JPH08211217A - Diffraction grating type polarizer and its production - Google Patents

Abstract

PURPOSE: To facilitate the production management and design of a diffraction grating type polarizer and to improve the stability of its performance in terms of the lapse of time. CONSTITUTION: This diffraction grating type polarizer consists of first regions where first optical elements 3, double refraction materials 1 and second optical elements 4 are joined in this order through adhesive layers and second regions where the first optical elements 3 and the second optical elements 4 are joined through adhesive layers. The refractive index nE1 of the first optical elements 3 constituting the first and second regions, the refractive index nE2 of the second optical elements 4, the refractive indices nB1 , nB2 for the two intrinsic linearly polarized light of the double refraction materials 1 and the thickness dB of the double refraction materials 1 nearly satisfy (nB2 -nE2 )dB=(M+1/2)λ(where M is an arbitrary number, λ is the wavelength of light) and nB1 =nE1 =nE2 .

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 polarizer excellent in mass productivity as an alternative to a conventional polarizer and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
The following various polarizers are known.

(1) Dichroic polarizer known as a so-called polaroid plate: This type of polarizer has a low extinction ratio and a large loss, so that it is difficult to use it for a precision optical component such as an optical isolator. there were.

(2) Polarizing prism using a birefringent crystal:
This type of polarizer uses a birefringent material such as quartz, calcite, magnesium fluoride, etc., and these must be cut out at a predetermined angle with respect to the crystal axis and processed into a prism shape, so the material cost is low. It was expensive and not easy to manufacture.

(3) Birefringent crystal plate: This type of polarizer has a function of selecting one polarization by shifting the beam of one polarization, and is a plate for use in a parallel beam system. It was necessary to increase the thickness and it was difficult to reduce the thickness.

(4) Polarizing glass: This type of polarizer has excellent characteristics and can be made thin, but it is difficult to manufacture and expensive.

On the other hand, as an alternative to the above-mentioned polarizer,
A birefringent diffraction grating type polarizer is known which is small in size and has high mass productivity.

(5) Birefringent Diffraction Grating-Type Polarizer: This type of polarizer separates optical paths by utilizing the difference in diffraction efficiency due to polarized light, and the following are known.

(5-1) According to JP-A-63-55501: A polarizer having a diffraction grating formed by subjecting lithium niobate to proton ion exchange. However, this polarizer has a problem that it cannot be manufactured at low cost because the single crystal substrate of lithium niobate that forms the diffraction grating is expensive, and it is difficult to control the polarization phase difference with high accuracy. There was a problem that it could not be manufactured stably with good performance.

(5-2) According to Japanese Patent Application Laid-Open No. 2-156205: A polarizer in which a dielectric layer is provided at the bottom of periodic grooves provided on the main surface of a crystal plate having optical anisotropy. However, although this polarizer can be manufactured at low cost,
Since it is difficult to precisely control the groove depth and the thickness of the dielectric layer, it is not possible to control the polarization phase difference with high precision, and as in (51), it is possible to manufacture with good reproducibility and stability. I couldn't.

(5-3) According to Japanese Patent Laid-Open No. 6-308326: It is an improved invention of the polarizer of (5-2) by the present inventor. In this polarizer, as shown in FIG. 6, the birefringent material 1 having a uniform thickness bonded to the upper surface of the optical element 10 is grooved to penetrate the optical element 10, and then the groove is bonded. The birefringent material 1 can be made to have a constant thickness regardless of the depth of the groove, because the birefringent material 1 is filled with the conductive filler 12. Therefore, the dependence of the performance of the polarizer on the accuracy of the groove depth is eliminated.

However, in the case of this polarizer, its performance depends on the refractive index of the adhesive filler filled in the groove, and therefore, in order to stably manufacture a polarizer having a certain performance, the adhesive filler is used. The mixing ratio of the agents (mixing ratio of the mixture which is a component of the adhesive filler), the curing conditions, and the like need to be constantly controlled, which is not easy to control. In addition, this polarizer has the following problems.

(1) In order to obtain a polarizer having desired performance, it is necessary to adjust the refractive index of the adhesive filler with high precision, and the precision of the adjustment is not good. For example, in the method of adjusting the refractive index of the epoxy resin cured product disclosed in JP-B-63-28448, the accuracy with which the refractive index can be adjusted is about 0.001.

(2) Since it was difficult to accurately predict the refractive index after curing before curing, the design efficiency of the deflector was not good (a considerable number of trials were required).

(3) Since the adhesive filler is a resin material, the environment resistance is poor and the refractive index of the adhesive filler changes over time, and the performance of the polarizer deteriorates (the extinction ratio decreases). was there.

Therefore, the present invention solves the above-mentioned problems depending on the adhesive filler in the polarizer of (53), facilitates manufacturing control and design, and has a highly stable performance with time. An object of the present invention is to provide a type polarizer and a manufacturing method thereof.

[0017]

In the diffraction grating type polarizer according to claim 1, the first optical element, the birefringent material and the second optical element are bonded in this order through an adhesive layer. It comprises a first region and a second region in which the first optical element and the second optical element are bonded to each other via an adhesive layer, and constitutes the first region and the second region. refractive index of the first optical element n _E1, the thickness of the refractive index n _B1, n _B2, and the birefringent material to the refractive index n _E2, 2 one unique linear polarization of the birefringent material of the second optical element d _B , (N _B2 −n _E2 ) d _B = (M + 1/2) λ (where M is an arbitrary integer and λ is the wavelength of light) and n _B1 = n _E1 = n _E2 are substantially satisfied. It is a thing.

A diffraction grating type polarizer according to a second aspect is the diffraction grating type polarizer according to the first aspect, in which both the first optical element and the second optical element are optical glass made of the same material, and The birefringent material is quartz.

A method of manufacturing a diffraction grating type polarizer according to a third aspect of the present invention is a method of manufacturing two types of linearly polarized light having refractive indices n _B1 and n _B2.
And a first optical element having a refractive index n _E1 having substantially the same refractive index n _{E1 as} that of n _B1 and a refractive index n _B2 before or after the bonding. And a refractive index n _{E2 that} is substantially the same as n _B1.
In the second optical element having, the thickness d of the birefringent material
_B is _{(n B2 -n E2) d B} = (M + 1/2) λ ( where M is an arbitrary integer, lambda is the wavelength of light) and polishing the birefringent material so as to satisfy, the birefringent A step of forming a plurality of first grooves in the material having a constant interval at a depth reaching the first optical element; and a second optical element having a constant depth substantially equal to the depth of the first groove. A step of forming a plurality of second grooves having a space, and the concave and convex portions of each of the member having the first groove and the member having the second groove, with a second adhesive interposed. It is characterized by comprising a step of fitting and joining. A method of manufacturing a diffraction grating type polarizer according to a fourth aspect is the diffraction grating type polarizer according to the third aspect, wherein both the first optical element and the second optical element are optical glass made of the same material, and The birefringent material is quartz.

[0020]

The diffraction grating type polarizer according to claim 1 will be described together with the operation principle of the diffraction grating type polarizer.

As shown in FIG. 1, a first area 8 and a second area 9
If the phase difference between the light passing through the first region 8 and the light passing through the second region 9 is φ, the intensity of the 0th-order diffracted light, that is, the transmittance T of the light traveling straight ahead is Is sufficiently thin, it is given by the following approximate expression.

T = cos ² (φ / 2) where the phase difference between one of the two orthogonal linearly polarized lights is φ1, the transmittance is T1, the phase difference between the other linearly polarized light is φ2, and the transmittance is If it is T2, it operates as a polarizer when T1 is approximately 1 (φ1 is approximately 0 deg) and T2 is approximately 0 (φ2 is approximately 180 deg). Usually, since the control of T1 is relatively easy, the accuracy of controlling T2 becomes a problem.

That is, when the extinction ratio T2 / T1 is small, it operates as a polarizer. Therefore, if T1 is approximately 1, the value of φ2 must be controlled with high accuracy so that the value of T2 approaches 0. For example, an extinction ratio of 0.000
In order to make it 5 or less, it is necessary to control φ2 to be 180 ± 2.6 deg.

On the other hand, in the diffraction grating type polarizer of the present invention, the birefringent material (thickness d _B ) constituting the first region constitutes the second region and the refractive indices n _B1 and n _B2 . The above-mentioned phase difference φ is caused by the difference in the refractive index n _E2 of the second optical element.

According to the diffraction grating type polarizer of the first aspect, the refractive index n _E1 of the first optical element and the refractive index n _E2 of the second optical element are substantially the same, and the influence of the bonding layer is small ( Since the thickness of the bonding layer is thin, its effect is small).
φ2 is given by the following equation.

Φ1 = {360 deg × (n _B1 −n _E2 ) d _B } / λ φ2 = {360 deg × (n _B2 −n _E2 ) d _B } / λ where the refractive index n _B1 of the birefringent material and the first If the refractive indices n _E2 of the second optical elements are made substantially the same, φ1 does not require any particular control. Regarding φ2, since the refractive index n _B1 of the birefringent material and the refractive index n _E2 of the second optical element are determined depending on the material, φ2 can be accurately manufactured by simply manufacturing the thickness d _B of the birefringent material. Can be controlled.

Also, before fabrication, the refractive index n of the second optical element is
_{Since E2} and the refractive index n _B2 of one of the birefringent materials can be accurately measured, it becomes easy to design the polarizer (setting the thickness d _B of the birefringent material, etc.) and control the phase difference φ 2.

According to the diffraction grating type polarizer of the second aspect, since both the first optical element and the second optical element use the optical glass made of the same material, it is more precise (± 0 at a practical level). It is possible to control the refractive index with an accuracy of 0.0002). Further, since the refractive index of the optical glass easily matches the refractive index of the crystal, it becomes easier to control the refractive index of the optical glass so that φ1 becomes 0 deg. Further, since the optical glass and the crystal are also excellent in environmental resistance, the refractive index is hardly changed with time and the performance of the polarizer is hardly deteriorated (the extinction ratio is decreased).

According to the manufacturing method of the diffraction grating type polarizer of the third aspect, the diffraction grating type polarizer of the first aspect can be stably manufactured with good reproducibility.

According to the manufacturing method of the diffraction grating type polarizer of the fourth aspect, the diffraction grating type polarizer of the second aspect can be stably manufactured with good reproducibility.

[0031]

EXAMPLE The polarizer of this example will be described with reference to the drawings in accordance with its manufacturing process.

Step 1: a birefringent material having refractive indices n _B1 and n _B2 for two unique linearly polarized lights, and a first optical element having a refractive index n _E1 and n _E2 substantially the same as n _B1 ; Prepare the optical element of. This birefringent material is made uniform to have a thickness d _B that satisfies (n _B2 −n _E2 ) d _B = (M + ½) λ (where M is an arbitrary integer and λ is the wavelength of light). Grind to thickness.

Step 2: As shown in FIG. 2, the refractive index n _E1
The first optical element 3 and the birefringent material 1 are bonded with an adhesive (forming the first adhesive layer 2). The step of polishing the birefringent material 1 to a predetermined thickness, which is performed in step 1, may be performed after this step (bonding step).

Step 3: As shown in FIG. 3, a plurality of first grooves 6 having a width w2 are formed in the birefringent material 1 at intervals w1 by using a dicing saw, a peripheral cutting machine or the like. Here, it is preferable that w1 be slightly narrower than w2. Further, the depth of the first groove 6 is determined so as to penetrate the birefringent material 1 and reach the first optical element 3. The thickness of the birefringent material 1 not removed in this step is always constant regardless of the depth of the first groove 6.

Step 4: Separately from Step 3, as shown in FIG. 4, a dicing solution is applied to the second optical element 4 having a refractive index n _E2 that is substantially the same as one refractive index n _B1 of the birefringent material 1. −
A second groove 7 having the same shape (same groove interval, width, and depth) as the first groove formed in the step 3 is formed by using an outer peripheral cutting machine or the like.

Step 5: As shown in FIG. 5, a portion (FIG. 3) composed of the first optical element 3, the birefringent material 1 and the first adhesive layer 2 produced in the step 3 and the step 4 is produced. The concave and convex portions provided on the respective portions formed of the second optical element 4 (FIG. 4) are adhesive (form the second adhesive layer 5).
And fit and join.

The polarizer thus obtained operates as follows for two unique linearly polarized lights. The thickness of the adhesive layer is assumed to be sufficiently thin and can be ignored.

(1) Linearly polarized light with respect to n _B1 One refractive index n _B1 of the birefringent material 1 and the first optical element 3,
The refractive indices n _E1 and n _E2 of the second optical element 4 are almost the same, and the phase difference φ1 of the light passing through the regions 1 and 2 is almost 0 deg, and the light does not diffract and goes straight without loss.

(2) Linearly polarized light with respect to n _B2 The refractive index n _B2 of one of the birefringent materials 1 and the refractive index n _E2 of the second optical element 4 are (n _B2 −n _E2 ) d _B = (M + 1/2) ) (Where M is an arbitrary integer and λ is the wavelength of light) is substantially satisfied, so that the phase difference φ2 of the light passing through the regions 1 and 2 becomes approximately 180 deg and the light is diffracted.

As the birefringent material, any transparent birefringent material can be used. Typical materials are quartz, calcite, sapphire, ADP,
Although there are KDP, rutile, and the like, quartz, which is particularly inexpensive and easy to process, is suitable as the birefringent material of the present invention.

As the first optical element and the second optical element, any transparent isotropic material can be used, but optical glass whose refractive index can be controlled with high precision is used. preferable. Also, the first optical element and the second
The optical elements may be made of different materials as long as they have the same refractive index, but the same material is preferable.

Further, quartz is used as the birefringent material, and the first
If optical glasses made of the same material are used as the second optical element and the second optical element, the phase difference φ is 0 because the refractive indexes n _E1 and n _E2 of the optical glass easily match one of the refractive indexes n _B1 of the crystal.
It is easier to make the deg.

If the thickness of the first adhesive layer and the second adhesive layer is sufficiently thin, the refractive index of the adhesive layer has almost no influence on the performance of the diffraction grating type polarizer, but the first optical element, Two
In order to reduce light scattering loss and reflection loss at the boundary between the optical element and the adhesive layer, the refractive index of the adhesive layer and the refractive index of the first optical element and the second optical element are the same. Is desirable. That is, when the refractive index of the adhesive layer and the refractive index of the first optical element and the second optical element are different, scattering loss and reflection loss occur depending on the roughness of the surface of the grooved recess. Is the refractive index of the adhesive layer and the first optical element and the second
If the refractive indexes of the optical elements are the same, there is no boundary portion having a different refractive index, so that scattering loss and reflection loss can be suppressed.

Next, an x-cut quartz plate is used as a birefringent material, and a material FEL is used as the first optical element and the second optical element.
A case where the optical glass No. 1 is used will be described by showing specific numerical values. Here, at a wavelength of 1550 nm, the refractive index of the ordinary light of the crystal is n _B1 = 1.52781, the refractive index of the extraordinary light is n _B2 = 1.53630, and the refractive index of FEL1 is n _E1 = n _E2.
= 1.52854.

First, the thickness d _B of the crystal plate is 100 μm.
((N _B2 -n _E2) was calculated from the d _B = λ / 2 of the equation)
The polishing process of step 1 was performed so that

Next, a joining step of Step 2 for joining the crystal plate and the optical glass was performed using an epoxy resin having a refractive index of 1.53 as the adhesive.

Subsequently, the groove processing of step 3 and step 4 was performed with w1 and w2 set to about 100 μm and the groove depth set to about 150 μm.

Finally, the bonding step of step 5 was performed using the same adhesive (epoxy resin having a refractive index of 1.53) as that used in step 2.

When the optical characteristics of the diffraction grating type polarizer produced as described above were evaluated, excellent characteristics with an extinction ratio of 0.0001 were obtained.

Since the refractive index of the optical glass varies depending on the lot, the refractive index is measured for each lot, and the thickness d _B of the birefringent material is determined according to the measured refractive index of the optical glass. Is desirable. Further, in the above embodiment, Mn is expressed by the formula (n _B2 −n _E2 ) d _B = (M + 1/2) λ.
However, when n _B2 > n _E2 , M = 0, n _B2 <
In the case of n _E2 , it is desirable to set M = −1, and in this case, the operating wavelength band becomes the widest.

[0051]

Since the present invention is configured as described above, it has the following effects.

(1) A diffraction grating type polarizer having excellent characteristics can be stably manufactured with good reproducibility only by precisely manufacturing the thickness of the birefringent material.

(2) Since the refractive indexes of the optical element and the birefringent material, which are the main constituent members, can be precisely measured before fabrication, it is easy to design the diffraction grating type polarizer and control the phase difference. .

(3) Since the optical element and the birefringent material having excellent environment resistance are used as the main constituent members, the performance of the diffraction grating type polarizer hardly deteriorates due to changes over time.

(4) When optical glass is used as the optical element and quartz is used as the birefringent material, it becomes easier to design the diffraction grating type polarizer and control the phase difference. Also, the environmental resistance is further improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the operating principle of a diffraction grating type polarizer.

FIG. 2 is a cross-sectional view showing step 2 of the production example of the polarizer of the present invention.

FIG. 3 is a cross-sectional view showing step 3 of a production example of a polarizer of the present invention.

FIG. 4 is a cross-sectional view showing step 4 of the production example of the polarizer of the present invention.

FIG. 5 is a cross-sectional view showing step 5 of a production example of a polarizer of the present invention.

FIG. 6 is a cross-sectional view showing a conventional polarizer.

[Explanation of symbols]

 1 Birefringent Material 2 First Adhesive Layer 3 First Optical Element 4 Second Optical Element 5 Second Adhesive Layer 6 First Groove 7 Second Groove 8 First Region 9 Second Region 10 Optics Element 11 Adhesive 12 Adhesive filler

Claims (4)

[Claims] 1. A first optical element, a birefringent material, and a second optical element, which are bonded in this order via an adhesive layer.
And a second region in which the first optical element and the second optical element are bonded together via an adhesive layer, and the first region and the second region are formed. refractive index n _E1 of the optical element, the refractive index of the second optical element n _E2, the refractive index for the two specific linear polarization of the birefringent material n _B1, n _B2, and the thickness d _B of the birefringent material, (N _B2 −n _E2 ) d _B = (M + 1/2) λ (where M is an arbitrary integer, λ is the wavelength of light) and n _B1 = n _E1 = n _E2 Type polarizer. 2. The diffraction grating type polarizer according to claim 1, wherein both the first optical element and the second optical element are optical glass made of the same material, and the birefringent material is quartz. The diffraction grating type polarizer according to claim 1. 3. Refractive index n for two unique linearly polarized lights
A step of joining a birefringent material having _B1 and n _B2 and a first optical element having a refractive index n _E1 substantially the same as that of n _B1 via a first adhesive, and before or after the joining In the birefringent material having a refractive index n _B2 and the second optical element having a refractive index n _E2 substantially the same as n _B1 , the thickness d _B of the birefringent material is (n _B2 −n _E2 ) d _B = (M + 1/2) λ (where M is an arbitrary integer, λ is the wavelength of light), the step of polishing the birefringent material, and the depth of the birefringent material reaching the first optical element. And forming a plurality of first grooves having a constant interval, and a plurality of second grooves having a constant interval in the second optical element at a depth substantially equal to the depth of the first groove. And the step of forming the first groove and the concave and convex portions of the member in which the first groove is formed and the member in which the second groove is formed, with a second adhesive interposed. A method of manufacturing a diffraction grating type polarizer, comprising the steps of existing and fitting and joining. 4. The diffraction grating type polarizer according to claim 3, wherein both the first optical element and the second optical element are optical glass made of the same material, and the birefringent material is quartz. The method for producing a diffraction grating type polarizer according to claim 3.