JP2003156615A - Polarizing hologram element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing hologram element which can improve the diffraction efficiency. SOLUTION: The polarizing hologram element is obtained by depositing an optically transparent anisotropic material 13 on an optically transparent isotropic substrate 11, forming a grating 14 having a rugged pattern on the surface of the optically transparent anisotropic material 13, and filling the grating with an isotropic material 15. In the above hologram element, the optical axis of the incident laser light is tilted from the perpendicular direction to the face forming the grating to the direction where the diffracted light is produced. Thereby, the efficiency of diffracted light practically used can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element for separating the polarization of incident light depending on the polarization state of the incident light, and its application relates to a polarization hologram element used in an optical pickup device for an optical disk, etc. In particular, the present invention relates to a polarization hologram element used in an optical pickup device that performs reading and writing on optical recording media having different recording densities.

[0002]

2. Description of the Related Art In recent years, optical pickup devices for various optical recording media have been researched and developed. One is wavelength 78
A CD (Compact Disc) type reading optical pickup device and a writing optical pickup device that use a 0 nm laser beam, and a DVD (Digital Versatile Disc) type reading and writing type that uses a laser beam having a wavelength of about 660 nm. Optical pickup device. Further, as a high-density optical disc in the future, research and development of an optical pickup device for an optical disc using a blue laser beam having a short wavelength are actively conducted. Although the optical pickup device shown above has individual technical problems, they have common problems such as miniaturization and cost reduction of the optical pickup part, and research and development for these problems are actively made.

An optical system using a polarization hologram element as a polarization separation element is adopted as a structure effective for downsizing and cost reduction of an optical pickup device. this is,
It is an element for separating the forward and return paths of the laser light, and not only solves the part where the optical system became large because it used a polarization beam splitter etc. in the past,
Since the signal detection element can be arranged on the same surface as the laser emission, there are advantages that the optical path can be easily designed and the number of parts can be reduced. Further, even when writing and reading of a plurality of types of optical recording media having different recording densities are performed by a single optical pickup device, the optical path can be shared, and it is considered to be an effective optical system. A conventional example of the polarization hologram element is shown below.

As a first conventional example, there is a polarization hologram element described in Japanese Patent Laid-Open No. 2000-199820, which is an example of a general polarization hologram element. In this conventional example, a polarization hologram element is manufactured using a lithium niobate substrate which is a birefringent material. In this case, there are problems that the substrate is expensive, it is difficult to narrow the pitch of the diffraction grating pattern due to its workability, and the diffraction angle cannot be made large. Therefore, it is not possible to supply the polarization hologram element at low cost and downsize the optical system using the polarization hologram element.

Next, as a second conventional example, Japanese Unexamined Patent Publication No. 200
There is a polarization separation element described in JP-A-0-221325. In this conventional example, a low-cost polarization separation element is provided by forming an organic film (polyacetylene alignment film) on an optically isotropic substrate. Further, as a third conventional example, there is a polarization separation element described in Japanese Patent Laid-Open No. 2000-75130. Also in this conventional example, a low-cost polarization separation element is provided by forming a polymer film having birefringence on an optically isotropic substrate. In these two conventional examples, it is possible to reduce the cost of the polarization separation element,
Since the grid pitch can be narrowed,
It is possible to supply elements at low cost and downsize an optical system using a polarization hologram element.

In the above-mentioned second and third conventional examples, the diffraction grating itself is formed in a rectangular shape. This is for increasing the diffraction efficiency and suppressing the transmittance (0th-order diffraction efficiency) with respect to the diffracted laser light of the polarization direction. However, when a rectangular diffraction grating is manufactured, the diffraction efficiency of ± first-order diffracted light is limited to about 40% at maximum. Therefore, in order to increase the signal detection efficiency, it is necessary to further improve the efficiency.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its main object is to realize a polarization hologram element having a structure capable of improving diffraction efficiency. More specifically, claims 1, 2, 3,
The invention according to No. 4 aims to improve the diffraction efficiency of the polarization hologram element. In the invention according to claim 5, an object is to improve the diffraction efficiency of the polarization hologram element and to improve the wavefront aberration characteristic. In addition to the object of claim 5, the invention according to claim 6 aims at cost reduction of the polarization hologram element. In addition to the object of any one of claims 1 to 6, the invention according to claim 7 aims at further cost reduction of the polarization hologram element. In the invention according to claim 8, in addition to the object of any one of claims 1 to 7, the purpose is to make the polarization hologram element multifunctional. In addition to the object of any one of claims 1 to 8, the invention according to claim 9 aims to improve the optical characteristics of the polarization hologram element.

[0008]

The structure and operation of the present invention for achieving the above object will be described. In the invention according to claim 1, an optically transparent anisotropic material is formed on an optically transparent isotropic substrate, and an uneven diffraction grating is formed on the surface of the optically transparent anisotropic material. In the polarization hologram element in which the grating is filled with an isotropic material, the optical axis of the incident laser light is inclined from the direction perpendicular to the grating formation surface to the diffracted light generation direction. The operation is to separate the polarized light of the laser light using a polarizing diffraction grating, and to separate the polarized light by changing the transmittance and the diffraction efficiency depending on two orthogonal polarization directions. Here, in order to improve the efficiency, the configuration is such that the optical axis of the incident laser light is inclined from the direction perpendicular to the grating formation surface to the diffracted light generation direction.

According to a second aspect of the present invention, in the polarization hologram element according to the first aspect, the optical axis is inclined by an angle of the optically transparent isotropic substrate. The operation is the same as in claim 1.

According to a third aspect of the present invention, in the polarization hologram element according to the first aspect, an optically transparent anisotropic material is angled to shape an isotropic substrate.
The optical axis is tilted. The operation is the same as in claim 1.

According to a fourth aspect of the present invention, in the polarization hologram element of the first, second or third aspect, the refractive index of the anisotropic film in the ordinary ray direction or the extraordinary ray direction and the refractive index of the anisotropic film are filled in the lattice. The isotropic materials are made to have substantially the same refractive index. The operation is the same as in claim 1.

According to a fifth aspect of the present invention, in the polarization hologram element according to the fourth aspect, an optically transparent isotropic substrate is formed above the surface on which the diffraction grating is formed, with an adhesive layer interposed therebetween. It is configured. The operation is as described in claim 1.
Is the same as.

According to a sixth aspect of the present invention, in the polarization hologram element according to the fifth aspect, the adhesive for adhering the optically transparent isotropic substrate is the same as the material for filling the diffraction grating. It has a certain structure. The operation is the same as in claim 1.

According to a seventh aspect of the present invention, in the polarization hologram element according to any one of the first to sixth aspects, the optically transparent anisotropic material is an organic material or a stretched polymer organic material. The configuration is The operation is
This is similar to claim 1.

According to an eighth aspect of the present invention, in the polarization hologram element according to any one of the first to seventh aspects, a polarization hologram element and a phase plate having a constant phase difference with respect to a used wavelength are provided. It is composed of one. The operation is
Although substantially the same as that of claim 1, the function of adding a phase difference to the laser light is added to the operation.

According to a ninth aspect of the present invention, in the polarization hologram element according to any one of the first to eighth aspects, a coating for reducing reflection with respect to a used wavelength is provided at a boundary with the outside of the polarization hologram element. It has been given a structure. The operation is the same as in claim 1 or 8.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The configuration, operation and action of the polarization hologram element of the present invention will be described in detail below with reference to the illustrated embodiments. First, the configuration, operation and action of the polarization hologram element according to the first embodiment of the present invention will be described with reference to FIG. Here, the polarization hologram element according to the present embodiment functions as a polarization separation element for laser light having a wavelength of 660 nm. In the configuration of this embodiment, the optical glass substrate 11 made of BK7 or the like is used as the optically transparent isotropic substrate,
An organic birefringent film 13 formed by stretching a polyester organic material as an optically transparent anisotropic material is formed on this optical glass substrate 11 through an adhesive layer 12 made of an acrylic ultraviolet curing adhesive material. A rectangular (concave-convex) diffraction grating 14 is formed on the organic birefringent film 13, an overcoat layer 15 made of an epoxy-based ultraviolet curable resin is formed on the upper portion of the diffraction grating 14, and the upper portion thereof is further formed. ,
An optical glass substrate 16 made of BK7 or the like is configured as an optically transparent isotropic substrate. Although not shown, the interface between the optical glass substrates 11 and 16 made of BK7 or the like and the air (the boundary with the outside of the element) is coated with an antireflection layer for the wavelength used. Further, here, the lower surface of the optical glass substrate 11 and the upper surface of the optical glass substrate 16 are provided with an inclination angle θ of 2 ° with respect to the lattice formation surface.

Next, the details of each component will be described. The optical glass substrates 11 and 16 formed of BK7 and the like above and below the polarization hologram element are both substrates having a thickness of about 1.0 mm with an inclination angle θ of 2 °. In order to avoid reflection at the interface as much as possible, the adhesive layer 12 uses an acrylic UV-curable adhesive whose refractive index matches that of an optical glass substrate made of BK7 or the like. The organic birefringent film 13 has a thickness of about 100 μm, and its refractive index is about 1.579 in the extraordinary ray direction and about 1.670 in the ordinary ray direction. The overcoat layer 15 has a thickness of about 40 μm.
And a material whose refractive index is approximately matched with the refractive index of the organic birefringent film 13 in the extraordinary ray direction is used. Here, the overcoat layer 15 also serves as an adhesive layer with the optical glass substrate 16 on the surface. The antireflection layer is composed of a multilayer film using MgF / TiO ₂ / SiO ₂ .

Next, the shape of the diffraction grating 14 formed on the surface of the organic birefringent film 13 will be described. The diffraction grating 14 is formed with a depth of 4.0 μm, a duty of about 0.5, and a grating pitch of 2.0 μm.

Next, a method of manufacturing the polarization hologram element according to this embodiment will be briefly described. First, the organic birefringent film 13 is formed on the optical glass substrate 11 made of BK7 or the like by the adhesive 1
Glue with 2. After that, through the photolithography process,
A diffraction grating shape is formed by dry etching. After that, an epoxy resin is potted as the overcoat layer 15 on the formed diffraction grating 14 and the optical glass substrate 16 made of BK7 or the like is adhered to produce a polarization hologram element.

Next, the diffraction characteristics of the polarization hologram element according to this embodiment will be described in detail with reference to FIG. In the case of the rectangular diffraction grating 14 as shown in this embodiment, a diffraction efficiency of about 40% is obtained when the laser light is vertically incident. When such a polarization hologram element is used as a polarization separation element used in an optical pickup device or the like, only the diffracted light on one side is used for the light receiving element, and the diffracted light on the other side is not used. That is, if only the diffraction efficiency of the diffracted light on one side can be improved, the light receiving efficiency will increase. FIG. 3 shows the diffraction efficiency when the incident light is tilted in the diffraction grating stripe direction (diffracted light generation direction) with respect to the diffraction grating surface of the polarization hologram element (actual measurement value). It can be seen from FIG. 3 that the diffraction efficiency of ± first-order diffracted light can be biased by changing the incident angle of the laser.

In the polarization hologram element of the first embodiment shown in FIG. 1, since the substrate angle is tilted by 2 ° and the optical axis of the laser incident light is tilted by 2 °, the diffraction efficiency is +1. It was possible to make it about 50% by the next-order diffracted light.
As a result, the utilization efficiency of laser light is increased. Further, at this time, there is a concern that the 0th-order diffracted light may increase, but as shown in FIG. 3, almost no increase is observed. On the other hand, since the diffraction grating is filled with the overcoat material having the above-mentioned structure, it exhibits a transmittance of about 99% for laser light whose polarization is rotated by 90 °.

In this embodiment, the optical glass substrates 11 and 16 which are optically transparent isotropic substrates are provided with an inclination angle θ on the substrate surfaces so that the optical axis of the incident laser light is relative to the grating formation surface. With the configuration in which the vertical direction is tilted from the vertical direction to the diffracted light generation direction, the diffraction efficiency of the diffracted light used can be improved. Further, the inside of the diffraction grating is filled with an overcoat material and its refractive index is matched with that of the birefringent material, so that the polarization separation element function is achieved with high functionality. Further, by adhering the optical glass substrate 16 which is an optically transparent isotropic substrate above the diffraction grating surface, it is possible to suppress the deterioration of the wavefront aberration characteristic, and the optical glass substrate 16 is overcoated with the overcoat layer 15. By adhering with each other, the resin can be made common and the cost can be reduced. Further, by using a stretched polymer organic film as the optically transparent anisotropic film (organic birefringent film) 13, it is possible to manufacture the device at a lower cost. In addition, characteristics such as transmittance and diffraction efficiency are improved by applying a non-reflective coating for the wavelength used on the element surface.

Next, the configuration, operation and action of the polarization hologram element of the second embodiment of the present invention will be described with reference to FIG. Here, the polarization hologram element according to the present embodiment functions as a polarization separation element for laser light having a wavelength of 660 nm. In the configuration of this embodiment, an optical glass substrate 21 made of BK7 or the like is used as an optically transparent isotropic substrate, and an optical layer is formed on the optical glass substrate 21 via an adhesive layer 22 made of an acrylic ultraviolet curing adhesive material. An organic birefringent film 23 formed by stretching a polyester organic material as a transparent anisotropic material is formed, and a rectangular (concave and convex) diffraction grating 24 is formed on the organic birefringent film 23. An overcoat layer 25 made of an epoxy-based ultraviolet curable resin was formed on the upper part of the grating to fill the diffraction grating 24, and a λ / 4 plate 27 was formed on the upper part of the overcoat layer 25 as an optically transparent isotropic substrate. Optical glass substrate 2 made of BK7 or the like
6 is composed. Although not shown, the interfaces of the optical glass substrates 21 and 26 made of BK7 or the like with the air (the boundaries with the outside of the element) are coated with an antireflection layer for the wavelength used. Further, here, when the organic birefringent film 23 is formed on the optical glass substrate 21, it is formed with an inclination angle θ of 4 ° as shown in FIG.

Next, the details of each component will be described. The optical glass substrates 21 and 26 made of BK7 and the like above and below the polarization hologram element are both substrates having a thickness of about 1.0 mm. In order to avoid reflection at the interface as much as possible, the adhesive layer 22 uses an acrylic UV-curable adhesive whose refractive index is matched with that of the optical glass substrate 21 made of BK7 or the like. The organic birefringent film 23 has a thickness of about 100 μm, and its refractive index is about 1.579 in the extraordinary ray direction and about 1.670 in the ordinary ray direction. Further, when the organic birefringent film 23 is bonded, the optical glass substrate 21 is bonded so that the angle θ with the substrate surface is about 4 °. The overcoat layer 25 has a thickness of about 40 μm and is made of a material having a refractive index substantially matched with that of the organic birefringent film 23 in the extraordinary ray direction. Here, the overcoat layer 25
Is an optical glass substrate 26 having a λ / 4 plate 27 formed on its surface.
It also has a structure that doubles as an adhesive layer. The λ / 4 plate 2
7 is a polyester-based retardation film with a film thickness of about 1
It is adhered to the optical glass substrate 26 with an adhesive material at a thickness of 00 μm. Further, as the antireflection layer, MgF / TiO _{2 is used.}
It is composed of a multilayer film using / SiO ₂ .

Next, the shape of the diffraction grating 24 formed on the surface of the organic birefringent film 23 will be described. The diffraction grating is formed with a depth of 4.0 μm, a duty of about 0.5 and a grating pitch of 2.0 μm, and the grating is formed perpendicular to the birefringent film surface. .

Next, a method for manufacturing the polarization hologram element according to this embodiment will be briefly described. First, the organic birefringent film 23 is formed on the optical glass substrate 21 made of BK7 or the like by the adhesive 2
2 is used to bond at an angle θ. afterwards,
After the photolithography process, a diffraction grating shape is formed by dry etching. After that, the formed diffraction grating 24
A polarization hologram element is manufactured by botting an epoxy resin as the overcoat layer 25 and bonding an optical glass substrate 26 made of BK7 or the like with a λ / 4 plate 27 thereon.

Next, the diffraction characteristics of the polarization hologram element according to this embodiment will be described in detail with reference to FIG. In the case of the rectangular diffraction grating 24 as shown in this embodiment, a diffraction efficiency of about 40% is obtained when the laser light is vertically incident. When such a polarization hologram element is used as a polarization separation element used in an optical pickup device or the like, only the diffracted light on one side is used for the light receiving element, and the diffracted light on the other side is not used. That is, if only the diffraction efficiency of the diffracted light on one side can be improved, the light receiving efficiency will increase. FIG. 3 shows the diffraction efficiency when the incident light is tilted in the diffraction grating stripe direction (diffracted light generation direction) with respect to the diffraction grating surface of the polarization hologram element (actual measurement value). It can be seen from FIG. 3 that the diffraction efficiency of ± first-order diffracted light can be biased by changing the incident angle of the laser.

In the polarization hologram element of the second embodiment shown in FIG. 2, the angle of the organic birefringent film 23 is tilted by 4 °,
Since the optical axis of the laser incident light is substantially tilted by 4 °, the diffraction efficiency could be about 56% for the + 1st order diffracted light. As a result, the utilization efficiency of laser light is increased. Further, at this time, there is a concern that the 0th-order diffracted light may increase, but as shown in FIG. 3, almost no increase is observed. On the other hand, since the diffraction grating 24 is filled with the overcoat material 25 having the above-described configuration, the laser beam having the polarized light rotated by 90 ° exhibits a transmittance of about 99%. Further, since the λ / 4 plate 27 is formed integrally with the optical glass substrate 26, when linearly polarized light is incident, it is emitted as circularly polarized light. This function makes it possible to separate the reciprocating optical path in an optical system having a reciprocating optical path such as an optical pickup device.

In this embodiment, the organic birefringent film 23 made of an optically transparent anisotropic material is provided with an inclination angle θ so that the optical axis of the incident laser light is perpendicular to the grating formation surface. By adopting the configuration in which the diffracted light is generated, the diffraction efficiency of the diffracted light used can be improved. Further, the inside of the diffraction grating 24 is filled with the overcoat material 25, and the refractive index thereof is matched with that of the birefringent material, so that the polarization separation element function is achieved with a high function.
Further, by adhering the optical glass substrate 26, which is an optically transparent isotropic substrate, above the diffraction grating surface, it is possible to suppress the deterioration of the wavefront aberration characteristic, and the optical glass substrate 26 is overcoated with the overcoat layer 25. By adhering with each other, the resin can be made common and the cost can be reduced. Further, by using a stretched polymer organic film as the anisotropic film (organic birefringent film) 23, it is possible to manufacture the device at a lower cost. Further, by integrating the phase plate (λ / 4 plate) 27 with the optical glass substrate 26, a function of converting linearly polarized light into circularly polarized light can be added. In addition, characteristics such as transmittance and diffraction efficiency are improved by applying a non-reflective coating for the wavelength used on the element surface.

In the first and second embodiments of the present invention, a polarization hologram element having a working wavelength of 660 nm has been described. However, a polarization hologram element having a working wavelength of 780 nm and a polarization hologram compatible with two wavelengths. It is possible to deal with elements and the like by changing the grating depth of the diffraction grating.

[0032]

As described above, according to the first aspect of the invention, the optically transparent anisotropic material is formed on the optically transparent isotropic substrate, and the optically transparent anisotropic material is formed. In a polarization hologram element in which a concave-convex diffraction grating is formed on the surface of an isotropic material and the grating is filled with an isotropic material, the optical axis of the incident laser light is changed from the direction perpendicular to the grating formation surface. By adopting a structure in which the diffracted light is generated, the efficiency of the diffracted light actually used can be improved.

According to a second aspect of the present invention, in the polarization hologram element according to the first aspect, an optical transparent isotropic substrate is angled so that the optical axis angle is inclined. The efficiency of the diffracted light used for can be improved.

According to a third aspect of the present invention, in the polarization hologram element according to the first aspect, an optically transparent anisotropic material is angled to shape an isotropic substrate.
With the configuration in which the optical axis angle is inclined, the efficiency of the diffracted light actually used can be improved.

According to a fourth aspect of the present invention, in the polarization hologram element according to the first, second or third aspect, the refractive index of the anisotropic film in the ordinary ray direction or the extraordinary ray direction and the refractive index of the anisotropic film are filled in the lattice. The diffraction efficiency of the element can be improved by adopting a configuration in which the refractive indices of the isotropic materials to be formed are substantially the same.

According to a fifth aspect of the present invention, in the polarization hologram element according to the fourth aspect, an optically transparent isotropic substrate is formed above the surface on which the diffraction grating is formed, with an adhesive layer interposed therebetween. With the configuration, the surface of the element can be flattened, and the wavefront aberration characteristic of the element can be improved.

According to a sixth aspect of the present invention, in the polarization hologram element according to the fifth aspect, the adhesive for adhering the optically transparent isotropic substrate is the same as the material for filling the diffraction grating. With a certain configuration, the materials can be made common and the cost of the element can be reduced.

According to a seventh aspect of the invention, in the polarization hologram element according to any one of the first to sixth aspects, the optically transparent anisotropic material is an organic material or a stretched polymer organic material. With such a configuration, it is possible to reduce the cost of the device by using an inexpensive material.

According to an eighth aspect of the invention, in the polarization hologram element according to any one of the first to seventh aspects, a polarization hologram element and a phase plate having a constant phase difference with respect to a used wavelength are provided. By being configured integrally, a function of giving a phase difference to incident light can be added to the polarization hologram, and multi-functionalization can be achieved.

According to a ninth aspect of the present invention, in the polarization hologram element according to any one of the first to eighth aspects, a coating for reducing reflection with respect to a used wavelength is provided at the boundary with the outside of the polarization hologram element. Since the reflection loss of the laser beam can be reduced by adopting the configuration, the optical characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional configuration diagram of a polarization hologram element showing a first embodiment of the present invention.

FIG. 2 is a schematic sectional configuration diagram of a polarization hologram element showing a second embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between the light incident angle and the diffraction efficiency when the incident light is inclined in the diffraction grating stripe direction (diffracted light generation direction) with respect to the diffraction grating surface of the polarization hologram element.

[Explanation of symbols]

11, 16, 21, 26: Optical glass substrate (optically transparent isotropic substrate) 12, 22: Adhesive layer 13, 23: Organic birefringent film (optically transparent anisotropic film) 14, 24 : Diffraction gratings 15 and 25: Overcoat layer (isotropic material filled in the grating) 27: λ / 4 plate (phase plate) θ: Inclination angle

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H049 AA03 AA25 AA43 AA50 AA53                       AA57 AA64 BA05 BA07 BA42                       BA45 BB03 BB65 BC21 CA01                       CA05 CA09 CA15 CA30                 2H099 AA05 BA17 CA00 CA17                 5D119 AA01 AA40 AA41 AA43 BA01                       EC27 EC47 JA12 JA14 JA31                       JA65                 5D789 AA01 AA40 AA41 AA43 BA01                       EC27 EC47 JA12 JA14 JA31                       JA65

Claims (9)

[Claims] 1. An optically transparent anisotropic material is formed on an optically transparent isotropic substrate, and an uneven diffraction grating is formed on the surface of the optically transparent anisotropic material. In a polarization hologram element in which an isotropic material is filled in the grating, the polarization axis of the incident laser light is tilted from the direction perpendicular to the grating formation surface to the diffracted light generation direction. element. 2. The polarization hologram element according to claim 1, wherein the optically transparent isotropic substrate is angled.
A polarization hologram element characterized by tilting the optical axis angle. 3. The polarization hologram element according to claim 1, wherein the optically transparent anisotropic material is angled to shape the isotropic substrate, and the optical axis angle is tilted. Polarization hologram element. 4. The polarization hologram element according to claim 1, 2 or 3, wherein the anisotropic film has an index of refraction in the ordinary or extraordinary direction and an isotropic material filled in the lattice. The polarization hologram element is characterized in that the refractive indexes of the two are almost the same. 5. The polarization hologram element according to claim 4, wherein an optically transparent isotropic substrate is formed above the surface on which the diffraction grating is formed via an adhesive layer. Hologram element. 6. The polarization hologram element according to claim 5, wherein the adhesive for adhering the optically transparent isotropic substrate is the same as the material for filling the diffraction grating. Polarization hologram element. 7. The polarization hologram element according to claim 1, wherein the optically transparent anisotropic material is an organic material or a stretched polymer organic material. Polarization hologram element to do. 8. The polarization hologram element according to claim 1, wherein the polarization hologram element and a phase plate having a constant phase difference with respect to a used wavelength are integrally formed. A polarization hologram element characterized by the above. 9. The polarization hologram element according to claim 1, wherein the boundary with the outside of the polarization hologram element is coated with a coating that reduces reflection with respect to the wavelength used. And a polarization hologram element.