JP2006338826A - Optical apparatus, optical pickup apparatus and optical disk apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain highly accurate and stable tracking operation. <P>SOLUTION: An optical apparatus comprises a light source 23 for emitting light, a diffraction grating 311 for dividing outgoing light emitted from the light source 23 into a main beam and two sub-beams, a hologram 312 for diffracting the return lights of the main beam and the sub-beams, and a light receiving part 25 for receiving the diffracted beams diffracted by the hologram 312; where the hologram 312 diffracts the return light of each sub-beam and divides the diffracted beam into two diffracted beams and the sizes and positions of light receiving areas of photodetectors 252b, 252c for receiving the diffracted beams of the return lights of the sub-beams in the light receiving part 25 are set so as to include a beam spot separated from the diffracted beam of the return light of the main beam out of respective beam spots based on the two diffracted beams. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical device, an optical pickup device, and an optical disk device. Specifically, the return light of the sub beam is diffracted and divided into a plurality of diffracted lights, and the light receiving region of the light receiving unit that receives the diffracted lights has a size and a size so as to include a beam spot based on a part of the divided diffracted lights. The position is set and the tracking error is detected.

  Conventionally, in an optical pickup device used for recording and / or reproducing information on an optical disc such as a CD (Compact Disc) or a DVD (Digital Versatile Disc), information is recorded on or recorded on the optical disc. In order to reproduce information, an optical device having a light source that emits laser light and a light receiving unit that receives return light from the optical disk is provided. In addition, the optical pickup device includes a diffractive objective lens for condensing the laser light emitted from the optical device on a recording surface of a CD and a DVD, a focusing direction parallel to the optical axis of the objective lens, and an objective lens. A lens driving mechanism is provided for driving and displacing the objective lens in a tracking direction orthogonal to the optical axis to focus the laser beam at a desired position on the recording surface of the optical disk.

  The optical device is provided with a semiconductor laser element that emits laser light on a substrate, such as the optical integrated unit of the invention of Patent Document 1, and a light receiving unit used when the optical disk is a CD on the substrate. And a light receiving unit used when the optical disk is a DVD. Furthermore, an inclined mirror for changing the emitting direction of the laser light is formed. In order to change the emission direction of the laser beam, a prism mirror or the like is also placed at a position facing the semiconductor laser element.

JP 2001-102676 A

  By the way, when detecting a tracking error by the three-beam method, as in the invention of Patent Document 1, minus first-order diffracted light obtained by diffracting the sub-beam by the hologram element is irradiated to the light-receiving area corresponding to the sub-beam of the light receiving unit. To do. At this time, if the size and position of the light receiving region corresponding to the sub beam of the light receiving unit are not set so that all the beam spots based on the minus first-order diffracted light are included, a tracking error cannot be detected correctly.

  Here, if the size of the light receiving region is set so that all beam spots based on the minus first-order diffracted light are included, the size of the light receiving region is increased. For this reason, the reflected light from the diffractive objective lens and stray light generated by irregular reflection in the optical device are likely to be incident on the light receiving area, and when this reflected light or stray light is incident on the light receiving area, a tracking error is detected. An error occurs in the result, and the tracking operation cannot be performed correctly. In addition, the reflected light and stray light incident on the light-receiving area change due to variations during assembly of the optical device, variations in the characteristics of the components that make up the optical device, eccentricity of the optical disk, lens shift of the objective lens, etc. The error detection result is likely to fluctuate and the tracking operation may become unstable.

  Therefore, the present invention provides an optical device, an optical pickup device, and an optical disk device that enable stable tracking operation with high accuracy.

  In the optical device, the optical pickup device, and the optical disk device according to the present invention, a light source that emits light, a first diffraction element that divides the emitted light emitted from the light source into a main beam and two sub beams, a main beam, A second diffractive element that diffracts the return light of the sub beam and a light receiving unit that receives the diffracted light diffracted by the second diffractive element are provided, and the second diffractive element diffracts the return light of the sub beam. The light receiving area that divides into a plurality of diffracted lights and receives the diffracted light of the return light of the sub beam in the light receiving unit is set in size and position so as to include a beam spot based on a part of the divided diffracted lights. For example, the second diffractive element has first and second diffractive regions, and diffracted return light is generated by the first and second diffractive regions to generate two diffracted beams. Of these two diffracted lights, the size and position are set so as to include a beam spot based on the diffracted light separated from the diffracted light of the return light of the main beam.

  According to this invention, the return light of the sub beam is diffracted by the second diffraction element and divided into a plurality of diffracted lights. In addition, the size and position of the light receiving region that receives the diffracted light of the return light of the sub beam in the light receiving unit is set so as to include a beam spot based on a part of the divided diffracted light. Therefore, in the light receiving region that receives the diffracted light of the sub-beam return light, the reflected light from the diffractive objective lens and the optical device are compared with the case where the size is set so as to include all the diffracted light of the sub-beam return light. It becomes difficult for the stray light inside to enter, and a stable and accurate tracking operation can be performed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the optical disc apparatus according to the present invention, a CD (Compact Disc) and a DVD (Digital Versatile Disc) are applied as optical discs.

  FIG. 1 shows a schematic configuration of an optical system provided in the optical pickup device. The optical pickup device 10 includes a light source that emits laser light and a light receiving unit that receives return light from the optical disk in order to record information on the optical disk 50 and to reproduce the recorded information. An optical device 20 is provided. In addition, the optical pickup device 10 is provided with a lens unit for condensing the laser light emitted from the optical device 20 on the recording surfaces of CDs and DVDs.

  The lens unit includes a collimator lens 41 and an objective lens 42. The collimator lens 41 converts the laser light emitted from the optical device 20 into parallel light. The collimator lens 41 condenses the return light from the optical disk 50 on the optical device 20.

  The objective lens 42 is a diffractive objective lens, and focuses the laser light from the optical device 20 on the recording surface of the optical disk 50 regardless of whether the optical disk 50 is a CD or a DVD. Further, the objective lens 42 condenses the return light from the optical disk 50 on the optical device 20 via the collimator lens 41. The objective lens 42 is driven and displaced in a direction perpendicular to the optical axis direction of the objective lens 42 and the optical axis direction by a lens driving mechanism (not shown).

  A direction conversion mirror 43 is provided between the collimator lens 41 and the objective lens 42, and the direction of the laser light emitted from the optical device 20 and the return light from the optical disk 50 is converted. For example, laser light is emitted from the optical device 20 substantially parallel to the optical disk 50, and the direction of the laser light is converted to a direction perpendicular to the disk surface of the optical disk 50. Further, the return light from the optical disk 50 is converted into a direction substantially parallel to the optical disk 50. Thus, by converting the directions of the laser light emitted from the optical device 20 and the return light from the optical disc 50, the size of the optical pickup device in the direction perpendicular to the disc surface of the optical disc 50 can be reduced. . That is, the optical disk device using the optical pickup device can be thinned.

FIG. 2 shows a main configuration of the optical device. The optical device 20 is configured using an optical integrated element 21 and a hologram element 31.
In the optical integrated element 21, a light source 23 and a prism mirror 24 are placed on a semiconductor substrate 22, and a light receiving unit 25 is provided on the semiconductor substrate 22.

  The light source 23 has a so-called LOP (Laser On Photodiode) structure in which a laser diode 231 is mounted on a photodiode 232. The laser diode 231 has a predetermined wavelength corresponding to the optical disk as emitted light, for example, a laser beam LBd having a first wavelength (about 650 nm) corresponding to DVD, and a second wavelength (about 780 nm) corresponding to CD. Laser beam LBc. In the laser diode 231, the light emitting points of the laser light are provided with an interval of about 100 to 120 μm, for example. Further, the laser light LBd having the first wavelength corresponding to an optical disk having a high information recording density, that is, a DVD, is set so as to pass through the optical axis position of the optical system such as the collimator lens 41 and the objective lens 42. The laser light LBc having the second wavelength corresponding to CD passes through a position offset with respect to the optical axis position.

  The photodiode 232 is formed with a photodetector (not shown) for detecting the output of the laser beam, and the output of the laser beams LBc and LBd is controlled to a desired level using the detection result of the photodetector. Is done.

  The prism mirror 24 is provided at a position facing the laser diode 231, and converts the directions of the laser beams LBc and LBd emitted from the laser diode 231 to the direction of the hologram element 31.

  The hologram element 31 is provided between the integrated optical element 21 and the collimator lens 41 described above. The hologram element 31 is made of a transparent resin, for example. A diffraction grating 311 as a first diffraction element is provided on the surface of the hologram element 31 on the optical integrated element side. A hologram 312 as a second diffraction element is formed on the surface of the hologram element 31 on the collimator lens side.

  The diffraction grating 311 divides the laser light LBc having the second wavelength emitted from the laser diode 231 into three beams including a 0th-order light that is a main beam and ± 1st-order lights that are side beams.

  The hologram 312 transmits the laser beams LBc and LBd emitted from the laser diode 231, diffracts the return light from the optical disk 50, divides it into a plurality of diffracted lights, and guides them to the light receiving unit 25. Note that the positions of the diffraction grating 311 and the hologram 312 are set so that the diffracted light is guided to the light receiving unit 25 without passing through the diffraction grating 311. Since the hologram 312 performs a tracking operation using a phase difference method, which will be described later, when the optical disk is a DVD, the substantially circular hologram region of the hologram 312 is represented by a linear dividing line L as shown in FIG. It is divided into semicircular hologram areas 312a and 312b which are first and second diffraction areas. The hologram patterns in the hologram areas 312a and 312b are formed so that the return light from the optical disk 50 is diffracted at different diffraction angles, and the focal positions of the diffracted lights are different from each other.

  On the hologram 312, a wavelength plate that gives a phase difference of ¼ wavelength to the laser beam LBd of the first wavelength and a phase difference of 1 wavelength to the laser beam LBc of the second wavelength (see FIG. (Not shown). In this case, since the laser light LBd having the first wavelength is converted from linearly polarized light to circularly polarized light and irradiated onto the optical disk 50, variations in deflection due to differences in characteristics of the optical disk 50 are reduced, and the optical disk 50 The influence of the difference in characteristics can be reduced. The return light from the optical disk 50 is linearly polarized in the direction orthogonal to the outgoing light by the wavelength plate and is diffracted by the hologram 312. Further, for the laser light LBc having the second wavelength, since the phase difference at the wave plate is one wavelength, the polarization of the outgoing light and the return light does not change.

  The light receiving unit 25 includes a photodetector that receives diffracted light from the hologram 312. Here, when the return light of the first wavelength and the second wavelength is diffracted by the hologram 312, in consideration of the fact that the diffraction angle by the hologram 312 is proportional to the wavelength, compared with the first wavelength. A photodetector 252 that receives the diffracted light of the second wavelength, which is a long wavelength, is formed at a position farther from the laser diode 231 than the photodetector 251 that receives the diffracted light of the first wavelength.

  As shown in FIG. 4, the photodetector 251 of the light receiving section 25 has light receiving areas PDda1, PDda2, PDdb, PDdc1, PDdc2, and PDdd. Since the second wavelength laser beam LBc is divided into a main beam and two sub beams, the photodetector 252 has a main beam photodetector 252a that receives the diffracted light of the main beam and the side beam return light. A pair of side beam photodetectors 252b and 252c for receiving the diffracted light is formed. The side beam photodetectors 252b and 252c are provided so as to sandwich the main beam photodetector 252a. The main beam photodetector 252a includes light receiving areas PDca, PDcb, PDcc, and PDcd. The side beam photodetector 252b has a light receiving area PDce, and the side beam photodetector 252c has a light receiving area PDcf.

  The photodetector 251 is irradiated with a pair of semicircular beam spots based on the diffracted light obtained by diffracting the return light having the first wavelength by the hologram 312. For example, in the light receiving areas PDda1, PDda2, and PDdb of the photodetector 251, a semicircular beam spot is formed by the diffracted light obtained by diffracting the return light having the first wavelength by the hologram area 312a of the hologram 312. Similarly, in the light receiving regions PDdc1, PDdc2, and PDdd, semicircular beam spots are formed based on the diffracted light obtained by diffracting the return light having the first wavelength by the hologram region 312b of the hologram 312.

  Similarly, a pair of beam spots based on the diffracted light obtained by diffracting the return light having the second wavelength by the hologram 312 is formed on the main beam photodetector 252 a in the light receiving unit 25. The laser beam LBd having the first wavelength is set so as to pass through the optical axis position of the optical system as described above, and the laser beam LBc having the second wavelength is a position where the optical axis position is offset. It is supposed to pass through. Therefore, the beam spot formed on the photodetector 251 has a substantially semicircular shape, and the beam spot formed on the photodetector 252 has a shape obtained by cutting an inclined ellipse.

  A pair of beam spots based on the diffracted light obtained by diffracting the return light having the second wavelength by the hologram 312 is formed on the sub-beam photodetectors 252b and 252c of the light receiving unit 25. Here, a case where the size and position of the light receiving region PDce of the side beam photodetector 252b and the light receiving region PDcf of the side beam photodetector 252c are set so as to include a pair of beam spots as shown in FIG. 4A will be described. In this case, since the area of the light receiving region is large, it is easily affected by the reflected light from the diffractive objective lens 42 and the stray light in the optical device 20, and the light receiving region corresponds to the return light of the sub beam of the second wavelength. There is a tendency that a signal cannot be generated correctly.

  Therefore, the light receiving region PDce of the side beam photodetector 252b and the light receiving region PDcf of the side beam photodetector 252c are based on a plurality of diffracted lights obtained by diffracting the return light of the sub beam by the hologram 312 as shown in FIG. 4B. The size and position are set so as to include a beam spot based on a part of the diffracted light among the beam spots. For example, one of the pair of beam spots based on the diffracted light obtained by diffracting the return light of the sub beam by the hologram regions 312 a and 312 b of the hologram 312 is set to be included.

  As described above, when the setting is made so as to include one beam spot, the area of the light receiving region is reduced, so that the reflected light from the diffractive objective lens 42 and the stray light in the optical device 20 can be made difficult to enter.

  Furthermore, if the light receiving area is set so as to include only a beam spot that is distant from the main beam beam spot, a main beam size or shape changes due to a focus shift or the like. Since the influence of the beam spot of the beam on the light receiving region provided for the sub beam can be reduced, a signal corresponding to the diffracted light of the return light of the sub beam can be correctly generated in the light receiving region.

  When the light receiving regions PDce and PDcf are set so as to include one beam spot, the width in the direction (track direction) orthogonal to the beam spot alignment direction corresponds to the main beam as shown in FIG. 4C. If the size is set to be narrower than the light receiving area and the size corresponds to the beam spot, the size of the light receiving area can be made smaller than that shown in FIG. 4B, so that it is less susceptible to the influence of reflected light and stray light. When the light receiving area is reduced to a size corresponding to the beam spot, it is a matter of course that the light receiving area is set in consideration of variations in the beam spot due to component dimensional errors, assembly errors, changes in operating temperature, and the like.

  In the optical pickup device configured as described above, a so-called spot size method using a substantially semicircular beam spot is used as a method for detecting a focusing error when using a CD or DVD. A so-called phase difference method is used as a tracking error detection method when a DVD is used, and a so-called three-spot method is used as a tracking error detection method when a CD is used.

  Here, when the output signals of the light receiving areas PDda1, PDda2, PDdb, PDdc1, PDdc2, and PDdd of the photodetector 251 are SPda1, SPda2, SPdb, SPdc1, SPdc2, and SPdd, the DVD reproduction signal RF (DVD) is expressed by the equation It can be calculated by (1). Further, the focus error signal FE (DVD) can be calculated by Expression (2). Further, the tracking error signal TE (DVD) can be calculated by Expression (3).

RF (DVD) = (SPda1 + SPda2) + SPdb + (SPdc1 + SPdc2) + SPdd (1)
FE (DVD) = ((SPda1 + SPda2) + (SPdc1 + SPdc2))
-(SPdb + SPdd) (2)
TE (DVD) = ((SPda1 + SPda2) + (SPdc1 + SPdc2))
Phase comparison of (SPdb + SPdd) (3)
The outputs of the light receiving areas PDca, PDcb, PDcc, and PDcd of the main beam photodetector 252a are SPca, SPcb, SPcc, SPcd, the output of the light receiving area PDce of the side beam photodetector 252b is SPce, and the light reception of the side beam photodetector 252c. When the output of the area PDcf is SPcf, the CD reproduction signal RF (CD) can be calculated by the equation (4). Further, the focus error signal FE (CD) can be calculated by Expression (5). Further, the tracking error signal TE (CD) can be calculated by equation (6).

RF (CD) = SPca + SPcb + SPcc + SPcd (4)
FE (CD) = (SPca + SPcc) − (SPcb + SPcd) (5)
TE (CD) = SPce−SPcf (6)
Since the light receiving regions PDce and PDcf are formed so as to include a beam spot that is distant from the beam spot of the main beam in the pair of beam spots as described above, the reflected light and stray light are received by the light receiving regions PDce and PDcf. It becomes difficult to enter. Therefore, the outputs SPce and SPcf of the light receiving regions PDce and PDcf are signals that are less influenced by reflected light and stray light and are based on the diffracted light of the return light of the side beam, and can generate a correct tracking error signal. For this reason, it is possible to perform accurate and stable tracking operation.

  The optical pickup device according to the present invention has been described with respect to the case where a CD or DVD is used as an optical disc. However, for example, a CD-R (Recordable) in which information can be additionally written and information can be rewritten. Of course, the present invention may be applied to other optical disks such as CD-R (Recordable), DVD-RW (ReWritable), and magneto-optical disk.

  Next, the configuration of the main part of an optical disk device using the above-described optical pickup device will be briefly described with reference to FIG. Note that the optical pickup 61 shown in FIG. 5 has the same configuration as the optical pickup device 10 described above, and a description of the optical pickup 61 is omitted.

  The optical pickup 61 provided in the optical disk device 60 irradiates the optical disk 50 placed on the disk table 71 with laser light, and based on the return light from the optical disk 50, a focus error signal And a tracking error signal is generated and supplied to the servo circuit 62. Further, a reproduction signal is generated and supplied to the signal processing circuit 63.

  The servo circuit 62 generates a focus drive signal based on the focus error signal, supplies the focus drive signal to a lens driving mechanism (not shown) of the optical pickup 61, and condenses the laser light on the recording surface of the optical disk 50. Further, a tracking drive signal is generated based on the tracking error signal and supplied to the lens driving mechanism of the optical pickup 61 so that the irradiation position of the laser light is controlled to be held at a position on the track of the optical disk 50.

  The signal processing circuit 63 performs demodulation processing and error correction processing on the reproduction signal to generate an output signal. Further, the address information obtained by performing the demodulation process is supplied to the control circuit 65. Furthermore, the optical disk 50 placed on the disk table 71 by the spindle motor 70 is desired by generating a motor drive signal based on the synchronization signal obtained by performing the demodulation process and supplying the motor drive signal to the spindle motor 70. Rotate at a speed of. Note that when an encoded video or audio signal is recorded on the optical disk 50, a decoding process is performed, and a video signal or an audio signal after the decoding process is output.

  The control circuit 65 controls the operation of the servo circuit 62 and the signal processing circuit 63. Further, when a signal recorded on the optical disk 50 is read with the position of the optical pickup 61 fixed, for example, the irradiation position of the laser beam is out of the tracking servo range. For this reason, a feed control signal is generated and supplied to the access control circuit 68, and the feed mechanism 69 is driven by the access control circuit 68, so that the irradiation position of the laser beam is not out of the tracking servo range. The optical pickup 61 is moved in the radial direction of the optical disk 50. Further, when the control circuit 65 moves to the track position away from the laser beam irradiation position, the control circuit 65 stops the tracking servo operation and then supplies a feed control signal to the access control circuit 68 so that the laser beam irradiation position is determined. The optical pickup 61 is moved in the radial direction of the optical disk 50 so as to be a desired track position or a position near the track position. Thereafter, a tracking servo operation is started and control is performed so that the irradiation position of the laser light is held at a position on the track of the optical disk 50.

  Thus, if it is used for the optical device, the optical pickup device and the optical disk device according to the present invention, it is possible to generate a tracking error signal that is less affected by stray light in the optical device, reflected light from the objective lens, etc. A stable tracking servo operation with high accuracy can be performed, and the optical disk device can be stably operated.

It is a figure which shows schematic structure of the optical system with which an optical pick-up apparatus is provided. It is a figure which shows the principal part structure of an optical apparatus. It is a figure which shows a 2 division hologram optical element. It is a figure which shows the structure of a light-receiving part. It is a figure which shows the principal part structure of an optical disc apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Optical pick-up apparatus, 20 ... Optical apparatus, 21 ... Optical integrated element, 22 ... Semiconductor substrate, 23 ... Light source, 24 ... Prism mirror, 25 ... Light-receiving part, DESCRIPTION OF SYMBOLS 31 ... Hologram element, 41 ... Collimator lens, 42 ... Objective lens, 43 ... Direction change mirror, 50 ... Optical disk, 60 ... Optical disk apparatus, 61 ... Optical pick-up , 62 ... Servo circuit, 63 ... Signal processing circuit, 65 ... Control circuit, 68 ... Access control circuit, 69 ... Feed mechanism, 70 ... Spindle motor, 71 ... Disk Table, 231 ... Laser diode, 232 ... Photo diode, 251,252 ... Photo detector, 252a ... Main beam photo detector, 252b, 252c ... sub-beam photodetector, 311 ... diffraction grating, 312 ... hologram, 312a, 312b ··· hologram area

Claims (5)

A light source that emits light;
A first diffractive element that splits outgoing light emitted from the light source into a main beam and two sub-beams;
A second diffractive element that diffracts the return light of the main beam and the sub beam;
A light receiving portion for receiving the diffracted light diffracted by the second diffraction element,
The second diffractive element diffracts the return light of the sub beam and divides it into a plurality of diffracted lights,
An optical device characterized in that a light receiving region that receives diffracted light of the return light of the sub beam in the light receiving unit is set in size and position so as to include a part of the beam spot based on the divided diffracted light. The light receiving region that receives the diffracted light of the sub beam is a beam based on diffracted light that is separated from the diffracted light of the return light of the main beam among a plurality of diffracted lights obtained by diffracting the returned light of the sub beam. 2. The optical apparatus according to claim 1, wherein a size and a position are set so as to include a spot. The second diffractive element has first and second diffractive regions, and diffracts the return light by the first and second diffractive regions to divide the light into two diffracted light. The optical apparatus according to 1. A light source that emits light;
A first diffractive element that splits outgoing light emitted from the light source into a main beam and two sub-beams;
A lens unit for condensing the main beam and the sub beam on the optical disc, and condensing the return light of the main beam and the sub beam from the optical disc;
A second diffractive element that diffracts the return light of the main beam and the sub beam;
A light receiving portion for receiving the diffracted light diffracted by the second diffraction element,
The second diffractive element diffracts the return light of the sub beam and divides it into a plurality of diffracted lights,
In the light receiving unit, a size and a position are set so that a light receiving region that receives the diffracted light of the return light of the sub beam in order to generate a tracking error signal includes a beam spot based on a part of the divided diffracted light. An optical pickup device characterized by that. In an optical disk device comprising an optical pickup for recording and / or reproducing information with respect to an optical disk, and a disk rotation driving means for rotating the optical disk,
The optical pickup is
A light source that emits light;
A first diffractive element that splits outgoing light emitted from the light source into a main beam and two sub-beams;
A lens unit for condensing the main beam and the sub beam on the optical disc, and condensing the return light of the main beam and the sub beam from the optical disc;
A second diffractive element that diffracts the return light of the main beam and the sub beam;
A light receiving portion for receiving the diffracted light diffracted by the second diffraction element,
The second diffractive element diffracts the return light of the sub beam and divides it into a plurality of diffracted lights,
In the light receiving unit, a size and a position are set so that a light receiving region that receives the diffracted light of the return light of the sub beam in order to generate a tracking error signal includes a beam spot based on a part of the divided diffracted light. An optical disc device characterized by that.

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