.
No. 246, a track shift of the light spots 152a, 152b, 152c with respect to an information track on the optical disk 101 can be detected by a so-called differential push-pull method, and an appropriate coefficient K is selected. , Optical spots 152a, 15a for information tracks on the optical disc 101.
Defocus signals of 2b and 152c can be detected. Track shift signal = (162a + 162b-162c-162d)-G (161a + 161b-161c-161d + 163a + 163b-163c-163d) ... (8) Defocus signal = (162a-162b-162c + 162d)-K (161a-161b-161c + 161d + 163a-163b-) 163c + 163d)… (9)

FIG. 13 is a schematic diagram showing a part of an optical disk device according to the fifth embodiment, and FIG. In the figure, the same reference numerals are given to the same or corresponding parts as those of the conventional apparatus and the above-described embodiment, and the description is omitted. FIG.
In the figure, reference numeral 150 denotes a diffraction grating that divides the light beam 103 emitted from the semiconductor laser 102 into a plurality of light beams 151a, 151b, and 151c, and is rotatably supported in a plane perpendicular to the light beam 103. . 170a and 170b are diffraction gratings
14 is a drive coil for rotating the light source 150 in a plane perpendicular to the light beam 103.
As shown in the figure, the light spots 152a, 152b and 152c are arranged at a distance of the track pitch Pd of the information track on the optical disk 101.

As shown in FIG. 14, the extension direction of the information track and the light spots 152a, 152a, By setting the angle formed by the light spot array composed of 152b and 152c to θ1, parallel recording and parallel reproduction can be performed. At the time of accessing the information track, the light spot array on the information track is rotated by rotating the diffraction grating 150 by the drive coils 170a and 170b, and the angle formed by the extension direction of the information track and the light spot array is changed from θ1 to θ2. Change. By doing so, the light spots 152a, 152b, and 152c are arranged at a distance of Pd / 2, which is a half of the track pitch Pd, as shown in FIG. At the time of access, the output of the photodetector unit 154 is calculated by the calculation processing circuit 145, and the groove interference signal can be removed from the defocus signal.

FIG. 15 is a schematic diagram showing a part of an optical disk device according to the sixth embodiment, and FIG. 16 is an optical path diagram showing details of the optical path of the dove prism unit in FIG. 15 in the sixth embodiment. In the figure, the same reference numerals are given to the same or corresponding parts as those of the conventional apparatus and the above-described embodiment, and the description is omitted. In FIG. 15, reference numeral 180 denotes a light beam split by the diffraction grating 150.
Dove prisms 181a and 181b for converting the optical path relationship between 151a, 151b and 151c are driving coils for rotating the dove prism 180 in a plane perpendicular to the light beam 103.

In the sixth embodiment, as shown in FIG.
At the time of tracking such as recording / reproduction, the light spot 152a,
The extending direction of the information track and the light spot are set so that 152b and 152c are arranged at a distance of the track pitch Pd.
The angle formed by the light spot train consisting of 152a, 152b, 152c is θ
By setting to 1, parallel recording and parallel reproduction can be performed. Then, at the time of accessing the information track as shown in FIG. 10, the light spot array on the information track is rotated by rotating the dove prism 180 by the drive coils 181a and 181b, and the angle formed by the extension direction of the information track and the light spot array Is changed from θ1 shown in FIG. 14 to θ2. By doing so, the light spots 152a, 152a as shown in FIG.
b, 152c are track pitches Pd in a direction perpendicular to the track.
Are arranged at a distance of half Pd / 2. At the time of access, the output of the photodetector section 60 is calculated by the calculation processing circuit 145, and the groove interference signal can be removed from the defocus signal.

FIG. 17 is a plan view showing a two-segment photodetector of the optical disk device according to the seventh embodiment (corresponding to the first aspect of the invention), and FIG. 18 is a partially enlarged view of the split band. In FIG. 17, reference numeral 218 denotes a two-segment photodetector, and 216 and 217 denote light receiving surfaces of the two-segment photodetector 218. Here, the split photodetector 21
The components of the optical disc device other than 8 are the same as those of the conventional example shown in FIG. 70. If the two-segment photodetector 209 in the conventional example is replaced with the two-segment photodetector 218, the optical disc device of this embodiment has the same configuration. it can. Reference numeral 219 denotes a divided band where the light receiving surfaces 216 and 217 face each other, and the longitudinal direction (the y direction in FIG. 17) of the divided band substantially coincides with the tangential direction of the upper edge 208 of the shielding plate. As shown in FIG. 18, the shape of the end of the light receiving surface in the divided band 219 is substantially triangular, and the ends of the two light receiving surfaces 216 and 217 are engaged with each other. Reference numeral 231 shown in FIG. 18 is a dividing line that forms a boundary between the two light receiving surfaces 216 and 217, and changes in a substantially triangular wave shape in the y direction. Here, d ₂ is divided band 219
And p is the pitch of the triangular wave-like portion in the dividing band 219.

FIG. 19 shows a dividing line 231 according to the seventh embodiment (corresponding to the second aspect of the present invention).
It is assumed that the width of 1 is negligibly small, and the origin of the yz coordinate system is set at the center of the division zone 219.
As is clear from FIG. 19, the dividing line 231 is expressed by the following equation. _{y = (p / d 2)} z + 2np y = - (p / d 2) z + (2n-1) p _{where, -d 2/2 ≦ z ≦} d 2/2, n: integer

Next, the operation of the seventh embodiment shown in FIG. 17 will be described with reference to FIGS. 70 to 76 used for describing the conventional example.
explain. However, in these figures, the two-part photodetector 20
9 is a case where the optical sensor is replaced by a two-part photodetector 218 shown in FIG. Also, the assumption here is that the pitch p of the triangular wave portion is negligibly smaller than the size of the converging spot on the two-divided photodetector 218. The operation of the optical disk device using the two-segment photodetector 218 is almost the same as that of the conventional example, but will be briefly described below.

As shown in FIGS. 71 and 72, when the converging point of the emitted light beam E is located on the optical disk 206, the reflected light beam R1 is on the two-segment photodetector 218 shown in FIG. The focal point of the reflected light beam R1 is located on the dividing band 219 shown in FIG.
The position of the split photodetector 218 is adjusted so that the output currents S1 and S2 from the light receiving surfaces 216 and 217 are equal.

Next, when the optical disk 206 approaches the objective lens 205, as shown in FIG. 75, the reflected light flux R1 is incident on the two-divided photodetector 218 before being converged. Therefore, the figure
As shown at 76, most of the reflected light flux R1 enters the light receiving surface 216 and hardly enters the light receiving surface 217. Conversely, if the distance between the optical disc 206 and the objective lens 205 increases,
As shown at 77, the reflected light flux R1 is collected before the two-split photodetector 209. Therefore, as shown in FIG.
Most of the light 1 enters the light receiving surface 217 and hardly enters the light receiving surface 216.

The light receiving surfaces 216 and 217 on which the reflected light beam R1 is incident generate output currents S1 and S2 proportional to the respective received light amounts, so that the focus error signal FES can be obtained by taking the difference between S1 and S2. . This is because the distance between the optical disk 206 and the objective lens 205 is appropriate and the converging point of the outgoing light beam E is exactly the same as shown in FIGS.
This is because the difference between S1 and S2 becomes zero when it is positioned above. Also, as shown in FIGS. 75 and 76, the optical disk
If the distance between the object 206 and the objective lens 205 is too short, the optical disk 20 is positive (or negative) as shown in FIGS.
If the distance between 6 and the objective lens 205 is too long, the distance becomes negative (or positive). The focus error signal FES obtained in this way is supplied to an objective lens actuator (not shown) through a phase corrector and an amplifier, and the emitted light beam E
Is always kept on the optical disk 206 as in the conventional example.

Next, referring to FIG.
Consider the linear zone of an optical disk device using Fig. 8. Now, y of the light flux incident on the two-segment photodetector 218
= Y ₁ (y ₁ is an arbitrary _{value), z = z 1 (-d} 2/2 ≦ z
₁ ≦ d _2/2) radius w (w around the think portions sufficiently small) compared to d _2. Now, when P is assumed to be sufficiently small compared to w, of the partial light fluxes (d _2/2 + z
₁ ) / d ₂ hits the light receiving surface 216 and (d ₂ / 2-z ₁ ) /
Since d ₂ hits the receiving surface 217, an output current S1, S2 of the light receiving surface 216, 217 with respect to the coordinate z ₁ of the partial light beams, split band
It changes linearly within 219. That is, the sensitivity distribution of the light receiving surfaces 216 and 217 is the same as that in FIG. Therefore, the split photodetector 21
It has been shown that increasing the width of the dividing band 219 of FIG. 8 can be equivalent to increasing the width of the dividing line 209a of the two-part photodetector 209 shown in the conventional example. Therefore, the linear zone can be expanded by increasing the width of the dividing band 219. Further, since it is not necessary to increase the width of the dividing line 231 of the two-segment photodetector 218, the frequency characteristics of the two-segment photodetector 218 do not deteriorate.

Next, a seventh embodiment (corresponding to the third and fourth aspects of the present invention) will be described. In fact the two-piece photodetector, so can not be below a certain width d ₂ of the divided band 219 from constraint creation process width can not below the pitch p also a value of the sawtooth or triangular section. Therefore, the convergence angle α (shown in FIG. 73) of the reflected light beam R incident on the two-segment photodetector 218 so that the diameter of the condensed spot on the two-segment photodetector 218 becomes sufficiently larger than the pitch p, ie, , The numerical aperture NA ₁ (NA ₁ = sin α) needs to be set. Assume that exactly half of the reflected light beam R is shielded by the shielding plate 207, and the other half is incident on the two-segment photodetector 218 as R1, and the focal point of the emitted light beam E is located exactly on the optical disk 206. spot diameter (diameter first light intensity is zero) 2w _y in a direction parallel to the dividing zone 219 (y-direction) is given by _{2w y = 1. 22 λ / NA} 1 ( Figure 20).

[0094] Here, as the value of the pitch p is constant, some values of NA ₁ of the reflected light beam (i.e., some values of the 2w _y) tried to calculate the focus error signal for. As shown in FIG. 21, the positional deviation in the y direction of the focusing spot with NA ₁ is larger affects the focus error signal, NA ₁ is becomes smaller than the following NAa NAa = 5λ / 8p, the focused spot The influence of the displacement in the y direction on the focus error signal is very small. Furthermore, NA ₁ is becomes smaller than the following NAa NAa = λ / 2p, the focused spot focus error signal be displaced in the y direction is not changed. Pitch p is 15μ
m, when the wavelength of the light source λ is 0. 78 .mu.m, the NAa becomes 0. 026, y-direction spot diameter 2w _y is 36.
6 μm. Figure 22 is given to the NA ₁ to 0.026, the pitch p of the divided band set 15 [mu] m, the width d ₂ of the divided band 88 .mu.m, NA of the objective lens showed focus error signal in the case of 0.53 It is. As can be seen from FIG. 22, a linear zone of 5 to 6 μm is obtained.

FIG. 23 is a plan view showing a two-divided photodetector of the optical disk device according to the eighth embodiment (corresponding to the fifth aspect of the present invention). Instead of forming the shape of the divided band 219 into a triangular wave shape as shown in FIG. 18, a configuration as shown in FIG. 23 may be used. In FIG. 23, 220 is a two-segment photodetector, 221 and 22.
Reference numeral 2 denotes a light receiving surface corresponding to the light receiving surfaces 216 and 217 of the embodiment shown in FIG. Reference numeral 223 denotes a minute light receiving surface disposed in the dividing band 219, and its area is sufficiently smaller than the diameter of the condensed spot on the two-part photodetector. A plurality of the minute light receiving surfaces exist in the divisional band 219, and are connected by the connection line 224. A plurality of connection lines 224 also exist in the divided band 219, and extend from the light receiving surfaces 221 and 222 in a direction crossing the divided band (in the z direction in the figure) with an interval of substantially P. The connection lines extending from the light-receiving surface 221 and the connection lines extending from the light-receiving surface 222 are alternately arranged. Light-receiving surface 22
Conversely, the connection line extending from 2 extends to just before the light receiving surface 221.
It does not reach the light receiving surface 221. In addition, one connection line 22
4 has a configuration in which the area decreases in proportion to the distance from the electrically connected light receiving surface 221 or 222, and the area near the center of the split band 219 Are arranged in the y-direction. In the vicinity of the light receiving surface 221 or 222, the area of the minute light receiving surface 223 is naturally maximum or minimum.

The difference between the two-divided photodetector 220 shown in FIG. 23 and the two-divided photodetector 218 shown in FIG. 17 is that the minute light receiving surface 223 in the divided band 219 is connected by a connection line 224. The basic operation is the same. For example, the two-part photodetector 220
Considering a partial light beam incident on the center line (coordinate z = 0) of the divisional band 219 of the light beam having a uniform intensity distribution, a minute light receiving surface connected to the light receiving surface 221 The remaining half is incident on the minute light receiving surface group connected to the light receiving surface 222. In this case, the output currents from the light receiving surfaces 221 and 222 are almost equal. Considering a portion incident on the line (z = z ₁ ) between the center line and the light receiving surface 221, the minute light connected to the light receiving surface 221 is proportional to the distance from the center line (here, z ₁ ). The amount of light incident on the light receiving surface group increases, and the amount of light incident on the minute light receiving surface group connected to the light receiving surface 222 decreases. Therefore, the light receiving surface 22
1, 222 output current for each unit amount (sensitivity) for the incident point z ₁ of the partial light beams, so that the same change as the sensitivity distribution shown in FIG. 96. The area of the region where the light receiving surface does not exist in the dividing band 219 is smaller than that of the conventional two-part photodetector, and the width of the dividing line of the two-part photodetector shown in the conventional example is increased. Obtained sensitivity distribution (Fig. 96)
Therefore, it is possible to obtain an optical disk device having a wide linear zone and no deterioration in frequency characteristics.

By the way, in FIG. 23, the minute light receiving surface 223 in the divided band 219 is circular. Can be set arbitrarily.

In Embodiments 7 and 8 shown in FIGS. 17 and 23, the light receiving surface extends in the direction (z direction) perpendicular to the divided band 219 within the divided band 219, but is shown in FIG. The configuration shown in the ninth embodiment (corresponding to the invention described in claim 6) may be adopted. In the ninth embodiment, a plurality of rectangular light receiving surfaces 225 and 226 are arranged in the divided band 219,
Or 222. The direction of the long side of the rectangular light receiving surfaces 225 and 226 is the y direction, and the light receiving surface 22
The group of rectangular light receiving surfaces 225 connected to 1 and the group of rectangular light receiving surfaces 226 connected to the light receiving surface 222 are alternately arranged in a comb shape. Moreover, the rectangular light receiving surface 225 or 226 is
In this configuration, the length of the short side decreases in proportion to the distance from 221 and 222. Of course, the width of the dividing line separating the light receiving surface and the light receiving surface is set to be sufficiently small. Also in this embodiment, a large number of rectangular light receiving surfaces are arranged in the divided band 219, and the length of each short side (width in the z direction) is sufficiently smaller than the spot diameter on the two-part photodetector 220. Figure 1
7, it is clear that it operates in the same way as the embodiment shown in FIG. Therefore, an optical disk device having a wide linear zone and no deterioration in frequency characteristics can be obtained by using the two-divided photodetector 220. In FIG. 24, the total number of the rectangular light receiving surfaces 225 and 226 in the divided band 219 is eight, but the length of the short side of the rectangular light receiving surfaces 225 and 226 is equal to the spot diameter on the two-divided photodetector 220. The number is arbitrary as long as it is sufficiently small compared to.

In the above description, the case where the present invention is applied to an optical disk device of an optical recording / reproducing device has been described.

Next, with respect to the invention as set forth in claims 7-14,
A description will be given based on the embodiment. First, a basic configuration for describing these inventions will be described with reference to FIGS. FIG. 25 is a configuration diagram showing a basic configuration of the optical disk device. 26 to 31 show the relationship between the state of defocus of the light spot on the information recording surface and the position and shape of the light spot on the photodetector of the present optical disk device. FIG.
, The symbols 301 to 308 and 320 to 323
Are the same as those in the conventional example shown in FIG. Reference numeral 324 denotes a light beam splitting element for splitting the light beam R reflected from the optical disk 305 into two or more light beams, and a diffraction grating is formed on a substantially half surface. In the light beam splitting element 324, reference numeral 341 denotes a diffraction grating portion on which a diffraction grating is formed, and reference numeral 342 denotes a non-diffraction grating portion having no diffraction grating. Further, the boundary between the diffraction grating portion 341 and the non-diffraction grating portion 342 is substantially equal to the reflected light flux R by approximately two.
They are arranged so as to be equally divided. In the figure, the light beam Ra from the non-diffraction grating portion 342 and the light beam R from the diffraction grating portion 341 are shown.
Although two of b are shown, when two or more light beams are generated by the diffraction action of the diffraction grating section 341, the light beam splitting element 324 splits the reflected light beam R into three or more light beams.

Reference numeral 325 denotes a two-segment photodetector for receiving the light beam Ra, which comprises two light receiving surfaces 326 and 327 arranged in a plane perpendicular to the optical axis A. Reference numeral 328 denotes a condensed spot on the split photodetector 325. Reference numeral 329 denotes a two-segment photodetector for receiving the light beam Rb, which comprises two light receiving surfaces 330 and 331 arranged in a plane perpendicular to the optical axis A. Reference numeral 332 denotes a condensed spot on the two-divided photodetector 329. The direction of the dividing line between the light receiving surface 326 and the light receiving surface 327, and the direction of the dividing line between the light receiving surface 330 and the light receiving surface 331 are determined by the diffraction grating portion 341 and the non-diffraction grating portion of the light beam splitting element 324.
342 substantially coincides with the direction of the boundary line (y direction).

Next, FESa is a focus error signal obtained from the two-segment photodetector 325, and represents the difference between the output signal from the light receiving surface 326 and the output signal from the light receiving surface 327. Similarly,
FESb is a focus error signal obtained from the two-divided photodetector 329, and represents the difference between the output signal from the light receiving surface 330 and the output signal from the light receiving surface 331. 337 and 338 are differential amplifiers for obtaining these focus error signals FESa and FESb.
The focus error signals FESa and FESb are added by the adder 340 to become a focus error signal FES.

Next, the operation of the optical disk device shown in FIG. 25 will be described with reference to FIGS. When recording and reproducing information, the outgoing light beam E emitted from the light source 301 becomes a parallel light beam by the collimator lens 302, is reflected by the beam splitter 303, and travels to the objective lens 304. Next, the emitted light beam E is condensed by the objective lens 304 and is radiated on the information recording surface 323 as a condensed spot 306. Then, the reflected light beam R reflected by the information recording surface 323 passes through the objective lens 304 and the beam splitter 303, and becomes a focused light beam by the focusing lens 308. Next, this light beam R enters the light beam splitting element 324, and the light beam Ra having a semicircular cross section incident on the non-diffraction grating portion 342 goes straight as it is,
It goes to the two-segment photodetector 325. The light beam Rb having a semicircular cross section incident on the diffraction grating portion 341 is deflected by the diffraction action of the diffraction grating portion and travels toward the two-divided photodetector 329.

As shown in FIGS. 26 and 27, when the focused spot 306 of the emitted light beam E is located on the information recording medium surface 323 of the optical disk 305, the focused spot 328 of the light beam Ra is two.
The position of the two-divided photodetector 325 is adjusted so that it is located on the divided photodetector 325 and the focused spot 328 is located on the dividing line between the light receiving surfaces 326 and 327. At the same time, the focused spot 332 of the light beam Rb is
The position of the two-segment photodetector 329 is also adjusted so that it is located above the light-receiving surface 330 and 331 so as to be located on the dividing line between the light-receiving surfaces 330 and 331. Here, the converged spot is a state in which the converged light beam is narrowed down to a minimum. Therefore, when the converging spot 306 of the outgoing light beam E is located on the information recording surface 323, the amounts of light incident on the light receiving surfaces 326 and 327 are equal, and the outputs from the light receiving surfaces 326 and 327 are also equal. At the same time, the amounts of light incident on the light receiving surfaces 330 and 331 are also equal, so that the outputs from the light receiving surfaces 330 and 331 are also equal. Accordingly, the focus error signals FESa and FESb both become zero, and the focus error signal FES which is the sum of these FESa and FESb also becomes zero.

Next, consider a case where the optical disk 305 approaches the objective lens 304 by Δz. As shown in FIGS. 28 and 29,
Before the light beams Ra and Rb are collected, they are split into two light detectors 325 and 329.
Incident on each of the. Accordingly, most of the light beam Ra enters the light receiving surface 327 and hardly enters the light receiving surface 326, and at the same time, most of the light beam Rb enters the light receiving surface 330 and hardly enters the light receiving surface 331. Since each light-receiving surface generates an output proportional to the amount of light received,
The output of 327 is larger than the output of the light receiving surface 326, and the focus error signal FESa, which is the difference between them, becomes positive. Similarly, the focus error signal F, which is the difference between the output of the light receiving surface 330 and the light receiving surface 331,
ESb also becomes positive. Therefore, these FESa and FESb
Is also positive.

Conversely, when the distance between the optical disk 305 and the objective lens 304 becomes longer by Δz, the light beams Ra and Rb are converged before the two-split photodetectors 325 and 329, respectively, as shown in FIGS. I do. Therefore, most of the light beam Ra enters the light receiving surface 326 and hardly enters the light receiving surface 327, and at the same time, most of the reflected light beam Rb enters the light receiving surface 331 and becomes light receiving surface 331.
The 330 is hardly incident. Since each light receiving surface generates an output proportional to the amount of received light, the light receiving surface 327
Is smaller than the output of the light receiving surface 326, and the focus error signal FESa, which is the difference between them, becomes negative. Similarly, the focus error signal FE, which is the difference between the output of the light receiving surface 330 and the light receiving surface 331,
Sb also becomes negative. Therefore, the focus error signal FES, which is the sum of these FESa and FESb, also becomes negative.

In summary, the distance between the optical disk 305 and the objective lens 304 is appropriate, and
When 6 is located exactly on the information recording surface 323, the focus error signal FES becomes zero. Further, the value is positive when the distance between the optical disk 305 and the objective lens 304 is too short, and negative when the distance between the optical disk 305 and the objective lens 304 is too long. FIG. 32 shows the defocus Δf (Δf is the focal spot 30).
6 and the information recording surface 323) and the focus error signal F
It is a figure which shows the relationship with ESa and FESb. Finally, the focus error signal FES is supplied to the objective lens driving mechanisms 321 and 322 through the phase corrector / amplifier 320, and the outgoing light beam E
Is always kept on the information recording surface 323 as in the conventional example.

As described above, the boundary between the diffraction grating portion 341 and the non-diffraction grating portion 342 of the light beam splitting element 324 has the same function as the ridge line 310 of the roof type prism 309 in the conventional example. , Diffraction grating section 341 and non-diffraction grating section 34
The direction of the boundary line between the two is the guide groove of the optical disc 305.
307 in a direction (y direction) substantially perpendicular to the tangential direction (x direction).
Direction). This is because the disturbance appearing in the focus error signal FES when the light spot 306 crosses the guide groove 307 of the optical disk 305 is kept as small as possible, as in the conventional example.

Further, if the structure of the diffraction grating is determined so that the light beam incident on the diffraction grating portion 342 can be almost diffracted, and a plurality of two-divided photodetectors are prepared so as to receive all the diffracted light beams, Approximately 100% of the light beam incident on the light beam splitting element 324 can be used for generating a focus error signal, and an efficient optical disk device can be configured. Further, if the diffraction grating unit 341 is configured such that the grating period of the diffraction grating is constant and the grating lines are substantially orthogonal to the boundary line, the light source 30
Since the light spot on the two-divided photodetector 329 moves only on the dividing line for a wavelength change of 1, no offset occurs in the focus error signal FESb and thus the FES.
At this time, the dividing line of the two-divided photodetector 325 and the dividing line of the two-divided photodetector 329 are substantially aligned.

The two split photodetectors 325 and 329 are provided to obtain the focus error signal FES.
This is because when the two split photodetectors are housed in one package, the offset in the focus error signal generated when the two split photodetectors are shifted in the direction perpendicular to the split line (the x direction in FIG. 25) can be reduced. . Here, it is clear from FIG. 25 that the displacement in the y direction does not affect the offset. The reason why the offset can be suppressed with respect to the displacement of the two-segment photodetector in the x direction is as follows. As shown in FIGS. 26 and 27, when the focused spot 306 of the emitted light beam E is located on the information recording medium surface 323 of the optical disc 305, the light receiving surface 32
The positions of the two-split photodetectors 325 and 329 are adjusted so that the outputs from the light receiving surfaces 6 and 327 are equal and the outputs from the light receiving surfaces 330 and 331 are also equal. Considering the case where the two-segment photodetectors 325 and 329 move by the same distance in the x direction, the light receiving surface 326
And the output of the light receiving surface 330 increases, and the light receiving surface 327 and the light receiving surface
As the output of 331 decreases, FESa decreases and FESb
To increase. Therefore, if the characteristics of FESa and FESb are the same, the FES which is the sum of FESa and FESb does not change. Even if the characteristics of FESa and FESb are not exactly the same, the two focus error signals FESa and FE
Since the signs of the offsets appearing in Sb are opposite to each other, the appearance of the offset of the focus error signal FES, which is their sum, can be made smaller than each of the focus error signals FESa and FESb.

The following three advantages are obtained by using the above-described light beam splitting element 324 instead of the roof type prism 309 in the conventional example.
There are two points. One is that the width of the boundary region between the diffraction grating portion 341 and the non-diffraction grating portion 342 can be made extremely small (for example, 10 μm or less), so that the scattering loss at this portion can be suppressed low. (Hence, this boundary area is called the boundary line). Another advantage is that the position accuracy of the boundary line in the beam splitting element 324 is
The advantage is that it can be easily maintained at 0 μm or less, and the manufacturing cost of the light beam splitting element can be reduced as compared with the roof prism. All of these are because, instead of optical polishing, a technique of photolithography or etching in a semiconductor process or a technique of creating holography can be used for manufacturing the light beam splitting element.

The seventh to thirteenth inventions will be specifically described based on the tenth embodiment with reference to the above configuration. In the present invention, as the light beam splitting element 324 having the above-described configuration, a light beam splitting element 343 in which the diffraction grating section 341 is a planar diffraction grating as shown in FIG. 33 is used. In FIG. 33, the refractive index of the substrate is n
2 shows a diffraction grating having a rectangular groove having a groove depth h, a period p _G , and a groove width a. The groove of this diffraction grating is straight and the period p _G is constant, and the boundary between the diffraction grating portion 341 and the non-diffraction grating portion 342 is substantially straight. In addition, the direction of the groove is substantially orthogonal to the direction of the boundary line.

The groove depth h and the groove width a of this diffraction grating are given by: h = λ / {2 (n−1)} (10) a = p _G / 2 ... (11) It is selected so that the above condition is almost satisfied. This corresponds to the fact that the diffraction grating applies a phase modulation with a duty of 50% and a depth of 180 degrees to the incident light beam. Assuming that there is no Fresnel loss on each of the front and back surfaces of the light beam splitting element 343, the light beam 4
0.5% is diffracted as first-order diffracted light, and 40.5% is diffracted as minus first-order diffracted light, so that no 0th-order diffracted light is generated. The remaining 20% is odd-order diffracted light of the third or higher order.

FIG. 34 is a block diagram showing an optical disc device according to Embodiment 10 of the seventh to thirteenth aspects of the invention. FIGS. 35 to 37 show the relationship between the state of defocus of the light spot on the information recording surface and the position and shape of the light spot on the photodetector of the present optical disk device. In FIG. 34, 301 to 308, 320 to 323
, 325 to 338, 341 and 342 are the same as those shown in FIG. Reference numeral 343 denotes a light beam splitting element for splitting the reflected light beam R from the optical disk 305 into three light beams Ra, Rb, and Rc. The boundary between the diffraction grating portion 341 and the non-diffraction grating portion 342 divides the reflected light beam R into approximately two equal parts. It is arranged to be. Here, Ra is a light beam that has passed through the non-diffraction grating portion 341 as it is, Rb is a light beam diffracted by the diffraction grating portion 342 as a plus first-order diffracted light, and Rc is a beam that is diffracted by the diffraction grating portion 342 in a direction opposite to Rb. This is a light beam diffracted as minus first-order diffracted light. Light beam R reflected by light beam splitting element 343
Is a circular beam having a uniform intensity distribution, and the light beam splitting element 34
Considering the case where the boundary line between the diffraction grating portion 341 and the non-diffraction grating portion 342 divides this circular beam exactly into two, 50% of the above beam is the luminous flux Ra and 20.25% is the luminous flux R
At b, 20.25% becomes the light flux Rc.

Since the remaining 9.5% of the beam is deflected at a larger angle as higher-order diffracted light, it cannot enter the photodetector in FIG. However, it is easy to prepare a photodetector for receiving these higher-order diffracted lights. Therefore, when three light beams of Ra, Rb, and Rc are used, about 90% of the light beam incident on the light beam splitting element 343 can be used for generating a focus error signal.
If diffracted light of the next order or higher is used, about 100% of the light beam incident on the light beam splitting element 343 can be used for generating a focus error signal. In FIG. 34, in addition to the two-part photodetector 325 for receiving the light beam Ra and the two-part photodetector 329 for receiving the light beam Rb shown in FIG. 25, a two-part light detector 333 for receiving the light beam Rc is shown. Have been. 2 split photo detector 33
3 denotes two light receiving surfaces 33 arranged in a plane perpendicular to the optical axis A.
4, 335, and 336 is a split photodetector 333
The upper light spot.

The direction of the dividing line between the light receiving surfaces 334 and 335 is also
The diffraction grating section 341 and the non-diffraction grating section 342 of the light beam splitting element 343
And the three dividing lines of the three split photodetectors 325, 329, and 333 are substantially aligned on a single straight line 347. I have.
FESa and FESb are two-split photodetectors 325 and 329, respectively.
Are the same as the embodiment shown in FIG. 25. FESc is a focus error signal obtained from the two-part photodetector 333, and represents the difference between the output signal from the light receiving surface 334 and the output signal from the light receiving surface 335. 339 is a differential amplifier for obtaining these focus error signals FESc. The focus error signals FESa, FESb, and FESc are added by the adder 344 to form a focus error signal FES.

Next, the operation of the tenth embodiment shown in FIG. 34 will be described with reference to FIGS. When recording and reproducing information, the outgoing light beam E emitted from the light emitting source 301 is converted into a parallel light beam by the collimator lens 302, reflected by the beam splitter 303, and travels to the objective lens 304.
The emitted light beam E is condensed by the objective lens 304 and is focused on the information recording surface.
The light is irradiated as a condensed spot 306 on 323. And
The reflected light flux R reflected by the information recording surface 323 is
4. The light passes through the beam splitter 303 and is converged by the converging lens 308 into a converged light beam. Up to this point, the configuration is the same as that of the optical disk device shown in FIG. Next, the reflected light beam R is split into three light beams Ra, Rb, and Rc by the light beam splitting element 343, Ra is split into two split light detectors 325, Rb is split into two split light detectors 329, and Rc is split into two split light beams. The light enters the detector 333. As shown in FIG. 34, the cross-sectional shapes of Ra, Rb, and Rc are substantially semicircular.

The focus error detecting operation of the tenth embodiment is almost the same as that of the optical disk apparatus shown in FIG.
c is used in the same manner as the light flux Rb. Figure 35
Denotes a two-segment photodetector when the focused spot 306 of the emitted light beam E is located on the information recording surface 323 of the optical disc 305.
This shows the respective states of the condensed light spots 328, 332, and 334 on 325, 329, and 333. Since the diffraction grating on the light beam splitting element 343 has a constant grating period and a straight grating line, the focused light beam incident on the diffraction grating portion is merely deflected in a direction perpendicular to the direction of the grating line. Therefore, the focusing spot
328, 332, 334 are arranged on one straight line 347. Further, in this case, since the amounts of light incident on the light receiving surfaces 334 and 335 are equal, the outputs from the light receiving surfaces 334 and 335 are also equal. Therefore,
The focus error signal FESc becomes zero like FESa and FESb, and the focus error signal FES which is the sum of these FESa, FESb and FESc also becomes zero.

FIG. 36 shows that the optical disk 305 is
7 shows the states of the condensed spots 328, 332, and 334 on the two-divided photodetectors 325, 329, and 333 when Δz approaches Δz. At this time, most of the light flux Rc is transmitted to the light receiving surface 334.
The focus error signal FESc, which is the difference between the output of the light receiving surface 334 and the light receiving surface 335, becomes positive similarly to FESa and FESb, and the sum of FESa, FESb, and FESc. Is also positive.

FIG. 37 shows a two-divided photodetector 325, 32 when the distance between the optical disc 305 and the objective lens 304 becomes far Δz.
This shows the respective states of the condensed spots 328, 332, and 334 on 9, 333. At this time, most of the light beam Rc enters the light receiving surface 335 and hardly enters the light receiving surface 334. Therefore, the focus error signal FESc, which is the difference between the output of the light receiving surface 334 and the light receiving surface 335, is FESa and FESb. Similarly, the focus error signal FES, which is the sum of FESa, FESb, and FESc, also becomes negative.

FIG. 38 shows a defocus Δf (Δf is a condensing spot)
12 is a graph showing the relationship between the focus error signals FESa, FESb, FESc, and FES. In order to keep disturbance in the focus error signal FES generated when the light spot 306 crosses the guide groove 307 of the optical disc 305 as small as possible, the direction of the boundary between the diffraction grating portion 341 and the non-diffraction grating portion 342 is The guide groove 307 is set in a direction substantially perpendicular to the tangential direction (x direction).

In order to obtain the focus error signal FES, the three split photodetectors 325, 329, and 333 are prepared because the three split photodetectors are housed in one package and are perpendicular to the split line. This is because the offset in the focus error signal FES that occurs when the focus error signal FES is shifted in an appropriate direction (the x direction in FIG. 25) can be reduced. Here, it is apparent from FIG. 34 that the displacement in the y direction does not affect the offset. The reason why the offset can be suppressed with respect to the displacement of the two-segment photodetector in the x direction is the same as the configuration of the optical disk device shown in FIG. Figure 35
As shown in the figure, when the focused spot 306 of the emitted light beam E is located on the information recording surface 323 of the optical disc 305, the outputs of the light receiving surfaces 326 and 327 are equal and the light receiving surfaces 330 and 327 are equal.
The positions of the two-divided photodetectors 325, 329, and 333 are adjusted so that the outputs of 331 are equal and the outputs of the light receiving surfaces 334 and 335 are also equal.

Considering the case where the two-divided photodetectors 325, 329, and 333 have moved by the same distance in the x direction, the light receiving surfaces 326, 33
0, 334 increases and the outputs of the light receiving surfaces 327, 331, 335 decrease, so that FESa decreases and FESb, FESc
Increase. Therefore, since the sign of the offset of the focus error signal FESa is opposite to the sign of the offset of FESb and FESc, the focus error signal F
The manner in which the ES offset appears is the focus error signal FESa,
It can be smaller than each of FESb and FESc.

Next, referring to FIG. 39, parameters of optical components when the embodiment 10 shown in FIG. 34 is applied to a typical optical disk device will be described. Numerical aperture N of objective lens 304
Aobj is 0.55, the diameter φobj of the entrance pupil of the objective lens is 3 mm, the focal length fobj of the objective lens is 3.3 mm, the focal length fs of the focusing lens is 33 mm, and the optical distance from the focusing lens 308 to the light beam splitting element 343. d ₃ is 11 mm,
The distance s from the center of the two-segment photodetector 329 (or 333) to the center of the two-segment photodetector 325 is set to 0.3 mm (in this case, the three two-segment photodetectors 325, 329, and 333 are one Packaged in one package). These values are the values in the conventional typical optical disk device described above.

The deflection angle θ by the diffraction grating is set so as to satisfy θ = Arctan {s / (fs−d ₃ )} (12), and the period p _{G of the} diffraction grating is determined by the wavelength λ of the light source. And the above θ ₃ , p _G = λ / sin θ ₃ (13) Assuming that λ is 0.78 μm, θ ₃ and p are θ ₃ = Arctan {0.3 / (33-11)} = 13.6 (mrad ₃ ) (14) p _G = 0.78 / sin ( 0.0136) = 57.2 (μm) (15) Therefore, the groove depth h and the groove width a of the diffraction grating can be calculated from the equations (10) and (11) as follows: h = 0.78 / {2 (1.5-1)} = 0.78 (μm) (16) A) = 57.2 / 2 = 28.6 (μm) (17) Groove depth 0.78 μm, groove width 28.6 μm
It is generally very easy to manufacture a diffraction grating having a rectangular groove by a technique such as optical lithography.

Further, consider a case where the wavelength λ of the light source 301 changes. At this time, since the deflection angle θ ₃ varies according to the equation (13), the positions of the converging spots 332 and 336 of the light beams Rb and Rc diffracted on the two-divided photodetectors 329 and 333 change. However, since the three converging spots 328, 332, 336 are originally on one straight line 347, and the dividing lines of the two-divided photodetectors 325, 329, 333 also exist on one straight line 347, The focusing spots 332, 336 only move on the dividing line. Further, since the diffraction grating having a constant grating period has no lens function, the size and shape of the condensed spot hardly change. Therefore, it can be said that the wavelength variation of the light source 301 hardly affects the focus error signal FES.

The case where the diffraction grating portion 341 and the non-diffraction grating portion 342 of the light beam splitting element 343 are transmissive has been described.
It goes without saying that these may be reflective.

In FIG. 33, the light beam splitting element 343 is placed in the focused light beam, but may be placed in the parallel light beam. In this case, the focusing lens 308 is
And two split photodetectors 325, 329, 333.

In FIG. 33, the diffraction grating portion 341 of the light beam splitting element 343 is formed of a flat diffraction grating having an uneven surface, but is a refractive index modulation type diffraction grating as shown in FIG. It can also be configured. In the figure, reference numeral 345 denotes a region in which the refractive index has changed by Δn compared to the refractive index n of the substrate. The region has a depth h, a width a, and a period p _G. h and a are desirably selected so that h = λ / (2Δn) (18) a = p _G / 2 (19) is almost satisfied. This condition is the same as Expressions (10) and (11), and corresponds to the fact that the diffraction grating applies a phase modulation with a duty of 50% and a depth of 180 degrees to the incident light beam.

FIG. 41 is a diagram showing the configuration of an optical disk device according to the eleventh embodiment. The two-divided detectors 325 and 329 shown in FIG.
Has a configuration similar to that of the two-segment detector 218 shown in FIG.
The split detectors 351 and 352 are replaced. The other configuration is the same as that shown in FIG. 25, and the same reference numerals are given and the description is omitted. In the present embodiment, in addition to the same effects as described with reference to FIG. 25, the range in which the focus error signal changes linearly with respect to defocus can be broadened compared to the conventional Foucault method. In this case, there is an effect that the deterioration of the frequency characteristic is small, the disturbance when crossing the guide groove of the focused spot image optical disc is small, and the fluctuation of the focus error signal due to the lateral displacement of the photodetector is small.

FIG. 42 is a block diagram showing an optical disk device according to the twelfth embodiment. The two-divided detectors 325, 329,
333 is replaced by two-piece detectors 353, 354, and 355 having the same configuration as the two-piece detector 218 shown in FIG. The other configuration is the same as that shown in FIG. 34, and the same reference numerals are given and the description is omitted. In this embodiment, in addition to the effect in FIG. 34, there is an effect equivalent to that of the above-described embodiment. It should be noted that the shape of the dividing line may be a substantially sinusoidal wave in addition to the substantially triangular wave (or substantially sawtooth) shown in FIGS.

FIG. 43 is an exploded perspective view showing an inclination adjusting unit of the optical disk device according to the thirteenth embodiment, FIG. 44 is a perspective view of a main part of an optical disk device equipped with the inclination adjusting unit of FIG. 43, and FIG. FIG. 46 is a sectional view taken along line II of FIG. 45, and FIG.
FIG. 2 is a sectional view taken along line II-II of FIG.

In FIG. 43, reference numeral 420 denotes an objective lens, 421 denotes a ring-shaped flat plate (hereinafter, referred to as “flat plate”), 422a and 422b.
Is a pair of upper projections provided on the flat plate 421, and the optical axis 408
Is provided on a first straight line L1 passing through. 423a, 423b
Is a pair of lower projections provided on the flat plate 421, and the optical axis 408
And is provided on a second straight line L2 orthogonal to the first straight line L1. 424 is an objective lens holder, 425 is a bearing, and 426 is a focusing coil.

In FIGS. 44 to 47, reference numeral 430 denotes a base, which has a light beam passage hole 430a on the side surface so that a light beam 431 emitted from a light source (not shown) can be incident from the side surface. A focus base 432 holds the lower end of the support shaft 433 coated with a fluororesin having a small coefficient of friction. Reference numerals 434a and 434b denote focusing magnets that are magnetized in the vertical direction, and are adhered and fixed to the focus base 432 together with the focusing yokes 435a and 435b.
It is fixed to the base 430 by 436b.

Reference numerals 437a and 437b denote tracking magnets magnetized in two poles in the left-right direction, and 438 denotes a launch mirror which reflects the light beam 431 incident from the side vertically upward, and is bonded and fixed to the base 430. ing. 439
Is a drive current applying FPC, 440 is a photo interrupter,
Reference numeral 442 denotes a photointerrupter fixing plate. The drive current applying FPC 439 and the photointerrupter 440 are fixed to the base 430 by screws 443 and 444, respectively.

Reference numeral 424 denotes an objective lens holder formed of a lightweight, high-rigidity plastic material or the like, so that a fin portion 424aa protruding in parallel with the support shaft 433 is arranged in the gap of the photo interrupter 440. It is provided integrally with the objective lens holder 424. 420 is an objective lens fixed to one end of the objective lens holder 424 in the longitudinal direction, 421 is a flat plate disposed between the objective lens holder 424 and the objective lens 420, and 447 is an objective lens 420 in the longitudinal direction of the objective lens holder 424. The balance weight is fixed to one end that is not arranged.

Reference numeral 425 denotes a bearing fixed to the objective lens holder 424 so as to have an axis parallel to the optical axis of the objective lens 420, and is fitted to the support shaft 433. 42
Reference numeral 6 denotes a focusing coil fixed to the objective lens holder 424 so as to be coaxial with the bearing 425,
Focus base 432 and focusing yoke 43
It is configured to be arranged in the magnetic gap formed by 5a and 435b. Reference numeral 450 denotes a movable portion FPC fixed to the objective lens holder 424, and tracking coils 451a and 451b adhered and fixed to both side surfaces of the objective lens holder 424.
It has a function of a relay board that connects between them and supplies a driving current to the focusing coil 426 and the tracking coils 451a and 451b through lead wires (not shown). The movable section 453 is composed of the above 424 to 452d. Reference numerals 454a to 454d denote dampers, which are fixed to projections 455a and 455b provided on the objective lens holder 424 and pin portions 456a to 456d provided on the base 430, respectively.
3 is slidably and rotatably supported on a support shaft 433. Reference numeral 457 denotes a cover, which is fixed to the base 430.

Next, the operation will be described. When performing the arrow A _4-direction tilt adjustment of the objective lens 420 shown in FIG. 43, the center upper projections provided on the flat plate 421 422a, the tip of the 422b, so that the objective lens 420 is tilted in the arrow A ₄ direction In addition, the desired force is applied to the object lens 420 at an appropriate point. Further, when the arrow B _4-direction tilt adjustment of the objective lens 420, similarly, the lower projections 423a, around the tip of 423b, as the objective lens 420 is tilted in the arrow B ₄ direction, the objective lens 420 Apply the desired force to the appropriate points.

The actual tilt adjustment amount is 10 mrad (about 0.57 de) in a general optical disk device.
g) is often adjusted. When the outer diameter of the objective lens 420 is about 5 mm, the amount of protrusion of the pair of upper protrusions 422a and 422b and the pair of lower protrusions 423a and 423b necessary for performing the adjustment of 10 mrad is about 25 μm. This is a value that does not cause any problem from the viewpoint of manufacturing.

After the tilt adjustment of the objective lens 420 is completed,
The flat plate 421 and the objective lens 420 are fixed to the objective lens holder 424 with an adhesive or the like.

The operation for driving the objective lens 420 is as follows.
To correct the focus shift of the light spot (not shown), a desired current is applied to the focusing coil 426, and the movable portion 45 is moved by the electromagnetic force obtained by the interaction with the magnetic force generated by the focusing magnets 434a and 434b.
3 thus the objective lens 420 arrow C ₄ and the direction to the drive control shown in FIG. 46, controls the focusing direction.
When correcting a track shift of a light spot (not shown), a desired current is applied to the tracking coils 451a and 451b, and an electromagnetic force obtained by interaction with a magnetic force generated by the tracking magnets 437a and 437b. Accordingly, the movable portion 453 is rotated in the arrow D ₄ direction indicated in FIG. 45 around the support shaft 433, controls the tracking direction of the objective lens 420.

FIG. 48 is an exploded perspective view showing the main part of the optical disk device according to Embodiment 14, and two of the four projections for giving an inclination to the objective lens 420 are formed on the objective lens holder 424. Since this embodiment is provided as 424b and 424c, the same operation as the embodiment shown in FIG. 43 can be expected in this embodiment.

FIG. 49 is an exploded perspective view showing an essential part of an optical disk apparatus according to Embodiment 15, and two of the four projections for imparting an inclination angle to the objective lens 420 are connected to the objective lens 42.
0 are provided as protrusions 420a and 420b, and in this embodiment,
The same operation as the embodiment shown in FIG. 43 can be expected.

FIG. 50 is an exploded perspective view showing a main part of an optical disk device according to Embodiment 16, and two of the four projections for imparting an inclination to the objective lens 420
0 are provided as protrusions 420a and 420b, and two are provided on the objective lens holder 424 as protrusions 424b and 424c. In this embodiment, the same operation as the embodiment shown in FIG. 43 can be expected.

FIG. 51 is an exploded perspective view showing a main part of an optical disk device according to Embodiment 17, wherein a flat plate 421 is provided with a tongue piece 421a for regulating in-plane rotation, and an objective lens holder 424 is provided.
This shows another embodiment in which a notch 424d into which the tongue piece 421a fits is provided, and it is possible to limit the direction of inclination adjustment of the objective lens 420.

FIG. 52 is an exploded perspective view showing a main part of an optical disk apparatus according to Embodiment 18, wherein a flat plate 421 is provided with a tongue piece 421a for restricting in-plane rotation and an objective lens.
The tongue 420c for restricting rotation in the in-plane direction is also provided on the 420, and fits into the notch 424d provided on the objective lens holder 424, which limits the direction of tilt angle adjustment of the objective lens 420. It is possible to do.

In each of the above embodiments, the case where the present invention is used for adjusting the inclination of the objective lens has been described. However, the present invention is also applicable to other lenses such as a collimator lens or to an optical system such as a reflection mirror. It goes without saying that you can do it.

In each of the above embodiments, the case where the present invention is used for adjusting the inclination of the objective lens alone has been described. However, the present invention includes the entire objective lens driving device or the objective lens driving device and the light source unit and the light detecting unit. Needless to say, it can be used for adjusting the tilt of the entire optical head device.

FIG. 53 is an exploded perspective view of a main part of an optical disk apparatus according to Embodiment 19, FIG. 54 is a plan view of a main part of FIG. 53, and FIG.
53 and FIG. 56 and FIG. 57 are main part cross-sectional views showing a driving state of the optical disc device of FIG. 53 in the focusing direction, and FIG. 58 is a detailed view showing the shape of the leaf spring part of FIG. is there.

53 to 58, reference numeral 501 denotes a base, which has a light beam passage hole 501a on its bottom surface so that a light beam 502 emitted from a light source (not shown) can enter from the bottom surface. The lower end of the support shaft 503 is held by the fixing hole 501b. Reference numerals 504a and 504b denote focusing magnets magnetized in the vertical direction, and are adhered and fixed to the base 501 together with the focusing yokes 505a and 505b.

Reference numerals 506a and 506b denote tracking magnets magnetized in two poles in the left-right direction. Tracking yokes 507a and 507b are provided on the back surface, respectively.

Reference numeral 510 denotes a lens holder formed of a plastic material, and reference numeral 511 denotes an objective lens fixed to one end of the lens holder 510 in the longitudinal direction.
Light is condensed as a condensed spot 514 on 512 information recording surfaces 513.

Reference numerals 516a and 516b denote a pair of leaf springs having an inner peripheral portion fixed to the support shaft 503 and an outer peripheral portion to the lens holder 510, and having a substantially concentric shape with respect to the support shaft 503. Support shaft
The axial positioning of the leaf springs 516a, 516b with respect to 503
This can be easily performed by the steps provided on the support shaft 503. A focusing coil 517 is fixed to the lens holder 510 so as to be coaxial with the leaf springs 516a and 516b, and is disposed at a position facing the focusing yokes 505a and 505b. Reference numerals 518a and 518b denote tracking coils adhesively fixed to both side surfaces of the lens holder 510.

Next, the operation will be described. Focusing spot
To correct the focus shift of 514, a desired current is applied to the focusing coil 517, and the lens holder 510 is moved along the support shaft 503 by the electromagnetic force obtained by the interaction with the magnetic force generated by the focusing magnets 504a and 504b. the objective lens 511 is driven and controlled in the drawing the arrow C ₄ direction by causing moved controls the focusing direction.

When correcting a track shift of the condensing spot 514, a desired current is applied to the tracking coils 518a and 518b, and the tracking magnets 506a and 506b are applied.
By electromagnetic force but obtained by interaction with the magnetic force generated, leaf springs 516a about the support shaft 503, 516b and rotate the lens holder 510 is deformed in a spiral shape in an arrow D ₄ direction in FIG. 54, the objective The tracking direction of the lens 511 is controlled.

FIG. 59 is a cross-sectional view of a main part of an optical disk device according to the twentieth embodiment. The same reference numerals as in FIG. 55 denote the same parts, and 515 denotes an objective lens 511 in the longitudinal direction of a lens holder 510. The balance weight is fixed to one end of the movable shaft, and is arranged such that the position of the center of gravity of the movable portion including the lens holder 510 and the like is arranged on the support shaft 503.

In this embodiment, a dynamic balance in the rotational direction about the support shaft 503 is ensured, and a rotational moment is generated in the movable portion even when the objective lens driving device performs a seek operation on the optical disk 512. Therefore, there is an advantage that unnecessary residual resonance does not occur after seeking.

FIG. 60 is an enlarged perspective view of a leaf spring used in the optical disk device according to the twenty-first embodiment. In the present embodiment, an example is shown in which the leaf springs 519a and 519b have bent portions 519c and 519d not only in a plane perpendicular to the support axis but also out of the plane. With the leaf spring having this shape, unnecessary torsional resonance mode of the leaf spring can be suppressed particularly at the time of driving control in the tracking direction.

FIG. 61 is an enlarged perspective view of a leaf spring used in the optical disk device according to the twenty-second embodiment. In the present embodiment, an example in which two leaf springs are mutually connected is shown. Since the leaf spring 520 having this shape can manage the spring constants in the focusing direction and the tracking direction by itself, it is possible to suppress variations in the frequency characteristics of the optical disk device and improve mass productivity.

FIG. 62 is a plan view of a main part of an optical disk device according to Embodiment 23, and the same reference numerals as in FIG. 54 denote the same parts. In this embodiment, the leaf springs 521a, 521b (521b
(Not shown) shows an example in which an elastic member 522 is arranged between the inner peripheral portion and the support shaft 503. In this embodiment, the resonance peak of the leaf spring can be reduced, and the spring constant of the leaf spring in the tracking direction, in which the spring constant tends to increase, can be easily set to a desired value.

FIG. 63 is an exploded perspective view showing a main part of an optical disk device according to Embodiment 24, and FIG. 64 is a plan view of the main part of FIG.
65 is a fragmentary cross-sectional view of FIG. 63, FIG. 66, in the optical disc apparatus shown in FIG. 63, the objective lens angle when the optical axis of the single objective lens has a tilt angle theta ₆ relative to the mounting surface It is a principal part sectional view showing the state after adjustment.

In FIGS. 63 to 66, reference numeral 601 denotes a base which is a fixed portion, and has a light beam passage hole 601a on the bottom surface so that a light beam 602 emitted from a light source (not shown) can be incident from the bottom surface. In addition, the fixing hole 601b holds the lower end of the support shaft 603 coated with a fluorine resin having a small coefficient of friction. Reference numerals 604a and 604b denote focusing magnets magnetized in the vertical direction, and are bonded and fixed to the base 601 together with the focusing yokes 605a and 605b.

Reference numerals 606a and 606b denote tracking magnets magnetized in two poles in the left-right direction, and tracking yokes 607a and 607b are provided on the back surface, respectively. 608 a to 608 d are screw holes provided in the base 601.

Reference numeral 610 denotes a lens holder formed of a plastic material, and 611 denotes an objective lens fixed to one end of the lens holder 610 in the longitudinal direction.
Light is condensed as a converging spot 614 on an information recording surface 613 in 612. A balance weight 615 is fixed to one end of the lens holder 610 where the objective lens 611 in the longitudinal direction is not arranged.

Reference numeral 616 denotes a bearing fixed to the lens holder 610 so as to have an axis parallel to the optical axis of the objective lens 611, and is fitted to the support shaft 603. A focusing coil 617 is fixed to the lens holder 610 so as to be coaxial with the bearing 616, and is disposed at a position facing the focusing yokes 605a and 605b. Reference numerals 618a and 618b denote tracking coils adhered and fixed to both side surfaces of the lens holder 610.

Reference numeral 620 denotes a cover which is a holding plate, which includes a light beam passing hole 621 and a holding hole 62 for holding the upper end of the support shaft 603.
2. Cover holes 624a and 624b for fitting with adjustment pins (not shown) for adjusting the position of the cover 620 body and the cover 62
Fixing screws 625a to fix the
It has screw holes 626a-626d into which 625d enters.

Next, the operation will be described. Objective lens 61
When performing angle adjustment of one of the arrow A ₄ direction (jitter direction), tilt the support shaft 603 in the arrow A ₄ direction by translating along the cover 620 on the upper surface of the arrow in the drawing direction AA based 601 As a result, the arrow A ₄ of the objective lens 611
Adjust the angle of the direction. When performing the angle-out adjustment of the arrow B ₄ direction of the objective lens 611 (tracking direction), a support shaft 603 arrow B ₄ by translating along the cover 620 on the upper surface of the arrow in the drawing direction BB base 601
Tilt direction, resulting in performing the arrow B ₄ the direction of angular adjustment of the objective lens 611.

If this angle adjustment is microscopically viewed, the support shaft 603
The rigidity of the fixing hole 601b and the holding hole 622 are slightly deformed because the rigidity of the fixing hole is higher than the rigidity of the base 601 and the cover 620.
Cover 620 for tilt adjustment of about 10 mrad
Is about 0.1 mm when the length of the support shaft 603 is about 10 mm, which is a value that does not cause any problem even in the actual manufacturing process.

After the angle adjustment of the objective lens 611 is completed,
The cover 620 is fixed to the base 601 using fixing screws 625a to 625d.

The operation of driving the objective lens 611 will be described. To correct the focus shift of the focused spot 614, a desired current is applied to the focusing coil 617, and the objective lens is formed by the electromagnetic force obtained by the interaction with the magnetic force generated by the focusing magnets 604a and 604b.
611 drives and controls the arrow C ₄ direction in FIG. 65, controls the focusing direction. When correcting the track shift of the condensing spot 614, the tracking coil 618 is used.
a, 618b, by applying a desired current to the magnetic force generated by the tracking magnets 606a, 606b.
610 is rotated in the arrow D ₄ direction in FIG. 64 by the electromagnetic force,
The tracking direction of the objective lens 611 is controlled.

FIG. 67 is a diagram showing the frequency characteristics in the focus direction of the present embodiment. Unnecessary resonance unlike the conventional example shown in FIG. 97 does not occur.

FIG. 68 is an enlarged sectional view showing a main part of an optical disk device according to Embodiment 25, and the same reference numerals as in FIG. 63 denote the same or corresponding parts. In this embodiment, instead of the support shaft 603 shown in FIG. 63, a support shaft 631 having both ends formed in a substantially semi-convex spherical shape is used, and a fixing hole 633 formed in a substantially semi-concave spherical shape is provided in the base 601. At the same time, the cover 620 is provided with a holding hole 634 formed in a substantially semi-concave spherical shape.
This embodiment shows another embodiment in which the angle of the objective lens 611 is adjusted by adjusting the position of 0 in the direction of the arrow AA or the like in a plane substantially perpendicular to the axis of the support shaft 631.
The same operation as the embodiment shown in FIG. 63 can be expected.

FIG. 69 is an enlarged sectional view showing a main part of an optical disk apparatus according to Embodiment 26, in which a support shaft 641 having a lower rigidity than the support shaft 603 shown in FIG. 63 is used, and the support shaft 631 is bent. By doing so, the angle of the objective lens 611 is adjusted. In the embodiment 26, the same operation as the embodiment 24 shown in FIG. 63 can be expected.

[0174]

Since the present invention is configured as described above, it has the following effects.

The optical disk device according to the first to fourth inventions
Since the two light receiving surface ends facing each other in the split band of the two-segment photodetector are formed in a sawtooth shape or a substantially triangular wave shape, and the two light receiving surface ends are configured to mesh with each other, a focus error occurs. The range in which the signal changes linearly with defocus can be expanded. Further, since it is not necessary to increase the width of the dividing line for separating the light receiving surface of the two-segment photodetector, the frequency characteristics of the two-segment photodetector are degraded even when the reflected light beam from the optical disk enters the dividing band. Absent. Therefore, even if this two-segment photodetector is used for the pupil occlusion method, it is possible to realize a stable focus control operation and an improvement in high frequency characteristics.

Further, the optical disc device according to the fifth aspect of the present invention
A large number of minute light receiving surfaces are arranged in the divisional band of the two-segment photodetector, and the connection lines that electrically connect these minute light receiving surfaces to one of the two light receiving surfaces cross the divisional band at substantially equal intervals. And the connecting lines extending from the respective light receiving surfaces are alternately arranged, and the minute light receiving surface connected by one connecting line is proportional to the distance from the electrically connected light receiving surface. Since the two-segment photodetector is configured to reduce the area, the range in which the focus error signal changes linearly with respect to defocus can be expanded. Further, since the area of the region where the light receiving surface does not exist in the divided band can be reduced, the frequency characteristics of the two-divided photodetector do not deteriorate even when the light from the optical disk enters the divided band. Therefore, even if this two-segment photodetector is used for the pupil occlusion method, it is possible to realize a stable focus control operation and an improvement in high frequency characteristics.

The optical disk device according to the sixth invention is
A large number of rectangular light receiving surfaces are arranged in a divided band of the two-segment photodetector, and adjacent rectangular light receiving surfaces are alternately connected to left and right light receiving surfaces, and a rectangular light receiving surface connected to each light receiving surface is provided. Since the length of the short side is reduced in proportion to the distance from the light receiving surface, the range in which the focus error signal changes linearly with respect to defocus can be expanded. Further, since the area of the region where the light receiving surface does not exist in the divided band can be reduced, the frequency characteristics of the two-divided photodetector do not deteriorate even when the light from the optical disk enters the divided band. Therefore, even if this two-segment photodetector is used for the pupil occlusion method, it is possible to realize a stable focus control operation and an improvement in high frequency characteristics.

The optical disk device according to the seventh to thirteenth aspects of the present invention
As a means for splitting the reflected light beam from the optical disc, a light beam splitting element in which a diffraction grating is formed on substantially a half surface is used.
Inexpensive and stable operation and high efficiency can be realized.

When a light beam splitting element having a flat diffraction grating is used, the flat diffraction grating is manufactured by an optical lithography or etching technique. The device can be realized.

In the optical disc apparatus according to the fourteenth aspect, the reflected light beam is split by the light beam splitting element in which the diffraction grating is formed on substantially the half surface, and the split light beam is divided into two opposite light receiving surface ends. Light is received by a two-segment photodetector that is approximately sawtooth, substantially triangular, or substantially sinusoidal with a pitch smaller than the diameter of the reflected light beam, so that focus control operation can be stabilized and high-frequency characteristics can be improved at low cost. And can be realized efficiently.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a part of an optical disc device according to a first embodiment.

FIG. 2 is a detailed view of a photodetector unit in FIG.

FIG. 3 is a schematic diagram showing a light spot arrangement relationship on an information track in the first embodiment shown in FIG. 1;

FIG. 4 is an enlarged conceptual diagram of an information track for showing a relationship between an information track of the optical disc device and a defocus signal of each light spot in the first embodiment shown in FIG. 1;

FIG. 5 is a diagram showing a defocus signal after calculation of the optical disc device in the first embodiment shown in FIG. 1;

FIG. 6 is a schematic diagram showing a defocus signal at the time of track access of the optical disc device in the first embodiment shown in FIG. 1;

FIG. 7 is a schematic diagram illustrating a part of an optical disc device according to a second embodiment.

FIG. 8 is a schematic diagram showing a light spot arrangement relationship on an information track in the second embodiment shown in FIG. 7;

FIG. 9 is a schematic diagram illustrating a part of an optical disc device according to a third embodiment.

FIG. 10 is a schematic diagram showing an arrangement relationship of light spot arrays on information tracks in a third embodiment shown in FIG. 9;

FIG. 11 is a schematic diagram illustrating a part of an optical disc device according to a fourth embodiment.

12 is a detailed view showing the photodetector section in FIG. 10 in the embodiment shown in FIG. 11;

FIG. 13 is a schematic diagram illustrating a part of an optical disc device according to a fifth embodiment.

14 is a schematic diagram showing a light spot arrangement relationship on an information track in the embodiment shown in FIG.

FIG. 15 is a schematic diagram illustrating a part of an optical disc device according to a sixth embodiment.

16 is an optical path diagram showing details of an optical path of a dove prism unit in FIG. 15 in the embodiment shown in FIG. 15;

FIG. 17 is a plan view showing a two-divided photodetector in the optical disc device according to the first to fourth inventions (Embodiment 7).

18 is an enlarged view of a split band portion of the two-segment photodetector shown in FIG.

FIG. 19 shows a dividing line of the two-part photodetector shown in FIG.
It is a figure shown on coordinates.

FIG. 20 is a diagram illustrating a shape of a converging spot irradiated on a two-segment photodetector when a converging point of an emitted light beam is located on an optical disc.

FIG. 21 is a focus error signal characteristic diagram in a case where a converging spot is shifted in a direction parallel to a split band in a two-segment photodetector.

22 is a characteristic diagram of a focus error signal in the embodiment shown in FIG.

FIG. 23 illustrates a second example of the optical disk device according to the eighth embodiment.
It is a top view which shows a division | segmentation light detector.

FIG. 24 illustrates a second example of the optical disc device according to the ninth embodiment.
It is a top view which shows a division | segmentation light detector.

FIG. 25 is a perspective view showing a basic configuration of an optical disc device according to seventh to thirteenth inventions.

FIG. 26 is a schematic diagram of an optical path when a converging spot of a light beam emitted from an objective lens is on an information recording surface in the embodiment shown in FIG. 25;

FIG. 27 is a diagram illustrating a state of a light beam at a light beam splitting element and a two-segment light detector when a focused spot of a light beam emitted from an objective lens is on an information recording surface in the optical disc device illustrated in FIG. 25;

FIG. 28 is a schematic diagram of an optical path when an information recording surface approaches an objective lens in the optical disc device shown in FIG.

FIG. 29 is a diagram showing a state of a light beam at a light beam splitting element and a two-split photodetector when an information recording surface approaches an objective lens in the optical disc device shown in FIG. 25.

30 is a schematic diagram of an optical path when an information recording surface is separated from an objective lens in the optical disc device shown in FIG.

FIG. 31 shows a light beam splitting element and a light beam splitting element when the information recording surface is separated from the objective lens in the optical disk device shown in FIG.
It is a figure which shows the state of the light beam in a division | segmentation light detector.

32 is a diagram showing a focus error signal obtained in the optical disc device shown in FIG. 25.

FIG. 33 is a perspective view of a light beam splitting element on which a planar diffraction grating having an uneven surface is formed.

FIG. 34 is a configuration diagram showing an optical disc device according to seventh to thirteenth inventions (Embodiment 10).

FIG. 35 is a diagram illustrating a state of a light beam at a light beam splitting element and a two-segment light detector when a converging spot of a light beam emitted from an objective lens is on an information recording surface in the tenth embodiment illustrated in FIG. .

FIG. 36 is a diagram illustrating a state of a light beam at a light beam splitting element and a two-segment light detector when an information recording surface approaches an objective lens in the tenth embodiment illustrated in FIG. 34.

FIG. 37 is a diagram illustrating a state of a light beam at the light beam splitting element and the two-segment light detector when the information recording surface is separated from the objective lens in the tenth embodiment illustrated in FIG.

FIG. 38 is a diagram showing a focus error signal obtained in the tenth embodiment shown in FIG. 34.

FIG. 39 is a diagram illustrating parameters of the optical component according to the tenth embodiment illustrated in FIG. 34.

FIG. 40 is a perspective view of a light beam splitting element on which a refractive index modulation type flat diffraction grating is formed.

FIG. 41 is a perspective view illustrating a configuration of an optical disc device according to an eleventh embodiment.

FIG. 42 is a perspective view of an optical disc device according to Embodiment 12.

FIG. 43 is an exploded perspective view showing an inclination adjusting unit in the optical disc device according to Embodiment 13.

FIG. 44 is a perspective view of a main part of an optical disc device equipped with the inclination adjusting unit shown in FIG. 43;

FIG. 45 is a plan view of a main part of an optical disc device equipped with the inclination adjusting unit shown in FIG. 43;

46 is a sectional view taken along line II of FIG. 45.

47 is a sectional view taken along the line II-II in FIG.

FIG. 48 is an exploded perspective view showing an inclination adjusting unit in the optical disc device according to the fourteenth embodiment.

FIG. 49 is an exploded perspective view showing an inclination adjusting unit in the optical disc device according to Embodiment 15;

FIG. 50 is an exploded perspective view showing an inclination adjusting unit in the optical disc device according to Embodiment 16;

FIG. 51 is an exploded perspective view showing an inclination adjusting unit in the optical disc device according to Embodiment 17;

FIG. 52 is an exploded perspective view showing an inclination adjusting unit in the optical disc device according to Embodiment 18.

FIG. 53 is an exploded perspective view showing a main part of an optical disc device according to Embodiment 19.

FIG. 54 is a plan view of a main part shown in FIG. 53.

FIG. 55 is a sectional view of a main part shown in FIG. 53;

FIG. 56 is a sectional view of a main part showing a driving state in the focusing direction of the embodiment shown in FIGS. 53 to 55;

FIG. 57 is a cross-sectional view of a main part showing a driving state in the focusing direction of the embodiment shown in FIGS. 53 to 55;

FIG. 58 is a plan view showing the shape of the leaf spring of the embodiment shown in FIGS. 53 to 57.

FIG. 59 is a cross-sectional view illustrating a main part of the optical disc device according to Embodiment 20;

FIG. 60 is a perspective view of a leaf spring used in the optical disc device according to Example 21;

FIG. 61 is a perspective view of a leaf spring used in the optical disc device according to Embodiment 22.

FIG. 62 is a plan view showing a main part of an optical disc device according to Embodiment 23;

FIG. 63 is an exploded perspective view showing a main part of an optical disc device according to Embodiment 24.

FIG. 64 is a plan view of a main part shown in FIG. 63.

FIG. 65 is a sectional view of a main part shown in FIG. 63;

FIG. 66 is a cross-sectional view of a main part showing a state after angle adjustment in the embodiment shown in FIGS. 63 to 65;

FIG. 67 is a focus direction frequency characteristic diagram in the embodiment shown in FIGS. 63 to 65.

FIG. 68 is an enlarged cross-sectional view illustrating a main part of an optical disc device according to Embodiment 25;

FIG. 69 is a cross-sectional view of a main part of the optical disc device according to Embodiment 26 in a state after the angle is adjusted;

FIG. 70 is a schematic view showing a part of a conventional optical disk device.

FIG. 71 is an enlarged conceptual diagram of an information track for illustrating a relationship between an information track of an optical disc and a defocus signal of each light spot in the conventional apparatus shown in FIG. 70;

FIG. 72 is a diagram showing a configuration of another conventional device.

73 is a diagram showing a state where the reflected light flux is focused in the conventional device shown in FIG. 72.

74 is a plan view showing a light receiving surface of the two-segment photodetector in the state shown in FIG. 73.

75 is a diagram showing a state where the reflected light beam is irradiated on the light receiving surface before focusing in the conventional device shown in FIG. 72.

76 is a plan view showing a light receiving surface of the two-segment photodetector in the state shown in FIG. 75.

FIG. 77 is a diagram showing a state in which the conventional device shown in FIG. 72 is focused before the reflected light beam is irradiated on the light receiving surface.

FIG. 78 is a plan view showing a light receiving surface of the two-segment photodetector in the state shown in FIG. 77.

FIG. 79 is a plan view showing a light receiving surface of the two-segment photodetector shown in FIG. 72.

FIG. 80 is a characteristic diagram of a focus error signal by the conventional device shown in FIG. 72.

FIG. 81 is a perspective view showing the configuration of still another conventional device.

FIG. 82 is a schematic diagram of an optical path when a converging spot of a light beam emitted from an objective lens is on an information recording surface in the conventional device shown in FIG. 81;

83 is a schematic diagram of an optical path when an information recording surface approaches an objective lens in the conventional device shown in FIG. 81.

84 is a schematic diagram of an optical path when an information recording surface is separated from an objective lens in the conventional device shown in FIG. 81.

FIG. 85 is a view for explaining parameters of optical components in the conventional device shown in FIG. 81.

86 is a diagram showing parameters of optical components in the conventional device shown in FIG. 81.

FIG. 87 is an exploded perspective view showing still another conventional device.

FIG. 88 is a schematic sectional view of the conventional device shown in FIG. 87.

FIG. 89 is a perspective view showing a main part of still another conventional device.

90 is a sectional view taken along line III-III of FIG. 89.

FIG. 91 is a sectional view of a main part of still another conventional device.

92 is a model diagram showing a state in which the adhesive as the fixing means after the angle adjustment becomes a spring element and a damping element in the conventional device shown in FIG. 91.

FIG. 93 is a diagram showing a defocus signal in the conventional device shown in FIG. 70;

FIG. 94 is a schematic diagram showing a defocus signal at the time of track access in the conventional device shown in FIG. 70;

FIG. 95 is a characteristic diagram of a focus error signal based on a detection signal from the light receiving surface shown in FIG. 79.

FIG. 96 is a characteristic diagram showing the sensitivity distribution of the two light receiving surfaces shown in FIG. 79.

97 is a focus direction frequency characteristic diagram of the conventional device shown in FIG. 91.

[Explanation of symbols]

101, 206, 305 Optical disc, 115 land, 116
Groove section, 122a, 122b, 142a-142e, 152a-152c Light spot, 124, 144 Photodetector section, 126 Adder, 127
Control circuit, 129 defocus signal, 145 arithmetic processing circuit, 150 diffraction grating, 160 photodetector, 170a, 170b, 18
1a, 181b Drive coil, 180 Dove prism, 201
Light-emitting source, 207 shielding plate, 216, 217, 221, 222 light-receiving surface,
218, 220, 325, 329, 333 2 split photodetector, 219 split band, 223 minute light receiving surface, 224 connection line, 225 short shape light receiving surface, 226 short shape light receiving surface, 231 split line, 301 light source, 304, 420 , 511, 611 Objective lens, 324, 343 Beam splitting element, 328, 332, 336 Focus spot, 341 Diffraction grating, 342 Non-diffraction grating, 408 Optical axis, 420a, 420
b, 424b, 424c Projection, 420c, 421a Tongue piece, 421 ring-shaped flat plate, 422a, 422b Upper projection, 423a, 423b Lower projection, 424 Objective lens holder, 424a Fin, 424d
Notch, 425 bearing, 426 Focusing coil, 503 support shaft, 510, 610 Lens holder, 515
Balance weight, 516a, 516b leaf spring, 601 base, 601b, 633 fixing hole, 603, 631, 641 support shaft, 62
0 Cover, 622, 634 Holding hole, FES, FESa, F
ESb, FESc Focus error signal, E Emitted light flux, R,
R1, R2 reflected light beam, Ra, Rb, Rc light beam, L1
First straight line, L2 Second straight line.

Continued on the front page (72) Inventor Mitsuru Irie 1 Baba Zoshosho, Nagaokakyo-shi, Kyoto Prefecture Mitsubishi Electric Corp. Imaging Systems Development Laboratory (72) Inventor Kazuhiko Nakane 8-1-1 Honcho Tsukaguchi, Amagasaki-shi, Hyogo Mitsubishi Inside Electric Industrial Co., Ltd. (72) Inventor Kenjiro Kimome 1 Baba Zhousho, Nagaokakyo-shi, Kyoto Prefecture Mitsubishi Electric Co., Ltd. Inside Imaging System Development Laboratory (72) Inventor Hideaki Kobachi 1 Baba Zhoujo, Nagaokakyo-shi, Kyoto Address Mitsubishi Electric Corporation Video Systems Development Laboratory (56) References JP-A-4-222933 (JP, A) JP-A-59-231736 (JP, A) (58) Fields investigated (Int. Cl. ⁶⁾ G11B 7/09-7/095 G11B 7/135

Claims (14)

(57) [Claims] 1. An optical disk, wherein light emitted from a light source is condensed and irradiated on an optical disk via an optical system, and a part of a reflected light beam from the optical disk is shielded so that two light receiving surfaces of a two-divided photodetector face each other. In an optical disc apparatus that irradiates near the band and obtains a focus error signal based on output signals from two light receiving surfaces of the two-divided photodetector, the shape of an end of the light receiving surface in the divided band of the two-divided photodetector is An optical disk device characterized in that the optical disk device has a substantially serrated or substantially triangular or substantially sinusoidal shape having a pitch smaller than the diameter of the reflected light beam and meshes with each other. 2. The method according to claim 1, wherein the pitch of the substantially triangular wave portion at the end of the light receiving surface of the two-segment photodetector is smaller than the diameter of the reflected light beam.
Let d be the width of the substantially triangular wave-shaped portion in the direction crossing the dividing band, and y
When the origin of the z-coordinate system is set at the center of the divisional band and the longitudinal direction of the divisional band is set in the y direction, the division line dividing the two light receiving surfaces is y = (p / d) z + 2npy = 2. The optical disk device according to claim 1, wherein-(p / d) z + (2n-1) p, where -d / 2≤z≤d / 2, n: an integer. 3. A pitch p of a substantially saw-toothed, substantially triangular or substantially sinusoidal portion at the end of the light receiving surface of the two-divided photodetector,
NA ₁ ≦ λ / 2p is established between the wavelength λ of the light source and the numerical aperture NA ₁ of the reflected light beam from the optical disk incident on the two-divided photodetector. Claim 1
An optical disk device as described in the above. 4. A width d in a direction crossing a divided band of a substantially saw-toothed, substantially triangular or substantially sinusoidal portion at an end of a light receiving surface of the two-divided photodetector, a wavelength λ of the light source, and the two-divided light. between the aperture NA ₁ of the reflected light beam from the optical disk is incident on the detector, as d ≧ λ / NA ₁ is satisfied, characterized in that have configured the two-divided optical detector according Item 2. The optical disk device according to item 1. 5. A light beam emitted from a light source is condensed and irradiated on an optical disk via an optical system, and a part of a reflected light beam from the optical disk is shielded so that two light receiving surfaces of a two-divided photodetector face each other. In an optical disc apparatus for irradiating near a band and obtaining a focus error signal based on output signals from two light receiving surfaces of the two-divided photodetector, a plurality of divided micro-elements are divided within the divided band of the two-divided photodetector. A light receiving surface is formed, and connection lines for electrically connecting these minute light receiving surfaces to one of the two light receiving surfaces are provided at substantially equal intervals in a direction crossing the dividing band, and extend from each light receiving surface. The connection lines are alternately arranged, and the small light receiving surface connected by one connection line is reduced in proportion to the distance from the light receiving surface electrically connected thereto. Make sure that a split photodetector is An optical disc device characterized by the following. 6. A light beam emitted from a light source is condensed and irradiated on an optical disk via an optical system, and a part of a reflected light beam from the optical disk is shielded so that two light receiving surfaces of a two-divided photodetector face each other. In an optical disc apparatus for irradiating near a band and obtaining a focus error signal based on output signals from two light receiving surfaces of the two-divided photodetector, a large number of rectangular light-receiving surfaces are provided within a divided band of the two-divided photodetector. The adjacent rectangular light receiving surfaces are alternately connected to the left and right light receiving surfaces, and the length of the short side of the rectangular light receiving surface connected to each light receiving surface is approximately equal to the distance from the light receiving surface. An optical disk device, wherein the two-divided photodetector is configured to decrease in proportion. 7. A light beam emitted from a light source is condensed and irradiated on an optical disk via an optical system, a reflected light beam from the optical disk is divided into three light beams, and each of the divided reflected light beams is divided into three light beams. A condensed spot is irradiated near the dividing line of the two-part photodetector, and when the emitted light from the light source is focused on the optical disk, the condensed spot of the reflected light beam is placed on the dividing line of the two-part photodetector. Is formed, and in the optical disc apparatus for obtaining a focus error signal based on a signal of the sum of the output difference signals of the three two-divided photodetectors, means for dividing the reflected light beam into three light beams is substantially equivalent to an incident surface. The light beam splitting element has a diffraction grating part on one side, and the light beam splitting element has a boundary line between the diffraction grating part and the non-diffraction grating part, and the direction of the straight line is the guide groove on the optical disk. Direction approximately perpendicular to the tangential direction of And the reflected light flux 2 generated by the diffraction grating section.
An optical disc device characterized in that a focus error signal is obtained using a single diffracted light beam and a single light beam that does not pass through a diffraction grating section. 8. A light beam emitted from a light source is condensed and irradiated on an optical disk via an optical system, a reflected light beam from the optical disk is divided into three light beams, and each of the divided reflected light beams is divided into three light beams. A condensed spot is irradiated near the dividing line of the two-part photodetector, and when the emitted light from the light source is focused on the optical disk, the condensed spot of the reflected light beam is placed on the dividing line of the two-part photodetector. Is formed, and in the optical disc apparatus that obtains a focus error signal based on a signal of the sum of output difference signals of the three two-divided photodetectors, a unit that divides the reflected light beam into three light beams, A substantially half surface is a diffraction grating portion on which a transmission type or reflection type planar diffraction grating is formed, and the remaining substantially half surface is configured by a light beam splitting element which is a transmissive or reflective non-diffraction grating portion, The light beam splitting element is The boundary line with the diffraction grating portion is a straight line, and the direction of the straight line is projected in a direction substantially orthogonal to the tangential direction of the guide groove on the optical disk. The boundary between the portion and the non-diffraction grating portion is geometrically arranged so as to substantially bisect the reflected light beam, and the two diffracted lights of the reflected light beam generated by the diffraction grating portion and the An optical disc apparatus characterized in that a focus error signal is obtained using one light beam from a non-diffraction grating portion. 9. The light beam splitting device, wherein the grating line of the diffraction grating portion is a straight line, the grating period is constant, and the direction of the grating line is equal to the boundary between the diffraction grating portion and the non-diffraction grating portion. 9. The optical disk device according to claim 7, wherein the optical disk device is substantially perpendicular to the direction. 10. The planar diffraction grating of the light beam splitting element has a size of 2
Value phase depth, and the phase modulation duty is approximately 5
9. The optical disk apparatus according to claim 8, wherein the phase modulation depth is approximately 180 degrees at 0%. 11. The optical disk device according to claim 8, wherein the phase modulation of the planar diffraction grating of the light beam splitting element is realized by unevenness of the surface or modulation of the refractive index. 12. The two-segment photodetector includes two two-segment photodetectors that receive a light beam obtained by the diffraction action of the diffraction grating part of the light beam splitting element and a non-diffraction grating part of the light beam splitting element. 9. The optical disk device according to claim 7, wherein one two-segment light detector for receiving a light beam is contained in one package. 13. The two-divided photodetector, wherein the dividing lines of each of the two-divided photodetectors are substantially straight, and all the dividing lines are present on one substantially straight line. An optical disk device according to claim 7 or 8. 14. A light beam emitted from a light source is condensed and irradiated on an optical disk via an optical system, and a reflected light beam from the optical disk is split into a plurality of light beams by a light beam splitting unit. In the vicinity of the dividing line of the plurality of two-divided photodetectors, and when the focused spot of the outgoing light is focused on the optical disc, the focused spot of the reflected light flux is approximately on the dividing line. An optical disc device in which the two-divided photodetectors are arranged so as to be positioned and a focus error signal is obtained based on output signals of the plurality of two-divided photodetectors.
The light beam splitting means is constituted by an element whose half surface is a diffraction grating portion, and the shape of the split line of the two-split photodetector is substantially saw-toothed with a pitch smaller than the diameter of the reflected light beam.
An optical disk device having a substantially triangular wave shape or a substantially sine wave shape.