JPH0355810B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an optical element composite, and in particular to a method for fixing and supporting at least one optical element, such as an electro-optical element or a magneto-optical element, on a predetermined mounting substrate. The present invention relates to an optical element composite body made of at least one optical element.

(Background Art) Conventionally, optical elements such as electro-optical elements and magneto-optical elements have generally been manufactured using synthetic resin adhesives, etc.
It is directly fixed to a predetermined mounting board and applied to the intended use. However, in the case of such a conventional mounting or supporting structure for an optical element, due to the difference in thermal expansion coefficient between the optical element and the substrate, the difference in thermal expansion coefficient between the optical element and the substrate changes as the environmental temperature changes. This has the inherent problem that stress is applied to the optical element, which changes its optical properties.

For example, fixing such an optical element to a predetermined substrate,
As for those using a supporting composite,
An optical sensor as shown in FIG. 1 can be mentioned. 1 is a light source, 2 is an optical fiber, 3 is an electro-optic crystal, 4a is a polarizer, 4b is an analyzer, 5 is a λ/4 plate, 6 is a rod lens, 7 is a light receiver, and 8 is an electro-optic crystal 3 At least the electro-optic crystal 3 of these electrodes has a structure in which it is directly adhered to and held by a predetermined mounting substrate 10 with a synthetic resin (adhesive) 9. has been done.

By the way, as is well known, the operating principle of an optical sensor is to utilize the electro-optic effect or magneto-optic effect. The effect refers to a phenomenon in which the optical properties of crystals change when a magnetic field is applied to the crystals. In the case of an optical sensor using a Pockels element such as lithium niobate (LiNbO ₃ ) or Bi ₁₂ SiO ₂₀ single crystal as the electro-optic crystal 3 in FIG. 1, the light emitted from the light source 1 is It passes through the polarizer 4a and becomes linearly polarized light,
Furthermore, it passes through an electro-optic crystal 3 and becomes elliptically polarized light.
Further, this elliptically polarized light passes through the λ/4 plate 5 and the analyzer 4b, and the amount of light is changed according to its ellipticity. This amount of light corresponds to the voltage applied to the electrode 8 provided on the electro-optic crystal 3, and by measuring this amount of light,
However, in a sensor with such a structure, the characteristics of the electro-optic crystal 3 bonded and held on the mounting board 10 change due to changes in the environmental temperature. This caused the problem that the output changed significantly.

In addition to the electro-optic crystal elements mentioned above, there are also magneto-optic crystal elements as optical elements, and these elements are attached to supporting substrates such as ceramic or metal substrates. When fixing or adhering, if there is a difference in the coefficient of thermal expansion between the two, stress will be applied to the optical element due to environmental temperature changes, changing the optical properties or deforming the optical element, causing a change in the traveling direction of light. In extreme cases, repeated environmental temperature changes may cause the bonded portion to fatigue and eventually break.

(Problem to be Solved) The present invention has been made against this background, and its purpose is to solve problems caused by environmental temperature changes in an optical element fixed to a predetermined substrate. An object of the present invention is to provide an optical element composite that can effectively prevent changes in optical properties due to stress caused by a difference in thermal expansion coefficient between the substrate and the optical element. Another object of the present invention is to provide an optical element composite structure, such as an optical sensor, which can stably output an output without being affected by changes in environmental temperature.

(Solution Means) In other words, in order to achieve the above object, the present invention provides a composite body in which an optical element having an electro-optic effect or a magneto-optic effect is fixed and supported on a predetermined substrate. The following formula: |α ₁ −α ₃ |<|α ₁ −α ₂ | (where α ₁ is the thermal expansion coefficient of the optical element and α ₂ is the thermal expansion coefficient of the substrate). The gist of the optical element composite is that the optical element and the substrate are fixed to each other with an adhesive through the interposition of at least one intermediate having a satisfactory coefficient of thermal expansion: α ₃ . That is.

In addition, in the present invention, the intermediate body may be composed of a plurality of bodies, and in that case,
The thermal expansion coefficient of the intermediate is gradually changed from the substrate toward the optical element, and the closer the intermediate is to the optical element, the closer the thermal expansion coefficient is to that of the optical element. be.

(Specific description of the structure) By the way, as the optical element fixed and supported on a predetermined substrate, in addition to the above-mentioned optical element having an electro-optic effect or magneto-optic effect, that is, an electro-optic crystal element or a magneto-optic crystal element, There are prism lenses, reflectors, etc., and the polarizer 4a, analyzer 4b, λ/4 plate 5, rod lens 6, etc. shown in FIG. When the present invention is applied to an optical element having an electro-optic effect or a magneto-optic effect, which is particularly sensitive to stress when fixed, problems caused due to differences in thermal expansion between the element and the substrate can be solved. A solution will be sought.

In addition, it is used as an optical crystal for optical sensors.
As the electro-optic crystal element, for example, LiNbO ₃
(lithium niobate), LiTaO ₃ (lithium tantalate), Bi ₁₂ SiO ₂₀ , Bi ₁₂ GeO ₂₀ , etc. Magneto-optic crystal elements include YIG, lead glass, ZnSe, etc. The present invention is advantageously applied to fixing and supporting such optical crystals, especially electro-optic crystal elements.

Further, as the substrate to which such an optical element is fixed and supported, materials made of various known materials may be appropriately selected and used, such as ceramic substrates, metal substrates, and the like.

According to the present invention, between at least one of the at least one optical element fixed and supported by such a substrate, according to the present invention,
At least one intermediate having a coefficient of thermal expansion similar to that of the optical element, and generally having a coefficient of thermal expansion intermediate between that of the optical element and the substrate, is interposed, and the material of this intermediate may be, for example, Any of ceramic, plastic, and metal can be used, and for the optical crystal described above, it is also possible to use an intermediate made of the same material.

Note that such an intermediate is generally in a plate shape and is interposed between an optical element and a substrate, and its thickness is equal to that of the adhesive layer between the optical element and the substrate, such as an adhesive layer 9. It is desirable that the thickness be thicker than that, and the thickness is usually about 100 μm to 10 mm.

In addition, such an intermediate is interposed between the optical element and the substrate in a laminated state at a ratio of at least one, and is fixed to each other, for example, fixed or glued, so that it can be fixed or bonded to the optical element and the substrate, so that the intermediate body is not affected by changes in environmental temperature. Even if a difference in coefficient of thermal expansion occurs between the optical element and the substrate, the stress caused by the difference in thermal expansion can be effectively absorbed by the presence of an intermediate having an appropriate coefficient of thermal expansion. It will be eased to
This makes it possible to effectively eliminate the influence of stress on the optical element.

By the way, in the present invention, as an intermediate exhibiting such characteristics, in the relationship between the thermal expansion coefficient of the optical element: α ₁ and the thermal expansion coefficient of the substrate: α ₂ , the following formula: |α ₁ −α ₃ | <|α ₁ − α ₂ | It has a coefficient of thermal expansion: α ₃ that satisfies the relationship, and by using an intermediate that has a coefficient of thermal expansion: α ₃ that satisfies such a relationship. Then,
Therefore, the object of the present invention can be achieved even more advantageously.

Furthermore, when a plurality of intermediates are interposed between an optical element and a substrate, the thermal expansion coefficients of these intermediates are changed stepwise from the substrate to the optical element, and The closer the intermediate is to the thermal expansion coefficient, the closer it is to the thermal expansion coefficient of the optical element, and the stress between the optical element and the substrate can be advantageously alleviated step by step. be.

Note that in order to interpose such an intermediate between the optical element and the substrate and to fix them to each other, an adhesion method using an appropriate resin adhesive is generally adopted, but other methods may also be used. However, there is no problem in fixing them integrally using methods such as screwing or welding.

(Examples) Below, some examples of the present invention will be shown to clarify the present invention more specifically, but the present invention is not limited in any way by the description of such examples. Needless to say, it is not something that can be accepted.

In addition to the following examples and the above-mentioned specific description, the present invention includes various changes, modifications, and changes based on the knowledge of those skilled in the art, as long as they do not depart from the spirit of the present invention. It should be understood that improvements and the like may be made.

Example 1 First, an electro-optic crystal 3 is used as an optical element,
Bi ₁₂ SiO ₂₀ with a size of 4.7 mm x 7 mm x 5.1 mm and an electrode part 8 provided on a 7 mm x 5.1 mm surface perpendicular to the optical path.
A crystal was used. Incidentally, when the thermal expansion coefficient of this crystal 3 was measured, it was 150×10 ^-7 /°C. Also,
As the substrate 10 supporting this optical element 3, a CaTiO ₃ polycrystal having a thermal expansion coefficient of 112×10 ⁻⁷ /° C. was used. In addition to these parts, there are also a rod lens 6, a polarizer 4a, an analyzer 4b, and a λ/4 plate 5.
The components were arranged as shown in FIG. 1 and adhered to the substrate 10 using epoxy resin to produce the intended transmission type optical sensor. Note that, since the λ/4 plate 5 is thin, after bonding it to the analyzer 4b with epoxy resin,
Furthermore, it was bonded to the substrate 10.

Furthermore, in order to improve the sensor measurement accuracy, a circuit was added to the detector to divide the output of the light receiver 7 into an alternating current component and a direct current component, and to electrically divide the alternating current component by the direct current component.

Then, in the optical sensor configured in this way,
When an AC signal of 50 V and 60 Hz was applied, the device was placed in a constant temperature oven, and the temperature change in the output signal was measured between -20°C and +80°C, it was found that there was a 3% output fluctuation.

On the other hand, as shown in Figure 2,
Between the Bi ₁₂ SiO ₂₀ single crystal 3 and the CaTiO ₃ substrate 10,
Thermal expansion coefficient: 130× ^10-7 /℃ Thickness: 1mm
A glass plate 11 was interposed therebetween and a sensor was made by bonding with resin in the same manner, and then tested under the same test conditions as above, the output fluctuation based on temperature change of the output signal was 1%. It was observed that the output fluctuation range was significantly improved.

Example 2 An electro-optic crystal 3, which is an optical element, is a 2 mm x 3 mm x 5 mm crystal with an electrode 8 provided on a 3 mm x 5 mm surface whose Z axis coincides with the optical path direction and is parallel to the optical path.
A LiNbO ₃ single crystal with a size of
A polycrystalline body of CaTiO ₃ was used. Furthermore, this
When we measured the thermal expansion coefficient of LiNbO ₃ single crystal, we found that
It was 38×10 ^-7 /°C (Z-axis direction), and 167×10 ^-7 /°C in the direction perpendicular to it. Together with these parts, a λ/4 plate 5 on which a rod lens 6, a polarizer 4 which also serves as an analyzer, and a mirror 12 made of a dielectric multilayer film are formed is mounted on a CaTiO ₃ substrate 10 using epoxy resin in the arrangement shown in FIG. and glue
We created a reflective optical sensor for the purpose. In addition,
Since this sensor has a reflective configuration for the purpose of miniaturization, a splitter 13 is provided between the light source 1 and the optical sensor.

Regarding the optical sensor having such a structure, the output change in the temperature range of -20° C. to +80° C. was investigated in the same manner as in Example 1, and it was found to be 4%.

On the other hand, between the LiNbO ₃ single crystal 3 and the CaTiO ₃ substrate 10, the length in the Z-axis direction is 5 mm, the width is 1 mm, and the thickness is 0.5 mm, and each has a thermal expansion coefficient of 60 ×
The glass plate 11a at ^{10 -7 /} ℃ and the glass plate 11b at 100
On the LiNbO ₃ single crystal 3 side, the latter is a CaTiO ₃ substrate 10
A layered layer of epoxy resin was bonded to the center of a 2 mm x 5 mm surface of the LiNbO ₃ single crystal 3 so that the two layers were located on the sides, thereby producing the intended optical sensor.

The two glass plates (11a and 11b) thus obtained as intermediates are LiNbO ₃ single crystal 3
When we measured the change in the output signal based on environmental temperature change under the same test conditions as above for the sensor interposed between the sensor and the CaTiO ₃ substrate 10, the output fluctuation was 0.5%. , it was recognized that there was a significant improvement.

Further, the present invention is also applied to an optical sensor using a magneto-optic crystal (YIG) 14 as an optical element as shown in FIG. An intermediate plate 11 is interposed between the substrate 14 and the substrate 10.
In addition, here, the magneto-optic crystal 14 of YIG is 3 mm.
The size is 3 mm x 3 mm, and the <111> axis direction is the optical path direction.

(Effects of the Invention) As is clear from the above description, the present invention provides a method for interposing a predetermined intermediate between an optical element having an electro-optic effect or a magneto-optic effect and a substrate supporting it. It is designed to effectively relieve the stress caused by the difference in thermal expansion between the optical element and the substrate, and is advantageous for optical element composites whose characteristics are stable against changes in environmental temperature. This is why the present invention has great industrial significance.

[Brief explanation of drawings]

FIGS. 1 and 3 are layout configuration diagrams of optical sensors made of conventional optical element composites produced in Examples, and FIGS. 2 and 4 are diagrams of optical sensors produced in Examples, respectively. FIG. 2 is a layout configuration diagram of an optical sensor made of an optical element composite according to the invention. Further, FIG. 5 is a layout diagram of an optical sensor using a magneto-optic crystal, and FIG. 6 is a layout diagram of such an optical sensor according to the present invention. 1: Light source, 2: Optical fiber, 3: Electro-optic crystal, 4a: Polarizer, 4b: Analyzer, 5: λ/4
plate, 6: rod lens, 7: light receiver, 8: electrode,
9: Adhesive, 10: Substrate, 11, 11a, 11
b: Glass plate, 12: Mirror, 13: Turnout, 1
4: Magneto-optic crystal.

Claims (1)

[Scope of Claims] 1. A composite body comprising an optical element having an electro-optic effect or a magneto-optic effect fixed and supported on a predetermined substrate, wherein between the optical element and the substrate,
Thermal expansion coefficient that satisfies the following formula: |α ₁ − _{α 3} | < | α ₁ − _{α 2} | (where α ₁ is the thermal expansion coefficient of the optical element and α ₂ is the thermal expansion coefficient of the substrate) : An optical element composite, characterized in that the optical element and the substrate are fixed to each other with an adhesive, with at least one intermediate having α ₃ interposed therebetween. 2. The intermediate body is composed of a plurality of intermediate bodies, and the coefficient of thermal expansion is changed stepwise from the substrate toward the optical element, so that the closer the intermediate body is to the optical element, the closer the coefficient of thermal expansion is to the coefficient of thermal expansion of the optical element. An optical element composite according to claim 1.