JP2007141323A - Optical pickup, optical recording and reproducing apparatus, and tracking error signal detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup in which offset of an objective lens is corrected without using a plurality of beams, and also to provide an optical recording and reproducing apparatus, and a tracking error detecting method. <P>SOLUTION: In the optical pickup, a diffraction element is provided in an optical path in which light is reflected by an optical recording medium and proceeded to a light receiving part, the light diffracted by this diffraction element has constitution having astigmatism of a five order, that is, W(ρ,θ) = Z(4ρ<SP>4</SP>-3ρ<SP>2</SP>)×sinθ(where, (ρ,θ) indicates radius and angle of polar coordinate making an optical axis as an original point, and Z indicates a coefficient expressing aberration quantity). Since intensity distribution of brightness and darkness is caused in a push-pull modulation region, a push-pull component is canceled, and only offset of the objective lens is detected. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical pickup, an optical recording / reproducing apparatus, and a tracking error detecting method used when optically recording / reproducing information on / from an optical recording medium such as an optical disk or an optical card.

  In recent years, various types of optical recording media having different recording densities have been developed as optical recording media. For example, in a disk-shaped optical recording medium, a CD (Compact Disc) in which the wavelength used for laser light is, for example, around 780 nm, Examples include DVD (Digital Versatile Disc) having a used wavelength of about 660 nm, BD (Blu-ray Disc) having a used wavelength of about 405 nm, and HD-DVD (High Definition DVD) having a used wavelength of about 405 nm. .

These optical recording media have different structures, and in order to increase the recording density, the track pitch, which was 1.6 μm in the CD type optical recording medium, is 0.74 μm in the DVD type optical recording medium, and BD type optical recording. In the medium, the track pitch is reduced to about 0.3 to 0.35 μm.
It is necessary to accurately position the light emitted from the light source on the target recording track with respect to the recording track with a reduced width.
As a conventional tracking method, a DPP (Differential Push-Pull) method is widely used as a method for correcting an offset of an objective lens in the push-pull method, that is, a correction for an optical axis shift of the objective lens (see, for example, Patent Document 1). .)
This DPP method divides light from a light source toward an optical recording medium into three parts, and sub-beams on both sides with respect to the central main beam in the radial direction on the disk surface of the optical recording medium, ½ the track pitch of the recording track. This is intended to cancel the offset of the objective lens by accurately irradiating the position shifted by 1 and detecting these lights at the light receiving section.

Japanese Patent Publication No. 4-34212

As described above, in the conventional tracking error detection method based on the DPP method, the light divided into three in the so-called light outward path from the light source to the optical recording medium is accurately placed at the target position with respect to the recording track of the optical recording medium. Irradiation is necessary. Therefore,
(A) Since the light is divided into three on the forward path, in the optical recording medium that performs recording and reproduction, the light use efficiency from the light source is lower than in the case where the light is not divided.
(B) The sub beam must be arranged with high accuracy with respect to the track of the optical recording medium.
(C) The main beam must be arranged with high accuracy on the seek axis (radial direction) of the optical recording medium.
(D) In an optical recording medium having a plurality of layers, unnecessary light from a layer on which recording / reproduction is not performed increases.
There are problems such as.
However, no method has been proposed for accurately correcting the offset of the objective lens without dividing the light on the forward path.

  In view of the above problems, the present invention provides an optical pickup, an optical recording / reproducing apparatus, and a tracking error detection method capable of correcting an offset of an objective lens in tracking error detection without using a plurality of beams. With the goal.

In order to solve the above problems, the present invention provides an optical system in which light from a light source is guided to an optical recording medium through an objective lens, and light reflected from the optical recording medium is guided to a light receiving unit, and is detected by the light receiving unit. An optical pickup device having an objective lens driving unit that drives an objective lens based on the optical output, and is configured such that at least a diffraction element is provided in the optical path reflected from the optical recording medium and directed to the light receiving unit, The light diffracted by the diffraction element is fifth-order astigmatism W (ρ, θ) = Z × (4ρ ⁴ −3ρ ² ) × sin θ (1)
(However, (ρ, θ) indicates the radius and angle of polar coordinates with the optical axis as the origin, and Z indicates a coefficient indicating the amount of aberration)
It is set as the structure which has.

  An optical recording / reproducing apparatus according to the present invention includes an optical system in which light from a light source is incident on an optical recording medium through at least an objective lens, and light reflected from the optical recording medium is guided to a light receiving unit, and an objective lens. An optical recording / reproducing apparatus having an optical head composed of an objective lens driving unit for driving, and performing recording and / or reproduction based on an optical output detected by a light receiving unit, comprising: an optical recording medium and a light receiving unit; A diffraction element is provided between them, and the diffracted light by this diffraction element has a fifth-order astigmatism defined by the above formula (1).

  Furthermore, the tracking error detection method according to the present invention is a tracking error detection method in which light incident on an optical recording medium from a light source via at least an objective lens is detected by a light receiving unit to detect a track position of the optical recording medium. Thus, a diffraction element is provided between the optical recording medium and the light receiving unit. The diffracted light by the diffractive element has the fifth-order astigmatism defined by the above formula (1), and the light that does not pass through the diffractive element or the 0th-order light of the diffractive element and the diffracted element A tracking error signal is detected from the ± first-order diffracted light.

According to the optical pickup, the optical recording / reproducing apparatus, and the tracking error detection method of the present invention described above, the light from the light source is irradiated to the optical recording medium without being divided, and the reflected light is received on the return optical path received by the light receiving unit. A diffractive element is provided, and this diffractive element has the above formula (1), that is, a fifth-order astigmatism of the Fringe Zernike polynomial.
At this time, the light intensity of ± 1st order diffracted light is not uniform in a region where the 0th order light and ± 1st order diffracted light generated by the guide groove of the optical recording medium overlap, that is, a so-called push-pull modulation region. An intensity distribution in which the phase is inverted occurs. As a result, the intensity change is offset.
If the ± 1st-order diffracted light having such an intensity distribution is detected by the light receiving unit divided into two in the track arrangement direction, and the difference signal in the track arrangement direction is detected, only the offset of the objective lens can be detected. It becomes possible. By subtracting the offset of the objective lens from the tracking error signal obtained from the light that does not pass through the diffractive element or the 0th-order light of the diffractive element, a tracking error signal in which the offset of the objective lens is corrected can be obtained. .
Therefore, according to the present invention, it is not necessary to accurately irradiate a target position with a plurality of beams on a track of an optical recording medium, and a good tracking error signal can be detected without impairing light use efficiency. A possible optical pickup, optical recording / reproducing apparatus, and tracking error signal detection method can be provided.

  According to the present invention, since an offset correction of a tracking error signal can be performed using one beam, an optical pickup capable of avoiding a decrease in light utilization efficiency and detecting a tracking error signal satisfactorily, An optical recording / reproducing apparatus and a tracking error signal detection method can be provided, and the optical system of the optical pickup and the optical recording / reproducing apparatus can be simplified.

Examples of the best mode for carrying out the present invention will be described below, but the present invention is not limited to the following examples.
FIG. 1 shows a schematic configuration diagram of a main part of an example of an optical recording / reproducing apparatus including an optical pickup for realizing a tracking error detection method according to the present invention.
The optical recording / reproducing apparatus 100 includes a light source 2 made of a semiconductor laser or the like, and an optical system that makes light emitted from the light source 2 enter an optical recording medium 10, for example, an optical disc. In this case, the optical system includes a polarization beam splitter 4, a collimator lens 5, a quarter-wave plate 6, and an objective lens 7. The optical system further includes an optical system that guides the light reflected from the optical recording medium 10 to the light receiving units 14 and 16. In this case, the objective lens 7, the quarter-wave plate 6, the collimator lens 5, the polarization beam splitter 4, and the beam splitter are included. And the like, a diffractive element 9, and a lens 15 such as a multi lens.
The objective lens 7 is connected to an objective lens driving unit 11 having an actuator 12 such as a biaxial actuator. The optical recording medium 10 is mounted and fixed on a rotation drive unit 16 such as a spindle motor, and is rotated at a predetermined speed during recording and reproduction.
Signals detected by the light receiving units 14 and 16 are output to the arithmetic circuit 17. In FIG. 1, the optical pickup 1 of the present invention is shown with a broken line.

In such a configuration, for example, laser light emitted from the light source 2 is incident on the polarization beam splitter 4, reflected on the polarization plane thereof, and converted into parallel light by the lens 5 made of, for example, a collimating lens, and is ¼. The light passes through the wave plate 6 and is incident on the recording track of the optical recording medium 10 through the objective lens 7.
The light reflected from the optical recording medium 10 passes through the quarter-wave plate 6 and the lens 5 through the objective lens 7. The light that has passed through the quarter-wave plate twice is changed in polarization direction in the polarization beam splitter 4 and passes through the polarization plane. In this case, the light path is separated by the separation unit 8 such as a beam splitter, The light is incident on the light receiving surface of the light receiving unit 14 via the diffraction element 9. The light of the other optical path separated by the separation unit 8 is incident on the light receiving surface of the light receiving unit 16 through a lens 15 such as a multi lens.

Here, the light receiving unit 14 that receives the light that has passed through the diffraction element 9 is divided into two in a direction corresponding to the direction in which the tracks of the optical recording medium 10 are arranged, that is, has a dividing line along the direction corresponding to the extension direction of the tracks. It consists of at least two divided light receiving elements, and these light receiving elements are arranged at positions that receive at least ± first-order diffracted light diffracted by the diffraction element 9. The light receiving unit 16 that receives the light that has passed through the lens 15 is divided into four in a direction corresponding to the direction in which the tracks of the optical recording medium 10 are arranged and the direction in which the tracks extend substantially perpendicular thereto. That is, when the optical recording medium 10 is a disk-shaped optical disc, the optical recording medium 10 is divided into four in the direction corresponding to the radial (radius) direction and the tangential (tangential) direction of the track. At the intersection of the dividing lines of the light receiving unit 16, the light receiving unit 16 is arranged so that the intensity centers of the light intensity distributions reflected from the optical recording medium and incident on the light receiving unit 8 substantially coincide.
As will be described later, since the 90-degree coordinates of the light that has passed through the diffraction element 3 given fifth-order astigmatism rotate, the track alignment direction and the track extension direction before passing through the diffraction element 3 are as follows. In the light receiving portion, the direction is rotated by 90 °.
The optical output detected by the light receiving units 14 and 16 is calculated by an arithmetic circuit 17 as an RF (high frequency) signal, a TE (tracking error) signal, and an FE (focus error) signal. For example, the RF signal is subjected to processing such as analog / digital conversion and error correction in an arithmetic circuit and is output as a recording / reproducing signal, the TE signal is output to the optical head driving unit 18 and / or the objective lens driving unit 11, and the FE signal is the objective signal. The servo is output to the lens driving unit 11 to perform focus servo and tracking servo.
The FE signal can be detected by the astigmatism method by giving astigmatism to the lens 15 made of, for example, a multilens. Further, various other focus error detection methods can be applied.

In the present invention, the diffractive element 9 described above has the above formula (1), that is, W (ρ, θ) = Z × (4ρ ⁴ −3ρ ² ) × sin θ (1)
(Where (ρ, θ) represents the radius and angle of polar coordinates with the optical axis as the origin, and Z represents a coefficient representing the amount of aberration)
The fifth-order astigmatism defined by the above equation, that is, the aberration of the thirteenth term in the Zernike fringe polynomial is given. Here, (ρ, θ) represents the radius and angle of polar coordinates centered on the optical axis.

When such an aberration is given, as described above, the intensity change in the portion where the 0th-order light and ± 1st-order diffracted light generated by the guide groove of the optical recording medium 10 overlap, that is, the push-pull modulation region, is not uniform. This will be described with reference to FIGS. 2A and 2B.
FIG. 2A shows an example of the light intensity distribution at the light receiving unit detected by a normal optical pickup. The direction in which the tracks of the optical recording medium are arranged is indicated by an arrow x, and the extending direction of the track substantially orthogonal to this is indicated by an arrow y. Normally, as shown in FIG. 2A, push-pull areas P1 and P2 are detected in the direction in which the tracks are arranged in the received light spot, that is, in the radial direction in the case of a disc-shaped optical recording medium. By subtracting the brightness of P2, that is, when the signals from the four light receiving areas of the light receiving section 16 are respectively A1, B1, C1, and D1, the difference signal (A1 + B1) in the radial direction of the signal from which the light intensity is detected. )-(C1 + D1) is calculated to obtain a push-pull signal component.

On the other hand, when the fifth-order astigmatism defined by the above equation (1) is given by the diffraction element 9, as shown in FIG. 2B, the push-pull regions P1 ′ and P2 ′ are rotated by 90 ° and detected. Is done. In this example, the track alignment direction is θ = 0 ° in the polar coordinates representing the aberration defined by the above formula (1).
Therefore, when this ± first-order diffracted light is detected, bright regions P1a and P2a and dark regions P1b and P2b are generated in the push-pull modulation regions P1 ′ and P2 ′, respectively, along the track extending direction indicated by the arrow y. The direction indicated by the arrow x is the direction in which the objective lens shifts. That is, in these areas P1 ′ and P2 ′, the phase is inverted between these bright and dark, and the intensity change due to the push-pull modulation component is canceled out. If this light is detected by the light receiving unit 14 divided into two in the track arrangement direction (direction indicated by the arrow x) and detected as a difference signal in the track arrangement direction, only the offset of the objective lens can be detected. Become.

3 to 5 show the results of analyzing the change in the signal amount with respect to the detrack between the 0th order light and the ± 1st order diffracted light. 3 shows zero-order light, that is, a normal output signal, and FIG. 4 shows an output signal in the case where there is fifth-order astigmatism. In this case, as shown in FIG. 2B, ± 1st-order diffracted light is obtained by receiving signals received by the light-receiving elements divided into four in the direction in which the tracks are arranged and the direction in which the tracks are substantially orthogonal, as shown in FIG. Shown as C2 and D2.
As shown in FIG. 3, in the normal case (0th order light), signals A1 to D1 from the light receiving elements divided into four in the track arrangement direction and the track extension direction in FIG. 2A are indicated by solid lines a1 to a4, respectively. Thus, the signals A1 and B1 are substantially equal, and the signals C1 and D1 are substantially equal.
On the other hand, as shown in FIG. 4, when the fifth-order astigmatism is given, the signal A2 and the signal C2 are substantially equal, and the signals B2 and D2 are substantially equal.
Therefore, as shown in FIG. 5, the push-pull signal in the normal case, that is, the signal (A1 + B1) − (C1 + D1) in FIG. 2A changes periodically with respect to the detrack as shown by the solid line c1, but the fifth order When the astigmatism is given, the signal (A2 + D2) − (B2 + C2) becomes substantially 0 as shown by the solid line c2. That is, it can be seen that the push-pull modulation component is not included.

FIG. 6 shows a direction in which the track alignment direction is defined as 0 degree in the polar coordinates of the fifth-order astigmatism defined by the above formula (1), and θ = 0 ° is defined within a range of ± 25 degrees from this direction. The result of changing and analyzing the change of the push-pull signal is shown. In FIG. 6, the solid line d1 is a normal case, and the solid lines d2 to d12 are push-pull signals in each case where the direction of θ = 0 ° is changed every 5 degrees from −25 degrees to +25 degrees from the track arrangement direction. Indicates.
From the result of FIG. 6, as the polar coordinates of the fifth-order astigmatism defined by the above formula (1), the direction of θ = 0 ° is set in the range of −25 degrees to +25 degrees from the track alignment direction. In this case, it can be seen that the push-pull modulation component can be suppressed to substantially zero or very small. Therefore, it can be said that the direction in which the polar coordinate θ = 0 ° in the above formula (1) can be within a range of ± 25 degrees from the direction in which the tracks are arranged.

  FIG. 7 shows an analysis of a normal push-pull signal and a push-pull signal obtained by the optical pickup of the present invention. A solid line e1 indicates a normal push-pull signal, that is, a signal (A1 + B1) − (C1 + D1) in FIG. 2A, and a solid line e2 is obtained by providing fifth-order astigmatism so as not to include a push-pull modulation component. 2B, a signal (A2 + D2) − (B2 + C2) in FIG. 2B is shown, and a solid line e3 shows a tracking error signal obtained by subtracting the objective lens shift from the push-pull signal. Thus, according to the present invention, it can be seen that a tracking error signal in which the shift of the objective lens is corrected can be detected.

FIG. 8 is a schematic configuration diagram of an embodiment of an arithmetic circuit 17 that calculates detection signals from the light receiving units 14 and 16 in the optical pickup shown in FIG.
In this example, as shown in FIG. 1, the light path is separated by the separating unit 8 and ± 1st-order diffracted light diffracted by the diffraction element 9 given fifth-order astigmatism is received by the light receiving unit 14, that is, the tracks are arranged. The light received by the two light receiving elements 14a and 14b divided into two in the direction corresponding to the direction and separated by the separating unit 8, that is, light that does not pass through the diffraction element 9, is a multi lens or the like. An example is shown in which astigmatism is added by a lens 15 and light is received by a light receiving unit 16 having a light receiving region divided into four in the direction in which the tracks are arranged and the direction in which the tracks extend.
As described above, the light intensity distribution is rotated by 90 ° by adding fifth-order astigmatism. In FIG. 8, the direction corresponding to the direction in which the tracks are arranged is indicated by an arrow x, and the direction corresponding to the extension direction of the track is indicated by an arrow y.

  In FIG. 8, assuming that signals detected by the light receiving elements divided into four in the light receiving unit 16 are A to D clockwise, these signals A to D are detected by voltage conversion by current-voltage conversion amplifiers (not shown). In the adders 21 and 22, the sum signals (A + D) and (B + C) of the light receiving areas divided in the track arranging direction and the track extending direction are calculated in the adders 21 and 22, respectively. The difference signal (A + D)-(B + C), that is, PPm is calculated.

  On the other hand, in the light receiving portions 14a and 14b, the signals E and F, G, and H detected in the light receiving regions divided in the direction in which the tracks are arranged are respectively detected by voltage conversion by current-voltage conversion amplifiers (not shown). In the subtracters 24 and 25, (E−F), that is, PPs1, and (G−H), that is, PPs2, are calculated. Further, the coefficient multipliers 26 and 27 multiply the signals PPs1 and PPs2 by the coefficients k1 and k2, respectively, and add them in the adder 28. Then, the subtractor 29 subtracts the signal (k1 × PPs1 + k2 × PPs2) for correcting the shift of the objective lens from PPm, and outputs it as a tracking error signal TES in which the shift of the objective lens is corrected.

That is, in this case, the tracking error signal TES is
TES = PPm− (k1 × PPs1 + k2 × PPs2)
PPm = (A + D)-(B + C)
PPs1 = EF
PPs2 = GH
More obtained.
K1 and k2 are correction coefficients for correcting the intensity distribution of incident light, the diffracted light quantity ratio of the diffraction element, and the like. k1 = k2 may be sufficient.
In this way, by taking the sum of the ± first-order diffracted lights, the allowable amount increases with respect to the relative positional deviation between the light beam and the light receiving unit. Therefore, there is an advantage that the adjustment accuracy of the arrangement position of the light receiving unit can be relaxed.

Further, the focus error signal FES uses signals A to D from the light receiving unit 16 that receives light given third-order astigmatism,
FES = (A + B)-(C + D)
More obtained.

  If another detection method is used as the focus error signal detection method, the 0th-order light that has passed through the diffraction element 9 may be used without providing the separation unit 8. In that case, instead of the light receiving unit 16 described above, a light receiving element for detecting 0th-order light is arranged in the light receiving unit 14 and the push-pull signal PPm is detected, thereby shifting the objective lens as in the above example. Can be detected.

As described above, according to the optical pickup, the optical recording / reproducing apparatus, and the tracking error detection method of the present invention, the offset of the objective lens can be corrected by using only one beam without using a sub beam, That is, a tracking error signal that does not generate an offset even when the objective lens is shifted from the optical axis can be easily obtained with a relatively simple optical system configuration. In addition, since the tracking error detection optical system can be configured with only one beam as described above, the following effects can be obtained.
1. Light utilization efficiency is improved.
2. The optical axis alignment of the optical system, the alignment of the beam, the alignment accuracy in the beam moving direction, etc. can be relaxed to simplify the assembly process, improve the productivity, and further reduce the yield.
3. Since a plurality of beams are not used, it is possible to suppress and reduce the generation of unnecessary light when recording / reproducing is performed on an optical recording medium having a plurality of recording layers.
4). Compatibility with optical recording media having different track pitches is obtained.

The optical pickup and the optical recording / reproducing apparatus of the present invention are not limited to the configurations described in the above-described embodiments, and various modifications and changes can be made without departing from the configurations of the present invention.
For example, in the optical recording / reproducing apparatus of the present invention, the focus error detection method is not limited to the above-mentioned astigmatism method, and other methods can be used.
The optical pickup, optical recording / reproducing apparatus, and tracking error signal detection method of the present invention are a dye type, phase change type, magneto-optical, except for an optical recording medium that employs a specific push-pull detection method such as a DVD-ROM. The present invention can be applied to recording / reproducing with respect to an optical recording medium having various guide grooves such as a recording mold and uneven pits. Note that when only the offset of the objective lens is detected, it can be applied to all optical recording media.

1 is a schematic configuration diagram of an embodiment of an optical recording / reproducing apparatus having an optical pickup according to the present invention. A is a diagram showing an intensity distribution of a light spot of a light receiving portion in a normal optical pickup. FIG. 7B is a diagram illustrating an intensity distribution of a light spot of a light receiving unit in an embodiment of an optical pickup according to the present invention. It is a figure which shows the result of having analyzed the output signal with respect to the detrack in a normal optical pick-up. It is a figure which shows the result of having analyzed the output signal with respect to a detrack in case there exists a 5th-order astigmatism. It is a figure which shows the result of having analyzed the push-pull signal when there is a normal push-pull signal and fifth-order astigmatism. It is a figure which shows the result of having analyzed the angle dependence of the 5th-order astigmatism in a push pull signal. It is a figure which shows the result of having analyzed the push pull signal in one embodiment of the normal optical pickup and the optical pickup of the present invention. 1 is a schematic configuration diagram of an embodiment of an arithmetic circuit of an optical pickup and an optical recording / reproducing apparatus according to the present invention.

Explanation of symbols

  1. Optical pickup, 2. Light source, 4. 4. polarization beam splitter; Lens, 6; Wave plate, 7. Objective lens, 8. 8. Separation unit Diffraction element, 10. 10. optical recording medium, Objective lens drive unit, 12. Actuator, 14. light receiving section, 15. Lens, 16. light receiving unit, 17. Arithmetic circuit, 18. 18. optical head driving unit; Rotational drive unit, 21. Adder, 22. Adder, 23-25. Subtractor, 26. Coefficient multiplier, 27. Coefficient multiplier, 28. Adder, 29. Subtractor, 100. Optical recording / reproducing device

Claims (7)

Based on an optical system in which light from a light source is guided to an optical recording medium through an objective lens, and light reflected from the optical recording medium is guided to a light receiving unit, and the light output detected in the light receiving unit An optical pickup device having an objective lens driving unit for driving an objective lens,
At least a diffractive element is provided in the optical path reflected from the optical recording medium and directed to the light receiving unit,
The diffracted light of the diffraction element has fifth-order astigmatism W (ρ, θ) = Z × (4ρ ⁴ −3ρ ² ) × sin θ
(However, (ρ, θ) indicates the radius and angle of polar coordinates with the optical axis as the origin, and Z indicates a coefficient indicating the amount of aberration)
An optical pickup characterized by comprising 2. The optical pickup according to claim 1, wherein in a polar coordinate defining the aberration of the diffractive element, a direction of θ = 0 ° is in a range of ± 25 degrees from a direction in which tracks of the optical recording medium are arranged. . The first and second light receiving portions that receive ± first-order diffracted light diffracted by the diffraction element are divided into two in the direction in which the tracks of the optical recording medium are arranged,
The third light-receiving unit that receives light that does not pass through the diffraction element or zero-order light from the diffraction element is divided into four in the direction in which the tracks are arranged and the direction in which the tracks extend. Optical pickup. The light traveling from the optical recording medium to the light receiving unit is separated by a separating unit,
The diffraction element is provided in one optical path separated by the separation unit,
The ± first-order diffracted light diffracted by the diffraction element is received by the first and second light receiving units,
The optical pickup according to claim 3, wherein the other light separated by the separation unit is received by the third light receiving unit. It comprises an optical system in which light from a light source is incident on an optical recording medium via at least an objective lens, and light reflected from the optical recording medium is guided to a light receiving unit, and an objective lens driving unit that drives the objective lens An optical recording / reproducing apparatus that has an optical head and performs recording and / or reproduction based on an optical output detected by the light receiving unit,
A diffraction element is provided between the optical recording medium and the light receiving unit,
The diffracted light of the diffraction element has fifth-order astigmatism W (ρ, θ) = Z × (4ρ ⁴ −3ρ ² ) × sin θ
(However, (ρ, θ) indicates the radius and angle of polar coordinates with the optical axis as the origin, and Z indicates a coefficient indicating the amount of aberration)
An optical recording / reproducing apparatus characterized by comprising: A tracking error detection method for detecting light incident on an optical recording medium from a light source through at least an objective lens by a light receiving unit to detect a track position of the optical recording medium,
A diffraction element is provided between the optical recording medium and the light receiving unit,
The diffracted light of the diffraction element has fifth-order astigmatism W (ρ, θ) = Z × (4ρ ⁴ −3ρ ² ) × sin θ
(However, (ρ, θ) indicates the radius and angle of polar coordinates with the optical axis as the origin, and Z indicates a coefficient indicating the amount of aberration)
And is configured to have
A tracking error signal detection method comprising: detecting a tracking error signal from light that does not pass through the diffraction element or zero-order light of the diffraction element and ± first-order diffracted light diffracted by the diffraction element. The ± first-order diffracted light from the diffractive element is received by the first and second light receiving parts divided into two in the direction in which the tracks of the optical recording medium are arranged,
Light that does not pass through the diffraction element or zero-order light of the diffraction element is received by a third light receiving unit that is divided into four in the direction in which the tracks of the optical recording medium are arranged and the direction in which the tracks extend,
The signals received by the first and second light receiving units are E and F, G, and H, respectively, and the signals received by the third light receiving unit are A to clockwise around the four divided light receiving regions. When D, the tracking error detection signal TES is
TES = PPm− (k1 × PPs1 + k2 × PPs2)
PPm = (A + D)-(B + C)
PPs1 = EF
PPs2 = GH
(K1 and k2 are arbitrary constants)
The tracking error signal detection method according to claim 6, wherein: