WO2006013897A1

WO2006013897A1 - Optical pickup

Info

Publication number: WO2006013897A1
Application number: PCT/JP2005/014219
Authority: WO
Inventors: Hiroaki Shimozono; Kouichi Murata; Kou Ishibashi
Original assignee: Asahi Glass Company, Limited
Priority date: 2004-08-04
Filing date: 2005-08-03
Publication date: 2006-02-09
Also published as: TW200615579A

Abstract

An optical pickup in which the positional shift of a light beam spot focused on a light-receiving element due to temperature variation is prevented even if a diffraction element is employed for multiplexing. The optical pickup comprises first and second light sources (201a, 201b) emitting light beams of first and second wavelengths, a going path optical system for directing the light beams of two wavelengths toward optical discs (207, 208), light-receiving elements (210a, 210b), and a returning path optical system for directing returning light beams from the optical discs (207, 208) to the light-receiving elements (210a, 210b). The going path optical system and the returning path optical system have a going path diffraction element (202) and returning path diffraction element (209) for diffracting at least one light beam of one wavelength and having an equal grating pitch and each diffraction element (202, 209) is so structured as to diffract each light beam of the wavelength with the same order.

Description

Specification

Optical pickup device

Technical field

TECHNICAL FIELD [0001] The present invention relates to an optical pickup device that records information on or reproduces information from or on an optical recording medium (hereinafter referred to as an “optical disk” t) having a different disc thickness or recording density, such as a CD or DVD. .

Background art

[0002] Conventionally, an optical pin capable of recording information on an optical disk or reproducing information (hereinafter referred to as “recording / reproducing”), in particular, recording / reproducing on different types of optical disks such as CDs and DVDs. A backup device is known. In general, it is known that a laser light source having a wavelength of about 780 nm is necessary for recording and reproducing a CD, and a laser light source having a wavelength of about 650 nm is necessary for recording and reproducing a DVD.

[0003] Conventionally, so-called two-laser type light in which two lasers having different oscillation wavelengths are mounted in order to perform recording and reproduction on optical disks having different wavelengths of light used in this way. A pickup device has been put into practical use. Normally, this type of optical pickup device is one in which individually manufactured lasers are mounted on a single pickup. In recent years, in order to reduce the size and cost of optical pickup devices, so-called twin lasers, in which a plurality of laser diodes with different oscillation wavelengths are integrated on a single substrate, have been developed and put into practical use. Yes.

[0004] The two-laser optical pickup device as described above, or an optical pickup device equipped with a twin laser, is different because an optical system such as a collimator lens and an objective lens is commonly used at two wavelengths. It is necessary to multiplex so that the optical axes of the two light beams emitted from the light sources arranged at the positions coincide with the optical axis of the optical system. If they do not match, there is a problem that light cannot be received by a common light receiving element.

[0005] In order to solve this problem, the conventional optical pickup device uses a diffractive element for two different wavelength light beams reflected by the information recording surface of the optical disk and returns one of the wavelengths. The light beam is diffracted in the first order and transmitted, and the light beam of the other wavelength is diffracted in the 0th order (substantially For example, Japanese Laid-Open Patent Publication No. 2001-307369 discloses a method in which the light beam is transmitted straight without being diffracted) and the converging points of the respective returning light beams emitted from the diffraction element force are matched. In addition, in an optical pickup device equipped with a twin laser, a diffraction element is used as a method of combining two light beams emitted from different positions and matching the optical axis after multiplexing with the optical axis of the optical system. A method of diffracting a light beam of one wavelength at the 0th order and diffracting a light beam of the other wavelength at the first order so that the optical axes of the respective light beams emitted from the diffraction element coincide with each other (for example, JP 2002—163837).

[0006] It is known that the wavelength of emitted light varies in a laser used in an optical pickup device depending on a change in its environmental temperature.

In order to avoid the influence of the change in the environmental temperature described above, for example, Japanese Patent Laid-Open No. 2002-116314 discloses a linear element instead of an organic material having a small linear expansion coefficient, which has been used as a diffraction element material. There is disclosed a technique that uses a synthetic resin having a large expansion coefficient and uses the fact that the pitch of the diffraction grating fluctuates due to a change in environmental temperature to offset the fluctuation of the diffraction angle due to the wavelength fluctuation.

[0007] Furthermore, in the two-laser optical pickup device, two light beams emitted from lasers arranged at different positions are combined, and the combined optical axis is made to coincide with the optical axis of the optical system. For example, a method using a beam splitter (or optical prism) is used (for example, Japanese Patent Laid-Open No. 2001-118279).

Disclosure of the invention

Problems to be solved by the invention

[0008] The conventional technique disclosed in Japanese Patent Application Laid-Open No. 2002-116314 has a problem that it is difficult to select an appropriate material that can cancel the fluctuation of the diffraction angle accompanying the change in the environmental temperature. In other words, the wavelength variation with respect to the temperature change of the laser is about 0.25 nmZ ° C, but in order to cancel this wavelength variation, a resin with a linear expansion coefficient of about 3 X 10 ^_4 Z ° C is desirable. On the other hand, so-called optical grade resin such as acrylic or polyolefin resin used in optical pickup devices has a linear expansion coefficient of about 7 X 10 ^_5 Z ° C. Characteristics cannot be obtained.

[0009] In addition, the above materials are made from laser light irradiation or other members whose thermal conductivity is small due to grease. It is difficult to reduce thermal distortion caused by local thermal expansion and contraction due to heat transfer.

[0010] When a diffractive element is used for multiplexing as described in Japanese Patent Laid-Open Nos. 2001-307369 and 2002-163837, the 0th-order light is transmitted straight through the diffractive element. Although it is not affected by wavelength fluctuations depending on the environmental temperature, the first-order diffracted light changes in proportion to the fluctuating wavelength because the diffraction angle depends on the environmental temperature. As a result, the optical axes of the two light beams do not coincide with each other, and the diffracted light beam shifts the position of the focused spot when it reaches the light receiving element.

[0011] Further, in the optical pickup device, the light receiving element is usually divided into a plurality of regions, and a focus servo or tracking is performed using a sum signal or a difference signal of a signal proportional to the amount of light for each of the divided regions. Servo is performed. However, if the position of the focused spot that reaches the light receiving element is shifted due to a factor other than the focus error or tracking error, accurate focus servo or tracking servo cannot be performed.

The present invention has been made in view of the above circumstances, and provides an optical pickup device in which the positional deviation of a spot on a light receiving element is suppressed with respect to a change in environmental temperature even when multiplexing by a diffraction element is used. The purpose is to provide.

Means for solving the problem

[0013] The contents of the present invention are introduced below.

1. Two light sources that emit light beams of two different wavelengths, an objective lens installed between the light source and the optical recording medium, and one or two installed between the objective lens and the optical recording medium In an optical pickup device comprising two diffractive elements and a light receiving element that detects a light beam reflected by an optical recording medium, the diffractive element diffracts the two light beams with the same order or different orders and guides them to the light receiving element. An optical pickup device characterized by the above.

2. A first light source that emits a light beam having a first wavelength, a second light source that emits a light beam having a second wavelength different from the first wavelength, and the 2 reflected by an optical recording medium An objective lens for condensing return beams of two wavelengths, and an objective lens disposed between the objective lens and its condensing point, diffracting and transmitting the return beams of two wavelengths incident through the objective lens 1 Two diffractive elements and before being focused by the objective lens and diffracted and transmitted by the diffractive element And a light receiving element that receives the return light beam, and the diffraction element diffracts and transmits the return light beam with the same order. 2. The optical pickup device according to 1 above, wherein the two wavelength condensing points are substantially matched on the light receiving surface of the light receiving element.

With this configuration, even when the environmental temperature changes, an optical pickup device in which the deviation of the condensing point with respect to the light beams of different wavelengths on the light receiving element surface is suppressed, and the problem of inconsistency of the condensing points is solved. Can offer

3. A first light source that emits a light beam with a first wavelength, a second light source that emits a light beam with a second wavelength different from the first wavelength, the light beam with the first wavelength, and the A forward optical system including an objective lens that guides a light beam having a second wavelength toward the optical recording medium; a first light receiving element that receives the return light beam having the first wavelength from the optical recording medium; and the optical recording medium. A second light receiving element for receiving the return light beam having the second wavelength from the optical recording medium, and guiding the return light beam having the first wavelength from the optical recording medium to the first light receiving element, and from the optical recording medium. And a return optical system including an objective lens that guides the return light beam having the second wavelength to the second light receiving element, and the forward optical system includes the light beam having the first wavelength and the light beam having the second wavelength. An outward diffraction element that diffracts at least one of the light beams, and the return optical system includes: A return diffraction element that diffracts at least one of a return light beam having a wavelength of 1 and a return light beam of the second wavelength, and the forward diffraction element and the return diffraction element are diffraction gratings having a grating pitch equal to each other 2. The optical pickup device according to 1, wherein the light beam having the first wavelength is diffracted with a diffraction order equal to each other, and the light beam with the second wavelength is diffracted with a diffraction order equal to each other.

With this configuration, the forward diffraction element and the backward diffraction element have diffraction gratings having the same grating pitch, diffract the light beams having the first wavelength at the same diffraction order, and have the second wavelength. Since the light beams are diffracted at the same diffraction order, the effect of the fluctuation of the environmental temperature on the positional deviation of the spot of the light beam collected on the light receiving element is affected even if the diffraction element is used for multiplexing. An optical pickup device that can be suppressed can be realized.

4. A first light source that emits a light flux of a first wavelength, a second light source that emits a light flux of a second wavelength different from the first wavelength, and the light flux from the light source Optical recording medium An objective lens that condenses the light, a light receiving element that detects a light beam collected by the objective lens and reflected by the optical recording medium, and a light flux emitted from the first light source and the second light source. Has a diffractive function, and does not have a diffractive function with respect to a light beam reflected by the optical recording medium, and a light beam emitted from the first light source and the second light source. Comprises a second diffractive element that does not have a diffractive function and has a diffractive function with respect to the light beam reflected by the optical recording medium, and the first diffractive element and the second diffractive element include The diffraction order of the first diffraction element with respect to the light beam of the first wavelength from the first light source having the same diffraction grating pitch, and the first wavelength of light reflected by the optical recording medium. The order of diffraction in the second diffractive element with respect to the luminous flux is equal The order of diffraction in the first diffraction element for the second wavelength light beam from the second light source, and the second wavelength light beam reflected by the optical recording medium. The first diffractive element and the second diffractive element, which are equal to the order of diffraction in the diffractive element, are arranged substantially in parallel between the light source and the objective lens, and the first diffractive element is The light beam having the first wavelength and the light beam having the second wavelength are combined and guided to the objective lens, and the second diffractive element demultiplexes the light beam reflected by the optical recording medium and supplies it to the light receiving element. 2. The optical pickup device according to 1 above.

According to the above configuration, when there is a change in wavelength due to a change in the environmental temperature, a change in the diffraction angle of diffraction by the first diffraction element that functions as a light beam from the light source and a light beam reflected by the optical recording medium. In contrast, the diffraction angle fluctuations of the diffraction by the second diffractive element functioning can be made almost the same, so the fluctuations of the respective diffraction angles are canceled out, and the deviation of the condensing spot position guided to the light receiving element can be suppressed. An optical pickup device can be realized. In addition, by arranging the first diffractive element and the second diffractive element approximately in parallel between the light source and the objective lens, the light source and the light receiving element can be arranged close to each other, and the size of the apparatus can be reduced.

5. The optical pickup device according to 2, 3 or 4, wherein the diffraction by the diffraction element uses first-order diffraction.

With this configuration, in addition to the effects described above, since the diffraction orders of the diffraction elements are all first-order, it is possible to realize an optical pickup device with high light use efficiency using diffracted light with high diffraction efficiency. 6. The diffractive element is a diffractive element in which linear or curved grooves are periodically formed on a transparent substrate, and the pitch of the groove period is 5 to 20 m. A backup device.

By setting the pitch of the groove period in this configuration, that is, if it is 5 m or more, the theoretical diffraction efficiency exceeds 82%, and if it is 20 m or less, the distance between the diffraction element and the light receiving element is within 15 mm. can do.

7. The optical pick-up device according to 3 above, wherein the forward diffraction element and the backward diffraction element have a wavelength selectivity capable of selecting a wavelength of light to be diffracted at a first or higher order of diffraction.

With this configuration, in addition to the above effects, each diffractive element has wavelength selectivity capable of selecting the wavelength of light to be diffracted at the first or higher order of diffraction. A device can be realized.

8. The forward diffraction element and the backward diffraction element both diffract the light beam having the first wavelength at the 0th-order diffraction order, and diffract the light beam at the second wavelength at the first-order diffraction order. 8. The optical pickup device according to 3 or 7 above.

In addition to the above effects, this configuration allows each diffraction element to diffract both the first wavelength light flux with the 0th order diffraction order and the second wavelength light flux both with the first order diffraction order. Therefore, it is possible to realize an optical pickup device with higher light utilization efficiency.

9. The diffraction grating includes a diffraction grating having a periodic structure in which a cross-sectional shape repeats a sawtooth shape, or a diffraction grating having a periodic structure in which a cross-sectional shape repeats a shape approximating a sawtooth shape by a stepped shape. The optical pickup device according to any one of 2 to 8. With this configuration, in addition to the above effects, each diffraction element has a diffraction grating with a periodic structure in which the cross-sectional shape repeats a sawtooth shape, so that the diffraction element can be easily manufactured, and the cross-sectional shape is a sawtooth shape. Since it has a diffraction grating with a periodic structure that repeats a shape approximated by a stepped shape, an optical pickup device that can manufacture a diffraction element more easily can be realized.

10. The first diffractive element and the second diffractive element are gratings in which a birefringent material layer and an isotropic material layer are formed on a transparent substrate by repeating convex portions having a sawtooth cross-sectional shape. 6. The optical pickup device according to 4 or 5 above, which is a polarizing diffractive element laminated so as to have an interface having a shape structure.

With this configuration, since the diffractive element is a diffractive element having a sawtooth cross-sectional shape, an optical pickup device with high light utilization efficiency can be realized.

11. The birefringent material layer of the first diffractive element is oriented so that the extraordinary refractive index corresponds to the light flux in the polarization direction of the first linearly polarized light, and the second diffractive material layer The birefringent material layer of the element is oriented so that the extraordinary refractive index corresponds to the second linearly polarized light orthogonal to the first linearly polarized light. The optical pickup device according to the item.

With this configuration, since the diffractive element is a polarization-selective diffractive element, it is possible to realize an optical pickup device with higher light utilization efficiency.

12. The optical pickup device according to any one of 4, 5, 9, 10 or 11, wherein the sawtooth shape of the lattice cross-sectional shape is a shape approximating a desired sawtooth shape in a staircase shape. The invention's effect

[0014] According to the present invention, it is possible to provide an optical pickup device in which the problem of inconsistency due to shift of the condensing point for light beams of different wavelengths on the light receiving element surface when the operating temperature fluctuates can be provided.

According to the present invention, the diffractive element is provided in each of the outward optical system and the backward optical system, and when there is a wavelength variation in the emitted light of the laser due to a change in the environmental temperature, The diffraction angle change of diffraction by the first diffraction element and the diffraction angle change of diffraction by the second diffraction element in the return path optical system can be made approximately the same, so by canceling each diffraction angle change, the light receiving element It is possible to provide an optical pickup device capable of suppressing the deviation of the focused spot position led to the light.

Brief Description of Drawings

FIG. 1 is a schematic configuration diagram of an optical pickup device according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing a part of a cross section of a cross-sectional diffraction element 8 having a stepped periodic structure according to an example of the first embodiment of the present invention.

FIG. 3 is a cross-sectional diffraction pattern having a serrated periodic structure according to the first embodiment of the present invention. FIG. 6 is a schematic cross-sectional view showing a part of the cross section of the element 8

4] A diagram conceptually showing one configuration example of the optical pickup device according to the second embodiment of the present invention.

[5] Schematic configuration diagram of an optical pickup device according to a third embodiment of the present invention.

6] A diagram showing an optical path of diffracted light by the diffraction element 8 according to the first embodiment of the present invention. 7] Schematic configuration diagram of an optical system showing the tilt of the diffraction element according to an example (Example 3) of the first embodiment of the present invention.

8] Explanatory drawing about the multiplexing performed by the optical pickup device 100 according to the example (Example 7) of the second embodiment of the present invention.

9] Explanatory drawing about the demultiplexing performed by the optical pickup device 100 according to the example (Example 7) of the second embodiment of the present invention.

圆 10] When the oscillation wavelength of each of the light sources la and lb according to the second embodiment of the present invention changes, the optical axis direction of the incident light beam to the forward diffraction element 202 and the optical axis direction of the diffracted light beam FIG.

[11] The incident direction of the light beam incident on the backward diffraction element 209 and the emission of the light beam emitted from the backward diffraction element 209 when the oscillation wavelengths of the light sources la and lb according to the second embodiment of the present invention change. Explanatory drawing which shows a direction.

12] A sectional view conceptually showing a part of a section of an outward diffraction element 202 according to an example (Example 7) of the second embodiment of the present invention.

13] A sectional view conceptually showing a part of a cross section of the return diffraction element 209 according to the example (Example 7) of the second embodiment of the present invention.

FIG. 14 is a diagram conceptually showing a configuration example of an optical pickup device according to an example (Example 8) of the second embodiment of the present invention.

15] An explanatory view of multiplexing performed by the optical pickup device 800 according to the example (Example 8) of the second embodiment of the invention.

16] Explanatory drawing about the demultiplexing performed by the optical pickup device 800 according to the example (Example 8) of the second embodiment of the present invention.

圆 17] A cross section of the forward diffraction element 202 according to the example (Example 8) of the second embodiment of the invention. Sectional drawing shown notionally.

FIG. 18 is a cross-sectional view conceptually showing a part of a cross section of a polarization diffraction grating 112 constituting the forward diffraction element 202 according to the second embodiment of the present invention.

FIG. 19 is a cross sectional view conceptually showing a cross section of a backward diffraction element 209 according to an example (Example 8) of the second embodiment of the present invention.

FIG. 20 is an explanatory view of a multiplexing action by the optical pickup device according to the third embodiment of the present invention.

FIG. 21 is an explanatory view of the demultiplexing effect by the optical pickup device according to the third embodiment of the present invention.

FIG. 22 is a schematic diagram conceptually showing the structure of the first diffraction element and the second diffraction element of the optical pickup device according to the third embodiment of the present invention.

Explanation of symbols

1: Light source

la, 201a, 301a: First light source

lb, 201b, 301b: Second light source

2, 203: Optical element

3, 204, 305: Collimator lens

4, 205, 306: Aperture

5, 206, 307: Objective lens

6, 7, 207, 208, D: Optical disc

6a, 7a, 207a, 208a: Information recording surface

8: Diffraction element

9, 210a, 210b, 308: Photo detector

21: Optical axis of the return light of the first wavelength

22: Optical axis after diffraction of return light of the first wavelength

23: Change in the traveling direction of the return light of the first wavelength due to the diffraction element

24: Focusing point of the return light of the first wavelength when there is no diffraction element

25: Optical axis of the return light of the second wavelength 26 :: Optical axis after diffraction of return light of second wavelength

27:: Change in traveling direction of return light of second wavelength due to diffraction element

28:: Focusing point of the return light of the second wavelength when there is no diffraction element

29:: Difference in incident angle between the return light of the first wavelength and the return light of the second wavelength

31: ： Diffraction element entrance surface

32:: Output surface of diffraction element

33:: Incident direction of the return light of the first wavelength

34:: Direction of incident light of the second wavelength

35:: Direction of return light after diffraction

41:: Incident surface

42:: Output surface

43:: Incident direction of the return light of the first wavelength

44:: Incident direction of the return light of the second wavelength

45:: Direction of return light after diffraction

202: Outward diffraction element,

209: Return diffraction element

221, 263, 291: Optical axis of the light beam emitted by the first light source la

222, 264, 292: Optical axis of luminous flux emitted from second light source lb

223, 265: Optical axis of luminous flux after combining

231, 273, optical axis of the light beam incident on the backward diffraction element 209

232, 253, 274, 101: Optical axis of luminous flux of the first wavelength after demultiplexing

233, 254, 275, 102: Optical axis of luminous flux of second wavelength after demultiplexing

241: Direction in which the light beam emitted from the first light source la exits the outward diffraction element 202

242: direction in which the light beam emitted from the second light source lb exits the forward diffraction element 202

251: The optical axis of the light beam from which the return light of the light beam emitted by the first light source la is incident on the backward diffraction element 209

252: Return light of the light beam emitted from the second light source lb is reflected by the light beam incident on the backward diffraction element 209. 261: Entrance surface of forward diffraction element 202

262: Outgoing surface of forward diffraction element 202

271: Incident surface of return path diffraction element 209

272:: Outgoing surface of return path diffraction element 209

100: Optical pickup device

111:: First wave plate

112: Polarized diffraction grating

113:: Second wave plate

121: Birefringent material layer

122:: Isotropic material layer

123, .124: Cover glass

131:: 1st wave plate

133:: Second wave plate

132: Polarization diffraction grating

302: First diffraction element

303: Second diffraction element

321: Birefringent material layer

322: Isotropic material layer

323, 324: Quartz glass substrate

304: 1Z4 wave plate

308a: First light receiving element

308b: Second light receiving element

D: First optical disc

a

D: Information recording surface of the first optical disc al

D: Second optical disc

b

D: Information recording surface bl of the second optical disc

: Optical axis of light flux with wavelength λ

α: Optical axis after diffraction of light beam of wavelength β

1 wavelength λ

Optical axis of 2 luminous flux

β

Optical axis after diffraction of 2 light beams with 2 wavelengths

Ύ

1 Optical axis after diffraction

Ύ

2 Optical axis of return beam

λ

1 First wavelength

λ Second wavelength

2

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

"First Embodiment"

In this embodiment, the case where there is one diffractive element is handled.

FIG. 1 which is a schematic configuration diagram of an optical pickup device according to a first embodiment of the present invention will be specifically described with reference to FIG. 1. However, the first embodiment of the present invention is not limited to the following description. The optical pickup device of the present invention includes a first light source la that emits a light beam having a first wavelength, a second light source lb that emits a light beam of a second wavelength, an optical element 2, a collimator lens 3, and a diaphragm.

2

4. An objective lens 5 and a light receiving element 9 for detecting a return light beam reflected by the information recording surface 6a of the first optical disc 6 or the information recording surface 7a of the second optical disc 7 are provided.

The light beam emitted from the first light source la is reflected by the optical element 2 and condensed on the information recording surface 6a of the first optical disc 6 through the collimator lens 3, the diaphragm 4, and the objective lens 5. Irradiated. Similarly, the light beam emitted from the second light source lb is reflected by the optical element 2 and collected on the information recording surface 7a of the second optical disc 7 through the collimator lens 3, the diaphragm 4, and the objective lens 5. Light is irradiated.

The return light beam reflected by the information recording surface 6 a or 7 a passes through the objective lens 5, the diaphragm 4, the collimator lens 3, and the optical element 2 and is guided to the light receiving element 9. Using the output signal detected by the light receiving element 9, the information recording surface 6a of the first optical disc 6 or the information recording surface 7a of the second optical disc 7 is read, the focus error signal, the traffic Error signal is obtained. The optical pickup device includes a mechanism (focus servo) for moving the lens in the optical axis direction based on the focus error signal and a lens substantially perpendicular to the optical axis based on the tracking error signal. Mechanism to move in the direction Racking servo) is provided, but is omitted in Fig. 1.

[0021] The first light source la is a semiconductor laser light source that emits a linearly polarized divergent light beam having a wavelength of about 650 nm, and the second light source lb is a linearly polarized divergent light beam that has a wavelength of about 780 nm. Although a semiconductor laser light source is illustrated, respectively, it is not limited to these. In addition, the first light source la and the second light source lb are not limited to those separately formed, and a so-called twin laser in which lasers having different wavelengths are integrated on a single semiconductor substrate. But you can. Here, the vicinity of wavelength 650 nm means the wavelength range of 630 to 670 nm, and the vicinity of wavelength 780 means the wavelength range of 760 to 800 nm!

The optical element 2 has a function of reflecting the light beam emitted from the first light source la and the second light source lb to the collimator one lens 3 side and transmitting the return light of the optical disc force to the light receiving element 9 It has. Examples of the powerful optical element include a half mirror and a polarizing beam splitter. When using a polarizing beam splitter, a 1Z4 wave plate is used between the optical element 2 and the optical discs 6 and 7, preferably between the optical element 2 and the collimator lens 3, and combined with the light source. Preferable to use effectively.

The collimator lens 3 has a function of converting the light beam reflected by the optical element 2 into substantially parallel light in the optical path from the light source to the optical disk. Also, in the optical path from the optical disk to the light receiving element, it is used in combination with an objective lens, which will be described later, and collects the return light beam from the optical disk, passes through the optical element 2 and the diffraction element 8, and the light receiving surface of the light receiving element 9 It has the function of concentrating on top.

The aperture 4 is configured to set the numerical aperture NA by selectively restricting the light beams from the light source la and the light source lb. Accordingly, when the numerical aperture for the first optical disc 6 and the numerical aperture for the second optical disc 7 are different during recording and reproduction of the optical disc, the numerical aperture can be adjusted by the diaphragm 4. The diaphragm 4 includes a mechanical diaphragm and an optical diaphragm, and is not particularly limited. The NA value is 0.65 for the first wavelength and the second wavelength.

For a 1 2 luminous flux, a force exemplified by 0.50 is not limited to this. If the numerical aperture for the first optical disk 6 and the numerical aperture for the second optical disk 7 are the same, the diaphragm 4 may not be used.

[0025] The objective lens 5 can be used in common for the first wavelength and the second wavelength. Is a single lens with aberration corrected at a time, and each of the first wavelength and the second wavelength

The parallel light 1 2 is collected on the information recording surface 6 a of the optical disc 6 and the information recording surface 7 a of the optical disc 7. As the powerful objective lens 5, for example, the objective lens disclosed in Japanese Patent Laid-Open No. 2001-344798 can be used in the f row.

[0026] The first optical disk 6 is used for recording and reproduction using a light beam having a wavelength, and has a protective layer thickness of 0.6 mm, for example. The second optical disk 7 is used for recording / reproduction using a light beam having a wavelength λ, and has a protective layer thickness of 1.2 mm, for example.

[0027] The diffractive element 8 diffracts and transmits each of the return light of the first wavelength and the return light of the second wavelength with the same first order and collects them at substantially the same point on the light receiving element. Configured. In this case, it is preferable to set the diffraction order to the first order because the diffraction efficiency is high.

[0028] It is preferable that the diffractive element includes a linear or curved groove periodically formed on the surface of the transparent substrate, and the pitch of the applied groove period is 5 to 20 m. If the pitch of the groove period is less than 5 μm, the theoretical diffraction efficiency of the diffraction element is 82% or less, and the diffraction efficiency of 80% or more required for use in the optical pickup device may not be obtained. In order to obtain high diffraction efficiency, 7 m or more is preferable. If it is 9 m or more, the theoretical diffraction efficiency of 88% is obtained, which is more preferable. If the pitch of the groove period exceeds 20 m, the distance between the diffraction element and the light receiving element must be more than 15 mm, and the optical pickup device may not be compact. For compactness, the pitch of the groove period is preferably 15 μm or less, and more preferably 12 μm or less.

[0029] It is preferable that the cross-sectional shape of the periodic groove is a sawtooth shape or a sawtooth shape approximated by a step shape because a high diffraction efficiency is obtained when the diffraction of the same order is performed. When the cross-sectional shape of the periodic groove is stepped as shown in the cross-sectional view of FIG. 2, if one period of the periodic structure is stepped with any number of steps from 6 to 32 steps, it is high. It is preferable because a diffraction element with diffraction efficiency can be easily manufactured. Such a diffractive element is called a binary blazed diffractive element. Further, it is preferable that the periodic groove has a sawtooth shape as shown in the cross-sectional view of FIG. 3 because a higher diffraction efficiency can be obtained.

[0030] By using such a diffractive element, the return light of each wavelength is condensed at substantially the same point on the light receiving element surface by a pickup device having a high diffraction efficiency and a compact configuration. It can be done.

Further, when the groove shape of the diffraction element is changed to a curved line instead of a straight line, for example, a function of reducing coma generated when a parallel plate type half mirror is used as the optical element 2 is provided. Or a function of reducing or appropriately setting the amount of astigmatism of the light beam when the astigmatism method is used for the focus detection means.

[0032] The material of the transparent substrate for forming the diffraction element is preferably a quartz glass having a small linear expansion coefficient because it can suppress thermal distortion to a small value, but is not limited thereto, and is transparent to the wavelength of the light source. It is also possible to use an inorganic material such as optical glass as long as it is a suitable material.

[0033] The diffractive element is preferably formed by forming the periodic groove on the optical substrate by known photolithography and etching, but other methods such as cutting and stamping methods are also applicable. . In addition, the periodic grooves having a sawtooth shape or a step shape in cross section may be formed by directly processing the substrate. However, a layer made of a transparent material is coated on the transparent substrate to cover the layer. May be formed by processing. According to the method of processing the coated layer, a diffractive element having a desired refractive index can be obtained by selecting a material forming the groove.

[0034] Alternatively, as the optical element, two diffractive elements are formed of materials having different refractive indexes, the two diffractive elements are disposed to face each other, and the two diffractive elements are arranged between the two diffractive elements. ! Alternatively, a diffractive element having a laminated structure in which a material having a refractive index, such as a material having a different refractive index, is sandwiched between the materials having different refractive indexes at any wavelength. It is preferable to use a diffractive element having such a laminated structure because the diffraction efficiency at each wavelength can be optimized.

[0035] The light receiving element 9 receives the reflected light of the information recording surface 6a of the optical disc 6 and the information recording surface 7a of the optical disc 7, and applies the reflected light to each of the information recording surfaces 6a and 7a based on the received reflected light. A read signal, a focus error signal, and a tracking error signal corresponding to the recorded information are generated and output to the outside.

"Second Embodiment"

In this embodiment, there are two diffractive elements, and two light sources and two light receiving elements. The case where the elements are arranged in different places will be handled.

FIG. 4 is a schematic configuration diagram of an optical pickup device according to the second embodiment of the present invention. In FIG. 4, an optical pickup device 100 includes a first light source 201a that emits a light beam with a wavelength, a second light source 201b that emits a light beam with a wavelength, and each light source 201a and 201b.

2

The forward diffraction element 202 that combines the light beams and the combined light beam are transmitted, and the return light from the information recording surface 207a of the first optical disk 207 and the information recording surface 208a of the second optical disk 208 is reflected. The optical element 203 that leads to the backward diffraction element 209 described later, the collimator lens 204 that converts the incident light beam into substantially parallel light, the stop 205, the objective lens 206, and the return from each of the information recording surfaces 207a and 208a A backward diffraction element 209 that demultiplexes light, a first wavelength light-receiving element 210a that receives a light beam of a wavelength after demultiplexing, and a light beam of a wavelength after demultiplexing

The second wavelength light receiving element 210b that receives 1 2 is provided.

Here, the above-mentioned “return light” is a light flux having a wavelength λ or a light flux having a wavelength λ.

1 2

A light beam reflected by the recording surface 207a or the information recording surface 208a and returning in the direction of the optical element 203. In the following, the wavelength is called the first wavelength, and the wavelength is called the second wavelength.

1 2

[0037] The light beam emitted from the first light source 201a is diffracted by the forward diffraction element 202, passes through the optical element 203, the collimator lens 204, the stop 205, and the objective lens 206 in this order, and is information on the first optical disc 2007. Condensed on the recording surface 207a. Similarly, the light beam emitted from the second light source 201b is diffracted by the forward diffraction element 202 and transmitted through the optical element 203, the collimator lens 204, the diaphragm 205, and the objective lens 206 in this order. Condensed on the information recording surface 208a. Hereinafter, an optical system that guides the light flux from the first light source 201a or the second light source 201b toward the information recording surface 207a of the first optical disc 207 or the information recording surface 208a of the second optical disc 208, respectively, in the forward path It is called an optical system.

[0038] The light beams condensed on the information recording surface 207a of the first optical disc 207 or the information recording surface 208a of the second optical disc 208 are reflected by the information recording surfaces 207a and 208a, respectively, and the object lens 206 and the aperture stop are reflected. 205, is transmitted through the collimator lens 204, reflected by the optical element 203, demultiplexed by the return path diffraction element 209, and enters the first light receiving element 210a or the second light receiving element 210b. Hereinafter, an optical system that guides the return light of the first wavelength from the information recording surface 207a to the first light receiving element 210a and guides the return light of the second wavelength from the information recording surface 208a to the second light receiving element 210b. This is called a return optical system.

Here, the output signal of the first light receiving element 210a is used to generate a read signal, a focus error signal, and a tracking error signal of information recorded on the optical disc recording surface 207a of the first optical disc 207. Similarly, the output signal of the second light receiving element 210b is used to generate a read signal, a force error signal, and a tracking error signal of information recorded on the optical disk recording surface 208a of the second optical disk 208.

[0040] The optical pickup device includes a mechanism (focus servo) for controlling the lens in the optical axis direction based on the focus error signal and a lens on the optical axis based on the tracking error signal! A mechanism (tracking servo) that controls in a direction almost perpendicular to the axis is provided, but is omitted in the configuration shown in Fig. 4.

[0041] The first light source 201a is composed of, for example, a semiconductor laser and emits a linearly polarized divergent light beam having a wavelength near 650 nm. Similarly, the second light source 201b is constituted by a semiconductor laser, for example, and emits a divergent light beam having a wavelength near 780 nm and linearly polarized light. Here, the wavelengths near 650 nm and 780 nm mean wavelengths in the range of 630 nm to 670 nm and 760 nm to 800 nm, respectively.

[0042] Although the first light source 201a and the second light source 201b are arranged separately, two semiconductor laser chips are mounted on the same substrate in the same package. Alternatively, it may be configured to form an hybrid two-wavelength laser light source. Alternatively, the first light source 201a and the second light source 201b are a monolithic two-wavelength laser light source having two light emitting points that emit different wavelengths (see, for example, Japanese Patent Application Laid-Open No. 2004-39898). It may be configured to make

[0043] The forward diffraction element 202 is configured by, for example, a diffraction grating, diffracts the light beams emitted from the light sources 201a and 201b, and is configured so that the optical axes of the diffracted light beams substantially coincide with each other at a predetermined temperature. Yes. That is, the forward diffraction element 2 is configured to multiplex the light beams emitted from the first light source 201a and the second light source 20 lb. Here, the same-order diffraction can be used for combining the light beams emitted from the first light source 201a and the second light source 201b. Also, one beam is diffracted at the 0th order, and the other beam is diffracted at an order other than the 0th order. It can also be combined by diffracting. Hereinafter, the forward diffraction element 202 is constituted by a diffraction grating, and the diffraction grating constituting the forward diffraction element 202 is simply referred to as “diffraction grating of the forward diffraction element 202”.

[0044] The optical element 203 transmits the light beam diffracted and combined by the forward diffraction element 202 to the collimator lens 204 side, and also the information recording surface 207a of the first optical disk 207 or the second optical disk. The return light from the information recording surface 208a 208 is reflected and guided to the return diffraction element 209 side.

The collimator lens 204 converts the light beam diffracted by the outward diffraction element 202 and combined into substantially parallel light.

The diaphragm 205 is configured to set the numerical aperture NA by selectively limiting the light flux from the first light source 201a or the second light source 201b. As a result, when the numerical aperture for the first optical disc 207 and the numerical aperture for the second optical disc 208 are different during recording and reproduction of the optical disk, the numerical aperture can be adjusted by the diaphragm 205. The numerical aperture NA is 0.65 for the first wavelength beam, and the numerical aperture NA for the second wavelength beam.

2

Was set to 0.50. The diaphragm 205 includes a mechanical diaphragm, an optical diaphragm, and the like, and is not particularly limited.

[0047] The objective lens 206 is a single lens whose aberration is corrected to such an extent that it can be used at each wavelength λ.

1 2

The parallel light of each of the first wavelength and the second wavelength is optical disc 20

1 2

The light is focused on the information recording surface 207a of No. 7 and the information recording surface 208a of the optical disc 208. As the objective lens 206, for example, an objective lens disclosed in Japanese Patent Laid-Open No. 2001-344798 can be used.

[0048] Note that the objective lens 206 is not limited to the above, and for example, has two wavelengths, λ

Of these, a configuration in which a lens that corrects aberrations occurring at one of the two wavelengths and an optical member having a function of correcting aberrations occurring at the other wavelength may be combined.

[0049] The first optical disc 207 is a recording medium for performing recording and reproduction using a light beam having the first wavelength, and has a protective layer thickness of 0.6 mm, for example. Similarly, the second optical disk 208 is a recording medium for recording / reproducing using a light beam having a wavelength, for example, 1.2 mm.

2

The protective layer thickness is [0050] The return path diffraction element 209 is constituted by, for example, a diffraction grating, diffracts the return light from the information recording surfaces 207a and 208a of the optical disks 207 and 208, and the direction of the optical axis of each light beam after diffraction is separated. It is configured to go. That is, the return path diffraction element 209 is configured to demultiplex the return light. The same order of diffraction can be used for demultiplexing the return light. Further, it is possible to divide one light beam by diffracting it with the 0th order and diffracting the other light beam with an order other than the 0th order. Hereinafter, the backward diffraction element 209 is constituted by a diffraction grating, and the diffraction grating constituting the backward diffraction element 209 is simply referred to as “diffraction grating of the backward diffraction element 209”.

Here, the grating pitch of the diffraction grating of the backward diffraction element 209 and the grating pitch of the diffraction grating of the forward diffraction element 202 are made substantially equal, and the return light of each wavelength and λ in the forward diffraction element 209

It is preferable to make the diffraction order of 1 2 equal to the diffraction order of the first diffraction element 2 from the following points. That is, by doing so, the oscillation wavelength of the light source changes due to a change in environmental temperature, and the direction of the light beam diffracted and emitted by the forward diffraction element 202 and the backward diffraction element 209 (hereinafter simply referred to as the emission direction). Change in the exit direction occurs in the forward diffraction element 202 and the backward diffraction element 209 so as to cancel out each other by substantially the same amount, so that the light of each light beam emitted from the backward diffraction element 209 The axial direction is not affected by changes in ambient temperature. Hereinafter, the surface of the diffraction element from which the incident light exits is referred to as an “exiting surface”.

[0052] The first light receiving element 210a receives the return light from the information recording surface 207a of the first optical disc 207, and according to the information recorded on the information recording surface 207a, a read signal, a focus error signal, and Each signal of the tracking error signal is generated and output to the outside. Similarly, the second light receiving element 210b receives the return light from the information recording surface 208a of the second optical disc 208, and reads a read signal, a focus error signal, and a focus error signal according to the information recorded on the information recording surface 208a. Each signal of the tracking error signal is generated and output to the outside.

Here, it is preferable that the distance between the first light receiving element 210a and the backward diffraction element 209 is substantially equal to the distance between the first light source 201a and the forward diffraction element 202. In addition, it is preferable that the distance between the second light receiving element 210b and the backward diffraction element 209 is substantially equal to the distance between the second light source 201b and the forward diffraction element 2202. [0054] Note that the first light receiving element 210a and the second light receiving element 210b are configured as a single light receiving element even if they are separately disposed, and receive different light depending on the position where each light beam is condensed. It may be configured to have a surface.

"Third embodiment"

In this embodiment, the case where there are two diffractive elements and two light sources and two light receiving elements are installed in the near V position is dealt with.

FIG. 5 shows an optical pickup device according to a third embodiment of the present invention, and this optical pickup device 310 includes a first light source 301a that emits a light beam having a wavelength (constituting a part of the light source 301). And a second light source 301b (a part of the light source 301).

2

The first diffractive element 302, the second diffractive element 303, the 1Z4 wavelength plate 304, the collimator lens 305, the stop 306, the objective lens 307, and the first diffractive light beam that receives the light beam of the wavelength. Light receiving element 308a (which constitutes part of light receiving element 308) and light beam with wavelength λ are received

2

And a second light receiving element 308b (which constitutes a part of the light receiving element 308).

The symbol D indicates an optical disk. Specifically, D indicates the first optical disk (D a

Is the information recording surface of the first optical disc D, and D is the second optical disc (D is the al a b bl b information recording surface of the optical disc D).

[0055] The first light source 301a is composed of a semiconductor laser that emits a divergent light beam having a wavelength (λ) near a wavelength of 650 nm, for example, as linearly polarized light in a predetermined polarization direction (referred to as a first polarization direction). .

In addition, the second light source 301b is configured to emit a divergent light beam having a wavelength (λ) near, for example, 780 nm.

2

It is composed of a semiconductor laser that emits linearly polarized light equivalent to the polarization direction of the light beam from the source 301a.

Note that the first light source 301a and the second light source 301b are not limited to separate bodies. For example, two semiconductor laser chips are mounted on a common substrate in a common package. A wavelength laser light source may be used. Alternatively, a monolithic two-wavelength laser light source having two emission points that emit different wavelengths may be used.

[0056] The first diffractive element 302 acts as a diffraction grating for linearly polarized light beams in the first polarization direction, and is a straight line in the second polarization direction orthogonal to the first polarization direction. For polarized light flux On the other hand, it is a polarizing diffraction element provided with a birefringent material that does not act as a diffraction grating. The first diffractive element 302 diffracts the first linearly polarized light beams emitted from the first light source 301a and the second light source 301b with the same order, and the optical axes of the diffracted light beams are These are configured to substantially coincide with each other at a predetermined temperature. That is, the first diffractive element 302 multiplexes the light beams emitted from the first light source 301a and the second light source 301b.

[0057] The return light beam reflected and returned from the information recording surface D of the optical disc D or the information recording surface D of the optical disc D is returned in the second polarization direction by the function of the 1Z4 wavelength plate 304 described later. Since it is linearly polarized light, the first diffractive element 302 transmits the return light beam without having a diffractive function.

[0058] The second diffractive element 303 does not act as a diffraction grating for a linearly polarized light beam in the first polarization direction, and is a straight line in the second polarization direction orthogonal to the first polarization direction. Although it is a polarizing diffractive element having a birefringent material that acts as a diffraction grating for a polarized light beam, each light beam diffracted by the first diffractive element 302 is transmitted. For the return beam, each beam is diffracted with the same order, and the direction of the optical axis of each beam is separated after diffraction. That is, the second diffractive element 303 demultiplexes each return light beam.

Note that the diffraction grating pitch of the second diffraction element 303 is substantially the same as the diffraction grating pitch of the first diffraction element 302, and the diffraction order of the first diffraction element 302 is equal to the light flux of each wavelength. It is desirable to have the same diffraction order as As a result, even if the oscillation wavelength of the light source changes depending on the environmental temperature and the angle at which the first diffraction element 302 and the second diffraction element 303 are diffracted changes, the first diffraction element 302 and the second diffraction element 302 Since the diffraction elements 303 of the second diffraction element 303 have almost the same amount of change and cancel each other, the optical axis direction of the light beam emitted from the second diffraction element 303 does not depend on the environmental temperature.

[0059] The 1Z4 wavelength plate 304 has a function of converting the linearly polarized light beam having the first polarization direction transmitted through the second diffraction element 303 into circularly polarized light. The 1Z4 wavelength plate 304 is a straight line in the second polarization direction perpendicular to the first polarization direction with respect to the return light beam reflected by the information recording surface of the optical disk and returned by the reversely circularly polarized light. It has a function of converting to polarized light. This 1Z4 wave plate 304 has a phase difference of 1Z4 waves for both the long and long wavelengths.

1 2

It is desirable to have a length. As such a wave plate, as described in JP 2001-101700 A A broadband retardation plate can be used.

The collimator lens 305 diffracts by the first diffraction element 302 and converts the combined light beam into substantially parallel light.

[0061] The stop 306 sets the numerical aperture NA by selectively limiting the light flux from the first light source 301a or the second light source 301b. If the numerical aperture for the first optical disc D and the numerical aperture for the second optical disc D are different during recording / reproduction of the optical disc D, the numerical aperture a b

Can be adjusted.

The diaphragm 306 includes a mechanical diaphragm and an optical diaphragm, and is not particularly limited.

[0062] The objective lens 307 is aberration-corrected so that both the wavelength and the wavelength can be used.

1 2

A single lens, and the respective light fluxes of wavelength and wavelength are optical

1 2 a Disc information recording surface D and optical disc information recording surface D of optical disc D are condensed.

al b bl

As the objective lens 307, for example, an objective lens disclosed in Japanese Patent Laid-Open No. 2001-344798 can be used. This objective lens is not limited to this. For example, aberration correction is performed at one of the two wavelengths 1 and 2, and aberration at the other wavelength is corrected by combining an optical element having an aberration correction function. Use a combination of objective lens and aberration correction function.

[0063] The first optical disk D is used for recording / reproduction with a light beam having a wavelength λ, for example, a 1

0.6 The protective layer thickness is 6 mm. In addition, the second optical disk D has a light beam of wavelength λ b 2

Used for recording and playback, for example, 1.2 mm protective layer thickness.

[0064] The first light receiving element 308a receives the return light flux of the information recording surface D of the first optical disc D a a

The information recorded on information recording surface D is read, the focus error signal, and the al

Each signal of the racking error signal is output. On the other hand, the second light receiving element 3 08b receives the return light of the information recording surface D force of the second optical disc D, and reads the information recorded on the information recording surface D b bl bl. Each signal of tracking error signal is output. It is desirable that the distance between the first light receiving element 308a and the second diffractive element 303 is substantially the same as the distance between the first light source 301a and the second diffractive element 303. Note that the first light receiving element 308a and the second light receiving element 308b are not limited to separate members. Separate light-receiving surfaces are provided in the same light-receiving element based on the position where each beam converges. It may be a thing.

Next, the operation of the third embodiment will be described.

The light beam having a wavelength emitted from the first light source 301 a is diffracted by the first diffraction element 302, and is diffracted by the second diffraction element 303, 1Z4 wavelength plate 304, collimator lens 305, aperture 306, and objective lens 307. The light is sequentially transmitted and condensed on the information recording surface D of the first optical disc D. The second a al

The light flux having a wavelength emitted from the light source 301b is diffracted by the first diffraction element 302, and the second

2

The light passes through the diffraction element 303, the 1Z4 wavelength plate 304, the collimator lens 305, the stop 306, and the objective lens 307 in this order, and is condensed on the information recording surface D of the second optical disc D.

b bl

The light beam condensed on the information recording surface D of the first optical disc D is the information on the optical disc D.

1 al a Reflected by the recording surface D and transmitted through the objective lens 307, aperture 306, and collimator lens 305 al

Then, it is diffracted by the second diffraction element 303, passes through the first diffraction element, and reaches the first light receiving element 308a. In addition, the light beam condensed on the information recording surface D of the second optical disc D is the optical disk b bl.

Reflected by the information recording surface D of the lens D, the objective lens 307, aperture 306, collimator lens 30 b bl

5, is diffracted by the second diffraction element 303, passes through the first diffraction element, and reaches the second light receiving element 308 b.

[0066] In this way, the read signal for the information recorded on the optical disc recording surface D of the first optical disc D, the four forces a al by the output signal output from the first light receiving element 308a.

Error signal and tracking error signal can be obtained. Also, the information recorded on the optical disc recording surface D of the second optical disc D is used for output information from the second light receiving element 308b.

Reading signal, focus error signal, and tracking error signal are obtained. The optical pickup device 310 includes a mechanism (focus servo) for moving the objective lens 307 in the optical axis direction based on the focus error signal, and an objective lens 307 based on the tracking error signal. Force that includes a mechanism (tracking servo) that moves in a direction almost perpendicular to the optical axis is omitted in the configuration shown in Fig. 15.

[0067] According to this embodiment, even if the oscillation wavelength of the light source changes depending on the environmental temperature and the angle at which diffraction is performed in the first diffraction element 302 and the second diffraction element 303 changes, the first The diffractive element 302 and the second diffractive element 303 have substantially the same amount of change, and cancel each other. In other words, if there is a wavelength variation due to changes in the ambient temperature, it will function on the luminous flux from the light source. The diffraction angle fluctuation of the diffraction by the first diffraction element and the diffraction angle fluctuation of the diffraction by the second diffraction element functioning with respect to the light beam reflected by the optical disk can be made approximately the same, so that each time The bending angle is canceled and the optical axis direction of the light beam emitted from the second diffractive element 303 does not depend on the environmental temperature.

For this reason, it is possible to realize an optical pickup device that can suppress the deviation of the focused spot position guided to the light receiving element 308. Further, by arranging the first diffractive element 302 and the second diffractive element 303 substantially in parallel between the light source 301 and the objective lens 307, the light source and the first light receiving element 308 can be arranged close to each other, The size of the apparatus can be reduced.

Example

[0068] [I] An example for the first embodiment is shown.

[0069] Examples 1 and 3 to 6 are Examples, and Example 2 is a Comparative Example.

[0070] [Example 1]

The optical arrangement of the optical pickup device according to this example is the same as the optical arrangement of the embodiment shown in FIG. That is, the optical pickup device of the present invention has a wavelength of 650 nm and λ =

1 2

Semiconductor laser light sources la and lb that emit linearly polarized divergent light beams of 780 nm, optical element 2, collimator lens 3, light beams from light source la and light source lb are selectively restricted, and the first wavelength 0.65 for the luminous flux, and for the second wavelength

1 2

A diaphragm 4 having a numerical aperture of 0.5, an objective lens 5 and a light receiving element 9 for detecting a return beam are provided. Here, as the light source, a two-wavelength light source with a distance between emission points d = 110 / z m is used, and as the optical element 2, a 0.5 mm-thick BK7 (trade name: manufactured by Schott) is used.

[0071] In the optical pickup device of this example, in order to make the condensing point of the return light beam of the first wavelength coincide with the condensing point of the return light beam of the second wavelength, each return light beam is firstly transmitted by the diffraction element 8. It is diffracted and transmitted through. In the following description, unless otherwise specified, the diffraction order in the diffraction element 8 is assumed to be the first order.

First, the function of the diffraction element 8 will be specifically described with reference to FIG. The return light of the first wavelength is incident on the diffraction element 8 in the direction of reference numeral 21, and the traveling direction is bent by an angle of reference numeral 23 by diffraction and is diffracted and transmitted in the direction of reference numeral 22. The return light of the second wavelength is The light beam is incident on the diffraction element 8 in the direction of reference numeral 25, and the traveling direction is bent by an angle of reference numeral 27 by diffraction and is diffracted and transmitted in the direction of reference numeral 26, which is the same direction as reference numeral 22. Reference numeral 29 denotes a difference between incident angles at which the return light having the first wavelength and the return light having the second wavelength are incident on the diffraction element 8.

Here, the first wavelength is obtained, the incident angle of the return light of the first wavelength to the diffraction element 8 is _α , the diffraction angle of the return light of the first wavelength by the diffraction element 8 is _α ′, The second wavelength of the second wavelength

1 2

The incident angle of the return light to the diffraction element 8 is α, and the return light of the second wavelength is diffracted by the diffraction element 8.

2

If the angle is α ′ and the pitch of the groove period of the diffraction element 8 is ρ, the relationship of Equations (1) and (2) holds.

2

One.

= a + λ / p (1)

'= + λ / ρ (2)

2 2 2

If the distance between the emission point of the first light source and the emission point of the second light source is d, the light beam diffracted by the diffraction element 8 is separated from the diffraction element by the distance shown in FIG. It has a condensing point at a point far away.

L = d / I α-α I (3)

1 2

[0073] From the above, in order to make the condensing points of the light fluxes of the respective wavelengths coincide, α ′ = α ′

1 2

It can be seen that p and L should be determined so as to satisfy Eq. (4).

\ λ-λ \ / p = d / L (4)

1 2

[0074] In the diffraction element 8 of this example, the step s is 0.254 μm and the stepped cross-sectional linear groove formed by six steps is periodic with a pitch of groove period p = 10 m. The quartz glass has a periodic structure formed in this way, and is formed by finely processing quartz glass by photolithography and etching.

FIG. 2 is a cross-sectional view of the vicinity of the optical axis of the outgoing light when the diffractive element 8 of this example is cut by a plane including the optical axes of the incident light 33 and 34 and the outgoing light 35. The surface having the periodic structure shown is the entrance surface for the return light beams of the first and second wavelengths, and the surface indicated by reference numeral 32 is the exit surface.

[0075] A light beam having a wavelength of 650 nm and a beam of 780 nm is emitted, and the distance between the light emitting points is d = 110 / z m 2

1 2

Using a wavelength light source, the incident angle to the diffraction element 8 in this example is applied to the light beams of wavelengths 1 and 2 Force S, α = 0.013rad, a = 0.

1 2

Is equal in diffraction angle to the normal direction of the diffraction element α '= α' = 0.078 rad

1 2

The light is diffracted and transmitted at, and is collected from the diffractive element at a condensing point at a distance L = 8.46 mm behind.

[0076] The diffraction efficiency at that time is that the luminous flux of the first wavelength (650 nm) and the second wavelength (

1 2

It is 82% with respect to the luminous flux of 780 nm), and a value of 80% or more necessary for application to the optical pickup device can be obtained.

Note that one period of the step-like periodic structure is not limited to the six steps used in this example. If one period of the periodic structure is 6 steps or more, the diffraction efficiency of the light beams having the two wavelengths can be further improved. As Table 1 summarizes the number of stepped steps and the diffraction efficiency (%) at that time, the diffraction efficiency is 84% for 8 steps, 86% for 10 steps, and 87% for 32 steps.

[0077] [Table 1]

[0078] In the following, how the optical axis direction (hereinafter referred to as the diffraction direction) of the light beam diffracted by the diffraction element 8 changes due to a change in environmental temperature (hereinafter also referred to simply as temperature change). explain.

Caused by the first variation of the wavelength of the light source la delta lambda when the temperature changes, the diffraction direction of change delta _alpha of the light beam of a first wavelength, represented by equation (5).

Δ α = Δ λ / ρ (5)

Here, the wavelength variation Δ λ of the first light source la is expressed by equation (6) using the wavelength variation rate W nmZ ° C and the temperature variation AT ° C due to the temperature variation of the first light source la. Therefore, Equation (7) is obtained as Δ α.

Δ λ = W · Δ Τ (6)

Δ a = W · Δ Τ / ρ (7)

Similarly, the change Δa in the diffraction direction y of the light beam having the second wavelength is equal to the second light source 2a. If the wavelength fluctuation rate due to temperature change is W nmZ ° C, Eq. (8) is obtained as Δ a.

twenty two

Δ hi = Δ λ / p = W · ΔΤ / ρ (8)

2 2 2

[0079] Accordingly, the deviation Δα in the direction of the light flux diffracted and emitted from the diffraction element 8 by the return light of the first wavelength and the return light of the second wavelength with respect to the temperature change of AT ° C is (9) It becomes an expression.

Δ α = | Δ α — Δ α |

1 2

= I (W -W) -AT / p I (9)

1 2

Here, the wavelength variation Δ λ per unit temperature of the first light source la (wavelength 650 nm) is about 0.2 OnmZ ° C, and the wavelength per unit temperature of the first light source 1 a (wavelength 780 nm) Since the variation Δ λ is about 0.25 nmZ ° C, the deviation Δ α in the diffraction direction of the light beams of two wavelengths is

2

(10).

Δ α = I 0.05 · ΔΤ / ρ | (10)

[0080] [Example 2]

When the optical pickup device of the present invention obtained in Example 1 is used, the deviation of the diffraction direction of the light flux of the two wavelengths is made to diffract and transmit the light beam of the first wavelength of 650 nm in the 0th order (that is, substantially Compared with the shift of the condensing point in the conventional optical pickup device using a diffraction element that diffracts and transmits the light beam of the second wavelength of 780 nm in the first order and matches the condensing point. Try.

In the conventional optical pickup device, the light beam having the first wavelength of 650 nm is diffracted and transmitted in the 0th order, so that the diffraction direction does not change even if the wavelength changes due to temperature change. On the other hand, the light beam with the second wavelength of 780 nm is first-order diffracted and diffracted and transmitted. Therefore, if a change in wavelength Δλ occurs due to a temperature change ΔΤ, a change in the diffraction angle Δ Δ represented by Eq.

twenty two

It is struck by force.

Δ α = Δ λ / p = W-ΔΤ / ρ (11)

2 2 2

As a result, the diffraction direction shift Δa due to the temperature change ΔΤ in this example is expressed by equation (12).

Δ α = I Δ α | = | W · ΔΤ / ρ | (12)

twenty two

Here, since W is about 0.25 nmZ ° C, equation (13) is established.

2

Δ α = I 0. 25 · ΔΤ / ρ | (13) Comparing Example 1 and Example 2, the difference in diffraction direction Δ α due to the temperature change ΔΤ in Example 1 is less than 1Z5 of the deviation in Example 2 obtained above and the return light of the first wavelength and the second It was shown that the shift of the focal point can be effectively suppressed by using the configuration of the optical pickup device of the present invention that first-order diffracts both the return light of the wavelengths.

[0082] [Example 3]

In Example 1, the diffractive element is installed perpendicular to the optical axis of the optical system. However, if the diffractive element is disposed obliquely with respect to the optical axis of the optical system, for example, a parallel plane half mirror is used as the optical element 2. It is preferable because it can have a function to reduce astigmatism that occurs in some cases. As shown in the configuration diagram around the diffraction element of the optical pickup device of the present invention shown in FIG. 7, when the diffraction element 8 is tilted 4 ° in the same direction as the tilt of the mirror mirror (hereinafter referred to as 4 ° tilt), The focal points of the return light of the two wavelengths are matched, and astigmatism is 0.03 λ for the first wavelength (for DVD) and 0.01 λ for the second wavelength (for CD) (both are wavefronts) Aberration RMS value. Hereinafter, the aberration value can be reduced to a wavefront aberration RMS value).

[0083] [Examples 4-6]

In Example 1, a straight and equidistant grating with parallel grooves is used as the diffraction element, but the present invention is not limited to this, and a diffraction element having a curved groove (hereinafter referred to as a curved groove diffraction element) may be used. Good. By using a diffractive element with a curved groove, for example, it is possible to provide a function for correcting coma and wrinkles or astigmatism that occurs when a parallel plate type half mirror is used as the optical element 2. It is preferable that a function for appropriately setting the amount of astigmatism of the light beam when using the astigmatism method for the focus detection means can be added.

The optical design of a diffractive element having a curved groove can be performed using a known phase function method.

That is, the phase function

[0084] [Equation 1]

0 = a _lo x + a _ol y + a _2O x ² + a ₁₁ xy + a _O2 y ² +-

_{^{_{+ A n0 x n + a n}}} L 11 -. + ■ - 11 -.. 1 dozen _{^{a 0n y n + · (14}} )

(a _u is the coefficient of each term, n is a positive integer) By optimizing each coefficient of It is possible to design the shape of a curved groove that has one or both of the function of removing the aberration generated by the element and the function of setting a predetermined amount of aberration and the function of matching the focal point .

[0085] When each diffractive element using a curved groove diffractive element having a phase function coefficient summarized in Table 2 is formed and replaced with the diffractive element in the optical pickup apparatus of Example 1, the optical pickup apparatus is configured as described above. The converging points of the return light of the two wavelengths are matched, and the coma and astigmatism summarized in Table 3 are obtained. The curved groove diffractive element in each example has a coma aberration reduction in example 4, coma and astigmatism reduction in example 5, coma aberration reduction and a desired value (0.5 λ in this example). The optical design is designed to obtain astigmatism.

[0086] In the optical pickup device using the diffractive elements having the curved grooves in Examples 4 to 6, the return light condensing points of the two wavelengths are made to coincide with each other. In Example 4, the astigmatism value is made equal to Example 1. Coma is reduced while maintaining. In Example 5, coma and astigmatism are simultaneously reduced. In Example 6, coma is reduced and the astigmatism value is adjusted to 0.5 °.

[0087] [Table 2]

[0088] [Table 3] Example 1 Example 3 Example 4 Example 5 Example 6 Coma aberration DVD 0. 047 A 0. 047 λ 0. 000 λ 0. 005 λ 0. 015 λ coma aberration CD 0. 023 λ 0. 023 λ 0. 000 λ 0. 001 λ 0. 006 λ Astigmatism DVD 0. 180 λ 0. 03 λ 0. 177 λ 0. 009 λ 0. 501 λ Astigmatism CD 0. 074 λ 0. 01 078 λ 0. 014 λ 0. 497 λ As described above, in the optical pickup device according to the first embodiment of the present invention, the diffractive element transmits each light flux of the return light having the first wavelength and the second return light having the wavelength. Since both are diffracted in the first order, the effect of changes in ambient temperature on each beam can be made comparable. Thereby, the shift of the condensing point of each return light on the light receiving surface of the light receiving element due to the change of the environmental temperature is suppressed.

[0090] In the above-described embodiment, the power described on the assumption that CD and DVD are compatible is compatible with Blu-ray Disc or HD—DVD (High Definition DVD) and DVD, or between Blu-ray Disc or HD—DVD and CD. It can be effectively applied to compatibility.

Further, in this embodiment, the optical system is configured as a so-called infinite optical system using a collimator lens, but the range to which the present invention is applied is limited to the infinite optical system. It is not limited, and it can be a finite optical system without using a collimator lens.

[II] Example for the second embodiment

[0092] In the optical pickup device according to the second embodiment, the forward optical system and the backward optical system have diffractive elements having the same grating pitch, and each diffractive element emits a light beam having the first wavelength. While diffracting with the same order, the second wavelength light beam is diffracted with the same order.

[0093] In the following, an example of a configuration in which each diffraction element has a first order of diffraction for diffracting a light beam of the first wavelength and a diffraction order power for diffracting a light beam of the second wavelength ^ For a configuration in which each diffraction element is of the order of the diffraction order that diffracts the light beam of the first wavelength, and the order of diffraction that diffracts the light beam of the second wavelength is the first order. An example will be described as [Example 8].

[0094] [Example 7]

As shown in FIG. 4, the optical pickup device 100 according to Example 7 includes a first light source 201a that emits a light beam with a first wavelength of 650 nm, and a second light source 201b that emits a light beam with a second wavelength of 780 nm. A light beam 205 emitted from each of the light sources 201a and 201b, an objective lens 206, a return diffraction element 209 for demultiplexing the return light from each information recording surface 207a and 208a, and a first wavelength after demultiplexing 6 includes a first light receiving element 210a that receives a light beam having a wavelength of 50 nm and a second light receiving element 210b that receives a light beam having a second wavelength of 780 nm after being demultiplexed. [0095] The optical pickup device 100 according to Example 7 includes a diffraction element 202, a 209 force, the first order of diffraction for diffracting a light beam having a first wavelength of 650 ηm, and a light beam having a second wavelength of 780 nm. The diffraction order is set to be the first order. Each diffraction element 202, 209 also has a diffraction grating force having the same grating pitch. First, multiplexing will be described.

FIG. 8 is an explanatory diagram of multiplexing performed by the optical pickup device 100 according to the seventh example. In FIG. 8, the light beams emitted from the first light source 201a and the second light source 201b are incident on the forward diffraction element 202 with the line indicated by reference numeral 221 and the line indicated by reference numeral 222 as optical axes, respectively. Hereinafter, the surface of the diffraction element on which the light beam enters is simply referred to as “incident surface”.

Here, each light beam enters the forward diffraction element 202 from a direction perpendicular to the incident surface of the forward diffraction element 202 (direction of a line indicated by reference numeral 223) and angles 0 and Θ. Hereafter, outbound trip a b

The angle formed by the light beam and the direction perpendicular to the incident surface of the folding element 202 is referred to as the incident angle. Each light beam incident on the outward diffraction element 202 exits from the outward diffraction element 202 in a substantially vertical direction. In addition, the direction of the light beam emitted from the forward diffraction element 202 is parallel to the optical axis of an optical system configured by the collimator lens 204, the objective lens 206, and the like (hereinafter referred to as the optical axis of the optical pickup device 100). It has become a direction.

[0098] When the wavelength of the light beam emitted from the first light source 201a is 650 nm and the grating pitch of the diffraction grating of the forward diffraction element 202 is P, the first light source 201a is emitted from the first light source 201a. A light beam having a different wavelength is incident on the forward diffraction element 202 at an incident angle of 0 expressed by equation (15).

1 a

Placed in position.

θ = λ / p (15)

a 1

Similarly, the wavelength of the light beam emitted from the second light source 201b is 780 nm, and the forward diffraction element

2

Assuming that the grating pitch of the diffraction grating 202 is p, the second light source 201b is configured such that the light beam having the wavelength emitted from the second light source 201b is incident on the forward diffraction element 202 with an incident angle represented by equation (16) 0 so

2 b Located at the incident position.

θ = λ / p (16)

b 2

By arranging the first light source 201a and the second light source 201b in this manner, the light emitted from each of the light sources 20 la and 20 lb is diffracted by the outward diffraction element 202 and emitted. The directions will match.

[0099] Next, demultiplexing will be described. FIG. 9 is an explanatory diagram of the demultiplexing performed by the optical pickup device according to Example 7. Hereinafter, the grating pitch of the diffraction grating of the backward diffraction element 209 is assumed to be q. Return light from the information recording surface 207a of the optical disc 207 or the information recording surface 208a of the optical disc 208 enters the entrance surface of the return diffraction element 209 substantially perpendicularly with the line indicated by reference numeral 231 in FIG. Diffracts at the following diffraction angles.

[0100] That is, the light flux of the wavelength emitted from the first light source 201a is diffracted at the diffraction angle represented by λ Zq, and the light flux of the wavelength emitted from the second light source 201b is

The light is diffracted at a diffraction angle represented by 2 λ 2 Zq and emitted from the backward diffraction element 209 using the line indicated by reference numeral 232 or the line indicated by reference numeral 233 as the optical axis.

Since the light beam emitted from the first light source 201a and the light beam emitted from the second light source 201b have different wavelengths, these light beams are demultiplexed by the backward diffraction element 209 as described above. . Here, the first light receiving element 210a is arranged such that the light receiving surface is positioned on a line indicated by reference numeral 232. Similarly, the second light receiving element 210b is arranged such that the light receiving surface is positioned on a line indicated by reference numeral 233.

[0101] The behavior of the optical pickup device according to Example 1 when the oscillation wavelength of the light source fluctuates with a change in environmental temperature is described below. FIG. 10 is a diagram illustrating the optical axis direction of the incident light beam to the forward diffraction element 202 and the optical axis direction of the diffracted light beam when the oscillation wavelengths of the light sources 201a and 201b change. Components similar to those shown are denoted by the same reference numerals.

[0102] First, the oscillation wavelength power of the first light source 201a +

Assume that Δ λ is changed. At this time, the diffraction angle when the light beam emitted from the first light source 201a is diffracted by the forward diffraction element 202 is expressed by Expression (17).

(λ + Μ) / ρ (17)

Due to the fluctuation of the oscillation wavelength of the first light source 201a, the diffraction angle fluctuates by ΔλΖΡ compared to when there is no fluctuation in wavelength. If this amount (Δ λ ΖΡ) is Δ 0,

1 1 a

The light beam travels along a direction (line direction indicated by reference numeral 223) perpendicular to the exit surface of the forward diffraction element 202 and a direction (line direction indicated by reference numeral 241) formed by an angle ΔΘ. Similarly, the oscillation wavelength λ 1S of the second light source 201b is changed by the change in the environmental temperature.

2

Suppose that it has changed to + Δλ. At this time, the light beam emitted from the second light source 201b is

twenty two

The diffraction angle when diffracting by the diffraction element 2 is expressed by the following equation (18).

(λ + Μ) / ρ (18)

b b

Δ λ b b due to the change in the oscillation wavelength of the second light source lb

The diffraction angle changes by ZP. If this amount (Δ λ ΖΡ) is Δ 0, the light flux b b after wavelength change

Is along a direction perpendicular to the exit surface of the forward diffraction element 202 (direction of a line indicated by reference numeral 223) and an angle ΔΘ (direction of a line indicated by reference numeral 242).

b

[0104] In this way, light fluxes whose emission directions from the forward diffraction element 202 are shifted by ΔΘa or ΔΘ due to fluctuations in the wavelength of the light source are the information recording surfaces 207a and b of the first optical disc 207, respectively.

When reflected by the information recording surface 208 a of the second optical disk 208, the light enters the backward diffraction element 209 at an angle Δ 0 or an angle Δ 0 with the direction perpendicular to the backward diffraction element 209.

a b

[0105] Hereinafter, the operation of the optical pickup device 100 when entering the return diffraction element 209 at an angle with the direction perpendicular to the incident surface of the return diffraction element 209 as described above will be described with reference to FIG. FIG. 11 is a diagram illustrating the incident direction of the light beam incident on the return path diffraction element 209 and the emission direction of the light beam output from the return path diffraction element 209 when the oscillation wavelengths of the light sources 201a and 201b change. Components similar to those shown in FIG. 9 are given the same reference numerals.

First, a light beam having a wavelength (λ + λ λ) is perpendicular to the incident surface of the return diffraction element 209 (the direction of the line indicated by reference numeral 231) and an angle Δ 0 (= Α λ

The diffraction angle when a 1 路 ρ) is incident on the backward diffraction element 209 and diffracted by the backward diffraction element 209 is expressed by the following equation (19).

(λ + Α λ) / q (19)

The light beam incident on the backward diffraction element 209 is diffracted in the direction with the line indicated by reference numeral 253 as the optical axis. The direction of diffraction at this time is the direction perpendicular to the backward diffraction element 209 (the line indicated by reference numeral 231). Direction) and an angle represented by the following equation (20).

(λ + Α λ) / q- M Zp (20)

Similarly, a light beam having a wavelength (λ + Δλ) is directed in a direction perpendicular to the incident surface of the return diffraction element 209 ( The direction of the line indicated by reference numeral 231) and the angle Δ 0 (= Δ λ Ζρ) and b 2

The diffraction angle when incident and diffracted by the backward diffraction element 209 is expressed by the following equation (21).

(λ + Μ) / q (21)

twenty two

The light beam incident on the backward diffraction element 209 is diffracted in the direction with the line indicated by reference numeral 254 as the optical axis. The direction of diffraction at this time is the direction perpendicular to the backward diffraction element 209 (the line indicated by reference numeral 231). Direction) and an angle represented by the following equation (22).

(λ + Μ) / q- M

2 2 2 Zp (22)

Here, if the grating pitch q of the diffraction grating of the backward diffraction element 209 is equal to the grating pitch P of the diffraction grating of the forward diffraction element 202, Δλ Zq and Δλ Zp in the above equation (20) cancel each other. In the meantime, the direction of the light beam after being diffracted by the backward diffraction element 209 indicated by reference numeral 253 is the same as the direction of the light beam indicated by reference numeral 232 in FIG. Similarly, the direction of the diffracted light beam indicated by reference numeral 254 is the same as the direction of the light beam indicated by reference numeral 233 in FIG.

[0107] This is caused by equalizing the grating pitch of the diffraction grating of the forward diffraction element 202 and the grating pitch of the diffraction grating of the backward diffraction element 209, thereby generating a circuit that occurs when multiplexing is performed due to the influence of wavelength variation. This shows that the change in bending angle and the change in diffraction angle that occurs when demultiplexing cancel each other, and even if the change in wavelength occurs, the exit direction after diffracting by the return path diffraction element 209 does not change. Therefore, even if a temperature change occurs, the position on the light receiving element where the light beam is collected does not change.

[0108] Specific configurations of the first diffraction element 202 and the second diffraction element 209 are shown below. FIG. 12 is a cross-sectional view conceptually showing a part of the cross section of the forward diffraction element 202 according to the present embodiment. Here, a surface denoted by reference numeral 261 is an incident surface on which light beams emitted from the light sources 201a and 201b are incident, and a surface denoted by reference numeral 262 is an output surface from which each light beam is emitted.

The light beam emitted from the first light source 201a and the light beam emitted from the second light source 201b are respectively derived from the direction of the arrow indicated by reference numeral 263 and the direction of the arrow indicated by reference numeral 264, respectively. Is incident on. Further, each light beam diffracted by the forward diffraction element 202 is emitted in a direction in which the directional force indicated by the arrow 265 also deviates.

[0110] The material of the outward diffraction element 202 is quartz glass, and the diffraction grating of the outward diffraction element 202 is It is formed using an etching technique. As shown in FIG. 12, the forward diffraction element 202 is constituted by a diffraction grating having a cross-sectional shape having a periodic structure in which a stepped shape repeats periodically. In this embodiment, the diffraction grating has a periodic structure in which one step is a step with 6 step force, and the step d of each step (step) is 0.254 m.

[0111] In addition, the width of the portion (hereinafter, referred to as a flat portion) substantially parallel to the exit surface of each floor was set to 1. so that the pitch was 10 m. Such a diffraction grating is called a binary blazed diffraction grating. As described above, by setting the number of steps (in other words, the total number of flat portions in one cycle) to 6 and setting each step d to 0.254 / zm, the first light source The diffraction efficiency of the first-order diffraction of the emitted light beam with a wavelength of 650 nm and the light beam with a wavelength of 780 nm emitted by the second light source can both be 80%.

FIG. 13 is a cross-sectional view conceptually showing a part of a cross section of the backward diffraction element 20 according to the present example.

Here, the surface denoted by reference numeral 271 is the incident surface of each return light, and the surface denoted by reference numeral 272 is the exit surface of the return path diffraction element 209.

[0113] The light beam emitted from the first light source 201a and the light beam emitted from the second light source 201b are reflected by the information recording surfaces 207a and 208a of the optical disks 207 and 208, respectively, and are reflected on the return path diffraction element 209. The light enters from a direction substantially perpendicular to the line (the direction of the line indicated by reference numeral 273). When the wavelength fluctuates, the light enters from the direction deviating from the line indicated by reference numeral 273 as described above.

[0114] The light flux of the wavelength diffracted by the backward diffraction element 209 (the light flux from the first light 201a)

A light beam having a wavelength (e.g., diffracted by the backward diffraction element 209)

2

2) is emitted in the direction of the arrow indicated by reference numeral 275. The material of the return path diffraction element 209 and the structure of the diffraction grating of the return path diffraction element 209 are the same as those of the forward path diffraction element 202.

[0115] [Example 8]

As shown in FIG. 14, the optical pickup device 800 according to Example 8 has the same optical elements as the optical pickup device 100 according to Example 1, but the optical pickup device 100 according to Example 1 is part of the optical member. The relative arrangement of is different. In FIG. 14, the optical pickup device 1 according to Example 1 is shown. The same reference numerals are assigned to optical members similar to those in 00.

[0116] The optical pickup device 800 according to Example 8 does not diffract the light beam having the first wavelength of 650 ηm (the diffraction order is 0th order), and diffracts the light beam of the second wavelength of 780 nm. (The order of diffraction is the first order). First, multiplexing will be described.

FIG. 15 is an explanatory diagram of multiplexing performed by the optical pickup device 800 according to Example 8.

In FIG. 15, the light beam emitted from the first light source 201a is incident substantially perpendicular to the incident surface of the forward diffraction element 202 (in the direction of the line indicated by reference numeral 291), and is not diffracted by the forward diffraction element 202. (Diffraction order is 0th order), the light is emitted in a direction substantially perpendicular to the exit surface of the forward diffraction element 202 (the direction of the line indicated by reference numeral 291).

[0118] The wavelength of the light beam emitted from the second light source 201b is 780 nm.

2

When the grating pitch of the folded grating is P, the second light source 201b has an optical axis of the light beam emitted from the second light source 201b and an angle Θ represented by the following equation (23) with the line indicated by reference numeral 291. Arranged as b

Is done.

θ = λ / p (23)

b 2

The incident direction of the light beam emitted from the second light source 201b to the forward diffraction element 202 is indicated by a line denoted by reference numeral 292. The forward diffraction element 202 causes the light beam emitted from the second light source 201b to enter from this direction, so that the forward diffraction element 202 performs first-order diffraction, and a direction perpendicular to the forward diffraction element 202 (a line denoted by reference numeral 291). The light is emitted along the direction of

In this way, the light beam emitted from the first light source 201a is diffracted by the 0th order by the forward diffraction element 202, and the light beam also emitted by the second light source 201b is diffracted by the first diffraction order by the forward diffraction element 202. By performing the above, the light beams emitted from the light sources 201a and 201b can be combined.

Next, demultiplexing will be described. FIG. 16 is an explanatory diagram of demultiplexing performed by the optical pickup device 800 according to Example 8. Here, the grating pitch of the diffraction grating of the backward diffraction element 209 is assumed to be q.

[0121] In FIG. 16, the return lights of the information recording surfaces 207a and 2078a of the optical disks 207 and 208 are incident substantially perpendicularly to the incident surface of the return diffraction element 209 (the direction of the line denoted by reference numeral 101). To do. Here, the light beam having the first wavelength (the light beam emitted from the first light source) is the second light beam. Without being diffracted by the folding element 9 (the order of diffraction is the 0th order), the light is emitted substantially perpendicular to the emission surface of the second diffraction element 9.

On the other hand, the light beam having the second wavelength (the light beam emitted from the second light source)

With respect to the direction perpendicular to the exit surface of 09, the light is emitted in a direction (direction of a line indicated by reference numeral 102) that forms an emission angle represented by the following expression (24).

λ / q (24)

2

Here, the first light receiving element 210 a is disposed on a line denoted by reference numeral 101, and the second light receiving element 210 b is disposed on a line denoted by reference numeral 102.

[0123] Hereinafter, the behavior of the optical pickup device according to Example 8 when the oscillation wavelength of the light source fluctuates with a change in environmental temperature will be described. In the optical pickup device according to Example 8, the light beam emitted from the first light 201a is not diffracted by the forward diffraction element 202 and the backward diffraction element 209 (the diffraction orders are both 0th order), so the oscillation wavelength varies. However, the light beam emitted from the first light source 2 Ola reaches the first light receiving element 210a without being affected by the emission direction from each of the diffraction elements 202 and 209.

Next, it can be considered that the light beam emitted from the second light source 201b is subjected to the same action as that described in the above (Example 1). That is, by making the grating pitch of the diffraction grating of the forward diffraction element 202 and the grating pitch of the diffraction grating of the backward diffraction element 209 equal, the fluctuation of the diffraction angle in the forward diffraction element 202 due to the fluctuation of the wavelength and the return diffraction element It is possible to cancel the fluctuation of the diffraction angle at 209 with substantially the same amount, and the optical axis direction of each light beam emitted from the return path diffusing element 209 is not affected by the change of the environmental temperature. Therefore, the light beam emitted from the backward diffraction element 209 reaches the second light receiving element 210b regardless of the change in wavelength.

[0125] Specific configurations of the forward diffraction element 202 and the backward diffraction element 209 according to the present embodiment are shown below. FIG. 17 is a sectional view conceptually showing a section of the forward diffraction element 202 according to the present example. The forward diffraction element 202 has a configuration in which a first wave plate 111, a polarization diffraction grating 112, and a second wave plate 113 are stacked and fixed. Here, the light flux of each wavelength λ is directly

1 2

Let it be linearly polarized light. The first diffractive element 2 needs to select whether or not the first-order diffraction is performed according to the wavelength. Therefore, the forward diffraction element 202 uses the first wavelength plate 111 to change the polarization direction of a light beam having a predetermined wavelength (hereinafter, referred to as a light beam having a wavelength λ) to a specific polarization direction, and to select other wavelengths (hereinafter, referred to as “wavelength λ”). The light beam with a wavelength of λ) is orthogonal to the polarization direction of the light beam of

2

Only the light beam in the direction is diffracted and the polarization direction is returned to the original by the second wave plate 113.

[0127] The polarization direction of the light beam (wavelength) emitted from the first light source 201a and the polarization direction of the light beam (wavelength) emitted from the second light source 2 Olb are the same in the forward direction. Diffraction element

2

A light source is arranged to be incident on the child 202. The first wave plate 111 fixes uniaxially stretched polycarbonate to a glass substrate, functions as a 5 × 2 wave plate with respect to a light beam having a wavelength λ emitted from the first light source 201a, and from the second light source 201b. Emitted wavelength λ

A retardation plate that functions as a two-wavelength plate for two luminous fluxes was created.

[0128] Since the first wave plate 111 has the function of the above-mentioned retardation plate, it acts as a 1Z2 wave plate with respect to the light flux of the wavelength, so that the polarization direction of the incident light of the wavelength is 90 ° Will rotate. On the other hand, incident light having a wavelength of 2 is substantially equivalent to the case where there is no waveplate, and the polarization direction does not rotate. In this way, by rotating the polarization direction of only a linearly polarized light beam having a predetermined wavelength (wavelength), the light (wavelength λ) emitted from the linearly polarized first light source 201a polarized in the same direction can be changed. The polarization direction of the outgoing light (wavelength) from the second light source 201b is orthogonalized.

2

FIG. 18 is a cross-sectional view conceptually showing a part of the cross section of the polarization diffraction grating 112 constituting the forward diffraction element 202. The polarization diffraction grating 112 is a cross-sectional shape having a periodic structure in which a birefringent material layer 121 and an isotropic material layer 122 are joined, and the birefringent material layer 121 repeats a stepped shape periodically. The isotropic material layer 122 is configured to fill the stepped portion.

Here, as the material of the birefringent material layer 121 and the isotropic material layer 122, a birefringent material and an isotropic material satisfying the two conditions described below were used.

First, the first condition is the configuration of the optical system in which the polarization direction of the light beam having the wavelength after passing through the first wave plate 111 is orthogonal to the longitudinal direction of the diffraction grating. The refractive index of the birefringent material layer 121 with respect to the luminous flux after the wavelength is η (λ) and isotropic When the refractive index of the material layer 122 is n (λ), the relationship expressed by the following equation (25) is almost satisfied.

twenty one

It is being done.

η (λ) = η (λ) (25)

11 a 2 a

The second condition is that the polarization direction of the light beam after transmission through the wave plate 111 is a diffraction grating.

2

The refractive index of the birefringent material layer 121 with respect to the light flux of the wavelength after passing through the wave plate 111 is η (λ), and the refractive index of the isotropic material layer 122 is

12 2

When the rate is η (λ), the relationship expressed by the following equation (26) is almost satisfied.

twenty two

The

η (λ) ≠ η (λ) (26)

12 b 2 b

By constructing the optical system and the polarization diffraction grating 112 so as to satisfy the above conditions, the light beam having the wavelength λ is not diffracted (the order of diffraction is the 0th order), and the light beam having the wavelength λ is polarized. The forward diffraction element 202 is provided with a selective diffraction function capable of diffracting a light beam having a wavelength of 2 with orthogonal directions. Here, a polymer liquid crystal was used as the birefringent material, and an epoxy ultraviolet curable resin was used as the isotropic material.

[0131] Table 4 shows the refractive indexes of the birefringent material and the isotropic material used for the polarizing diffraction grating 112.

[0132] [Table 4]

[0133] The polarization diffraction grating 112 is fixed by being overlapped with a 0.5 mm-thick cover glass (glass material K7) 123 on the side of the isotropic material layer 122 and fixed on the birefringent material layer 121 side. A 0.5mm cover glass (glass material BK7) 124 is overlaid and fixed. In this example, the width of the flat part of each step is set so that one cycle of the scale is composed of 8 steps, each step has a height of 0.449 / zm and the pitch of the grid is 10 m. 1. A 25 m shaped diffraction grating was fabricated. [0134] By configuring the forward diffraction element 202 as described above, the transmittance of the light beam having a wavelength of 65 Onm that performs 0th-order diffraction is 95%, and the diffraction efficiency of the first-order diffraction of a light beam having a wavelength of 780nm is 83% Can be. Here, similarly to the first wave plate 111 described above, the second wave plate 113 also has a uniaxially stretched polycarbonate fixed to a glass substrate, and a light beam of a wavelength emitted from the first light source 201a. In contrast, it functions as a 5Z2 wave plate and a phase difference plate that functions as a two-wave plate for the light beam having the wavelength λ emitted from the second light source 201b.

2

Created.

[0135] Since the second wave plate 113 has the function of the above-mentioned retardation plate, it acts as a 1Z2 wave plate for the wavelength beam, so that the polarization direction of the incident light at the wavelength is 90 ° Will rotate. On the other hand, there is no wave plate for incident light with a wavelength.

2

This is substantially equivalent to the case, and no rotation of the polarization direction occurs. In this way, by rotating the polarization direction of only a linearly polarized light beam having a predetermined wavelength (wavelength), the light emitted from the linearly polarized first light source 201a (wavelength λ) and the second light source The polarization direction of the outgoing light (wavelength λ) from 201b can be returned to the polarization direction when entering the forward diffraction element 202.

2

Togashi.

FIG. 19 is a cross-sectional view conceptually showing a cross section of the backward diffraction element 209 according to the present example. The return path diffraction element 209 is configured by a first wave plate 131, a polarization diffraction grating 132, and a second wave plate 133, similarly to the forward path diffraction element 202. In addition, the material used for manufacturing the backward diffraction element 209 and the structure of the diffraction grating of the backward diffraction element 209 were the same as the material used for manufacturing the forward path diffraction element 202 and the structure of the diffraction grating.

[0137] In the above embodiment, the power described on the assumption that CD and DVD are compatible is currently being put into practical use, such as BLURAY (registered trademark) disc or HD-DVD (High Definition DVD), It can also be effectively applied to combinations with other DVDs. Similarly, the present invention can be effectively applied to a combination of BLURAY (registered trademark) disc or HD-DVD and CD.

In this embodiment, the optical system is configured as a so-called infinite optical system using a collimator lens, but the range to which the present invention is applied is limited to the infinite optical system. The optical system is not limited and may be a finite optical system that does not use a collimator lens. [0139] In the present embodiment, the diffraction element having a diffraction grating having a periodic structure in which the cross-sectional shape repeats a sawtooth shape has been described. However, the present invention combines a wavelength plate and a polarization diffraction grating. However, the present invention is not limited to the configuration using the diffraction element. Specifically, even if a diffraction element having a diffraction grating having a periodic structure in which a cross-sectional shape approximates a sawtooth shape by a stepped shape is used, a diffraction element having diffraction gratings having other cross-sectional shapes is used. May be used.

[0140] Furthermore, in the present embodiment, an element combining a wave plate and a polarization diffraction grating has been described as a diffraction element having wavelength selectivity. However, the present invention includes a wave plate and a polarization diffraction grating. It is not limited to the structure using the combined diffraction element. Specifically, a combination of an organic pigment and a filler that has a refractive index equal to one wavelength even in a diffraction grating in which the grating depth is converted to an optical path length and is an integral multiple of one wavelength. Either a configuration using a diffraction grating or a configuration using other diffraction elements.

[0141] As described above, in the optical pickup device according to the embodiment of the present invention, the forward diffraction element and the backward diffraction element have diffraction gratings having the same grating pitch, and the light flux having the first wavelength. Are diffracted at the same diffraction order, and the light beams of the second wavelength are diffracted at the same diffraction order. It is possible to suppress the influence of changes in the environmental temperature on the positional deviation of the spot of the condensed light beam.

[0142] Furthermore, since the diffraction orders of the diffraction elements are all first-order, it is possible to realize an optical pickup device with high use efficiency of light using diffraction with high diffraction efficiency.

[0143] Furthermore, each diffraction element has a wavelength selectivity that can select the wavelength of light to be diffracted by the first or higher order of diffraction, so that an optical pickup device with high light utilization efficiency can be realized.

[0144] In addition, since each diffraction element diffracts both the light flux of the first wavelength at the 0th-order diffraction order and diffracts the light flux of the second wavelength together at the first-order diffraction order, Highly efficient V and optical pickup device can be realized.

[0145] Furthermore, each diffraction element has a diffraction grating with a periodic structure in which the cross-sectional shape repeats a sawtooth shape, so that the diffraction element can be easily manufactured. [0146] Further, each diffraction element has a diffraction grating having a periodic structure in which a cross-sectional shape is similar to a stepped shape approximated to a sawtooth shape, so that the diffraction element can be manufactured more easily.

[III] Example for the third embodiment

[Example 9]

An embodiment according to Example 9 will be described below with reference to FIG.

As shown in FIG. 5, the optical arrangement of the optical pickup device 310 includes a first light source 301a that emits a linearly polarized light beam with a wavelength of 650 nm and a second light source 301b that emits a linearly polarized light beam with a wavelength of 780 nm. First diffraction element 302 for combining light beams from the light source, quarter wave plate 304, = 3 refraction lens 305, aperture 306, objective lens 307, optical disk D or D A b al bl for demultiplexing the light beam reflected on the information recording surface (D or D)

A second diffractive element 303, a first light receiving element 8a for receiving a demultiplexed light beam having a wavelength of 650 nm, and a second light receiving element 8b for receiving a light beam having a demultiplexed wavelength of 780 nm are provided.

In the optical pickup device 310 of the present embodiment, the diffraction by the first diffractive element 302 and the diffraction by the second diffractive element 303 are both the first-order diffraction with respect to the light beam having the first wavelength. The diffraction by the first diffractive element 302 and the diffraction by the second diffractive element 303 both use the first-order diffraction for the light flux having the wavelength.

First, the multiplexing will be described.

FIG. 20 is an explanatory diagram of the multiplexing action performed by the optical pickup device 310. In FIG. 20, the light beams emitted from the first light source 301a and the second light source 301b are respectively perpendicular to the first diffractive element 302 with respect to the first diffractive element 302 with respect to the optical axis α, j8 force. Direction (sign Ύ

Angle from (line shown by 1) 0

a, Θ

The light enters in the state of b, and exits almost perpendicularly to the first diffraction element 302. Further, the emission direction coincides with the optical axis of an optical system including the collimator lens 305, the objective lens 307, and the like.

[0148] Here, the first light source 301a has an incident angle 0 force of the light beam emitted from the first light source 301a on the first diffractive element 302. The wavelength of the first light source 301a is obtained, and the grating of the first diffractive element 302 The pitch of pa 1

As shown in FIG.

θ = λ / p (27)

a 1

On the other hand, the second light source 301b includes the first diffraction element 30 of the light beam emitted from the second light source 301b. Incident angle to 2 0 force The wavelength of the second light source 301b is obtained, and the diffraction b 2 of this first diffraction element 302

The pitch of the lattice is set as p, and it is arranged so as to satisfy equation (28).

θ = λ / p (28)

B B

As described above, by arranging the first light source 301a and the second light source 301b, the emission directions of the light beams emitted from the respective light sources la and lb after being diffracted by the first diffraction element 302 are changed. -It will match. The combined light beam passes through the second diffraction element 303, passes through the 1 Z4 wavelength plate 304, the collimator lens 305, the stop 306, and the objective lens 307, and passes through the optical disk information recording surface (D or D). Reflected by. And this reflected light flux is the above al bl

In the reverse order of the traveling direction, the light passes through the objective lens 307, the diaphragm 306, the collimator lens 305, and the quarter wavelength plate 304, and is demultiplexed by the second diffraction element 303.

[0150] Next, demultiplexing will be described below.

FIG. 21 is an explanatory diagram of the demultiplexing effect performed by the optical pickup device 310. FIG. Here, the pitch of the diffraction grating of the second diffraction element 303 is q.

In FIG. 21, the return beam is such that the optical axis γ is substantially perpendicular to the second diffraction element 303.

2

In this state, the incident light beam from the right side of the figure (the light beam emitted from the first light source) is diffracted at the diffraction angle expressed by Equation (29), and is emitted with the line indicated by the symbol α as the optical axis.

2

λ Zq (29)

On the other hand, the light flux of the wavelength (the light emitted from the second light source) is the diffraction angle expressed by equation (30).

2

Diffracted at the sign j8

The line indicated by 2 is emitted as the optical axis.

λ Zq (30)

2

Thus, the second diffraction element 303 demultiplexes light beams having different wavelengths. The first light receiving element 308a is on the line indicated by the symbol α, and the second light receiving element 308b is the symbol

2

Place on the line indicated by. The demultiplexed light beams pass through the first diffraction grating 302.

2

And reaches the light receiving element 308a or 308b.

As described above, the first diffractive element 302 and the second diffractive element 303 are each made of a birefringent material in order to increase the diffraction efficiency in both the reciprocal force and the reciprocal force using diffraction of different orders. The polarizing diffraction element is provided.

[0151] The first diffractive element 302 has a diffractive function for linearly polarized light beams that also emit light. The direction of the slow axis of the birefringent material constituting the first diffraction element 302 is made to coincide with the polarization direction of the linearly polarized light from the light source so that the first diffraction grating 302 has a periodic direction. Is perpendicular to the direction of the slow axis.

On the other hand, the second diffraction grating 303 is directed in the direction of the slow axis of the birefringent material constituting the second diffraction element 303 so that it does not have a diffraction function with respect to the linearly polarized light beam emitted from the light source. Are matched with the direction orthogonal to the polarization direction of the linearly polarized light from the light source, and the periodic direction of the second diffraction grating 303 is the direction of the slow axis.

[0152] Hereinafter, specific configurations of the first diffraction element 302 and the second diffraction element 303 will be described.

FIG. 22 is a schematic diagram illustrating the configuration of the first diffractive element 302 and the second diffractive element 303. The first diffractive element 302 includes two birefringent material layers 321 and isotropic material layers 322. The quartz glass substrate (323, 324) is sandwiched between the outer surfaces (325, 326) of each quartz glass, and an antireflection film for the wavelength used is applied.

By using a polymer liquid crystal as the birefringent material layer 321 described above, a polymer liquid crystal layer is formed on a quartz glass substrate 323, and the surface is subjected to photolithography processing, thereby repeating convex portions having a sawtooth cross-sectional shape. A lattice plane is formed. Then, using an epoxy-based ultraviolet curable resin as an isotropic material, the concave portions of the lattice surface are filled and laminated so that the surface becomes smooth (isotropic material layer 322), cured, and quartz Power bar with glass (glass substrate 324).

Here, the polymer liquid crystal used for the birefringent material layer 321 includes an ultraviolet curable epoxy film having an ordinary refractive index at the first wavelength of 650 nm and the second wavelength of 780 nm, which is used as the isotropic material layer 322. A material having substantially the same refractive index as that of fat and having a large difference between ordinary light refractive index and extraordinary light refractive index of 0.221 and 0.211 is used. Table 1 shows the refractive index of the material.

[0153] [Table 5] 6 5 0 nm 7 80 0 nm

Birefringent material Ordinary refractive index 1.5 5 6 1 1.5 3 9

Extraordinary refractive index 1.7 6 7 1. 7 5 0

Isotropic material Refractive index 1.5 4 2 1.5 5 9

[0154] The first diffractive element 302 has a slow axis of the birefringent material layer 321 constituting the first diffractive element 302 so as to have a diffractive function with respect to linearly polarized light flux that also emits light source power. The direction is matched with the polarization direction of the linearly polarized light from the light source, and the periodic direction of the diffraction grating is orthogonal to the direction of the slow axis.

Referring to FIG. 22, the polarization direction of linearly polarized light that is also emitted from a light source force not shown is defined as the y direction, and the slow axis of the polymer liquid crystal used for the birefringent material layer 321 is defined as the y direction. The periodic direction of the diffraction grating formed in the birefringent material layer 321 is defined as the X direction. In this example, as a specific diffraction grating shape, one period of the periodic structure of the diffraction grating is composed of 8 steps, and the step of each step is 0.41 m. In addition, the width of the flat part of each staircase is set to 1. so that the pitch is 10 m.

[0155] By setting as described above, the diffraction efficiency of the first-order diffraction for the light beams having the wavelength of 650 nm and the wavelength of 780 nm can be both 84%. The transmittance (0th-order diffraction efficiency) is 99% at both wavelengths.

In the above embodiment, a blazed shape that is processed using a gray scale mask is used instead of approximating the force saw-tooth shape, which forms the structure of one period of the grating by 8 steps, in a multi-step manner. If used, a diffraction efficiency of 87% is obtained with a first-order diffraction efficiency for any wavelength, which is more desirable. The transmittance is 99% at both wavelengths.

The structure of the second diffractive element 303 is also basically the same as that of the first diffractive element 302 described above. The direction of the slow axis of the polymer liquid crystal used as the force birefringent material layer is different. Referring to FIG. 22, the polarization direction of linearly polarized light emitted from the light source force is defined as the y direction, and the slow axis of the polymer liquid crystal used for the birefringent material layer 321 is defined as the X direction. The periodic direction of the diffraction grating formed in the birefringent material layer 321 is also the X direction. In this example, as a specific diffraction grating shape, one period of the periodic structure of the diffraction grating is composed of 8 steps, and the step of each step is set to 0.41 μm. The width of the flat part of each staircase was set to 1.25 m so that the pitch would be 10 m. By setting in this way, the diffraction efficiency of the first-order diffraction of a light beam having a wavelength of 650 nm and a wavelength of 780 nm can be made 85%. The transmittance (0th-order diffraction efficiency) is 99% at both wavelengths.

In the second diffractive element 303 as well, as in the first diffractive element 302, the structure of one period of the grating is configured by the 8-step staircase. However, if the sawtooth shape is approximated by a multi-step staircase shape, Using a blazed shape that is covered by using a gray scale mask, a diffraction efficiency of 87% is obtained with the first-order diffraction efficiency for any wavelength, which is more desirable. The transmittance is 99% at both wavelengths.

[0157] As described above, the optical pickup device according to the present invention uses two polarizing diffraction elements such as a grating pitch on the light receiving element for the light flux accompanying the wavelength variation due to the change in the environmental temperature. The fluctuation | variation of the condensing position can be suppressed. In the above-described embodiment, the description has been made on the assumption that CD and DVD are compatible. The present invention can also be effectively implemented for a combination of BLURAY or HD DVD and a conventional DVD that are currently being put into practical use. Alternatively, it can be effectively implemented for a combination of B LURAY or HD—DVD and CD. The optical pickup device of the present invention is configured as a so-called infinite optical system using a collimator lens. However, the scope to which the present invention is applied is not limited to an infinite optical system, It may be a finite optical system that does not use a collimator lens. Further, although the second diffraction element 303 and the 1Z4 wave plate 304 are configured separately, they may be laminated and integrated.

[0158] It should be noted that the power described in the first, second and third embodiments of the present invention is not limited to these embodiments at all, and various modifications can be made without departing from the scope of the present invention. It can implement in the aspect of.

Industrial applicability

[0159] The pickup device of the present invention has the effect of suppressing the fluctuation of the light condensing position on the light receiving element due to the change of the wavelength due to the change of the operating temperature by providing two diffraction elements having the same grating pitch. And is effectively used for an optical pickup device that records and reproduces a plurality of different types of optical disks. In August 2004, this patent application was filed 2004–227846, 2004 8 Japanese Patent Application No. 2004-252148 filed on May 31, and Japanese Patent Application No. 2004-266596 filed on September 14, 2004 Full content of claims, drawings and summary It is cited here and incorporated as the disclosure of the specification of the present invention.

Claims

The scope of the claims

[1] Two light sources that respectively emit light beams of two different wavelengths, an objective lens installed between the light source and the optical recording medium, and one or two installed between the objective lens and the optical recording medium In an optical pickup device comprising two diffractive elements and a light receiving element that detects the light beam reflected by the optical recording medium, the diffractive element diffracts the two light beams with the same or different orders and guides them to the light receiving element. An optical pickup device characterized by the above.

[2] A first light source that emits a light beam having a first wavelength, a second light source that emits a light beam having a second wavelength different from the first wavelength, and the 2 reflected by an optical recording medium An objective lens for condensing return light fluxes of one wavelength; and an objective lens disposed between the objective lens and a condensing point thereof, and diffracting and transmitting the return light beams of the two wavelengths incident through the objective lens 1 Two diffraction elements, and a light receiving element that is disposed at a condensing point of the return light beams of the two wavelengths that are collected by the objective lens, diffracted by the diffraction element, and transmitted, and that receives the return light beam. 2. The optical pickup device according to claim 1, wherein the diffraction element diffracts and transmits the return light beam with the same order so that the light collection points of the two wavelengths substantially coincide on the light receiving surface of the light receiving element.

[3] A first light source that emits a light beam having a first wavelength, a second light source that emits a light beam having a second wavelength different from the first wavelength, the light beam having the first wavelength, and the A forward optical system including an objective lens that guides the light flux of the second wavelength toward the optical recording medium, a first light receiving element that receives the return light beam of the first wavelength from the optical recording medium, and the optical recording A second light receiving element that receives the return light beam having the second wavelength from the medium, and a return light beam having the first wavelength from the optical recording medium to the first light receiving element and from the optical recording medium. A return optical system including an objective lens that guides the return light beam of the second wavelength to the second light receiving element,

The outward optical system includes an outward diffraction element that diffracts at least one of the light beam having the first wavelength and the light beam having the second wavelength,

The return path optical system has a return path diffraction element that diffracts at least one of the return light beam of the first wavelength and the return light beam of the second wavelength,

The forward diffraction element and the backward diffraction element are diffraction gratings having an equal grating pitch. 2. The optical pick-up device according to claim 1, wherein the first wavelength light beam is diffracted with the same diffraction order, and the second wavelength light beam is diffracted with the same diffraction order.

[4] A first light source that emits a light beam having a first wavelength, a second light source that emits a light beam having a second wavelength different from the first wavelength, and the light beam from the light source An objective lens for focusing on the optical recording medium, a light receiving element for detecting a light flux collected by the objective lens and reflected by the optical recording medium, and a light beam emitted from the first light source and the second light source The first diffractive element having a diffraction function and having no diffraction function with respect to the light beam reflected by the optical recording medium, the first light source, and the second light source emit light. A second diffractive element that does not have a diffractive function for a light beam and has a diffractive function for a light beam reflected by the optical recording medium,

The first diffraction element and the second diffraction element have the same diffraction grating pitch. The order of diffraction in the first diffraction element with respect to the light beam having the first wavelength from the first light source. And the order of diffraction in the second diffraction element with respect to the light beam having the first wavelength reflected by the optical recording medium is equal to

The order of diffraction in the first diffraction element with respect to the light beam having the second wavelength from the second light source, and the second light beam with respect to the light beam having the second wavelength reflected by the optical recording medium. Is equal to the order of diffraction in a diffractive element

The first diffractive element and the second diffractive element are disposed substantially parallel between the light source and the objective lens,

The first diffractive element combines the first wavelength light flux and the second wavelength light flux and guides them to the objective lens, and the second diffractive element reflects the light flux reflected by the optical recording medium. 2. The optical pickup device according to claim 1, wherein the optical pickup device is demultiplexed and guided to the light receiving element.

5. The optical pickup device according to claim 2, 3 or 4, wherein first-order diffraction is used for diffraction by the diffraction element.

6. The diffraction element according to claim 2 or 5, wherein the diffraction element is a diffraction element in which linear or curved grooves are periodically formed on a transparent substrate, and the pitch of the grooves is 5 to 20 m. Optical pick-up device.

7. The optical pick-up device according to claim 3, wherein the forward diffraction element and the backward diffraction element have wavelength selectivity capable of selecting a wavelength of light to be diffracted by a first-order diffraction order or higher.

[8] The forward diffraction element and the backward diffraction element both diffract the light beam having the first wavelength at the 0th diffraction order, and both the light beam at the second wavelength at the first diffraction order. 8. The optical pickup device according to claim 3, wherein the optical pickup device is diffracted.

[9] The diffraction grating is a periodic structure diffraction grating whose cross-sectional shape repeats a sawtooth shape, or a periodic structure diffraction grating whose cross-sectional shape repeats a shape approximating a sawtooth shape by a staircase shape. The optical pickup device according to any one of claims 2 to 8.

[10] The first diffractive element and the second diffractive element each include a birefringent material layer and an isotropic material layer on a transparent substrate, each of which is a convex portion having a sawtooth cross-sectional shape. 6. The optical pickup device according to claim 4, wherein the optical pickup device is a polarizing diffraction element laminated so as to have an interface having a lattice structure.

[11] The birefringent material layer of the first diffractive element is oriented so that the extraordinary refractive index corresponds to the light flux in the polarization direction of the first linearly polarized light, and

The birefringent material layer of the second diffractive element is oriented so that the extraordinary refractive index corresponds to the second linearly polarized light orthogonal to the first linearly polarized light. of

The optical pickup device according to item 1, wherein V is a deviation.

12. The optical pickup device according to any one of claims 4, 5, 9, 10, or 11, wherein the sawtooth shape having a lattice cross-sectional shape is a shape that approximates a desired sawtooth shape in a staircase shape.