JP2000180627A - Polarizing separation element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing separation element of diffraction grating type easy to fabricate at a low cost and capable of increasing the polarizing angle and/or the efficiency. SOLUTION: A polarizing separation element is composed of a first element 2 of such a structure that a first diffraction grating shape 6 having surface unevenness is formed on the surface of an optically anisotropic film 5 provided on a first optically isotropic board 4 and a second element 3 having the same refractive index as that of the anisotropic film 5 in the abnormal beam direction (or the refractive index in the normal beam direction) and structutred so that a second diffraction grating shape 9 having surface unevenness is formed on the surface of an optically anisotropic film 8 provided on a second optically isotropic board 7, and the intended polarizing separator element 1 can be fabricated easily by adhering the two elements 2 and 3 to each other through engagement of the surface unevennesses of the two members furnished with grating shapes 6 and 9, wherein the works to put a filler in grooves in the first diffraction grating shape 6 do not require much labor and can manage with a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffraction grating type polarization separator which is used in an optical pickup or the like and has a function of separating a polarization direction completely transmitting through an element and a polarization direction diffracted according to the polarization direction of light. Related to the element.

[0002]

2. Description of the Related Art Various types of polarization splitting elements have been proposed which are used as optical components for optical pickups for optical disks, magneto-optical disks, or the like, or as optical isolators, and differ in diffraction efficiency depending on the polarization direction. A description will be given using several examples.

A first conventional example is disclosed in, for example,
As shown in Japanese Patent No. 287117, there is a polarizing beam splitter in which a diffraction grating shape is formed on an optically anisotropic substrate, and a groove having the diffraction grating shape is filled with a material having a defined refractive index. As a result, the polarization separation angle and efficiency can be improved, and the range of materials can be increased by defining the refractive index of the material to be filled.

[0004] As a second conventional example, Japanese Patent Application Laid-Open No. 9-6162 is disclosed.
There is a polarizing beam splitter disclosed in Japanese Patent Application Laid-Open No. 7-107. This is an improvement of the example proposed in JP-A-7-287117, in which a titanium oxide film is used as the optically anisotropic film, the magnitude of the anisotropy of the refractive index is increased, and the lattice depth and the like are increased. The film thickness is improved. In addition, the film has a stable refractive index with respect to temperature and improves stability.

[0005] As a third conventional example, Japanese Patent Laid-Open No. 9-1273 is disclosed.
As shown in Japanese Patent Publication No. 33, an element that separates polarized light by forming a diffraction grating shape on an optically anisotropic substrate, wherein the diffraction grating shape portion and the optical element are bonded using an adhesive or the like. In some cases, it is not affected by dust or the like by bonding.

[0006]

However, even with the configuration as in the first conventional example, when a design for increasing the polarization separation angle or a design for increasing the efficiency is performed, the diffraction grating pitch is increased. In this case, the pitch must be reduced and the diffraction grating must be formed deep. As a result, it becomes difficult to fill the groove portion with the material, and the filling process becomes complicated. Further, even when the groove is filled by applying the liquid member, a large undulation may be generated on the surface, and the wavefront may be disturbed. At the same time, in the configuration of the first conventional example, since a crystal having optical anisotropy is used as a substrate, the cost is high. These points are the same in the case of the second conventional example.

Further, in the configuration of the third conventional example, the selection (refractive index) of the adhesive is limited, and the optical element is completely integrated via the adhesive. It is expected that the deviation will occur and that the number of manufacturing steps will increase. In addition, optical deviation occurs due to the shift in parallelism, and there is a concern that the yield may decrease.

In other words, according to these conventional examples, it can be said that it is difficult to easily manufacture a polarization beam splitting element that can increase the polarization angle and efficiency.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a diffraction grating type polarization splitting element which can be easily manufactured at low cost and can increase the polarization angle and efficiency.

Another object of the present invention is to provide a polarization beam splitting element that can easily match the refractive index and achieve in-plane uniformity of the characteristics in order to realize the above object.

In addition, another object of the present invention is to provide a polarization beam splitting element capable of improving the efficiency and further reducing the cost and increasing the efficiency in realizing the above object.

[0012]

According to the first aspect of the present invention,
A first optically anisotropic film formed on a first optically isotropic substrate, the first of which is formed with an uneven first diffraction grating shape on the surface thereof.
And the optically isotropic film having the same refractive index as one of the ordinary light direction refractive index and the extraordinary light direction refractive index of the optically anisotropic film is a second optically isotropic film. A second diffractive grating having a concave-convex shape formed on a substrate and meshed with and adhered to the first diffractive grating of the first element, formed on the surface of the optically isotropic film; And an element.

[0013] Diffraction is performed by the first diffraction grating shape formed on the optically anisotropic film, but this alone causes diffraction irrespective of the direction of polarized light and cannot separate polarized light. Here, the refractive index in the ordinary ray direction and the extraordinary ray direction refractive index of the optically anisotropic film, that is, the same refractive index as one of the refractive index in the fast axis direction and the slow axis direction The second element having the second diffraction grating shape formed by the optically isotropic film of the above is aligned with the diffraction grating shape surface of the first element, and the irregularities are mutually engaged and adhered to each other, whereby one polarized light is formed. The structure does not sense the diffraction grating in the direction, and the light in the polarization direction is transmitted through the element as it is. On the other hand, light in another orthogonal polarization direction has a periodic change in refractive index and is diffracted and separated from light in the transmitted polarization direction.
Therefore, the polarization separation element can be easily manufactured by engaging and bonding the unevenness between the diffraction grating-shaped surfaces of the first element and the second element, and it takes time and effort to fill the groove portion of the diffraction grating with the material. Low cost.

According to a second aspect of the present invention, the first diffraction grating shape and the second diffraction grating shape of the polarization splitting element of the first aspect have the same concavo-convex shape.

Therefore, in realizing the polarized light separating element according to the first aspect, since the concave and convex shapes engaged by the first and second elements are the same, a uniform polarized light separating element with high surface alignment accuracy can be manufactured. .

According to a third aspect of the present invention, the material of the optically anisotropic film and the optically isotropic film of the polarized light separating element of the first or second aspect is the same.

Therefore, it is possible to easily match the refractive index in realizing the polarized light separating element according to the first or second aspect. As a result, in-plane uniformity of the characteristics can be ensured. Because it is good, the selection of the material is also easy.

According to a fourth aspect of the present invention, the first and second diffraction grating shapes of the concavo-convex shape of the polarization splitting element of the first, second or third aspect are optically transparent. It is bonded by a suitable resin.

Accordingly, the polarized light separating element according to the first, second or third aspect can be realized without causing light scattering at the bonding portion or impairing the transmittance.

According to a fifth aspect of the present invention, the refractive index of the resin of the polarized light separating element of the fourth aspect is the same as the refractive index of the optically isotropic film.

Therefore, the efficiency of the device can be improved in realizing the polarized light separating device according to the fourth aspect.

The invention according to claim 6 is the invention according to claims 1 to 5
The polarizing beam splitter according to any one of the above, has a guide for positioning with respect to one of the first optically isotropic substrate and the second optically isotropic substrate.

Accordingly, in realizing the polarized light separating element according to any one of claims 1 to 5, the assembly process can be simplified.

The invention according to claim 7 is the invention according to claims 1 to 6
The optically anisotropic film of the polarization beam splitting element according to any one of the above, is formed by oblique evaporation.

Therefore, in order to realize the polarization beam splitting device according to any one of claims 1 to 6, the oblique vapor deposition can increase the optical anisotropy and improve the efficiency and the diffraction grating shape. The range of design can be expanded.

According to an eighth aspect of the present invention, the material of the optically anisotropic film of the polarization beam splitting element according to the seventh aspect is tantalum oxide.

Accordingly, the polarized light separating element according to claim 7 can be suitably realized.

[0028]

FIG. 1 shows a first embodiment of the present invention.
It will be described based on. The polarization beam splitter 1 of the present embodiment has a combination structure of a first element 2 and a second element 3. The first element 2 is formed by forming an optically anisotropic film 5 on an optically isotropic substrate (first optically isotropic substrate) 4, and forming a periodic film on the surface of the optically anisotropic film 5. In this case, a rough irregular diffraction grating shape (first diffraction grating shape) 6 is formed. The second element 3 is an optically isotropic substrate (a second optically isotropic substrate)
An optically isotropic film 8 is formed on 7, and a periodic uneven diffraction grating shape (second diffraction grating shape) 9 is formed on the surface of the optically isotropic film 8. Here, as the optically isotropic film 8, a film having the same refractive index as one of the ordinary light direction refractive index and the extraordinary light direction refractive index of the optically anisotropic film 5 is used. . The first element 2 and the second element 3 are bonded and fixed such that the surfaces on which the diffraction grating shapes 6 and 9 are formed are aligned with each other so that their irregularities mesh with each other. For this bonding, an optically transparent resin having the same refractive index as the optically isotropic film 8 is used.

Each part will be described in more detail. Pyrex glass is used for the optically isotropic substrates 4 and 7. The optically anisotropic film 5 is a tantalum pentoxide film produced by oblique evaporation, and has a thickness of 5 μm. Regarding the optically anisotropic film 5, the refractive index difference between the ordinary ray direction and the extraordinary ray direction showing anisotropy is 0.06. That is,
When the applied wavelength is 635 nm, the refractive index in the ordinary ray direction is 1.65, and the refractive index in the extraordinary ray direction is 1.59. The diffraction grating shape 6 has a 1 μm line (convex portion) and a 1 μm line.
2μ due to periodic repetition with μm space (recess)
It is an irregular pattern with m periods, and its lattice depth is 5.3μ.
m. The diffraction grating shape 6 in which such rectangular diffraction gratings are arranged is formed on the optically anisotropic film 5 by anisotropic dry etching using a resist mask. In this case, a fluorine-based CF ₄ gas, CHF ₃ gas, or the like is used as an etching gas.

The optically isotropic film 8 is formed by applying an acrylic resin on the optically isotropic substrate 7 and thermally curing the same, and has a thickness of 6 μm. here,
In the present embodiment, a resin having a refractive index of 1.59, that is, a resin adjusted to a refractive index of 1.59 in the extraordinary ray direction in the optically anisotropic film 5 is used as the acrylic resin. The diffraction grating shape 9 has a 1 μm line (convex portion) and a 1 μm line.
2μ due to periodic repetition with μm space (recess)
It is an irregular pattern with m periods, and its lattice depth is 5.3μ.
m. That is, the diffraction grating shape 9 has the same irregularities as the diffraction grating shape 6 including the period. The diffraction grating shape 9 in which such rectangular diffraction gratings are arranged is formed on the optically isotropic film 8 by anisotropic dry etching using a resist mask. In this case, an oxygen gas is used as an etching gas.

In such a configuration, in FIG. 1, if the direction of the ordinary ray refractive index of the optically anisotropic film 5 is a direction parallel to the page and the direction of the extraordinary ray is perpendicular to the page,
In the ordinary ray direction of the optically anisotropic film 5, it is the same as the case where the concave portion of the diffraction grating is filled with a material having the same refractive index as the extraordinary ray direction, and there is a diffraction grating having a refractive index difference of 0.06. Will be. That is, light in the polarization direction in the ordinary ray direction is diffracted by passing through the polarization splitting element 1, and diffracted light is generated. However, for light in the polarization direction in the extraordinary ray direction, the periodic structure of refractive index has a periodic structure. A state equivalent to the non-existent one is transmitted through the polarization beam splitter 1 without causing diffraction. Here, even for the polarized light in the extraordinary ray refractive index direction, the zero-order diffracted light exists. This is transmitted light,
By setting the groove depth of the diffraction grating portion to 5.3 μm,
The phase of the transmitted light in the high refractive index portion and the phase of the transmitted light in the low refractive index portion are canceled by a half wavelength shift, and the transmitted light by the zero-order diffracted light does not exist. Thereby, the polarized light can be completely separated.

In the polarization beam splitting element 1 of the present embodiment exhibiting such a polarization beam splitting function, the first element 2 and the second element 3 are aligned with the surfaces on which the diffraction grating shapes 6 and 9 are formed. The projections and depressions are formed by adhering and fixing them so as to mesh with each other, and do not require any operation such as filling the diffraction grating portion with a liquid resin, and can be easily manufactured at low cost. At this time, since the periods of the diffraction grating shapes 6 and 9 are exactly the same, the alignment accuracy of the diffraction grating surfaces, that is, the accuracy of the element can be increased at low cost. Also,
Since the optically transparent resin having the same refractive index as that of the optically isotropic film 8 is used to bond the first and second elements 2 and 3 to each other, light scattering and efficiency at the bonded portion are reduced. The reduction can be prevented, and the efficiency of the device can be improved. In addition, since the optically anisotropic film 5 is formed by oblique vapor deposition of tantalum pentoxide, the controllability of the refractive index and the refractive index distribution can be reduced, and the efficiency of the device can be further improved. Can be.

A second embodiment of the present invention will be described with reference to FIG. The same parts as those described in the first embodiment (FIG. 1) are denoted by the same reference numerals, and description thereof is omitted (the same applies to the following embodiments). The polarization splitting element 11 of the present embodiment has basically the same configuration as the polarization splitting element 1 except that the optically isotropic film 12 on the optically isotropic substrate 7 on the second element 3 side is formed. It is formed by the same material as the optically anisotropic film 5, that is, by oblique evaporation of a tantalum pentoxide film. The thickness of the optically isotropic film 12 is 6 μm, and the refractive index is 1.59 (the same as the refractive index of the optically anisotropic film 5 in the extraordinary ray direction 1.59). Other points are the same as those in the first embodiment.

The polarization splitting function of the polarization splitting element 11 is the same as that of the polarization splitting element 1.

The same effect as that of the polarization beam splitting element 1 can be obtained by the polarization beam splitting element 11 of the present embodiment.
In particular, in the present embodiment, since the optically isotropic film 12 is formed of the same material as the optically anisotropic film 5, it is possible to easily and surely match the refractive indexes between the two. It is possible to make it the same, so the choice of materials is expanded,
This is advantageous in reducing costs.

A third embodiment of the present invention will be described with reference to FIG. The polarization beam splitting element 21 of the present embodiment has basically the same configuration as the polarization beam splitting element 11 (of course, the polarization beam splitting element 1 may be used).
A guide 22 for surface alignment is integrally formed on both ends of one of the two (here, the optically isotropic substrate 7).
The guide 22 is used to shift the positions of the first and second elements 2 and 3 and to make the surfaces parallel. The guide 22 is formed simultaneously with the dry etching of the optically isotropic film 12 in the second element 3. . Other points are the same as those in the second embodiment.

The polarization splitting function of the polarization splitting element 21 is the same as that of the polarization splitting element 11.

Although the same effects as those of the polarization splitting element 11 can be obtained by the polarization splitting element 21 of the present embodiment, in particular, in the present embodiment, the first and second elements 2 and 3 Since the alignment guide 22 is provided, the use of the guide 22 during the meshing and bonding of the diffractive surfaces facilitates assembly, improves the accuracy of the alignment, and increases the parallelism, thereby improving the element performance. improves.

The pitch, groove depth, etc. of the shape of the diffraction grating are appropriately set according to the use of the polarized light separating element. The numerical examples shown in these embodiments are merely examples, and may be various. Can take a value. The same applies to the material of the optically anisotropic film or the optically isotropic film, and a material may be used as appropriate.

[0040]

According to the first aspect of the present invention, a polarization separation element can be easily manufactured by engaging and bonding irregularities between diffraction grating-shaped surfaces of a first element and a second element.
There is no need to load the material into the grooves of the diffraction grating shape, and the cost can be reduced.

According to the second aspect of the present invention, in order to realize the polarization beam splitting element according to the first aspect, the unevenness of the diffraction grating shape in which the first and second elements are engaged is the same. A uniform polarization separation element having high alignment accuracy can be manufactured.

According to the third aspect of the present invention, it is possible to easily match the refractive index in realizing the polarized light separating element according to the first or second aspect, and as a result, the in-plane uniformity of the characteristics is also improved. Since the same material can be used, the material can be easily selected.

According to the fourth aspect of the present invention, light is not scattered at the bonding portion and the transmittance is not impaired.
The polarization separation element described in 2 or 3 can be realized.

According to the fifth aspect of the invention, the efficiency of the element can be improved in realizing the polarization splitting element of the fourth aspect.

According to the sixth aspect of the present invention, in realizing the polarized light separating element according to any one of the first to fifth aspects, it is possible to simplify the assembling process and improve the accuracy of the surface alignment. Can be improved.

According to the seventh aspect of the present invention, the optically anisotropic film is formed by oblique deposition to realize the polarization separation element according to any one of the first to sixth aspects. The anisotropy can be increased, and the design range of the efficiency and the shape of the diffraction grating can be widened.

According to the eighth aspect of the present invention, by using tantalum oxide as the material of the optically anisotropic film, the polarization separation element according to the seventh aspect can be suitably realized.

[Brief description of the drawings]

FIG. 1 is a sectional structural view showing a polarization splitting element according to a first embodiment of the present invention.

FIG. 2 is a sectional structural view showing a polarization beam splitter according to a second embodiment of the present invention.

FIG. 3 is a sectional structural view showing a polarization beam splitter according to a third embodiment of the present invention.

[Explanation of symbols]

 2 first element 3 second element 4 first optically isotropic substrate 5 optically anisotropic film 6 first diffraction grating shape 7 second optically isotropic substrate 8 optically isotropic Film 9 Second diffraction grating shape 12 Optically isotropic film 22 Guide

Claims (8)

[Claims] An optically anisotropic film formed on a first optically isotropic substrate, a first element having an uneven first diffraction grating formed on a surface thereof, and An optically isotropic film having the same refractive index as one of the ordinary light direction refractive index and the extraordinary light direction refractive index of the optically anisotropic film is formed on the second optically isotropic substrate. The first
A second element formed on the surface of the optically isotropic film with a concave-convex second diffraction grating shape meshed with and adhered to the first diffraction grating shape of the element. 2. The polarization separation element according to claim 1, wherein the first and second diffraction gratings have the same concavo-convex shape. 3. The polarization separation element according to claim 1, wherein the material of the optically anisotropic film and the material of the optically isotropic film are the same. 4. The polarization splitting element according to claim 1, wherein said first and second diffraction grating shapes having a concave and convex shape which mesh with each other are bonded by an optically transparent resin. . 5. The polarization separation element according to claim 4, wherein the refractive index of the resin is the same as the refractive index of the optically isotropic film. 6. The first optically isotropic substrate and the second optically isotropic substrate.
The polarization separation element according to any one of claims 1 to 5, further comprising a guide for alignment with one of the optically isotropic substrates described above. 7. The polarization separation element according to claim 1, wherein the optically anisotropic film is formed by oblique evaporation. 8. The polarization separation element according to claim 7, wherein the material of the optically anisotropic film is tantalum oxide.