JPH113532A - Optical information detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extend the allowance of grating arrangement precision by allowing dividing lines of detectors to make errors of spot positions of a +1st-order light and a -1st-order light generated on two detectors in accordance with the arrangement state in a grating optical system roughly correspond to loci of deviations of spot positions. SOLUTION: Beam spots of ±1st-order sub-beams S2, S3 function as offset detection sensors. A required accuracy in adjusting the rotation angle position of a grating is mitigated by forming dividing lines between light receiving areas E2, F2 and between light receiving areas E3, F3, circular-arc shapes symmetrical with respect to the center of a main spot S1 on photodetectors 62, 63 and by making the photodetector elements 62, 63 rectangular shapes in which directions along which the circular-arcs progress become longer sides. Then, even when the rotation angle position of the grating is shited a little, inconvenience is not generated by making the dividing lines of the photodetector elements circular-arc shapes such as to follow up deviations of irradiating positions of the bean spots S2, S3 and by making them have long light receiving areas in the directions of them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information detecting device called, for example, an optical pickup, and is particularly suitable as an optical pickup for performing recording and reproduction on an optical disk.

[0002]

2. Description of the Related Art In a recording apparatus and a reproducing apparatus for an optical recording medium such as an optical disk and a magneto-optical disk, an optical pickup is moved to a target track of the disk in order to record information data on a predetermined track on the disk. Then, the laser beam must be irradiated on the target track. For this purpose, it is necessary to position the optical pickup at the target position. There is a tracking servo system as a servo system for moving an optical pickup to a target position in a radial direction of an optical disk.

[0003] The tracking servo system comprises a tracking coil and a tracking servo circuit of the actuator system in the optical pickup. The tracking servo circuit generates a servo drive signal from a tracking error signal obtained from reflected light information obtained by the optical pickup and applies the servo drive signal to a tracking coil. Then, as an actuator system, the objective lens of the optical pickup is finely moved by the tracking by the two-axis actuator based on the signal supplied from the tracking servo circuit to the tracking coil.

A tracking operation by a push-pull method used in a conventional land / groove recording method will be described with reference to FIG. In FIG. 11 (a), lands / landes for recording data are formed on groove portions G1, G2 and G3 on the disk recording surface and lands L1, L2 and L3 between the groove portions G1, G2 and G3. In the groove recording method, adjacent groove portions G1, G2, G3
Alternatively, it is necessary to perform tracking on each of the groove portions G1, G2, G3 and the land portions L1, L2, L3 in order to record data in the land portions L1, L2, L3.

In the push-pull method, the light reflected and diffracted by the groove portions G1, G2, and G3 on the recording thin film on the disk is output difference (ie, push-pull signal) at a light receiving surface divided into two on a photodetector (photodiode). ) To detect a tracking error. That is, as shown in FIG. 11A, when the laser spot and the center of the groove portions G1, G2, G3 or the center of the laser spot and the land portions L1, L2, L3 are aligned, the just tracking state is set. The tracking error detected as the tracking error signal becomes zero.

As shown in FIG. 11B, a tracking error signal TE is obtained as a symmetrically reflected and diffracted light distribution, but the just tracking state corresponds to a zero cross point of the tracking error signal TE. In other cases, the tracking is deviated, and an S-shaped curve is formed as a reflected diffracted light distribution having different amplitudes in which the light intensity is deviated left and right on the photodetector. By performing the tracking servo so that the tracking error signal TE becomes “0”, the center of the groove portions G1, G2, G3,
Alternatively, tracking can be performed at the centers of the lands L1, L2, and L3.

However, as shown in FIG. 12, an offset may occur due to the movement of the objective lens during the tracking operation. In FIG. 12, when the objective lens 141 is moved in the track crossing direction (radial direction) of the optical disc 140 by the tracking coil of the biaxial actuator in the optical pickup during the tracking operation, the photodetector 142 is moved in accordance with the movement. In this case, the beam spot of the reflected light of the optical disk 140 moves by Δx, so that the push-pull signal is offset.

An offset may also occur due to a radial tilt (radial tilt) of the optical disk. In FIG. 13, when the optical disc 150 has a tilt of Δθ with respect to a plane orthogonal to the optical axis of the laser beam, the reflected light of the optical disc 150 is shifted by f · 2Δθ with respect to the focal length f of the objective lens 151 on the photodetector 152. Since the beam spot moves, the push-pull signal is offset due to imbalance in light intensity.

As shown in FIG. 14A, when the beam spot S1 is located at the center of the photodetector 160 having the light receiving areas E1 and F1 divided into two, when the beam spot S1 crosses the track of the optical disk, , The zero-cross point of the tracking error signal TE becomes the track center. Thus, tracking can be performed using the tracking error signal TE. However, as shown in FIG. 14B, when the beam spot S1 moves out of the center of the photodetector 160, that is, when the objective lens is driven in the radial direction by the tracking operation, or when the optical disc has a radial tilt. Since the light intensity distribution of the beam spot S1 moves on the photodetector 160, the tracking error signal TE becomes a signal having an offset component OF that has a slow swell.
Tracking cannot be performed correctly using the tracking error signal TE having such an offset OF.

[0010] Therefore, there has been proposed a system for canceling the offset component included in the tracking error signal TE. That is, as shown in FIG. 15 and FIG.
tialPush-Pull). In FIG.
A grating (not shown) is provided on the optical path for irradiating the optical disk 170 with a laser beam from the laser diode to generate diffracted light. As a result, the zero-order light S1 as the main beam, the + 1st-order light S2 as the sub-beam, and the -1st-order light are shifted in the tangential direction of the tracks forming the pits 171 on the optical disk 170 and shifted by half a track in the radial direction. Light S3 is formed.

As shown in FIG. 16, the 0th-order light S1 of the main beam, the + 1st-order light S2 of the sub-beam, and the -1st-order light S
The three reflected lights are received by the three light receiving elements 181, 182, and 183 of the photodetector 180, respectively. Each of the light receiving elements 181, 182, 183 is divided into two by a dividing line orthogonal to the direction corresponding to the radial direction of the disk.
(E1, F1) (E2, F2) (E3, F
3). The light receiving element 181 having the light receiving regions E1 and F1 receives the 0th order light S1 of the main beam. The light receiving element 182 having the light receiving regions E2 and F2 receives the + 1st order light S2 of the sub beam. The light receiving element 183 having the light receiving areas E3, F3 receives the sub-beam -1st order light S3. Further, difference signals of the respective light receiving sections in the respective light receiving elements 181, 182, 183, that is, the push-pull signals PPS1, PPS1, P2
An arithmetic circuit 184 that calculates PS2 and PPS3 and outputs a push-pull signal PP is provided.

In such an apparatus, as shown in FIG. 15, the + 1st-order light S2 and the -1st-order light S3 of the sub beam are shifted from the 0th-order light S1 of the main beam by half a track in the radial direction. +1 order light S2 of the sub beam,
Push-pull signals PPS2, PP of the difference signal of the primary light S3
S3 has an opposite phase to the push-pull signal PPS1 of the difference signal of the zero-order light S1 of the main beam. On the other hand, the offset due to the movement of the objective lens shown in FIG. 12 and the offset due to the imbalance of the light intensity due to the radial tilt shown in FIG.
The push-pull signals PPS2 and PPS3 of the difference signal of No. 3 are the push-pull signals PP of the difference signal of the zero-order light S1 of the main beam.
Becomes in phase with S1. Therefore, the offset can be canceled by taking the difference between these two signals.

Therefore, in the calculation circuit 184 shown in FIG. 16, the following calculation (Equation 1) is performed using an appropriate coefficient k to generate a push-pull signal in which the offset is canceled, that is, the tracking error signal TE. Obtainable. Here, the coefficient k is 0th order light, + 1st order light, −1
The intensity of the next light is determined to be calibrated, and if these three lights have the same intensity, the coefficient k = 1/2 is the optimum value.

## EQU1 ## PP = PPS1-k (PPS2 + PPS3)

[0014]

However, in this offset canceling method, the 0th order light S1 of the main beam, the + 1st order light S2 of the sub beam, It is necessary to form the -1st order light S3, and therefore, it is necessary to adjust the rotation of the grating with high accuracy, to adjust the power loss of each beam, etc. There is a restriction on the configuration of the optical pickup in that the moving position of the objective lens must always be on the center line of the optical disk so that there is no difference in the appearance of each beam on the outer peripheral side. Accordingly, high mechanical mounting accuracy of the optical pickup and high accuracy of a mechanism (thread mechanism) for moving the disk from the inner circumference to the outer circumference are required. There is also a disadvantage that a swing arm type optical pickup cannot be used.

In view of such a point, the present applicant first eliminates the positional restriction on the disc of the + 1st-order light S2 and the -1st-order light S3 of the sub-beam, so that the moving position of the objective lens is always on the optical disc. A technique for removing the restriction of being on the center line and relaxing the grating rotation adjustment accuracy was proposed (Japanese Patent Application No. Hei 8-3203).
No. 14).

This technique uses an offset signal by lowering the resolution of the + 1st order beam spot and the −1st order beam spot below the track density of the disk so that the beam spot is not modulated by track traversal. Output only. In other words, as information on the reflected light of the + 1st-order light and the -1st-order light, information related to a pit row or a land / groove that causes a tracking error is not included, so that the beam spot is applied to any position on the disk. To be able to be. However, as for the grating rotation adjustment accuracy, the accuracy requirement for the position of the sub-beam on the track is resolved, but the accuracy is required as a condition for the light receiving position of the photodetector that receives the reflected light of the sub-beam. In other words, as a result, the accuracy of adjusting the rotational position of the grating arranged in the optical system is not reduced so much, and the effort for adjusting the grating in the optical system still remains.

FIG. 17 shows the influence on the photodetector due to the grating rotational position accuracy. FIG. 17A shows a photodetector 18 used in the DPP method shown in FIG.
Although the light receiving elements 181, 182, and 183 are shown as 0,
The beam spot S2 of the + 1st order light and the beam spot S3 of the -1st order light are irradiated on the centers of the light receiving elements 182 and 183, respectively, so that push-pull signals (PPS2 and PPS3 in FIG. 16) for obtaining the offset component are generated. Good obtained.

However, if the grating has an arrangement error in the direction of rotation about the optical axis, the photodetector 180
, The + 1st-order light beam spot S2 and the -1st-order light beam spot S3 are shifted in the direction of rotation about the 0th-order light beam spot S1. For example, the beam spots are deviated on the trajectory shown by the dashed line in FIG. 17B, and in some cases, as shown in FIG.
Greatly deviates from the centers of the light receiving elements 182 and 183. Naturally, a correct push-pull signal cannot be obtained in this state. That is, by adjusting the rotational position of the grating about the optical axis, the irradiation positions of the primary light beam and the −1st light beam spot on the photodetector can be changed as shown in FIG.
It must be brought to a state as shown in (a) (or a state close to that and within a range where a good push-pull signal can be obtained).

[0019]

SUMMARY OF THE INVENTION In view of the above problems, the present invention irradiates each light detector (light receiving element) of a primary light beam and a -1st light beam spot to each light detector (light receiving element) in a light detector such as a photodetector. It is an object of the present invention to enlarge the allowable range of the position, thereby relaxing the rotational position accuracy of the grating.

For this purpose, in the optical information detecting device, the light detecting means for detecting the intensity of the light from the optical recording medium includes at least a detection area divided by a dividing line substantially orthogonal to the track crossing direction of the optical recording medium. 0 to have
A first photodetector capable of detecting a push-pull signal as tracking information from the next light, and a detection area divided by a dividing line, and capable of detecting a signal for obtaining offset information of the tracking information from the + 1st light A second photodetector and a third photodetector having a detection area divided by a division line and capable of detecting a signal for obtaining offset information of tracking information from −1st-order light are provided. Here, the + 1st-order light and the -1st-order light are formed by a grating disposed in an optical system between the light source, the optical recording medium, and the light detecting means. Each division line of the second photodetector and the third photodetector is formed so as to roughly correspond to the trajectories of the + 1st-order light and the -1st-order light in the rotational direction about the optical axis of the 0th-order light. I do.

That is, if an error occurs in the rotation direction about the optical axis as the arrangement state of the grating in the optical system, the + 1st order light on the second and third photodetectors is thereby reduced. , -1 order light spot position has an error in the direction of rotation about the optical axis of the 0 order light. If the displacement of the spot position becomes large, it becomes impossible to generate a push-pull signal for offset detection satisfactorily. However, in the present invention, a dividing line forming two detection areas for obtaining a push-pull signal is designated as a spot position. By roughly corresponding to the trajectory of the deviation, the spot position deviation can be allowed in a certain wide range. That is, the allowable range of the accuracy of the grating arrangement can be widened.

In particular, in the second photodetector and the third photodetector, the size of the detection area in the direction in which each division line travels is different from the direction in which the division line travels in the first photodetector. By making the size larger than the detection area size, the allowable range can be effectively expanded.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a disk recording / reproducing apparatus provided with an optical pickup as an embodiment of an optical information detecting apparatus according to the present invention will be described. The optical disk used in this embodiment may be, for example, a compact disk (CD) type CD-DA, CD-ROM, CD-R, or a DVD (DIGITAL VERSATILE DISC /
It may be a disc called DIGITAL VIDEO DISC). Of course, the present invention can be applied to other types of optical disks and magneto-optical disks, but this example will be described as an example of a disk for optically recording / reproducing and a recording / reproducing apparatus.

FIG. 1 is a block diagram showing the configuration of the optical disk recording / reproducing apparatus of this embodiment. This recording / reproducing apparatus includes an optical disk rotation drive control system, a coarse feed drive control system, an optical pickup control system, a servo control circuit 5 for controlling these respective servo systems, and a laser power supplied to the optical pickup 2. A laser control circuit 6 for controlling the read / write operation, and an IV conversion matrix circuit 8 for obtaining a reproduction RF signal, a focus error signal, and a tracking error signal from the reflected light of the laser beam applied to the optical disc 1.
And a signal processing circuit 7.

The optical disk rotation drive control system has a spindle servo circuit 9 and a spindle motor 3, and drives the optical disk 1 to rotate. The coarse feed drive control system includes a thread servo circuit 10 and a thread motor 4.
The optical pickup control system includes the optical pickup 2 and I-
V conversion matrix circuit 8 and focus servo circuit 11
, A tracking servo circuit 12 and a laser control circuit 6. Here, the IV conversion matrix circuit 8
Is a photodetector 21 having a light receiving element for detecting the reflected light of the laser on the four-divided surface, a light receiving element for detecting the reflected light on the two-divided surface, and the like. Is performed. The matrix calculation unit 22 generates and outputs a reproduction RF signal, a focus error signal, and a tracking error signal from the output of the photodetector 21. In addition, the laser control circuit 6 includes a PWM driver 14 that performs pulse width modulation on the laser light, and a laser diode 13 that emits the laser light.

As will be described later, in this recording / reproducing apparatus,
In particular, the optical pickup 2 includes a laser diode 13 as a light beam emitting unit and an optical disk 1 as a recording medium.
Are configured to have a grating as an optical diffractor having an area smaller than the cross-sectional area of the light beam of the light beam. In FIG. 1, the laser diode 1 is shown as a separate block for explanation.
3. The photodetector 21 is provided integrally with the optical system in the optical pickup 2. Further, the matrix operation unit 2
2 may be formed in the optical pickup 2 in some cases.

The signal processing circuit 7 has a system controller 19 for controlling each section of the recording / reproducing apparatus, an ECC encoder 16 for adding a re-error correction code to recording data by a Reed-Solomon product code, and an error correction code. A modulation circuit 15 for EFM-modulating the recording data, a demodulation circuit 17 for EFM-demodulating the reproduction data and supplying a servo signal to the spindle servo circuit 9, and performing an error correction process on the reproduction data by using a read-solomon product code. And an ECC decoder 18 for outputting data.

The operation of the optical disk recording / reproducing apparatus thus configured will be described. When the recording / reproducing apparatus records or reproduces an information signal on / from the optical disk 1 in response to a request from a host computer (not shown), the system controller 19 seeks the optical pickup 2 to a target track position on the optical disk 1 by the thread motor 4. After the operation and positioning, the tracking servo circuit 1
2 and the focus servo circuit 11 drives the re-tracking coil and the focus coil to finely adjust the tracking and the focus to match the target value.

At the time of recording, the laser power is previously set to the erase power level by the laser control circuit 6 to erase the information of the portion not to be recorded, and the laser power is adjusted to the write power level to shift the information signal to the target track position. When reproducing, the laser control circuit 6 adjusts the laser power to the read power level to reproduce the information signal recorded at the target track position.

The recording data is processed by the ECC encoder 16 and the modulation circuit 15 to be converted into a data form to be recorded on the disk 1, pulse width modulated by a PWM driver, and applied to the laser diode 13 as a drive signal.
Then, the laser diode 13 performs a laser emission operation according to the PWM-modulated recording data, so that data recording on the disk 1 is performed.

At the time of reproduction, a continuous laser emission operation of read power from the laser diode 13 is performed, and a recording spot on the disk 1 is irradiated with a laser spot.
Then, the reflected light is detected by the photodetector 21, and the RF signal as the reproduction information is transmitted to the matrix operation unit 2.
2 is generated. This RF signal is subjected to EFM demodulation in the demodulation circuit 17, subjected to error correction processing in the ECC decoder 18, and output as reproduction data.

When performing these recording / reproducing operations, servo control for each of the spindle motor 3, the optical pickup 2, and the sled motor 4 is required. First, at the start of the recording / reproducing operation, the system controller 19 supplies a rotation command to the spindle servo circuit 9 of the servo control circuit 5 based on a recording / reproduction start instruction from the host computer in order to rotate the spindle motor 3. I do. Spindle servo circuit 9
Supplies a redrive signal to the spindle motor 3 in response to this command to rotate the spindle motor 3.

The operation of the spindle servo system is started at a certain point after the start of rotation. That is, a spindle error signal as rotation error information is supplied from the demodulation circuit 17 to the spindle servo circuit 9 based on the reproduced RF signal, and the spindle servo circuit applies power to the spindle motor 3 according to the spindle error signal. CLV
Rotation driving in a system (constant linear velocity) is performed.

The matrix operation unit 22 extracts a tracking error signal TE and a focus error signal FE from the output of the photodetector 21 as signals used for operations of the focus servo, tracking servo, and thread servo system of the optical pickup 2. These signals are supplied to the servo control circuit 5.

The servo control circuit 5 generates various servo drive signals (focus drive signal, tracking drive signal, slide drive signal) based on these signals, a track jump command, an access (seek) command from the system controller 19 and the like. Then, focus servo, tracking servo, and thread servo are executed.

The focus servo is an operation for controlling the laser beam output from the optical pickup 2 so as to focus on the recording surface of the disk 1 rotated by the spindle motor 1. In order to obtain the focus error signal FE, a four-divided detector is prepared in the photodetector 21, and focus error information is extracted by a so-called astigmatism method. That is, when each area of the four-divided detector is A, B, C, and D, and the detectors that form a diagonal pair are A, D, and B, C, the matrix calculator 22 calculates (A + D)-(B + C). And the result is used as the focus error signal FE.

In the servo control circuit 5, the focus servo circuit 11 performs a phase compensation process, an amplification process, and the like on the focus error signal FE to generate a focus drive signal, and applies power to a focus coil of a two-axis actuator in the optical pickup 2. Perform As a result, the objective lens is driven in a direction in which the objective lens approaches and separates from the disk 1. This movement of the objective lens is controlled so that the focus error signal FE always becomes zero so that the focused state of the laser light is maintained.

To realize such focus control, the objective lens must be located at a position within the focus pull-in range. As is already known, the focus pull-in range is a range in which the focus error signal FE changes linearly. If the focus error range is not within this range, it is possible to correctly control the zero cross point of the focus error signal FE as an appropriate focus position. Can not. For this reason,
At the time of startup for performing the recording / reproducing operation, a focus search operation is performed. In this focus search operation, the focus servo circuit 11 turns off the focus servo loop, and then turns off the system controller 19.
In response to the instruction from, power is applied to the focus coil so that the objective lens is forcibly moved within the movable range. Then, for example, when it is detected from the focus pull-in range by a sum signal or the like generated by the matrix operation unit 22, the focus servo is turned on.

The tracking servo uses the optical pickup 2
This is an operation for controlling the laser beam output from the optical disk so as to follow the track (land / groove or pit row) of the disk 90 being rotated by the spindle motor 1. In order to obtain the tracking error signal TE,
The photodetector 21 and the matrix calculation unit 22 have a configuration based on the push-pull system and a configuration for offset cancellation. These will be described later.

The servo control circuit 5 controls the tracking servo circuit 12 so that the tracking error signal TE
, A tracking drive signal is generated, and power is applied to the tracking coil of the two-axis actuator in the optical pickup 2. Thus, the objective lens is driven in the radial direction of the disk 1. The movement of the objective lens 3 is controlled so as to be always performed in a direction where the tracking error signal TE becomes zero, so that the tracking state of the laser light is maintained.

The thread servo is a control in the disk radial direction similar to the tracking servo. However, by moving the entire optical pickup 2 within a range that cannot be followed by the tracking servo, the laser light output from the optical pickup 2 is reduced. This is an operation of irradiating a predetermined position on the disk 1. The thread error signal is extracted, for example, as a low-frequency component of the tracking error signal TE. That is, the thread servo circuit 10 generates a thread error signal by low-pass filter processing on the tracking error signal TE,
A slide drive signal in a direction in which the thread error signal becomes zero is supplied to the thread motor 4. The sled motor 4 drives the optical pickup 2 in response to such a slide drive signal.
Move the whole. Of course, in a track jump operation such as an access operation, a slide drive signal is generated from the thread servo circuit 10 in accordance with an instruction from the system controller 19, and the thread motor 4 is driven.

By performing each operation of the servo control circuit 5 as described above, the above-described operations of erasing / recording / reproducing are properly realized. Such a servo control circuit 5 is often actually formed as a DSP (digital signal processor). In this case, a servo drive signal as a PWM signal is generated based on the digitized servo error signal,
In many cases, the drive power is extracted by a low-pass filter.

Here, in this example, particularly, the optical pickup 2
In the optical path between the laser diode 13 as the light beam emitting unit and the optical disk 1 as the recording medium, the optical path is made to have a grating as an optical diffractor having an area smaller than the cross-sectional area of the light beam of the light beam. By reducing the aperture ratio of the grating as a diffractor, ± 1
The sub-beam spot of the next light is enlarged to be used only for detecting the offset signal. This allows DP
As in the P method, the offset component can be removed from the tracking error signal TE obtained as a push-pull signal, and the restriction on the positional relationship of the sub-beam for detecting the offset component with respect to the track on the disk is eliminated. Like that. That is, the tracking information is not included in the reflected light information of the sub beam.

FIG. 2 shows the configuration of an optical system in the optical pickup 2 (including the laser diode 18 and the photodetector 21). In this optical system, a laser beam output from a laser diode 13 is collimated by a collimator lens 20 and then +1 by a grating 27.
Next-order light and minus first-order light are generated into three beams. Then, the light is reflected by the beam splitter 28 toward the optical disk 1 by 90 degrees, and is emitted from the objective lens 29 to the disk 1.
The objective lens 29 can be finely adjusted in the track direction by a tracking coil (not shown) constituting a two-axis actuator.

The light reflected by the disk 1 enters the beam splitter 28 via the objective lens 29, passes through the beam splitter 28 as it is, and reaches the condenser lens 30. After being condensed by the condensing lens 30, the light is incident on the photodetector 21 via a cylindrical lens (cylindrical lens) 31.

In such an optical system, in this example, the area of the grating 27 as the light diffracting body is smaller than the cross-sectional area of the light beam of the light beam. The opening of the grating 27 is smaller than the opening of the objective lens 29. Here, the aperture refers to the size of the light passing through the objective lens 29 and the grating 27.

As shown in FIG. 7, the photodetector 21, which is also used for detecting a tracking error signal, has a direction crossing the far-field image of a spirally formed track on the optical disc 1 as a recording medium. A light receiving element (61, 62, 63) having at least one parting line in a direction substantially perpendicular to the light receiving surface for receiving the reflected light of the light beam irradiated on the recording medium for each divided light receiving area. . Then, a difference between the light intensity signals of the reflected light in the light receiving areas divided by each light receiving element is detected, and a tracking error signal is generated from the difference signal.

As described above, in order to obtain a focus error signal by the astigmatism method, the light receiving element 61 corresponding to the main beam spot S1 has four light receiving areas A,
It is a quadrant detector having B, C, and D. By the way, the detector dividing line for tracking error detection is set to the direction crossing the far-field image of the track for the following reason. When the astigmatism focus error detection method is used, the image is apparently rotated by 90 degrees on the photodetector 21, so that the direction of the dividing line must also be rotated by 90 degrees. For this reason, a dividing line is required in a direction orthogonal to the direction crossing the track. Therefore, the far-field image of the track was used instead of the direction crossing the track.

Further, the grating 2 as an optical diffractor
The opening in the direction transverse to the far-field image of the track spirally formed on the recording medium of No. 7 has an optical cutoff spatial frequency determined by the opening substantially smaller than the spatial frequency of the track pitch. In this case, the spatial frequency of the optical cutoff determined by the aperture of the grating 27 does not need to be strictly lower than the spatial frequency of the track pitch, and may be slightly higher. The aperture ratio of the grating 27 in the tangential direction of the track spirally formed on the disk 1 is smaller than the aperture ratio of the objective lens 29. Further, the grating 27 as an optical diffractor is arranged so that the diffracted light by the grating 27 as an optical diffractor appears in the tangential direction of the spirally formed track on the disk 1.

Also, a grating 2 as an optical diffractor
7 are provided with a grating 27 as an optical diffracting body.
And another diffractive portion for deflecting the other diffracted light in a different direction or a different diffraction angle from the diffracted light due to the above.

FIG. 3 shows the structure of the grating 27.
The grating 27 has, at the center, a groove 33 formed by an ellipse with a radius r in the radial direction of the optical disc 1 and a flat portion 32 on the outer periphery. The grating 27 is made of, for example, a glass plate. As shown in the drawing, the groove portion 33 has a plurality of concaves and convexes in the surface of the glass plate in the radial direction of the optical disc 1, and the flat portion 32 remains in the glass plate state. It is.

FIG. 4 shows the operation of the grating 27.
Here, the configuration is simplified for the sake of explanation, and the light beam emitted from the laser diode 13 is directly diffracted by the grating 27, and
An example in the case of irradiating on the recording surface of FIG. In FIG.
The light beam emitted from the laser diode 13 passes through the flat portion 32 of the grating 27, and the light beam portion is diffracted by the groove 33 and enters the objective lens 29. A zero-order light S1 is formed on the recording surface of the optical disc 1 by a light beam transmitted through the flat portion 32 of the ligrating 27 by the objective lens 29 and a light beam not diffracted by the groove portion 33. Also,
The + 1st-order light S2 and the -1st-order light S3 on the recording surface of the optical disc 1 by the light flux diffracted by the groove 33 of the grating 27.
Is formed.

Next, the operation of generating ± first-order light by the grating in this embodiment will be described with reference to FIG. Here, the configuration is simplified for the sake of explanation, and the laser diode 13
Beam spot emitted from
7 shows an example in which the light is diffracted by 7 and is irradiated on the recording surface of the optical disc 1 by the objective lens 29. First, the operation of the grating 27 will be described. The light beam is diffracted by the grating 27 having the groove of the period d, and assuming that the laser wavelength is λ, the angle θg and the opening NA ′ of the groove 33 are provided.
Is represented by the following (Equation 2).

## EQU2 ## sin θg = n · λ / d (n is an order, n = 0,
± 1, ± 2) NA ′ = nsin θg = r ′ / f (f is the focal length)

At this time, ± 1st order light is sin θg = λ / d
It is. Similarly, the light beam is diffracted by the optical disk 1 having the track with the track pitch tp. The angle θdisk is determined by the track pitch tp, and is given by the following (Equation 3) similarly to the grating 27.

## EQU3 ## sin θdisk = n · λ / tp (n = 0, ± 1, ± 2)

At this time, the lateral shift of the ± first-order light is represented by f sin θ disk = f where the focal length of the objective lens 29 is f.
f · λ / tp. Here, in the portion where the laterally shifted portion of the ± 1st order light and the 0th order light overlap, interference with the 0th order light occurs, and as a result, the light intensity becomes bright and dark. However, when the lateral shift becomes larger than the beam luminous flux diameter 2r, they do not overlap. This is the cutoff of the optical system and is expressed by 2r = f · λ / tp. Where r /
Since f = NA (aperture ratio), 1 / tp = (2 · r / f)
/ Λ, it becomes as shown in (Equation 4).

1 / tp = 2NA / λ

That is, the cutoff frequency of the optical system having the laser wavelength λ and the aperture ratio NA is represented by (1 / tp =) 2NA / λ. At this time, the track pitch (tp =) is λ / 2
NA.

The light beam that is not diffracted by the grating 27 becomes the zero-order light Sg1, and the groove 3 of the grating 27
The light beam diffracted by 3 is condensed by the objective lens 29 to become + 1st-order light Sg2 and -1st-order light Sg3, and forms a beam spot on the optical disc 1.

Then, the 0th-order light Sg1, the + 1st-order light Sg2, and the −th-order light Sg3 are further diffracted by the optical disc 1, respectively. Here, the zero-order light Sg1 is further transmitted to the optical disc 1
0th order light S1, + 1st order light S2, -1st order light S3
Here is an example. Although the diffracted light is reflected by the optical disk 1, it is illustrated and described so as to be transmitted here for convenience. The diffraction angle θdisk by the optical disk 1 is sin θdisk
= Λ / tp. The light beam guided to the photodetector 21 by the objective lens 29 is inside the circle of the zero-order light S1. At this time, the + 1st-order light S2 and the -1st-order light S3 overlap with the 0th-order light S1 as indicated by oblique lines, thereby making the 0th-order light S1 bright and dark within a circle. Can detect retracking. That is, the light intensity (brightness / darkness) changes depending on where the beam spot is on the track. The condition for the overlap at this time is fsinθdi
sk <2r, ie, f · λ / tp <2r, thus 1
From (/ tp <(2 · r / f) / λ), (Expression 5) is obtained.

## EQU5 ## 1 / tp <2NA / λ

Next, the operation of diffracted light by the groove 33 of the grating 27 will be described with reference to FIG. Grating 2
+ 1st-order light Sg2 and -1st-order light Sg3, which are diffraction lights by
Are the same, only the operation of the -1st order light Sg3 is shown. -1 order light Sg3 diffracted by the grating 27
Are condensed by the objective lens 29 to form a beam spot on the optical disc 1. Then, the optical disc 1 further causes the zero-order light Sg3-1, the + 1st-order light Sg3-2,-
The primary light Sg3-3 is diffracted. Here, similarly, the description will be made such that the light is transmitted through the optical disc 1 for convenience.

The diffraction angle θdisk by the optical disk 1 is sin
θdisk = λ / tp. At this time, NA 'is NA
(R '<r), the 0th order light Sg3-1 contains:
The + 1st order light Sg3-2 and the -1st order light Sg3-3 do not overlap. As described above, when the + 1st-order light Sg3-2 and the -1st-order light Sg3-3 do not overlap with the 0th-order light Sg3-1, the light intensity is constant regardless of where the beam spot is on the track. . Therefore, only the offset due to the objective lens shift or the disc tilt is detected. Thus, the + 1st-order light Sg3-2 and the -1st-order light Sg
The condition where 3-3 does not overlap with the zero-order light Sg3-1 is when fsin θdisk> 2r ′, that is, f · λ / t
Since p> 2r ′, 1 / tp> 2 · r ′ / f / λ, which is the case of (Equation 6).

1 / tp> 2NA'λ

As can be seen from the above, the + 1st order light Sg
Unlike the normal DPP method, the second- and first-order light Sg3 may be at a track position with respect to the zero-order light Sg1. Therefore, there is no need to shift by half a track, and there is no need to adjust the angle of the grating 27 in the sense of defining the spot position on the disk.

The + 1st-order light Sg3-2 and the -1st-order light Sg
Whether 3-3 is reflected by the optical disk 1 and returns to the objective lens 29 to enter the photodetector 21 is determined by N
It depends on the values of A, NA 'and tp. Therefore, the diffracted light from the grating 27 and the diffracted light from the optical disc 1
Although the next light does not overlap, it may return to the objective lens 29 and be detected again by the photodetector 21.

On the other hand, when the diffracted light by the grating 27 and the 0th-order light by the optical disc 1 do not overlap, the diffracted light does not return to the objective lens 29 and is not detected by the photodetector 21 under the following conditions. fsi
This is when nθdisk <r + r ′ (Equation 7).

1 / tp> (NA + NA ′) / λ

At this time, the +1 order light and the −1 order light of the diffracted light are:
Since it does not contribute to the offset detection due to the objective lens shift and the disc tilt, the detection sensitivity apparently increases. However, this condition means that NA ′ is further reduced, that is, r ′ must be smaller, and the light for offset detection is smaller. However, offset detection can be performed even under such conditions.

The operation of the optical system of the present embodiment as described above is summarized as follows. Flat portion 32 of grating 27
The radius of the luminous flux passing through is large corresponding to the opening of the objective lens 29. Then, the objective lens 29 forms the zero-order light Sg1 on the recording surface of the disk 1 by the light beam transmitted through the flat portion 32 of the grating 27 and the light beam not diffracted by the groove portion 33. At this time, the grating 27
The aperture of the objective lens 29 for the light beam transmitted without being diffracted is large. The aperture is determined by the radius of the aperture (the radius of the laser beam) and the focal length. Also, the light disc diffracted by the groove 33 of the grating 27 is
+ 1-order light and -1st-order light are formed on the recording surface of. At this time, the aperture of the objective lens 29 for the light beam diffracted by the groove 33 and passing therethrough becomes small.

Therefore, the beam spot formed by the zero-order light beam transmitted through the grating 27 without being diffracted is condensed on the recording surface of the disk 1 and formed as a beam spot having a size appropriate for the track pitch. However, the + 1st-order light and the -1st-order light formed by the beam spot transmitted through the groove 33 form a beam spot larger than the track pitch. That is, the groove 33
The aperture ratio is determined by the radius in the radial direction, and the optical cutoff frequency determined by the aperture ratio is set to be lower than the track pitch. In other words, the radius of the groove 33 in the radial direction is determined so that the spatial frequency of the track pitch becomes higher than the cutoff frequency.

By doing so, the laser spot of +1 order light and −1 order light formed on the recording surface of the disk 1 by the laser beam diffracted by the groove 33 of the grating 27 becomes large, and the track radial The position in the direction cannot be detected. That is,
The tracking error signal cannot be obtained from the +1 order light and the −1 order light, but only the offset signal can be obtained.

FIG. 7 shows the position of the beam spot on the optical disk 1 and the configuration of the tracking error detection system. FIG.
In the above, on the recording surface of the optical disk 1, a groove G of a guide groove is formed spirally, and a land L is formed between the grooves G.

The photo detector 21 has three light receiving elements 60, 61 and 62. At this time, the beam spot of the zero-order light S1 as the main beam is
The beam spot of the + 1st-order light S2 is received by the light-receiving element 62, and the beam spot of the -1st-order light S3 is received by the light-receiving element 63. Light receiving element 61
Has four divided light receiving areas A, B, C and D, while the light receiving element 62 has two divided light receiving areas E2 and F2 and the light receiving element 63 has two divided light receiving areas E3 and F3. .
The light receiving area (E2, F2) of each light receiving element 62, 63 (E
3, F3) is a direction orthogonal to the radial direction.

As this tracking error detection system,
In order to obtain the tracking error signal TE by calculating the output of each of the light receiving elements 61, 62, 63, the matrix calculator 22 shown in FIG.
4, 65, 68, adders 69, 70, 71, and gain amplifiers 66, 67.

The adder 70 receives the light receiving area A of the light receiving element 61,
Add the output of D. The adder 71 adds the outputs of the light receiving areas B and C of the light receiving element 61. Then, the subtractor 63 outputs the difference between the output of the adder 70 and the output of the adder 71. That is, the output of the subtractor 63 is (A + D)-(B + C),
A push-pull signal TE1 having information as a tracking error signal is obtained.

The light receiving element 62 receives the beam spot of the + 1st-order light S2 in the two divided light receiving areas E2 and F2 and outputs detection signals E2 and F2, and the light receiving element 63 is -1 in the two divided light receiving sections E3 and F3. It receives the beam spot of the next light S3 and outputs detection signals E3 and F3. Subtractor 6
4 outputs a subtraction output TE2 (= E2-F2), and the subtractor 65 outputs a subtraction output TE3 (= E3-F3). The gain amplifier 67 outputs a gain output G2 · TE3.
The adder 69 outputs an addition output (TE2 + G2 · TE3). The gain amplifier 66 has a gain output G1 · (TE2 +
G2 · TE3). The output of the gain amplifier 66 is a signal corresponding to the offset component of the push-pull signal from the subtractor 63.

Accordingly, by subtracting the output of the gain amplifier 66 from the push-pull signal TE1 from the subtractor 63, the tracking error signal TE in which the offset component has been canceled can be output. That is, the tracking error signal TE is as shown in (Equation 8).

## EQU8 ## TE = TE1−G1 · (TE2 + G2 · TE3)

Here, the beam spots S1, S2, S3
Where A1, A2, and A3 are the intensities of B and the offset is B, the balance adjustment and the gain adjustment are calibrated with the intensities of the three beam spots in an ideal state, and G1 = A1 / (2 ·
A2), G2 = A2 / A3, each TE1, TE
2, the offset B component of TE3 can be canceled. Also, TE1 is a sine wave signal because it appears every time a track is traversed, whereas TE2 and TE3 are irregular signals that appear due to an objective lens shift or radial tilt of the disk.

As described above, since the zero-order light beam having a radius r is incident on the objective lens, the NA is, for example, about 0.5, and the zero-order light S1 condensed by the objective lens 29 is obtained.
Is formed in an appropriate size, for example, about 1 micron, so that a tracking error signal can be detected and the resolution is sufficient. On the other hand, since the + 1st-order light and the -1st-order light are only diffracted with a radius r 'and are incident on the objective lens 29, the NA' of this light flux is, for example, about 0.3, and the beam spot diameter of the + 1st-order light S2 and The beam spot diameter of the primary light S3 becomes about 2 microns, and it becomes impossible to detect a track of 1 micron or less. Therefore, it is not modulated by track traversal, and has only information as an offset signal.

That is, in the ordinary DPP system, the beam spots S2 and S3 must be shifted by a half track with respect to the beam spot S1, but in this example, the beam spots S2 and S3 may be located anywhere on the track.

FIG. 8 shows the offset detection operation of ± first order light. FIG. 8A shows a case where the beam spot of the + 1st-order light S2 is located at the center of the light receiving areas E2 and F2 of the light receiving element 62.
2. The subtraction output TE2 of F2 outputs “0”. -
FIG. 8B shows a case where the beam spot of the + 1st-order light S2 is shifted from the center of the light receiving areas E2 and F2 of the light receiving element 61 due to the movement of the objective lens due to the tracking operation, and the tracking error information is not output. , Only the offset information 70 is output. The phenomena of FIGS. 8A and 8B are the same for the subtraction output TE3 for the −1st order light S3.

Therefore, the ± 1st order light S2 (S3) of the sub beam
Since the beam spot functions as an offset detection sensor, the tracking error signal T from which the offset has been removed by the tracking error detection system shown in FIG.
E can be obtained. That is, the grating 27 having the groove 33 of NA ′ smaller than the NA of the objective lens 29.
, The offset signal can be canceled without adding a mechanical configuration or an electrical circuit configuration.

As can be understood from the above description, in the case of the present example, the offset component is basically canceled from the tracking error signal TE obtained as the push-pull signal, thereby achieving a good tracking operation and reducing the offset component. ± 1 order light for detection is
On the disk 1, the position with respect to the track is not specified. That is, it may be anywhere unless there is a particular problem. Thereby, the moving position of the objective lens 29 is always
The constraint of having to be on the centerline of
The mechanical mounting accuracy of the optical pickup 2 and the accuracy of the thread mechanism are reduced. It is also possible to use a swing arm type optical pickup. Further, the adjustment of the rotation angle position of the grating 27 is not strictly required from the viewpoint of the spot position on the disk.

However, it is needless to say that the difference signals of at least the ± 1st-order light beam spots S2 and S3 must be detected by the light receiving elements 62 and 63.
Then, the light receiving areas E2 (E2) of the beam spots S2 and S3
In order for the difference between 3) and the light receiving area F2 (F2) to be correct offset information, the beam spots S2 and S3 are set so that the difference becomes 0 in a state where there is no offset as described with reference to FIG. Must be specified. Therefore, the rotation angle position adjustment of the grating is strictly required.

However, in this example, as shown in FIG. 7, the dividing lines of the light receiving areas E2 (E3) and F2 (F2) in the light receiving elements 62 and 63 are
The center of the main beam spot S1 (the division center of the light receiving element 61) is symmetrical and formed in an arc shape, and the light receiving elements 62 and 63 are formed in a rectangular shape in which the direction in which the arc advances is a long side. The accuracy required for adjusting the rotation angle position of the grating 27 can be eased.

FIG. 9A shows a spot position on the photodetector 21 in a state where the rotation angle position of the grating 27 without the optical system is most appropriately adjusted and there is no offset. The beam spot S1 of the zero-order light is applied to the center of the light receiving element 61, and the beam spot S2 of the +1 order light and the beam spot S3 of the −1 order light are also applied to the center of the light receiving elements 62 and 63, respectively. Then, assuming that there is no offset, the signals TE2 = E2-F2 = 0, and the signals TE3 = E3-F3 =
The light spots (E2, F2) (E3, F3) are evenly irradiated with the beam spots (S2, S3) so as to be 0.

Here, if the rotation angle position of the grating 27 is deviated, the influence is caused by the beam spots S2 and S3.
Is shifted in the rotational direction about the beam spot S1. For example, as shown in FIGS. 9B and 9C, the beam spots S2,
The irradiation position of S3 is shifted in the rotation direction. FIG. 9 (b)
(C) is also a spot position in a state where there is no offset. However, as can be seen from the examples shown in FIGS. 9B and 9C, in each case, the beam spot S2 is formed because the dividing line is formed in an arc shape and the light receiving region is long in the dividing line direction. Is irradiated almost equally to the light receiving areas E2 and F2, and the beam spot S3 is
3, F3 is irradiated almost equally. That is, even if the rotational angle position of the grating 27 is shifted and the state shown in FIG. 9B or FIG.
2. From S3, the offset can be detected satisfactorily.

As described above, in this example, the light receiving elements 62 and 63
Is formed in an arc shape that follows the deviation of the irradiation position of the beam spots S2 and S3 due to the deviation of the rotation angle position of the grating 27, and by having a long light receiving area in the direction of the division line, Even if the rotation angle position of the grating 27 is slightly shifted, there is no inconvenience. For this reason, strictness is not required for the adjustment of the grating, and the adjustment process can be greatly simplified, and the efficiency of production can be improved.

FIG. 10 shows another example of the dividing lines of the light receiving elements 62 and 63. The light receiving elements 62A and 6A in FIG.
3A is an example in which the upper and lower portions of the dividing line are formed in an arc shape, and the central portion is formed on a straight line. The light receiving elements 62B and 63B in FIG. 10B are examples in which the dividing lines are formed by three straight lines of an upper part, a central part, and a lower part. The light receiving elements 62C and 63C in FIG. 10C are examples in which the dividing line is formed by two straight lines of an upper part and a lower part. Each of the examples has a shape that substantially follows the displacement of the irradiation position of the beam spots S2 and S3 due to the displacement of the rotation angle position of the grating 27. Therefore, even if these dividing line shapes are employed, the mounting accuracy of the grating can be eased. of course,
Other than these, the shape of the dividing line can be considered.

[0086]

As described above, according to the present invention, the second light generated according to the arrangement state of the grating in the optical system.
+ 1st order light on the photodetector and the third photodetector,-
An error in the spot position of the primary light is allowed in a certain wide range by making the dividing lines of the second photodetector and the third photodetector roughly correspond to the locus of the spot position deviation. (I.e., a certain degree of deviation does not affect the offset detection), thereby increasing the allowable range of the accuracy of the grating arrangement. Therefore, simplification of the manufacturing process, simplification of the adjustment operation, and the like can be realized, and the accuracy of the tracking error signal is also improved.

The spatial frequency of the optical cutoff determined by the aperture ratio of the grating and the wavelength of the light from the light source is set lower than the spatial frequency of the track on the optical recording medium, so that the + 1st order light and −1 There is no restriction on the irradiation position of the next light on the recording medium, that is, the offset due to the movement of the objective lens and the radial tilt can be detected satisfactorily irrespective of the position accuracy with respect to the center line of the disk or the tracking state.

The division lines of the second photodetector and the third photodetector correspond to the trajectories of the + 1st order light and the −1st order light around the optical axis of the 0th order light in the rotational direction. By providing the arcuate portion, the state of the division line corresponding to the locus of the spot position deviation can be enhanced, and the adverse effect due to the grating placement error can be reduced.

The second photodetector and the third photodetector each have a detection area size in the direction in which each division line travels.
Since the size of the detection area of the first photodetector is larger than the detection area in the direction in which the dividing line travels, the range that can cope with the spot position error can be further expanded, and the demand for the grating arrangement accuracy is increased. Can be more gradual.

[Brief description of the drawings]

FIG. 1 is a block diagram of a recording and reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an optical system according to an embodiment.

FIG. 3 is an explanatory diagram of a grating according to an embodiment.

FIG. 4 is a diagram illustrating the operation of the grating according to the embodiment.

FIG. 5 is an explanatory diagram of an operation of generating ± first-order light of the grating according to the embodiment.

FIG. 6 is an explanatory diagram of an operation of −1st order light by the grating according to the embodiment.

FIG. 7 is an explanatory diagram of a tracking error detection system according to the embodiment.

FIG. 8 is an explanatory diagram of offset information according to the embodiment;

FIG. 9 is an explanatory diagram of a dividing line of the light receiving element according to the embodiment.

FIG. 10 is an explanatory diagram of an example of another dividing line of the light receiving element according to the embodiment.

FIG. 11 is an explanatory diagram of tracking by the push-pull method.

FIG. 12 is an explanatory diagram of an offset due to movement of an objective lens.

FIG. 13 is an explanatory diagram of an offset due to a disk skew.

FIG. 14 is an explanatory diagram of tracking error detection by the DPP method.

FIG. 15 is an explanatory diagram of a beam spot according to the DPP method.

FIG. 16 is an explanatory diagram of a tracking error detection system of the DPP method.

FIG. 17 is an explanatory diagram of an influence of a grating position shift.

[Explanation of symbols]

1 disk, 2 optical pickup, 3 spindle motor, 4 thread motor, 5 servo control circuit, 6 laser control circuit, 7 signal processing circuit, 8 I-
V conversion matrix, 13 laser diodes, 21 photodetector, 22 matrix operation section, 27 grating, 29 objective lens, 32 flat section, 33 groove section, 61, 62, 63 light receiving element, 63, 64, 65,
68 subtractor, 66, 67 gain amplifier, 69, 70,
71 Adder

Claims (4)

[Claims] 1. An optical recording medium comprising: light detecting means for detecting the intensity of light from an optical recording medium, wherein the light detecting means is divided by at least a dividing line substantially orthogonal to a direction corresponding to a track crossing direction of the optical recording medium. A first photodetector capable of detecting a push-pull signal as tracking information from the zero-order light by having a detection region, and at least two detection regions divided by a dividing line,
A second photodetector capable of detecting a signal for obtaining offset information of tracking information from + 1st-order light, and at least two detection regions divided by a division line;
A third photodetector capable of detecting a signal for obtaining offset information of tracking information from the −1st order light, wherein the + 1st order light and the −1st order light are a light source, an optical recording medium, and the light detection Formed by a grating arranged in the optical system between the means, and each of the dividing lines of the second photodetector and the third photodetector is:
An optical information detection device, which is formed so as to substantially correspond to the trajectories of the + 1st-order light and the -1st-order light in the rotational direction about the optical axis of the 0th-order light. 2. An optical cut-off spatial frequency determined by an aperture ratio of the grating and a wavelength of light from the light source is set lower than a spatial frequency of a track of an optical recording medium. 3. The optical information detection device according to claim 1. 3. A dividing line of each of the second photodetector and the third photodetector is provided with the + line centered on the optical axis of the zero-order light.
The optical information detection device according to claim 1, wherein an arc-shaped portion is provided according to the trajectories of the primary light and the primary light in the rotation direction. 4. The second photodetector and the third photodetector each have a detection area size in a direction in which each division line travels,
2. The optical information detecting apparatus according to claim 1, wherein a size of the first photodetector is larger than a size of a detection area in a direction in which the dividing line travels.