JP2005346885A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device, of which a misalignment of optical axes can be suppressed, caused by fluctuation of a diffractive angle in association with a change in a using wavelength due to fluctuation of an operation temperature. <P>SOLUTION: This optical pickup device is equipped with a 1st light source 1a for emitting a luminous flux of a 1st using wavelength, a 2nd light source 1b for emitting a luminous flux of a 2nd using wavelength, and a diffraction element 2 for diffracting on same order and transmitting each of the luminous flux emitted from the 1st light source 1a and the luminous flux emitted from the 2nd light source 1b. The diffraction element 2 is constituted to diffract so that, after the luminous flux emitted from the 1st light source 1a and the luminous flux emitted from the 2nd light source 1b are diffracted and transmitted, an angle mutually made by the optical axes of each luminous flux is close to as compared with an angle before the diffraction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical pickup device for recording information on or reproducing information from an optical recording medium (hereinafter referred to as an optical disk) having a different thickness or recording density of a disk such as a CD or a DVD.

  Conventionally, recording of information on an optical disk or reproduction of information from an optical disk (hereinafter simply referred to as recording / reproduction of an optical disk. For specific recording media such as CD and DVD, “recording / reproduction of CD”, “DVD There is known an optical pickup device that can be used between different types of optical disks such as CD and DVD. Here, it is known that a laser light source having a working wavelength near 780 nm is necessary for recording / reproducing a CD, and a laser light source having a working wavelength near 650 nm is necessary for recording / reproducing a DVD.

  In order to enable recording / reproduction of optical discs between optical discs having different use wavelengths, a so-called two-laser type optical pickup device equipped with two lasers having different oscillation wavelengths has been put into practical use. It was done. In this method, individually manufactured lasers are mounted on one optical pickup device. In recent years, so-called twin lasers in which a plurality of laser diodes having different oscillation wavelengths are integrated on a single substrate have been developed and put into practical use in order to reduce the size and cost of optical pickup devices.

  In the above-described two-laser optical pickup device or an optical pickup device equipped with a twin laser, optical components such as a collimator lens, an objective lens, and a light receiving element are used in common at two used wavelengths, so that they are at different positions. It is necessary to multiplex so that the optical axes of the two light beams emitted from the arranged light sources coincide.

  In a conventional optical pickup device, as a method of combining two optical beams emitted from lasers arranged at different positions using a diffraction element so that the optical axes of the optical beams coincide with each other, a light beam having one of the working wavelengths is zero-order. Diffraction in which the light axis of the other used wavelength is diffracted and transmitted in the first order (hereinafter, diffracted and transmitted is referred to as “diffraction transmission”), and the optical axes of the respective light beams emitted from the diffraction element coincide with each other. A method of determining the arrangement of elements has been taken.

  Here, the wavelength of the laser beam varies depending on the operating temperature. When the wavelength of the laser beam varies due to the variation of the operating temperature, the zero-order light is hardly affected by passing through the diffraction element. The diffraction angle of the next diffracted light changes in proportion to the wavelength by being diffracted and transmitted through the diffraction element. For this reason, the first-order diffracted light is diffracted and transmitted through the diffractive element, so that the diffraction angle also fluctuates as much as the wavelength fluctuates, making it impossible to match the optical axes of the two light beams.

For this reason, a technique for avoiding the influence of such temperature fluctuation has been disclosed (for example, see Patent Document 1). Here, Patent Document 1 discloses that a synthetic resin having a large linear expansion coefficient is used instead of an inorganic material having a small linear expansion coefficient, which has been used as a material for diffraction elements. By using a synthetic resin having a large linear expansion coefficient and utilizing the fact that the pitch of the diffraction grating fluctuates due to temperature fluctuations, an attempt is made to offset fluctuations in the diffraction angle due to changes in operating wavelength due to fluctuations in operating temperature.
JP 2002-116314 A

However, the conventional technique disclosed in Patent Document 1 has a problem that it is difficult to select an appropriate material that can cancel the variation in diffraction angle accompanying the variation in operating temperature. Specifically, the wavelength variation with respect to the temperature change of the laser is about 0.25 (nm / ° C.). For this wavelength variation, a resin having a linear expansion coefficient α of about 3 × 10 ⁻⁴ is desirable. On the other hand, the linear expansion coefficient of so-called optical grade resin such as acrylic or polyolefin resin used in the optical pickup device was about 7 × 10 ⁻⁵ .

  Further, as the optical grade resin used for the diffraction element, since it is disposed in the vicinity of the laser, a material with little thermal strain is desired. However, since it is a resin, it is difficult to reduce the thermal strain.

  The present invention has been made to solve such a problem, and does not cancel the fluctuation of the diffraction angle due to the fluctuation of the operating temperature by using the linear expansion, and the circuit accompanying the change of the operating wavelength due to the fluctuation of the operating temperature. Provided is an optical pickup device capable of suppressing optical axis mismatch due to bending angle fluctuation.

  In view of the above, the invention according to claim 1 emits a first light source that emits a light beam having a first use wavelength and a light beam having a second use wavelength that is different from the first use wavelength. A second light source, a diffraction element that diffracts and transmits each of the light beam emitted from the first light source and the light beam emitted from the second light source, and optical recording of the light emitted from each light source An optical pickup device comprising: an objective lens that condenses on a medium; and a light receiving element that receives light collected by the objective lens and reflected by the optical recording medium, wherein the diffraction element is the first light source Diffracting and transmitting the light beam emitted from the second light source and the light beam emitted from the second light source, and then diffracting such that the angle formed by the optical axes of the light beams is closer than the angle formed before diffraction have.

  With this configuration, the diffractive element diffracts and transmits each of the light beam emitted from the first light source and the light beam emitted from the second light source, so that the influence of fluctuations in operating temperature on each light beam is the same. Light that can suppress optical axis mismatch due to fluctuations in diffraction angle due to changes in operating wavelength due to fluctuations in operating temperature without offsetting fluctuations in diffraction angles due to fluctuations in operating temperature using linear expansion. A pickup device can be realized.

  The invention according to claim 2 is the structure according to claim 1, wherein the diffraction element diffracts the light beam emitted from the first light source and the light beam emitted from the second light source is first order. Have.

  With this configuration, in addition to the effect of the first aspect, since the order of diffraction by the diffraction element is the first order, an optical pickup device that can use a light beam with high diffraction efficiency can be realized.

  According to a third aspect of the present invention, in the first or second aspect, the diffractive element diffracts a light beam having center wavelengths of 650 nm and 780 nm, respectively, with a first-order diffraction efficiency of 80% or more. .

  With this configuration, in addition to the effects of the first or second aspect, the diffractive element diffracts a light beam having center wavelengths of 650 nm and 780 nm, respectively, with a first-order diffraction efficiency of 80% or more. An optical pickup device capable of ensuring

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the diffractive element has a configuration including a diffraction grating having a periodic structure having a sawtooth cross section.

  With this configuration, in addition to the effect of any one of claims 1 to 3, since the diffraction element is constituted by a diffraction grating having a periodic structure with a sawtooth cross section, the light that can be easily manufactured. A pickup device can be realized.

  According to a fifth aspect of the present invention, in any one of the first to third aspects, the diffractive element has a configuration including a diffraction grating having a periodic structure having a stepped cross section.

  With this configuration, in addition to the effect of any one of claims 1 to 3, since the diffraction element is configured by a diffraction grating having a periodic structure with a stepped cross section, light that can be easily manufactured. A pickup device can be realized.

  According to a sixth aspect of the present invention, in the fifth aspect, the diffractive element has a configuration in which one period of the periodic structure of the diffraction grating includes steps of 6 steps or more and 32 steps or less.

  With this configuration, in addition to the effect of the fifth aspect, since one period of the diffraction grating having a periodic structure is composed of steps of 6 steps or more and 32 steps or less, an optical pickup capable of further easily manufacturing a diffraction element having a high diffraction efficiency. A device can be realized.

  The invention according to claim 7 has a configuration in any one of claims 1 to 6, wherein the material of the diffraction element is an inorganic material.

  With this configuration, in addition to the effect of any one of claims 1 to 6, since the material of the diffractive element is an inorganic material, an optical pickup device having a diffractive element with little thermal distortion as a constituent element can be realized.

  In the present invention, since the diffraction element diffracts and transmits each of the light beam emitted from the first light source and the light beam emitted from the second light source with the same order, the influence of the fluctuation of the operating temperature on each light beam is the same. Therefore, it is possible to suppress the mismatch of the optical axis due to the fluctuation of the diffraction angle due to the change of the operating wavelength due to the fluctuation of the operating temperature without using the linear expansion to cancel the fluctuation of the diffraction angle due to the fluctuation of the operating temperature. It is possible to realize an optical pickup device that can

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

FIG. 1 is a diagram showing a conceptual configuration of an optical pickup device according to an embodiment of the present invention. 1, the optical pickup apparatus, the first light source 1a that emits a light beam of the used wavelength lambda _a, a second light source 1b that emits a light beam of the used wavelength lambda _b, for multiplexing the light beams from the light sources 1a, 1b Diffractive element 2, optical element 3 such as a polarizing beam splitter, collimator lens 4 that converts an incident light beam into substantially parallel light, an aperture 5, an objective lens 6, and a first optical disk 7 (7 a is an information recording surface of the optical disk 7. ), The second optical disk 8 (8a is the information recording surface of the optical disk 8), and the light receiving element 9.

  The light beam emitted from the first light source 1 a is diffracted through the diffraction element 2 and then transmitted (hereinafter simply referred to as “diffraction transmission”), passes through the optical element 3 and the collimator lens 4, and passes through the stop 5. Then, the light passes through the objective lens 6 and is condensed on the information recording surface 7 a of the first optical disk 7. Similarly, the light beam emitted from the second light source 1 b is diffracted and transmitted through the diffraction element 2, transmitted through the optical element 3 and the collimator lens 4, passed through the diaphragm 5, and transmitted through the objective lens 6. The light is condensed on the information recording surface 8 a of the optical disk 8.

  The light beams condensed on the information recording surface 7a of the first optical disc 7 or the information recording surface 8a of the second optical disc 8 are reflected by the information recording surfaces 7a and 8a, respectively, and transmitted through the objective lens 6. The light passes through the diaphragm 5, passes through the collimator lens 4, is reflected by the optical element 3, and enters the light receiving element 9.

  Using an output signal from the light receiving element 9, a read signal, a focus error signal, and a tracking error signal for information recorded on the information recording surface 7a of the first optical disc 7 or the information recording surface 8a of the second optical disc 8 are used. Can be obtained. The optical pickup device has a mechanism for moving the lens in the optical axis direction (focus servo) based on the focus error signal, and the lens is moved in a direction substantially perpendicular to the optical axis based on the tracking error signal. 1 is included in the configuration shown in FIG.

  The first light source 1a is composed of, for example, a semiconductor laser, and emits a divergent light beam with linearly polarized light at a wavelength near 650 nm. Similarly, the second light source 1b is composed of, for example, a semiconductor laser, and emits a divergent light beam with linearly polarized light at a wavelength near 780 nm. Here, the first light source 1a and the second light source 1b are not limited to those separately formed, and a so-called twin, in which lasers having different wavelengths are integrated on a single semiconductor substrate. A laser may be used. Further, the vicinity of the wavelength of 650 nm refers to the range from 630 to 670 nm, and the vicinity of the wavelength of 780 nm refers to the range from 760 to 800 nm.

  The diffractive element 2 is configured so that the light beams emitted from the first light source 1a and the second light source 1b are diffracted and transmitted, and the directions of the optical axes of the light beams after diffracted and transmitted substantially coincide. That is, the diffraction element 2 is configured to multiplex the light beams emitted from the first light source 1a and the second light source 1b. For such multiplexing, light beams diffracted and transmitted with the same order are used. Specifically, a light beam diffracted and transmitted in the first order is used. The details of the diffraction element 2 will be described in detail in Examples.

  The optical element 3 transmits the light beam combined by diffracting and transmitting through the diffraction element 2 to the collimator lens 4 side, and information on the information recording surface 7a of the first optical disk 7 or the information on the second optical disk 8. The return light reflected by the recording surface 8 a is reflected and guided to the light receiving element 9.

  The collimator lens 4 converts the light beam combined by diffracting and transmitting through the diffraction element 2 into substantially parallel light.

The diaphragm 5 is configured to set the numerical aperture NA by selectively restricting the aperture of the light beams from the light source 1a and the light source 1b. As a result, when the numerical aperture for the first optical disc 7 and the numerical aperture for the second optical disc 8 are different during recording and reproduction of the optical disc, the numerical aperture can be adjusted by the diaphragm 5. For the light flux of the first wavelength used lambda _a set to be 0.65 NA, for the light flux of the second wavelength used lambda _b was set to be 0.50 NA. When the numerical aperture for the first optical disc 7 and the numerical aperture for the second optical disc 8 are the same, the diaphragm 5 is usually unnecessary. The diaphragm 5 includes a mechanical diaphragm and an optical diaphragm, and is not particularly limited.

The objective lens 6 is a single lens whose aberration is corrected to the extent that it can be used in common at the first use wavelength λ _a and the second use wavelength λ _b , and the first use wavelength λ _a and the second use wavelength λ. The respective parallel beams _b are condensed on the information recording surface 7a of the optical disc 7 and the information recording surface 8a of the optical disc 8. As the objective lens 6, for example, an objective lens disclosed in Japanese Patent Laid-Open No. 2001-344798 can be used.

The first optical disk 7 is used for writing or reading information using a light beam having _a wavelength λa, and has a protective layer thickness of 0.6 mm, for example. Further, a second optical disk 8 is intended to be used for writing or reading information using the light flux of the wavelength lambda _b, for example, a protective layer thickness of 1.2 mm.

  The light receiving element 9 receives the reflected light from the information recording surface 7a of the optical disc 7 and the information recording surface 8a of the optical disc 8, and is recorded on each of the information recording surfaces 7a and 8a based on the received reflected light. Each signal of a reading signal, a focus error signal, and a tracking error signal corresponding to the information is generated and output to the outside.

Specific examples based on the above-described embodiments of the present invention will be described below. Here, the optical arrangement of the optical pickup device according to the present embodiment is the same as the optical arrangement shown in FIG. The optical pickup apparatus according to the present embodiment, for multiplexing, the light flux of the first wavelength used lambda _a and the second used wavelength lambda _b, in which both diffracts transmitted through the diffraction element 2 in the same order . Particularly, the optical axes of the light beams diffracted and transmitted in the first order are made coincident and combined. Hereinafter, unless otherwise specified, the diffraction order in the diffraction element 2 is assumed to be the first order.

Hereinafter, the multiplexing will be specifically described. FIG. 2 is an explanatory diagram of multiplexing performed by the optical pickup device according to the embodiment of the present invention. In FIG. 2, the light beams emitted from the first light source 1a and the second light source 1b are incident on the diffraction element 2 at angles θ _a and θ _b with the paths 21 and 22 as optical axes, respectively, and substantially the same path 23 is obtained. Is emitted in the direction of the optical element 3 as an optical axis. Here, the arrangement of the first light source 1a is incident angle theta _a to the diffraction element 2 of the light flux the first light source 1a is emitting the wavelength of the first light source 1a (the first used wavelength) lambda _a , Where p is the pitch of the diffraction grating of the diffraction element 2,
θ _a = λ _a / p
To do so.

The arrangement of the second light source 1b is incident angle theta _b of the diffraction element 2 of the light beam a second light source 1b is emitting the wavelength of the second light source 1b (second used wavelength) as lambda _b ,
θ _b = λ _b / p
To do so. By arranging the first light source 1a and the second light source 1b as described above, the diffracted optical axes of the light beams emitted from the respective light sources coincide with each other.

  FIG. 3 is a cross-sectional view conceptually showing a part of the cross section of the diffraction element 2 according to the present embodiment. The cross-sectional view shown in FIG. 3 is a cross-sectional view of a partial region in the vicinity of the optical axis of outgoing light, with the plane including the optical axis of outgoing light as a cross section. Here, the surface of the diffractive element 2 indicated by reference numeral 31 is an incident surface of a light beam emitted from the light sources 1a and 1b, and the surface of the diffractive element 2 indicated by reference numeral 32 is an output surface of a light beam diffracted and transmitted. The material of the diffraction element 2 according to the present example is quartz glass having a linear expansion coefficient and thermal strain smaller than so-called optical grade resin such as acrylic or polyolefin resin. The diffraction grating 2 is formed using an etching technique.

  The diffraction grating 2 is constituted by a diffraction grating having a periodic structure having a stepped cross section. That is, a flat region of concentric annular zones is formed, and jumps corresponding to steps of steps are formed between the annular zones. In this embodiment, one period of the periodic structure of the diffraction grating is constituted by six steps. Such a diffraction grating is called a binary blazed diffraction grating. Further, the step d of each staircase was set to 0.254 μm.

As described above, by setting the total number of flat surfaces of the stairs to 6, and setting the step d of each stairs to 0.254 μm, respectively, the luminous flux of the first use wavelength λ _a (650 nm), and Both the diffraction efficiencies of the first-order diffraction of the light beam having the second use wavelength λ _b (780 nm) can be 80% or more. In the above description, one period of the periodic structure of the diffraction grating 2 is six steps. However, one period of the periodic structure of the diffraction grating 2 is not limited to six steps, and may be six steps or more. If 6 or more steps, can light flux of the first wavelength used lambda _a, and, in one or more 80% both the diffraction efficiency of the diffracted light flux of the second wavelength used lambda _b. That is, it is 84% for 8 steps, 86% for 10 steps, and 87% for 32 steps.

  In particular, one period of the periodic structure of the diffraction grating 2 according to the present embodiment is preferably composed of steps having any number of steps from 6 steps to 32 steps. By providing a stepped periodic structure in the sectional structure of the diffraction element 2 and setting the number of steps to 6 steps or more and 32 steps or less, the diffraction efficiency can be kept high and the diffraction element 2 can be easily manufactured. Further, the diffraction element 2 may be configured by a diffraction grating having a periodic structure with a sawtooth cross-sectional shape. Here, the limit obtained by infinitely increasing the number of steps of the staircase forming the periodic structure can be considered as a sawtooth periodic structure.

The following describes how the direction of the optical axis of the light beam after diffraction (hereinafter referred to as the diffraction direction) changes due to the wavelength variation due to the change in operating temperature (hereinafter simply referred to as temperature fluctuation). Hereinafter, the wavelength change per unit temperature due to the temperature variation of the light source emitting a light flux of the first wavelength used lambda _a (first light source 1a) and L _{a (nm} / ℃), the second used wavelength lambda _b The wavelength change per unit temperature due to the temperature variation of the light source (second light source 1b) that emits the light beam is defined as L _b (nm / ° C.).

At this time, the change Δθ _{a in the} diffraction direction due to the wavelength variation Δλ _{a in} the diffraction direction of the light beam emitted from the first light source 1a is:
Δ Δθ _a = Δλ _a / p
Here, p is the pitch of the diffraction grating.

As a result, the change Δθ _{a in the} diffraction direction due to the temperature variation ΔT of the light beam emitted from the first light source 1a is:
Δθ _a = L _a · ΔT / p
It becomes.

Similarly, the change Δθb in the diffraction direction due to the temperature variation ΔT of the light beam emitted from the second light source 1b is:
Δθb = L _b · ΔT / p
It becomes.

Therefore, the difference ΔΘ in the change in the diffraction direction of the light beams emitted from the first light source 1a and the second light source 1b is
ΔΘ = | Δθ _a −Δθb |
= | (L _a -L _b ) · ΔT / p |
It becomes.

Here, wavelength change _{L a} of the per unit temperature for the first light source 1a (used wavelength 650 nm) is about 0.20 (nm / ℃), for the first light source 1a (used wavelength 780 nm) since the wavelength change L _b per unit temperature above a certain degree 0.25 (nm / ℃), difference ΔΘ diffraction direction of change of the light beam first light source 1a and the second light source 1b is emitted,
ΔΘ = | 0.05 ・ ΔT / p |
It becomes.

  The difference ΔΘ in the change in the diffraction direction of the light beams emitted from the first light source 1a and the second light source 1b obtained in this embodiment is the difference obtained in the conventional optical pickup device, that is, the diffraction element is the first. Compared with the difference obtained when the light beam having the use wavelength of 650 nm is diffracted (transmitted) in the 0th order and the light beam having the second use wavelength of 780 nm is diffracted and transmitted in the first order is combined.

In the conventional optical pickup device, since the light beam having the first use wavelength of 650 nm is diffracted (transmitted) in the 0th order, the diffraction direction does not vary due to the wavelength variation caused by the temperature variation. On the other hand, the light beam having the second use wavelength of 780 nm is diffracted and transmitted in the first order, and therefore, due to the wavelength fluctuation caused by the temperature fluctuation ΔT,
Δθ = L _b · ΔT / p
Change.

As a result, the difference ΔΘ ′ in the change in the diffraction direction of the light beams emitted from the first light source 1a and the second light source 1b is
ΔΘ ′ = | Δθ | = | L _b · ΔT / p |
It becomes. Here, since L _b is about 0.25 (nm / ° C.), the difference ΔΘ ′ in the change in the diffraction direction of the light flux is
ΔΘ '= | 0.25 · ΔT / p |
It becomes.

  From the above comparison, the difference ΔΘ in the change in the diffraction direction in which the first-order diffraction is used for both light beams emitted from the first light source 1a and the second light source 1b is the difference ΔΘ ′ obtained in the conventional optical pickup device. Thus, the difference in the diffraction direction change due to the temperature fluctuation is small, and as a result, the optical axis shift due to the temperature fluctuation can be reduced.

  In the above embodiment, the description has been made on the assumption that the CD and the DVD are compatible. However, the BLURAY (registered trademark) disk or the HD-DVD (High Definition DVD) which is about to be put into practical use and the conventional DVD are used. It can be effectively applied to compatibility. Similarly, the present invention can be effectively applied to the compatibility between a BLURAY (registered trademark) disk or an HD-DVD and a 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 not limited to the infinite optical system. The optical system may be a finite system that does not use a collimator lens.

  In this embodiment, an example in which the diffraction element is formed using quartz glass is described. However, the diffraction element is not limited to quartz glass, and may be formed using an inorganic material such as optical glass.

  As described above, in the optical pickup device according to the embodiment of the present invention, the diffraction element diffracts and transmits each of the light beam emitted from the first light source and the light beam emitted from the second light source with the same order. As a result, the influence of fluctuations in operating temperature on each luminous flux could be made to the same extent.Therefore, changes in operating wavelength due to fluctuations in operating temperature without using linear expansion to offset fluctuations in diffraction angle due to fluctuations in operating temperature. It is possible to suppress the mismatch of the optical axes due to the fluctuation of the diffraction angle due to.

  In addition, since the diffraction element is diffracted by the first order, a light beam with high diffraction efficiency can be used.

  In addition, since the diffraction element diffracts a light beam having center wavelengths of 650 nm and 780 nm, respectively, with a first-order diffraction efficiency of 80% or more, a light beam having sufficient power for recording and reproduction can be secured.

  In addition, since the diffraction element is configured by a diffraction grating (including a binary blazed diffraction grating) having a periodic structure with a sawtooth or stepped cross-sectional shape, the diffraction element can be easily manufactured.

  In addition, since one period of the diffraction grating having a periodic structure is composed of steps of 6 steps or more and 32 steps or less, a diffraction element with good diffraction efficiency can be manufactured more easily.

  In addition, since the material of the diffraction element is an inorganic material, a diffraction element with little thermal distortion can be realized.

  The optical pickup device according to the present invention uses the linear expansion to cancel the fluctuation of the diffraction angle due to the fluctuation of the operating temperature, and does not match the optical axis due to the fluctuation of the diffraction angle due to the change of the operating wavelength due to the fluctuation of the operating temperature. It can also be applied to uses such as an optical pickup device that performs recording and reproduction of different optical recording media.

The figure which shows the notional structure of the optical pick-up apparatus which concerns on embodiment of this invention. Explanatory drawing about the multiplexing which the optical pick-up apparatus which concerns on embodiment of this invention performs. Sectional drawing which shows notionally a part of cross section of the diffraction element which concerns on the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b Light source 2 Diffraction element 3 Optical element 4 Collimator lens 5 Aperture 6 Objective lens 7, 8 Optical disk 7a, 8a Information recording surface 9 Light receiving element 21, 22, 23 Path of light beam 31 Entrance surface of diffraction element in which light beam enters 32 The exit surface of the diffraction element from which the light beam exits θ _a , θ _b The incident angle of the light beam incident on the diffraction element d

Claims (7)

A first light source that emits a light beam having a first use wavelength; a second light source that emits a light beam having a second use wavelength different from the first use wavelength; and a light beam emitted by the first light source. And a diffraction element that diffracts and transmits each of the light beams emitted from the second light source, the objective lens that condenses the light emitted from each light source onto an optical recording medium, and the light collected by the objective lens. An optical pickup device comprising a light receiving element that receives light reflected by the optical recording medium,
The diffraction element diffracts and transmits the light beam emitted from the first light source and the light beam emitted from the second light source, and then the angle formed by the optical axes of the light beams is an angle formed before diffraction. An optical pickup device that diffracts so as to come closer.   2. The optical pickup device according to claim 1, wherein the order in which the diffraction element diffracts the light beam emitted from the first light source and the light beam emitted from the second light source is first order.   3. The optical pickup device according to claim 1, wherein the diffraction element diffracts a light beam having center wavelengths of 650 nm and 780 nm, respectively, with a first-order diffraction efficiency of 80% or more.   4. The optical pickup device according to claim 1, wherein the diffractive element is configured by a diffraction grating having a periodic structure having a sawtooth cross-sectional shape. 5.   4. The optical pickup device according to claim 1, wherein the diffractive element is configured by a diffraction grating having a periodic structure having a stepped cross section. 5.   6. The optical pickup device according to claim 5, wherein the diffractive element is configured by steps in which one period of the periodic structure of the diffraction grating is 6 steps or more and 32 steps or less. The optical pickup device according to claim 1, wherein the diffraction element is made of an inorganic material.

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