JPH08334616A - Polarizing prism - Google Patents

Abstract

PURPOSE: To prevent total reflection from a joint part joined with a prism. CONSTITUTION: In a polarizing prism formed by joining plural prisms 1, 2 composed of an optical crystal >=2.0 in refractive index, an optical noneffective region having larger joint surface interval than that of an optical effective region is provided in the joint surface of the prism, a joint layer 5>=1.7 in refractive index is formed in a region including the optical effective region and the outer periphery of effective diameter of the joint surface of the prism is sealed by a resin 6.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to LiNbO ₃ , LiTa.
The present invention relates to a polarizing prism in which prisms made of optical crystals such as O ₃ are joined.

[0002]

2. Description of the Related Art A polarizing prism obtained by joining a plurality of prisms made of a birefringent crystal is used as a Wollaston prism or a lotion prism. As this birefringent crystal, artificial quartz is used as described in JP-A-5-181016, and the artificial quartz is bonded with an adhesive to form a prism.

In this case, a low-viscosity UV-curable adhesive is often used as the adhesive because of its good assembling property. In addition, as a means for this bonding, a method called optical contact in which mirror surfaces having high flatness are vacuum-sucked is used. Since the birefringent crystal has a higher refractive index than artificial quartz, in recent years, LiNbO ₃ , LiTaO ₃ , and TiO ₂ (rutile) have been used.
Are used.

[0004]

The refractive index of artificial quartz is almost equal to that of the adhesive (artificial quartz: 1.46, adhesive:
Since 1.4 to 1.6), there is almost no reflection at the interface, and even if the refractive index of the adhesive is slightly different from that of synthetic quartz, the reflection is reduced by applying an antireflection coating to the joint surface of the synthetic quartz. It is possible. However, LiNbO
_{Since 3} and LiTaO ₃ have a refractive index of 2.0 or more, the refractive index differs greatly from that of an adhesive that is normally used, and the reflection at the interface cannot be ignored.

In such a case, even if the reflection of the vertically incident light is prevented by using the antireflection coating, the reflection of the obliquely incident light cannot be prevented and the light is totally reflected. In order to prevent this total reflection, it is necessary to deviate from the Snell total reflection condition. If the incident angle to the cemented surface is θ, the refractive index of the prism on the incident side is n ₁ , and the refractive index of the cement is n ₂ , It is necessary not to satisfy n ₁ sin θ ≧ n ₂ . Therefore, for example, in a prism having a refractive index of 2.0, it is necessary to use a bonding agent having a refractive index of 1.7 or more when the incident angle is about 58.2 °. However, the refractive index of the bonding agent sold as a high refractive index bonding agent is about 1.58, and even the high refractive index organic optical material that is actively developed as an eyeglass lens has a refractive index of about 1.66 (made by Asahi Glass Co., Ltd.). However, it is difficult to obtain a refractive index of 1.7 or more with a normal bonding agent. From the above, it was extremely difficult to produce a polarizing prism that satisfies n ₁ sin θ ≧ 1.7.

On the other hand, in the optical contact as the joining means, the joining interval is extremely small and reflection at the interface does not occur, but the joining strength is low, and the problem of peeling easily due to temperature change and moisture and the working environment are extremely high. A high degree of cleanliness is required and the external dimensions cannot be corrected by the bonding layer. Therefore, in order to create a highly accurate polarizing prism, there is a problem that the accuracy of the prism itself needs to be maximized.

The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a polarizing prism made of a birefringent crystal having a high refractive index.

[0008]

The polarizing prism of the present invention is a polarizing prism in which a plurality of prisms made of optical crystals having a refractive index of 2.0 or more are cemented, and an optically effective area is provided in the cemented surface of the prisms. An optical non-effective area having a bonding surface spacing wider than the bonding surface spacing is provided, and a bonding layer having a refractive index of 1.7 or more is formed in the area including the optical effective area, and the effective diameter outer circumference of the bonding surface of the prism is set. It is characterized by being sealed with a resin. In this case, it is desirable that the bonding layer be formed of one of sulfur, bromine, phosphorus, iodine, or a combination thereof.

The minimum required properties of the bonding agent are:
They are a liquid or a viscous substance at the time of joining, and the refractive index of the joining agent when used as a prism satisfies the condition that total reflection does not occur. The latter condition that does not cause total internal reflection is determined from the relationship between the refractive index of the prism, the refractive index of the bonding agent, and the incident angle of the light beam. The refractive index of the bonding agent is 1. 7 or more, and preferably 1.8 or more.

As a result of studies, it was found that a liquid obtained by dissolving the above-mentioned phosphorus, sulfur, iodine and bromine compounds in a solvent such as benzene or water satisfies this condition. Therefore, basically, by filling these liquids between prisms and sealing the outer periphery with an adhesive, it is possible to obtain a polarizing prism made of a birefringent crystal having a high refractive index.

However, since the solvent is basically volatile, it volatilizes over a long period of time and is non-volatile.
Only iodine and bromine compounds remain, the volume of the bonding agent is significantly reduced, and bubbles are generated on the bonding surface.
When this bubble is generated in the optically effective area, it is totally reflected at the bubble portion and cannot be used as a prism.

In the present invention, when the parallel surfaces of the prisms have a high degree of parallelism, there is no regularity in the place where bubbles are generated.
As a result of diligent research, it was found that when the parallelism of the joint surface of the prism is poor, bubbles are generated in a wide gap between the joint surfaces.

Therefore, in the present invention, the optically ineffective region is
The bonding interval is wider than that of the optically effective area, and the bubbles are concentrated in this optically ineffective area to prevent the bubbles from being generated in the optically effective area and deteriorating the optical characteristics. . In this case, it is not necessary to make all the joint surface spacings of the optically ineffective region wider than the joint surface spacings of the optically effective area, and to provide a wide joint surface spacing only to the optically ineffective area sufficiently distant from the optically effective area. May be.

The method of controlling the joining surface interval is not particularly limited, and any method may be used. For example, the following method can be adopted as appropriate. (1) A spacer is provided in advance in a part of the optically ineffective region and then bonded. (2) Spherical or curved surface polishing is performed on at least one prism bonding surface so that the optically effective area becomes high. (3) The outer circumference of the optically effective area of at least one prism is chamfered. (4) When the optically effective area is off the center of the cemented surface, the prisms are tilted and cemented without making the cemented surfaces parallel to each other, and the distance between the cemented surfaces in the vicinity of the optically effective area is narrower than that outside the effective area. To be

In the case of the methods (1) and (4), the difference between the joining surfaces is about 0.5 to 2 μm and the inclination is 5'to 2
About 0'is preferable. This is because the concentration of air bubbles is not sufficient below this range, and above this range there is a high possibility that the dimensional error as a prism will exceed the design tolerance, depending on the optical design specifications.

[0016]

【Example】

(Embodiment 1) FIG. 1 is a perspective view of Embodiment 1 of the present invention, FIG. 2 is a plan view thereof, and FIG. 3 is a sectional view taken along a direction perpendicular to a joint surface. In these figures, 1 and 2 are prisms made of LiNbO ₃ (hereinafter, referred to as LM), and have a polarizing film 3 on the surface 1A, an antireflection film 4 on the surfaces 1B and 2A, and a surface 2B. The antireflection film 8 is provided by vacuum vapor deposition. Table 1 shows the structure of the polarizing film 3, Table 2 shows the structure of the antireflection film 4, and Table 3 shows the structure of the antireflection film 8. The configurations of the polarizing film 3 and the antireflection films 4 and 8 are common to the other examples described later.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

Reference numeral 5 is a bonding layer composed of a refractive index bonding agent disposed between the prisms 1 and 2. In this embodiment, a solvent of a matching liquid (made by Karnew Optical Co., Ltd.) having a refractive index of 1.78 is volatilized. It consists of residual solids containing sulfur as a main component. 6 is an adhesive for sealing, which is made of a cured product of an ultraviolet curable adhesive. In this example, the optically effective area is off center.

The manufacturing method of this embodiment will be described with reference to FIG. First, the prisms 1 and 2 made of LN are combined and held, and a UV-curable adhesive 6 having a trade name of “326LVUV” (manufactured by Loctite (Inc.)) is applied to the joint portion 7a on the side surface and slightly impregnated inside the joint surface. Occasionally, ultraviolet rays are irradiated to cure the adhesive 6. Next, a similar adhesive 6 is applied and cured on the joint portion 7b on the opposite side surface.

At this time, as shown in FIG. 5 (b), the joint surface spacing is smaller at the joint portion 7a where the adhesive is first applied than at the joint portion 7b where the adhesive is later applied, that is, It is performed so that the wedge-shaped joining surfaces are spaced. It should be noted that whether or not it has a wedge shape depends on the interference fringes 20 due to the difference in the air gap at the joint.
If the interference fringes 20 are not substantially horizontal and have an appropriate number as shown in FIG. 5A, the prisms 1 and 2 are peeled off, washed, and reassembled. There is a need. In this embodiment, about 6 to 8 lines are set as the acceptance line.

Next, the high-refractive-index liquid is injected from one side 7c of the remaining joint surface by utilizing the capillary phenomenon. As a result, the high refractive index liquid permeates the entire inside surface of the joint surface. If left to dry in this state, the solvent of the matching liquid is volatilized, and an air layer 21 called bubbles or sink marks is concentrated and generated in the optically ineffective area 21 in the joint surface (see FIG. 3). After being sufficiently dried, the above-mentioned adhesive 6 is applied to the joint portions 7c and 7d on the side surfaces, penetrated by capillarity, and cured to seal the outer circumference of the effective diameter of the prism.

The above-mentioned bonding agent having a high refractive index used for the bonding layer 5 has a refractive index of 1.78 in a liquid state and a refractive index of 1.82 after drying in a solvent. Therefore, the refractive index is high enough,
Moreover, since it exists in the entire optically effective region of the joint surface, total reflection can be prevented. Furthermore, since the outer periphery of the prism bonding surface is sealed with the adhesive 6 as shown in FIG. 3,
The prisms 1 and 2 are also sufficiently fixed to each other.

Next, with reference to FIG. 4, the principle of forming a wedge-shaped joint surface interval will be described. First, before applying the adhesive,
The joining surface distance t is substantially uniform, and is constant due to the viscosity of the atmosphere and the pressure acting in the direction normal to the joining surface. In this state, when the adhesive is permeated from the joint portion 7a and cured, the joint surface distance ta near the joint portion 7a, that is, the adhesive 6 is ta.
Is slightly narrower than before curing due to the curing shrinkage of the adhesive,
Approximately ta = t × (1−P). Here, P is a thickness reduction rate that is approximately equal to the shrinkage rate of the adhesive, and this P is about 0.01 to 0.1 (at least 1 or less). On the other hand, the joint surface distance tb in the vicinity of the joint portion 7b on the opposite side slightly expands due to the reaction and becomes tb = t × (1 + P).

Next, when the adhesive 6 is permeated through the joint 7b and cured, the adhesive 6 is cured and shrunk, whereby the joint 7 is contracted.
The joining surface spacing in the vicinity of b is slightly narrowed, and tb ′ = t ×
A (1 + P) × (1 -P) = t × (1-P 2). Here, since P is 1 or less, ta <tb.

When the wedge shape is confirmed by interference fringes, by using halogen light, the difference in the thickness of the air layer between the two interference fringes becomes λ / 2 (λ: wavelength), and the wavelength λ is about If it is 500 nm, it will be 250 nm. Therefore, 2 μm
In the case of providing a thickness difference of about a degree, it is sufficient to generate about eight interference fringes if desired. Further, if the interference fringes are slanted, the bubble generation portion may overlap the optical effective range, which is not preferable.

Although total reflection does not occur at the junction surface and the emission surface of the LN prism, reflection of several percent occurs due to the difference in refractive index. Therefore, it is effective to prevent the energy loss by providing an antireflection film. Is. In this embodiment, it is possible to provide a polarizing prism that does not cause total reflection of incident light by the bonding layer 5 and does not cause deterioration or performance change due to environmental changes.

(Embodiment 2) The construction of this embodiment will be described with reference to FIGS. 1 and 2 are made of LiNbO ₃ (hereinafter,
It is described as made by LN. ), The polarizing film 3 is provided on the surface 1A, the antireflection film 4 is provided on the surfaces 1B and 2A, and the antireflection film 8 is provided on the surface 2B. It is provided. Reference numeral 5 is a bonding layer made of a high-refractive-index bonding agent, which contains sulfur as a main component. An adhesive layer 6 for sealing is made of a cured product of an ultraviolet curable adhesive.

In the manufacture of this embodiment, first, the prisms 1 and 2 made of LN are combined and held, and the joint portion 7a on the side surface is sold under the trade name "325UV-BLUE" (manufactured by Loctite Corporation).
When the ultraviolet curable adhesive 6 is applied and the inside of the joint surface is slightly impregnated, ultraviolet rays are irradiated to cure the adhesive 6. The same adhesive 6 is applied to the side surface joint portion 7b on the opposite side,
Let it cure. At this time, as shown in FIG. 5B, the joint surface spacing is so-called wedge-shaped, that is, the joint portion 7a to which the adhesive 6 is first applied is narrower than the joint portion 7b to which the adhesive 6 is subsequently applied. It becomes the joint surface interval. Next, one side of the remaining joint surface 7c
Then, a high refractive index liquid in which sulfur is dissolved in chlorobenzene is injected by utilizing the capillarity. If left to dry in this state, chlorobenzene is volatilized, and air bubbles are concentrated and generated in the optically ineffective region inside the bonding surface.
(See FIG. 3), sulfur remains. And finally,
After sufficiently drying, the adhesive 6 is applied to the side joints 7c and 7d.
Is applied, permeated, and cured to seal the outer circumference of the effective diameter of the joint surface.

In the present embodiment, sulfur has a refractive index of 1.8, has a sufficiently high refractive index, and is present in the entire optically effective region of the joint surface, so that total reflection can be prevented. The sulfur and chlorobenzene used in this example are easily available and inexpensive, and thus have high mass productivity. Also,
Since the outer periphery of the prism bonding surface is sealed with the adhesive 6, the prisms 1 and 2 are sufficiently fixed to each other. Other actions are similar to those of the first embodiment. In this embodiment, the prisms 1 and 2 are made of LiTaO ₃ (hereinafter, L
It is described as made by T. ) Can be used and has the same effect. Also in this embodiment, it is possible to obtain a polarizing prism which does not cause total reflection of incident light by the bonding layer 5 and does not cause deterioration or performance change due to environmental changes.

(Embodiment 3) The construction of this embodiment will be described with reference to FIGS. Numerals 1 and 2 are prisms made of TiO ₂ (rutile), the polarizing film 3 on the surface 1A, the antireflection film 4 on the surface 1B and FIG. 2A, and the antireflection film 8 on the surface 2B. It is provided by vacuum vapor deposition in the configuration as shown in FIG. 5 is a bonding layer made of a high refractive index bonding agent,
The main component is sulfur. 6 is an adhesive layer for sealing, which is made of a cured product of an ultraviolet curable adhesive.

In the manufacture of this embodiment, first, the rutile prisms 1 and 2 are combined and held, and the side joint portion 7a is formed.
A UV-curable adhesive 6 having a trade name of “326UV-BLUE” (manufactured by Loctite Co., Ltd.) is applied to the above, and when the inside of the joint surface is slightly infiltrated, ultraviolet rays are irradiated to cure the adhesive 6. The same adhesive 6 is applied to the side surface joint portion 7b on the opposite side.
Apply and cure. At this time, the bonding surface spacing is as shown in FIG.
As shown in (b), the joint portion 7a to which the adhesive is first applied has a wedge-shaped joint surface space narrower than the joint portion 7b to which the adhesive is applied later. Next, a high-refractive-index liquid in which sulfur is dissolved in chlorobenzene is injected from one side 7c of the remaining bonding surface by utilizing a capillary phenomenon. If left to dry in this state, chlorobenzene is volatilized and air bubbles are concentrated and generated in the optically ineffective region inside the bonding surface, while sulfur is generated in the optically effective region 22 (see FIG. 3). To remain. And finally, after drying sufficiently, the side joint 7
The adhesive 6 is applied to c and 7d, penetrated, and cured to seal the outer circumference of the effective diameter.

Sulfur used in the bonding layer 5 of this embodiment has a refractive index of 1.8, a sufficiently high refractive index, and is present in the entire optical effective region 22 of the bonding surface, so that total reflection can be prevented. it can. Furthermore, since the outer periphery of the prism bonding surface is sealed with the adhesive 6, the prisms 1 and 2 are fixed to each other and sufficiently. In this embodiment, TiO ₂ (rutile) has a very high refractive index of 2.7 and has a very high optical anisotropy, so that a large separation angle between ordinary light and extraordinary light can be obtained, and a prism with higher performance can be obtained. Obtainable. Other operations are the same as those in the first embodiment. Also in this embodiment, it is possible to obtain a polarizing prism which does not cause total reflection of incident light by the bonding layer 5 and does not cause deterioration or performance change due to environmental changes.

(Embodiment 4) FIG. 6 is a plan view of this embodiment, a side view perpendicular to the joint surface and a side view parallel to the joint surface. In FIG. 6, 9 and 10 are made of LiNbO ₃ (LNbO ₃
Manufactured by a vacuum evaporation method. The polarizing film 3 is provided on the surface 9A, the antireflection film 4 is provided on the surface 9B and the surface 10A, and the antireflection film 8 is provided on the surface 10B. It is provided. The outside of the optically effective region on the lower side of the prisms 9 and 10 in the present embodiment is obliquely polished, so that the bonding interval is wide in this region. Reference numeral 5 is a high-refractive-index bonding agent that forms the bonding layer, and is made of the same material as in Example 1. 6 is an adhesive layer for sealing, which has a trade name of "311".
3 "(manufactured by ThreeBond (Inc.)) is cured by curing an ultraviolet curable adhesive.

In the manufacture of this embodiment, first, the prisms 9 and 10 are manufactured.
The portion 13 that is out of the optically effective area is obliquely polished so as to be chamfered. Next, the prisms 9 and 10 are combined and held, and the ultraviolet curable adhesive 6 (trade name "326UV-BLUE", manufactured by ThreeBond (Inc.)) is applied to the side joint portion 7a (see FIG. 4) and joined. When the inside of the surface is slightly infiltrated, ultraviolet rays are irradiated to cure the adhesive 6.
The same adhesive 6 is applied and cured on the joint portion 7b (see FIG. 4) on the opposite side surface. At this time, as shown in FIG. 6, the joining surface spacing is such that the chamfered portion 13 that is obliquely polished has a triangular joining surface spacing. Next, a high-refractive-index liquid in which sulfur is dissolved in chlorobenzene is injected from one side 7c (see FIG. 4) of the remaining bonding surface by utilizing a capillary phenomenon. If left to dry in this state, chlorobenzene is volatilized, and bubbles are generated by concentrating in the chamfered portion 13 which is an optically ineffective region, while sulfur remains in the optically effective region 22. And finally, after sufficiently drying, the side joints 7c, 7
The adhesive 6 is applied to d (see FIG. 4), allowed to penetrate, and cured to seal the outer periphery.

In this embodiment, in addition to the function of the first embodiment, the prisms are processed in advance so that the bonding distance of the sufficiently distant portion outside the optically effective region is widened, so that a wedge shape is formed. No need to join. Therefore, it is not necessary to strictly align the prisms with each other, and the yield is improved. Further, since a large amount of the high-refractive-index liquid can be injected into the volume of the optical effective range, the bonding agent can be left in a wider area, and the yield is further improved. In addition,
In this embodiment, both the prisms 9 and 10 are obliquely polished, but the same effect can be achieved by polishing only one prism obliquely. It is also effective to chamfer the entire outer circumference of the joint surface of the prism. In this embodiment, a prism that does not cause total reflection of incident light by the bonding layer 5 and does not cause deterioration or performance change due to environmental changes can be obtained with a high yield.

(Embodiment 5) FIG. 7 shows the structure of this embodiment. In the polarizing prism of this embodiment, the optically effective region is located at the center of the cemented surface. 11 and 12 are LiNbO ₃ (LN
The surface 11B of the prism 11 is convexly polished with the center 11B 'of the surface 11B as the apex. The polarizing film 3, the surface 11B and the surface 12A are provided on the surface 11A.
The antireflection film 4 on the surface 12B, and the antireflection film 8 on the surface 12B.
It is provided by vacuum vapor deposition with a configuration such as a few.
Using these prisms, bonding was performed in the same manner as in Example 4 to produce the polarizing prism shown in FIGS. 8 and 9. In this case, FIG. 8 is a sectional view taken along the joint surface, and FIG.
It is the figure which looked at the A line from above. Reference numeral 5 is a high refractive index bonding agent as a bonding layer, which is made of the same material as in Example 1. 6 is an adhesive layer for sealing, which is formed by curing an ultraviolet curable adhesive (trade name "3113", manufactured by ThreeBond (Inc.)).

In this embodiment as described above, in addition to the effect of preventing total reflection by the high-refractive-index bonding agent 5, the bonding surface 11B of the prism 11 is spherically polished in a convex shape. The center 11B 'of the region has the smallest distance from the joint surface 12A of the prism 12. Therefore, the bonding agent 5 remains in the optically effective area.

Further, since the spherical surfaces have been polished in advance, it is not necessary to join them in a wedge shape, and it suffices if they are joined so as to maintain the dimensional accuracy of the outer shape, resulting in excellent productivity. In this embodiment, a polarizing prism that does not cause total reflection of incident light by the bonding layer 5 and does not cause deterioration or performance change due to environmental changes can be obtained with a high yield.

[0041]

As described above, in the present invention, a high refractive index substance is used for the bonding layer of the prism using the high refractive index crystal,
Since this high-refractive substance is effectively left in the optically effective region, it is possible to provide a stable polarizing prism that does not cause total reflection of incident light by the bonding layer.

[Brief description of drawings]

FIG. 1 is a perspective view of a polarizing prism of Examples 1 to 3.

FIG. 2 is a plan view of FIG.

FIG. 3 is a vertical sectional view of a joint surface.

FIG. 4 is an assembly diagram for manufacturing a polarizing prism.

FIG. 5A is a side view for explaining the quality of joining, and FIG.
FIG. 3 is a cross-sectional view showing a joint structure.

FIG. 6 is a cross-sectional view showing a prism of Example 4.

FIG. 7 is an exploded perspective view of a prism according to a fifth exemplary embodiment.

FIG. 8 is a sectional view of the fifth embodiment.

9 is a plan view taken along the line AA of FIG.

[Explanation of symbols]

 1 Prism 2 Prism 5 Bonding layer 6 Adhesive

Claims (2)

[Claims] 1. A polarizing prism in which a plurality of prisms made of an optical crystal having a refractive index of 2.0 or more are cemented, and an optical element having a cemented surface spacing wider than a cemented surface spacing of an optically effective region in a cemented surface of the prism. A polarizing prism, characterized in that a non-effective region is provided, a bonding layer having a refractive index of 1.7 or more is formed in a region including the optically effective region, and an outer circumference of an effective diameter of a bonding surface of the prism is sealed with a resin. 2. The polarizing prism according to claim 1, wherein the bonding layer is formed of one of sulfur, bromine, phosphorus, iodine, or a combination thereof.