JP2002323677A - Optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that it is difficult to make optical axes easily match with each other, since a degree of freedom on the mechanism design is easy to be restricted, although two laser beams are emitted as mutually parallel light beams in the so-called 1CAN2LD type laser beam source where two laser beam sources are housed in one package. SOLUTION: When S-polarized light waves of a 2nd laser beam LB2 are made incident on diffraction gratings 7a and 8a of an optical member 6 at an angle which satisfies the Bragg condition, the S-polarized light waves are respectively subjected to primary diffraction, and emitted in an X2 direction as shown in a Figure. Moreover, P/S-polarized light waves of the 1st laser beam LB1 are subjected to zero-order transmission with the diffraction gratings 7a and 8a. By setting a facing interval t of a gap 9 so that the intersection Q of the first and second laser beams LB1 and LB2 is positioned on the grating 8a, the optical axes O1 and O2 of the first and second laser beams LB1 and LB2 emitted from the optical member 6 can be made as the same emission optical axis O3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device mounted on a pickup device for a CD and a DVD, and more particularly, to aligning laser beams emitted in parallel from two light sources having different optical axes on the same optical axis. The present invention relates to an optical device which incorporates a laser beam and has an improved laser beam utilization efficiency.

[0002]

2. Description of the Related Art The wavelength of a laser for a CD (compact disk) is 780 nm, and the wavelength of a laser for a DVD (digital versatile disk) is 650 nm. Therefore, two laser light sources are required in a compatible disk device for recording or reproducing both a CD and a DVD.

In an optical device such as a pickup mechanism in a disk device of this type, a first laser light source for 780 nm and a second laser light source for 650 nm are separately arranged, and the optical device is installed in the optical device. The optical axis of the emitted light is made to coincide by the provided beam splitter, and is set so that it can be guided by one objective lens with respect to the recording surface of the disk.

[0004]

In the above-mentioned conventional optical device, the first and second laser light sources can be arranged in the optical device in a relatively free state with few design restrictions. These optical axes could be easily matched.

However, recently, a so-called 1CAN2LD type laser light source in which the first and second laser light sources are housed in one package has been developed, and such a laser light source is composed of first and second laser beams. Are emitted as light rays parallel to each other, so that the degree of freedom in mechanism design is likely to be limited, and there is a problem that it is difficult to easily match the optical axes.

Further, in a configuration in which laser beams emitted from two laser light sources are handled by using separate optical members, there is a problem that the number of parts increases and the size of the optical device increases.

Further, there is a problem that it is difficult to increase the emission efficiency (use efficiency) of both laser beams by the conventional method.

The present invention has been made to solve the above-mentioned conventional problems, and uses a common optical member for the optical axes of two laser beams emitted in parallel from a laser light source (light emitting means) in one package. It is an object of the present invention to provide an optical device which can be set on the same optical axis.

It is another object of the present invention to provide an optical device in which the use efficiency of laser beams emitted from two laser light sources is improved.

[0010]

An optical device according to the present invention is characterized in that a first laser beam having a wavelength λ1 and a second laser beam having a wavelength λ2 different from the wavelength λ1 have optical axes parallel to each other. Light emitting means for emitting light,
An optical device having a laser beam and an optical member on which the second laser beam is incident, wherein the optical device includes a first diffraction grating arranged in parallel with each other and inclined with respect to the optical axis. A second diffraction grating is provided, the first diffraction grating and the second diffraction grating have the same shape, the distance between the first diffraction grating and the second diffraction grating, the shape of both diffraction gratings, The angle of incidence of each laser beam is set as follows.

(1) The first laser beam of wavelength λ1 is:
Regardless of whether it is an S-polarized wave or a P-polarized wave, the first-order diffraction grating and the second diffraction grating transmit the zero-order diffracted light.

(2) The second laser beam of wavelength λ2 is
First-order diffracted light of S-polarized light is transmitted by the first diffraction grating and the second diffraction grating.

(3) The optical axis of the 0th-order diffracted light of the first laser beam transmitted through the first diffraction grating, and the first time of the second laser beam transmitted through the first diffraction grating. The optical axis of the folded light is incident on the substantially same position Q of the second diffraction grating, and the emission optical axis of the 0th-order diffraction light from the second diffraction grating and the 1st diffraction light from the second diffraction grating. The exit optical axis of the next-order diffracted light is located substantially coaxially.

Here, the refractive index of the medium on the incident side to the first diffraction grating is n1, the refractive index of the medium between the first diffraction grating and the second diffraction grating is n2, and the refractive index of the second diffraction grating is n2. The refractive index of the medium on the emission side from the diffraction grating is n3, the incident angles of the first laser beam and the second laser beam of the first laser beam on the first diffraction grating are θ1, 2
When the emission angles of the 0th-order diffracted light and the 1st-order diffracted light from the diffraction grating are θ2, the relationship of n1 · sinθ1 = n3 · sinθ2 holds.

Further, a lens and a half-wave plate are disposed between the light emitting means and the optical member, and P-polarized waves of the first laser beam and the second laser beam emitted from the light emitting means are provided. , And is converted into an S-polarized wave by the half-wave plate and is incident on the first diffraction grating.

The first diffraction grating, the second diffraction grating, and the incident angle θ1 satisfy the following relationship. 2d · n1 · sin θ1 = m · λ where d is the pitch of the grating and m is an integer.

For example, the optical member is a combination of right-angled triangular prisms having the same refractive index, and a first diffraction grating and a second diffraction grating are provided on the slopes of both prisms, respectively. Diffraction gratings are opposed via a space, and the first laser beam and the second laser beam have their optical axes incident perpendicular to the outer surface of one of the prisms,
The optical axis of the light emitted from the second diffraction grating is perpendicularly emitted from the outer surface of the other prism.

Alternatively, the optical member has a structure in which the first diffraction grating is provided on one surface of a plate material and the second diffraction grating is provided on the other surface.

Further, it is preferable that the light emitted from the second diffraction grating is condensed by a condenser lens and irradiated on a recording medium.

In the present invention, the optical axes of two laser beams emitted in parallel from different light sources and having different wavelengths can be set on one optical axis.

When the incident angle is set to a predetermined angle, the second laser beam can be transmitted through the optical member with high diffraction efficiency, so that the utilization efficiency of the laser beam can be improved.

By adjusting the distance between one surface and the other surface of the optical member, that is, in the case of a combination of right-angled triangular prisms, the opposing distance between the prisms is set to an appropriate distance, and In the case where the diffraction gratings are provided on both surfaces, the optical axis of the first laser beam and the optical axis of the second laser beam can be set coaxially by setting the thickness to an appropriate plate thickness. Therefore, CD
The optical axes of the laser beams emitted from the light sources for DVD and DVD can be matched using a common optical member, so that the pickup device can be downsized.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram schematically showing a first embodiment of the optical device of the present invention, FIG. 2 is an enlarged view showing a main part of FIG. 1, and FIG. 3 is a plate-like embodiment as a second embodiment. FIG. 4 is an enlarged view showing a main part similar to FIG. 2, FIG. 4 is a view showing a relationship between an incident angle of a diffraction grating and a diffraction efficiency with respect to a laser beam having a wavelength λ2 = 650 nm, and FIG. FIG. 6 is a diagram showing the relationship between the grating pitch of the diffraction grating and the diffraction efficiency for laser light having a wavelength of λ2 = 650 nm.
FIG. 7 is a diagram showing the relationship between the incident angle of the diffraction grating for 780 nm laser light and the diffraction efficiency, and FIG. 7 is a diagram showing the relationship between the grating pitch of the diffraction grating and the diffraction efficiency for laser light of wavelength λ1 = 780 nm.

The optical device 1 shown in FIG. 1 comprises a laser light source unit 2 provided on the X1 side in the figure and an optical member 6.

The laser light source section 2 includes a light emitting means 3 for emitting laser beams of different wavelengths, a lens 4, and 1 / which are used incidentally according to the type of polarized wave emitted by the light source.
And a two-wavelength plate 5.

The light emitting means 3 is a so-called 1CAN2L having a first laser light source 3A for outputting a first wavelength λ1 and a second laser light source 3B for outputting a second wavelength λ2.
It is a D-type light source. For example, the first wavelength λ1 is CD
780 nm for DVD, and the second wavelength λ2 is 6 nm for DVD.
50 nm. Normally, both the first laser beam LB1 and the second laser beam LB2 emitted from the first and second laser light sources 3A and 3B of the light emitting means 3 are configured to emit P-polarized waves. The first laser beam LB1 is emitted along the optical axis O1, and the second laser beam LB2 is emitted along the optical axis O2 in the X2 direction in the drawing. Note that the optical axis O1 and the optical axis O2 are parallel.

The lens 4 has a first laser beam LB
It has a function of preventing the diffusion of the first and second laser beams LB2 and bringing them closer to parallel light, and for example, a collimator lens or the like can be used. The half-wave plate 5 includes a first
And the plane of polarization of the linearly polarized light of the second laser beam is 90 [d
eg] has a function of rotating, and converts a P-polarized wave into an S-polarized wave. However, only a specific wavelength, here, the wavelength λ2 (= 650 nm) of the second laser beam LB2 is converted from a P-polarized wave to an S-polarized wave, and the first laser beam λ2
The conversion of 1 (= 780 nm) LB1 may not be performed. Accordingly, the half-wave plate 5 has at least the second
Is used when the first laser light source 3B emits a P-polarized wave, and is not used when the second laser light source 3B emits an S-polarized wave from the beginning.

The optical member 6 is composed of two prisms 7 and 8 having a right triangular prism shape. That is, the inclined surface 7A of the prism 7 and the prism 8 and the prism 8
The inclined surfaces 8A are arranged to face each other in parallel, and a gap (space) 9 having a predetermined facing interval t is formed between the two inclined surfaces 7A and 8A. In addition, prisms 7 and 8
Are arranged so as to be perpendicular to the optical axes of the first laser beam LB1 and the second laser beam LB2. Therefore, both inclined surfaces 7A and 8A are
The first laser beam LB1 and the second laser beam L
It is arranged to be inclined with respect to the optical axis of B2.

A first diffraction grating 7a and a second diffraction grating 8a are formed in the planes of the inclined surfaces 7A and 8A, with the direction perpendicular to the plane of the drawing being the orientation direction and the inclination direction being the width direction. ing. The first and second diffraction gratings 7a, 8a
Is a relief type having a fine uneven shape such as a sine wave, a triangle, and a trapezoid. The first diffraction grating 7a and the second diffraction grating 8a have the same shape,
Also, the grating pitch d is the same.

A condenser lens 10 is provided on the X2 side of the optical member 6 in the figure. The condensing lens 10
Is opposed to a recording surface of a disk D such as a CD and a DVD, and is movable in the radial direction of the disk D together with the optical device 1.

As shown in FIG. 1, the first laser light source 3A
The first and second laser beams LB1 and LB2 emitted from the second laser light source 3B are made substantially parallel by the lens 4, and then are made to enter the half-wave plate 5 perpendicularly. At this time, the polarization plane of the second laser beam LB2 is rotated by 90 [deg], and is emitted toward the optical member 6 in a state where the P-polarized wave is converted into the S-polarized wave.
On the other hand, the first laser beam LB <b> 1 is emitted toward the optical member 6 while being converted into an S-polarized wave in the half-wave plate 5 or as a P-polarized wave without being converted.

A first laser beam LB1 which is a P-polarized wave or an S-polarized wave (P / S polarized wave) and a second laser beam LB2 which is an S-polarized wave face in parallel with the half-wave plate 5. The light is perpendicularly incident on the outer surface 7B of the prism 7.

As shown in FIG. 2, the second laser beam L
B2 travels straight on the optical axis O2 as it is, and is incident on the first diffraction grating 7a on the inclined surface 7A at an incident angle θ1.

At this time, the incident angle θ1 of the second laser beam LB2 is set so as to satisfy the following Bragg condition with respect to the first diffraction grating 7a. 2d · n · sin θ1 = m · λ where d is the pitch of the grating, m is an integer, λ is the wavelength of the laser beam, and n is the refractive index of the incident side medium.

Here, referring to FIGS. 4 and 5, if the incident angle θ1 is set to an angle near θ1 = 34 ° and the grating pitch d is set to d = 0.385 μm so as to satisfy the Bragg condition,
The S-polarized wave, which is the second laser beam LB2 having a wavelength of λ2 = 650 nm, is primarily transmitted through the first diffraction grating 7a, and is emitted after being polarized by approximately 90 degrees in the Y1 direction.

At this time, as shown in FIGS. 4 and 5, the diffraction efficiency of the first-order transmitted light of the S-polarized wave of the second laser beam LB2 is about 91%, and the zero-order transmitted light of the S-polarized wave is transmitted. Has a diffraction efficiency of about 2%. Therefore, the first-order diffracted light of the S-polarized wave can be emitted into the gap 9 with high efficiency, and the utilization efficiency of the laser beam can be increased.

On the other hand, the first laser beam LB1 having a wavelength λ1 = 780 nm emitted from the first laser light source 3A
Goes straight on the optical axis O1 in the prism 7 and enters the first diffraction grating 7a on the inclined surface 7A. At this time, the first laser beam LB1 that has advanced into the gap 9 is refracted in the first diffraction grating 7a based on the refractive index n1 of the prism 7 and the refractive index n2 of the gap 9. That is, assuming that the incident angle of the first laser beam LB1 with respect to the first diffraction grating 7a is θ1, and the emission angle is θ4, n1 · sin θ1 = n
The light is refracted in a relation of 2 · sin θ4.

As shown in FIGS. 6 and 7, when the first laser beam LB1 at this time is an S-polarized wave,
It is a zero-order transmitted light having a diffraction efficiency of about 80%, and a P-polarized wave is a zero-order transmitted light having a diffraction efficiency of about 87%. Therefore, the first laser beam LB1 can be transmitted with high utilization efficiency regardless of whether it is an S-polarized wave or a P-polarized wave.

In the above, the second in the gap 9
Laser beam LB2 and first laser beam LB1 intersect at intersection Q. The gap t of the gap (space) 9 is set so that the intersection point Q is located on the inclined surface 8A (diffraction grating 8a). Therefore,
The primary transmitted light of the S-polarized wave of the second laser beam LB2 is emitted at a polarization of approximately 90 ° [deg] in the X2 direction in the figure to satisfy the Bragg condition even at the intersection Q on the inclined surface 8A. Can be. Therefore, the optical axis O2 of the second laser beam LB2 is parallel to the emission optical axis O3 of the primary transmission light of the S-polarized wave of the second laser beam LB2 emitted into the prism 8 from the intersection Q. . And then n
1 · sin θ1 = n3 · sin θ2 holds. However, when the prism 7 and the prism 8 are the same medium, n1 = n3, and sin θ1 = n3 · sin θ2, that is, θ1 = θ2.

In this case, the incident angle on the second diffraction grating 8a is θ3, but the laser beam has a refractive index n1.
Unlike the case in which the light travels from the medium (prism) toward the medium (air) having the refractive index n2 (in the case of the first diffraction grating 7a),
The laser beam is converted from the medium (air) having the refractive index n2 to the refractive index n
3 is directed toward the medium (prism), so that θ1 (90 [deg] ≒ θ1 +
θ3) satisfies the above Bragg condition.

On the other hand, the first laser beam LB1 is refracted at the intersection Q based on the difference in the refractive index between the gap 9 and the prism 8. At this time, assuming that the incident angle of the first laser beam LB1 with respect to the inclined surface 8A is θ4 and the emission angle is θ2, a relationship of n2 · sin θ4 = n3 · sin θ2 holds. Therefore, the first laser beam LB
At 1, n1 · sinθ1 = n2 · sinθ4 = n3 · sinθ
2 holds. When the prism 7 and the prism 8 are the same medium, n1 = n3, so that also sin θ1 = n3 · sin θ2, that is, θ1 = θ2 holds.

The optical axis O1 of the first laser beam LB1
And the optical axis O2 of the second laser beam LB2 is
After passing through, it becomes the same straight line. That is, by using the common optical member 6 for the first laser beam LB1 and the second laser beam LB2, the emission optical axis O3 of the laser beam emitted from the optical member 6 can be matched.
Therefore, the number of components of the optical member can be reduced.

Accordingly, each of the emitted light beams of the first and second laser beams LB1 and LB2, which travels straight on the emission optical axis O3 in the X2 direction shown in FIG. Is done. Therefore, by providing the condenser lens 10 on the exit optical axis O3, 1CAN2L
The laser beams of different wavelengths emitted from the two D-type first laser light sources 3A and the second laser light sources 3B can be incident on a recording medium such as a disk by using the condenser lens 10.

In the second embodiment shown in FIG. 3, another optical member 12 is used in place of the optical member 6 shown in the first embodiment.

The optical member 12 is a plate-shaped transparent glass substrate or a resin substrate, and the incident surface 12A on the X1 side and the exit surface 12B on the X2 side are parallel to each other. The first and second inclined planes 12A and the exit plane 12B have a direction perpendicular to the plane of the drawing as an orientation direction and an inclination direction as a width direction.
Second diffraction gratings 12a and 12b are formed. The cross section of the first and second diffraction gratings 12a and 12b in the width direction is a relief type having a fine uneven shape such as a sine wave, a triangle, and a trapezoid. The first diffraction grating 12a and the second diffraction grating 12b have the same grating pitch.

The first and second laser beams LB1 and LB2 incident on the optical member 12 have a wavelength λ1 = 780 nm, as in the first embodiment.
And the second laser beam is an S-polarized wave having a wavelength λ2 = 650 nm.

The first and second laser beams LB1, L
B2 is incident on the first diffraction grating 12a at an incident angle θ3. However, the incident angle θ1 and the incident angle θ3 in the first embodiment are substantially complementary angles (90 ° ≒ θ).
1 + θ2).

Here, if an angle near θ3 = 56 [deg] (a complementary angle of θ1 = 34 [deg]) is selected as the incident angle θ3 satisfying the above Bragg condition, the refractive index n of the incident side medium becomes equal to that of air. As the refractive index n1 (n = n1), the wavelength λ2 = 650n
m second laser beam LB2, which is approximately 9
At 0 [deg], the light can be emitted in the illustrated Y1 direction.

At this time, although not shown, the diffraction efficiency of the primary transmitted light of the S-polarized wave is 90% or more. Therefore,
The primary transmitted light of the second laser beam LB2 can be refracted with high diffraction efficiency, and the utilization efficiency of the laser beam can be increased.

On the other hand, the first laser beam LB1 emitted from the first laser light source 3A having the wavelength λ1 = 780 nm
Is the refractive index n1 of the first diffraction grating 12a and the optical member 12
Is refracted based on the ratio of the refractive index n2.

At this time, although not shown, when the first laser beam LB1 is an S-polarized wave, the first laser beam LB1 is a 0-order transmitted light having a diffraction efficiency of about 80%, and when the first laser beam LB1 is a P-polarized wave. Is a zero-order transmitted light having a diffraction efficiency of about 87%. Therefore, also in this case, the first laser beam LB1 can be transmitted and refracted with high diffraction efficiency, and the utilization efficiency of the laser beam can be increased.

The thickness T of the optical member 12 is such that the intersection Q between the second laser beam LB2 and the first laser beam LB1 traveling on the optical member 12 is located on the exit surface 12B (diffraction grating 12b). Is set to Therefore,
The S-polarized wave of the second laser beam LB2 is
At the intersection Q on 2B, the Bragg condition is satisfied and almost 9
At 0 [deg], it can be emitted in the X2 direction shown. In addition, the optical axis O2 of the second laser beam LB2 before incidence,
The emission optical axis O3 of the second laser beam LB2 after emission is parallel.

At the same time, the first laser beam LB1 is also refracted at the point Q on the exit surface 12B, and
A parallel relationship is maintained between the optical axis O1 of the laser beam LB1 and the emission optical axis O3 of the first laser beam LB1 after emission. Therefore, the optical axis O of the first laser beam LB1
By using the common optical member 12 for the optical axis O2 of the first and second laser beams LB2, the same emission optical axis O3 can be set. Therefore, the number of components of the optical member can be reduced.

Then, the first laser beam LB1 and the second
By providing the condenser lens 10 on the common emission optical axis O3 with the laser beam LB2, the 1CAN2LD type light emitting means 3, that is, the two first laser light sources 3A and 3 The first and second laser beams LB1 and LB2 emitted in parallel from the two laser light sources 3B can be handled by the common condenser lens 10.

By using the optical device 1 as described above, the pickup mechanism in the disk device can be configured with a small number of components, and the pickup mechanism can be downsized.

In the first and second embodiments, the light emitting means 3 emits the first laser beam LB1 having the wavelength λ1 = 780 nm, the laser light source 3A and the wavelength λ1.
Although the case where the laser light source 3B that emits the second laser beam LB2 of 2 = 650 nm has been described, the light emitting unit 3 having another combination of wavelengths may be used.

[0058]

According to the present invention described in detail above, the optical axes of two laser beams emitted in parallel from a laser light source in one package can be matched by a common optical member.

Further, the utilization efficiency of the laser beams emitted from the two laser light sources can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an outline of a first embodiment of an optical device of the present invention;

FIG. 2 is an enlarged view showing a main part of FIG. 1,

FIG. 3 is an enlarged view showing a main part similar to FIG. 2 when a plate-shaped optical member is used as a second embodiment;

FIG. 4 is a diagram showing a relationship between an incident angle of a diffraction grating and a diffraction efficiency with respect to a laser beam having a wavelength of λ2 = 650 nm;

FIG. 5 is a diagram showing the relationship between the grating pitch of the diffraction grating and the diffraction efficiency for a laser beam having a wavelength of λ2 = 650 nm;

FIG. 6 is a diagram showing a relationship between an incident angle of a diffraction grating and a diffraction efficiency with respect to a laser beam having a wavelength of λ1 = 780 nm;

FIG. 7 is a diagram showing a relationship between a grating pitch of a diffraction grating and a diffraction efficiency with respect to a laser beam having a wavelength of λ1 = 780 nm;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical device 2 Laser light source part 3 Light emitting means 3A 1st laser light source 3B 2nd laser light source 5 1/2 wavelength plate 6,12 Optical member 7A Inclined surface 8B Inclined surface 7a, 12a First diffraction grating 8b, 12b Second diffraction grating 9 Gap (space) 12A Incident surface 12B Exit surface LB1 First laser beam LB2 Second laser beam O1 Optical axis of first laser beam O2 Optical axis of second laser beam O3 Emission optical axis

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 AA03 AA13 AA50 AA57 AA64 AA68 BA05 BA46 BC21 2H099 AA05 BA17 CA08 CA11 CA17 DA07 5D119 AA41 AA43 BA01 BB01 BB04 EC45 EC47 FA08 JA27

Claims (7)

[Claims] 1. A light emitting means for emitting a first laser beam having a wavelength λ1 and a second laser beam having a wavelength λ2 different from the wavelength λ1 so that the optical axes of both laser beams are parallel to each other; An optical device having a first laser beam and an optical member on which the second laser beam is incident, wherein the optical device has a first diffraction grating arranged parallel to each other and inclined with respect to the optical axis. A first diffraction grating and a second diffraction grating, wherein the first diffraction grating and the second diffraction grating have the same shape, and a distance between the first diffraction grating and the second diffraction grating; An optical device, wherein the shape and the incident angle of each laser beam are set as follows. (1) Whether the first laser beam of wavelength λ1 is an S-polarized wave or a P-polarized wave, the first diffraction grating and the second
The 0th-order diffracted light is transmitted by the diffraction grating. (2) As for the second laser beam having the wavelength λ2, the first diffraction light of the S-polarized wave is transmitted through the first diffraction grating and the second diffraction grating. (3) the optical axis of the zero-order diffracted light of the first laser beam transmitted through the first diffraction grating, and the light of the first-order diffracted light of the second laser beam transmitted through the first diffraction grating; Axis is incident on the substantially same position Q of the second diffraction grating, and the emission optical axis of the zero-order diffraction light from the second diffraction grating and the first-order diffraction light of the first diffraction light from the second diffraction grating The emission optical axis is located substantially coaxially. 2. The refractive index of a medium on the incident side to the first diffraction grating is n1, the refractive index of a medium between the first diffraction grating and the second diffraction grating is n2, and the second diffraction is The refractive index of the medium on the emission side from the grating is n3, and the first laser beam is applied to the first diffraction grating by the first diffraction grating.
When the incident angles of the laser beam and the second laser beam are θ1 and the exit angles of the zero-order diffracted light and the first-order diffracted light from the second diffraction grating are θ2, n1 · sin θ1 = n3 · sin θ2 The optical device according to claim 1, wherein the following relationship is established. 3. A lens and a half-wave plate are arranged between the light emitting means and the optical member, and P-polarized waves of the first laser beam and the second laser beam emitted from the light emitting means are provided. The optical device according to claim 1, wherein the half-wave plate converts the light into an S-polarized wave and enters the first diffraction grating. 4. The optical device according to claim 1, wherein a pitch d of the first diffraction grating and the second diffraction grating and an incident angle θ satisfy the following expression. 2d · n · sin θ = m · λ2 where n is the refractive index of the incident side medium, and m is an integer. 5. The optical member is a combination of right-angled triangular prisms having the same refractive index, and a first diffraction grating and a second diffraction grating are provided on the slopes of both prisms, respectively. Diffraction gratings are opposed to each other via a space, and the first laser beam and the second laser beam are:
The optical axis of the prism is perpendicularly incident on the outer surface of one of the prisms, and the optical axis of the light emitted from the second diffraction grating is perpendicularly emitted from the outer surface of the other prism. Optical device. 6. The optical member according to claim 1, wherein the first diffraction grating is provided on one surface of a plate member, and the second diffraction grating is provided on the other surface. An optical device according to claim 1. 7. The light emitted from the second diffraction grating is condensed by a condenser lens and irradiated on a recording medium.
7. The optical device according to any one of items 6 to 6.