JPH02178604A - Cross diffraction grating and polarized wave rotation detecting device using same - Google Patents

Abstract

PURPOSE:To obtain much information by a small-sized cross diffraction grating by providing two gratings which cross each other in one plane containing the optical axis of an optical anisotropic substrate and making the two gratings different in refractive index to mutually orthogonal polarized light components from the optical anisotropic substrate. CONSTITUTION:The optical anisotropic substrate 1 is provided with 1st diffraction gratings 3a and 3b in mutual crossing relation, and the optical axis 2 of the optical anisotropic substrate 1 is in a (-y) direction; and the 1st diffraction grating 3a is provided in a (z) direction on one surface of the substrate and the 1st diffraction grating 3b is provided in a (y) direction. When incident light 11 in an (x) direction is made incident on this cross diffraction grating, the polarized light component which vibrates mainly in the (y) direction is diffracted by the 1st diffraction grating 3a to obtain two primary diffracted light beams 16 and 17. Further, a polarized component which vibrates mainly in the (z) direction is diffracted by the 1st diffraction grating 3b to obtain two primary diffracted light beams 18 and 19 and undiffracted light travels straight to pass. Consequently, the cross diffraction grating which diffracts diffracted light beams in different polarizing directions to perform polarization plane detection and a magneto-optical head which is reducible in weight and size are obtained.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a crossed diffraction grating formed by intersecting two gratings, and in particular to a crossed diffraction grating that is suitably used for detecting minute changes in the plane of polarization of incident light. Regarding diffraction gratings. Furthermore, the present invention relates to a polarization rotation detection device using the above-mentioned crossed diffraction grating, particularly to a magneto-optical head.

[Prior Art] As a polarizing optical element (polarizing beam splitter) used to detect the plane of polarization of incident light or detect changes in the plane of polarization, (a) two rectangular prisms bonded together; Conventionally, materials in which one bonding surface is coated with a dielectric multilayer film, and materials using crystals with high birefringence such as (Cl) calcite have been widely used. Also (c) JP-A-61
No. 240204 discloses a polarizing beam splitter consisting of a fine pitch diffraction grating. Furthermore, (iv) JP-A-55501 discloses a pre-polarizing plate in which a diffraction grating of an H ion exchange region is formed on a lithium niobate crystal plate.

For example, the polarizing optical element (11) above separates incident light into two parts due to the difference in the refractive index of the medium for ordinary rays and extraordinary rays. That is, light 50 incident on a medium 49 with large birefringence (for example, calcite) shown in FIG.
．． Separate into 52 parts. Here, the refracted light 52 is polarized light in a direction parallel to the paper surface, and the refracted light 51 is polarized light in the direction of the frames placed on the paper surface.

A magneto-optical head is a polarization plane detection device using the above polarization optical element (polarization beam splitter).

FIG. 12 shows a schematic configuration of an example of a magneto-optical head.

In FIG. 12, 41 is a semiconductor laser (laser light source)
, 42 is a collimating lens, 43 is a beam splitter,
44 is an objective lens, and 21 is a magneto-optical disk. The laser beam emitted from the semiconductor laser 41 is made into parallel light by the collimating lens 42 and then sent to the beam splitter 43.
The light is transmitted through the lens, focused by the objective lens 44, focused on the magneto-optical disk 21, and reflected. This reflected light (
Laser light) The polarization plane of Ll is rotated by the Kerr effect, and after passing through the objective lens 44 again, it is reflected by the beam splitter 43 and heads toward the beam splitter 15.

The reflected light Ll incident on the beam splitter 15 is
A portion of the light is reflected and enters a sensor lens 46 consisting of a condensing lens and a cylindrical lens, and is focused on a four-part photodiode (detector) 45 .

A comparison circuit 47 receiving the output from the four-division photodiode 45 detects the focus and tracking state, and a servo mechanism (not shown) performs focusing and tracking.

On the other hand, the transmitted light of the reflected light L1 enters the polarizing beam splitter 20, is transmitted or reflected, and is transmitted to the photodetector 38.
Detected at 39. Here, if a slight change occurs in the polarization state of the reflected light L1 reflected by the magneto-optical disk 21, a change occurs in the light intensity of the light directed toward the photodetectors 38 and 39. Therefore, the outputs of the rain detectors 38 and 39 are differentially detected by the differential detector 48, and the magneto-optical disk 21 is
You can continue to receive information.

In addition, as an example of the structure of a magneto-optical head,
No. 247941 discloses a magneto-optical head using a grating element in which grating grooves are formed in an anisotropic plate having refractive index anisotropy and the grooves are filled with a filling material having a predetermined refractive index.

[Problems to be Solved by the Invention] Since the polarizing optical elements (a) to (d) above separate incident light into two lights with different polarization planes, a magneto-optical head having the configuration as shown in FIG. When used in a camera, multiple beam splitters 1 are required to separate the reflected light LL when performing focus and tracking state detection and differential detection.
5.20, the magneto-optical head cannot be made compact and also requires many expensive polarizing optical elements.

This invention was made in view of the above problems, and aims to provide a crossed diffraction grating in which a plurality of diffracted lights have different polarization directions and can detect the plane of polarization, and a magneto-optical head that can be made lightweight and compact. There is.

[Means for Solving the Problems] In order to achieve the above object, the crossed diffraction grating of claim (1) of this application has two gratings that intersect with each other in one plane including the optical axis of the optically anisotropic substrate. Cross diffraction according to claim 2, characterized in that two gratings are provided, and each of the two gratings has a refractive index different from that of the optically anisotropic substrate for polarization components that are mainly orthogonal to each other. In claim (1), the lattice is
Cross diffraction grating according to claim (3), characterized in that two first diffraction gratings intersecting each other are provided in the depth direction on one surface including the optical axis of the optically anisotropic substrate. In this case, the depths of the two first diffraction gratings are different from each other.

The crossed diffraction grating of claim (4) is characterized in claim (1) by:
Two first diffraction gratings intersecting each other are provided in the depth direction on one surface including the optical axis of the optically anisotropic substrate, and a transparent film layer is provided in the same direction as the first diffraction gratings. A second diffraction grating is stacked, and the second diffraction grating is formed so as to cancel out the phase difference caused by the first diffraction grating with respect to mutually orthogonal polarization components. In the crossed diffraction grating according to claim (5), the optically anisotropic substrate is an X-ring or Z-axis lithium niobate crystal plate,
The first diffraction grating is provided on one main surface of the lithium niobate crystal plate by H ion exchange.

The crossed diffraction grating of claim (1) can be combined with a detector for detecting the polarization of incident light by detecting the diffracted light obtained by the crossed diffraction grating.
) is used for polarization rotation detection devices.

Further, the crossed diffraction grating according to claim (1) above includes a photodetector that receives the transmitted light from the crossed diffraction grating and detects either a tracking state or a focus state, or both, and a photodetector that receives the diffracted light and detects the tracking state or the focused state. A photodetector for reading information on a magneto-optical recording medium is provided, and the information is read using reflected light or passing light from the magneto-optical recording medium.
7) It can be used for the magneto-optical head.

[Work] The operation of the present invention will be explained with reference to the drawings.

8 to 10 are schematic explanatory diagrams for explaining the function of the crossed diffraction grating of the present invention, in which the surface including the optical axis 2 of the optically anisotropic substrate 1 has a refractive index different from that of the substrate. A first diffraction grating 3 is provided.

Here, the optical axis of the anisotropic substrate is in the -X direction (as shown in FIG. 8), and the first diffraction grating is formed in the y direction (as shown in FIG. 8).

Let the refractive index difference between the substrate and the first diffraction grating be ΔNo for the ordinary light component and ΔNe for the No light component. Here, the ordinary light component and the extraordinary light component refer to light whose polarization direction is determined by the optical axis direction of the substrate, and in a -axial crystal, the polarization directions are perpendicular to each other. When the thickness of the first diffraction grating 3 is D, the optical path length difference between the light passing through the first diffraction grating and the light passing only through the substrate is given by the product of the thickness D and the above-mentioned refractive index difference. It will be done. That is, if the optical path length difference for the ordinary light component is ΔOP0, and the optical path length difference for the extraordinary light component is ΔOPe, then Δ0Po−ΔNo−D Δ0Pe=ΔNe−D. Considering the function as a diffraction grating, in a range where the optical path length difference is equal to or less than the wavelength of incident light, the diffraction efficiency increases as the optical path length difference increases. For example, in Fig. 8, if 1Δ0Pel)lΔ0P01,
The ordinary light component (
The light of the polarized light component vibrating in the y direction is the above! The light is hardly diffracted by the diffraction grating, and passes straight through the substrate 1 as zero-order light 12. On the other hand, the extraordinary light component (polarized light component vibrating in the X direction) of the incident light is diffracted by the first diffraction grating, becomes first-order diffracted light 13 and 14, and exits from the substrate l. In order to increase the extinction ratio of separation by polarized light components, it is desirable that the ratio between ΔOPe and ΔOP0 is large.

FIG. 9 shows a schematic configuration diagram when the second diffraction grating 4 made of a transparent film is laminated on the substrate of FIG. 8. If the second diffraction grating is formed under conditions that cancel out the phase difference for either the ordinary light component or the extraordinary light component, the diffraction efficiency of the light of that polarization component can be made zero. For example, in FIG. 9, the height of the second diffraction grating 4 on the first diffraction grating 3 is Hl, the refractive index is nl, and the height of the second diffraction grating other than on the first diffraction grating is If the distance is H2 and the refractive index is nt, if ΔOPo<O, then ΔOPo
When a second diffraction grating satisfying +(n+H1nlH*)=0 is stacked, the diffraction efficiency for the ordinary light component becomes zero. In other words, all the ordinary light components travel in a straight line, and the transmitted light 1
2) Only the extraordinary light component is diffracted (first-order diffracted light 1
3.14).

By the way, the second diffraction grating has a surface on which the first diffraction grating is not formed, in order to eliminate the phase difference between the optically anisotropic substrate and the first diffraction grating for the ordinary light component or the extraordinary light component. It may be laminated on top. FIG. 1θ is a schematic perspective view showing the case where the second diffraction grating 4 is formed on the surface where the first diffraction grating is not formed. Here, the first
The height of the second diffraction grating on the diffraction grating is Hl, the refractive index is nl, the height of the second diffraction grating other than on the first diffraction grating is H2, and the refractive index is 1. Then, the above ΔO
If Pe is ΔOPe>O, if a second diffraction grating satisfying ΔOPe + (n+H+ntHt) = 0 is stacked, the diffraction efficiency for the extraordinary light component of the incident light 11 becomes zero.

In other words, the light of the extraordinary light component travels straight through the transmitted light 12), and the light of the ordinary light component is diffracted (first-order diffracted light 13, 14).

The crossed diffraction grating of the present invention has two first diffraction gratings shown in FIGS. 8 to 10 formed on one surface of an optically anisotropic substrate so as to intersect with each other.

[Example 1] FIG. 1 is a schematic perspective view showing a first example of a crossed diffraction grating of the present invention, in which first diffraction gratings 3a and 3b cross each other on an optically anisotropic substrate l. It is provided. Here, the optical axis 2 of the optically anisotropic substrate 1 is in the -y direction (the first
The optically anisotropic substrate has a first diffraction grating 3a in two directions (as shown in FIG. 1) and a first diffraction grating 3b in the y direction (as shown in FIG. 1) on one surface of the optically anisotropic substrate. have. Here, the depth Da of the first diffraction grating 3a is between the optically anisotropic substrate and the first diffraction grating for the extraordinary light component of the incident light.
The difference in refractive index with the diffraction grating is large, 1Δ0Pel)Δ0
It is formed under the condition of P01. On the other hand, the depth Db of the first diffraction grating 3b is set under the condition that the refractive index difference between the optically anisotropic substrate and the first diffraction grating for the ordinary light component of the incident light is large and is 1Δ0Pol)1Δ0Pel. It is formed of. These intersections 5 have the above-mentioned depth Da.
The depth is the sum of Db and Db. When incident light 11 h4 in the X direction is incident on this crossed diffraction grating, the first diffraction grating 3a diffracts the light with a polarized component vibrating mainly in the y direction, and two first-order diffracted lights 16 and 17 are obtained. Further, the first diffraction grating 3b diffracts the polarized light component vibrating mainly in two directions, thereby obtaining two first-order diffracted lights 18 and 19. The light that is not diffracted goes straight and passes through (transmitted light 1
2).

As a method for forming the first diffraction grating, ions (
■゛) Any method such as the exchange method or Ti thermal diffusion method can be used.

Furthermore, in this embodiment, the two first diffraction gratings 3a and 3b
Although the depths of the two first diffraction gratings are different from each other, polarization components orthogonal to each other may be diffracted by changing the method of forming the two first diffraction gratings. Further, the first diffraction grating may be formed by providing a groove in the optically anisotropic substrate and filling the groove with a filling material having a predetermined refractive index.

In this embodiment, in order to increase the extinction ratio of polarization separation, one of the first diffraction gratings (for example, 3a) has a refractive index that is different from that of the optically anisotropic substrate for the ordinary light component of the incident light. The refractive index difference is large and the refractive index difference is small for the extraordinary light component, and furthermore, the other first diffraction grating (for example, 3b) has the above-mentioned optical anisotropy for the extraordinary light component of the incident light. It is necessary to have a large refractive index difference with the substrate and a small refractive index difference with respect to the ordinary light component.

2 and 3 are schematic diagrams showing a second embodiment of the crossed diffraction grating of the present invention, in which a first
Diffraction gratings 3a, 3b are formed on the optically anisotropic substrate, and the first diffraction gratings 3a, 3b are formed on the optically anisotropic substrate, respectively.
Second diffraction gratings 4a and 4b are stacked in the same direction as b. FIG. 2 is a schematic perspective view of the crossed diffraction grating of this embodiment, and the optical axis 2 of the substrate is in the -yX direction (as shown in the second figure), and the first
Alternatively, the second diffraction gratings 3a, 4a are set in two directions (as shown in FIG. 2), and the first or second diffraction gratings 3b, 4b are set in the X direction. The first diffraction gratings 3a and 3b provided on the substrate have a refractive index higher than that of the substrate for extraordinary light components and lower than that of the substrate for ordinary light components. Here, the second diffraction grating 4b is elevated above the first diffraction grating 3b, and is formed under the condition that the phase difference with respect to the ordinary light component is zero. Further, the second diffraction grating 4a is lowered above the first diffraction grating 3a, and is formed under the condition that the phase difference with respect to the extraordinary light component is zero. Figures 3a to 3d show the cross diffraction gratings of this embodiment, 1-11■-■, [[l-[11,
It is a schematic cross-sectional view taken along the line ■-■. In Figures 3a to 3d, D is the first diffraction grating 3bo':J
The depth, D, is the depth of the first diffraction grating 3a, and D is the depth of the first diffraction grating 3a.
This is the depth of the layer 5 at the intersection of a and 3b. Also, Sl is the second
The top 6 of the second diffraction grating 4b and the top 7 of the second diffraction grating 4a
The step, S, is between the bottom 8 of the above 4b and the bottom 9 of the above 4a.
S3 is the step between the top 7 and bottom 9 of 4a,
S4 is a step between the top 6 and bottom 8 of 4b. The above-mentioned through D3 and Sl through S4 are the optically anisotropic substrate and the first diffraction grating 3a or 3b.
The refractive index difference for the ordinary light component or the extraordinary light component between the good.

Incident light 11 in the X direction (shown in Figure 2) enters this crossed diffraction grating.
When incident, only the polarized light component vibrating in the X direction is diffracted by the first diffraction grating 3a and the second diffraction grating 4a, and two first-order diffracted lights 16 and 17 are obtained. Further, the first diffraction grating 3b and the second diffraction grating 4b
Only the light of the polarized component vibrating in the direction is diffracted, and two first-order diffracted lights 18 and 19 are obtained. The light that is not diffracted goes straight and passes through (transmitted light 12).

As explained above, the crossed diffraction grating of the present invention allows
(- Diffracted light and transmitted light with different light components can be obtained.

By making the grating shape of the second diffraction grating blazed, the intensities of the two first-order diffracted lights 16.17 (or I8.19) can be made different, and the diffracted light 16 ( or 17) and 18 (or 19)
It is also possible to obtain only

Note that the intersection angle of the first or second diffraction grating of the crossed diffraction grating of the present invention can be set to any angle from 00 to 90'. Further, as the substrate, any transparent optically anisotropic substrate can be used. An X-axis or Z-axis lithium niobate crystal plate is preferably used because the first diffraction grating can be manufactured easily. The transparent film layer forming the second diffraction grating may include a dielectric film such as MgF*, 3i0, etc.
A polymer resin film or the like is optional.

The refractive index of the first diffraction grating for the substrate may be high for both the ordinary light component and the extraordinary light component, high for one and low for the other, or even low for both. You can. FIG. 4 is a schematic perspective view showing a third embodiment of the crossed diffraction grating of the present invention, and the refractive index of the first diffraction gratings 3a and 3b of this embodiment is different from the ordinary light component as well as the extraordinary light component. It is also higher than the substrate 1. Therefore, the second diffraction gratings 4a and 4b are provided so that the portions where the first diffraction gratings 3a and 3b are formed are concave portions, respectively. The depth of the first diffraction grating and the height of the second diffraction grating are determined by the grating 3a.
The conditions for making the phase difference for the extraordinary light component zero by 4a and the conditions for making the phase difference for the ordinary light component zero by using the gratings 3b and 4b may be set as appropriate.

(Example 1) Hereinafter, one embodiment of the present invention will be described in detail.

An aluminum film pattern of 401 pitches was provided in the z-axis direction of an X-cut lithium niobate substrate whose both sides were polished. By immersing this substrate in a benzoic acid melt, ion exchange was performed to replace Li with Ho, and a first diffraction grating 3a with a pitch of 40 um and a refractive index different from that of the substrate was formed in the Z-axis direction of the substrate. . Here, the depth DI (ion exchange depth) of the first diffraction grating is 2.3 μm. Next,
Similarly, an aluminum film pattern with a pitch of 40 μm was provided in the Y-axis direction of the substrate on the surface on which the first diffraction grating 3a was formed. Then, by performing ion exchange in the same way, 40
A first diffraction grating 3b with a μm pitch was formed (ion exchange depth was 2.3 μm). Therefore, the first
The diffraction gratings 3a and 3b are formed in orthogonal directions, and the grating depth is large at the intersection, which is 4.6 μ-, and the grating depth outside the intersection is 2.3 μ. . Note that the refractive index of the lithium niobate substrate is 0.633 μ-
The refractive index is 2.200 for the extraordinary light component and 2.236 for the ordinary light component, and the refractive index for the extraordinary light component increases by 0.13 due to the above ion exchange, and the refractive index for the ordinary light component increases by 0.13. 04 decrease.

A transparent film layer made of a photosensitive resin was laminated on the substrate on which the first diffraction grating was formed, and a second diffraction grating was formed by the following method. First, 1 part of a copolymer of crotyl methacrylate and methyl methacrylate and 0.8 parts of m-benzoylbenzophenone were spin-coded to a thickness of 2.5 μm. Next, exposure was performed for 7 minutes using a 250W mercury lamp through a 40u-pitch photomask that shielded the portion where the first diffraction grating 3a was not formed.

Furthermore, exposure was performed for 25 minutes using the same mercury lamp through a photomask with a pitch of 404 m, which shielded the portion where the first diffraction grating 3b was formed. This board was heated to 95°C, 012°C.
The mixture was heated in an atmosphere of a@Hg for 4 hours to remove unreacted benzoylbenzophenone.

As a result of the above, the crossed diffraction grating shown in the schematic perspective view of FIG. 2 was obtained. In addition, the above-mentioned Sl is 0.14 μm, and the above-mentioned S.

is Q, 43μs, above S, is 0.43ua+, above S
4 was 0.14 μm.

FIG. 2 shows a schematic perspective view of the crossed diffraction grating produced as described above. The optical axis 2 of the optically anisotropic substrate 1 is in the -y direction (as shown in FIG. 2), and the directions of the first diffraction grating 3a formed in the substrate are in two directions (as shown in FIG. 2). Further, the direction of the first diffraction grating 3b is the y direction. A He-Ne laser beam is applied to the crossed diffraction grating in a direction perpendicular to the substrate.
When the light is incident from the direction (as shown in FIG. 2), diffraction light 16 is generated by the first diffraction grating 3a and the second diffraction grating 4a in two directions.
, [7 is the polarized light component in the y direction, and the diffracted light 18 due to the first diffraction grating 3b and the second diffraction grating 4b in the y direction
．． No. 19 had two polarization directions. In other words, the crossed diffraction grating has characteristics as a polarizing beam splitter. Transmitted light 12'' is also emitted from the crossed diffraction grating, and the intensity of the ±1st-order diffracted light from the diffraction gratings 3a and 4a in the two directions is equal to the intensity of the ±1st-order diffracted light from the diffraction gratings 3b and 4b in the y direction. Since the ratio of the transmitted light intensity is 2:2:l, the crossed diffraction grating also functions as a three-split beam splitter.

FIG. 5 is a schematic diagram of a magneto-optical head using the above-mentioned crossed diffraction grating. The laser light emitted from the semiconductor laser 41 in FIG. 5 passes through a collimating lens 42, a beam splitter 43, and a pair of object lenses 44, and then is focused on a magneto-optical recording medium (disk) 21, and its reflected light L1
enters the beam splitter 43 again and is reflected, passes through the cylindrical lens 40 for servo detection, heads toward the crossed diffraction grating 10, and is split into four diffracted lights L2, L3, L4, L5 and one transmitted light L6. be done. The transmitted light L6 enters a photoelectric conversion element (detector) 22 for servo detection and obtains a servo detection signal 23.

On the other hand, diffracted light 2 to L5 are photoelectric conversion elements 24 to 2, respectively.
Enter 7. Here, the diffracted light L2. L3 enters photoelectric conversion elements (detectors) 24 and 25, respectively, and intensity signals 28 and 29 are obtained. Also, a diffraction grating 3b in another direction,
The diffracted lights L4 and L5 by 4b enter the photoelectric conversion elements 28.29, respectively, and an intensity signal 30.31 is obtained. The above intensity signals 28, 29 (30, 31) are added to the adding circuit 32 (
33) by putting the phase signal 34 from one grating into
(35) is obtained.

This sum signal is amplified by a differential amplifier circuit 36 to obtain a difference signal 37 based on information recorded on the magneto-optical disk.

Note that since the difference in the emission angles of the diffracted lights 1 and 2 to L5 is not large, the photoelectric conversion elements 24 to 27 are provided on a small substrate.

The operating principle of this magneto-optical head will be explained below.

FIG. 6 shows the arrangement angle of the crossed diffraction grating IO, and shows the traveling direction of the reflected light Ll reflected from the beam splitter 43 in FIG. 5 set to the X direction in FIG. For example, the crossed diffraction grating IO is set in a direction in which the diffraction grating 3a (4a) (zz direction) and the diffraction grating 3b (4b) (yyX direction are orthogonal to each other, and the grating 3a (4a) and the Both the angle φl and the angle φ2 between the grating 3b (4b) and the X direction are set to 90°.Therefore, the polarization of the reflected light LL is inclined at θ=45° with respect to the xy plane, resulting in cross diffraction. When incident on the grating 10, the diffraction grating 3
The amounts of light diffracted by a (4a) and 3b (4b) (the sum of L2 and L3, and the sum of L4 and L5, respectively) become equal.

Here, if the part of the magneto-optical disk 21 that reflects the emitted light is not magnetized, the polarization of the reflected light L1 is inclined at θ=45° with respect to the xy plane, as shown by the solid line in FIG. Then, the reflected light L1 is set to be directed toward the intersecting diffraction grating IO. In this case, both lattices 3a (4a), 3b (
Since the polarizations for 4b) are the same, there is no difference in the sum signal 34.35 in FIG. On the other hand, if the part of the magneto-optical disk 21 that reflects the emitted light is magnetized,
Due to the Kerr effect, the plane of polarization is rotated by Δ, and as shown by the broken line in Figure 6, the polarization of the reflected light L1 is tilted smaller (or larger) than 45° with respect to the xy plane, and the reflected light L1 undergoes cross-diffraction. Head to the grid IO. In this case, both diffraction gratings 3
Since the polarizations for a (4a) and 3b (4b) are different, the sum signal 34.35 in FIG. 5 varies contradictoryly as shown in FIG. 7. Therefore, the difference signal 37, which is the difference between the sum signals 34.35, fluctuates as shown in FIG.
1 information is read.

[Effects of the Invention] As explained above, according to the invention of each claim of this condyle, the crossed diffraction grating consists of two gratings that intersect with each other in one plane including the optical axis of the optically anisotropic substrate. The two gratings have different refractive indexes for polarized light components that are orthogonal to each other than the optically anisotropic substrate, so that the light is separated depending on the polarization direction of the incident light, and Some of the light is transmitted. Therefore, a lot of information can be obtained with one small crossed diffraction grating.

In particular, in the crossed diffraction grating of claim (4), two first diffraction gratings that intersect with each other are provided in the depth direction on a plane including the optical axis of the optically anisotropic substrate, and the first diffraction grating By providing the second diffraction grating made of a transparent film layer in the same direction as the grating, the phase difference of the polarized light components perpendicular to each other due to the first diffraction grating is canceled out, so that the polarization separation of the crossed diffraction grating is improved. Extinction ratio is improved.

In the crossed diffraction grating of the present invention, according to claim (5), the long plate is an X-axis or Z-axis lithium niobate crystal plate, and one main surface of the lithium niobate crystal plate has H ion exchange. It is preferable to form the two first diffraction gratings by doing this, since it has good manufacturability.

The polarization rotation detection device according to claim (6), which includes a crossed diffraction grating according to the present application, obtains a large amount of information with one crossed diffraction grating, so the device can be made small.

According to the invention of claim (7), since the information detection signal and the servo signal for the magneto-optical recording medium are obtained by one crossed diffraction grating, the number of parts is reduced and the magneto-optical head is made smaller.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of a first embodiment of a crossed diffraction grating of the present invention, FIG. 2 is a schematic perspective view of a second embodiment of a crossed diffraction grating of the present invention, and FIGS. 3a to 3d are FIG. 3a is a partial sectional view taken along line I-1, FIG. 3b is a partial sectional view taken along line ■■, and FIG. 3c is a partial sectional view taken along line II.
FIG. 4c is a partial sectional view taken along the line I-I[[, FIG. A schematic configuration diagram of a magneto-optical head using the crossed diffraction grating of the invention, FIG. 6 is a perspective view showing the arrangement angle of the crossed diffraction grating, FIG. 7 is a characteristic diagram of the magneto-optical head using the crossed diffraction grating, and FIG. 10 through 10 are schematic perspective views for explaining the action of the crossed diffraction grating of the present invention, FIG. 11 is a schematic diagram of a polarizing optical element using a medium with large birefringence, and FIG. 12 is a conventional magneto-optical device. FIG. 2 is a schematic configuration diagram of a head. l... Optically anisotropic substrate, 2... Optical axis, 3a, 3b... First diffraction grating, 4a, 4b... Second diffraction grating (transparent film layer), 10
... Cross diffraction grating 11 ... Incident light, 12 ... Transmitted light, 16-19 ... Diffraction light, 21 ... Magneto-optical recording medium, 22, 24-27 ... Charge conversion element ( photodetector), 4
1... Semiconductor laser (laser light source), L
~・Laser light, L2-L5...Diffracted light, L6...Transmitted light. 3a, 3b 16.17 18.19 Optically anisotropic substrate optical axis First diffraction grating Incident light 12: Diffracted light by transmitted light 3o Diffracted light by 3b Fig. 2 Fig. 3o Fig. 4a, 4b + second diffraction Lattice Diagram Diagram Diagram Diagram θ Diagram Semiconductor Laser (Laser Light Source) Diagram Diagram ○ Diagram Diagram May 9, 1999

Claims (7)

[Claims] (1) Two gratings that intersect with each other are provided on one surface including the optical axis of the optically anisotropic substrate, and each of the two gratings has a refractive index for polarized light components that are orthogonal to each other. A crossed diffraction grating characterized by being different from an anisotropic substrate. (2) The intersection according to claim 1, characterized in that two first diffraction gratings that intersect with each other are provided in the depth direction on one surface including the optical axis of the optically anisotropic substrate. Diffraction grating. (3) The crossed diffraction grating according to claim 2, wherein the depths of the two first diffraction gratings are different from each other. (4) Two first diffraction gratings intersecting each other are provided in the depth direction on one surface including the optical axis of the optically anisotropic substrate, and the two first diffraction gratings are provided in the same direction as the first diffraction grating. A second diffraction grating made of a transparent film layer is laminated, and the second diffraction grating is laminated.
2. The crossed diffraction grating according to claim 1, wherein the diffraction grating is formed so as to cancel the phase difference between the polarization components orthogonal to each other due to the first diffraction grating. (5) The optically anisotropic substrate is an X-axis or Z-axis lithium niobate crystal plate, and the first diffraction grating is formed by H^+ ion exchange on one main surface of the lithium niobate crystal plate. The crossed diffraction grating according to claim 2 or 4, characterized in that it is provided by. (6) A polarization rotation detection device comprising the crossed diffraction grating according to claim 1 and a detector that detects the polarization state of incident light by detecting the diffracted light obtained by the crossed diffraction grating. (7) In a magneto-optical head that focuses laser light from a laser light source onto a magneto-optical recording medium and reads information using reflected light or transmitted light, one Two gratings that intersect with each other are provided on the surface, and each of the two gratings has a refractive index different from that of the optically anisotropic substrate mainly for polarized light components that are orthogonal to each other. a crossed diffraction grating that receives reflected light or transmitted light and emits transmitted light and diffracted light; a photodetector that receives the transmitted light and detects either a tracking state or a focus state, or both;
and a photodetector that receives the diffracted light and reads information on the magneto-optical recording medium.