JP2013008405A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct a focus error offset that occurs in an optical pickup arranged to perform reading operation of a signal by laser beams emitted from a two wavelength laser diode.SOLUTION: An optical pickup device includes: an objective lens 11 that collects, on a signal recording layer, a first laser beam and a second laser beam that have been converted into parallel light beams by a collimator lens 8 on which the first laser beam and the second laser beam emitted from a two wavelength laser diode 1 are projected; and a photodetector 13 on which a first light receiving unit on which return light reflected from a first optical disk D1 is projected and a second light receiving unit on which return light reflected from a second optical disk D2 is projected are formed and incorporated on the same substrate. By displacing the collimator lens 8 in an optical axis direction, a focus error offset that occurs in the first light receiving unit or the second light receiving unit is corrected.

Description

  The present invention relates to an optical pickup device configured to be able to read a signal recorded on an optical disc or record a signal on an 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 the optical pickup device configured to perform the reading operation of the signal recorded on the optical disc of the CD standard and the reading operation of the signal recorded on the optical disc of the DVD standard by the focusing operation of the same objective lens, The light beam of the laser beam incident on the objective lens is limited in accordance with the numerical aperture according to the laser wavelength of the laser diode to be used.

In order to perform the numerical aperture changing operation, a wavelength selection filter is used, an aperture stop having a different aperture diameter is mechanically reduced, or a liquid crystal shutter is used. In addition, as a method for reading out signals recorded on optical discs of the CD standard and DVD standard using the same objective lens, a method using an objective lens having a diffraction ring formed on the surface is often adopted. Yes. (See Patent Document 1)
An optical pickup device configured to be able to read out signals recorded on optical disks of different standards described above incorporates two laser diodes that emit laser beams of different wavelengths. In order to simplify the configuration, a first laser element that emits first laser light and a second laser element that emits second laser light having a wavelength different from that of the first laser light are provided in the same package. Those using laser diodes called two-wavelength laser diodes have been commercialized.

  The optical pickup device using the above-described two-wavelength laser diode causes the laser spot generated by the focusing operation of the objective lens to be focused on the signal recording layer provided on the optical disc and to follow the signal track. A photodetector for receiving the return light reflected from the signal recording layer in order to generate a control signal for performing a tracking control operation, that is, a focus error signal or a tracking error signal, is provided. As described in Patent Document 2 and Patent Document 3, a light receiving unit corresponding to each laser beam is provided.

JP 2000-81666 A JP 2001-307362 A Japanese Patent Laid-Open No. 2004-22051

  In an optical pickup device using a two-wavelength laser diode, it also serves as an optical system for guiding the first laser light and the second laser light emitted from the laser diode to the objective lens and is reflected from the signal recording layer provided on the optical disk. And an optical system that guides the return light to the photodetector.

  In the two-wavelength laser diode, the first laser element that generates and emits the first laser light and the second laser element that generates and emits the second laser light are arranged in the same package. Are not identical but very small but far apart.

  As described above, since the position of the light emitting point of the first laser element and the position of the light emitting point of the second laser element are different, in the optical pickup device sharing the same optical system, the optical axis is shifted. Become. In addition, since the refractive indexes of the lenses and prisms constituting the optical system are different, a focus error offset is generated in the laser spot irradiated and generated on the light receiving unit provided for each laser beam in the photodetector.

  Conventionally, such a focus error offset is electrically removed, so that there is a problem that not only the configuration becomes complicated but also the cost becomes high.

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

  In the present invention, a first laser element that emits a first laser beam and a second laser element that emits a second laser beam having a wavelength longer than the wavelength of the first laser beam are provided in the same package. A laser diode; a collimating lens that receives the first laser light and the second laser light emitted from the two-wavelength laser diode; and converts the incident laser light into parallel light; The converted first laser light and second laser light are incident, the first laser light is focused on a signal recording layer provided on the first optical disk, and the second laser light is standardized on the first optical disk. An objective lens for focusing on a signal recording layer provided on a second optical disc different from the above and reflected from the signal recording layer of the first optical disc The first light receiving unit that generates the focus error signal while irradiating the reflected light is the same as the second light receiving unit that receives the return light reflected from the signal recording layer of the second optical disc and generates the focus error signal. A light detector formed and incorporated on the substrate and displacing the collimating lens in the optical axis direction to correct a focus error offset generated in the first light receiving unit or the second light receiving unit. It is characterized by that.

  In the present invention, the optical design is performed with the position of the collimating lens suitable when the first laser beam is used as a reference fixing position, and the collimating lens is displaced from the reference fixing position when the second laser beam is used. It is characterized by comprising.

  The present invention is characterized in that the objective lens is optically designed so as to correct the spherical aberration generated when the collimating lens is displaced when the second laser beam is used.

  The present invention is a light configured to be able to read out signals recorded on optical discs of different standards by using the first laser light and the second laser light emitted from the two-wavelength laser diode. In the pickup device, the focus error offset generated in the photodetector provided to generate the focus error signal is corrected by displacing the collimating lens in the optical axis direction, that is, only the displacement operation of the collimating lens. Since the focus error offset is corrected by the above, the optical configuration of the optical pickup device can be simplified.

  In the present invention, the position of the collimating lens with respect to one laser beam is set as a reference fixed position, and the collimating lens is displaced when the other laser beam is used. Since the position of the lens is not displaced, there is an advantage that it is possible to easily control the displacement position of the collimating lens.

It is the schematic for demonstrating the optical system of the optical pick-up apparatus which concerns on this invention. It is the schematic which shows the photodetector which concerns on this invention.

  The present invention relates to an optical pickup device configured to perform a read operation of a signal recorded on an optical disc of different standards by a first laser beam and a second laser beam emitted from a two-wavelength laser diode.

  FIG. 1 shows an optical pickup configured to condense a first laser beam and a second laser beam emitted from a two-wavelength laser diode onto a signal recording layer provided on an optical disc of different standards by one objective lens. FIG. 2 is a schematic diagram for explaining an optical system of the apparatus, and in this embodiment, it is possible to perform a reading operation of signals recorded on a DVD standard first optical disc D1 and a CD standard second optical disc D2. An explanation will be given by taking the constructed optical pickup device as an example.

  In the figure, reference numeral 1 denotes a first laser element 2 that emits a first laser beam having a wavelength suitable for reading a signal recorded on a first optical disc D1 that is a DVD standard, for example, 650 nm, and a second standard that is a CD standard. A second laser element 3 that emits a second laser beam having a wavelength suitable for reading a signal recorded on the optical disc D2, for example, 780 nm, is disposed on the same substrate and provided in the same package. This is a two-wavelength laser diode.

  Reference numeral 4 denotes a diffraction grating on which the first laser light and the second laser light emitted from the two-wavelength laser diode 1 are incident and which has a diffracting action on the first laser light and the second laser light. The main beam that is zero-order light and the sub-beam that is ± first-order light are separated.

  Reference numeral 5 denotes a half-wave plate that receives laser light that has passed through the diffraction grating 4 and converts the laser light into P-polarized light, and reference numeral 6 denotes a first laser that passes through the diffraction grating 4 and the half-wave plate 5. A polarization beam splitter into which the light and the second laser light are incident, and a control film 6a that reflects P-polarized light and transmits S-polarized light is provided.

  Reference numeral 7 denotes a quarter-wave plate on which the first laser light and the second laser light reflected by the control film 6a provided on the polarizing beam splitter 6 are incident. The incident laser light is converted into linearly polarized light. The light is converted from circularly polarized light to circularly polarized light and vice versa. A collimating lens 8 receives the first laser light and the second laser light transmitted through the quarter-wave plate 7 and converts the incident light from diverging light to parallel light, and conversely from parallel light to convergent light. The motor 9 is configured to be displaced in the optical axis direction, that is, in the directions of the arrows A and B, by the rotational driving force of the motor 9.

  A rising mirror 10 is provided at a position where the first laser light and the second laser light transmitted through the collimating lens 8 are incident, and is configured to reflect the incident laser light toward the objective lens 11. Has been. The objective lens 11 condenses the incident first laser beam on the signal recording layer L1 provided on the first optical disc D1, and the signal recording layer L2 provided on the second optical disc D2. A diffracting ring zone or the like is formed on the incident surface so that the light is condensed.

  Since the first laser beam and the second laser beam emitted from the two-wavelength laser diode 1 are incident on the objective lens 11 through the optical path constituted by the optical components described above, the signal recording layer L1 of the first optical disc D1 and The first laser beam and the second laser beam are collected by the focusing operation of the objective lens 11 on the signal recording layer L2 of the second optical disc D2, and a laser spot suitable for reading the signal recorded on each optical disc is generated. Is done.

  With this operation, a laser spot is generated on the signal recording layer L1 of the first optical disc D1 and the signal recording layer L2 of the second optical disc D2. At the same time, each laser beam is emitted from the signal recording layer L1 and the signal recording layer L2. It will be reflected as return light.

  The return light of the first laser beam and the second laser beam reflected in this way is incident on the polarization beam splitter 6 through the objective lens 11, the rising mirror 10, the collimator lens 8 and the quarter wavelength plate 7. become. Since such return light is converted into linearly polarized light in a different direction, that is, S-polarized light by the phase changing operation by the quarter wavelength plate 7 as is well known, the control film 6a of the polarization beam splitter 6 is used. The light passes through the control film 6a without being reflected.

  Reference numeral 12 denotes an anamorphic lens into which laser light transmitted through the control film 6a of the polarizing beam splitter 6 is incident as control laser light. The control laser is applied to a light receiving portion provided in a photodetector 13 called a PDIC. It has the effect of adding astigmatism to the light and irradiating it.

  The light detector 13 incorporates a light receiving section as shown in FIG. 2, and the configuration of the light receiving section will be described next.

  In FIG. 2, 13A irradiates and generates the first laser main beam DM in the return light that is the reflected light of the first laser light focused and irradiated on the signal recording layer L1 provided on the first optical disc D1. The first laser main beam detectors 13B and 13C are the first laser sub-beams in the return light, which is the reflected light of the first laser light focused on the signal recording layer L1 provided on the first optical disc D1. The first laser sub-beam first light-receiving unit and the first laser sub-beam second light-receiving unit irradiated with and generated by the DS1 and the first laser sub-beam DS2, and the first laser main beam light-receiving unit 13A arranged linearly. The signal recording layer of the first optical disc D1 is formed by the first light receiving portion 13B for the first laser sub beam and the second light receiving portion 13C for the first laser sub beam. Is the return light reflected from 1 is configured to form a first light receiving portion P1 to be irradiated.

  Reference numeral 13a denotes a second laser main that is irradiated with the second laser main beam CM in the return light that is the reflected light of the second laser light focused and irradiated on the signal recording layer L2 provided on the second optical disc D2. The beam receivers 13b and 13c are the second laser sub-beam CS1 and the second laser beam in the return light, which is the reflected light of the second laser beam focused on the signal recording layer L2 provided on the second optical disc D2. The second laser sub-beam first light-receiving unit and the second laser sub-beam second light-receiving unit irradiated with the laser sub-beam CS2 and arranged in a straight line, the second laser main beam light-receiving unit 13a and the second laser Reflected from the signal recording layer L2 of the second optical disk D2 by the first light receiving portion 13b for the sub beam and the second light receiving portion 13c for the second laser sub beam. That return light is configured to form a second light receiving portion P2 to be irradiated.

  Reflected from the signal recording layer L2 provided on the first light receiving portion P1 and the second optical disc D2 irradiated with the return light of the first laser light reflected from the signal recording layer L1 provided on the first optical disc D1. The second light receiving part P2 irradiated with the return light of the second laser light is configured as described above. The first light receiving part P1 and the second light receiving part P2 are arranged as shown in FIG. 2, and the arrangement interval is the first laser element 2 and the second laser diode 2 incorporated in the two-wavelength laser diode 1. It is set based on the interval between the light emitting points of the two laser elements 2.

  The first light receiving part P1 and the second light receiving part P2 provided in the photodetector 13 are arranged based on the interval between the light emitting points of the first laser element 2 and the second laser element 2 as described above. Since the refractive index of the optical element such as the lens and the polarizing beam splitter 6 constituting the optical system through which both the first laser beam and the second laser beam pass differs depending on the wavelength difference between the first laser beam and the second laser beam. The first laser main beam DM, the first laser sub-beam DS1, and the first laser sub-beam DS2 generated by the return light of the laser beam are used as the first laser main beam light receiving unit 13A, the first laser sub beam first light receiving unit 13B, and The first laser sub-beam second light receiving unit 13C is irradiated and generated in an optimal state, and the second laser beam is generated by the return light of the second laser beam. The laser main beam CM, the second laser sub beam CS1, and the second laser sub beam CS2 are supplied to the second laser main beam light receiving unit 13a, the second laser sub beam first light receiving unit 13b, and the second laser sub beam second light receiving unit 13c. It was not possible to generate the irradiation in the optimal state.

  A two-wavelength laser diode 1, a first light receiving part P1, and a second light receiving element in which a first laser element and a second laser element that generate and emit first laser light and second laser light having different wavelengths are incorporated in the same package. In the optical pickup device in which the light detector 13 in which the part P2 is arranged on the same substrate is incorporated, as described above, each light receiving part is irradiated with the deviation of the optical axis or the refractive index of each laser light. A phenomenon called a focus error offset occurs because the irradiation and condensing state of the generated main beam and sub beam cannot be optimized.

  If a focus error offset occurs in the first light receiving part P1 and the second light receiving part P2, it is impossible to generate an accurate focus error signal from each light receiving part, so that the focus control operation and the second laser when using the first laser light are not possible. There is a problem that the focus control operation cannot be accurately performed when using light.

  The object of the present invention is to solve the problem that the focus control operation cannot be performed accurately due to the occurrence of such a focus error offset. The motor 9 of the collimator lens 8 is used to correct the focus error offset. This is characterized in that it is carried out by a displacement operation in the direction of the optical axis by the rotation operation.

  The present invention fixes the focus error by fixing the collimating lens 8 at the reference position for the first laser light having a short wavelength and displacing the collimating lens 8 in the optical axis direction for the second laser light. This is intended to suppress the occurrence of offset.

  That is, when the first laser beam is used, the collimating lens 8 is fixed at the reference fixed position, and under such conditions, each light receiving unit constituting the first light receiving unit P1 incorporated in the photodetector 13 is used. On the other hand, the optical design is performed for all the optical elements constituting the optical pickup device so that a focus error offset does not occur. By performing such an optical design, it is possible to accurately perform a focus error signal generation operation that can perform a focus control operation without any trouble when the first laser beam is used without performing a displacement operation of the collimating lens 8.

  When the second laser beam is used, the focus error offset generated in the second light receiving unit P2 is corrected by displacing the collimating lens 8 in the optical axis direction by the rotational driving operation of the motor 9 when using the first laser beam. It is configured as follows. That is, the collimating lens 8 is displaced in the optical axis direction, that is, in the direction of the arrow A or the direction of the arrow B, so that the light flux of the second laser light is converted and adjusted in the diverging direction or the convergence direction.

  When the light beam direction of the second laser light is converted and adjusted to the divergence direction or the convergence direction by the displacement operation of the collimator lens 8 in the optical axis direction, each light receiving unit constituting the second light receiving unit P2 is irradiated and generated. Since the condensing positions of the two-laser main beam CM, the second laser sub-beam CS1, and the second laser sub-beam CS2 change, it can be adjusted to a state without a focus error offset.

  As described above, when the second laser beam is used, the focus error offset generated in the second light receiving portion P2 can be corrected by the displacement operation of the collimating lens 8 in the optical axis direction. It is possible to accurately perform a focus error signal generation operation that can perform a focus control operation without any trouble when using a laser beam.

  When the light beam direction of the second laser light is converted and adjusted to the divergence direction or the convergence direction by the displacement operation of the collimator lens 8 in the optical axis direction, the second laser light incident on the objective lens 11 is not parallel light. In such a case, spherical aberration occurs in the laser spot condensed and generated on the signal recording layer L2 provided on the second optical disc D2 by the objective lens 11. Therefore, in the present invention, an optical design for correcting such spherical aberration is performed on the diffraction zone formed in the objective lens 11. That is, by performing such an optical design, it is possible to correct the spherical aberration that occurs due to the displacement operation of the collimating lens 8 in the optical axis direction when the second laser beam is used, and it is provided in the second optical disc D2. The shape of the laser spot condensed and generated on the signal recording layer L2 can be made suitable for the signal reading operation.

  In this embodiment, the collimator lens 8 is fixed at the reference position when the first laser beam is used, and the collimator lens 8 is displaced to a position where the focus error offset is corrected when the second laser beam is used. It is also possible to fix the collimating lens 8 at the reference position when using the laser beam and to displace the collimating lens 8 to a position for correcting the focus error offset when using the first laser beam.

  The present invention is applied not only to an optical pickup device that performs a read operation of a signal recorded on an optical disc of DVD standard and CD standard, but also to an optical pickup device that performs a read operation of a signal recorded on an optical disc of a different standard. I can do it.

DESCRIPTION OF SYMBOLS 1 2 wavelength laser diode 2 1st laser element 3 2nd laser element 4 Diffraction grating 6 Polarizing beam splitter 7 1/4 wavelength plate 8 Collimate lens 11 Objective lens 13 Photodetector P1 1st light-receiving part P2 2nd light-receiving part

Claims (3)

A two-wavelength laser diode in which a first laser element that emits a first laser beam and a second laser element that emits a second laser beam having a wavelength longer than the wavelength of the first laser beam are provided in the same package; A collimating lens that converts the incident laser light into parallel light upon incidence of the first laser light and the second laser light emitted from the two-wavelength laser diode, and the first laser light converted into parallel light by the collimating lens. The first laser beam and the second laser beam are incident, the first laser beam is focused on the signal recording layer provided on the first optical disc, and the second laser beam is different from the standard of the first optical disc. An optical pickup device having an objective lens for focusing on a signal recording layer provided on an optical disc, and recording signals on the first optical disc The first light receiving unit that irradiates the return light reflected from the light source and generates a focus error signal and the second light receiving unit that irradiates the return light reflected from the signal recording layer of the second optical disc and generates the focus error signal Includes a photodetector formed on the same substrate, and corrects a focus error offset generated in the first light receiving unit or the second light receiving unit by displacing the collimating lens in the optical axis direction. An optical pickup device characterized by that. The optical design is performed with the position of the collimating lens suitable for using the first laser light as a reference fixed position, and the collimating lens is displaced from the reference fixed position when using the second laser light. The optical pickup device according to claim 1. 3. The optical pickup device according to claim 2, wherein the objective lens is optically designed so as to correct spherical aberration that occurs in association with the displacement of the collimating lens when the second laser light is used.

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