JP2005122869A - Optical pickup and disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain a quality improvement of a tracking error signal by reducing an influence caused by eccentricity, etc., of a disk-like recording medium. <P>SOLUTION: The recording or reproducing operation of the information signal with respect to a plurality of kinds of disk-like recording media 100 having different using wavelengths is attained, and a diffraction element 10 is provided, which has a plurality of areas for dividing laser beams having different wavelengths emitted from a light emitting element 9 respectively into main luminous flux, a pair of 1st sub-luminous flux and a pair of 2nd sub-luminous flux, and when a distance between a spot center of the 1st sub-luminous flux and a spot center of the 2nd sub-luminous flux formed on a recording surface of an optional one kind of disk-like recording medium by being separated in the nearly radial direction of the disk-like recording medium, is expressed as D, n is a natural number, and a track pitch of the optional one kind of disk-like recording medium is expressed as P, the distance D is set so as to be approximately (2a-1)×P/2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to the technical field of optical pickups and disk drive devices. More specifically, the present invention relates to a technical field for improving the quality of a tracking error signal by reducing the influence of eccentricity of a disk-shaped recording medium.

  2. Description of the Related Art There is a disk drive device that records and reproduces information signals on a disk-shaped recording medium. Such a disk drive device moves in the radial direction of the disk-shaped recording medium mounted on a disk table and moves to the disk-shaped recording medium. And an optical pickup that records or reproduces an information signal by irradiating a laser beam through an objective lens.

  In the optical pickup, focusing is adjusted by detecting the focusing error signal and displacing the objective lens in a direction away from or contacting the recording surface of the disk-shaped recording medium (focusing direction). Tracking adjustment is performed by displacing the lens in a substantially radial direction (tracking direction) of the disk-shaped recording medium.

  The push-pull method is known as a tracking error signal detection method. However, this method has a problem that a large direct current fluctuation (DC offset) signal is likely to occur when the objective lens is displaced in the tracking direction.

  Therefore, a differential push-pull method capable of reducing the DC offset signal is widely used as a tracking error signal detection method (see, for example, Patent Document 1).

  In the differential push-pull method, a laser beam is divided into a main light beam and a pair of sub light beams by a diffractive element, and as shown in FIG. The sub-spots S and S are positioned between the adjacent tracks T and T, so that the distance between the main beam spot (main spot) M and each of the sub-spots S and S is 2 of the track pitch P. I try to be a fraction.

  Thus, in the differential push-pull method, the distance between the main spot M and the sub-spots S and S is set to one half of the track pitch, so that the phase of the tracking error signal detected from the main light flux The DC offset signal is canceled by inverting the phase of the tracking error signal detected from the sub-beam (see FIG. 11).

JP-A-61-94246

  However, when the above-described differential push-pull method is employed, if there is an angle shift (difference in the rotation direction) of the diffraction element due to the eccentricity of the disk-shaped recording medium or an environmental change such as temperature, two sub- A positional deviation occurs between the adjacent tracks T and T of the spots S and S. Due to this positional shift, the phase of the tracking error signal detected from the two sub-beams is relatively shifted, and as shown in FIG. 12, the amplitude of the tracking error signal detected from the sub-beams is reduced, and the differential There is a problem that the amplitude of the push-pull (DPP) signal decreases.

  In particular, when the disc-shaped recording medium is eccentric, the amplitude of the DPP signal changes during one rotation of the disc-shaped recording medium, and the tracking servo performance is likely to deteriorate.

  On the other hand, the disc drive apparatus can record or reproduce information signals on a plurality of types of disc-shaped recording media having different operating wavelengths, for example, both CD (Compact Disc) and DVD (Digital Versatile Disc). There is something.

  In such a disk drive device, the track pitch varies depending on each disk-shaped recording medium, and when a common diffraction element is used for each wavelength, the diffraction angle of the sub-beams varies depending on the wavelength. In each disk-shaped recording medium, it is difficult to position a sub spot between adjacent tracks.

  Therefore, in such a case, for example, if only one disc-shaped recording medium is set so that the sub-spot is positioned between adjacent tracks, in particular, when recording or reproducing information signals on the other disc-shaped recording medium. In some cases, the amount of change in the amplitude of the DPP signal increases and the DC offset signal increases. In addition, it is considered that the sub-spot is positioned at an intermediate position between the optimum positions of each disk-shaped recording medium. In this case, however, the information signal is recorded or reproduced on each disk-shaped recording medium. In this case, a change in the amplitude of the DPP signal and a DC offset signal are generated, which deteriorates the performance of the tracking servo.

  The above case can be dealt with by using a dedicated diffractive element for each disc-shaped recording medium. In this case, however, a plurality of diffractive elements are required, which increases the number of parts and A new problem of rising costs will arise. Further, in the case of a disk-shaped recording medium having the same wavelength used, for example, DVD, DVD-ROM (Read Only Memory), DVD ± R (Recordable), DVD-RW (Rewritable), and DVD-RAM (Random Access Memory). Since the track pitch is different, the use of a dedicated diffraction element corresponding to all types of DVDs further increases the number of parts and the cost.

  Accordingly, it is an object of the present invention to overcome the above-described problems and to improve the quality of a tracking error signal by reducing the influence of eccentricity of the disk-shaped recording medium.

  In order to solve the above-described problem, the optical pickup of the present invention has a plurality of regions for dividing the laser light emitted from the light emitting element into a main light beam, a pair of first sub light beams, and a pair of second sub light beams. And a spot center of the first sub-beam and a spot center of the second sub-beam formed on the recording surface of the disk-shaped recording medium so as to be spaced apart in a substantially radial direction of the disk-shaped recording medium. When the distance is D, n is a natural number, and the track pitch of the disk-shaped recording medium is P, the distance D is approximately (2n−1) × P / 2.

  In order to solve the above-described problem, another optical pickup according to the present invention is capable of recording or reproducing information signals with respect to a plurality of types of disk-shaped recording media having different operating wavelengths, and lasers having different wavelengths emitted from light emitting elements. A diffraction element having a plurality of regions each dividing light into a main light beam, a pair of first sub-light beams and a pair of second sub-light beams is provided, and the diffraction element is disposed on the recording surface of any one type of disk-shaped recording medium. The distance between the spot center of the first sub-beam and the spot center of the second sub-beam formed separately from each other in the substantially radial direction of the disk-shaped recording medium is D, n is a natural number, When the track pitch of the disk-shaped recording medium is P, the distance D is approximately (2n-1) × P / 2.

  In order to solve the above-described problems, the disk drive device according to the present invention divides the laser light emitted from the light emitting element into a main light beam, a pair of first sub-light beams, and a pair of second sub-light beams. And a second sub-beam and a spot center of the first sub-beam formed on the recording surface of the disk-shaped recording medium so as to be spaced apart in a substantially radial direction of the disk-shaped recording medium. The distance D is approximately (2n-1) × P / 2 where D is the distance from the center of the spot, n is a natural number, and P is the track pitch of the disk-shaped recording medium. .

  In order to solve the above-described problem, another disk drive device of the present invention enables information signals to be recorded or reproduced on a plurality of types of disk-shaped recording media having different operating wavelengths, and is emitted from a light emitting element to an optical pickup. Provided with a diffraction element having a plurality of regions for dividing laser beams of different wavelengths into a main light beam, a pair of first sub-light beams and a pair of second sub-light beams, respectively. The distance between the spot center of the first sub-beam and the spot center of the second sub-beam formed on the recording surface in the substantially radial direction of the disc-shaped recording medium is D, n is a natural number, The distance D is approximately (2n−1) × P / 2 where P is the track pitch of any one type of disk-shaped recording medium.

  Therefore, in the optical pickup and the disk drive device according to the present invention, in the laser light whose distance D is approximately (2n−1) × P / 2, the first and second sub-beams are used. The phase of the detected tracking error signal is reversed and canceled.

  The optical pickup of the present invention is an optical pickup that moves in the radial direction of a disk-shaped recording medium mounted on a disk table and irradiates the disk-shaped recording medium with laser light emitted from a light emitting element through an objective lens. A diffractive element having a plurality of regions for dividing a laser beam emitted from a light emitting element into a main light beam, a pair of first sub-light beams and a pair of second sub-light beams, and recording on a disk-shaped recording medium D is the distance between the spot center of the first sub-beam and the spot center of the second sub-beam formed on the surface in the substantially radial direction of the disk-shaped recording medium, and n is a natural number. When the track pitch of the recording medium is P, the distance D is approximately (2n−1) × P / 2.

  Therefore, the detection of the tracking error signal can reduce the influence of the eccentricity of the disk-shaped recording medium and the rotational deviation of the diffraction element, and the quality of the tracking error signal can be improved.

  In addition, since the influence of the rotational shift of the diffraction element is reduced, it is possible to omit the rotation adjustment of the diffraction element, and it is possible to provide a low-cost and highly reliable optical pickup.

  In the invention described in claim 2, the first sub-beam and the second sub-beam are formed on the recording surface of the disk-shaped recording medium so as to be separated from each other in the substantially radial direction of the disk-shaped recording medium. Since the plurality of regions are formed in the diffraction element so that the amount of light is substantially the same, the tracking error signal detected from each sub-beam can be canceled reliably, and the tracking control operation is reliable. Can be improved.

  In the invention described in claim 3 and claim 4, since the arrangement direction of the plurality of regions of the diffraction element is the tangential direction of the disk-shaped recording medium, the laser incident on the diffraction element at the time of tracking control operation There is no change in the relative position between the light beam and each region of the diffractive element, and the sub-beam generation by the diffractive element is not adversely affected.

  Further, during the tracking control operation, the relationship between the main beam and the original laser beam before diffraction does not change, and the modulation is not adversely affected.

  Another optical pickup of the present invention is capable of recording or reproducing information signals on a plurality of types of disc-shaped recording media having different operating wavelengths, and moves in the radial direction of the disc-shaped recording media mounted on a disc table. An optical pickup that irradiates a disc-shaped recording medium with laser light emitted from a light-emitting element and having a wavelength corresponding to the type of the disc-shaped recording medium through an objective lens, and lasers having different wavelengths emitted from the light-emitting element. A diffraction element having a plurality of regions each dividing light into a main beam, a pair of first sub-beams, and a pair of second sub-beams, on the recording surface of any one type of disc-shaped recording medium; The distance between the spot center of the first sub-beam and the spot center of the second sub-beam formed separately from each other in the substantially radial direction of the disc-shaped recording medium is D, and n And a natural number, the track pitch of the arbitrary one type of the disc-shaped recording medium is taken as P, and characterized in that the distance D is set to be substantially (2n-1) × P / 2.

  Accordingly, the quality of the tracking error signal can be improved during recording or reproduction of the information signal on the disk-shaped recording medium, and the disk-shaped recording medium can be detected with respect to a specific disk-shaped recording medium with respect to detection of the tracking error signal. This can reduce the influence of the eccentricity and the rotational deviation of the diffraction element.

  In addition, when performing recording or reproduction on different types of disc-shaped recording media, it is possible to share the diffraction element, so that the quality of the tracking error signal can be improved without increasing the number of components and increasing the cost. You can plan. In the invention described in claim 6, the first sub-beam and the second sub-beam are formed on the recording surface of the disk-shaped recording medium so as to be separated from each other in the substantially radial direction of the disk-shaped recording medium. Since the plurality of regions are formed in the diffraction element so that the amount of light is substantially the same, the tracking error signal detected from each sub-beam can be canceled reliably, and the tracking control operation is reliable. Can be improved.

  In the invention described in claims 7 and 8, since the arrangement direction of the plurality of regions of the diffraction element is the tangential direction of the disk-shaped recording medium, the laser incident on the diffraction element during the tracking control operation There is no change in the relative position between the light beam and each region of the diffractive element, and the sub-beam generation by the diffractive element is not adversely affected.

  Further, during the tracking control operation, the relationship between the main beam and the original laser beam before diffraction does not change, and the modulation is not adversely affected.

  The disk drive device according to the present invention has a disk table on which a disk-shaped recording medium is mounted and rotated, and an objective lens driving device is supported on a moving base and moves in the radial direction of the disk-shaped recording medium mounted on the disk table. An optical pickup for irradiating a disc-shaped recording medium with laser light through an objective lens, wherein the optical pickup is configured to transmit laser light emitted from a light emitting element to a main light beam and a pair of light beams. A diffractive element having a plurality of regions divided into a first sub-beam and a pair of second sub-beams, and formed on the recording surface of the disk-shaped recording medium so as to be separated in a substantially radial direction of the disk-shaped recording medium The distance between the spot center of the first sub-beam and the spot center of the second sub-beam is D, n is a natural number, The rack pitch is taken as P, and characterized in that the distance D is set to be substantially (2n-1) × P / 2.

  Therefore, the detection of the tracking error signal can reduce the influence of the eccentricity of the disk-shaped recording medium and the rotational deviation of the diffraction element, and the quality of the tracking error signal can be improved.

  Further, since the influence of the rotational deviation of the diffraction element is reduced, it is possible to omit the rotation adjustment of the diffraction element, and it is possible to provide a low-cost and highly reliable disk drive device.

  In the invention described in claim 10, the first sub-light beam and the second sub-light beam are formed on the recording surface of the disk-shaped recording medium so as to be separated from each other in the substantially radial direction of the disk-shaped recording medium. Since the plurality of regions are formed in the diffraction element so that the amount of light is substantially the same, the tracking error signal detected from each sub-beam can be canceled reliably, and the tracking control operation is reliable. Can be improved.

  In the invention described in claims 11 and 12, since the arrangement direction of the plurality of regions of the diffraction element is the tangential direction of the disk-shaped recording medium, the laser incident on the diffraction element during the tracking control operation The relative position between the light beam and each region before diffraction does not change, and the generation of the sub beam by the diffraction element is not adversely affected.

  Further, during the tracking control operation, the relationship between the main beam and the original laser beam before diffraction does not change, and the modulation is not adversely affected.

  Another disk drive apparatus according to the present invention is capable of recording or reproducing information signals for a plurality of types of disk-shaped recording media having different operating wavelengths, a disk table on which the disk-shaped recording medium is mounted, and a moving base. The objective lens driving device is supported on the disk and moved in the radial direction of the disk-shaped recording medium mounted on the disk table. The light emitted from the light-emitting element is emitted to the disk-shaped recording medium according to the type of the disk-shaped recording medium. A disk drive device including an optical pickup that irradiates a laser beam having an objective lens through an objective lens, wherein the optical pickup is configured to emit a laser beam having a different wavelength emitted from a light emitting element and a pair of first light beams. A diffraction element having a plurality of regions divided into a sub-beam and a pair of second sub-beams, The distance between the spot center of the first sub-beam and the spot center of the second sub-beam formed on the recording surface of the disc-shaped recording medium so as to be separated from each other in the substantially radial direction of the disk-shaped recording medium is D, and n Is a natural number, and the track pitch of any one type of disc-shaped recording medium is P, the distance D is approximately (2n-1) × P / 2.

  Accordingly, the quality of the tracking error signal can be improved during recording or reproduction of the information signal on the disk-shaped recording medium, and the disk-shaped recording medium can be detected with respect to a specific disk-shaped recording medium with respect to detection of the tracking error signal. This can reduce the influence of the eccentricity and the rotational deviation of the diffraction element.

  In addition, when performing recording or reproduction on different types of disc-shaped recording media, it is possible to share the diffraction element, so that the quality of the tracking error signal can be improved without increasing the number of components and increasing the cost. You can plan.

  In the invention described in claim 14, the first sub-beam and the second sub-beam are formed on the recording surface of the disk-shaped recording medium so as to be separated from each other in the substantially radial direction of the disk-shaped recording medium. Since the plurality of regions are formed in the diffraction element so that the amount of light is substantially the same, the tracking error signal detected from each sub-beam can be canceled reliably, and the tracking control operation is reliable. Can be improved.

  In the invention described in claims 15 and 16, since the arrangement direction of the plurality of regions of the diffraction element is the tangential direction of the disk-shaped recording medium, the laser incident on the diffraction element during the tracking control operation There is no change in the relative position between the light beam and each region of the diffractive element, and the sub-beam generation by the diffractive element is not adversely affected.

  Further, during the tracking control operation, the relationship between the main beam and the original laser beam before diffraction does not change, and the modulation is not adversely affected.

  The best mode of an optical pickup and a disk drive apparatus according to the present invention will be described below with reference to the accompanying drawings.

  The disk drive device 1 is configured by arranging required members and mechanisms in an outer casing 2 (see FIG. 1), and the outer casing 2 has a disk insertion slot (not shown).

  A chassis (not shown) is disposed in the outer casing 2, and the disk table 3 is fixed to the motor shaft of a spindle motor attached to the chassis.

  Parallel guide shafts 4 and 4 are attached to the chassis, and a lead screw 5 that is rotated by a feed motor (not shown) is supported.

  The optical pickup 6 includes a moving base 7, required optical components provided on the moving base 7, and an objective lens driving device 8 disposed on the moving base 7, and is provided at both ends of the moving base 7. The bearing portions 7a and 7b are slidably supported by the guide shafts 4 and 4, respectively. When a nut member (not shown) provided on the moving base 7 is screwed into the lead screw 5 and the lead screw 5 is rotated by the feed motor, the nut member is sent in a direction corresponding to the rotation direction of the lead screw 5, The pickup 6 is moved in the radial direction of the disc-shaped recording medium 100 mounted on the disc table 3.

  As the disc-shaped recording medium 100, for example, a CD 100a and a DVD 100b are used.

  In the disk drive device 1 configured as described above, when the disk table 3 is rotated in accordance with the rotation of the spindle motor, the disk-shaped recording medium 100 mounted on the disk table 3, that is, the CD 100a or the DVD 100b is loaded. At the same time, the optical pickup 6 is moved in the radial direction of the disc-shaped recording medium 100 to perform a recording operation or a reproducing operation on the disc-shaped recording medium 100.

  As shown in FIG. 2, the optical pickup 6 includes a light emitting element 9, a diffraction element 10, a beam splitter 11, a collimator lens 12, a rising mirror 13, an objective lens 14, an optical axis synthesizing element 15, an adjusting lens 16, and a light receiving element. 17, the light emitting element 9, the diffractive element 10, the beam splitter 11, the collimator lens 12, the rising mirror 13, the optical axis synthesizing element 15, the adjusting lens 16 and the light receiving element 17 are arranged on the moving base 7, and the objective lens 14 Are provided in the objective lens driving device 8.

  The light emitting element 9 has two light emitting points that emit laser light having different wavelengths. From the first light emitting point, for example, laser light having a wavelength of 785 nm (first wavelength) is emitted. From the light emitting point, for example, laser light having a wavelength of 660 nm (second wavelength) is emitted. When an information signal is recorded or reproduced on one disc-shaped recording medium 100, that is, the CD 100a, a laser beam having a wavelength of 785 nm is emitted from the first emission point, and the other disc-shaped recording medium 100, ie, When an information signal is recorded or reproduced on the DVD 100b, laser light having a wavelength of 660 nm is emitted from the second light emitting point.

  The first light emission point and the second light emission point of the light emitting element 9 are arranged at a predetermined interval, and the laser light having the second wavelength is aligned on the optical axis of the optical system. The laser beam having the first wavelength is shifted from the optical axis of the optical system.

  As the diffraction element 10, for example, a grating is used, which is divided into a first region 10a and a second region 10b (see FIG. 3). The laser light R is incident across the first region 10a and the second region 10b, and the laser light incident on the first region 10a is a main light beam (zero order light) and a pair of first sub-light beams (± Laser light that has been split into a primary beam and incident on the second region 10b is split into a main beam (zero-order beam) and a pair of second sub-beams (± primary beam).

  The beam splitter 11 is, for example, a reflection type, and reflects the laser light emitted from the light emitting element 9 by the separation surface 11 a and guides it to the collimator lens 12, and the return light of the laser light reflected by the disc-shaped recording medium 100. And transmits the light to the optical axis combining element 15.

  The collimator lens 12 has a function of converting the incident laser beam into a parallel beam, and the rising mirror 13 has a function of reflecting the laser beam and guiding it to the objective lens 14 or the collimator lens 12. 14 has a function of condensing incident laser light on a recording track of the disk-shaped recording medium 100.

  The optical axis synthesizing element 15 has a function of correcting the optical axis direction of the laser light having the first wavelength shifted from the optical axis of the optical system and making it incident on a predetermined light receiving point of the light receiving element 17.

  The adjustment lens 16 is a lens for adjusting the magnification of the laser beam.

  The light receiving element 17 has three light receiving areas for receiving zero-order light and ± first-order light of the laser light.

  In the optical pickup 6 configured as described above, when a laser beam having a first wavelength, that is, a laser beam having a wavelength of 785 nm corresponding to the CD 100a is emitted from the light emitting element 9, the laser beam is emitted from the diffraction element 10. And is divided into a main light beam, a pair of first sub light beams, and a pair of second sub light beams.

  The diffracted laser light is reflected by the separation surface 11 a of the beam splitter 11, converted into a parallel light beam by the collimator lens 12, raised by the rising mirror 13, and mounted on the disk table 3 via the objective lens 14. The recording surface is irradiated. The laser light applied to the recording surface of the CD 100 a is reflected by the recording surface and is incident on the beam splitter 11 again through the objective lens 14, the rising mirror 13 and the collimator lens 12 as return light. The return light incident on the beam splitter 11 is transmitted through the separation surface 11 a of the beam splitter 11, the optical axis direction is corrected by the optical axis synthesizing element 15, and is incident on the light receiving element 17 through the adjustment lens 16.

  In the optical pickup 6, when the track pitch of the CD 100a is Pa and n is a natural number, each of the centers of the sub-spots S1a and S1b of the first sub-beam of the laser light having the first wavelength and the second The diffractive element 10 is designed so that the distances Da to the sub-spots S2a and S2b of the sub-beams are approximately (2n−1) × Pa / 2. That is, as shown in FIG. 4, the sub-spots S1a and S1b of the first sub-beam are positioned 180 ° opposite to each other across the main spot M, and the sub-spots S2a and S2b of the second sub-beam are mutually main. The sub-spot S1a of the first sub-beam and the sub-spot S2a of the second sub-beam are positioned 180 ° apart from each other across the spot M, and are separated from each other in the substantially radial direction of the CD 100a. The sub-spot S1b of the light beam and the sub-spot S2b of the second sub-light beam are similarly spaced apart in the substantially radial direction of the CD 100a. The distance Da between the center of the sub-spot S1a and the center of the sub-spot S2a and the sub-spot S1b The distance Da between the center of the sub-spot S2b and the center of the sub-spot S2b is approximately (2n-1) × Pa / 2.

  Accordingly, the track pitch of the CD 100a is set to about 1.6 μm in the standard, and therefore the distance Da is set to about 0.8 μm (when n = 1).

  When the return light is incident on the light receiving element 17, the tracking error signal is detected based on the main light beam and the sub light beam received by the light receiving element 17. As described above, the distance Da is set for the sub light beam. Since the track pitch Pa is approximately one half of the track pitch Pa, the phase of the tracking error signal detected by the sub spot S1a and the sub spot S2a is inverted and the tracking error signal detected by the sub spot S1b and the sub spot S2b The phase of is inverted. Therefore, as shown in FIG. 5, the tracking error signal of the entire sub-light beam has an amplitude of 0, and only the DC offset signal generated when the objective lens 14 is displaced in the tracking direction is detected. A tracking error signal is detected for the main beam, and a DC offset signal is also detected. However, by canceling the DC offset signal detected by the sub beam and the DC offset signal detected by the main beam, an appropriate tracking error is detected. A signal can be detected.

  Since the distance Da between the sub-spots of the sub-light beam is uniquely determined by the design of the diffraction element 10, a tracking error signal detected from the main light beam and a tracking error signal detected from the sub-light beam due to the eccentricity of the CD 100a. Even if a phase change occurs, the tracking error signal is canceled for the entire sub-beam, so that there is no problem of a decrease in the amplitude of the DPP signal due to the eccentricity of the CD 100a.

  On the other hand, when laser light having a second wavelength, that is, laser light having a wavelength of 660 nm corresponding to the DVD 100b is emitted from the light emitting element 9, the laser light is diffracted by the diffraction element 10 and is paired with the main light flux. It is divided into one sub-beam and a pair of second sub-beams.

  The diffracted laser light is reflected by the separation surface 11 a of the beam splitter 11 to be converted into a parallel light beam by the collimator lens 12, raised by the rising mirror 13, and mounted on the disk table 3 via the objective lens 14. The recording surface is irradiated. The laser light applied to the recording surface of the DVD 100b is reflected by the recording surface and is incident on the beam splitter 11 again through the objective lens 14, the rising mirror 13 and the collimator lens 12 as return light. The return light incident on the beam splitter 11 is transmitted through the separation surface 11 a of the beam splitter 11 and is incident on the light receiving element 17 through the optical axis synthesizing element 15 and the adjustment lens 16.

  In the optical pickup 6, as described above, in the case of the CD 100a, the diffraction is performed so that the distance Da between the centers of the sub-spots of the first sub-beam is approximately (2n-1) × Pa / 2. Element 10 is designed. Since the diffraction angle of the diffractive element 10 is proportional to the wavelength, the distance Db between the centers of the sub-spot S1c of the first sub-beam and the sub-spot S2c of the second sub-beam for the laser light having the second wavelength, and The distance Db between the centers of the sub-spot S1d of the first sub-beam and the sub-spot S2d of the second sub-beam is calculated by Db = (660/785) × Da, and Da = 0.8 μm. Db = 0.67 μm.

  At this time, when the DVD 100b is a DVD-ROM, DVD ± R, or DVD-RW, the track pitch Pb is 0.74 μm on the standard, so the distance Db is a value close to the track pitch Pb. Therefore, in this case, as shown in FIG. 6, the sub-spots S1c, S1d, S2c, and S2d of the sub-beams are all positioned between the adjacent tracks T and T, and are described in the section “Background Art”. The tracking error signal can be detected by the differential push-pull method.

  On the other hand, when the DVD 100b is a DVD-RAM, the track pitch Pb 'is 1.23 [mu] m on the standard, so the distance Db (= 0.67 [mu] m) is about one-half of the track pitch Pb'. Accordingly, in this case, as in the case of the CD 100a, the phase of the tracking error signal detected by the sub spot S1c and the sub spot S2c is substantially inverted and the tracking error detected by the sub spot S1d and the sub spot S2d The phase of the signal is substantially inverted, and the amplitude of the tracking error signal for the entire sub-beam is substantially zero. Therefore, an appropriate tracking error signal can be detected by canceling with the DC offset signal detected by the sub-beam and the DC offset signal detected by the main beam.

  In the above, the example in which the distance Da is set to approximately (2n−1) × Pa / 2 at the time of recording or reproduction of the CD 100a has been described, but conversely, as shown below, at the time of recording the DVD 100b. Alternatively, at the time of reproduction, the distance (this distance is assumed to be Dd) may be approximately (2n−1) × Pb / 2.

  When the track pitch of the DVD 100b is Pb and n is a natural number, as shown in FIG. 7, the distance Dd between the center of the sub-spot S1c and the center of the sub-spot S2c of the laser light having the second wavelength and the sub-spot The diffractive element 10 is designed so that the distance Dd between the center of S1d and the center of the sub-spot S2d is approximately (2n−1) × Pb / 2.

  Accordingly, the track pitch of the DVD 100b is about 0.74 μm in the standard in the case of DVD-ROM, DVD ± R or DVD-RW, and therefore the distance Dd is about 1.11 μm (when n = 2). It is said. Thus, for the sub-beam, the distance Dd is about 1.5 times the track pitch Pb, so that the phase of the tracking error signal detected by the sub-spot S1c and the sub-spot S2c is inverted and the sub-spot S1d. The phase of the tracking error signal detected by the sub-spot S2d is inverted, the tracking error signal of the entire sub-beam has an amplitude of 0, and only the DC offset signal generated when the objective lens 14 is displaced in the tracking direction is detected. . A tracking error signal is detected for the main beam, and a DC offset signal is also detected. However, by canceling the DC offset signal detected by the sub beam and the DC offset signal detected by the main beam, an appropriate tracking error is detected. A signal can be detected.

  On the other hand, for the laser light having the first wavelength corresponding to the CD 100a, the distance Dc between the sub-spot S1a of the first sub-beam and the sub-spot S2a of the second sub-beam and the sub-spot S1b of the first sub-beam. Dc is calculated by Dc = (785/660) × Dd and Dd = 1.11 μm, and Dc = 1.32 μm.

  At this time, since the track pitch Pa of the CD 100a is 1.6 μm on the standard, the distance Dc is close to the track pitch Pa. Therefore, in this case, the sub-spots S1a, S1b, S2a, and S2b of the sub-beams are all positioned between the adjacent tracks T and T, and are tracked by the differential push-pull method described in “Background Art”. An error signal can be detected.

  When the DVD 100b is a DVD-RAM, the track pitch Pb 'is 1.23 [mu] m according to the standard, so the distance Dd (= 1.11 [mu] m) is close to the track pitch Pb'. Accordingly, also in this case, the sub-spots S1c, S1d, S2c, and S2d of the sub-beams are all positioned between the adjacent tracks T and T, and are tracked by the differential push-pull method described in the section “Background Art”. An error signal can be detected.

  As described above, the optical pickup 6 can improve the quality of the tracking error signal at the time of recording or reproducing the information signal with respect to the disc-shaped recording medium 100. The influence of the eccentricity of the disc-shaped recording medium 100 and the rotational deviation of the diffraction element 10 can be reduced with respect to the specific disc-shaped recording medium 100.

  Further, when performing recording or reproduction with respect to different types of disc-shaped recording media 100, the diffraction element 10 can be shared, so that the quality of the tracking error signal can be improved without increasing the number of components and increasing the cost. Improvements can be made.

  Further, since the DVD can support all of DVD-ROM, DVD ± R, DVD-RW, and DVD-RAM, the quality of the tracking error signal can be improved regardless of the type of DVD.

  In the above, when n is a natural number, the case where n = 1 or n = 2 is shown as an example, but the range in which the natural number n can be taken in the present invention is arbitrary.

  In the above, the optical pickup 6 using two wavelengths having different lengths is shown as an example, but the present invention can also be applied to an optical pickup using laser light having three or more wavelengths. When laser light having three or more wavelengths is used, the distance D between the spots of the sub-beams may be approximately (2n−1) × P / 2 in any laser light.

  The present invention can also be applied to an optical pickup that uses laser light having only one wavelength. In this case, in the laser light to be used, the distance D between the spots of the sub-beams is set to be approximately (2n−1) × P / 2.

  Therefore, even when the present invention is applied to an optical pickup that uses laser light of only one wavelength, it is possible to reduce the influence of the eccentricity of the disk-shaped recording medium and the rotational deviation of the diffraction element in detecting the tracking error signal. The quality of the tracking error signal can be improved.

  In addition, since the influence of the rotational shift of the diffraction element is reduced, it is possible to omit the rotation adjustment of the diffraction element, and it is possible to provide a low-cost and highly reliable optical pickup.

  Next, FIGS. 8 and 9 show modifications of the diffraction element.

  The diffraction element 10A shown in FIG. 8 is formed at a position where the formation positions of the first region 10c and the second region 10d are orthogonal to the formation positions of the first region 10a and the second region 10b of the diffraction element 10. Has been.

  Even when the diffraction element 10A is used instead of the diffraction element 10, the laser light is divided into a main light beam and two pairs of sub light beams, and the main spot and two pairs of sub light beams are recorded on the recording surface of the disk-shaped recording medium 100. Spots can be formed.

  In the diffractive element 10B shown in FIG. 9, a plurality of first regions 10e, 10e,... And a plurality of second regions 10f, 10f,. .. And the second regions 10f, 10f,... Are tangential to the disc-shaped recording medium 100.

  In the diffractive element 10B, the number of divided regions is larger than that of the diffractive elements 10 and 10A.

  Here, in general, in an optical pickup, the light emitting element and the objective lens are not arranged close to each other but are spaced apart from each other, so that the opening of the objective lens for the laser light emitted from the light emitting element is provided. There may be a difference in the amount of light between the sub-beams irradiated on the recording surface of the disk-shaped recording medium due to the influence of the incident angle, the incident position and the diffraction on the recording medium. For example, when one sub-beam is entirely incident on the aperture of the objective lens, the other sub-beam is incident on a position outside the aperture and the other is incident on the aperture. There will be a difference between the light quantity of one sub-spot formed on the recording surface and the light quantity of the other sub-spot.

  However, like the diffractive element 10B, by increasing the number of divided regions, the laser light R can be divided into a plurality of first regions 10e, 10e,... And a plurality of second regions 10f, 10f,. And the second area for generating the second sub-beam in the laser beam R and the total area of the first regions 10e, 10e,... That generate the first sub-beam in the laser beam R. The total area of the regions 10f, 10f,. Accordingly, the light amounts of the sub-spots S1 and the sub-spots S2 that are formed in the substantially radial direction of the disc-shaped recording medium 100 are substantially equal, and the tracking error signal detected from each sub-beam can be reliably canceled. Thus, the reliability of the tracking control operation can be improved.

  Further, during the tracking control operation, the objective lens 14 is moved in the substantially radial direction of the disc-shaped recording medium 100. Therefore, as described above, the first regions 10e, 10e,. , 10f,... By making the direction of alignment with the tangential direction relative to the laser light R and the first regions 10e, 10e,... And the second regions 10f, 10f,. There is no change in position, and there is no adverse effect on sub-beam generation.

  Further, since the push-pull signal is changed in the substantially radial direction of the disc-shaped recording medium 100, as described above, the first regions 10e, 10e,... And the second regions 10f, 10f,. By making the arrangement direction of the tangential direction, the relationship between the main beam and the original laser beam before diffraction does not change, and the modulation is not adversely affected.

  The specific shapes and structures of the respective parts shown in the above-described best mode are merely examples of the implementation of the present invention, and the technical scope of the present invention is limited by these. It should not be interpreted in a general way.

2 to 9 show the best mode for carrying out the present invention, and this figure is a schematic perspective view of a disk drive device. FIG. It is a conceptual diagram which shows the structure of an optical pick-up. It is a conceptual diagram which shows a diffraction element. It is a conceptual diagram showing the positional relationship between the spot of the laser beam corresponding to the CD and the track when the distance between the sub-spots is set to half the track pitch for the laser beam corresponding to the CD. It is a graph which shows a tracking error signal. It is a conceptual diagram showing the positional relationship between a spot of a laser beam corresponding to a DVD and a track when the distance between the sub-spots is set to one half of the track pitch for the laser beam corresponding to the CD. It is a conceptual diagram showing the positional relationship between a spot of a laser beam corresponding to a DVD and a track when the distance between the sub-spots is set to one half of the track pitch for the laser beam corresponding to the DVD. It is a conceptual diagram which shows the modification of a diffraction element. It is a conceptual diagram which shows another modification of a diffraction element. It is a conceptual diagram which shows the state of the spot of the laser beam at the time of using the differential push pull method in the conventional optical pick-up. It is a graph which shows the tracking error signal at the time of using the differential push pull method in the conventional optical pick-up. It is a graph which shows the conventional problem.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Disc-shaped recording medium, 1 ... Disc drive apparatus, 3 ... Disc table, 6 ... Optical pick-up, 7 ... Moving base, 8 ... Objective lens drive device, 9 ... Light emitting element, 10 ... Diffraction element, 10a ... 1st Area, 10b ... second area, 10c ... first area, 10d ... second area, 10e ... first area, 10f ... second area, 14 ... objective lens, 10A ... diffraction element, 10B ... diffraction element

Claims (16)

An optical pickup that moves in a radial direction of a disk-shaped recording medium mounted on a disk table and irradiates the disk-shaped recording medium with a laser beam emitted from a light emitting element through an objective lens,
A diffractive element having a plurality of regions for dividing laser light emitted from the light emitting element into a main light beam, a pair of first sub light beams, and a pair of second sub light beams;
Let D be the distance between the spot center of the first sub-beam and the spot center of the second sub-beam formed on the recording surface of the disk-shaped recording medium so as to be separated from each other in the substantially radial direction of the disk-shaped recording medium. An optical pickup characterized in that the distance D is approximately (2n-1) × P / 2 where is a natural number and the track pitch of the disk-shaped recording medium is P. The first sub-beam and the second sub-beam are formed on the recording surface of the disk-shaped recording medium so as to be separated from each other in the substantially radial direction of the disk-shaped recording medium, so that the amount of light is substantially the same. The optical pickup according to claim 1, wherein the plurality of regions are formed in a diffraction element. The optical pickup according to claim 1, wherein an arrangement direction of the plurality of regions of the diffraction element is a tangential direction of the disc-shaped recording medium. The optical pickup according to claim 2, wherein an arrangement direction of the plurality of regions of the diffraction element is a tangential direction of the disc-shaped recording medium. Information signals can be recorded on or reproduced from a plurality of types of disc-shaped recording media having different wavelengths, and the disc-shaped recording media mounted on the disc table move in the radial direction and emit light to the disc-shaped recording media. An optical pickup that emits laser light emitted from the element and having a wavelength corresponding to the type of the disk-shaped recording medium, through an objective lens,
A diffractive element having a plurality of regions that divide laser beams of different wavelengths emitted from the light emitting element into a main light beam, a pair of first sub light beams, and a pair of second sub light beams,
The distance between the spot center of the first sub-beam and the spot center of the second sub-beam formed on the recording surface of any one type of disk-shaped recording medium and spaced apart in the substantially radial direction of the disk-shaped recording medium The distance D is approximately (2n−1) × P / 2, where D is D, n is a natural number, and the track pitch of any one type of disk-shaped recording medium is P. And optical pickup. The first sub-beam and the second sub-beam are formed on the recording surface of the disk-shaped recording medium so as to be separated from each other in the substantially radial direction of the disk-shaped recording medium, so that the amount of light is substantially the same. The optical pickup according to claim 5, wherein the plurality of regions are formed in a diffraction element. The optical pickup according to claim 5, wherein an arrangement direction of the plurality of regions of the diffraction element is a tangential direction of the disc-shaped recording medium. The optical pickup according to claim 6, wherein an arrangement direction of the plurality of regions of the diffraction element is a tangential direction of the disc-shaped recording medium. A disk table mounted with a disk-shaped recording medium and rotated, and an objective lens driving device supported on a moving base and moved in the radial direction of the disk-shaped recording medium mounted on the disk table A disk drive device comprising an optical pickup for irradiating a laser beam through an objective lens,
The above optical pickup
A diffractive element having a plurality of regions for dividing laser light emitted from the light emitting element into a main light beam, a pair of first sub light beams, and a pair of second sub light beams;
Let D be the distance between the spot center of the first sub-beam and the spot center of the second sub-beam formed on the recording surface of the disk-shaped recording medium so as to be separated from each other in the substantially radial direction of the disk-shaped recording medium. Is a natural number, and the distance D is approximately (2n-1) × P / 2, where P is the track pitch of the disk-shaped recording medium. The first sub-beam and the second sub-beam are formed on the recording surface of the disk-shaped recording medium so as to be separated from each other in the substantially radial direction of the disk-shaped recording medium, so that the amount of light is substantially the same. The disk drive device according to claim 9, wherein the plurality of regions are formed in a diffraction element. The disk drive device according to claim 9, wherein an arrangement direction of the plurality of regions of the diffraction element is a tangential direction of the disk-shaped recording medium. The disk drive device according to claim 10, wherein an arrangement direction of the plurality of regions of the diffraction element is a tangential direction of the disk-shaped recording medium. Information signals can be recorded or reproduced on a plurality of types of disc-shaped recording media having different operating wavelengths, and a disc table on which the disc-shaped recording media is mounted and rotated, and an objective lens driving device is supported on the moving base. The laser beam having a wavelength corresponding to the type of the disk-shaped recording medium is emitted from the light emitting element to the disk-shaped recording medium by moving in the radial direction of the disk-shaped recording medium mounted on the disk table via the objective lens. A disk drive device comprising an optical pickup for irradiation,
The above optical pickup
A diffractive element having a plurality of regions that divide laser beams of different wavelengths emitted from the light emitting element into a main light beam, a pair of first sub light beams, and a pair of second sub light beams,
The distance between the spot center of the first sub-beam and the spot center of the second sub-beam formed on the recording surface of any one type of disk-shaped recording medium and spaced apart in the substantially radial direction of the disk-shaped recording medium The distance D is approximately (2n−1) × P / 2, where D is D, n is a natural number, and P is the track pitch of any one type of disk-shaped recording medium. Disk drive device. The first sub-beam and the second sub-beam are formed on the recording surface of the disk-shaped recording medium so as to be separated from each other in the substantially radial direction of the disk-shaped recording medium, so that the amount of light is substantially the same. The disk drive device according to claim 13, wherein the plurality of regions are formed in a diffraction element. The disk drive device according to claim 13, wherein an arrangement direction of the plurality of regions of the diffraction element is a tangential direction of the disk-shaped recording medium. The disk drive device according to claim 14, wherein an arrangement direction of the plurality of regions of the diffraction element is a tangential direction of the disk-shaped recording medium.

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