JP2013054799A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively manufacture a diffraction grating assembled in an optical pickup device which performs the readout operation of a signal by using a laser beam emitted from a two-wavelength laser diode.SOLUTION: An optical pickup device includes a diffraction grating 4 on which a first laser beam and a second laser beam emitted from a two-wavelength laser diode 1 are incident and which separates the incident laser beams into a main beam and sub-beams. The diffraction grating 4 is divided into three regions of a first diffraction region, a second diffraction region, and a third diffraction region in the arrangement direction of a first laser element 2 and a second laser element 3. The first diffraction region and the second diffraction region are utilized as a diffraction grating for the first laser beam emitted from the first laser element 2, and also the second diffraction region and the third diffraction region are utilized as a diffraction grating for the second laser beam emitted from the second laser element 3.

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, a light receiving portion corresponding to each laser beam is provided.

JP 2000-81666 A JP 2001-307369 A

  In the optical pickup device using the two-wavelength laser diode, as described in Patent Document 2, the optical system that guides the first laser beam and the second laser beam emitted from the laser diode to the objective lens is used as an optical disc. An optical system that guides return light reflected from the provided signal recording layer to the photodetector is also used.

  In the optical pickup device having such a configuration, a diffraction grating that separates the first laser beam and the second laser beam into a main beam and two sub beams is also used. For example, when a DVD standard optical disk is used, an inline type is used. When a diffraction grating is used and a CD standard optical disc is used, a simple diffraction grating is used.

  When using a diffraction grating that separates laser light of different wavelengths, which is used to read out signals recorded on optical discs with different standards, into a main beam and a sub beam, each laser uses the same diffraction region. Since it is configured to perform a diffraction operation suitable for light, the conventional diffraction grating is configured to be designed and manufactured with wavelength selectivity in order to perform a diffraction operation suitable for each wavelength. . As a result, there is a problem that the structure of the diffraction grating becomes complicated and expensive.

  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, and a diffraction grating that receives the first laser light and the second laser light emitted from the two-wavelength laser diode and separates the incident laser light into a main beam and a sub beam; The first and second diffraction regions are divided into three regions of a first diffraction region, a second diffraction region, and a third diffraction region in the arrangement direction of the one laser element and the second laser device, and the first diffraction region and the second diffraction region are divided by the first laser device. A second laser beam is used as a diffraction grating for the emitted first laser light, and the second and third diffraction regions are emitted from the second laser element. It is characterized in that it has to be used as a diffraction grating for over light.

  Further, the present invention is characterized in that the width of the second diffraction region is configured to be the same as the interval between the first laser element and the second laser element.

  The present invention is characterized in that the position of the diffraction grating is adjusted so that the center of the first laser beam is positioned on the boundary line between the first diffraction region and the second diffraction region.

  According to the present invention, the first and second laser beams emitted from the two-wavelength laser diode are incident and the diffraction grating that separates the main beam and the sub-beam into the first laser element and the second laser element in the arrangement direction. The first diffraction region and the second diffraction region are divided into three regions, a first diffraction region, a second diffraction region, and a third diffraction region, and the first diffraction region and the second diffraction region are used as a diffraction grating for the first laser light emitted from the first laser element. In addition, since the second diffraction region and the third diffraction region are configured to be used as a diffraction grating for the second laser light emitted from the second laser element, for example, a grating having a diffraction effect is formed on the resin material. The diffraction operation suitable for each laser beam of the first laser beam and the second laser beam emitted from the two-wavelength laser diode is performed with a simple configuration as described above. Can. Therefore, according to the present invention, an inexpensive optical pickup device can be manufactured.

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 diffraction grating which concerns on this invention. It is the schematic for demonstrating the 2 wavelength laser diode 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. .

  Reference numeral 9 denotes a rising mirror 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 10. Has been. The objective lens 10 focuses the incident first laser beam on the signal recording layer L1 provided on the first optical disc D1, and the second laser beam on 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 light and the second laser light emitted from the two-wavelength laser diode 1 are incident on the objective lens 10 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 10 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 lights of the first laser beam and the second laser beam reflected in this way are incident on the polarization beam splitter 6 through the objective lens 10, the rising mirror 9, 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 11 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 12 called a PDIC. It has the effect of adding astigmatism to the light and irradiating it. As such a light detector 12, a light receiving unit corresponding to each laser beam can be provided, or a common light receiving unit for receiving both laser beams can be provided, but such a technique can be used. Therefore, the description is omitted.

  As described above, the optical pickup device according to the present invention is configured. Next, the configuration of the diffraction grating 4 which is the gist of the present invention will be described with reference to FIGS.

  FIG. 3 illustrates the positional relationship between the first laser element 2 and the second laser element 3 incorporated in the two-wavelength laser diode 1, and as illustrated, they are spaced apart by L1. Since the first laser element 2 and the second laser element 3 are manufactured by a monolithic technique, the distance L1 between them is extremely accurate, and the first laser light that is a laser beam for DVD and the CD laser beam. In the two-wavelength laser diode that generates and emits the second laser light, which is the laser light, the length is about 110 μm.

  FIG. 2 shows a diffraction grating 4 according to the present invention. The first diffraction region 4A and the second diffraction are arranged in the arrangement direction of the first laser element 2 and the second laser element 3 incorporated in the two-wavelength laser diode 1. FIG. The region is divided into three regions, a region 4B and a third diffraction region 4C. The width L2 of the second diffraction region 4B is configured to be equal to the distance L1 between the first laser element 2 and the second laser element 3.

  In FIG. 2, a circle S1 indicated by a solid line indicates a cross section of the light beam of the first laser light emitted from the first laser element 2, and the center thereof is located on the boundary line between the first diffraction region 4A and the second diffraction region 4B. Is configured to do. A circle S2 indicated by a broken line indicates a light beam cross section of the second laser light emitted from the second laser element 3, and the width L2 of the second diffraction region 4B is the same as that of the first laser element 2 and the second laser beam. Since it is configured to be equal to the interval L1 of the laser element 3, the center thereof is located on the boundary line between the second diffraction region 4B and the third diffraction region 4C.

  As is apparent from the drawing, the first diffraction region 4A and the second diffraction region 4B constituting the diffraction grating 4 act as a diffraction grating for the first laser beam, and the second diffraction region 4B and the third diffraction region 4C are formed. It will act as a diffraction grating for the second laser beam. As described above, the diffraction grating 4 according to the present invention functions only as the diffraction grating for the first laser beam and the diffraction grating for the second laser beam only in the second diffraction region 4B, that is, the first diffraction region 4A and the third diffraction region. Since 4C functions as a diffraction grating dedicated to the first laser beam and the second laser beam, design and manufacture suitable for each wavelength can be performed.

  The full width at half maximum of the laser light emitted from the light emitting point of the laser diode is 15 degrees, and the distance between the light emitting point of the two-wavelength laser diode 1 and the incident surface of the diffraction grating 4 is 0.5 mm. The radius of the spot of the laser beam on the incident surface of the grating 4 is 70 μm. As a result, the spot of the first laser light irradiated and formed on the first diffraction region 4A and the second diffraction region 4B constituting the diffraction grating 4 does not protrude into the third diffraction region 4C. Similarly, the spot of the second laser light irradiated and formed on the second diffraction region 4B and the third diffraction region 4C constituting the diffraction grating 4 does not protrude into the first diffraction region 4A.

  Since the two-wavelength laser diode 2 and the diffraction grating 4 can be arranged close to each other as described above, the present invention has a great effect on reducing the thickness of the optical pickup device.

  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 Polarization beam splitter 7 1/4 wavelength plate 8 Collimate lens 10 Objective lens 12 Photodetector

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; An optical pickup device including a diffraction grating for separating the incident laser light into a main beam and a sub beam while the first laser light and the second laser light emitted from the two-wavelength laser diode are incident thereon, Is divided into three regions of a first diffraction region, a second diffraction region, and a third diffraction region in the arrangement direction of the first laser element and the second laser element, and the first diffraction region and the second diffraction region are divided into the first laser. Used as a diffraction grating for the first laser light emitted from the element, and the second and third diffraction areas are released from the second laser element. Optical pickup device characterized by being adapted for use as a diffraction grating for the second laser light. 2. The optical pickup device according to claim 1, wherein the width of the second diffraction region is configured to be equal to the interval between the first laser element and the second laser element. 3. The optical pickup device according to claim 2, wherein the position of the diffraction grating is adjusted so that the center of the first laser beam is located on a boundary line between the first diffraction region and the second diffraction region.

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