JPH0736234B2 - Optical disk device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A Field of Industrial Application The present invention relates to an optical disc device, and more particularly to improving the tracking performance.

B. Summary of the Invention The present invention is an optical disk device for condensing three lights on a disk surface through an objective lens and performing recording signal reproduction and tracking control. By converting so that the ratio of the amount of light in the peripheral portion to the amount of light is increased and entering the objective lens,
It has improved tracking performance.

C Conventional Technology Conventionally, in an optical disc device, for example, by using a configuration as shown in FIG. 8, a track 3 on a rotary disc 2 in which recording pits 1 having a duty corresponding to recorded information are juxtaposed. The laser light is irradiated, and the reflected light of the reflected laser spot 4 is detected to reproduce the recorded information.

That is, the optical slider 5 movably provided in the radial direction of the disk 2 includes a laser light source 6 made of, for example, a semiconductor laser, a spectroscopic diffraction grating 7, a beam splitter 11,
The laser light LA emitted from the laser light source 6 having the objective lens 8 is diffracted and dispersed by the diffraction grating 7 and then focused on the disk 2 via the beam splitter 11 and the objective lens 8.

The laser spots 4, 1 mainly formed by the 0th-order diffracted light are formed on the disk 2 by the diffraction of the laser light LA by the diffraction grating 7.
A laser spot 9 is formed by the next diffracted light and a laser spot 10 is formed by the -1st diffracted light.

Of these, the primary and negative first-order laser spots 9 and 10 are irradiated at positions slightly deviated inward and outward with respect to the track 3, and the reflected light from the disk 2 of each laser spot 9 and 10 is an objective. After being reflected by the beam splitter 11 via the lens 8, it is guided to the corresponding photoelectric conversion elements 12 and 13 formed of, for example, photodiodes. The reflectance differs between the pit 1 and the portion other than the pit, and when the 0th-order laser spot 4 deviates from the track 3 based on the detection signals from the photoelectric conversion elements 12 and 13, the 1st-order and -1st-order laser spots 9
A tracking error is detected by differentially changing the amount of reflected light from the tracks 3 of 10 and 10, and tracking control is performed by this tracking error signal.

In this way, the 0th-order laser spot 4 is irradiated onto the track 3, and the reflected light from the laser spot 4 from the track 3 is reflected by the objective lens 8 and the beam splitter 11.
The information recorded on the track 3 is reproduced on the basis of the detection signal from the photoelectric conversion element 14 which is a photodiode, for example.

D Problem to be Solved by the Invention In order to accurately reproduce the recorded information recorded on the disk 2 to such an extent that it is practically sufficient, it is necessary to appropriately perform tracking control. Therefore, a tracking error signal that responds to the shift amount with high sensitivity is required, and is conventionally output from the photoelectric conversion element 12 as shown in the following equation TER = EF ... (1). A detection signal E corresponding to the amount of reflected light of the primary laser spot 9 and a -1st-order laser spot 10 output from the photoelectric conversion element 13.
The difference of the detection signal F according to the amount of reflected light is used as the tracking error signal TER.

By the way, there are a plurality of standards for the disk 2, and there are track pitches of 1.4 [μm] and 2.0 [μm], for example. It is conceivable to separately configure the optical system of the optical slider 5 for each disk of each track pitch. Significant merits can be expected in terms of productivity such as the number of production lines.

However, in the conventional optical system, as shown in FIG.
Between the track pitch and the tracking error signal TER, the tracking error signal TER when the 0th laser spot 4 is located on the track 3 is -2.7 [dB] when the track pitch is 1.4 [μm]. However, the track pitch is 1.3 [dB] when the track pitch is 2.0 [μm], and it differs greatly depending on the difference in the track pitch, and it cannot be said to have sufficient versatility.

The present invention has been made in consideration of the above points, and it is an object of the present invention to provide an optical disk device capable of performing accurate tracking control with respect to a plurality of disks having different track pitches by the same optical system. .

E Means for Solving the Problems In order to solve the problems, the light source 6 is used in the present invention.
And stripes and grooves are alternately arranged, and the width of the stripes or grooves is formed to change into a barrel shape. The emitted light LA emitted from the light source 6 is reproduced light and tracking first light. And the second light, and at least the light amount distributions of the first and second lights for tracking are increased so that the light amount ratio of the peripheral portion to the light amount of the central portion is increased when viewed in the radial direction of the disk 2. The diffraction grating 7 for converting the light quantity, the reproduction light emitted from the diffraction grating 7 and the first and second lights for tracking are respectively disc 2
An objective lens 8 for condensing light on the upper track 3 is provided.

F action A part of the light incident on the objective lens 8 is diffracted by the peripheral portion of the objective lens 8. Therefore, the light quantity distribution of the spots 9 and 10 corresponding to the first and second light beams for tracking formed by being condensed on the surface of the disk 2 is also affected by diffraction.

When the light amount distribution of the first and second light beams for tracking of the objective lens 8 is larger than the light amount of the central portion in the radial direction of the disk 2, the spots 9 and 10 for improving the tracking performance. It was found as a result of the examination that the

Therefore, as the diffraction grating 7, stripes and grooves are alternately arranged and the width of the stripes or grooves is formed to change into a barrel shape, and the first and second light beams for tracking are used. The tracking performance can be improved by converting the light quantity distribution so that the light quantity ratio of the peripheral area with respect to the light quantity of the central area increases.

G Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings.

First, the relationship between the shapes of the laser spots 9 and 10 for tracking control and the tracking error signal TER will be examined with reference to FIG. When the laser light is reflected by the pit 1, the reflected signal is diffracted from the pit 1, and the height from the disk surface of the pit 1 is selected to be about ¼ of the wavelength λ of the laser light. The amount of reflected light that reaches the photoelectric conversion elements 12 and 13 is small due to the interference that occurs because of this. On the other hand, the amount of reflected light from the surface of the disk 2 on which the pit 1 is not formed is larger than that.

Since the disk 2 is rotating, the amount of reflected light reaching the photoelectric conversion elements 12 and 13 is large, and the laser spots 9 and 10 that irradiate on the track 3 on which the pits 1 are arranged side by side and the parts other than the track 3 are radiated. It depends on the ratio of laser spots 9 and 10. That is, the larger the ratio of the laser spots 9 and 10 deviating from the track 3, the larger the amount of reflected light detected, and conversely, the larger the ratio of irradiating the track 3 is, the smaller the amount of reflected light.

Here, laser spots 9 and 10 for tracking control
2A has a shape of an ellipse extending in a direction orthogonal to the longitudinal direction of the track 3 along the disk surface (disk radial direction) as shown in FIG. Even if the laser spots 9 and 10 are slightly deviated from the locked state, the ratio of irradiation of the laser spots 9 and 10 onto the track 3 does not change so much. On the other hand, when the laser spots 9 and 10 have a small oval shape in the disk radial direction as shown in FIG. 2C, even if the laser spots 9 and 10 deviate by the same amount from the locked state, The rate at which 10 is irradiated on the track 3 changes rapidly. When the laser spots 9 and 10 are substantially circular as shown in FIG. 2 (B), when the laser spots 9 and 10 deviate from the lock state by the same amount, the track 3 is irradiated with light. Change in the middle.

Therefore, when the tracking is removed from the locked state,
In order to obtain a highly sensitive tracking error signal TER, it is desirable to make the laser spots 9 and 10 for tracking control a short ellipse in the disk radial direction of the track 3 as shown in FIG. 2 (C).

Also, as shown in FIG. 2 (C), the laser spot 9 and
If the shape of 10 is selected, it is possible to obtain the tracking error signal TER even with respect to the disk 2 having a small track pitch, without being affected by the adjacent track 3 as much as possible. Incidentally, in the case of an elliptical shape which is long in the disk radial direction as shown in FIG. 2 (A), an adverse effect due to the adjacent track is less than that in the case of an elliptical shape which is short in the disk radial direction shown in FIG. 2 (C). The range of track pitch values you will receive is large. Therefore, it is desirable that the laser spots 9 and 10 have an elliptical shape that is short in the radial direction of the disk even when the versatility of the various disks 2 having different track pitches is intended.

By the way, there is the following relationship between the light quantity distribution of the incident laser light on the objective lens 8 and the light quantity distribution on the disk surface of the laser spot emitted from the objective lens 8 and condensed on the disk 2. As a result of the examination, it was discovered.

Actually, the size of the objective lens 8 to be used is not so different from the beam diameter of the incident lens light, and therefore, a part of the objective lens 8 is diffracted at the peripheral edge of the objective lens 8 and is reflected on the surface of the disk 2. To reach. Therefore, the laser spots (9, 10) corresponding to the incident laser light having a large amount of light on the peripheral portion are more strongly influenced by the diffraction by the objective lens 8.

For example, as shown in FIG. 3 (A1), the incident laser light LI1 having a Gaussian distribution light quantity distribution in which the light quantity in the central portion is large and the light quantity decreases toward the periphery is transmitted through the objective lens 8 to the disk 2 When the light is focused on the upper side, the light quantity distribution (FIG. 3 (A2)) of the focused laser spot LS1 becomes almost Gaussian distribution shape with almost no influence of diffraction.

Further, as shown in FIG. 3 (B1), the light quantity distribution (FIG. 3 (B2)) of the focused laser spot LS2 corresponding to the incident laser light LI2 having the light quantity distribution of the uniform distribution shape is the laser spot. The distribution has a 0th-order light narrower than the 0th-order light of LS1 and a 1st-order and -1st-order laser light having a smaller light amount than the 0th-order light.

Furthermore, as shown in FIG. 3 (C1), the focused laser spot LS3 corresponding to the incident laser light LI3 having a light quantity distribution in which the light quantity exponentially increases as the light quantity shifts from the central portion to the peripheral portion. The light quantity distribution (Fig. 3 (C2)) has the 0th, 1st, and -1st order lights, which are narrower than the 0th, 1st, and -1st order lights of the laser spot LS2. The distribution of the amount of light is larger than the primary and −1st order light of the laser spot LS2.

Here, since the light quantities of the 1st-order light and the -1st-order light are smaller than the light quantity of the 0th-order light, the 0th-order light is mainly considered, and the diffraction by the peripheral portion of the objective lens 8 is used to show in FIG. 2 (C). Such a laser spot 9 or 10 that is oblong in the longitudinal direction.
To obtain the above, it is understood that the incident laser light LI3 having a light quantity distribution in which the light quantity in the peripheral portion is larger than the center in the disk radial direction is incident on the objective lens 8 as shown in FIG. 3 (C). .

By the way, the light intensity distributions of the incident laser beams LI1 to LI3 and the spatial frequency characteristics (MTF (Modul
ation Transfer Function)) has a relationship as shown in FIG. That is, which laser light LI1 to LI3
The spatial frequency characteristics MTF _{LI1 to} MTF _LI3 are also the spatial frequency (horizontal axis) of the numerical aperture NA of the objective lens 8 and the laser beams LI1 to L.
The contrast (vertical axis) monotonically decreases as it increases toward the cutoff frequency 2NA / λ determined by the wavelength λ of I3, but the range AR of the spatial frequency value corresponding to the track pitch that the disk 2 can take Laser light LI
The reduction rate of the spatial frequency characteristic MTF _{LI1 with} respect to 1 is the largest, and the reduction rate of the spatial frequency characteristic MTF _{LI3 with} respect to the laser beam LI3 is the smallest (takes almost a constant value with almost no reduction).

Therefore, the incident laser beam LI3 to the objective lens 8 for improving the tracking performance can be rephrased as having the spatial frequency characteristic MTF _LI3 having a partially constant value shown in FIG. It can be seen that whether or not the light quantity distribution of the laser light is appropriate can be determined by the curve shape of the spatial frequency characteristic.

However, in practice, the light quantity distribution of the laser light LA emitted from the laser light source 6 (FIG. 8) is close to that having a Gaussian distribution shape as shown in FIG. The generated first-order light and −1st-order light also have a Gaussian distribution shape.

Therefore, if the laser spots 9 and 10 are formed in an elliptical shape that is short in the radial direction of the disk to improve the tracking performance, the primary and negative first-order laser beams for tracking control obtained by the diffraction grating are emitted. 3) (C) (or FIG. 3 (B)) is converted through the distribution conversion means so as to increase the ratio of the light quantity of the peripheral part to the light quantity of the central part, and the result is given to the objective lens 8. Requires.

An embodiment of the present invention will be described with reference to FIG. In this embodiment, the shape of the diffraction grating 7 (FIG. 8) is appropriately selected, and the diffraction grating 7 is controlled by laser light for tracking control (first order, −1st order).
In addition to being used as a light splitting means for splitting the laser light for signal reproduction (0th order), it is also used as a light quantity distribution converting means.

The diffraction grating 7 is a phase type diffraction grating as shown in FIG. 1, and has a concavo-convex shape in which stripe portions 31 and groove portions 32 of equal thickness are alternately arranged on a glass plate 30. The repeating direction Y is slightly inclined with respect to the longitudinal direction of the track 3.

The width W1 of the stripe portion 1 is formed symmetrically with respect to the center line so as to change into a barrel shape as it goes in the extension direction, that is, the X direction, and is widest in the central portion and narrowest in the end portions. Therefore, the width W2 of the groove 22 is conversely narrowest at the center and widest at the ends.

When the laser light L5 having a light quantity distribution in which the light quantity in the central portion is slightly larger than the light quantity in the peripheral portion is incident on the diffraction grating 7 having such a shape, as shown in FIG. And a laser beam for -1st order tracking control
L6 and L7 have a light amount distribution in which the light amount in the peripheral portion is larger than the light amount in the central portion when viewed in the X direction (almost disk radial direction).

Laser light (first-order,-
The primary) MTF characteristic C1 is shown. It can be seen that, compared with the MTF characteristic C2 of the laser light that does not pass through the diffraction grating 7, there is a tilt in the range corresponding to the used track pitch.

Therefore, as apparent from the examination of FIGS. 2 to 4, according to the embodiment in which the diffraction grating 7 of FIG. 8 is formed as shown in FIG. 1, the tracking control formed on the disk 2 is controlled. The laser spots 9 and 10 for use in the disk have a narrow shape in the radial direction of the disk, and when the tracking deviates from the locking state, it is possible to obtain a tracking error signal TER corresponding to high sensitivity, thereby improving the tracking accuracy. Thus, the optical slider 5 having general versatility can be easily configured for the disks 2 having different track pitches.

For example, as shown in FIG. 7, according to this embodiment, a tracking error signal TER for a disk having a track pitch of 1.4 [μm] is -1.0 [dB] and a tracking error signal TER is 2.0.
Tracking error signal TE for [μm] disk
As R is 0.3 [dB], the fluctuation of the tracking error signal TER between the disks of different track pitches is significantly smaller than that of the conventional device.

Further, in the case of the optical disc device using the diffraction grating 7 of FIG. 1 as in this embodiment, laser light for signal reproduction (zero-order light)
As shown in FIG. 5, L8 has a higher light amount ratio in the central portion than the incident laser light L5, and also has an effect of reducing crosstalk from an adjacent track.

H Effect of the Invention As described above, according to the present invention, when the light amount distribution of the first and second light beams for tracking is viewed in the radial direction of the disk using the diffraction grating, the light amount of the peripheral portion is larger than that of the central portion. After converting to a large size, it is made to enter the objective lens, so that the shape of the laser spot is determined by the diffraction of the peripheral edge of the objective lens, which is suitable for tracking control and also for discs with different track pitches. What can be easily applied can be realized.

[Brief description of drawings]

FIG. 1 is a perspective view showing a diffraction grating used in an embodiment of an optical disk device according to the present invention, FIG. 2 is a schematic diagram for explaining the relationship between laser spot shape and tracking performance, and FIG. 3 is an objective lens. 4 is a schematic diagram for explaining the relationship between the light quantity distribution of the incident light on the disk surface and the light quantity distribution on the disk surface, and FIG. 4 is a schematic diagram showing the relationship between the light quantity distribution of the laser light and the spatial frequency characteristic. FIG. 7 is a schematic diagram for explaining the conversion of the light amount distribution by the diffraction grating 7, FIG. 6 is a schematic diagram showing the spatial frequency characteristics of an optical disk device using the diffraction grating 7, and FIG. 7 is the optical disk device. FIG. 8 is a schematic diagram showing the relationship between the track pitch and the tracking error signal, FIG. 8 is a block diagram showing the schematic configuration of the optical disk device, and FIG. 9 is a schematic view showing the relationship between the track pitch and the tracking error signal of the conventional device. It is a diagram 1 ... pit, 2 ... disk, 3 ... track, 4,
9, 10 ... Laser spot, 6 ... Laser light source, 7 ...
Diffraction grating, 8 ... Objective lens.

Claims (1)

[Claims] 1. A light source and stripes and grooves are alternately arranged, and the stripes or grooves are formed so that the width thereof changes into a barrel shape, and the light emitted from the light source is reproduced. The light is split into the light and the first and second light for tracking, and at least the light amount distribution of the first and second light for tracking is viewed in the radial direction of the disk, and the light intensity distribution in the peripheral portion with respect to the light amount in the central portion is A diffraction grating that converts the light quantity so that the light quantity ratio increases, and an objective that collects the reproduction light and the tracking first and second lights emitted from the diffraction grating on a track on the disk, respectively. An optical disk device that is equipped with a lens.