JP2643555B2 - Optical information recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus, and more particularly, to a signal detection system of an optical information recording / reproducing apparatus.

[Conventional technology]

Conventionally, as shown in FIG. 8, this type of optical information recording / reproducing apparatus includes a laser diode 5, a collimating lens 4 for converting divergent light emitted from the laser diode 5 into parallel light, and a collimating lens 4. Two beam splitters 48 and 49 for separating the light transmitted and directed to the optical information recording medium 1 and the reflected return light from the optical information recording medium 1
An objective lens 2 that converges light transmitted through these beam splitters 48 and 49 on the surface of the optical information recording medium 1;
A converging lens 50 for converging the reflected return light reflected by the optical information recording medium 1 and passing through the objective lens 2 and separated by the beam splitter 48; Wollaston prism 51 for separating into two polarization components, and Wollaston prism 51
A recorded information signal detection system having a two-divided photodetector 52 for independently detecting the two light beams separated by the light source; and for separating reflected return light from the optical information recording medium 1 transmitted through the beam splitter 48. Beam splitter 49,
A converging lens 53 for converging the reflected return light separated from the beam splitter 49, and a beam for separating the light beam converged by the converging lens 50 into light for track error detection and light for focus error detection Splitter 55,
A two-divided photodetector 54 for detecting a track error, and a knife edge 56 for detecting a focus error by a knife edge method.
And a spot position error signal detection system provided with a two-segment photodetector 54; and the recording information signal detection system and the spot position error signal detection system are independent.

[Problems to be solved by the invention]

The above-mentioned conventional optical information recording / reproducing apparatus has a disadvantage that the number of components increases because the recording information signal detection system and the spot position error detection system are independent. Further, since two beam splitters exist between the laser diode and the objective lens, there is a drawback that if the use efficiency of the light for signal detection is increased, the use efficiency of the outgoing light is reduced. At the same time, there is a disadvantage that the amount of light distributed to the spot position error detection system fluctuates due to the recording information signal, and the recording information wraps around the spot position error detection signal. Furthermore, since the focus error is detected by the knife edge method, a certain amount of light is shielded by the knife edge, so that there is a disadvantage that the light use efficiency of the focus error detection system is low.

[Means for solving the problem]

The optical information recording / reproducing apparatus of the present invention comprises a laser diode, a collimating lens for converting divergent light emitted from the laser diode into parallel light, light from the laser diode toward an optical information recording medium, and the optical information. A beam splitter for separating reflected return light from a recording medium, an objective lens for converging light transmitted through the beam splitter and directed to the optical information recording medium on the optical information recording medium surface, and the optical information recording medium Is divided into at least four regions in a plane perpendicular to the optical axis of the reflected light, and at least four components of the divided reflected light are divided with respect to the optical axis of the reflected light. An optical path splitter for separating the light beams so as to have independent emission angles, and at least four light beams separated by the optical path splitter. A converging lens, a birefringent double-image polarizing prism that separates each of the at least four light beams converged by the converging lens into at least eight polarization components orthogonal to each other, and is separated into the at least eight polarization components. It comprises a photodetector composed of at least four two-divided photodetectors for detecting light beams independently and at least four independent photodetectors.
The track pitch of the optical information recording medium is P (μ
m), the wavelength of light emitted from the laser diode is λ (nm), the numerical aperture of the objective lens is NA, and the radius of the entrance pupil is a (mm), and (NA · P−λ) ≦ 0. And r
= A · λ / (NA · P), and the optical path splitter sets the track direction of the optical information recording medium in the plane perpendicular to the optical axis to the Y axis with the intersection point of the optical axis and the plane as the origin. And, when the direction orthogonal to the track is the X axis, the dividing line of the optical path splitter starts from the approximate origin, An extension line passing through An extension line passing through An extension line passing through And an extended line passing through.

Further, the four regions formed by the optical path splitter start from the origin of the division line, and a region sandwiched by an extension line passing through the point L and an extension line passing through the point I is a region A. A region sandwiched by an extension passing through and the extension passing through the point J is a region B, a region sandwiched by an extension passing through the point J and an extension passing through the point K is a region C, A region sandwiched between an extended line passing through and the extended line passing through the point L is defined as a region D, and the components of the return light divided into the regions A, B, C, and D correspond to the respective regions, and return to the respective regions. light components a, B, together with the C and D, 2 two polarization components each of which may after passing the convergent lens and the birefringent double image polarizing prisms are perpendicular to each other, the light flux a _o and the light beam a _e, the light beam B _o And luminous flux
B _e, separated into a light flux C _o and the light beam C _e and flux D _o and the light beam D _e,
In addition, the light receiving surfaces of the at least four split light detecting portions of the photodetector are light receiving surfaces a, b, c, d, e, f, g, and h, respectively, and the at least four independent light detection portions are provided. the light-receiving surface i of the light receiving surface of the parts, and j, k and l, the light beam a _o is the light receiving surface a and the b, on the light flux a _e is the light receiving surface e and f, the light beam B _o is the light receiving on the face c and d, the light beam B _e is the light receiving surface on g and h, the light beam C _o is the light receiving plane j, the light beam C _e is the light receiving surface on l, the light beam D _o is the light receiving surface i And the light flux _De is irradiated onto the light receiving surface k, and the light receiving surfaces a, b, c, d,
The outputs of e, f, g, h, i, j, k and l are V (a), V
(B), V (c), V (d), V (e), V (f), V (g), V
(H), V (i), V (j), and V (l), as focus error F, F = {V (a) + V (d) + V (e) + V (h)} − { V (c) + V (b) + V (g) + V (f)}, and as an error signal T, T = {V (i) + V (k)} − {V (j) + V (L)｝
検 出 V (a) + V (b) + V (c) + V (d) + V (i) + V (j)} − ｛V (e) + V (f) + V (g) + V (h) + V (k) + V (l)}, and as a signal of the reflected light amount fluctuation, {V (a) + V (b) + V (c) + V (d) + V (e) + V (f) + V (g) + V (h)}.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 2 is a diagram showing an outline of the optical information recording / reproducing apparatus of the present invention. In FIG. 2, divergent light emitted from a laser diode 5 is converted into parallel light by a collimator lens 4 and condensed on the surface of the optical information recording medium 1 by an objective lens 2 via a beam splitter 3. The reflected return light from the surface of the optical information recording medium 1 is again separated from the incoming light by the beam splitter 3 via the objective lens 2. The reflected return light obtained from the beam splitter 3 is passed through an optical path splitter 6, a converging lens 7, and a birefringent double-image polarizing prism 8 arranged so as to coincide with the optical axis of the reflected return light. 9
Is detected by

FIG. 1 is a basic configuration diagram showing one embodiment of the present invention.
The basic configuration shown in FIG. 1 corresponds to the optical path splitter 6 shown in FIG.
, A Wollaston prism 46 is used as the birefringent double-image polarizing prism 8, and a 12-divided photodetector 47 is used as the photodetector 9.

FIG. 3 is a view showing the pattern of the return light beam and the setting of the X axis and the Y axis with respect to the return light optical axis.

FIG. 4 is a diagram showing divided areas in one embodiment of the optical path splitter.

FIG. 5 is a diagram showing a relationship between a return light beam and a pattern in one embodiment of the optical path splitter shown in FIG.

Here, the track pitch of the optical information recording medium 1 used is 1.6 μm, the wavelength of light emitted from the laser diode 5 used is 0.83 μm, and the numerical aperture of the objective lens 2 is 0.5.
When the radius of the entrance pupil is 2.15 mm, as shown in FIG. 3, FIG. 4, and FIG. 5, in the plane orthogonal to the optical axis of the reflected return light 62, When the intersection between the optical axis and a plane perpendicular to the optical axis is defined as the origin 0, the Y axis is taken in the track direction of the optical information recording medium 1, and the X axis is taken in the direction perpendicular to the track, the dividing line is expressed in units. mm, a half line starting at point (0,0) and passing through point (1.12,1.84), a half line starting at point (0,0) and passing through point (1.12, −1.84), and point (0,0) 0) as a starting point, a half line passing through the point (−1.12, −1.84), and a half line passing through the point (−1.12, 1.84) starting from the point (0,0). A (58), area B
(59), a region C (60) and a region D (61). Then, these areas A (58) to D (61)
Uses a four-divided prism 45 in which cotton perpendicular to the optical axis has an independent angle and the rear surface of the optical path is parallel to the orthogonal plane.

It is needless to say that the effect of the four-segment prism 45 is the same even if the surface parallel to the orthogonal plane and the surface having four independent angles are reversed in the optical path.
Further, the optical path splitter 6 is not limited to the prism, and has the above-described divided areas A (58) to D (61), and includes the areas A (58) to D (61) after passing through the optical path splitter 6. The optical path of the passing light is
What is necessary is to have an independent angle with respect to the optical axis, and it is possible to use one using a diffracted light such as a hologram element, a combination of reflection mirrors, and the like, and it is also possible to integrally form it with the converging lens 7. is there.

Next, the components of the reflected return light 62 split by the split areas A to D of the optical path splitter 6 are respectively set as return light components A, B, C, and D corresponding to the areas. These four return light components A ~
D passes through the converging lens 7 and the Wollaston prism 46, and is separated into two orthogonal polarization components.

Here, with respect to the polarized light component separated by the Wollaston prism 46, the suffix o is added to the ordinary line, and the suffix e is added to the extraordinary ray. That is, the four return light component A~D each _{A o, A e, B o} , B e, C o, C e, is separated into eight light flux D _o and D _e.

The birefringent double-image polarizing prism 8 is a birefringent polarizing prism, as long as it can separate two components of ordinary light and extraordinary light. Needless to say, a Rochon prism or the like can be used as another method.

Then, eight light beam A _o described _{above, A e, B o, B} e, C o, C e, D o and D _e
Are converged on the respective light receiving surfaces of the light detecting section of the 12-split photodetector 47 shown in FIG.

Then, as shown in FIG. 7, the light beam A _o (37) is on the light receiving surface a (15) and light receiving surface b (16) of the two-segment light detection unit, and the light beam A _e (38) is two-segment light detection. on the light-receiving surface e (19) and the light-receiving surface f (20) parts, the light flux C _o (41) is on the two-divided light detector of the light receiving surface c (17) and a light-receiving surface d (18), the light beam C _e (42) on the light receiving surface of the two-split photo detector g (21) and the light-receiving surface h (22), the light flux B _o (39) is formed on the light receiving surface j (34), the light flux B _e (40) is received on the face l (36), the light flux D _o (43) is formed on the light receiving surface i (33), the light flux D _e (44) is formed on the light receiving surface k (35), 12-segment photodetector to match each 47 are arranged. At this time, each light receiving surface a, b, c, of the 12-divided photodetector 47
The outputs of d, e, f, g, h, i, j, k, and l are V (a), V
(B), V (c), V (d), V (e), V (f), V (g), V
(H), V (i), V (j), and V (l): (1) The focus error F is: F = ｛V (a) + V (d) + V (e) + V (h) {− {V (c) + V (b) + V (g) + V (f)} (2) When the error signal T is: T = {V (i) + V (k)} − {V (j) + V (l) (3) The magneto-optical signal is expressed as follows: {V (a) + V (b) + V (c) + V (d) + V (i) + V (j)} − ΔV (e) + V (f) + V (g) + V (H) + V (k) + V (l)｝ (4) Reflected light amount fluctuation signal (write-once type / phase change signal)
｛V (a) + V (b) + V (c) + V (d) + V (e)
+ V (f) + V (g) + V (h)} is calculated by using an arithmetic circuit (not shown) to detect a recording information signal and a spot position error signal.

〔The invention's effect〕

As described above, in the optical information recording / reproducing apparatus of the present invention, the recording information signal detection system and the spot position error signal detection system are composed of only the optical path splitter, the convergent lens, the birefringent double image polarizing prism, and the photodetector. The configuration has an effect that the number of components can be reduced. Further, with this configuration, since there is no light-shielding portion due to the knife edge in the error detection portion, the light use efficiency is increased and the signal amplitude can be increased. In addition, since the recording information signal and the spot position error signal are detected using the same light, it is possible to keep the reflectance of the beam splitter low, and in addition to reducing the number of beam splitters to one, This has the effect of increasing the efficiency of using light in the optical path from the diode to the optical information recording medium. That is, since a sufficient light emission output is obtained as an outgoing optical path, there is also an effect that the reflectivity of the beam splitter is increased to increase both the recording information signal and the spot position error signal. Further, since the light from which most of the first-order diffracted light component is removed is extracted as a beam for focus error detection by the optical path splitter, a stable focus error signal can be obtained with a very small wraparound of the track error signal. Since the spot position error signal is detected using substantially the entire amount of the return reflected light, there is an effect that the rounding of the error signal of the magneto-optical signal can be greatly reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a basic configuration diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an outline of an optical information recording / reproducing apparatus of the present invention, FIG.
The figure shows the return light beam pattern and X with respect to the return light optical axis.
FIG. 4 is a diagram showing the setting of the axis and the Y axis, FIG. 4 is a diagram showing a divided area in one embodiment of the optical path splitter, and FIG. 5 is a diagram showing a return light beam and a pattern in one embodiment of the optical path splitter in FIG. FIG. 6 is a diagram showing a light receiving surface of a 12-split photodetector which is an embodiment of the photodetector, and FIG. 7 is a diagram showing a light-receiving surface of the 12-split photodetector shown in FIG. FIG. 8 is a diagram showing an example of a relationship with a beam spot obtained, and FIG. 8 is a basic configuration diagram showing a conventional example. DESCRIPTION OF SYMBOLS 1 ... Optical information recording medium, 2 ... Objective lens, 3 ... Beam splitter, 4 ... Collimating lens, 5 ... Laser diode, 6 ... Optical path splitter, 7 ... Convergent lens,
8 Birefringent double image polarizing prism, 9 Photodetector, 10
… Origin 0, 11… Point I, 12… Point J, 13… Point K, 14
... Point L, 15 to 22, 33 to 36... Light receiving surface, 37 to 44.
_o , A _e , B _o ~ D _e 45... 4-split prism, 46... Wollaston prism, 47... 12-split photodetector, 58.
... Area B, 60... Area C, 61... Area D, 62.

Claims (1)

(57) [Claims] A laser diode; a collimating lens for converting divergent light emitted from the laser diode into parallel light; light traveling from the laser diode toward an optical information recording medium; and reflection returning from the optical information recording medium. A beam splitter for separating light from the light, an objective lens for converging light transmitted through the beam splitter and traveling toward the optical information recording medium onto the optical information recording medium surface, and the reflected return light from the optical information recording medium Is divided into at least four regions in a plane perpendicular to the optical axis of the reflected return light, and at least 4 regions of the divided reflected return light are divided.
An optical path splitter for decomposing the three components so as to have independent emission angles with respect to the reflected return optical axis; a converging lens for converging at least four light beams split by the optical path splitter; and a converging lens. A birefringent polarizing prism that separates each of the converged light beams into at least eight polarization components orthogonal to each other; and at least four light beams that independently detect the light beams separated into the at least eight polarization components. An optical path splitter, the convergent lens, the birefringent polarizing prism, and the optical detector, wherein an optical axis of the reflected return light from the optical information recording medium is provided. An optical information recording / reproducing apparatus disposed so as to coincide with the optical information recording medium; The P (μm), the wavelength of light emitted from the laser diode lambda (m
m), the numerical aperture of the objective lens is NA, and the radius of the entrance pupil is a
(Mm), (NA · P−λ) ≦ 0, and r = a · λ
/ (NA · P), wherein the optical path splitter has, in a plane perpendicular to the optical axis, an intersection point between the optical axis and the plane as an origin, a track direction of the optical information recording medium as a Y axis, and When the direction orthogonal to the track is the X axis, the dividing line of the optical path divider has the origin as a starting point, An extension line passing through An extension line passing through An extension line passing through An optical information recording / reproducing apparatus, comprising: