JP2011086323A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device that properly performing tracking control operation or focus control operation even when the shape of a spot radiated and formed in a photodetector is distorted due to a comma aberration generated from a half mirror. <P>SOLUTION: The optical pickup device includes a half mirror 31 which receives a laser beam radiated from a laser diode 28, reflects the laser beam toward an objective lens 35 for converging the beam on a signal recording layer L formed in an optical disk D, and transmits return light reflected from the signal recording layer L to a photodetector 36. A means for causing the photodetector 36 to generate astigmatism is fixed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical pickup apparatus that performs an operation of reading a signal recorded on an optical disc and an operation of recording a signal on the optical disc.

  2. Description of the Related Art Optical disk apparatuses that can perform signal reading operation and signal recording operation by irradiating a signal recording layer of an optical disk with laser light emitted from an optical pickup device have become widespread.

  As an optical disk apparatus, an apparatus using an optical disk called a CD or a DVD is widely used. As a laser beam for performing an operation for reading a signal recorded on a CD standard optical disk, an infrared light having a wavelength of 780 nm is used, and a laser beam for performing an operation for reading a signal recorded on a DVD standard optical disk. In this case, red light having a wavelength of 650 nm is used.

  The protective layer provided on the upper surface of the signal recording layer in the CD-standard optical disc has a thickness of 1.2 mm, and an aperture of an objective lens used for performing a signal reading operation from the signal recording layer. The number is defined as 0.45. Further, the thickness of the protective layer provided on the upper surface of the signal recording layer in the DVD standard optical disc is 0.6 mm, and the numerical aperture of the objective lens used for performing the signal reading operation from the signal recording layer Is defined as 0.6.

  In addition to such CD standard and DVD standard optical disks, Blu-ray standard optical disks have recently become widespread. Laser light having a short wavelength, for example, blue-violet light having a wavelength of 405 nm, is used as a laser light for performing an operation of reading a signal recorded on such a Blu-ray standard optical disc.

  The thickness of the protective layer provided on the upper surface of the signal recording layer in such a Blu-ray standard optical disc is 0.1 mm, and the objective lens used for performing a signal read operation from the signal recording layer is used. The numerical aperture is set to 0.85.

  FIG. 8 is a schematic diagram showing an optical system constituting an optical pickup device that performs a reproducing operation of a signal recorded on a signal recording layer L provided in an optical disc D of Blu-ray standard. The configuration of the optical pickup device will be described.

  In the figure, 1 is a laser diode that emits laser light that is blue-violet light having a wavelength of 405 nm, 2 is a diffraction grating provided at a position where the laser light emitted from the laser diode 1 is incident, The main beam as 0th order diffracted light and the sub beam as ± 1st order diffracted light are separated and generated. Reference numeral 3 denotes a half-wave plate on which the laser light transmitted through the diffraction grating 2 is incident, and has an action of adjusting the polarization direction of the laser light emitted from the laser diode 1 to linearly polarized light in the S direction or P direction. It is to be made.

Reference numeral 4 denotes a half mirror provided at a position where the laser beam transmitted through the diffraction grating 2 and the half-wave plate 3 is incident. The half mirror 4 reflects the laser beam in the direction of the optical disc D and the signal recording layer of the optical disc D. A control film that transmits the return light reflected from L is formed. Reference numeral 5 denotes a collimating lens provided at a position where the laser beam reflected by the half mirror 4 is incident, and functions to convert the incident laser beam into parallel light.

  Reference numeral 6 denotes a rising mirror that receives the laser light converted into parallel light by the collimating lens 5 and reflects the laser light, and changes the direction of the optical axis by 90 degrees. A quarter wave plate 7 is provided at a position where the laser beam reflected by the rising mirror 6 is incident. The laser beam incident from the rising mirror 6 side is circularly polarized from linearly polarized light. The return light, which is laser light incident on the light and from the opposite side, is polarized from circularly polarized light to linearly polarized light.

  An objective lens 8 is provided at a position where the laser beam transmitted through the quarter-wave plate 7 is irradiated. The objective lens 8 reproduces the laser beam by condensing the laser beam on the signal recording layer L provided on the optical disc D. Or a spot having a shape suitable for performing a recording operation. The laser beam condensed on the signal recording layer L provided on the optical disc D by the objective lens 8 is reflected by the signal recording layer L and is incident on the objective lens 8 from the optical disc D side as return light. .

  The return light incident on the objective lens 8 passes through the objective lens 8 and then enters the quarter wavelength plate 7, and is converted from circularly polarized light to linearly polarized light by the quarter wavelength plate 7. The return light polarized in this way is incident on the collimating lens 5 after being reflected by the rising mirror 6.

  The return light incident on the collimator lens 5 is transmitted through the collimator lens 5 and incident on the half mirror 4, and the return light incident on the half mirror 4 in this way is the quarter wavelength plate. Since the polarization direction of the linearly polarized light is reversed by the reciprocal transmission operation with respect to 7, the light is not reflected by the control film provided on the half mirror 4, but is transmitted through the control film.

  The half mirror 4 has an action of adding astigmatism to generate a focus error signal for performing a focus control operation on the transmitted return light, but coma aberration is generated due to its characteristics. There is a problem. Reference numeral 9 denotes an AS plate provided at a position where the return light transmitted through the half mirror 4 is incident. The astigmatism generated by the half mirror 4 has a size suitable for generating a focus error signal. The zoom lens is configured to have a function of enlarging and to correct a coma aberration generated in the half mirror 4.

  Reference numeral 10 denotes a photodetector provided at a position where the return light transmitted through the AS plate 9 is irradiated, and a focus error signal and a tracking error signal are obtained by utilizing a change in spot shape generated by irradiation. Configured to generate.

  As described above, the optical system of the optical pickup device generally used in the related art is configured. Next, the generation operation of the tracking error signal and the focus error signal will be described with reference to FIG.

  As shown in FIG. 4, the light receiving unit of the photodetector 10 is divided into a four-divided sensor unit 10a irradiated with the main beam M in the return light and a two-divided sensor unit 10b irradiated with the sub beams S1 and S2. And 10c. The quadrant sensor unit 10a is composed of sensors A, B, C, and D as shown, and the bipartite sensor units 10b and 10c are composed of a sensor EF and a sensor GH, respectively.

In such a configuration, if the spot position of the laser beam is deviated in the radial direction of the optical disc D with respect to the signal track formed in the signal recording layer L provided in the optical disc D, that is, if tracking is deviated, 4 The position of the main beam M and the positions of the sub-beams S1 and S2 irradiated on the divided sensor unit 10a and the two-divided sensor units 10b and 10c are displaced in the direction of the arrow A or B. The amount will change.

  The circuit diagram shown in FIG. 4 is for performing a tracking control operation called a differential push-pull method. In the figure, 11 is a first adder for adding signals obtained from sensors A and D irradiated with a main beam M, 12 is a second adder for adding signals obtained from sensors B and C, A first differential unit 14 subtracts an output signal obtained from the second adder 12 from an output signal of the first adder 11, and a signal 14 obtained from the sensor F from a signal obtained from the sensor E irradiated with the sub beam S1. A second differential unit 15 for subtracting is a third differential unit for subtracting a signal obtained from the sensor H from a signal obtained from the sensor G irradiated with the sub beam S2.

  16 is a third adder for adding the output signal of the second differential 14 and the output signal of the third differential 15, and 17 is the output signal of the third adder 16 multiplied by K (K is the main beam). An amplification circuit 18 for subtracting the output signal of the amplification circuit 17 from the output signal of the first differential 13. The differential signal is output from the output terminal 19 as a tracking error signal.

When the signals obtained from the sensors A, B, C, D, E, F, G, and H are A, B, C, D, E, F, G, and H, and the tracking error signal is TE, the tracking error is obtained. The signal TE is
TE = (A + D) − (B + C) −K {(E−F) + (G−H)}
The tracking error signal TE can be obtained from the circuit shown in FIG. A technique related to an optical pickup device that performs the tracking control operation by the differential push-pull method is described in Patent Document 1.

  The generation operation of the tracking error signal TE used for the tracking control operation is performed as described above. Next, the generation operation of the focus error signal FE used for the focus control operation will be described.

  In the circuit shown in FIG. 4, 20 is a fourth adder for adding signals obtained from the sensor units A and C constituting the 4-divided sensor unit 10a, and 21 is a sensor constituting the 4-divided sensor unit 10a. A fifth adder for adding the signals obtained from the parts B and D, 22 is a fifth differential for subtracting the output signal of the fifth adder 21 from the output signal of the fourth adder 20, and its output. The signal is output to the output terminal 23 as a focus error signal.

  As is well known, the focus error signal FE is expressed as FE = (A + C) − (B + D). This is based on the astigmatism generated with the displacement of the objective lens 8 in the focus direction. Is obtained by utilizing the characteristic that the shape of the shape changes from an ellipse to a circle and from a circle to an ellipse. Since the focus control operation using such a focus error signal FE is well known, its description is omitted.

  Although the conventional optical pickup device is configured as described above, the structure of the photodetector 10 used in the above-described optical pickup device will be described next.

FIG. 9 is a cross-sectional view showing a photodetector incorporated in a conventional optical pickup device, in which a light receiving element 25 constituting a sensor unit is fixed on a substrate 24 and transmitted with respect to the wavelength of laser light used. It is covered with a translucent resin 26 having a high rate. Further, extraction of a signal generated from the light receiving element 25 is performed by wire bonding, and such fixing and protection of the wire is generally performed by the transparent resin 26.

  Epoxy resin is generally used as the transmissive resin, but a laser beam having a wavelength as short as 405 nm, such as the laser diode 1 used for reading a signal recorded on a Blu-ray standard optical disc, is used. There is a problem that the transmittance decreases when irradiated. As a method for solving such a problem, generally, a method of forming a through hole 27 on the incident surface of the light receiving element 25 as shown in FIG.

JP-A-8-339556

  7A, 7B, and 7C show states in which the main beam M in the return light is irradiated to the four-divided sensor unit 10a, and FIGS. 7A and 7C show signal tracks. On the other hand, a state in which the spot position of the laser beam is shifted is shown, and (B) shows a state in which the spot of the laser beam is positioned on the signal track.

  As is clear from this figure, the spot shape of the main beam M generated by being irradiated on the four-divided sensor unit 10a is a circular shape close to a perfect circle. This is because the coma aberration that occurs is corrected. When the spot shape of the main beam M is a circular beam as described above, a well-balanced push-pull signal can be obtained, so that the tracking control operation can be performed accurately.

  In such an optical pickup device in which the AS plate 9 is incorporated, there is a problem that the tracking error signal cannot be accurately performed because an offset is generated in the tracking error signal when the surface of the AS plate 9 becomes dirty.

  In the conventional optical pickup device shown in FIG. 8, it is conceivable to delete the AS plate 9 in order to reduce the cost. When such AS plate 9 is deleted, the astigmatism expansion operation cannot be performed. Therefore, although the focus error signal generation operation is affected, the focus control operation can be performed without any trouble by devising a detection circuit. It was confirmed that it could be done.

  On the other hand, when the AS plate 9 is deleted, the coma aberration generated by the half mirror 4 cannot be corrected, so the spot of the main beam M generated by being irradiated on the four-divided sensor unit 10a. The shape is a distorted circular shape as shown in FIG. When such a distorted circular main beam is irradiated onto the quadrant sensor unit 10a, the push-pull signal, which is the signal output in the track direction, becomes unbalanced, so that an accurate tracking error signal generation operation is performed. As a result, there is a problem that the tracking control operation cannot be performed accurately, so that the cost cannot be reduced.

  The present invention is intended to provide an optical pickup device that can solve the above-described problems.

In the present invention, the laser beam emitted from the laser diode is incident and the laser beam is reflected in the direction of the objective lens for condensing the laser beam on the signal recording layer provided on the optical disc, and the return light is reflected from the signal recording layer. Is provided with a half mirror that transmits light in the direction of the photodetector, and means for generating astigmatism is fixed to the photodetector.

  Further, the present invention is characterized in that the light receiving portion provided in the photodetector is covered by means for generating astigmatism.

  The present invention is characterized in that a cylindrical lens is used as means for generating astigmatism.

  Further, the present invention is characterized in that glass is used as a material for the cylindrical lens.

  Furthermore, the present invention is characterized in that the surface of a glass cylindrical lens is covered with an epoxy resin.

  In addition, the present invention is characterized in that a light-resistant resin is used as a material for the cylindrical lens.

  The present invention is characterized in that the division in the tracking direction of the sensor unit is performed in accordance with the spot shape of the irradiated return light.

  In addition, the present invention is characterized in that the sensor unit is constituted by a four-divided sensor.

  In the present invention, the laser beam emitted from the laser diode is incident and the laser beam is reflected in the direction of the objective lens for condensing the laser beam on the signal recording layer provided on the optical disc, and the return light is reflected from the signal recording layer. In the optical pickup device having a half mirror that transmits light toward the photodetector, the means for generating astigmatism is fixed to the photodetector, so that the tracking error used for the tracking control operation even if the AS plate is deleted It is possible to generate a focus error signal used for a signal and a focus control operation.

  In the optical pickup apparatus of the present invention, the means for generating astigmatism is fixed to the photodetector, that is, the number of components of the optical system that are individually arranged and fixed is reduced, so that assembly adjustment work can be easily performed. Has the advantage.

  In the present invention, the division of the tracking direction of the sensor unit provided in the photodetector is performed according to the shape of the return light to be irradiated, so that a well-balanced push-pull signal is obtained from the sensor unit. I can do it. Therefore, according to the present invention, the tracking control operation and the focus control operation using the push-pull signal can be accurately performed even if the AS plate for correcting the coma aberration generated from the half mirror is deleted. The cost of the apparatus can be reduced.

It is the schematic which shows the optical system which comprises the optical pick-up apparatus which concerns on this invention. It is sectional drawing which shows the photodetector which comprises the optical pick-up apparatus which concerns on this invention. It is sectional drawing which shows the photodetector which comprises the optical pick-up apparatus which concerns on this invention. It is a block circuit diagram which generates a tracking error signal. It is a top view which shows one Example of the photodetector which concerns on this invention. It is a top view for demonstrating the relationship between a photodetector and a spot. It is a top view for demonstrating the relationship between a photodetector and a spot. It is the schematic which shows the optical system which comprises the conventional optical pick-up apparatus. It is sectional drawing which shows the photodetector which comprises the conventional optical pick-up apparatus.

  By providing means for generating astigmatism in a photodetector provided to generate a focus error signal for performing a focus control operation and a tracking error signal for performing a tracking control operation in an optical pickup device Assembly adjustment work of the optical pickup device can be simplified.

  FIG. 1 is a schematic view showing an optical system constituting an optical pickup device according to the present invention. In the figure, 28 is a laser diode that emits laser light that is blue-violet light having a wavelength of 405 nm, 29 is a diffraction grating provided at a position where the laser light emitted from the laser diode 28 is incident, The main beam as 0th order diffracted light and the sub beam as ± 1st order diffracted light are separated and generated. Reference numeral 30 denotes a half-wave plate on which the laser light transmitted through the diffraction grating 29 is incident, and has an action of adjusting the polarization direction of the laser light emitted from the laser diode 28 to linearly polarized light in the S direction or the P direction. It is to be made.

  A half mirror 31 is provided at a position where the laser beam transmitted through the diffraction grating 29 and the half-wave plate 30 is incident. The half mirror 31 reflects the laser beam in the direction of the optical disc D and the signal recording layer of the optical disc D. A control film that transmits the return light reflected from L is formed. Reference numeral 32 denotes a collimating lens provided at a position where the laser beam reflected by the half mirror 31 is incident, and functions to convert the incident laser beam into parallel light.

  Reference numeral 33 denotes a rising mirror that receives the laser light converted into parallel light by the collimating lens 32 and reflects the laser light, and changes the direction of the optical axis by 90 degrees. Reference numeral 34 denotes a quarter-wave plate provided at a position where the laser beam reflected by the rising mirror 33 is incident. The laser beam incident from the rising mirror 33 side is changed from linearly polarized light to circularly polarized light. The return light, which is laser light incident on the light and from the opposite side, is polarized from circularly polarized light to linearly polarized light.

  Reference numeral 35 denotes an objective lens provided at a position where the laser beam transmitted through the ¼ wavelength plate 34 is irradiated. The objective lens 35 performs a reproducing operation by condensing the laser beam on the signal recording layer L provided on the optical disc D. Or a spot having a shape suitable for performing a recording operation. The laser light focused on the signal recording layer L provided on the optical disc D by the objective lens 35 is reflected by the signal recording layer L and is incident on the objective lens 35 from the optical disc D side as return light. .

  The return light incident on the objective lens 35 passes through the objective lens 35 and then enters the quarter-wave plate 34, and is converted from circularly polarized light to linearly-polarized light by the quarter-wave plate 34. The return light polarized in this way is reflected by the raising mirror 33 and then enters the collimating lens 32.

The return light incident on the collimator lens 32 passes through the collimator lens 32 and is incident on the half mirror 31. The return light incident on the half mirror 31 in this way is the quarter wavelength plate. Since the polarization direction of the linearly polarized light is reversed by the reciprocal transmission operation with respect to 34, the light is not reflected by the control film provided on the half mirror 31, but is transmitted through the control film.

  Reference numeral 36 denotes a photodetector provided at a position where the return light transmitted through the half mirror 31 is irradiated, and a focus error signal and a tracking error signal are generated by utilizing a change in the spot shape generated by irradiation. Configured to generate. As is apparent from the figure, the optical system of the optical pickup device according to the present invention increases the amount of astigmatism of the return light transmitted through the half mirror 31 and corrects coma generated in the half mirror 31. The AS board has been deleted.

  FIG. 5 shows a divided shape of the four-divided sensor unit 36a incorporated in the photodetector 36 according to the present invention so that it is divided in accordance with the spot shape of the main beam M which is a distorted circular shape. It is configured. That is, a signal obtained by adding the signal obtained from the sensor A and the signal obtained from the sensor D, the signal obtained from the sensor B, and the sensor in accordance with the spot shape generated when the return light is irradiated to the four-divided sensor unit 36a. The signal obtained by adding the signal obtained from C is divided so as to be equal. By setting the division shape of the four-divided sensor unit 36a in this way, a push for obtaining a tracking error signal even if the spot shape caused by the return light transmitted through the half mirror 31 becomes a distorted circular shape due to coma aberration. A well-balanced signal can be obtained as a pull signal.

  Therefore, according to the present invention, by removing the AS plate provided to correct the coma aberration generated from the half mirror 31, the spot shape generated by irradiating the photodetector 36 with the return light is distorted. Even if this occurs, an accurate tracking error signal generation operation can be performed.

  Further, the signal obtained by adding the signal obtained from the sensor A and the signal obtained from the sensor D constituting the four-divided sensor unit 36a, the signal obtained from the sensor B, and the signal obtained by adding the signal obtained from the sensor C are equal. In this condition, the signal obtained from the sensor A and the signal obtained from the sensor C are added, the signal obtained from the sensor B, and the signal obtained from the sensor D are added. If the signal is divided so as to be equal, the focus error signal generation operation performed using the main beam M can be performed accurately, and the focus control operation can also be performed without any trouble.

  As described above, the optical system of the optical pickup device of the present invention is configured. Next, the configuration of the photodetector 36 will be described with reference to FIGS.

  FIG. 2 is a cross-sectional view showing a photodetector 36 incorporated in the optical pickup device of the present invention. A light receiving element 38 constituting a sensor unit is fixed on a substrate 37 by a synthetic resin 39. The operation of extracting the signal generated from the light receiving element 38 is performed by wire bonding, and the fixing and protecting of the wire is performed by the synthetic resin 39.

  A cylindrical lens 40 is disposed on the light receiving element 38 on the side where the return light is incident and generates astigmatism. The cylindrical lens 40 is provided as a cover at a position covering the opening 41 of the light receiving element 38. That is, the return light transmitted through the half mirror 31 is irradiated to the light receiving element 38 through the cylindrical lens 40 provided in the opening 41 of the light receiving element 38 provided in the photodetector 36. Return light with astigmatism generated and added by the cylindrical lens 40 is irradiated to the light receiving element 38.

Therefore, each signal suitable as a tracking error signal used for the tracking control operation or a focus error signal used for the focus control operation is generated from the four-divided sensor unit and the two-divided sensor unit provided in the light receiving element 38. I can do it.

  In this embodiment, a cylindrical lens is used as the cover 40. However, when glass is used as the material of such a cylindrical lens, the lens made of glass is resistant to short-wavelength laser light such as blue-violet laser light. However, since the light resistance is high, good characteristics can be maintained for a long time.

  FIG. 3 shows an embodiment in which a glass cylindrical lens is used as the cylindrical lens 40, and the surface of the cylindrical lens 40 is covered with an epoxy resin 42. In such a case, both can be integrated by using an epoxy resin as the synthetic resin 39 for fixing the light receiving element 38 and the like.

  In this embodiment, the case where the AS plate is used as the optical component provided to correct the coma generated in the return light transmitted through the half mirror has been described. However, the optical component called an anamorphic lens may be deleted. Can respond.

  Further, the case where glass is used as the material of the cylindrical lens 10 has been described. However, a synthetic resin material having high light resistance that can ignore the influence of blue-violet laser light, for example, light resistance called ZEONEX 340R manufactured by ZEON Corporation. Of course, it is possible to use a resin.

  As the cylindrical lens 40 fixed to the photodetector 36, a toric lens as well as a convex lens and a concave lens can be used.

  INDUSTRIAL APPLICABILITY The present invention can be implemented not only in an optical pickup device that performs a read operation of a signal recorded on a Blu-ray standard optical disc D, but also in an optical pickup device used for an optical disc of a DVD standard or a CD standard. It can also be applied to.

28 Laser Diode 29 Diffraction Grating 30 1/2 Wave Plate 31 Half Mirror 32 Collimating Lens 34 1/4 Wave Plate 35 Objective Lens 36 Photodetector 38 Light Receiving Element 40 Cylindrical Lens D Optical Disk

Claims (8)

The laser beam emitted from the laser diode is incident, and the laser beam is reflected in the direction of the objective lens for focusing on the signal recording layer provided on the optical disc, and the return light reflected from the signal recording layer is detected by the photodetector. An optical pickup device comprising a half mirror that transmits light in the direction, and means for generating astigmatism is fixed to the photodetector. 2. The optical pickup device according to claim 1, wherein a light receiving portion provided in the photodetector is covered with means for generating astigmatism. 2. The optical pickup device according to claim 1, wherein a cylindrical lens is used as means for generating astigmatism. The optical pickup device according to claim 2, wherein glass is used as a material of the cylindrical lens. The optical pickup device according to claim 4, wherein the surface of the cylindrical lens is covered with an epoxy resin. 4. The optical pickup device according to claim 3, wherein a light-resistant resin is used as a material for the cylindrical lens. 2. The optical pickup device according to claim 1, wherein the division of the sensor unit in the tracking direction is performed in accordance with the spot shape of the return light to be irradiated. The optical pickup device according to claim 7, wherein the sensor unit is configured by a four-divided sensor.

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