JP2004004161A - Polarizing hologram element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing hologram element of new configuration in order to achieve an improvement in the diffraction efficiency of the polarizing hologram element and shortening of the working time accompanying the same and the like. <P>SOLUTION: The polarizing hologram element 10 consisting of an optically transparent anisotropic substrate (an optically anisotropic substrate) 11, an optically transparent anisotropic material (an optically anisotropic material) 13 formed on the optically isotropic substrate, a diffraction grating 16 of a rugged shape formed on the surface of the optically isotropic material, an anisotropic material 14 packed in the grating, and an optically transparent substrate (optically anisotropic substrate) 15 covering the surface thereof is configured by inclining the forming direction of the diffraction grating 16 from the direction perpendicular to the substrate plane, thereby improving the efficiency of the diffracted light to be actually used. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polarization hologram element for separating polarized light according to the polarization state of incident light and a method for manufacturing the same. The application relates to a polarization hologram element used for an optical pickup optical system for an optical disk, and particularly to a polarization hologram element used for an optical pickup optical system for reading or writing on optical recording media having different recording densities. It relates to a hologram element.
[0002]
[Prior art]
In recent years, optical pickup devices corresponding to various optical recording media have been researched and developed. One is an optical pickup device for reading and writing a CD (Compact Disc) optical disk using a laser beam of a wavelength of 780 nm, and a DVD (Digital Versatile Disc) optical disk using a laser beam of a wavelength of about 660 nm. This is an optical pickup device for reading and writing. Also, as a future high-density optical disk, an optical pickup device for an optical disk using blue laser light has been actively researched and developed. Although the optical pickup device described above has individual technical problems, it has common problems such as miniaturization of the optical pickup portion and cost reduction, and developments for these problems are being actively pursued.
[0003]
As a configuration effective for reducing the size and cost of the optical pickup device, an optical system using a polarization hologram element as a polarization separation element is employed. This polarization hologram element is an element for separating the forward path and the return path of a laser beam using the diffraction of light by a diffraction grating (hologram). Conventionally, a polarization beam splitter or the like is used as a polarization separation element. In addition to solving the part where the optical system was enlarged, the signal detection element can be arranged on the same plane as the laser emission, so that the design of the optical path is easy and the number of parts can be reduced. I have. In addition, even when writing and reading of a plurality of types of optical recording media having different recording densities are performed by one optical pickup device, the optical path can be shared, and thus it is considered to be an effective optical system. Hereinafter, a conventional example of the polarization hologram element will be described.
[0004]
As a first conventional example, a method for manufacturing a polarization hologram element described in JP-A-2000-199820, which is an example of a general polarization hologram element, will be described. In this conventional example, a polarization hologram element is manufactured using a lithium niobate (LiNbO ₃ ) substrate that is a birefringent material.
However, in this conventional example, since a lithium niobate (LiNbO ₃ ) substrate is used, the substrate is expensive, and it is difficult to narrow the pitch of the diffraction grating pattern due to its workability. There is a problem that it is not possible to take a large amount. Therefore, in this conventional example, it is impossible to supply a polarization hologram element at low cost and to downsize an optical system using the polarization hologram element.
[0005]
Next, as a second conventional example, a polarization separation element described in JP-A-2000-221325 will be described. 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.
As a third conventional example, a polarization separation element described in JP-A-2000-75130 is shown. 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, the cost of the element can be reduced, and the grating pitch can be reduced. Therefore, the optical system using the low-cost supply of the element and the polarization hologram element is required. It is possible to reduce the size.
[0006]
[Problems to be solved by the invention]
In the second and third conventional examples, the diffraction grating itself is formed in a rectangular shape. This is to increase the diffraction efficiency with respect to the laser light in the polarization direction to be diffracted, and to suppress the transmittance (zero-order diffraction efficiency).
However, when a rectangular diffraction grating is manufactured, the ± 1st-order diffraction efficiency is limited to about 40% at the maximum. Therefore, in order to increase the signal detection efficiency, it is necessary to further improve the efficiency.
[0007]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polarization hologram element having a novel configuration that solves the conventional problems and a method for manufacturing the same. The purpose of the present invention is to reduce the processing time associated with this. More specifically, the polarization characteristics of the polarization hologram element and the diffraction efficiency are improved, the cost of the element is reduced due to the material cost reduction, the processing characteristics are improved with materials that are easy to process, the diffraction efficiency is improved, and the wavefront aberration is improved. The objective is to improve the characteristics, reduce the cost of the element by using common materials, increase the functionality of the polarization hologram element, and improve the optical characteristics by improving the transmittance of the polarization hologram element. It is an object of the present invention to provide a method for easily processing an element.
[0008]
[Means for Solving the Problems]
As means for achieving the above object, the invention according to claim 1 includes an optically transparent isotropic substrate (hereinafter referred to as an optically isotropic substrate) and an optically isotropic substrate. The formed optically transparent anisotropic material (hereinafter referred to as the optically anisotropic material), the uneven diffraction grating formed on the surface of the optically anisotropic material, and the In a polarization hologram element composed of an isotropic material to be filled and an optically transparent isotropic substrate (optically isotropic substrate) further covering the surface, the direction in which the diffraction grating is formed is set to the substrate surface. It is configured to be inclined from the vertical direction.
The operation of this polarization hologram element is to separate the polarization of the laser beam using a polarizing diffraction grating formed on the surface of an optically anisotropic material, and to determine the transmittance and diffraction efficiency by two orthogonal polarization directions. Is changed to change the polarization. Here, in order to improve the efficiency, the polarization hologram element is configured such that the direction of forming the diffraction grating is inclined from the direction perpendicular to the substrate surface. Thereby, the diffraction efficiency of the required direction of the first-order diffracted light can be improved.
[0009]
According to a second aspect of the present invention, in the polarization hologram element according to the first aspect, any one of a refractive index of the optically anisotropic material in a normal ray direction and an extraordinary ray direction is included in the diffraction grating. The isotropic material to be filled has the same refractive index.
The invention according to claim 3 is the polarization hologram element according to claim 1 or 2, wherein the optically anisotropic material is an organic material.
Further, the invention according to claim 4 is the polarization hologram element according to claim 3, wherein the optically anisotropic material is a stretched polymer organic material.
[0010]
According to a fifth aspect of the present invention, there is provided the polarization hologram element according to any one of the first to fourth aspects, wherein an optically transparent isotropic substrate (optically isotropic) is provided on a surface on which the diffraction grating is formed. Substrate) is formed with an adhesive layer interposed therebetween.
According to a sixth aspect of the present invention, in the polarization hologram element according to the fifth aspect, an adhesive bonding the optically isotropic substrate is the same as a material filling the diffraction grating. It is what it was.
Furthermore, the invention according to claim 7 is the polarization hologram element according to any one of claims 1 to 6, wherein the polarization hologram element and a phase plate having a constant phase difference with respect to a used wavelength are integrally formed. The configuration is as follows.
The invention according to claim 8 is the polarization hologram element according to any one of claims 1 to 7, wherein a coating is applied to a boundary between the polarization hologram element and the outside of the polarization hologram element to reduce reflection with respect to a used wavelength. It has a certain configuration.
[0011]
The invention according to claim 9 is a manufacturing method for manufacturing the polarization hologram element according to any one of claims 1 to 8, wherein an optically anisotropic material is formed on an optically isotropic substrate. Forming, forming an uneven diffraction grating on the surface of the optically anisotropic material, filling the grating with an isotropic material, and further covering the surface with an optically isotropic substrate, In the method for manufacturing a polarization hologram element in which the formation direction of the diffraction grating is inclined from a direction perpendicular to the substrate surface, the diffraction grating portion is processed by an anisotropic dry etching method, and the substrate is arranged to be inclined from the etching direction. By doing so, the angle of the diffraction grating is defined and the device is manufactured.
The operation of the manufactured polarization hologram element is the same as that of the polarization hologram element of claims 1 to 7. Here, by forming the substrate by anisotropic dry etching while tilting the substrate, it is possible to configure the polarization hologram element such that the direction of forming the diffraction grating is tilted from the direction perpendicular to the substrate surface.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the configuration, operation and operation of the present invention will be described in detail based on the illustrated embodiment.
[0013]
[Example 1]
First, a polarization hologram element according to a first embodiment of the present invention will be described. FIG. 1 is a schematic sectional view of a polarization hologram element showing a first embodiment of the present invention.
The polarization hologram element 10 according to the present embodiment is, for example, a polarization hologram element for laser light having a wavelength of 660 nm.
[0014]
In the polarization hologram element 10 according to the present embodiment, a BK7 substrate is used as an optically transparent isotropic substrate (optically isotropic substrate) 11, and the BK7 substrate 11 is bonded to the BK7 substrate 11 with an acrylic ultraviolet curing adhesive. An organic birefringent film 13 formed by stretching a polyester-based organic material was adhered via a layer 12. Then, a rectangular diffraction grating 16 is formed on the substrate on which the organic birefringent film 13 is formed, and an overcoat layer 14 made of an epoxy-based ultraviolet curable resin is formed thereon so as to embed the grating therein. A BK7 substrate 15 is bonded as a transparent isotropic substrate (optically isotropic substrate). Here, an anti-reflection layer for the wavelength to be used is provided on the interface between the upper and lower BK7 substrates 11 and 15 with air. Here, the diffraction grating 16 is formed at an angle from a plane perpendicular to the substrate, as shown in FIG. The angle has an inclination of 2 °.
[0015]
Next, details of each configuration will be described. The upper and lower BK7 substrates 11 and 15 above and below the polarization hologram element 10 are both about 1.0 mm thick. In order to minimize reflection at the interface, an acrylic UV curable adhesive whose refractive index is matched to that of the BK7 substrate 11 is used for the adhesive layer 12. The thickness of the organic birefringent film 13 is 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 14 has a thickness of about 40 μm and is made of a material whose refractive index is substantially matched with the refractive index of the organic birefringent film 13 in the extraordinary ray direction. Here, the overcoat layer 14 is configured to also serve as an adhesive layer with the BK7 substrate 15 on the upper surface side. Further, the antireflection layers provided on the upper and lower substrate surfaces are composed of a multilayer film using MgF / TiO ₂ / SiO ₂ .
[0016]
Next, the shape of the diffraction grating 16 will be described. The diffraction grating is formed to have a depth of 4.0 μm, a duty of about 0.5, and a pitch of the grating of 2.0 μm. Here, the grid is formed at an angle from a plane perpendicular to the substrate 11. The angle has an inclination of 2 °.
[0017]
Next, a process of manufacturing the polarization hologram element 10 according to the present embodiment will be briefly described. First, the organic birefringent film 13 is adhered on the BK7 substrate 11 using the adhesive layer 12 made of an acrylic ultraviolet curing adhesive. Thereafter, through a known photolithography process, a diffraction grating shape is formed by dry etching. At this time, as shown in FIG. 4, the substrate 16 of the dry etching apparatus is etched by tilting the substrate holder by 2 ° from the plasma irradiation direction (that is, by tilting the substrate at an angle θ = 2 ° with respect to the horizontal plane), thereby forming the grid 16. Is formed at an angle of 2 ° from a plane perpendicular to the substrate 11. Thereafter, an epoxy-based ultraviolet curable resin is botted as an overcoat layer 14 on the formed diffraction grating 16, and a BK7 substrate 15 is adhered thereon, thereby manufacturing the polarization hologram element 10.
[0018]
Next, the diffraction characteristics of the polarization hologram element 10 according to the present embodiment will be described in detail with reference to FIG. In the case of a rectangular diffraction grating 16 as shown in this embodiment, when laser light is vertically incident, a diffraction efficiency of about 40% can be obtained. When such an element is used for a polarization splitting element such as an optical pickup, 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 on one side can be improved, the light receiving efficiency will increase. FIG. 3 shows the diffraction efficiency when the incident light is inclined in the stripe direction of the diffraction grating (the direction in which the diffraction light is generated) with respect to the diffraction grating surface (actually measured values). As shown in FIG. 3, it can be seen that by changing the incident angle of the laser light, it is possible to provide a bias in the diffraction efficiency of the ± first-order light. In the first embodiment, the formation direction of the diffraction grating is inclined by 2 °, and the laser incident light is substantially inclined by 2 °, so that the diffraction efficiency can be about 50% in the +1 order. As a result, the utilization efficiency of the laser light increases. At this time, there is a concern that the 0th-order diffracted light increases, but as shown in FIG. 3, almost no increase is observed. On the other hand, since the lattice is filled with the overcoat material having the above configuration, the transmittance of the laser beam whose polarization is rotated by 90 ° is about 99%.
[0019]
Next, a usage example of the polarization hologram element of the present embodiment will be described. FIG. 5 is a schematic configuration diagram showing an example of an optical pickup optical system using the polarization hologram element of the present embodiment. In FIG. 5, laser light emitted from a semiconductor laser (for example, LD having a wavelength of 660 nm) 31 passes through the polarization hologram element 10 having the configuration shown in FIG. The light passes through a plate (for example, λ / 4 plate) 33, is condensed by a collimating objective lens 34, and is irradiated on an optical disc (for example, a DVD-based optical disc) 35. The reflected light from the optical disc 35 passes through the collimating objective lens 34 in the reverse direction and becomes substantially parallel light. The reflected light has information for reading and writing on the optical disc 35. When the light passes through the polarization hologram element 10 again to read the information of the reflected light, the polarization direction is rotated by approximately 90 ° due to the effect of the phase plate (for example, λ / 4 plate) 33 arranged in the optical path. Accordingly, the light is diffracted by the diffraction grating 16 of the polarization hologram element 10. Therefore, the optical path can be branched at a diffraction efficiency of about 50%, and the diffracted light is received by the photodiode (PD) 36, and a track signal, a focus signal, and an information signal are detected.
[0020]
As described above, in the polarization hologram element 10 of the present embodiment, the diffraction efficiency of the diffracted light to be used can be improved by forming the diffraction grating 16 in a direction inclined from the substrate surface. Further, by filling the inside of the grating of the diffraction grating 16 with the overcoat material 14 and matching the refractive index with the birefringent material of the organic birefringent film 13, the polarization hologram element can achieve the polarization separation function with high function. I have. Further, by using a polymer organic film stretched as an optically anisotropic film, it is possible to produce a device at lower cost. In addition, by bonding the optically isotropic substrate 15 above the diffraction grating surface, it is possible to suppress a decrease in wavefront aberration characteristics, and by bonding with the overcoat layer 14, it is possible to use a common resin. And cost can be reduced. In addition, by applying an anti-reflection coating for the wavelength used on the surface of the polarization hologram element 10, characteristics such as transmittance and diffraction efficiency are improved. Further, as for a method of forming a diffraction grating, a desired shape can be formed by an easier method, and therefore, it can be easily manufactured.
[0021]
[Example 2]
Next, a polarization hologram element according to a second embodiment of the present invention will be described. FIG. 2 is a schematic sectional view of a polarization hologram element showing a second embodiment of the present invention.
The polarization hologram element 20 according to the present embodiment is, for example, a polarization hologram element for laser light having a wavelength of 660 nm.
[0022]
In the polarization hologram element 20 according to the present embodiment, a BK7 substrate is used as an optically transparent isotropic substrate (optically isotropic substrate) 21, and the BK7 substrate 21 is bonded with an acrylic ultraviolet curing adhesive. An organic birefringent film 23 formed by stretching a polyester-based organic material was adhered via a layer 22. Then, a rectangular diffraction grating 27 is formed on the substrate on which the organic birefringent film 23 is formed, and an overcoat layer 24 made of an epoxy-based ultraviolet curable resin is formed on the upper surface of the rectangular diffraction grating 27 so as to embed the grating. As a transparent isotropic substrate (optically isotropic substrate), a BK7 substrate 26 on which a phase plate (for example, λ / 4 plate) 25 is formed in advance is bonded. Here, an anti-reflection layer for the wavelength to be used is provided at the interface between the upper and lower BK7 substrates 21 and 26 with air. Here, as shown in FIG. 2, the grating formation direction of the diffraction grating 26 is formed at an angle from a plane perpendicular to the substrate. The angle has an inclination of 4 °.
[0023]
Next, details of each configuration will be described. The upper and lower BK7 substrates 21 and 26 above and below the polarization hologram element 20 are both about 1.0 mm thick. In order to avoid reflection at the interface as much as possible, an acrylic UV curable adhesive whose refractive index is matched to that of the BK7 substrate 21 is used for the adhesive layer 22. The thickness of the organic birefringent film 23 is 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. When the organic birefringent film 23 is bonded, the organic birefringent film 23 is bonded so that the angle with the BK7 substrate 21 surface is about 4 °. Further, the overcoat layer 24 is made of a material having a thickness of about 40 μm and a refractive index substantially matching the refractive index of the organic birefringent film 23 in the extraordinary ray direction. Here, the overcoat layer 24 is configured to also serve as an adhesive layer with a BK7 substrate 26 having a λ / 4 plate 25 formed on the surface in advance. Here, the λ / 4 plate 25 is made of a polyester-based retardation film, has a thickness of about 100 μm, and is adhered to the BK7 substrate 26 using an adhesive. Further, the antireflection layers provided on the upper and lower substrate surfaces are composed of a multilayer film using MgF / TiO ₂ / SiO ₂ .
[0024]
Next, the shape of the diffraction grating will be described. The diffraction grating is formed to have a depth of 4.0 μm, a duty of about 0.5, and a pitch of the grating of 2.0 μm. Here, the formation direction of the grating is formed at an angle from a plane perpendicular to the substrate. The angle has an inclination of 4 °.
[0025]
Next, a process of manufacturing the polarization hologram element 20 according to the present embodiment will be briefly described. First, the organic birefringent film 23 is adhered on the BK7 substrate 21 using the adhesive layer 22 made of an acrylic ultraviolet curing adhesive. Thereafter, through a known photolithography process, a diffraction grating shape is formed by dry etching. At this time, as shown in FIG. 4, etching is performed by tilting the substrate holder of the dry etching apparatus by 4 ° from the plasma irradiation direction (that is, by tilting the substrate at an angle θ = 4 ° with respect to a horizontal plane), thereby performing the grating 27. Is formed at an angle of 4 ° from a plane perpendicular to the substrate 21. Thereafter, an ultraviolet curing resin of an epoxy type is botted as an overcoat layer 24 on the formed diffraction grating 27, and a BK7 substrate 26 on which a λ / 4 plate 25 is previously formed is adhered to the surface from above. The polarization hologram element 20 is manufactured.
[0026]
Next, the diffraction characteristics of the polarization hologram element 20 according to the present embodiment will be described in detail with reference to FIG. In the case of a rectangular diffraction grating 16 as shown in this embodiment, when laser light is vertically incident, a diffraction efficiency of about 40% can be obtained. When such an element is used for a polarization splitting element such as an optical pickup, 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 on one side can be improved, the light receiving efficiency will increase. FIG. 3 shows the diffraction efficiency when the incident light is inclined in the stripe direction of the diffraction grating (the direction in which the diffraction light is generated) with respect to the diffraction grating surface (actually measured values). As shown in FIG. 3, it can be seen that by changing the incident angle of the laser light, it is possible to provide a bias in the diffraction efficiency of the ± first-order light. In the second embodiment, since the direction of forming the diffraction grating is inclined by 4 ° and the laser incident light is substantially inclined by 4 °, the diffraction efficiency can be about 56% in the +1 order. As a result, the utilization efficiency of the laser light increases. At this time, there is a concern that the 0th-order diffracted light increases, but as shown in FIG. 3, almost no increase is observed. On the other hand, since the lattice is filled with the overcoat material having the above configuration, the transmittance of the laser beam whose polarization is rotated by 90 ° is about 99%. Further, since the λ / 4 plate 25 is integrally formed, when linearly polarized light is incident, the light is emitted as circularly polarized light. This function makes it possible to separate a reciprocating optical path in an optical system having a reciprocating optical path such as an optical pickup.
[0027]
Next, a usage example of the polarization hologram element of the present embodiment will be described. FIG. 6 is a schematic configuration diagram illustrating an example of an optical pickup optical system using the polarization hologram element of the present embodiment. 6, a laser beam emitted from a semiconductor laser (for example, an LD having a wavelength of 660 nm) 41 passes through the polarization hologram element 20 having the configuration shown in FIG. 2, passes through a coupling lens 42, becomes a substantially parallel light beam, and is collimated. The light is condensed by the objective lens 43 and irradiated onto an optical disc (for example, a DVD-based optical disc) 44. Then, the reflected light from the optical disk 44 passes through the collimating objective lens 43 in the reverse direction and becomes substantially parallel light, and the reflected light has information for reading and writing on the optical disk 44. When the reflected light passes through the polarization hologram element 20 again to read the information of the reflected light, the polarization direction is approximately 90 ° due to the effect of the phase plate (λ / 4 plate) 25 integrally disposed in the element. Because it is rotated, it is diffracted by the diffraction grating 27 of the polarization hologram element 20. Therefore, the optical path can be branched at a diffraction efficiency of about 56%, and the diffracted light is received by the photodiode (PD) 45, and a track signal, a focus signal, and an information signal are detected.
[0028]
As described above, in the polarization hologram element 20 of this embodiment, the diffraction efficiency of the diffracted light to be used can be improved by forming the diffraction grating 27 in a direction inclined from the substrate surface. Further, by filling the inside of the diffraction grating 27 with the overcoat material 24 and matching the refractive index thereof with the birefringent material of the organic birefringent film 23, the polarization separation function of the polarization hologram element is achieved with high performance. I have. Further, by using a polymer organic film stretched as an anisotropic film, it is possible to manufacture a device at lower cost. Further, by bonding the optically isotropic substrate 26 above the diffraction grating surface, it is possible to suppress a decrease in wavefront aberration characteristics, and by bonding with the overcoat layer 24, it is possible to use a common resin. And cost can be reduced. Further, by integrating the phase plate (λ / 4 plate) 25, a function of converting linearly polarized light into circularly polarized light can be added. Further, by applying an anti-reflection coating for the wavelength used on the surface of the polarization hologram element 20, characteristics such as transmittance and diffraction efficiency are improved. Further, as for a method of forming a diffraction grating, a desired shape can be formed by an easier method, and therefore, it can be easily manufactured.
[0029]
Although the embodiments of the present invention have been described above, the present invention is not limited to the materials and configurations as in the above-described embodiments, and also does not limit the thickness and the refractive index of each material. Instead, an optimal design is made depending on the optical system or system used. Further, in the embodiment of the present invention, an element having a wavelength of 660 nm is taken as an example. However, an element for a wavelength of 780 nm or a wavelength for two wavelengths can be dealt with by changing the grating depth.
[0030]
【The invention's effect】
As described above, in the invention according to claim 1, an optically transparent isotropic substrate (optically isotropic substrate) and an optically transparent isotropic substrate formed on the optically isotropic substrate. Anisotropic material (optically anisotropic material), an uneven diffraction grating formed on the surface of the optically anisotropic material, an isotropic material to be filled in the grating, and the surface In the polarization hologram element composed of an optically transparent isotropic substrate (optically isotropic substrate) covering the substrate, the direction in which the diffraction grating is formed is inclined from the direction perpendicular to the substrate surface. The efficiency of the diffracted light actually used can be improved. Along with this, the same efficiency can be obtained by reducing the lattice depth, so that the processing time of the element can be shortened.
[0031]
According to the second aspect of the present invention, in the polarization hologram element according to the first aspect, any one of a refractive index of the optically anisotropic material in the ordinary ray direction and an extraordinary ray direction is included in the diffraction grating. Since the configuration is such that the refractive index of the filled isotropic material is substantially the same, the polarization characteristics of the polarization hologram element and the diffraction efficiency can be improved.
Further, in the invention according to claim 3, in the polarization hologram element according to claim 1 or 2, the optically anisotropic material is configured to be an organic material, so that the cost of the material is reduced and the workability is improved. Can be achieved.
Further, in the invention according to claim 4, in the polarization hologram element according to claim 3, the optically anisotropic material is configured to be a stretched polymer organic material, so that the cost of the material can be reduced and the processing can be performed. It is possible to achieve an improvement in performance.
[0032]
According to a fifth aspect of the present invention, in the polarization hologram element according to any one of the first to fourth aspects, an optically transparent isotropic substrate (optically isotropic) is provided on a surface on which the diffraction grating is formed. The flexible substrate is formed with an adhesive layer interposed therebetween, so that the diffraction efficiency can be improved and the wavefront aberration characteristics can be improved.
According to a sixth aspect of the present invention, in the polarization hologram element according to the fifth aspect, an adhesive bonding the optically isotropic substrate is the same as a material filling the diffraction grating. Therefore, the cost can be reduced by using the same material in the configuration of claim 5.
Furthermore, in the invention according to claim 7, in the polarization hologram element according to any one of claims 1 to 6, the polarization hologram element and a phase plate having a constant phase difference with respect to a used wavelength are integrally formed. With such a configuration, multi-functionalization of the polarization hologram element can be achieved.
Further, in the invention according to claim 8, in the polarization hologram element according to any one of claims 1 to 7, a coating that reduces reflection with respect to a wavelength used is applied to a boundary between the polarization hologram element and the outside. With a certain configuration, the optical characteristics can be improved by improving the transmittance of the polarization hologram element.
[0033]
According to the ninth aspect of the present invention, there is provided a method for producing the polarization hologram element according to any one of the first to eighth aspects, wherein an optically anisotropic material is formed on an optically isotropic substrate. Forming, forming an uneven diffraction grating on the surface of the optically anisotropic material, filling the grating with an isotropic material, and further covering the surface with an optically isotropic substrate, In the method for manufacturing a polarization hologram element in which the formation direction of the diffraction grating is inclined from a direction perpendicular to the substrate surface, the diffraction grating portion is processed by an anisotropic dry etching method, and the substrate is arranged to be inclined from the etching direction. In this case, the angle of the diffraction grating is defined and manufactured. Therefore, it is possible to provide an easy processing method of the polarization hologram element according to any one of claims 1 to 8. .
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a polarization hologram element showing a first embodiment of the present invention.
FIG. 2 is a schematic sectional view of a polarization hologram element showing a second embodiment of the present invention.
FIG. 3 is a diagram showing a relationship between a light incident angle and diffraction efficiency in the polarization hologram elements of the first and second embodiments of the present invention.
FIG. 4 is an explanatory diagram when a diffraction grating shape is formed on an organic birefringent film on a substrate by dry etching.
FIG. 5 is a schematic configuration diagram showing an example of an optical pickup optical system using the polarization hologram element shown in FIG.
FIG. 6 is a schematic configuration diagram showing an example of an optical pickup optical system using the polarization hologram element shown in FIG.
[Explanation of symbols]
10, 20: polarization hologram element 11, 15, 21, 26: BK7 substrate (optically isotropic substrate)
12, 22: adhesive layers 13, 23: organic birefringent film (optically anisotropic material)
14, 24: Overcoat layer (isotropic material)
16, 27: diffraction grating 25: phase plate (λ / 4 plate)
31, 41: Semiconductor laser (LD)
32, 42: coupling lens 33: phase plate (λ / 4 plate)
34, 43: collimating objective lenses 35, 44: optical disks 36, 45: photodiode (PD)
θ: The angle between the substrate and the horizontal plane during dry etching

Claims (9)

An optically transparent isotropic substrate (hereinafter, referred to as an optically isotropic substrate) and an optically transparent, anisotropic material formed on the optically isotropic substrate (hereinafter, referred to as an optically isotropic substrate). Anisotropic material), an uneven diffraction grating formed on the surface of the optically anisotropic material, an isotropic material filled in the grating, and an optically transparent material covering the surface. In a polarization hologram element composed of an isotropic substrate (optically isotropic substrate),
A polarization hologram element, wherein the formation direction of the diffraction grating is inclined from a direction perpendicular to a substrate surface. The polarization hologram element according to claim 1,
The optically anisotropic material is characterized in that the refractive index of either the ordinary light direction refractive index or the extraordinary light direction refractive index is substantially the same as the refractive index of the isotropic material filled in the diffraction grating. Polarization hologram element. The polarization hologram element according to claim 1 or 2,
The polarization hologram element, wherein the optically anisotropic material is an organic material. The polarization hologram element according to claim 3,
The polarization hologram element, wherein the optically anisotropic material is a stretched polymer organic material. The polarization hologram element according to any one of claims 1 to 4,
A polarizing beam splitter, wherein an optically transparent isotropic substrate (optically isotropic substrate) is formed above a surface on which the diffraction grating is formed via an adhesive layer. The polarization hologram element according to claim 5,
A polarizing hologram element, wherein an adhesive bonding the optically isotropic substrate is the same as a material filling the diffraction grating. The polarization hologram element according to any one of claims 1 to 6,
A polarization hologram element, wherein a polarization hologram element and a phase plate having a constant phase difference with respect to a used wavelength are integrally formed. The polarization hologram element according to any one of claims 1 to 7,
A polarization hologram element, wherein a coating for reducing reflection with respect to a used wavelength is applied to a boundary between the polarization hologram element and the outside. A method for producing the polarization hologram element according to claim 1, wherein an optically anisotropic material is formed on an optically isotropic substrate, and wherein the optically anisotropic material is formed. Forming an uneven diffraction grating on the surface of the isotropic material, filling the isotropic material in the grating,
In a method for manufacturing a polarization hologram element, the surface of which is further covered with an optically isotropic substrate, and a direction in which the diffraction grating is formed is inclined from a direction perpendicular to the substrate surface.
The said diffraction grating part is processed by the anisotropic dry etching method, and the angle of the diffraction grating is defined and manufactured by arranging the substrate inclined from the etching direction. Method.

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