JP2008176905A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve an optical pickup device which performs stable tracking error detection for a plurality of optical information recording media the pitches of the guide groove of which are different while keeping the advantage of an in-line type DPP system. <P>SOLUTION: A pickup device is provided with diffraction grating 12 for branching an out-going light beam emitted from a light source into at least three light beams. The diffraction grating 12 is divided into four regions by a straight line extending in a direction in parallel with the tangent of track of an optical information recording medium. Phase of the periodic structure in the second region 12B is different by about 180 degrees from that of the periodic structure in the third region 12C, Phase of the periodic structure in the first region 12A is different by about 180 degrees from that of the periodic structure in the fourth region 12D. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup device used in an optical information processing apparatus that performs processing such as recording information on an optical information recording medium and reproducing or erasing information recorded on the optical information recording medium.

  Reading of a record from an optical information recording medium (optical disc) such as a CD (Compact Disc) and a DVD (Digital Versatile Disc) is performed by recording a light beam emitted from a light source such as a semiconductor laser device using an objective lens. The light is collected on a track and the reflected light from the optical disk is converted into an electric signal by a photodetector. In order to focus a light beam accurately on a desired recording track for an optical disk rotating at high speed, a focus error signal and a tracking error signal are detected, and the objective lens is adjusted in accordance with surface deflection and eccentricity of the optical disk. Perform position control.

  As a typical method for detecting a tracking error signal, a differential push-pull (DPP) method is known. In the DPP method, a light beam is split into three beams, a main beam, a + 1st order diffracted light, and a −1st order diffracted light, and the divided beams are provided in three guide grooves provided adjacent to each other at a predetermined pitch on the optical disc. Condensate. The phases of the push-pull signals obtained by detecting and calculating the reflected light of each beam are shifted from each other by 180 degrees between the main beam, the + 1st order diffracted light, and the −1st order diffracted light. Therefore, by calculating each push-pull signal, it is possible to selectively cancel only the offset component included in each push-pull signal and to detect a good tracking error signal. Therefore, in particular, the DPP method is widely used in DVD recording optical pickups (see, for example, Patent Document 1).

  There are various standards for optical disks that are widely used at present, and the pitch of the guide grooves varies depending on the standards of the optical disks. For example, the pitch of guide grooves such as write-once DVD-R (Recordable) and rewritable DVD-RW (Disk ReWritable) is 0.74 μm, and guide grooves such as rewritable DVD-RAM (Random Access Memory) are used. The pitch is 1.23 μm. There is a demand for an optical pickup that enables recording and reproduction with a single device for two or more types of optical discs having different standards. In response to such a demand, the following optical pickup device has been proposed (see, for example, Patent Document 2).

In the optical pickup device disclosed in Patent Document 2, a special diffraction grating for splitting a light beam is divided into three regions, and the phases of grating grooves periodically provided in each region are sequentially shifted by 90 degrees. Yes. A tracking error detection method called an inline DPP method using such a special diffraction grating enables stable tracking error detection to be performed on a plurality of optical information recording media having different guide groove pitches.
Japanese Patent Publication No. 4-34212 JP 2004-145915 A

  However, the conventional optical pickup device using the conventional inline type DPP method has the following problems.

  FIG. 18 shows a condensing spot obtained by condensing a light beam on an optical information recording medium by a conventional optical pickup device. The focused spot 101 corresponding to the + 1st order diffracted light has a higher intensity on the right side and a lower intensity on the left side with respect to the radial direction X of the optical information recording medium. On the other hand, the intensity of the focused spot 102 corresponding to the −1st order diffracted light decreases on the right side and increases on the left side. This can be explained as follows.

  As shown in FIG. 19, in the special diffraction grating used in the conventional in-line DPP method, the phase of the grating groove 119a in the region 119 is advanced by 90 degrees with respect to the grating groove 120a in the central region 120. The phase of the grating groove 121a is delayed by 90 degrees. Therefore, the phase of the + 1st order diffracted light transmitted through the region 119 is advanced by 90 degrees with respect to the phase of the + 1st order diffracted light transmitted through the central region 120, and the phase of the + 1st order diffracted light transmitted through the region 121 is delayed by 90 degrees. On the other hand, for the −1st order diffracted light, the relationship between the phase of the grating grooves and the phase of the diffracted light is reversed. That is, the phase of the −1st order diffracted light transmitted through the region 119 is delayed by 90 degrees with respect to the phase of the −1st order diffracted light transmitted through the central region 120, and the phase of the −1st order diffracted light transmitted through the region 121 is advanced by 90 degrees. .

  For this reason, the intensity of the converging spot 101 corresponding to the + 1st order diffracted light on the optical information recording medium is higher on the right side and lower on the left side than the intensity distribution on the side of the region 121 where the phase is delayed. On the other hand, the intensity of the focused spot 102 corresponding to the −1st order diffracted light becomes smaller and the intensity on the left side becomes larger than the intensity distribution on the 119 side where the phase is delayed.

  FIG. 20 shows a signal waveform of the DPP signal obtained with the above-described focused spot. In FIG. 20, the vertical axis indicates the signal intensity, and the horizontal axis indicates the relative position of the focused spot on the optical information recording medium. MPP is the push-pull signal of the main beam corresponding to the 0th-order diffracted light, SPP1 is the push-pull signal of the preceding sub-beam corresponding to the + 1st-order diffracted light, SPP2 is the push-pull signal of the subsequent sub-beam corresponding to the −1st-order diffracted light, and DPP is the equation It is a tracking error signal (differential push-pull signal) obtained from MPP, SPP1, and SPP2 shown in (1).

DPP = MPP−k × (SPP1 + SPP2) (1)
Here, k is an arbitrary amplification factor. Since the intensity distributions of the focused spots corresponding to the + 1st order diffracted light and the −1st order diffracted light are asymmetrical, the phases of SPP1 and SPP2 are moved back and forth from 180 degrees with respect to MPP. For this reason, if a signal intensity difference occurs between SPP1 and SPP2, the DPP deviates from an appropriate value, so that each focused spot cannot be formed on the same guide groove, and stable tracking error signal detection by the inline DPP method can be performed. become unable. In FIG. 20, the positions where SPP1, SPP2, and DPP are appropriate values are indicated by alternate long and short dash lines.

  The present invention solves the above-described conventional problems, and can realize an optical pickup device that stably detects tracking errors for a plurality of optical information recording media having different guide groove pitches while maintaining the advantages of the inline DPP method. The purpose is to do so.

  In order to achieve the above object, according to the present invention, an optical pickup device includes a diffraction grating divided into four regions having different phases.

  Specifically, an optical pickup device according to the present invention is directed to an optical pickup device that records information on an optical information recording medium and reads and erases information recorded on the optical information recording medium, and emits light from the light source. A diffraction grating that branches the emitted light beam into at least three light beams, and a photodetector that receives the reflected light reflected by the optical information recording medium. A dividing line extending in a direction parallel to the tangential direction of the track of the medium is divided into a first area, a second area, a third area, and a fourth area, each having a periodic structure having a different phase. The second region and the third region are sequentially arranged between the first region and the fourth region from the first region side, and the phase of the periodic structure in the second region is the third region. In the area of Unlike phase and approximately 180 degrees of the periodic structure, the phase of the periodic structure in the first region is characterized by different phase substantially 180 ° of the periodic structure in the fourth region.

  In the optical pickup device of the present invention, the phase of the periodic structure in the second region is approximately 180 degrees different from the phase of the periodic structure in the third region, and the phase of the periodic structure in the first region is in the fourth region. A diffraction grating that is approximately 180 degrees different from the phase of the periodic structure is provided. Therefore, with respect to the second region and the third region, the phase of the + 1st order diffracted light transmitted through the first region advances with respect to the phase of the + 1st order diffracted light transmitted through the second region, and the fourth region The phase of the + 1st order diffracted light transmitted through the region advances with respect to the phase of the + 1st order diffracted light transmitted through the third region. In the case of -1st order diffracted light, both are delayed. Therefore, a phenomenon in which the spot shape is not asymmetrical as in the conventional inline DPP method does not occur, and the intensity distribution is symmetric about the direction in which the guide groove extends. As a result, it is possible to realize an optical pickup device that performs stable tracking error detection for a plurality of optical information recording media having different guide groove pitches.

  In the optical pickup device of the present invention, the distance between the dividing line dividing the first area and the second area, the dividing line dividing the second area and the third area, the second area, The distances between the dividing line dividing the third area and the dividing line dividing the third area and the fourth area are preferably equal to each other.

  In the optical pickup device of the present invention, each light beam preferably includes 0th-order diffracted light, + 1st-order diffracted light, and −1st-order diffracted light.

  In the optical pickup device of the present invention, a plurality of guide grooves are periodically arranged on the recording surface of the optical information recording medium, and each light beam is focused on one of the plurality of guide grooves. It is preferable to do.

  The optical pickup device of the present invention preferably further includes an arithmetic processing circuit that detects a tracking error signal by a differential push-pull method based on an output signal from the photodetector.

  In the optical pickup device of the present invention, it is preferable that the photodetector has at least three light receiving elements corresponding to the respective reflected lights, and each light receiving element is divided into a plurality of light receiving regions.

  In the optical pickup device of the present invention, it is preferable that the center of the outgoing light beam emitted from the light source is disposed in the second region or the third region.

  In the optical pickup device of the present invention, the light source includes a first light source and a second light source, and the center of the emitted light beam emitted from the first light source and the center of the emitted light beam emitted from the second light source The straight line connecting the two lines divides the dividing line dividing the first area and the second area, the dividing line dividing the second area and the third area, and the third area and the fourth area. Preferably, it intersects with at least one of the dividing lines.

  In the optical pickup device of the present invention, the light source includes a first light source and a second light source, and connects the center of the light beam emitted from the first light source and the center of the light beam emitted from the second light source. It is preferable that the straight line intersects a dividing line that divides the second region and the third region.

  In the optical pickup device of the present invention, there are a plurality of light sources, and the center of at least one of the light beams respectively emitted from the plurality of light sources is arranged in the second region or the third region. Is preferred.

  In the optical pickup device of the present invention, the phase of the periodic structure in the first region of the diffraction grating is preferably different from the phase of the periodic structure in the second region in the range of 10 degrees to 350 degrees.

  The optical pickup device of the present invention further includes an objective lens that condenses at least three light beams and irradiates them as independent focused spots on the recording surface of the optical information recording medium. It is preferable that a portion where an effective beam diameter range determined by the aperture diameter of the objective lens in the incident light beam includes the first area, the second area, the third area, and the fourth area.

  In this case, the total of the width of the second region and the width of the third region is preferably in the range of 10% to 40% of the effective beam diameter.

  According to the optical pickup device of the present invention, it is possible to realize an optical pickup device that performs stable tracking error detection on a plurality of optical information recording media having different guide groove pitches while maintaining the advantages of the inline DPP method. .

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of an optical pickup device according to an embodiment.

  As shown in FIG. 1, the optical pickup device of the present embodiment is a semiconductor laser that emits a light beam 31 for recording information on the optical information recording medium 51 and reproducing information recorded on the optical information recording medium 51. A light source 11 such as an element; a diffraction grating 12 that diffracts the light beam 31 into at least a 0th-order diffracted light main beam, a + 1st-order diffracted light subbeam, and a -1st-order diffracted light subbeam (all not shown); The half mirror 15 that guides the beam 31 to the optical information recording medium 51 and the integrated circuit board 17 on which the photodetector 16 that receives the reflected light reflected by the optical information recording medium 51 is mounted.

  A collimator lens 18 and an objective lens 19 are provided between the half mirror 15 and the optical information recording medium 51. The light beam 31 emitted from the light source 11 is diffracted and branched into at least three light beams of 0th-order light, + 1st-order diffracted light, and −1st-order diffracted light by the diffraction grating 12, and then reflected by the half mirror 15. It passes through the collimating lens 18 and reaches the objective lens 19. The 0th-order light, the + 1st-order diffracted light, and the −1st-order diffracted light diffracted by the diffraction grating 12 are independently condensed on the recording surface of the optical information recording medium 51 by the objective lens 19 to form three condensed spots. Form.

  FIG. 2 shows a circuit configuration of the integrated circuit board 17 on which the photodetector 16 in the optical pickup device shown in FIG. 1 is mounted. As shown in FIG. 2, the integrated circuit board 17 includes a light receiving element 21A, a light receiving element 21B, and a light receiving element 21C, and an arithmetic processing circuit 23 that calculates a signal from the light receiving element. The main beam 31a branched from the light beam 31 by the diffraction grating 12 and the two sub beams 31b and 31c are received by the light receiving element 21A, the light receiving element 21B, and the light receiving element 21C, respectively. The light receiving element 21A, the light receiving element 21B, and the light receiving element 21C are each divided into a plurality of light receiving regions.

  Signals detected by the light receiving element 21A, the light receiving element 21B, and the light receiving element 21C are input to the arithmetic processing circuit 23. The arithmetic processing circuit 23 receives the signals from the light receiving element 21A, the light receiving element 21B, and the light receiving element 21C, respectively, and outputs the outputs of the subtractor 24, the subtracter 25, and the subtractor 26, and the subtractor 24, the subtracter 25, and the subtractor 26, respectively. An adder 27, an amplifier 28, and a subtractor 29 are provided. The subtractor 24, subtractor 25, and subtractor 26 receive signals from the light receiving element 21A, the light receiving element 21B, and the light receiving element 21C, respectively, and output push-pull signals MPP, SPP1, and SPP2. Of the arithmetic processing circuit 23, the adder 27, the amplifier 28, and the subtractor 29 will be described later.

  FIG. 2 shows a circuit configuration in which each light receiving element is divided into two light receiving areas, but each light receiving element may be divided into three or more light receiving areas. In FIG. 2, the shape of each beam in each light receiving element is schematically represented in a circular shape, but the shape of the beam is not limited to this. Further, when the astigmatism method is adopted for the focus error signal, each beam on each light receiving element is rotated by approximately 90 degrees. Therefore, each light receiving element needs to be rotated by 90 degrees.

  The optical pickup device of the present embodiment is characterized by the diffraction grating 12 that diffracts the light beam (emitted light beam) emitted from the light source 11, in particular, its periodic structure. FIG. 3 shows a periodic structure, that is, a grating pattern of the diffraction grating 12.

  As shown in FIG. 3, the grating surface of the diffraction grating 12 is substantially parallel to the direction in which the guide groove of the optical information recording medium 51 extends (hereinafter referred to as the Y direction), that is, the tangential direction of the track of the optical information recording medium 51. A dividing line D1, a dividing line D2, and a dividing line D3 extending in different directions are divided into four areas, ie, a first area 12A, a second area 12B, a third area 12C, and a fourth area 12D. In this case, the parallel direction means a parallel direction in consideration of an optical system provided between the diffraction grating 12 and the optical information recording medium 51. The first region 12A and the second region 12B are adjacent to each other with the dividing line D1 interposed therebetween, the second region 12B and the third region 12C are adjacent to each other with the dividing line D2 interposed therebetween, and the third region 12C The fourth region 12D is adjacent to the parting line D3.

  As shown in FIG. 3, the first area 12A, the second area 12B, the third area 12C, and the fourth area 12D are respectively in the radial direction of the optical information recording medium 51 (hereinafter referred to as the X direction). The lattice grooves 12a, the lattice grooves 12b, the lattice grooves 12c, and the lattice grooves 12d are periodically provided along the grooves. In the present embodiment, the widths of the lattice grooves 12a, the lattice grooves 12b, the lattice grooves 12c, and the lattice grooves 12d and the widths of the portions (projections) between the lattice grooves are set to be the same.

  The phase of the periodic structure formed by the grating grooves 12a formed in the first region 12A is substantially 90 degrees ahead of the phase of the periodic structure formed in the second region 12B ( +90 degrees off.) That is, the arrangement period of the grating grooves 12a in the first region 12A is shifted in the + Y direction by a quarter period with respect to the arrangement period of the grating grooves 12b in the second region 12B. Further, the phase of the periodic structure formed in the fourth region 12D is substantially 90 degrees behind the phase of the periodic structure formed in the second region 12B (-90 degrees shifted). .) That is, the arrangement period of the grating grooves 12d in the fourth region 12D is shifted in the −Y direction by a quarter of the period from the arrangement period of the grating grooves 12b in the second region 12B. Therefore, the phase of the periodic structure in the first region 12A is substantially 180 degrees different from the phase of the periodic structure in the fourth region 12D. Further, the phase of the periodic structure in the third region 12C is substantially shifted by 180 degrees with respect to the phase of the periodic structure in the second region 12B. That is, the arrangement period of the grating grooves 12c in the third region 12C is shifted in the + Y direction by a half period with respect to the arrangement period of the grating grooves 12b in the second region 12B.

  Note that the phase shift of the periodic structure in each region does not need to be exactly 90 degrees or 180 degrees. Since the focused spot on the recording surface of the optical information recording medium 51 only needs to have a shape as described later, it may include an error of about ± 10 degrees.

  In the present embodiment, as shown in FIG. 3, the center (light emission point center) L1 of the emitted light beam emitted from the light source 11 is arranged at the position of the dividing line D2 within the range of the assembly accuracy of the apparatus.

  The outgoing light beam incident on the diffraction grating 12 is converted into sub-beams having a predetermined phase difference by the periodic structures respectively formed in the first region 12A, the second region 12B, the third region 12C, and the fourth region 12D. The light is branched and guided to the optical information recording medium 51.

  The reason why the tracking error can be stably detected for the optical information recording media having different guide groove periods by the optical pickup device of this embodiment will be described below.

  FIG. 4 shows the shape of the focused spot on the recording surface of the optical information recording medium 51 of the main beam 31a of the light beam generated by the diffraction grating 12, and the two sub beams 31b and 31c. 4, the X direction indicates the radial direction of the optical information recording medium, and the Y direction indicates the direction in which the guide groove extends.

  The second region 12B and the third region 12C of the diffraction grating 12 are 180 degrees different in phase of the diffraction grating. Therefore, the diffracted light transmitted through the second region 12B and the diffracted light transmitted through the third region 12C cancel each other, and the sub beam 31b and the sub beam 31c shown in FIG. 4 are recorded on the recording surface of the optical information recording medium 51. In the intensity distribution of the focused spot, the intensity at the center is small. In this case, it is only necessary to reduce the intensity of the central portion of the converging spots of the sub beam 31b and the sub beam 31c, and the phase shift between the second region 12B and the third region 12C is an error of about ± 10 degrees with respect to 180 degrees. There is no problem even if it contains.

  Further, the phase of the diffraction grating in the first region 12A is advanced by 90 degrees with respect to the second region 12B, and the phase of the diffraction grating in the fourth region 12D is advanced by 90 degrees with respect to the third region 12C. Yes. Accordingly, the phase of the + 1st order diffracted light transmitted through the first region 12A is advanced by 90 degrees with respect to the phase of the + 1st order diffracted light transmitted through the second region 12B, and the phase of the + 1st order diffracted light transmitted through the fourth region 12D. Advances 90 degrees with respect to the phase of the + 1st order diffracted light transmitted through the third region 12C. Conversely, the phase of the −1st order diffracted light is delayed by 90 degrees. Therefore, a phenomenon in which the spot shape is not asymmetrical as in the conventional inline type DPP method does not occur, and the intensity distribution is symmetric with respect to the Y direction as an axis. Even in this case, the phase shift between the first region 12A and the second region 12B and the phase shift between the fourth region 12D and the third region 12C are about ± 10 degrees with respect to 90 degrees, respectively. There is no problem even if errors are included.

  As shown in FIG. 4, a plurality of guide grooves 51 a are periodically arranged on the recording surface of the optical information recording medium 51. Further, as shown in FIG. 4, the condensed spots obtained by collecting the main beam 31a, the sub beam 31b, and the sub beam 31c of the light beam 31 by the objective lens 19 are arranged in the same guide groove 51a.

  The main beam 31a, the sub beam 31b, and the sub beam 31c are respectively reflected at each focused spot, and the reflected light corresponding to each focused spot is received by the light receiving element 21A, the light receiving element 21B, and the light receiving element 21C provided in the photodetector 16. Each is received. The light receiving element 21A, the light receiving element 21B, and the light receiving element 21C output a push-pull signal MPP corresponding to the main beam 31a, a push-pull signal SPP1 corresponding to the sub-beam 31b, and a push-pull signal SPP2 corresponding to the sub-beam 31c.

  The offset components of MPP, SPP1, and SPP2 due to the radial shift of the objective lens 19 (shift in the radial direction of the optical information recording medium) and the tilt of the optical information recording medium 51 are the radial shift of the objective lens 19 or the optical information recording medium 51. It occurs on the same side (in-phase) for each of the slopes. Therefore, the operation push-pull (DPP) signal in which the offset caused by the radial shift of the objective lens 19 and the inclination of the optical information recording medium 51 is canceled is obtained by using the adder 27, the amplifier 28 and the subtractor 29 shown in FIG. It can be detected by performing arithmetic processing as shown in equation (2).

DPP = MPP−k × (SPP1 + SPP2) (2)
Where k is the amplification factor of the amplifier 28.

  FIG. 5 shows an output waveform of the DPP signal obtained based on the push-pull signal MPP, the push-pull signal SPP1, the push-pull signal SPP2, and the equation (2). In FIG. 5, the vertical axis indicates the signal intensity, and the horizontal axis indicates the relative position of the focused spot on the optical information recording medium 51. As shown in FIG. 5, the phases of SPP1 and SPP2 are accurately shifted by 180 degrees with respect to the phase of MPP. Therefore, even if there is a difference in signal strength between SPP1 and SPP2, the DPP signal obtained based on Equation (2) has an appropriate value, so that each focused spot can be formed on the same guide groove.

  As shown in FIG. 2, the input side of the adder 27 is connected to the outputs of the subtractor 25 and the subtractor 26, and the input of the amplifier 28 is connected to the output of the adder 27. The input of the subtractor 29 is connected to the outputs of the subtractor 24 and the amplifier 28. Thereby, the calculation shown in Formula (2) can be performed. The coefficient k in Expression (2) is for correcting the difference in light intensity between the main beam 31a, the sub beam 31b, and the sub beam 31c reflected from the optical information recording medium 51. When the ratio of the light intensity of the main beam 31a, the sub beam 31b, and the sub beam 31c is a: b: b, the coefficient k may be a / 2b. That is, the coefficient k is a constant determined according to the optical information recording medium 51. A signal processing circuit having a conventional configuration may be used.

  The optical information recording medium 51 is not particularly limited, and includes DVDs including DVD-ROM, DVD-RAM, DVD-R, DVD-RW, and CDs including CD-ROM, CD-R, CD-RW, and the like. Can be used. The wavelength of the light beam 31 may be determined according to the optical information recording medium 51. In the case of DVD and CD, the wavelength may be about 650 nm to about 780 nm. For DVDs, stable tracking error signal detection is possible regardless of whether the guide groove pitch of DVD-R or the like is 0.74 μm or the guide groove pitch of DVD-RAM or the like is 1.23 μm. Is possible.

  Further, in the present embodiment, the case where the diffraction grating 12 is disposed between the light source 11 and the half mirror 15 in the optical system shown in FIG. 1 has been described, but instead, the diffraction grating 12 is replaced with, for example, the half mirror 15. You may arrange | position between the collimating lenses 18. FIG. Further, instead of the optical system shown in FIG. 1, an optical system in which a light source and a photodetector are integrated (for example, an optical system that does not use a half mirror) is used, and a diffraction grating is disposed between the light source and the collimating lens. May be.

  In this embodiment, all the grating grooves provided in the respective regions of the diffraction grating 12 are formed along the X direction which is the radial direction of the optical information recording medium. Instead, the grating grooves are arranged in the X direction. On the other hand, it may be provided in an oblique direction. In addition, although the example in which the width of the second region 12B of the diffraction grating 12 is equal to the width of the third region 12C is shown, it is not necessarily required to be equal.

  Further, in the present embodiment, the case where there is one outgoing light beam emitted from the light source has been described, but instead, the same applies to an optical pickup device that has a plurality of light sources and emits a plurality of light beams. The effect is obtained.

  For example, as shown in FIG. 6, within the range of the assembly accuracy of the apparatus, the emission point center L1 of the first light source is located on the dividing line D2, and the emission point center L2 of the second light source is on the dividing line D3. You may make it locate in. Further, as shown in FIG. 7, within the range of the assembly accuracy of the apparatus, the light emitting point center L1 of the first light source is located on the dividing line D2, and the light emitting point center L2 of the second light source is near the dividing line D3. It may be located within the fourth region 12D. Further, as shown in FIG. 8, within the range of the assembly accuracy of the apparatus, the light emission point center L1 of the first light source is located in the second region 12B, and the light emission point center L2 of the second light source is the third. It may be located within the region 12C. Further, as shown in FIG. 9, within the range of the assembly accuracy of the apparatus, the light emission point center L1 of the first light source is located in the first region 12A near the dividing line D1, and the light emission point of the second light source. The center L2 may be positioned in the fourth region 12D in the vicinity of the dividing line D3.

  Further, the number of light sources is not limited to two, and may be three or more. For example, when there are three light sources, as shown in FIG. 10, the center of the light emitting point of at least one light source is located in the second region 12B or the third region 12C within the range of assembly accuracy of the apparatus. The position of the light emitting point center of the remaining light source need not be particularly limited.

  Furthermore, in the present embodiment, an example is shown in which the entire diffraction grating 12 is divided into a first region 12A, a second region 12B, a third region 12C, and a fourth region 12D. However, the first to fourth regions need only be divided in the region within the effective beam diameter range determined by the aperture diameter of the objective lens in the diffraction grating 12, and the region outside the effective beam diameter range. May have different split states. For example, as shown in FIG. 11, the second region 12B and the third region 12C may not be formed in a region outside the effective beam diameter range.

  In the present embodiment, the phase of the periodic structure of the first region 12A and the phase of the periodic structure of the second region 12B are shifted by 90 degrees, and the phase of the periodic structure of the fourth region 12D and the phase of the third region 12C The case where the phase of the periodic structure is shifted by 90 degrees is shown. However, the phase of the first region 12A and the phase of the fourth region 12D are substantially different by 180 degrees, and the phase of the second region 12B and the phase of the third region 12C are substantially different by 180 degrees. If so, the phase shift of the first region 12A and the phase of the second region 12B and the phase shift of the third region 12C and the phase of the fourth region 12D may be any value. However, considering the manufacturing error when forming the periodic structure in the diffraction grating 12, the phase shift between the first region 12A and the second region 12B and the phase between the fourth region 12D and the third region 12C. It is preferable that the deviations be 10 degrees or more and 350 degrees or less, respectively. Moreover, it is more preferable to set it to 70 degree | times or more and 290 degrees or less.

  In FIG. 12, the phase of the first region 12A and the fourth region 12D is substantially different by 180 degrees, the phase of the second region 12B and the third region 12C is substantially different by 180 degrees, This shows a case where the phase of the region 12A and the second region 12B and the phase of the fourth region 12D and the third region 12C are substantially different by 45 degrees. 13 shows that the phase of the periodic structure of the first region 12A and the periodic structure of the fourth region 12D are substantially different by 180 degrees, and the periodic structure of the second region 12B and the period of the third region 12C are different. A case where the phase with the structure is substantially different by 180 degrees, and the phase between the first area 12A and the second area 12B and the phase between the fourth area 12D and the third area 12C are different by 180 degrees, respectively. Yes. Even in such a case, the same effect as the diffraction grating shown in FIG. 3 can be obtained.

  FIGS. 14A to 14C show the relationship between the shift amount of the objective lens 19 and the DPP signal amplitude when a DVD-RAM is used as the optical information recording medium 51. FIG. (A)-(c) has each shown the case where the phase shift | offset | difference of 1st area | region 12A and 2nd area | region 12B is 0 degree | times, 90 degree | times, and 180 degree | times. In FIG. 14, the vertical axis indicates a value normalized by assuming that the value of the DPP signal amplitude when the shift amount of the objective lens 19 is 0 μm is 100%. The phase of the periodic structure in the first region 12A and the phase of the periodic structure in the fourth region 12D are substantially different by 180 degrees, and the phase of the periodic structure in the second region 12B and the third region 12C Is substantially 180 degrees different from the phase of the periodic structure.

  As shown in FIG. 14, when the phase shift between the periodic structure of the first region 12A and the periodic structure of the second region 12B is 180 degrees, the objective lens shifts. Along with this, the change in the DPP signal amplitude is large.

  FIG. 15 shows the relationship between the amount of phase shift between the first region 12A and the second region 12B and the change rate of the DPP signal amplitude. Here, the change rate of the DPP signal amplitude is shown as a ratio of the DPP signal amplitude when the shift amount of the objective lens is 300 μm with respect to the DPP signal amplitude when the shift amount of the objective lens is 0 μm.

  As shown in FIG. 15, when the phase shift between the periodic structure of the first region 12A and the periodic structure of the second region 12B is 180 degrees, the rate of change of the DPP signal amplitude is the closest to 100%. As the deviation of the angle approaches 0 degree or 360 degrees, the change rate of the DPP signal amplitude decreases.

  In the optical pickup, even if the objective lens is shifted, it is preferable that the DPP signal amplitude is constant. Therefore, the change rate of the DPP signal amplitude is preferably close to 100%. Therefore, it is sufficient that the phase shift between the periodic structure of the first region 12A and the periodic structure of the second region 12B is 10 degrees or more and 350 degrees or less, but the DPP signal amplitude is made more uniform. From the viewpoint, it is preferable that the angle is 70 degrees or more and 290 degrees or less.

  Further, in order to reduce the rate of change of the DPP signal amplitude, a portion of the light beam that is effectively used is transmitted through the first region 12A of the diffraction grating 12, a portion that is transmitted through the second region 12B, It is preferable to include a portion that has passed through the third region 12C and a portion that has passed through the fourth region 12D. That is, the first region 12A to the fourth region 12D are included in the portion where the range of the effective beam diameter determined by the aperture diameter of the objective lens 19 is incident in the region where the outgoing light beam in the diffraction grating 12 is incident. Preferably it is.

  Specifically, when the light source is a DVD system, the width W1 + W2 that is the sum of the width W1 of the second region 12B and the width W2 of the third region 12C of the diffraction grating 12 depends on the aperture diameter of the objective lens 19. It is preferable to be within a range of 10% to 40% of the determined effective beam diameter. The effects of such a configuration will be described below.

  First, a case where the width W1 + W2 is smaller than 10% of the effective beam diameter determined by the aperture diameter of the objective lens 19 will be described. FIG. 16 shows the relationship between the change rate of the DPP signal amplitude of the DVD-RAM and the ratio of the width W1 + W2 to the effective beam diameter determined by the aperture diameter of the objective lens 19. The change rate of the DPP signal amplitude is the ratio of the DPP signal amplitude when the objective lens shift amount is 300 μm to the DPP signal amplitude when the objective lens shift amount is 0 μm. When the width W1 + W2 is smaller than 10% of the effective beam diameter determined by the aperture diameter of the objective lens 19, the change rate of the DPP signal amplitude is smaller than 66% as shown in FIG. Thus, the DPP signal amplitude is reduced by 34% or more on the basis of the DPP signal amplitude when the shift amount of the objective lens is 0 μm, and the change of the DPP signal amplitude is increased, which is not preferable.

  Next, a case where the width W1 + W2 is larger than 40% of the effective beam diameter determined by the aperture diameter of the objective lens 19 will be described. FIG. 17 shows the sum of the signal amplitude of the push-pull signal SPP1 and the signal amplitude of the push-pull signal SPP2 (SPP amplitude) of the DVD-RAM and the ratio of the width W1 + W2 to the effective beam diameter determined by the aperture diameter of the objective lens 19. Showing the relationship. As shown in FIG. 17, when the width W1 + W2 becomes larger than 40% of the effective beam diameter determined by the aperture diameter of the objective lens 19, the signal amplitude approaches zero. In this way, the absolute value of the signal amplitude is reduced, and the characteristics of the optical pickup device are deteriorated.

  As described above, the width W1 + W2 is preferably not less than 10% and not more than 40% of the effective beam diameter determined by the aperture diameter of the objective lens.

  Further, when two light sources of the DVD system and the CD system are used, the width W1 + W2 that is the sum of the width W1 of the second region 12B and the width W2 of the third region 12C of the diffraction grating 12 is the opening of the objective lens 19. It is preferably in the range of 10% to 35% of the effective beam diameter in the DVD system determined by the aperture.

  As described above, the optical pickup device according to the present embodiment can cope with various optical information recording media having different guide groove pitches, and can achieve more stable recording / reproduction. Signal detection is achieved. That is, the optical pickup device according to the present embodiment can achieve downsizing, simplification, cost reduction, high efficiency, and the like in DVD and CD recording and reproducing devices. Further, in an optical information processing apparatus that performs processing such as recording, reproduction, and erasing of information on an optical information recording medium such as an optical disk, a reproduction signal, a recording signal, and various servos used for the optical head device that is a key component thereof As an optical pickup device having a function of detecting a signal or the like, the optical pickup device according to this embodiment is very useful.

  The optical pickup device of the present invention can realize an optical pickup device that performs stable tracking error detection for a plurality of optical information recording media having different guide groove pitches while maintaining the advantages of the inline DPP method. The present invention is useful as an optical pickup device used in an optical information processing apparatus that performs processing such as recording information on a recording medium and reproducing or erasing information recorded on the optical information recording medium.

1 is a block diagram illustrating an optical pickup device according to an embodiment of the present invention. It is a circuit diagram which shows the photodetector of the optical pick-up apparatus which concerns on one Embodiment of this invention. It is a top view which shows the diffraction grating of the optical pick-up apparatus which concerns on one Embodiment of this invention. It is a top view which shows the shape of the condensing spot formed on the recording surface of the optical information recording medium with the optical pick-up apparatus which concerns on one Embodiment of this invention. It is a graph which shows the waveform of the signal obtained by the optical pick-up apparatus which concerns on one Embodiment of this invention. It is a top view which shows an example of the positional relationship of the diffraction grating of the optical pick-up apparatus which concerns on one Embodiment of this invention, and the center of a light beam. It is a top view which shows an example of the positional relationship of the diffraction grating of the optical pick-up apparatus which concerns on one Embodiment of this invention, and the center of a light beam. It is a top view which shows an example of the positional relationship of the diffraction grating of the optical pick-up apparatus which concerns on one Embodiment of this invention, and the center of a light beam. It is a top view which shows an example of the positional relationship of the diffraction grating of the optical pick-up apparatus which concerns on one Embodiment of this invention, and the center of a light beam. It is a top view which shows an example of the positional relationship of the diffraction grating of the optical pick-up apparatus which concerns on one Embodiment of this invention, and the center of a light beam. It is a top view which shows the modification of the diffraction grating of the optical pick-up apparatus which concerns on one Embodiment of this invention. It is a top view which shows the modification of the diffraction grating of the optical pick-up apparatus which concerns on one Embodiment of this invention. It is a top view which shows the modification of the diffraction grating of the optical pick-up apparatus which concerns on one Embodiment of this invention. (A)-(c) is a graph which shows the relationship between the shift amount of the objective lens of the optical pick-up apparatus which concerns on one Embodiment of this invention, and the variation | change_quantity of the amplitude of a differential push pull signal, (a)-( c) shows cases where the phase shift between the first region and the second region is 0 degree, 90 degrees and 180 degrees, respectively. 6 is a graph showing the relationship between the amount of deviation between the phase of the first region and the phase of the second region of the diffraction grating of the optical pickup device according to one embodiment of the present invention and the rate of change in the amplitude of the differential push-pull signal. is there. It is a graph which shows the relationship between the width | variety of the 2nd area | region and 3rd area | region of the diffraction grating of the optical pick-up apparatus which concerns on one Embodiment of this invention, and the change rate of the amplitude of a differential push pull signal. It is a graph which shows the relationship between the width | variety of the 2nd area | region and 3rd area | region of the diffraction grating of the optical pick-up apparatus which concerns on one Embodiment of this invention, and the amplitude of a push pull signal. It is a top view which shows the shape of the condensing spot formed on the recording surface of the optical information recording medium with the optical pick-up apparatus which concerns on a prior art example. It is a top view which shows the diffraction grating of the optical pick-up apparatus which concerns on a prior art example. It is a graph which shows the waveform of the signal obtained by the optical pick-up apparatus which concerns on a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Light source 12 Diffraction grating 12A 1st area | region 12B 2nd area | region 12C 3rd area | region 12D 4th area | region 12a Lattice groove 12b Lattice groove 12c Lattice groove 12d Lattice groove 15 Half mirror 16 Photo detector 17 Integrated circuit board 18 Collimator Lens 19 Objective lens 21A Light receiving element 21B Light receiving element 21C Light receiving element 23 Arithmetic processing circuit 24 Subtractor 25 Subtractor 26 Subtractor 27 Adder 28 Amplifier 29 Subtractor 31 Light beam 31a Main beam 31b Sub beam 31c Sub beam 51 Optical information recording medium 51a Guide groove

Claims (18)

An optical pickup device that records information on an optical information recording medium and reads and erases information recorded on the optical information recording medium,
A light source;
A diffraction grating for branching an outgoing light beam emitted from the light source into at least three light beams;
A light detector that receives the reflected light reflected by the optical information recording medium in each light beam;
The diffraction grating includes a first region, a second region, and a third region, each having a periodic structure having a phase different from each other by a dividing line extending in a direction parallel to a tangential direction of the track of the optical information recording medium. Divided into a region and a fourth region,
The second region and the third region are sequentially arranged between the first region and the fourth region from the first region side,
The phase of the periodic structure in the second region is approximately 180 degrees different from the phase of the periodic structure in the third region,
The phase of the periodic structure in the first region is approximately 180 degrees different from the phase of the periodic structure in the fourth region,
The optical pick-up apparatus, wherein the light source includes a first light source and a second light source.   A distance between a dividing line dividing the first area and the second area and a dividing line dividing the second area and the third area; and the second area and the third area 2. The optical pickup device according to claim 1, wherein a distance between a dividing line that divides the first area and a dividing line that divides the third area and the fourth area is equal to each other.   3. The optical pickup device according to claim 1, wherein the light beam includes zero-order diffracted light, + 1st-order diffracted light, and −1st-order diffracted light. A plurality of guide grooves are periodically arranged on the recording surface of the optical information recording medium,
4. The optical pickup device according to claim 1, wherein each of the light beams is condensed in one guide groove of the plurality of guide grooves. 5.   5. The arithmetic processing circuit according to claim 1, further comprising an arithmetic processing circuit that detects a tracking error signal by a differential push-pull method based on an output signal from the photodetector. 6. Optical pickup device. The photodetector has at least three light receiving elements respectively corresponding to the reflected lights,
The respective light receiving elements are each divided into a plurality of light receiving regions.   A straight line connecting the center of the emitted light beam emitted from the first light source and the center of the emitted light beam emitted from the second light source divides the first region and the second region. Intersecting with at least one of a dividing line for dividing, a dividing line for dividing the second area and the third area, and a dividing line for dividing the third area and the fourth area. The optical pickup device according to claim 1, wherein the optical pickup device is characterized in that:   A straight line connecting the center of the emitted light beam emitted from the first light source and the center of the emitted light beam emitted from the second light source divides the second region and the third region. The optical pickup device according to claim 1, wherein the optical pickup device intersects a dividing line.   The center of the emitted light beam emitted from the first light source is substantially located on a dividing line dividing the second region and the third region, and the emitted light beam emitted from the second light source. 7. The optical pickup device according to claim 1, wherein the center of the optical pickup device is substantially located on a dividing line dividing the third region and the fourth region.   The center of the emitted light beam emitted from the first light source is substantially located on a dividing line dividing the second region and the third region, and the emitted light beam emitted from the second light source. The center of is located on the fourth region in the vicinity of a dividing line that divides the third region and the fourth region. The optical pickup device described.   The center of the emitted light beam emitted from the first light source is located in the second region, and the center of the emitted light beam emitted from the second light source is located in the third region. The optical pickup device according to claim 1, wherein the optical pickup device is an optical pickup device.   The center of the outgoing light beam emitted from the first light source is located in the first region in the vicinity of the dividing line that divides the first region and the second region, and from the second light source. The center of the emitted light beam emitted is located on the fourth region in the vicinity of a dividing line that divides the third region and the fourth region. The optical pickup device according to any one of the above.   The center of the emitted light beam emitted from the first light source is substantially located on a dividing line dividing the second region and the third region, and the emitted light beam emitted from the second light source. The center of is located on the third region in the vicinity of a dividing line that divides the third region and the fourth region. The optical pickup device described.   2. The phase of the periodic structure in the first region of the diffraction grating is different from the phase of the periodic structure in the second region in a range of 10 degrees to 350 degrees. The optical pickup device according to any one of 1 to 10.   The phase of the periodic structure in the first region of the diffraction grating is approximately 90 degrees different from the phase of the periodic structure in the second region. The optical pickup device described in 1.   The phase of the periodic structure in the first region of the diffraction grating is approximately 270 degrees different from the phase of the periodic structure in the second region. The optical pickup device described in 1. An objective lens for condensing each of the at least three light beams and irradiating the light information recording medium on the recording surface of the optical information recording medium as independent condensing spots;
In the diffraction grating, a portion where an effective beam diameter range determined by the aperture diameter of the objective lens is incident on the emitted light beam is the first area, the second area, the third area, and the fourth area. The optical pickup device according to claim 1, further comprising:   18. The optical pickup device according to claim 17, wherein the sum of the width of the second region and the width of the third region is in a range of 10% to 40% of the effective beam diameter. .

Images