JP2001051122A - Double refraction periodic structure, phase plate, diffraction grating type polarizing beam splitter and their manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double refraction element having large double refractivity having an optical axis in a face, capable of having a large opening area with a small optical path length, and capable of being manufactured at a low cost, by laminating a high refractive index medium, and low refractive index medium by repeating the shape in every period, on a substrate having periodic grooves or the like. SOLUTION: This structure is a multilayer structure in the z-axis direction comprising two or more kinds of transparent bodies having different refractive indices, and the shape of a layer which is a unit of lamination in each transparent body has a cyclic uneven structure in the x-axis direction. This structure is a double refraction periodic structure having a periodic or non-periodic uneven structure, uniform in the y-axis direction or having a larger length than that in the z-axis direction, and formed by being laminated in a layered shape in the z-axis direction by repeating the shape in every cycle shorter than a first Bragg condition in the z-axis direction. This double refraction periodic structure has a high refractive index medium layer 1 mainly composed of Si or TiO2 or Ta2O5 or Nb2O5 or Si3N4 and a low refractive index medium layer 2 mainly composed of SiO2, alternately.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for an optical device utilizing a birefringence phenomenon of light, and is capable of detecting incident light having a linear polarization component in a specific direction and a linear polarization component orthogonal thereto in a plane. The present invention relates to a birefringent element which provides functions such as phase difference control and polarization-dependent diffraction by birefringence having an optical axis, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a material exhibiting birefringence, artificial or natural uniaxial anisotropic crystals such as rutile, calcite, and quartz have been known. However, uniform growth is difficult for artificial crystals, and optically uniform and large-sized natural crystals are difficult to obtain and expensive.

[0003] A phase plate is an element for converting linearly polarized light into elliptically polarized light and vice versa, or converting azimuth of linearly polarized light into a desired azimuth. Usually, the phase plate is formed by using the above-described uniaxial anisotropic crystal, and cutting and polishing the optical axis set in a plane. For example 1/2
When a wave plate or a quarter-wave plate is manufactured using these crystals, the thickness becomes several tens μm or less, which is difficult to manufacture by polishing, and furthermore, handling is inconvenient. For example, wavelength 0.
In the case of a half-wave plate for 4 μm, the thickness is 20 μm. In order to avoid this, a method of making the thickness an odd multiple of a half wavelength, or a difference in thickness gives a phase difference of a half wavelength2
There is a method in which two elements are bonded with their optical axes shifted by 90 ° from each other. However, the former has a problem that the operating wavelength range is narrow, and the latter has a problem that the process is complicated.

[0004] In addition, as a technique of utilizing a birefringent element,
This is indispensable for pickups for optical disks.
One method is to spatially separate two polarization components orthogonal to one of them. As a general method, polarization separation is performed by inclining the crystal axis of the uniaxially anisotropic crystal from the light propagation direction. However, in order to obtain a sufficiently large separation width, it is necessary to make the thickness of the element 10 times the separation width, and it is inevitable that the element becomes large and the optical system becomes large. As another method, a method has been proposed in which regions having different refractive indices are provided in stripes by subjecting a LiNbO ₃ crystal, which is an anisotropic crystal, to proton exchange to form a phase diffraction grating (Nano, Nishimoto, Ota, Spring 1988 Related Conference of the Japan Society of Applied Physics, 29a-ZH-9.) But with this method,
It is difficult to reduce the grating interval to several tens of μm or less, so that the polarization separation angle is limited to 1 ° or less due to diffraction conditions.
As a result, the enlargement of the optical system is inevitable.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a large birefringence having an in-plane optical axis and a small optical path length. An object of the present invention is to provide a birefringent element which can have a large opening area and can be manufactured at low cost industrially.

[0006]

In order to achieve the above object, a medium made of a transparent material and having in-plane structural anisotropy is formed by a simple and excellent method of reliability and reproducibility. is necessary. For this purpose, a film including a high-refractive index medium and a low-refractive index medium, at least partially including dry etching, is formed on a substrate having periodic grooves or periodic linear projections or elongated projections or elongated depressions. It is effective to stack the layers while repeating the shape in each cycle depending on the forming method (S. Kawakami, T. Kawashima, and T. Sato, "Mecha
nism ofshape-formation of 3D periodic nanostructur
es by bias sputtering, "Applied Physics Letters, v
ol. 74, no. 3, pp. 463-465, 18 January 1999.). By this method, a birefringent element having an in-plane optical axis can be manufactured.

[0007]

If a birefringent medium can be artificially formed by the means described in the preceding paragraph, a surface-type phase control element can be easily realized with good reproducibility by controlling its thickness.
Further, by periodically repeating the birefringent laminated structure portion and the non-birefringent laminated structure portion in a striped manner, it can be used as a phase diffraction grating.

[0008]

[Embodiment 1] FIG. 1 is a diagram showing the structure of an embodiment of the present invention. In this figure, reference numeral 1 denotes an amorphous Si layer, and reference numeral 2 denotes an amorphous SiO ₂ layer. The period Lx in the x-axis direction is 0.45 μm, and the period L in the z-axis direction
z is 0.36 μm. The SiO ₂ layer and the Si layer have a periodically bent shape.

The manufacturing method is described below. First, a periodic groove as shown in FIG. 2 is formed on a substrate by electron beam lithography and dry etching. Reference numeral 3 is a quartz glass substrate, and reference numeral 4 is an enlargement of a groove portion. Groove width is 0.35μ
m, and the depth of the groove is 0.2 μm. In order to prevent reflection at the boundary surface, an antireflection film indicated by reference numeral 5 is provided if necessary.
In this case, the cross-sectional shape of the groove is triangular, but other shapes such as a rectangle and a semicircle may be used. On this substrate, alternate multilayer films are laminated by using a combination of sputter deposition and sputter etching, using SiO ₂ and Si targets. At this time, it is important to form a film while preserving the periodic uneven shape in the x-axis direction of each layer. The conditions were as follows. Si
In forming the layer, the gas pressure was 2 mTorr and the target applied high frequency power of 400 W. In the case of the SiO ₂ layer, the gas pressure was 6 mTorr and the target applied high frequency power was 400 W. Sputter etching was performed after the SiO ₂ layer was formed. The applied high frequency power is 180W. The SiO ₂ layer and the Si layer each had a thickness of 0.18 μm, and were repeated eight cycles. Therefore, the thickness of the multilayer film is about 2.9 μm.

Due to the structural anisotropy, birefringence having an optical axis in the longitudinal direction of the groove is generated. Light having a wavelength of 1.5 μm was incident on this structure from a direction perpendicular to the plane, and the birefringence was confirmed. When the polarization of the incident light was a linear polarization of 45 ° with respect to the groove, the polarization of the output light was rotated by 90 ° with respect to the incident polarization. This indicates that the periodic structure provided a half-wave phase difference. Similarly, when a multilayer film having four periods was stacked, the phase difference was a quarter wavelength, and linearly polarized light could be converted to circularly polarized light.

FIG. 3 shows the result of calculating the relationship between the frequency and the wave number vector in this periodic structure by the FDTD method (finite difference time domain method) using a periodic boundary condition. The horizontal axis represents a value kz Lz / π obtained by normalizing the phase when the phase advances one cycle in the z direction with π, and the vertical axis represents the normalized frequency Lz / λ. Here, λ is the wavelength of the incident light, and kz is the z component of the wave number vector. Solid lines and broken lines indicate TEs propagating through the periodic structure, respectively.
4 shows dispersion curves for a wave (polarization in which an electric field is parallel to a groove) and a TM wave (electric field is perpendicular to a groove). In the above case, Lz = 0.4
From 5 μm and a wavelength of 1.5 μm, the frequency Lz / λ = 0.3. TE
Intersection points of the dispersion curves of the wave and the TM wave and the straight line of Lz / λ = 0.3 are assumed to be A and B, respectively. The difference in phase change when the TE wave and the TM wave propagate for one cycle in the z direction is π / 8 from the difference 0.125 between the values of the horizontal axis kz Lz / π that provides the points A and B. Therefore, in a structure in which a multilayer film is stacked eight periods,
It can provide a phase difference of π and operates as a half-wave plate. Further, in a structure in which four periods are stacked, a phase difference of π / 2 can be given, and the structure operates as a 波長 wavelength plate.

[Embodiment 2] In this embodiment, a polarization-dependent phase diffraction grating using a periodic structure as shown in Embodiment 1 will be described.

FIG. 4 is a diagram showing the configuration of the present embodiment. Reference numeral 6 denotes a quartz glass substrate, on which a multilayer film is laminated while keeping the concavo-convex shape. Two regions (symbols 7 and 8) having different concavo-convex cross-sectional shapes are periodically repeated at a period L. Reference numeral 9 denotes a low refractive index layer, and reference numeral 10 denotes a high refractive index layer. This time, the period L was 4 μm, and the low and high refractive index materials were amorphous SiO ₂ and amorphous, respectively.
TiO ₂ was used. Further, in the region indicated by reference numeral 7, the period Lx in the x-axis direction is 0.15 μm, and the period Lz in the z-axis direction is 0.12 μm. In the region indicated by reference numeral 8, the period in the x-axis direction is infinite,
That is, a flat structure having no unevenness was obtained.

The fabrication method is described below. First, a region having a periodic groove as shown in FIG. 2 and a flat region are processed to have a period of 4 μm on the substrate by electron beam lithography and dry etching. Groove width 0.1 μm, period 0.1
5 μm and the depth of the groove is 0.1 μm. Although a triangular groove shape is shown here, other shapes such as a rectangle and a semicircle may be used. On this substrate, using a TiO ₂ and SiO ₂ target, alternate multilayer films are stacked by combining sputter deposition and sputter etching. Here, the TiO ₂ layer may be formed by sputtering a Ti target with a gas containing oxygen. At this time, it is important to form a film while preserving a periodic uneven shape in the x-axis direction of each layer. The conditions were as follows. In forming the TiO ₂ layer, the gas pressure was 2 mTorr and the target applied RF power was 300
In forming the W and SiO ₂ layers, the gas pressure is 6 mTorr and the target applied high frequency power is 300 W. Sputter etching is performed after the SiO ₂ layer is formed, and the gas pressure is ₂ mTorr and the substrate applied high frequency power is 100 W. However, a different sputtering apparatus from that of Example 1 was used. Si
Each of the O ₂ layer and the TiO ₂ layer was set to 0.06 μm, and the cycle was repeated eight times. Therefore, the thickness of the multilayer film is 0.96 μm.

When light having a wavelength of 0.4 μm is incident on the structure from a direction perpendicular or oblique to the substrate surface, as shown in FIG. 5, a polarization component parallel to the groove and a polarization component perpendicular to the groove are spatially formed. Can be separated. Here, the operation principle at normal incidence will be described for simplicity.

FIG. 6 shows the dispersion relationship (solid line and broken line) between the y-polarized wave (TE wave) and the x-polarized wave (TM wave) in the periodic structure denoted by reference numeral 7, and the one-dimensional (1D) periodic structure denoted by reference numeral 8. Shows the dispersion relationship (dotted line). In the above case, Lz = 0.12μm, wavelength
Since it is 0.4 μm, the frequency is Lz / λ = 0.3. Lz / λ =
Kz, which gives the intersection of the straight line of 0.3 and the dispersion curve, is the propagation constant of each light wave in the z direction. From FIG.
The phase change amount when propagating one cycle through the two-dimensional periodic structure is different by π / 8 between the y polarization and the x polarization. On the other hand, the phase constant of the one-dimensional periodic structure denoted by reference numeral 8 is x
Equivalent to polarization. That is, when light is incident on the structure shown in FIG. 5, the phase distribution after emission is flat for x polarization, but y
In polarization, the phase distribution is modulated with a period L and an amplitude π. Therefore, while the x-polarized light is emitted in the z-axis direction, the y-polarized light is emitted in the direction of angle θ (= sin ⁻¹ (λ / L)) by diffraction, so that both can be separated. In the structure of the present invention, L
Is 4 μm, so that a separation angle θ = 5 ° is obtained.

A modification of the above embodiment will be described. In the above-described embodiment, an example has been described in which a birefringent region having an optical axis in a plane and a uniform region having no optical axis in a plane are periodically arranged. Of course, two or more types of regions having different in-plane periods, lamination periods, and uneven steps may be combined. In addition, it is possible to combine not only the direction of the groove and the projection in one direction but also the regions in different directions.

A blazed diffraction grating is shown as an example.
As shown in FIG. 7, a region in which the period of the unevenness is continuously changed from Lx1 to Lx2 is further repeated at period L. In this structure, the phase distribution of the x polarization is flat as in the above example, but the phase distribution of the y polarization has a sawtooth shape with a period L. The number of layers is adjusted so that the amplitude of the phase distribution becomes π. As a result, a diffraction grating can be obtained in which x-polarized light travels straight and y-polarized light separates 100% in the direction in which the phase distribution is inclined.

[Embodiment 3] In this embodiment, an example is shown in which the phase plate shown in Embodiment 1 is directly manufactured on an optical component having a flat surface.

FIG. 8 is a diagram showing the configuration of this embodiment. Mark
Reference numeral 11 denotes a prism made of optical glass, and the prism
Periodic groove rows are machined. The structure has a period in the plane
The depth of the groove is 0.1 μm. Symbol 12 is amole
Fasu TiO_TwoAnd amorphous SiO _TwoA multilayer film consisting of
The surface has a periodically bent shape. In plane
The period is 0.15 μm, and the period in the direction perpendicular to the surface is 0.12 μm.

When light is incident on this structure in the direction of the arrow, the light is subjected to polarization rotation by the phase plate, and then enters the prism and is refracted. In this way, the phase plate and the prism can be integrally manufactured, so that the number of parts can be reduced, the interface with air is reduced, so that an antireflection film is not required, and advantages such as being effective for integration are provided. There is.

Here, a prism is shown as an example of the optical component, but the present invention can also be applied to a mirror, a polarization separation element, a polarizer, and a lens. Alternatively, an initial concave-convex pattern may be processed on a film-like substrate or a thin glass substrate, and a multilayer film may be laminated on the substrate, and then may be attached to the surface of the optical component.

[Embodiment 4] In Embodiments 1 to 3,
As a means for laminating layers while repeating the shape of the layers, sputter deposition and sputter etching are performed independently with a time lag, but lamination may be performed by a bias sputtering method which is performed simultaneously. For example, a TiO ₂ layer is
An O ₂ layer is formed by bias sputtering. Detailed experimental conditions are shown below. TiO ₂ film is used for gas pressure (oxygen and Ar
(Mixing ratio: 10%) by sputtering at 2 mTorr. On the other hand, the SiO ₂ film is formed at a gas pressure of 6 mTorr using only Ar, with a target applied high-frequency power of 300 W and a bias power of 80 W. SiO ₂ layer and TiO ₂
Each layer was set to 0.06 μm, and was repeated for 8 cycles. Therefore, the thickness of the multilayer film is 0.96 μm.

As a deposition method, a chemical vapor deposition (CV) method is used.
D) or a vapor deposition method may be used. Further, an optical glass such as VIREX may be used as the low refractive index material in addition to amorphous SiO ₂ .

Also, amorphous Si or Ti may be used as the high refractive index material.
Other than O ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , Si ₃ N ₄ or the like may be used. An example of manufacturing conditions will be described. The Ta ₂ O ₅ film is formed by sputtering a Ta ₂ O ₅ target at a gas pressure (mixing ratio of oxygen and Ar: 5%) of 1 mTorr. On the other hand, the SiO ₂ film has a gas pressure of 5 mTorr and a high frequency power of 300 W applied to the target, and the sputter etching is performed after the SiO ₂ layer is formed, and has a gas pressure of ₂ mTorr and a high frequency power of 100 W applied to the substrate. The thicknesses of the SiO ₂ layer and the Ta ₂ O ₅ layer were each 0.08 μm, the in-plane unevenness period was 0.18 μm, and 10 cycles were repeated. Ta ₂ O ₅ has a band edge wavelength of about 300 nm, which is shorter than TiO ₂ .
Therefore, it is characterized by having an optical advantage that not only the refractive index is high at 2.2 near the wavelength of 400 nm but also the refractive index dispersion and absorption loss are small. This wavelength range is a useful wavelength range that can be used in high-density recording optical disks and the like due to the development of a blue-violet laser.

The cross-sectional shapes of the laminated films are shown in Examples 1 to 3.
Are V-shaped, but various cross-sectional shapes such as a rectangle and a triangular prism are also possible.

The grooves and the linear projections can be formed not only as straight lines but also as curved lines, so that a more complicated phase difference distribution can be given.

The laminated film thus produced is preferably cut after applying a non-reflective coating to the front surface / interface and the back surface of the substrate. In addition to being able to fabricate many devices at once,
Polishing is unnecessary and the cutting process is simple. In addition, the thickness of the laminated film has reproducibility, and there is little change in the characteristics of the element. On the other hand, high precision is not required for the shape of the groove to be initially machined on the substrate, so it is not limited to electron beam lithography, and it can be manufactured by simpler methods such as nanoprinting technology using a mold with uneven shape. It is possible. As a result, an inexpensive element can be provided, and can be used in a wide range such as an optical disk pickup.

[0029]

The birefringent element manufactured by the film forming method including the sputter etching action of the present invention has a small thickness in the light transmission direction, and a large-area laminated film can be obtained by one film forming process. Polishing is not required when individual elements are manufactured, and cutting is easy. On the other hand,
It is possible to design an arbitrary birefringence index and an arbitrary phase difference control according to the wavelength band to be used. Further, it is possible to draw a birefringent structure in an arbitrary pattern on the substrate. Birefringent elements such as a phase control element and a phase diffraction grating using such a birefringent medium are widely used in industrial applications such as optical disk pickups, and can replace conventional birefringent elements.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a first embodiment.

FIG. 2 is a diagram showing a substrate having a groove on a surface.

FIG. 3 is a diagram showing a relationship between a frequency and a wave vector in the first embodiment.

FIG. 4 is a diagram showing a structure of a second embodiment.

FIG. 5 is a diagram illustrating a polarization separation operation in the second embodiment.

FIG. 6 is a diagram showing a relationship between a frequency and a wave vector in the second embodiment.

FIG. 7 is a diagram showing a structure of a second embodiment.

FIG. 8 is a diagram illustrating a relationship between a frequency and a wave vector in the third embodiment.

[Explanation of symbols]

1 SiO ₂ layer 2 Si layer 3 substrate 4 grooves partially enlarged 5 antireflection film 6 region 9 SiO ₂ layer 10 TiO ₂ layer having a large uneven shape of the region 8 plane period having small irregularities of the substrate 7 surface cycle of DESCRIPTION OF SYMBOLS 11 Prism 12 Thin film with uneven shape

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuo Odera 1-6-16-1 Doi, Aoba-ku, Aoba-ku, Sendai City, Miyagi Prefecture Co., Ltd. Kaneko 201 (72) Inventor Takayuki Kawashima Thirty Persons Kawauchi, Aoba-ku, Sendai City, Miyagi Prefecture Town No. 45-5 Le Village 203 No. 72 (72) Inventor Kenta Miura 3-81-12 Yagiyama Minami 3-chome, Taihaku-ku, Sendai City, Miyagi Prefecture Apartment house No. 101 Yagiyama

Claims (14)

[Claims] 1. In three-dimensional rectangular coordinates x, y, z,
A multilayer structure in the z-axis direction comprising two or more types of transparent bodies having different refractive indices, wherein a layer serving as a unit of lamination for each transparent body has a periodic uneven structure in the x-axis direction and a y-axis direction. It has a periodic or aperiodic uneven structure having a length that is uniform in the direction or longer than the x-axis direction, and its shape is repeated at intervals shorter than the first Bragg condition in the z direction.
A birefringent periodic structure characterized by being laminated in layers in the axial direction. 2. The birefringent periodic structure according to claim 1, wherein the structure is Si, TiO _2, Ta ₂ O _5, Nb ₂ O _5, or Si ₃ N.
A birefringent periodic structure, characterized by having alternately high refractive index medium layers mainly composed of ₄ and low refractive index medium layers mainly composed of SiO ₂ . 3. A film containing a high-refractive-index medium and a low-refractive-index medium, at least partially including dry etching, on a substrate having periodic grooves or periodic linear projections or elongated projections or elongated depressions. A method of manufacturing a birefringent periodic structure, wherein the birefringent periodic structure is laminated with a period shorter than the first Bragg condition in the z-direction with the longitudinal direction of the concave-convex shape as an optical axis, wherein . 4. Periodic grooves or periodic linear projections or
On a substrate with elongated protrusions or recesses,
Or TiO_TwoOr Ta_TwoO_FiveOr Nb_TwoO_FiveOr Si _ThreeN_FourThe main
High refractive index medium and SiO_TwoLow-refractive-index medium whose main component is
Quality and at least part of the film type including dry etching
Laminating while repeating the irregular shape every period by the forming method
Characterized in that the longitudinal direction of the uneven shape is the optical axis
A method for producing a birefringent periodic structure. 5. The birefringent periodic structure according to claim 1, wherein when light enters the xy plane perpendicularly or obliquely, x
A phase plate, wherein a phase difference is provided between a polarization having an electric field component in a direction and a polarization having an electric field component in a y direction. 6. The birefringent periodic structure according to claim 1, wherein the structure is Si, TiO _2, Ta ₂ O _5, Nb ₂ O _5, or Si ₃ N.
_It consists of a high-refractive-index medium whose main component is ₄ and a low-refractive-index medium whose main component is SiO _2. When light is incident perpendicularly or obliquely to the xy plane, it has polarization in the x direction and electric field components in the y direction. A phase plate for providing a phase difference between polarized waves having an electric field component. 7. A film containing a high-refractive-index medium and a low-refractive-index medium at least in part on a substrate having periodic grooves or periodic linear projections or elongated projections or elongated recesses, at least partially including dry etching. A birefringent periodic structure having a longitudinal direction of an uneven shape as an optical axis, wherein the shape is repeated while repeating a shape in each cycle by a forming method, and the uneven shape is formed when light having a component in a stacking direction is incident. Providing a phase difference between the polarization in the longitudinal direction and the polarization in the vertical direction. 8. A periodic groove or periodic linear projection or
On a substrate with elongated protrusions or recesses,
Or TiO_TwoOr Ta_TwoO_FiveOr Nb_TwoO_FiveOr Si _ThreeN_FourThe main
High refractive index medium and SiO_TwoLow-refractive-index medium whose main component is
Quality, at least partially including dry etching
Laminate while repeating the shape every period by film formation method
A birefringent periodic structure, characterized in that
Longitudinal direction of uneven shape when light with component in the direction is incident
It provides a phase difference between the polarization of
A method for manufacturing a phase plate. 9. The birefringent periodic structure according to claim 1, wherein the birefringent periodic structure comprises two or more stripe-shaped regions having different periods in the x-axis direction or the z-axis direction or steps in the uneven shape. A diffraction grating type polarization beam splitter. 10. Si or TiO ₂ or Ta ₂ O ₅ or Nb ₂ O _5
2. The birefringent periodic structure according to claim 1, further comprising a high-refractive-index medium containing Si ₃ N ₄ as a main component and a low-refractive-index medium layer containing SiO ₂ as a main component. 3. A diffraction grating type polarizing beam splitter comprising two or more stripe-shaped regions having different periods in the direction or steps of unevenness. 11. On a substrate having periodic grooves or periodic linear projections or elongated projections or elongated depressions,
A high-refractive-index medium and a low-refractive-index medium are formed at least in part by a film forming method including dry etching while repeating the shape in each period while repeating the shape thereof. A method for manufacturing a polarizing beam splitter. 12. On a substrate having periodic grooves or periodic linear projections or elongated projections or elongated depressions,
Dry etching is performed on at least part of a high-refractive index medium mainly composed of Si or TiO ₂ or Ta ₂ O ₅ or Nb ₂ O ₅ or Si ₃ N ₄ and a low refractive index medium mainly composed of SiO _2. A method of manufacturing a diffraction grating type polarizing beam splitter comprising a birefringent periodic structure, wherein the lamination is performed while repeating a shape in each cycle by a film forming method including the same. 13. A birefringent periodic structure region according to claim 1, and a periodic structure region having a multilayer structure in the z-axis direction and being uniform in the x-axis direction and the y-axis direction. Grating type polarizing beam splitter. 14. Si or TiO ₂ or Ta ₂ O ₅ or Nb ₂ O ₅
Or a high refractive index medium mainly composed of Si ₃ N ₄ and a low refractive index medium layer mainly composed of SiO ₂ , wherein the birefringent periodic structure region according to claim 1 and a multilayer structure in the z-axis direction are formed. A diffraction grating type polarization beam splitter having a periodic structure region that is uniform in the x-axis direction and the y-axis direction.