JP2007305245A - Optical pick up device and optical recording medium driving unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent offset generation in a tracking error signal even if a photo detector slightly deviates in the direction orthogonal to a track of an optical recording medium due to a temporal change, and finely record and reproduce a single layer optical disk or double layer optical disk. <P>SOLUTION: In a light path of a return light from an optical recording medium (optical disk) 1, a diffractive element 20 which has an inner periphery circular diffractive grating 20a, a ring light transmitting section 20b, and an outer periphery diffractive grating 20c is arranged by centering on a central point Op corresponding to an intersection point at which a central line X of a track T formed on a signal plane 1b (or 1c, 1d) of the optical disk 1 and a line Y intersecting the central line X at right angles and passing through the central point of the optical disk meet, and the light detector 19 receives the return light from the optical recording medium (optical disk) 1 via a cylindrical lens 18 by diffracting to the direction orthogonal to the track T by the inner periphery circular diffractive grating 20a and the outer periphery circular diffractive grating 20c of the diffractive element 20. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is configured to be selectively applicable to a first optical recording medium having a single-layer signal surface and a second optical recording medium having a two-layer signal surface, and is reflected by each signal surface. A track formed on the signal surface of an optical recording medium by a time-dependent change in the position of a photodetector when the laser beam is diffracted by a diffraction element and then detected by a photodetector via a cylindrical lens. The second optical recording medium having a two-layer signal surface can be prevented even when the position is slightly shifted in the direction orthogonal to the tracking error signal, and when the offset of the tracking error signal is prevented. The present invention relates to an optical pickup device and an optical recording medium driving device that can prevent an offset of a focus error signal that occurs in FIG.

  Generally, a disk-shaped or card-shaped optical recording medium has a high density on a track in which information signals such as video information, audio information, and computer data are spirally or concentrically formed on the signal surface of a light-transmitting substrate. It is frequently used because a desired track can be accessed at high speed when a recorded and recorded track is reproduced.

  In recording or reproducing various information signals on the signal surface of the optical recording medium using an optical pickup, in general, an optical pickup device uses a laser beam emitted from a laser light source as a signal of the optical recording medium. A laser beam irradiation optical system that irradiates a track formed on the surface; and a return light detection optical system that detects return light of the laser beam reflected by the signal surface of the optical recording medium.

  Then, the laser beam emitted from the laser light source in the optical pickup is narrowed down by the objective lens to obtain a laser beam, and this laser beam is incident from the incident surface of the light transmissive substrate (or light transmissive protective film), and When the laser beam is focused in a spot shape on a track formed on the signal surface at a predetermined distance from the incident surface, the spot laser beam follows the track formed on the signal surface, and The objective lens is servoed in the tracking direction and the focus direction so as to be focused on the signal surface.

FIG. 16 is a perspective view showing a general optical pickup device,
17 is an enlarged view of the photodetector shown in FIG.
18 (a) and 18 (b) show a general optical pickup apparatus in which a light detector whose mounting position has been adjusted is slightly positioned in one or the other in the disk radial direction perpendicular to the track formed on the signal surface of the optical disk. It is the figure which showed the state which shifted | deviated.

  The general optical pickup device 10 shown in FIG. 16 is configured to be able to record or reproduce a disk-shaped or card-shaped optical recording medium 1.

  Here, before explaining the general optical pickup device 10, the optical recording medium 1 will be briefly described. When an optical disc is applied as the optical recording medium 1, the optical recording medium 1 (hereinafter referred to as the optical disc 1) is used. Is formed in a disk shape using a transparent resin material such as polycarbonate, and a signal surface 1b is formed at a position separated from the incident surface 1a on which the laser beam LB is incident. In FIG. 16, the optical disk 1 formed in a disk shape is partially cut away.

  A track T having a predetermined width is formed on the signal surface 1b of the optical disc 1 in a spiral or concentric manner for recording or reproducing information signals such as video information, audio information, and computer data.

  At this time, a virtual center line on one track T is represented by X, and the direction along the track T is referred to as a track direction (or tangential direction), and is orthogonal to the center line X of the track T and the optical disc 1. An imaginary line passing through the center of the disk is represented by Y, and the direction along the line Y is referred to as a disk radial direction (or radial direction) and will be described below.

  The optical disk 1 described above is mounted on a turntable fixed to a spindle motor shaft (not shown), and is rotatably provided integrally with the turntable. An optical pickup for recording / reproducing is provided below the optical disk 1. An apparatus 10 is provided so as to be movable in the radial direction of the optical disc 1.

  Here, the general optical pickup device 10 is configured such that a laser beam L emitted from a laser light source 11 using a semiconductor laser (hereinafter referred to as a semiconductor laser 11) is on a track T formed on the signal surface 1b of the optical disc 1. And a return light detection optical system for detecting return light of the laser light reflected by the signal surface 1b of the optical disc 1.

  First, the laser light irradiation optical system in the optical pickup device 10 will be described. Laser light L having a reference wavelength λ corresponding to the type of the optical disk 1 is emitted from the semiconductor laser 11, and this laser light L is linearly polarized light. The divergent light. The divergent light is converted into parallel light by the collimator lens 12 and then incident on the polarization beam splitter 13. Here, since the polarization direction of the laser light L emitted from the semiconductor laser 11 is P-polarized light, the laser light L incident into the polarization beam splitter 13 is polarized-selective dielectric multilayer film (P-polarized light: (Transmitted, S-polarized light: reflected) 13a is transmitted and incident on the λ / 4 plate 14, and is transmitted through the λ / 4 plate 14 to become circularly polarized light. At this time, the λ / 4 plate 14 gives a phase difference of λ / 4 when transmitting the laser light L having the reference wavelength λ. Further, the laser light L transmitted through the λ / 4 plate 14 is incident on the objective lens 16 mounted in the lens holder 15.

  The objective lens 16 has a numerical aperture (NA) corresponding to the type of the optical disc 1, and the laser beam LB obtained by focusing the laser light L with the objective lens 16 is incident from the incident surface 1 a of the optical disc 1. Incident light is irradiated in a spot shape on the track T formed on the signal surface 1b located at a predetermined distance from the incident surface 1a.

  Next, the return light detection optical system in the optical pickup device 10 described above will be described. The return light of the laser beam LB reflected by the signal surface 1b of the optical disc 1 is contrary to the objective lens 16, λ / The light passes through the four plates 14 in order, and when passing through the λ / 4 plate 14, the 90-degree polarization plane is changed to S-polarized light, and the polarization-selective dielectric multilayer film of the polarization beam splitter 13 (P-polarized light: transmitted, S Polarized light (reflected) is reflected by 13a and turned about 90 °, and then sequentially passes through the detection lens 17 and the cylindrical 18 that generates astigmatism with respect to the return light, and the return light passes through a plurality of detection regions. A circular spot is imaged on the photodetector 19 so that the photodetector 19 can receive the light.

  At this time, the above-described cylindrical lens 18 is not necessary when a photodetector 19 detects a tracking error signal, which will be described later, using a known push-pull method. This is necessary when detecting using the point aberration method, and the track direction of the return light reflected by the signal surface 1b of the optical disc 1 is such that the center line X of the track T formed on the signal surface 1b of the optical disc 1 is X. It is arrange | positioned so that it may incline 45 degrees with respect to. As a result, the track direction and the disk radial direction of the return light that has passed through the cylindrical lens 18 are rotated by 90 ° with respect to the incident time of the objective lens 16, so that X and Y are also rotated by 90 ° on the photodetector 19. Return light is imaged in a circular spot shape.

  Here, as shown in an enlarged view in FIG. 17, the above-described photodetector 19 has a square interior divided into a plurality of regions. For example, the track T (formed on the signal surface 1 b of the optical disc 1 ( 16) and the center of the track T (FIG. 1) formed on the signal surface 1b of the optical disc 1 and the first dividing line 19a passing through the center point O of the photodetector 19 in the direction corresponding to the center line X of FIG. The inside of the photodetector 19 is divided into four by the second dividing line 19b that passes through the center point O of the photodetector 19 in the direction corresponding to the line Y orthogonal to the line X, and has four detection areas (A). To (D) are formed.

  Then, the light amount of the spot SP of the return light from the optical disk 1 formed in a circular shape on the photodetector 19 is photoelectrically converted in the four detection areas (A) to (D), and each detection area (A). The detection signals A to D are output from (D) to (D).

  At this time, the technical idea of applying the tracking servo and the focus servo to the objective lens 16 with respect to the optical disc 1 using the detection signals A to D detected by the photodetector 19 is as follows. 1.

  According to this non-patent document 1, the tracking error signal TE for causing the laser beam LB to follow the track T (FIG. 16) formed on the signal surface 1b of the optical disc 1 is 4 of the photodetector 19 shown in FIG. A well-known push-pull method is used for the detection signals A to D from the two detection areas (A) to (D), and specifically, formed on the signal surface 1 b of the optical disc 1 on the photodetector 19. After being divided into two detection areas (A, B) and (C, D) by a dividing line 19a that faces the direction corresponding to the center line X of the track T (FIG. 16) and passes through the center point O, The difference between the received light amounts from the two detection areas (A, B) and (C, D) across the dividing line 19a is calculated by the following equation 1, and the objective lens 16 is tracked by this tracking error signal TE. Servo is applied.

[Equation 1]
TE = (A + B)-(C + D) ......... Formula 1

  Further, the focus error signal FE for focusing the laser beam LB on the signal surface 1b of the optical disc 1 causes astigmatism in the cylindrical lens 17 with respect to the return light from the optical disc 1, and is shown in FIG. A known astigmatism method is used for the detection signals A to D from the four detection areas (A) to (D) of the photodetector 19, and specifically, each other on the photodetector 19. Light is received by one diagonal area (A, C) and the other diagonal area (B, D) in four detection areas (A) to (D) divided by orthogonal dividing lines 19a, 19b. The difference between the amounts of received light is calculated by the following equation (2), and the focus servo is applied to the objective lens 16 by the focus error signal FE.

[Equation 2]
TE = (A + C)-(B + D) ......... Formula 2

  Further, the data signal RF for reproducing the data (information signal) recorded on the signal surface 1b of the optical disc 1 is received by the respective light receiving areas in the detection areas (A) to (D) on the photodetector 19 shown in FIG. The amount added is calculated from the following equation (3), and this data signal RF is signal-processed in accordance with the format of the optical disc 1.

[Equation 3]
RF = A + B + C + D ......... Formula 3

  On the other hand, in order to reduce the influence of the shift of the objective lens, an optical pickup capable of performing good tracking control by receiving reflected light from an optical disk with a photodetector via a diffraction element, a cylindrical lens, and a spot lens. A tracking error detection method and an optical pickup device are disclosed in Patent Document 1 below.

According to this Patent Document 1, although not shown, the reflected light from the optical disc is divided into 0th order light and ± 1st order light by the diffraction element, and the objective lens is shifted in the prescribed direction of the disc radial. The amount of light incident on the first light receiving element is increased and the amount of light incident on the second light receiving element is decreased, so that a difference signal between the output signal of the first light receiving element and the output signal of the second light receiving element is obtained. On the basis of this, it is disclosed that a tracking error signal can be obtained by correcting the push-pull signal so that good tracking can be performed without being affected by the shift of the objective lens.
JP 2003-123279 A (page 10, FIG. 2) Illustrated Compact Disc Reader Published by Ohm

  By the way, when the general optical pickup device 10 shown in FIG. 16 is assembled, the photodetector 19 shown in FIG. 17 has a dividing line 19 a passing through the center point O formed on the signal surface 1 b of the optical disc 1. Assembly is performed while adjusting the mounting position in advance so as to coincide with the center line X of the track T (FIG. 16).

  However, in the conventional optical pickup device 10 described above, the photodetector 19 whose mounting position has been adjusted is formed on the signal surface 1b of the optical disc 1 as shown in FIGS. When the center of the return light spot S is shifted with respect to the center point O of the photodetector 19 when it is slightly shifted in one or the other in the disk radial direction orthogonal to the track T (FIG. 16), tracking is performed. An offset occurs in the error signal TE.

  That is, the spot SP of the return light from the optical disk 1 imaged on the photodetector 19 generally has a strong light quantity at the center corresponding to the light intensity distribution of the laser beam LB. When the position is slightly shifted in the radial direction of the disk as shown in FIG. 18A due to the change over time, the center portion of the spot SP having a high light quantity is directed to the upper detection areas (A) and (B). When the detection signals A + B, C + D from the two detection areas (A, B), (C, D) sandwiching the dividing line 19a are calculated to move, A + B> C + D, and the tracking error signal TE is offset. Greatly occurs on the + side.

  On the other hand, when the photodetector 19 is slightly displaced in the radial direction of the disk as shown in FIG. 18 (b) due to a change with time, the center portion of the spot SP having a high light amount is located in the lower detection area (C ), (D), when calculating the detection signals A + B, C + D from the two detection areas (A, B), (C, D) across the dividing line 19a, A + B <C + D. The offset of the tracking error signal TE is greatly generated on the negative side.

  At this time, the focus error signal FE is detected even if the photodetector 19 whose mounting position has been adjusted is slightly displaced in the radial direction of the disk perpendicular to the track T (FIG. 16) formed on the signal surface 1b of the optical disk 1 due to changes over time. And the data signal RF is not affected. Further, even if the photodetector 19 whose mounting position has been adjusted is slightly displaced in the track direction due to a change over time, the tracking error signal TE, the focus error signal FE, and the data signal RF are not affected.

  On the other hand, according to the tracking error detection method and the optical pickup device disclosed in Patent Document 1 described above, in the optical path of the reflected light (returned light) from the optical disk, the zero-order light and the ± first-order light are converted. Although the diffraction element for dividing is provided, this diffraction element has the same grating pitch over the entire surface, and the width of the peak and valley of the diffraction grating corresponding to the shift of the objective lens Therefore, it is not a diffractive element having a diffraction grating portion corresponding to the deviation of the mounting position of the photodetector.

  Therefore, when the first optical recording medium having a single-layer signal surface and the second optical recording medium having a two-layer signal surface are selectively and satisfactorily recorded or reproduced, light detection with an adjusted mounting position is performed. Even if the device is slightly misaligned in the direction perpendicular to the track of the optical recording medium due to changes over time, the occurrence of the tracking error signal offset can be prevented. There is a demand for an optical pickup device and an optical recording medium driving device that can prevent a focus error signal offset occurring in a second optical recording medium having two signal surfaces.

The present invention has been made in view of the above problems, and the invention according to claim 1 is a first optical recording medium having a single-layer signal surface and a second optical recording medium having a two-layer signal surface. And a laser beam irradiation optical system for irradiating a laser beam onto a track on each signal surface of the first and second optical recording media, and the reflected light from each signal surface In an optical pickup device provided with a return light detection optical system that detects a return light of a laser beam with a diffraction element after being diffracted by a diffraction element, with a photodetector.
The diffraction element is
A grid having a predetermined diameter and a circle centered on a center point corresponding to an intersection point of a center line of the track and a line perpendicular to the center line of the track and passing through the center of the optical recording medium. Is set in a direction orthogonal to the track, and a non-imaging region is generated in the vicinity of the center point on the photodetector without transmitting the first luminous flux on the inner circumference side of the return light. And an inner circumference that images the first ± first-order light obtained by diffracting the first light flux in a direction orthogonal to the track on the photodetector in a direction orthogonal to the track across the non-image forming region. A side circular diffraction grating part;
Zero-order light that is formed in a ring shape along the outer periphery of the inner circumferential circular diffraction grating portion and transmits a second ring-shaped light beam positioned outside the first light beam among the return light, A ring-shaped light transmitting portion that forms an image along the outer periphery of the non-imaging region on the photodetector;
A third light beam on the outer peripheral side, which is formed outside the ring-shaped light transmitting portion and has a grating orientation set in a direction orthogonal to the track, is located outside the second light beam in the return light. An outer peripheral side that forms each part of the second ± first-order light diffracted in the direction orthogonal to the track on the photodetector in the direction orthogonal to the track outside the first ± first-order light. An optical pickup device having a diffraction grating portion.

The invention according to claim 2 is an optical recording medium driving device to which the optical pickup device according to claim 1 is applied,
A first dividing line that passes through the center point and corresponds to the center line of the track, and a second dividing line that passes through the center point and is orthogonal to the first dividing line. Is divided into four areas,
Differences in received light amounts respectively received by the two detection regions divided into two by the first dividing line for each of the zero-order light, the first ± first-order light, and the second ± first-order light. A tracking servo circuit that generates a tracking error signal by calculating a push-pull method,
Receiving light received by each of the diagonal areas and the other diagonal areas in the four areas, respectively, of the zero-order light, the first ± first-order light, and the second ± first-order light. A focus servo circuit unit that calculates a difference in amount by an astigmatism method and generates a focus error signal;
An optical recording medium driving device comprising:

  According to the optical pickup device of the first aspect, in the optical path of the return light from the optical recording medium (optical disk), the center line of the track formed on the signal surface of the optical disk and the center of the optical disk perpendicular to the center line. A diffraction element having an inner circumferential circular diffraction grating portion, a ring-shaped light transmission portion, and an outer circumferential diffraction grating portion is arranged around the center point corresponding to the intersection point where the line passing through the optical axis intersects the optical recording medium (optical disk). Is diffracted in a direction orthogonal to the track by the inner circular circular diffraction grating portion and the outer peripheral diffraction grating portion in which the direction of the grating is set in a direction orthogonal to the track, and then a photodetector through a cylindrical lens. Even if the photo detector whose mounting position has been adjusted slightly shifts in the direction perpendicular to the track of the optical recording medium (optical disk) due to changes over time, the inner circumference side circular shape The occurrence of the offset of the tracking error signal can be prevented by the folding grating portion. When the occurrence of the offset of the tracking error signal is prevented, two layers are formed by the inner circumferential circular diffraction grating portion and the outer circumferential diffraction grating portion. It is possible to prevent the focus error signal from being offset in the second optical recording medium having the signal surface.

  Further, according to the optical recording medium driving device according to claim 2, when the optical pickup device according to claim 1 is applied, each of the zero-order light, the first ± first-order light, and the second ± first-order light A tracking servo circuit unit that generates a tracking error signal by calculating a difference between received light amounts respectively received by two detection areas divided into two by a first dividing line of a photodetector by a push-pull method; Receiving amounts of light received by each of the diagonal region and the other diagonal region in the four regions of the photodetector for each part of the secondary light, the first ± primary light, and the second ± primary light. And a focus servo circuit that generates a focus error signal by calculating an astigmatism method, so that the photodetector is slightly misaligned in the direction perpendicular to the track of the optical recording medium due to changes over time. Even if you Since no offset of the king error signal occurs, the tracking servo of the objective lens can be performed satisfactorily and the signal surface of the single-layer optical disk is reproduced or the first signal surface of the two-layer optical disk is reproduced. In this case, or in the case of reproducing the second signal surface of the two-layer optical disc, the focus error signal is not offset, so that each signal surface can be recorded or reproduced satisfactorily.

  An embodiment of an optical pickup device and an optical recording medium driving device according to the present invention will be described below in detail with reference to FIGS.

  The optical pickup device and the optical recording medium driving device according to the present invention are configured to be able to record or reproduce a disk-shaped or card-shaped optical recording medium. In the following description, a signal surface is a single layer as an optical recording medium. An example in which an optical recording medium and an optical recording medium having a two-layer signal surface are selectively applicable will be described.

FIG. 1 is a cross-sectional view when an optical recording medium applied to an optical pickup device according to an embodiment of the present invention is configured in conformity with the DVD standard. FIG. 1 (a) shows an optical disc having a single signal surface. , (B) is a diagram showing an optical disc having a two-layer signal surface;
FIG. 2 is a perspective view showing an optical pickup device according to an embodiment of the present invention.
FIG. 3 is an enlarged view of a diffractive element, which is a main part of the embodiment, in the optical pickup device according to the embodiment of the present invention.
FIG. 4A is an optical path diagram when the return light of the laser beam reflected by the signal surface of the optical disc is diffracted by the diffraction element of the embodiment in the optical pickup device according to the embodiment of the present invention. ) Is a diagram showing the return light of the laser beam incident on each part of the diffraction element of the example,
FIG. 5 shows a case where the signal surface of a single-layer optical disk is reproduced using the optical pickup device according to the embodiment of the present invention, and the return light of the laser beam reflected by the single-layer signal surface is reflected by the diffraction element of the embodiment. A diagram showing a state in which an image is formed on a photodetector whose position has been adjusted after diffracting,
FIG. 6 is a block diagram showing an optical recording medium driving device to which an optical pickup device according to an embodiment of the present invention is applied.
7 (a) and 7 (b) show a case in which the optical detector with the mounting position adjusted is a single-layer optical disc when the signal surface of the single-layer optical disc is reproduced using the optical pickup device according to the embodiment of the present invention. The figure which showed the state slightly shifted in one or the other of the disk radial direction orthogonal to the track formed in the signal surface,
FIGS. 8A to 8C are diagrams for explaining the offset amount (%) of the tracking error signal.

  Before describing the optical pickup device 10A (FIG. 2) according to the embodiment of the present invention, the optical recording medium 1 applied to the optical pickup device 10A will be described with reference to FIGS. 1 (a) and 1 (b).

  In this embodiment, when the optical recording medium 1 is configured in accordance with, for example, the well-known DVD (Digital Versatile Disc) standard, the first light having a single signal surface 1b as shown in FIG. A recording medium 1A (hereinafter referred to as optical disk 1A) and a second optical recording medium 1B (hereinafter referred to as optical disk 1B) having two layers of first and second signal surfaces 1c and 1d as shown in FIG. 1B. The optical discs 1A and 1B are both formed in a disc shape with an outer diameter of 120 mm and a center hole diameter of 15 mm, and both optical discs 1A and 1B have a wavelength λ of 650. Recording or reproduction is selectively performed using a semiconductor laser 11 (FIG. 2) that emits a laser beam L of a certain degree.

  First, as shown in FIG. 1A, in an optical disc 1A having a single-layer signal surface 1b, the laser beam LB from the objective lens 16 provided in the lens holder 15 is separated by 0.6 mm from the incident surface 1a. A signal surface 1b is formed at the position. At this time, the objective lens 16 is subjected to tracking servo and focus servo by the tracking coil 21 and the focus coil 22 attached to the lens holder 15. At this time, since the objective lens 16 is optically designed based on the single-layer signal surface 1b having a substrate thickness of 0.6 mm, the focus error signal is not offset with respect to the single-layer signal surface 1b. It is like that.

  Next, as shown in FIG. 1B, in the optical disc 1B having the two layers of the first and second signal surfaces 1c and 1d, the laser beam LB from the objective lens 16 is incident to the incident surface 1a from the incident surface 1a. A first signal surface 1c is formed at a position separated by 57 mm, and a second signal surface 1d is formed at a position separated by 0.64 mm from the incident surface 1a. At this time, spherical aberration occurs when a two-layer optical disc 1B is recorded or reproduced with the objective lens 16 optically designed with reference to the one-layer signal surface 1b having a substrate thickness of 0.6 mm. A countermeasure for offsetting a focus error signal generated due to aberration will be described later.

  In the following description, the optical disk 1 will be described unless it is necessary to distinguish between the single-layer optical disk 1A and the double-layer optical disk 1B.

  Next, the optical pickup device 10A according to the embodiment of the present invention shown in FIG. 2 is different from the configuration of the general optical pickup device 10 described above with reference to FIG. Or the same configuration except that a diffractive element 20 is newly added between the polarizing beam splitter 13 and the detection lens 17 in the optical path of the return beam of the laser beam LB reflected by 1c, 1d). Here, for convenience of explanation, the same constituent members shown above are denoted by the same reference numerals, and will be appropriately described as necessary, and different points from the general optical pickup device 10 will be mainly described. .

  As shown in FIG. 2, the optical pickup apparatus 10A according to the embodiment provided below the rotatable optical disc 1 has a signal surface 1b (or 1c, 1d) of the optical disc 1 with the laser light L emitted from the semiconductor laser 11. And a detection lens 17 after diffracting the return light of the laser beam reflected by the signal surface 1b (or 1c, 1d) of the optical disc 1 by the diffraction element 20 and irradiating the track T formed on And a return light detection optical system for detection by a photodetector 19 through a cylindrical lens 18. In FIG. 2, the optical disk 1 formed in a disk shape is partially cut away.

  First, the laser light irradiation optical system in the optical pickup device 10A described above has the same configuration as the conventional example, and the P-polarized light of the laser light L emitted from the semiconductor laser 11 is converted into parallel light by the collimator lens 12. After that, the light passes through the polarization-selective dielectric multilayer film (P-polarized light: transmitted, S-polarized light: reflected) 13a of the polarizing beam splitter 13 and is incident on the λ / 4 plate 14 and transmitted through the λ / 4 plate 14. The laser beam LB obtained by narrowing down the circularly polarized light with the objective lens 16 attached in the lens holder 15 is incident from the incident surface 1a of the optical disc 1 and has a predetermined distance with respect to the incident surface 1a. The light is irradiated on the track T formed on the signal surface 1b (or 1c, 1d) located at a distance.

  Here, for example, when the above-mentioned DVD is recorded or reproduced as the optical disk 1, a laser beam L having a reference wavelength λ of around 650 nm is emitted from the semiconductor laser 11, and the laser beam L has a numerical aperture (NA) of 0. A laser beam LB obtained by focusing with about six objective lenses 16 is incident from the incident surface 1a of the optical disc 1, and in the case of a single-layer optical disc 1A, the laser beam LB is separated by 0.6 mm from the incident surface 1a. While irradiating a certain signal surface 1b, in the case of a two-layer optical disc 1B, the first signal surface 1c located at a position separated by 0.57 mm from the incident surface 1a or the second signal located at a position separated by 0.64 mm from the incident surface 1a. Recording or reproduction can be performed by irradiating the signal surface 1d.

  Next, the return light detection optical system in the optical pickup device 10A described above is partly different from the conventional example, in which the return light detection optical system is provided with a diffractive element 20, and the signal surface 1b (or the optical disc 1) (or In contrast to the above, the return light of the laser beam LB reflected by 1c and 1d) passes through the objective lens 16 and the λ / 4 plate 14 in this order, and when passing through the λ / 4 plate 14, a 90 ° polarization plane. Is changed to S-polarized light, and is reflected by the polarization-selective dielectric multilayer film (P-polarized light: transmitted, S-polarized light: reflected) 13a of the polarization beam splitter 13 and turned about 90 °, and then the diffraction element 20 Is incident on.

  The above-described diffraction element 20 is a member constituting the main part of the embodiment. As will be described later, the light detector 19 whose mounting position has been adjusted is applied to the signal surface 1b (or 1c, 1d) of the optical disc 1 due to a change over time. Even when the position is slightly shifted in the direction orthogonal to the formed track T, the occurrence of the offset of the tracking error signal can be prevented. When the occurrence of the offset of the tracking error signal is prevented, the two signal surfaces 1c and 1d are formed. This is provided to prevent the offset of the focus error signal that occurs in the optical disc 1B having the above.

  Specifically, as shown in an enlarged view in FIG. 3, the diffraction element 20 is formed in a square shape with an outer shape □ S = □ 5.6 mm using a light-transmitting substrate.

  In addition, inside the diffraction element 20 of the embodiment, the inner circumferential side circular diffraction grating portion 20a and the center line X of the track T (FIG. 1) formed on the signal surface 1b (or 1c, 1d) of the optical disc 1 and A circle having a diameter φD1 = φ1.8 mm is formed around a center point Op corresponding to an intersection point intersecting with the line Y passing through the center of the optical disc 1 perpendicular to the center line X, and an inner circumference side circle A ring-shaped light transmitting portion 20b is formed in a ring shape within the range of diameter φD1 = φ1.8 mm to diameter φD2 = φ3.67 mm along the outer periphery of the shape diffraction grating portion 20a. The outer peripheral diffraction grating portion 20c is formed on the outer side in the range of diameter φD2 = φ3.67 mm to 囗 S = 囗 5.6 mm. A circle indicated by a dotted line in the drawing has a diameter φD3 = φ3.8 mm, and a third light flux L3 on the outer peripheral side described later within a range of the diameter φD2 = φ3.67 mm to the diameter φD3 = φ3.8 mm (FIG. 4). Is incident.

  At this time, the directions of the gratings of the inner circular diffraction grating portion 20a and the outer diffraction grating portion 20c of the diffraction element 20 of the embodiment are along the disk radial direction perpendicular to the track direction. A direction in which the first and third light beams L1 and L3 (FIG. 4) of light are orthogonal to the track T (FIG. 1) formed on the signal surface 1b (or 1c, 1d) of the optical disc 1 by the diffraction grating portions 20a and 20c. It is designed to be diffracted.

That is, as shown in enlarged views in FIGS. 4A and 4B, the diffractive element 20 causes the inner circumferential side circular diffraction grating portion to transmit the first luminous flux L1 on the inner circumferential side in the return light of the laser beam LB. The first light beam L1 is transmitted through the inner circumferential circular diffraction grating portion 20a in a direction orthogonal to the track T (FIG. 1) formed on the signal surface 1b (or 1c, 1d) of the optical disk 1 without passing through 20a. The first ± first-order beams SP ₊₁₁ and SP- ₁₁ are obtained by diffracting, and these first ± first-order beams SP ₊₁₁ and SP- ₁₁ are placed on the photodetector 19 via the detection lens 17 and the cylindrical 18. Each is imaged.

Further, the second light flux L2 ring of which is located outside the first light flux L1 among the laser beams LB of the return light is transmitted through the ring-shaped light transmitting portion 20b, a detection lens 17 and cylindrical zero order light SP ₀ An image is formed on the photodetector 19 via 18.

Further, of the return light of the laser beam LB, the outer peripheral third light beam L3 positioned outside the second light beam L2 is formed on the signal surface 1b (or 1c, 1d) of the optical disc 1 by the outer peripheral diffraction grating portion 20c. track T (FIG. 1) orthogonal second ± 1-order light _SP +12 diffracts in a direction to have to give _{an SP -12,} these second ± 1 order light _{SP +12, SP -12} detection lens 17 In addition, a part of the image is formed on the photodetector 19 through the cylindrical 18 as will be described later.

Then, the zero-order light SP ₀ and the ± first-order light SP ₊₁₁ and SP _{-11 and the} ± first-order light SP ₊₁₂ and SP _-12 that have passed through the diffraction element 20 are astigmatism with respect to the detection lens 17 and the return light. When the light passes through the cylindrical 18 in order, the track direction and the disk radial direction of each light beam that has passed through the cylindrical lens 18 are rotated by 90 ° with respect to the incident time of the objective lens 16. As shown, each light beam is imaged on the photodetector 19 in a state where X and Y are rotated by 90 ° on the photodetector 19 as well.

  In this embodiment, unlike the above, the detection lens 17 may be disposed between the cylindrical 18 and the photodetector 19, but the diffractive element 20 is disposed between the polarization beam splitter 13 and the cylindrical 18. Is something that must be placed in

  Here, as shown in an enlarged view in FIG. 5, the photodetector 19 is formed on the track T (FIG. 1) formed on the signal surface 1 b (or 1 c, 1 d) of the optical disc 1 in the same manner as described in the prior art. A first dividing line 19a passing through the center point O of the photodetector 19 in a direction corresponding to the center line X, and a track T (FIG. 1) formed on the signal surface 1b (or 1c, 1d) of the optical disc 1 The inside of the photodetector 19 is divided into four by the second dividing line 19b passing through the center point O of the photodetector 19 in the direction corresponding to the line Y orthogonal to the center line X of the four detection areas ( A) to (D) are formed.

  At this time, the photodetector 19 has an outer shape of 120 μm corresponding to the outer shape of the diffraction element 20 being 5.6 mm, and the position of the dividing line 19 a is the signal of the optical disc 1. The mounting position is adjusted in advance so as to coincide with the center line X of the track T (FIG. 1) formed on the surface 1b (or 1c, 1d), and in the disk radial direction perpendicular to the track direction. The position is not misaligned.

  When the signal surface 1b of the single-layer optical disc 1A is reproduced, the light quantity of the return light from the optical disc 1 imaged on the photodetector 19 is photoelectrically converted in the four detection areas (A) to (D). The detection signals A to D are output from the detection areas (A) to (D).

  Here, in the return light from the optical disc 1, the first light beam L1 on the inner peripheral side does not pass through the inner peripheral circular diffraction grating portion 20a {FIG. 3, FIG. 4 (a)} of the diffraction element 20. Further, on the photodetector 19 shown in FIG. 5, the diameter φD1 = φ1.8 mm of the inner circumferential circular diffraction grating portion 20a of the diffraction element 20 with the non-imaging region 19s centered on the center point O {FIG. As compared with FIG. 4 (b)}, the diameter φd1 = 28 μm and a circular shape.

Further, the inner circumferential side circular diffraction of the diffraction element 20 in which the first light beam L1 on the inner circumferential side of the return light from the optical disc 1 is set in a direction orthogonal to the track T (FIG. 1). ± 1st order beams SP ₊₁₁ and SP _-11 diffracted in the direction orthogonal to the track T (FIG. 1) by the grating portion 20a {FIG. 3, FIG. 4 (a)} are obtained from the photodetector 19 shown in FIG. Images are formed in a circular shape with a diameter φd1 = 28 μm in the direction orthogonal to the track T (FIG. 1) across the circular non-imaging region 19s on the dividing line 19b. At this time, the light amounts of the ± first-order lights SP ₊₁₁ and SP- ₁₁ can compensate for the shortage of the light amount in the circular non-imaging region 19s generated around the center point O on the detector 19. It has become.

Then, the circular non-imaging region 19 s and the ± first-order light SP ₊₁₁ , SP _{− are} formed on the photodetector 19 by the inner peripheral circular diffraction grating portion 20 a {FIG. 3, FIG. 4A} of the diffraction element 20. _As will be described later, when the photodetector 19 whose mounting position has been adjusted is slightly displaced in the direction perpendicular to the track T (FIG. 1) of the optical disk 1 due to a change with time, the tracking error signal The occurrence of offset is prevented.

Further, among the return light of the laser beam LB, the ring-shaped second light beam L2 positioned outside the first light beam L1 is transmitted through the ring-shaped light transmitting portion 20b {FIG. 3, FIG. 4 (a)} of the diffraction element 20. The zero-order light SP ₀ thus formed is imaged in a ring shape along the outer periphery of the circular non-imaging region 19s on the photodetector 19 shown in FIG. At this time, the zero-order light SP ₀ is centered on the center point O of the photodetector 19 and has a diameter φD1 = φ1.8 mm to a diameter φD2 = φ3.67 mm of the ring-shaped light transmission portion 20b of the diffraction element 20 {FIG. The image is formed in a ring shape with a diameter φd1 = 28 μm to a diameter φd2 = φ58 mm with respect to FIG.

Further, of the return light of the laser beam LB, the third light beam L3 on the outer peripheral side located outside the second light beam L2 is a diffraction element 20 in which the direction of the grating is set in a direction orthogonal to the track T (FIG. 1). ± 1st order beams SP ₊₁₂ and SP ₋₁₂ diffracted in the direction orthogonal to the track T (FIG. 1) by the outer peripheral diffraction grating portion 20c {FIG. 3, FIG. 4 (a)} are the light shown in FIG. A third light beam L3 that is divided above and below in the direction (disk radial direction) perpendicular to the track T on the outside of the ± first-order light SP _{+ 11} , SP- ₁₁ on the detector 19 and that passes through the outer diffraction grating portion 20c. The diameter φD3 = φ3.8 mm {FIG. 3, FIG. 4 (b)} and each part is imaged in an arc ring shape with an outer diameter φd3 = 60 mm, and ± primary light SP ₊₁₂ , SP ₋₁₂ Each remaining portion of the jumps in the disk radial direction outside the photodetector 19. It is. At this time, the outer diffraction grating portion 20c {FIG. 3, FIG. 4 (a)} of the diffractive element 20 has a portion of ± first-order light SP ₊₁₂ and SP _{-12 in} a circular ring shape on the light emitter 19, respectively. It is formed at a predetermined lattice pitch so that an image can be formed.

The operation of obtaining each part of the ± first-order beams SP ₊₁₂ and SP _-12 on the photodetector 19 by the outer peripheral diffraction grating portion 20c {FIG. 3, FIG. 4 (a)} of the diffraction element 20 is the inner peripheral side. When the occurrence of the tracking error signal offset is prevented by the circular diffraction grating portion 20a {FIG. 3, FIG. 4 (a)}, as will be described later, it occurs in the second optical recording medium having two signal surfaces. This prevents the offset of the focus error signal.

  Next, as shown in FIG. 6, in the optical recording medium driving device 30A of the embodiment in which the optical pickup device 10A according to the embodiment is mounted, the tracking is provided on the output side of the photodetector 19 provided in the optical pickup device 10A. The servo circuit unit 31, the focus servo circuit unit 32, and the RF signal processing circuit unit 33 are connected.

Here, FIG. 4, FIG. 5, and FIG. 6 will be described together. In the case where the tracking error signal TE is generated in the tracking servo circuit unit 31 described above, FIG. The detection signals A to D from the four detection areas (A) to (D) of the photodetector 19 shown in FIG. 4 are calculated using a well-known push-pull method. The detector 19 is divided into two detection areas (A, B) and (C, D) by a dividing line 19a which passes through the center point O in a direction corresponding to the center line X of the track T (FIG. 1), and The zero-order light SP ₀ and ± first-order light SP ₊₁₁ , SP imaged on the photodetector 19 in a state where a circular non-imaging region 19 s is generated in the vicinity of the center point O of the photodetector 19. _-11 and ± 1 order light _{SP +12,} split photodetector 19 each portion of _{SP -12} Light is received in two detection areas (A, B) and (C, D) across 19a, and the difference between the received light amounts from the two detection areas (A, B) and (C, D) is shown first. The tracking error signal TE = {(A + B) − (C + D)} is applied to the tracking coil 21 attached to the lens holder 15 while calculating the tracking error signal TE = {(A + B) − (C + D)} with respect to the objective lens 16 in the lens holder 15. It is over.

At this time, as shown in FIG. 5, the signal surface 1b of the single-layer optical disk 1A is reproduced, and the 0th-order light SP ₀ and ± 1 after the return light from the signal surface 1b passes through the diffraction element 20 A part of each of the next-order light SP ₊₁₁ and SP _{-11 and} ± 1st-order light SP ₊₁₂ and SP _-12 is respectively obtained in two regions (A, B) and (C, D) sandwiching the dividing line 19a of the photodetector 19. When light is received, each of the zero-order light SP ₀ and the ± first-order lights SP ₊₁₁ and SP _{-11 and the} ± first-order lights SP ₊₁₂ and SP _-12 are vertically and symmetrically arranged in a ring shape and a circle via the dividing line 19a. Since each image is formed in a shape, the difference between the received light amounts from the two detection areas (A, B), (C, D) is equal, that is, A + B = C + D. There is no offset.

Further, when the focus error signal FE is generated in the focus servo circuit unit 32, astigmatism is generated by the cylindrical lens 17 with respect to the return light from the optical disc 1 as described in the prior art. The detection signals A to D from the four detection areas (A) to (D) of the photodetector 19 shown in FIG. 5 are calculated using a known astigmatism method. Is divided into four detection areas (A) to (D) by dividing lines 19 a and 19 b orthogonal to each other on the photodetector 19, and a circular non-circumference is formed in the vicinity of the center point O of the photodetector 19. Each portion of the 0th order light SP ₀ and ± 1st order light SP ₊₁₁ , SP- _{11 and} ± 1st order light SP ₊₁₂ , SP _-12 imaged on the photodetector 19 with the imaging region 19 s generated. By the dividing lines 19a and 19b of the photodetector 19. Light is received by the four divided detection areas (A) to (D), and one diagonal area (A, C) and the other diagonal area (B) in these four detection areas (A) to (D). , D) and the difference between the amounts of received light received by the above-described equation (2), and this focus error signal FE = {(A + C) − (B + D)} is applied to the focus coil 22 attached to the lens holder 15. However, focus servo is applied to the objective lens 16 in the lens holder 15.

At this time, as shown in FIG. 5, the signal surface 1b of the single-layer optical disk 1A is reproduced, and the 0th-order light SP ₀ and ± 1 after the return light from the signal surface 1b passes through the diffraction element 20 Each part of the next-order light SP ₊₁₁ , SP _{-11 and} ± 1st-order light SP ₊₁₂ , SP _-12 is divided into one diagonal area (A, C) and the other diagonal area (B, D) in the photodetector 19. And the other diagonal regions (A, C) and the other diagonal region depending on the imaging state of each of the light beams SP ₀ , SP ₊₁₁ , SP _-11 , SP ₊₁₂ , SP _-12. Since the difference between the received light amounts received at (B, D) is equal, that is, A + C = B + D, no offset of the focus error signal occurs.

  However, in a two-layer optical disk 1B having a substrate thickness different from that of the single-layer optical disk 1A, a focus error signal offset occurs due to spherical aberration generated during recording or reproduction as described later. Describe.

Further, when the data signal RF is generated in the RF signal processing circuit unit 33, the detection signals A to D from the four detection regions (A) to (D) in the photodetector 19 shown in FIG. Is added by the above-described equation 3 to obtain the data signal RF = {A + B + C + D}. At this time, as described above, although there is no light amount from the circular non-imaging region 19s on the photodetector 19, the light amount corresponding to the circular non-imaging region 19s is changed to ± primary light SP ₊₁₁ , Since each of the SP- ₁₁ light amounts is compensated, there is no shortage of light amount with respect to the data signal RF.

  Here, in the optical recording medium driving device 30A of the embodiment in which the optical pickup device 10A of the embodiment configured as described above is mounted, the photodetector 19 whose mounting position has been adjusted is slightly positioned in the disk radial direction due to a change with time. FIGS. 7A and 7B show the shifted state.

  At this time, as described above with reference to FIGS. 3 to 5, when the photodetector 19 whose mounting position has been adjusted is slightly displaced in the radial direction of the disk due to a change with time, the inner circumference side circle of the diffraction element 20 Although the shape diffraction grating portion 20a functions to prevent the occurrence of the tracking error signal offset, the outer peripheral side diffraction grating portion 20c of the diffraction element 20 is the inner peripheral side circular diffraction grating portion 20a and the tracking error signal offset. In the case where the occurrence of this is prevented, an offset of the focus error signal that occurs in the two-layer optical disc 1B is prevented, so that no influence is exerted on the tracking error signal.

  Specifically, as shown in FIG. 7A, the photodetector 19 changes from the normal position shown in FIG. 5 due to the change with time to the diameter φd1 = 28 μm of the circular non-imaging region 19s. For example, it is assumed that the position is shifted in the radial direction of the disk by 3 μm downward in the figure.

In the state shown in FIG. 7A, the signal surface 1b of the single-layer optical disk 1A is reproduced, and the 0th-order light SP ₀ and ± after the return light from the signal surface 1b passes through the diffraction element 20 Two detection regions (A, B), (C, D) each of a part of the primary light SP ₊₁₁ , SP _{-11 and} ± primary light SP ₊₁₂ , SP _-12 sandwiching the dividing line 19a of the photodetector 19 The circular non-imaging region 19s moves toward the detection regions (A) and (B) above the center point O of the photodetector 19, and the zero-order light SP _{0 is received.} And ± 1st order light beams SP ₊₁₁ and SP- ₁₁ and a part of ± 1st order light beams SP ₊₁₂ and SP- ₁₂ are also directed toward the detection areas (A) and (B) above the center point O of the photodetector 19. In this case, A + B≈C due to the presence of the circular non-imaging region 19s. Since + D, the offset of the tracking error signal does not occur. On the other hand, when the diffraction element is not used as in the conventional example described above with reference to FIG. 18A, the offset of the tracking error signal is greatly generated on the + side. However, the offset amount of the tracking error signal can be greatly improved as compared with the conventional example.

  On the other hand, as shown in FIG. 7 (b), the photodetector 19 changes from the normal position shown in FIG. 5 due to a change with time, for example, 3 .mu.m with respect to the diameter .phi. It is assumed that the disk is displaced in the disk radial direction only upward in the figure.

In the state shown in FIG. 7B, the signal surface 1b of the single-layer optical disc 1A is reproduced, and the 0th-order light SP ₀ and ± after the return light from the signal surface 1b passes through the diffraction element 20 Two detection regions (A, B), (C, D) each of a part of the primary light SP ₊₁₁ , SP _{-11 and} ± primary light SP ₊₁₂ , SP _-12 sandwiching the dividing line 19a of the photodetector 19 The circular non-imaging region 19s moves toward the detection regions (C) and (D) below the center point O of the photodetector 19, and the zero-order light SP _{0 is received.} And ± 1st order light beams SP ₊₁₁ and SP- ₁₁ and a part of ± 1st order light beams SP ₊₁₂ and SP- ₁₂ are also directed toward the detection regions (C) and (D) below the center point O of the photodetector 19. Even in this case, A + B≈ due to the presence of the circular non-imaging region 19s. Since C + D, the tracking error signal offset does not occur. On the other hand, when the diffraction element is not used as in the conventional example described above with reference to FIG. 18B, the offset of the tracking error signal is greatly generated on the minus side. However, the offset amount of the tracking error signal can be greatly improved as compared with the conventional example.

  In this embodiment, only the case where the single-layer optical disk 1A is reproduced has been described. However, even when the two-layer optical disk 1B is reproduced, the inner peripheral circular shape of the diffractive element 20 can be obtained by the same technical idea as above. Occurrence of an offset of the tracking error signal can be prevented by the diffraction grating portion 20a.

  Here, when the definition of the offset amount (%) of the tracking error signal is illustrated using FIGS. 8A to 8C, FIG. 8A shows a state when the tracking error signal offset amount is 0%. (B) shows the state when the offset amount of the tracking error signal is 50%, and (c) shows the state when the offset amount of the tracking error signal is 100%.

  When the diffractive element is not used as in the conventional example described above with reference to FIG. 18B, the offset amount of the tracking error signal is 72%, but the diffractive element 20 is used as in this embodiment. If this occurs, the tracking error signal offset can be greatly improved to 29%.

  As described in detail above, in this embodiment, the center line X of the track T (FIG. 1) formed on the signal surface 1b (or 1c, 1d) of the optical disk 1 in the optical path of the return light from the optical disk 1 The inner circumferential circular diffraction grating portion 20a, the ring-shaped light transmission portion 20b, and the outer circumferential side diffraction grating are centered on the center point Op corresponding to the intersection point of the line Y perpendicular to the center line X and passing through the center of the optical disk. A diffraction element 20 having a portion 20c is arranged, and the return light from the optical disc 1 is diffracted in a direction perpendicular to the track T by the inner circular diffraction grating portion 20a and the outer diffraction grating portion 20c of the diffraction element 20 When the light is received by the detector 19, a circular non-imaging region 19 s corresponding to the inner circumferential circular diffraction grating portion 20 a of the diffraction element 20 is generated in the vicinity of the center point O of the light detector 19. Aligned Detector 19 can be prevented from occurring offset of the tracking error signal be shifted slightly located in the direction (disk radial direction) perpendicular to the track direction change over time.

  Next, the offset of the focus error signal with respect to the single-layer optical disk 1A and the double-layer optical disk 1B when the optical pickup apparatus 10A according to the embodiment of the present invention is used will be described with reference to FIGS.

FIG. 9 is a diagram showing the characteristics of a focus error signal when the signal surface of a single-layer optical disk is reproduced using the optical pickup device according to the embodiment of the present invention.
FIG. 10 shows the case where the first signal surface of the two-layer optical disk is reproduced using the optical pickup device according to the embodiment of the present invention, and the return light of the laser beam reflected by the first signal surface is diffracted by the diffraction element. After that, a diagram showing a state in which the image is formed on the photodetector whose position has been adjusted,
FIG. 11 is a characteristic analysis diagram of a focus error signal when the first signal surface of a two-layer optical disk is reproduced using the optical pickup device according to the embodiment of the present invention. FIG. FIG. 5B shows an imaging state on the photodetector when only the circular diffraction grating portion is diffracted, and FIG. 5B shows a result on the photodetector when only the outer peripheral diffraction grating portion of the diffraction element is diffracted. Figure showing the image state,
FIG. 12 is a diagram illustrating the characteristics of a focus error signal when the first signal surface of a two-layer optical disk is reproduced using the optical pickup device according to the embodiment of the present invention.
FIG. 13 shows the case where the second signal surface of the two-layer optical disk is reproduced using the optical pickup device according to the embodiment of the present invention, and the return light of the laser beam reflected by the second signal surface is diffracted by the diffraction element. After that, a diagram showing a state in which the image is formed on the photodetector whose position has been adjusted,
FIG. 14 is a characteristic analysis diagram of the focus error signal when the second signal surface of the two-layer optical disk is reproduced using the optical pickup device according to the embodiment of the present invention, and (a) is the inner circumference side of the diffraction element. FIG. 5B shows an imaging state on the photodetector when only the circular diffraction grating portion is diffracted, and FIG. 5B shows a result on the photodetector when only the outer peripheral diffraction grating portion of the diffraction element is diffracted. Figure showing the image state,
FIG. 15 is a diagram showing the characteristics of the focus error signal when the second signal surface of the two-layer optical disk is reproduced using the optical pickup device according to the embodiment of the present invention.

First, FIG. 9 shows the characteristics of the focus error signal when the signal surface 1b of the single-layer optical disc 1A is reproduced using the optical pickup device 10A (FIG. 2) of the embodiment. As described with reference to FIG. 5, the 0th-order light SP ₀ and ± 1 after the return light from the signal surface 1b of the single-layer optical disk 1A passes through the diffraction element 20 {FIG. 3, FIG. 4 (a)}. When the secondary lights SP ₊₁₁ and SP _{-11 and the} ± primary lights SP ₊₁₂ and SP _-12 are received by two regions (A, B) and (C, D) sandwiching the dividing line 19a of the photodetector 19, respectively. In addition, each of the zero-order light SP ₀ and the ± first-order light SP ₊₁₁ , SP _{-11 and the} ± first-order light SP ₊₁₂ , SP _-12 is vertically and symmetrically divided into a ring shape and a circular shape via the dividing line 19a, respectively. Since the image is formed, one diagonal area (A, C) and The difference between the received light amounts in the other diagonal area (B, D) is equal, that is, A + C = B + D, so that the offset of the focus error signal as shown in FIG. Therefore, the signal surface 1b of the single-layer optical disc 1A can be recorded or reproduced satisfactorily.

  Next, as shown in FIG. 10, when the first signal surface 1c of the two-layer optical disk 1B is reproduced using the optical pickup apparatus 10A (FIG. 2) of the embodiment, the first signal surface 1c is one layer. Since the substrate thickness is different from the signal surface 1b of the optical disc 1A, spherical aberration occurs.

Therefore, among the 0th-order light SP ₀ and the ± 1st-order lights SP ₊₁₁ and SP- _{11 and the} ± 1st-order lights SP ₊₁₂ and SP ₋₁₂ after passing through the diffraction element 20 {FIG. 3, FIG. 4A}. The 0th-order light SP ₀ has a major axis in the inclination direction of −45 ° with respect to the X axis with the center point O of the photodetector 19 as the center, and is substantially directed toward the other diagonal region (B, D). An image is formed in an elliptical shape, and a non-imaging region 19 s has a major axis in the inclination direction of + 45 ° with respect to the X axis, and is substantially elliptical toward one diagonal region (A, C). Has occurred. Further, the ± first-order beams SP ₊₁₁ and SP- ₁₁ are + 45 ° with respect to the X axis that is in the same direction as the non-imaging region 19s across the non-imaging region 19s on the dividing line 19b of the photodetector 19. The image is formed in a substantially elliptical shape with a major axis in the tilt direction. Furthermore, each of the ± first-order light SP ₊₁₂ and SP _-12 is −45 on the photodetector 19 with respect to the X axis in the region A and the region C outside the ± first-order light SP ₊₁₁ and SP _−11. An image is formed in an elliptical ring shape with a long axis in the tilt direction of °, and the remaining portions of the ± first-order light SP ₊₁₂ and SP _-12 protrude in the disk radial direction outside the photodetector 19. .

  Here, the characteristic analysis of the focus error signal when the first signal surface 1c of the two-layer optical disc 1B is reproduced will be described with reference to FIGS.

First, as shown in FIG. 11 (a), the tracking error signal of the return light from the first signal surface 1c of the two-layer optical disc 1B with respect to the first light beam L1 (FIG. 4) on the inner peripheral side If only the inner circumferential circular diffraction grating portion 20 a of the diffraction element 20 formed to prevent the occurrence of offset is diffracted, the non-imaging region 19 s is centered on the center point O of the photodetector 19. And is generated in a substantially elliptical shape toward one diagonal region (A, C) with a major axis in an inclination direction of + 45 ° with respect to the X axis, and ± first-order light SP ₊₁₁ , SP- ₁₁ is light An image is formed in a substantially elliptical shape with a major axis in the inclined direction of + 45 ° with respect to the X axis which is in the same direction as the non-imaging region 19 s across the non-imaging region 19 s on the dividing line 19 b of the detector 19. Of the return light from the first signal surface 1c of the two-layer optical disc 1B. The second light flux L2 (FIG. 4) by the zero-order light SP ₀ is with a major axis in the direction of inclination of the X-axis Nitaishite 45 ° around the center point O of the optical detector 19 other diagonal regions ( The image is formed in a substantially elliptic shape toward B, D).

  From the above, when only the inner circumferential circular diffraction grating portion 20a of the diffraction element 20 is diffracted, the area of the non-imaging region 19s in FIG. 11A is on the side of one diagonal region (A, C). Is larger than the other diagonal region (B, D) side, so that the amount of light received in one diagonal region (A, C) and the other diagonal region (B, D) is A + C. Since <B + D, the focus error signal has a minus (-) offset as shown in FIG.

On the other hand, as shown in FIG. 11 (b), the outer periphery of the diffraction element 20 with respect to the third light beam L3 (FIG. 4) on the outer peripheral side in the return light from the first signal surface 1c of the two-layer optical disc 1B. If only the side diffraction grating portion 20c is diffracted, each part of the ± first-order light SP ₊₁₂ and SP _-12 is −45 with respect to the X axis in the region A and the region C on the photodetector 19. An image is formed in an elliptical ring shape with a major axis in an inclination direction of °, and the first and second light beams L1 and L2 among the return light from the first signal surface 1c of the two-layer optical disk 1B (see FIG. According to 4), the zero-order light SP ₀ is directed to the other diagonal region (B, D) with the major axis in the inclination direction of −45 ° with respect to the X axis around the center point O of the photodetector 19. The image is formed in a substantially elliptical shape.

From the above, in the case where only allowed if diffracts the outer peripheral side grating portion 20c of the diffraction element 20, the other diagonal regions (B, D) in FIG. 11 (b) light quantity of the zero-order light SP ₀ side is on the outside Since the amount of light received in one diagonal region (A, C) and the other diagonal region (B, D) is A + C> B + D because it gradually decreases in the direction of FIG. As shown by the connection with ■, the focus error signal has a + (plus) offset.

  Accordingly, when both the inner circumferential circular diffraction grating portion 20a and the outer circumferential diffraction grating portion 20c of the diffraction element 20 are diffracted with respect to the return light from the first signal surface 1c of the two-layer optical disc 1B, the inner circumferential side Since the-(minus) offset of the focus error signal generated by the circular diffraction grating portion 20a and the + (plus) offset of the focus error signal generated by the outer peripheral side diffraction grating portion 20c cancel each other, a ▲ mark in FIG. As shown in the connection, the offset of the focus error signal does not finally occur, and the first signal surface 1c of the two-layer optical disc 1B can be recorded or reproduced satisfactorily.

  Next, as shown in FIG. 13, when the second signal surface 1d of the two-layer optical disk 1B is reproduced using the optical pickup device 10A (FIG. 2) of the embodiment, the second signal surface 1d is one layer. Since the substrate thickness is different from the signal surface 1b of the optical disc 1A, spherical aberration occurs.

  At this time, when the second signal surface 1d of the optical disk 1B is reproduced, the imaging state of each light beam on the photodetector 19 is different from that when the first signal surface 1c of the optical disk 1B is reproduced via the dividing line 19b. The left and right are reversed.

Therefore, among the 0th-order light SP ₀ and the ± 1st-order lights SP ₊₁₁ and SP- _{11 and the} ± 1st-order lights SP ₊₁₂ and SP ₋₁₂ after passing through the diffraction element 20 {FIG. 3, FIG. 4A}. The zero-order light SP ₀ is substantially elliptical toward one diagonal region (A, C) having a major axis in the direction of inclination of + 45 ° with respect to the X axis with the center point O of the photodetector 19 as the center. The non-imaging region 19s has a major axis in the inclination direction of −45 ° with respect to the X axis, and is substantially elliptical toward the other diagonal region (B, D). Has occurred. Further, the ± first-order beams SP ₊₁₁ and SP- ₁₁ are −45 ° with respect to the X axis which is in the same direction as the non-imaging region 19s across the non-imaging region 19s on the dividing line 19b of the photodetector 19. The image is formed in a substantially elliptical shape with a major axis in the tilt direction. Further, each of the ± first-order light SP ₊₁₂ and SP _-12 is partially + 45 ° on the photodetector 19 with respect to the X axis in the region B and the region D outside the ± first-order light SP ₊₁₁ and SP _-11 . Are formed in an elliptical ring shape with a major axis in the tilt direction, and the remaining portions of the ± first-order beams SP ₊₁₂ and SP _-12 protrude in the disk radial direction outside the photodetector 19.

  Here, the characteristic analysis of the focus error signal when the second signal surface 1d of the two-layer optical disc 1B is reproduced will be described with reference to FIGS.

First, as shown in FIG. 14 (a), the tracking error signal of the return light from the second signal surface 1d of the two-layer optical disc 1B with respect to the first light beam L1 (FIG. 4) on the inner peripheral side. If only the inner circumferential circular diffraction grating portion 20 a of the diffraction element 20 formed to prevent the occurrence of offset is diffracted, the non-imaging region 19 s is centered on the center point O of the photodetector 19. Are generated in a substantially elliptical shape toward the other diagonal region (B, D) with a major axis in the inclination direction of −45 ° with respect to the X axis, and ± 1st order beams SP ₊₁₁ and SP ₋₁₁ are generated. On the parting line 19b of the photodetector 19, the non-imaging region 19s is sandwiched between the non-imaging region 19s and the ellipse has a major axis in the inclined direction of −45 ° with respect to the X axis that is in the same orientation as the non-imaging region 19s Of the returned light from the second signal surface 1d of the two-layer optical disk 1B, the image is formed The second light flux L2 (FIG. 4) by the zero-order light SP ₀ with a major axis is in the direction of inclination of + 45 ° to the center point O in the center with respect to the X axis of the light detector 19 one diagonal region (A , C).

  From the above, when only the inner circumferential circular diffraction grating portion 20a of the diffractive element 20 is diffracted, the area of the non-imaging region 19s in FIG. 14A is on the side of one diagonal region (A, C). Since the other diagonal area (B, D) side is larger than the other diagonal area (A, C) and the other diagonal area (B, D), each received light amount is A + C. Since> B + D, the focus error signal has an offset of + (plus) as shown by the connection with ♦ in FIG.

On the other hand, as shown in FIG. 14 (b), the outer periphery of the diffraction element 20 with respect to the third light beam L3 (FIG. 4) on the outer peripheral side in the return light from the second signal surface 1d of the two-layer optical disc 1B. If only the side diffraction grating portion 20c is diffracted, each part of the ± first-order light SP ₊₁₂ and SP _-12 is + 45 ° with respect to the X axis in the region B and the region D on the photodetector 19. Are formed in an elliptical ring shape with a major axis in the tilt direction of the first and second light beams L1 and L2 (FIG. 4) among the return light from the second signal surface 1d of the two-layer optical disc 1B. ), The zero-order light SP ₀ has a major axis in the direction of inclination of + 45 ° with respect to the X axis with the center point O of the photodetector 19 as the center, and is substantially directed toward the other diagonal region (B, D). The image is formed in an elliptical shape.

From the above, in the case where only allowed if diffracts the outer peripheral side grating portion 20c of the diffractive element 20, one of the diagonal region (A, C) in FIG. 14 (b) light quantity of the zero-order light SP ₀ side is on the outside Since the amount of light received in one diagonal area (A, C) and the other diagonal area (B, D) is A + C <B + D, since it gradually decreases in the direction of FIG. As indicated by the black squares, the focus error signal has a minus (-) offset.

  Accordingly, when both the inner circumferential circular diffraction grating portion 20a and the outer circumferential diffraction grating portion 20c of the diffraction element 20 are diffracted with respect to the return light from the second signal surface 1d of the two-layer optical disc 1B, the inner circumferential side Since the + (plus) offset of the focus error signal generated by the circular diffraction grating portion 20a and the-(minus) offset of the focus error signal generated by the outer peripheral side diffraction grating portion 20c cancel each other, a ▲ mark is shown in FIG. As shown in the connection, the focus error signal offset does not eventually occur, and the second signal surface 1d of the two-layer optical disc 1B can be recorded or reproduced satisfactorily.

1 is a cross-sectional view when an optical recording medium applied to an optical pickup device according to an embodiment of the present invention is configured in conformity with a DVD standard, (a) shows an optical disc having a single signal surface, (b) ) Is a diagram showing an optical disc having two signal surfaces. It is the perspective view which showed the optical pick-up apparatus based on the Example of this invention. In the optical pickup device according to the embodiment of the present invention, it is an enlarged view of a diffractive element as a main part of the embodiment. (A) is an optical path diagram when the return light of the laser beam reflected by the signal surface of the optical disk is diffracted by the diffraction element of the embodiment in the optical pickup device according to the embodiment of the present invention, (b) It is the figure which showed the return light of the laser beam which injects into each part of the diffraction element of an Example. When the signal surface of a single-layer optical disk is reproduced using the optical pickup device according to the embodiment of the present invention, the return light of the laser beam reflected by the single-layer signal surface is diffracted by the diffraction element of the embodiment. It is the figure which showed the state imaged on the photodetector by which the attachment position was adjusted later. 1 is a configuration diagram illustrating an optical recording medium driving device to which an optical pickup device according to an embodiment of the present invention is applied. (A), (b) is a signal surface of a single-layer optical disk in which the optical position is adjusted when the signal surface of the single-layer optical disk is reproduced using the optical pickup device according to the embodiment of the present invention. FIG. 6 is a diagram showing a state where the position is slightly shifted to one or the other in the disk radial direction orthogonal to the tracks formed in FIG. (A)-(c) is a figure for demonstrating the offset amount (%) of a tracking error signal. FIG. 6 is a diagram illustrating the characteristics of a focus error signal when a signal surface of a single-layer optical disk is reproduced using the optical pickup device according to the embodiment of the present invention. When the first signal surface of the two-layer optical disk is reproduced using the optical pickup device according to the embodiment of the present invention, after the return light of the laser beam reflected by the first signal surface is diffracted by the diffraction element, It is the figure which showed the state imaged on the photodetector by which the attachment position was adjusted. FIG. 6 is a characteristic analysis diagram of a focus error signal when the first signal surface of a two-layer optical disk is reproduced using the optical pickup device according to the embodiment of the present invention, and FIG. (B) shows the imaging state on the photodetector when only the outer peripheral diffraction grating portion of the diffraction element is diffracted. FIG. It is the figure which showed the characteristic of the focus error signal when reproducing | regenerating the 1st signal surface of a two-layer optical disk using the optical pick-up apparatus based on the Example of this invention. When the second signal surface of the two-layer optical disk is reproduced using the optical pickup device according to the embodiment of the present invention, the return light of the laser beam reflected by the second signal surface is diffracted by the diffraction element, It is the figure which showed the state imaged on the photodetector by which the attachment position was adjusted. It is a characteristic analysis figure of a focus error signal when reproducing the 2nd signal surface of a two-layer optical disk using the optical pick-up apparatus concerning the example of the present invention, and (a) is inner side circular diffraction of a diffraction element. (B) shows the imaging state on the photodetector when only the outer peripheral diffraction grating portion of the diffraction element is diffracted. FIG. It is the figure which showed the characteristic of the focus error signal when reproducing | regenerating the 2nd signal surface of a two-layer optical disk using the optical pick-up apparatus based on the Example of this invention. It is the perspective view which showed the general optical pick-up apparatus. It is the figure which expanded and showed the photodetector shown in FIG. (A), (b) is a general optical pickup device, in which a photodetector whose mounting position has been adjusted is slightly displaced in one or the other in the radial direction of the disk perpendicular to the track formed on the signal surface of the optical disk. It is the figure which showed the state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical recording medium (optical disk), 1a ... Incident surface,
1A: First optical recording medium (single-layer optical disk), 1b: Signal surface,
1B: second optical recording medium (two-layer optical disk), 1c: first signal surface, 1d: second signal surface,
10A: optical pickup device of the embodiment,
11 ... Laser light source (semiconductor laser), 12 ... Collimator lens,
13 ... Polarizing beam splitter, 14 ... 1 / 4λ plate,
15 ... Lens holder, 16 ... Objective lens,
17 ... Detection lens, 18 ... Cylindrical lens,
19 ... photodetector, 19a ... first dividing line, 19b ... second dividing line,
19s ... non-imaging area,
20 ... Diffraction element,
20a ... inner circumferential circular diffraction grating part, 20b ... ring-shaped light transmission part,
20c ... outer peripheral side diffraction grating part,
21 ... Tracking coil, 22 ... Focus coil,
30A: Optical recording medium driving device of embodiment,
31 ... Tracking servo circuit section, 32 ... Focus servo circuit section,
33. RF signal processing circuit section,
(A) to (D) ... detection area of the photodetector,
A to D: detection signals from photodetectors,
L ... Laser light, LB ... Laser beam,
FE: Focus error signal, TR: Tracking error signal,
O ... center point of the photodetector, Op ... center point of the diffraction element,
SP ₀ ... 0th order light, SP ₊₁₁ , SP _-11 ... 1st ± 1st order light,
SP ₊₁₂ , SP _-12 ... Second ± first order light.

Claims (2)

A first optical recording medium having a single-layer signal surface and a second optical recording medium having a two-layer signal surface are selectively applicable, and the first and second optical recording media A laser beam irradiation optical system for irradiating a laser beam on the track of each signal surface, and a photodetector through a cylindrical lens after diffracting the return light of the laser beam reflected by each signal surface by a diffraction element In an optical pickup device including a return light detection optical system for detecting,
The diffraction element is
A grid having a predetermined diameter and a circle centered on a center point corresponding to an intersection point of a center line of the track and a line perpendicular to the center line of the track and passing through the center of the optical recording medium. Is set in a direction orthogonal to the track, and a non-imaging region is generated in the vicinity of the center point on the photodetector without transmitting the first luminous flux on the inner circumference side of the return light. And an inner circumference that images the first ± first-order light obtained by diffracting the first light flux in a direction orthogonal to the track on the photodetector in a direction orthogonal to the track across the non-image forming region. A side circular diffraction grating part;
Zero-order light that is formed in a ring shape along the outer periphery of the inner circumferential circular diffraction grating portion and transmits a second ring-shaped light beam positioned outside the first light beam among the return light, A ring-shaped light transmitting portion that forms an image along the outer periphery of the non-imaging region on the photodetector;
A third light beam on the outer peripheral side, which is formed outside the ring-shaped light transmitting portion and has a grating orientation set in a direction orthogonal to the track, is located outside the second light beam in the return light. An outer peripheral side that forms each part of the second ± first-order light diffracted in the direction orthogonal to the track on the photodetector in the direction orthogonal to the track outside the first ± first-order light. An optical pickup device having a diffraction grating portion. An optical recording medium driving device to which the optical pickup device according to claim 1 is applied,
A first dividing line that passes through the center point and corresponds to the center line of the track, and a second dividing line that passes through the center point and is orthogonal to the first dividing line. Is divided into four areas,
Differences in received light amounts respectively received by the two detection regions divided into two by the first dividing line for each of the zero-order light, the first ± first-order light, and the second ± first-order light. A tracking servo circuit that generates a tracking error signal by calculating a push-pull method,
Receiving light received by each of the diagonal areas and the other diagonal areas in the four areas, respectively, of the zero-order light, the first ± first-order light, and the second ± first-order light. A focus servo circuit unit that calculates a difference in amount by an astigmatism method and generates a focus error signal;
An optical recording medium driving device comprising:

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