Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
  • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
  • G11B7/0901—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following only
  • G11B7/0903—Multi-beam tracking systems
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
  • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
  • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
  • G11B7/1353—Diffractive elements, e.g. holograms or gratings
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
  • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
  • G11B7/0941—Methods and circuits for servo gain or phase compensation during operation

Definitions

• the present invention relates to an optical pickup, and more particularly to an optical pickup that records, reproduces, and erases information on an information recording medium such as an optical disk.
• DPP Different Push Pull
• the light emitted from the semiconductor laser 101 is divided into three beams by the diffractive optical element 102, and then condensed on the optical disk 106 by the collimator lens 103 and the objective lens 105. Then, the reflected light from the optical disk 106 is reflected by the beam splitter 104 and guided to the photodetector 108 through the condenser lens 107.
• the main beam 109, the primary beam sub beam 110, and the primary beam sub beam 111 are arranged in the tangential direction of the track on the optical disk 106.
• the X direction is a direction perpendicular to the track of the optical disk 106
• the Y direction is a direction parallel to the track of the optical disk 106.
• the sub beams 110 and 111 are arranged at positions shifted in the radial direction by 1 Z2 track pitch with respect to the track T on which the main beam 109 is condensed. Then, the reflected lights of the main beam 109 and the sub beams 110 and 111 are received by the two-divided photodetectors 112, 113, and 114 each having a dividing line in the direction parallel to the track as shown in FIG. Then, difference signals from the respective two-divided photodetectors 112, 113, and 114, that is, push-pull signals MPP, SPP1, and SPP2 are generated.
• the coefficient k is when the light intensity of the main beam 109 is a, and the light intensity of the sub beam 110 and sub beam 111 is b.
• this DPP method requires that the sub-beam 110 and sub-beam 111 be shifted from the main beam 109 by 1Z2 track pitches in the radial direction (X direction) of the disk. This is a problem when recording and playing back different types of optical disks with a single optical pickup.
• JP-A-10-162383 proposes an optical disc recording / reproducing method capable of canceling a push-pull offset by a method different from the background art 1 described above.
• the light emitted also by the semiconductor laser force (not shown) is divided into three beams by the diffractive optical element 102 and condensed on the optical disk 106 by the objective lens 105.
• the groove 102a of the diffractive optical element 102 is formed only at the center of the effective light beam.
• Reference numeral 102b denotes a flat portion, which is formed around the groove 102a in the diffractive optical element 102.
• the beam diameters of the sub beam 110 and the sub beam 111 generated by the groove 102a are smaller than the effective light beam diameter (the aperture diameter of the objective lens 105). Therefore, for the ⁇ first-order light of the diffractive optical element 102, the numerical aperture of the objective lens 105 with respect to the diffracted light is substantially reduced. However, the 0th-order light of the diffractive optical element 102 is less than the objective lens. Since it is set to be larger than the aperture of 105, a diffraction limited beam spot determined by the numerical aperture of the objective lens 105 is formed on the optical disc 106.
• the main beam 109 is a beam having an appropriate size with respect to the track pitch.
• the sub beams 110 and 111 form a beam spot that is large with respect to the track pitch.
• the diffractive optical element 102 of FIG. 17 described above when used, the light intensity of the main beam 109 including the 0th-order light is opposite to the flat part 102b in the groove 102a of the diffractive optical element 102. As a result, the light intensity of the flat portion 102b, which is the outer peripheral portion of the diffractive optical element 102, is relatively increased. Further, regarding the phase of the 0th-order light, an optical phase difference is generated in the groove 102a with respect to the flat portion 102b. As a result, the shape of the condensed beam of the main beam 109 on the optical disk 106 changes, and the recording / reproducing characteristics deteriorate.
• the present invention has been made in view of the above problems, and can easily and inexpensively correct the offset of the tracking error signal using the push-pull method without reducing the light use efficiency.
• the purpose is to do.
• the present invention has the following features. [0017] Firstly, according to the present invention, a main beam and at least two sub beams are condensed on a disk, and an optical pickup for detecting a tracking error signal from each push-pull signal is generated from the first sub beam. The phase of the push-pull signal to be generated and the phase of the push-pull signal from which the second sub beam generator is also generated are shifted by approximately 180 °.
• the present invention includes a diffractive optical element that generates first and second sub-beams, and gives a phase difference to a part of the first and second sub-beams by the diffractive optical element. It is characterized by being.
• the diffractive optical element gives the first sub-beam a phase difference of about 90 ° on a substantially half surface divided by a dividing line parallel to the track of the disk.
• the sub beam is characterized in that a phase difference of about 90 ° is given to a substantially half surface divided by the dividing line, which is different from the first sub beam.
• the diffractive optical element according to the present invention is characterized in that a diffraction function generating element is provided in a portion through which the main beam passes.
• the present invention includes at least two light sources having different wavelengths, and the diffractive optical element generates a main beam and at least two sub beams from light beams emitted from the respective light sources.
• the periodic structure is provided with a phase difference of approximately 90 ° on a substantially half surface divided by a dividing line in a direction parallel to the track of the disk in the first sub-beam for each light source.
• the second sub-beam is characterized in that a phase difference of about 90 ° can be given to a substantially half-face different from the first sub-beam among the substantially half-faces divided by the dividing line.
• the diffractive optical element is divided into at least three regions in the radial direction of the disc by a dividing line in a direction parallel to the track of the disc, and the divided diffractive optical elements are adjacent to each other.
• the phase of the periodic structure of the region differs by approximately 90 °, and the dividing line passes through the center of each sub beam.
• FIG. 1 is a diagram showing a configuration of a first embodiment of an optical pickup according to the present invention.
• FIG. 3 is a schematic diagram showing the periodic structure of the diffractive optical element in FIG.
• FIG. 4 is a schematic diagram showing another periodic structure of the diffractive optical element in FIG.
• FIG. 5 Array of spots on the optical disk by the diffractive optical element of FIG.
• FIG. 8 is a diagram showing the configuration of a second embodiment of the optical pickup according to the present invention.
• FIG. 9 is a schematic diagram showing the periodic structure of the diffractive optical element in FIG.
• FIG. 10 is a schematic diagram showing another periodic structure of the diffractive optical element in FIG.
• FIG. 11 Array of spots on the optical disk by the diffractive optical element of FIG.
• FIG. 12 Array of spots on the optical disk by the diffractive optical element of FIG.
• FIG. 14 Array of spots on the optical disc in the optical pickup of FIG.
• FIG. 15 is a detailed view of the photodetector in the optical pickup of FIG.
• FIG. 18 Array of spots on the optical disc in the optical pickup of FIG.
• FIG. 1 is a configuration diagram of a first actual example of an optical pickup according to the present invention.
• the light emitted from the semiconductor laser 1 is divided into a main beam and two sub beams by the diffractive optical element 2, and is then made almost parallel by the collimator lens 3. Thereafter, the light is condensed on the optical disk 6 by the objective lens 5, and the reflected light is again made almost parallel light through the objective lens 5, reflected by the beam splitter 4, and guided to the photodetector 8 by the condenser lens 7.
• FIG. 2 is a diagram showing a configuration of the photodetector 8.
• the main beam and the two sub beams are received by the two-split photodetectors 12, 13, and 14 each having a split line parallel to the track direction (Y direction). Then, the difference signal push-pull signals MPP, SPP1, and SPP2 from the two-divided photodetectors 12, 13, and 14 are obtained.
• the first embodiment is characterized by the periodic structure formed in the diffractive optical element 2.
• Figure 3 shows the periodic structure.
• the periodic structure of the diffractive optical element 2 is divided into four regions 17 to 20 by a dividing line D1 in the radial direction (X direction) of the optical disc 6 and a dividing line D2 in the track direction (Y direction) of the optical disc 6.
• the phase of the periodic structure of the region 18 adjacent in the X direction with respect to one region 17 is different from the periodic structure of the region 17 by + 90 °, and also in the region 19 adjacent to the region 18 in the Y direction.
• the phase force of the periodic structure of the region 20 adjacent in the X direction is different from the periodic structure of the region 19 by + 90 °.
• 9 is a main beam
• 10 and 11 are sub-beams.
• One sub-beam 10 of the two sub-beams 10 and 11 is generated only from two regions adjacent to each other in the X direction in FIG. 3 (that is, the region 17 and the region 18), and the other sub-beam 11 is generated from the two regions 17
• the pitch of the periodic structure is set so that it is generated only from two other regions adjacent to each other in the Y direction and 18 and to each other in the X direction (ie, the region 19 and the region 20).
• the configuration is such that the Y-direction dividing line D2 is approximately the center of the sub-beam generation region.
• a phase difference of about 90 ° is given to a substantially half surface divided by the division line D2 in the Y direction.
• a phase difference of about 90 ° is given to a substantially half surface different from the one of the substantially half surfaces divided by the dividing line D2.
• the periodic structure force S in the region through which the main beam 9 passes is cut, and the sub beams 10, 11 are not substantially semicircular circles.
• the regions 17 to 20 for generating the sub-beams 10 and 11 may be arranged so that With the configuration shown in FIG. 4, the loss of light quantity of the main beam 9 due to the periodic structure can be suppressed, and the light utilization efficiency of the main beam 9 can be improved.
• the spot on the optical disc 6 with 1 has the shape shown in FIG.
• the spot on the optical disc 6 of the main beam 9 and the sub beams 10 and 11 generated by the diffractive optical element 2 having the configuration shown in FIG. 4 has the shape shown in FIG.
• push-pull signals SPP 1 and SPP 2 using sub-beams 10 and 11 are signals that are 180 ° out of phase as shown in FIG.
• the amplitude of the push-pull signal SPP which is the sum of SPP1 and SPP2, obtained by the circuit of FIG.
• the periodic structure that generates the sub-beams 10 and 11 is changed from a linear structure parallel to the radial direction (X direction) to a periodicity in the direction parallel to the track (y direction).
• X direction radial direction
• y direction a periodicity in the direction parallel to the track
• multiple types of optical disks with different track pitches that do not require the sub-beams to be shifted in the radial direction by exactly 1Z2 track pitch with respect to the main beam can be It can be played back with a pickup.
• the condensing spot shape of the main beam on the optical disc 6 does not change.
• FIG. 8 is a diagram showing the configuration of the second embodiment of the optical pickup of the present invention.
• This optical pick-up includes two semiconductor lasers 1 and 21 with different wavelengths and light emitting points arranged in the radial direction (X direction). These semiconductor lasers 1 and 21 are preferably arranged in a narrow region of, for example, 200 ⁇ m or less along the radial direction of the disk 6.
• Figure The optical pickup shown in FIG. 1 splits the emitted light from the two semiconductor lasers 1 and 21 into a main beam and two sub-beams by the diffractive optical element 2, and then makes almost parallel light by the collimator lens 3.
• the light is condensed on the optical disk 6 by the objective lens 5, and the reflected light is again made almost parallel light through the objective lens 5, reflected by the beam splitter 4, and guided to the photodetector 8 by the light collecting lens 7.
• two rays with different wavelengths are represented by a solid line and a broken line.
• the configuration of the photodetector 8 in FIG. 8 is the same as that shown in FIG.
• the main beams 9 and 28 and the two sub beams 10, 11, 29, and 30 shown in FIG. 9 are divided into two-part photodetectors each having a dividing line parallel to the track direction (Y direction) as shown in FIG. Light is received at 12, 13, and 14.
• the difference signal push-pull signals MPP, SPP 1, and SPP2 from the two-split photodetectors 12, 13, and 14 are obtained.
• the second embodiment is characterized by the periodic structure formed in the diffractive optical element 2.
• Figure 9 shows the periodic structure.
• the periodic structure of the diffractive optical element 2 is divided into six regions 22 to 27 by a dividing line D1 in the radial direction (X direction) of the optical disc 6 and dividing lines D21 and D22 in the track direction (Y direction) of the optical disc 6. ing.
• the phase of the periodic structure of the region 23 adjacent in the X direction with respect to one of the regions 22 is different from the periodic structure of the region 22 by + 90 °, and another region adjacent to the region 23 in the X direction.
• the phase of 24 periodic structures differs from the periodic structure of region 23 by –90 °.
• the phase of the periodic structure in the region 26 adjacent to the region 22 and the region 27 adjacent in the Y direction differs from the periodic structure of the region 27 by ⁇ 90 ° with respect to the region 27 adjacent to the region 22 in the Y direction.
• the phase of the periodic structure in the other adjacent region 25 is different from the periodic structure in the region 26 by + 90 °.
• the phase of the periodic structure in the region 24 is + 90 ° different from the periodic structure of the region 23, and the phase of the periodic structure in the region 25 is 90 ° different from the periodic structure of the region 26.
• one of the two sub-beams 10, 11, 29, 30 generated with respect to the light emitted from each of the two semiconductor lasers 1, 21 is adjacent to each other in the X direction. It is generated from two regions 23, 24 and only two regions 22, 23.
• the other sub-beams 11 and 30 are generated from only the two regions 25 and 26 adjacent to the two regions in the Y direction and adjacent to each other in the X direction, and the two regions 26 and 27.
• the pitch is set, and the dividing line D1 in the X direction is approximately at the center of the sub-beam generation region.
• one of the two sub-beams generated by the periodic structure for the light emitted from each of the two semiconductor lasers 1 and 21 is divided by the dividing lines D 21 and D22 in the Y direction.
• a phase difference of about 90 ° is given to the substantially half surface, and a phase difference of about 90 ° is given to a substantially half surface different from the one sub-beam among the substantially half surfaces divided by the dividing lines D21 and D22 for the other sub beam.
• the periodic structure of the region through which the main beams 9, 28 pass is cut, and the sub beams 10, 11, 29, 30 are, for example, substantially semicircular.
• a configuration in which the regions 22 to 27 for generating the sub-beams 10, 11, 29, and 30 are arranged so as not to have such a circle may be adopted.
• the loss of light quantity of the main beams 9 and 28 due to the periodic structure can be suppressed, and the light utilization efficiency of the main beams 9 and 28 can be improved.
• the spots on the optical disc 6 of the main beams 9 and 28 and the sub beams 10, 11, 29 and 30 generated by the diffractive optical element 2 having the configuration shown in FIG. 9 have the shape shown in FIG. Further, the spots on the optical disc 6 of the main beams 9, 28 and the sub beams 10, 11, 29, 30 generated by the diffractive optical element having the configuration shown in FIG. 10 have the shape shown in FIG. At this time, push-pull signals SPP1 and SPP2 using sub-beams 10 and 11 or sub-beams 29 and 30 are signals that are 180 ° out of phase as shown in FIG. Is almost zero.
• the coefficient k is used to correct the difference in light intensity between the main beams 9 and 28 and the sub beams 10, 11, 29, and 30.
• a linear structure parallel to the radial direction (X direction) is given periodicity in the direction parallel to the track (Y direction).
• X direction a linear structure parallel to the radial direction
• Y direction a linear structure parallel to the track
• multiple optical discs with different track pitches that do not need to be arranged in the radial direction by exactly 1Z2 track pitch with respect to the main beam, as in Background Art 1 can be used as a single optical pickup. It is possible to play with.
• the focused spot shape of the main beam on the optical disc 6 does not change.
• the light emitting points of two semiconductor lasers 1 and 21 having different wavelengths in a narrow area within, for example, 200 ⁇ m along the disk radial direction are arranged.
• the diffractive optical element 2 three regions 22, 23, 24 and regions 25, 26, 27, which give a phase difference of 90 °, are arranged alternately in the radial direction of the disk, and the central regions 23, 26 have two wavelengths.
• the configuration is shared by the beams, multiple types of optical discs with different track pitches that do not require the sub-beams to be shifted in the radial direction by exactly 1Z2 track pitch with respect to the main beam as in Background Art 1, It is possible to reproduce with one optical pickup, and at the same time, the optical pickup can be easily implemented without changing the shape of the condensing spot of the main beam on the optical disc 6 as in Background Art 2. It can be.
• the region that gives a phase difference of 90 ° in the diffractive optical element 2 is defined as the disk radius.
• the optical pickup of the present invention can easily and inexpensively correct the tracking error signal offset using the push-pull method without reducing the light utilization efficiency. It is useful as an optical pickup that can be used for a plurality of different disks.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Optical Recording Or Reproduction (AREA)
• Optical Head (AREA)

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Citations (6)

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• 2005
  • 2005-02-15 JP JP2005037010A patent/JP2006228260A/ja not_active Withdrawn
  • 2005-09-21 WO PCT/JP2005/017338 patent/WO2006087843A1/ja not_active Ceased
  • 2005-09-21 CN CNA2005800225409A patent/CN1981332A/zh active Pending
  • 2005-09-21 KR KR1020067026738A patent/KR20070104208A/ko not_active Withdrawn
  • 2005-09-21 US US11/660,101 patent/US20080074966A1/en not_active Abandoned
  • 2005-09-21 EP EP05785942A patent/EP1860653A1/en not_active Withdrawn
• 2006
  • 2006-02-14 TW TW095104811A patent/TW200629259A/zh unknown

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