JPH11242115A - Optical element without temperature dependence - Google Patents

Abstract

(57) [Problem] To provide an optimum optical element configuration by examining an optical element whose characteristic temperature dependence is almost zero in accordance with actual manufacturing. Kind Code: A1 A transparent body due to a temperature change is formed by bonding a plate-like body having a larger thermal expansion coefficient than that of a transparent body thin sheet and made of a material different from that of the transparent body thin sheet from above reflective films on both surfaces of the transparent body thin sheet. The change in the optical distance of the sheet is approximately invariant due to the expansion of the plate. However, in practice, the wavelength of the output light, which indicates the operating state of the transparent thin plate as a solid etalon, slightly changes due to a change in temperature, causing a wavelength shift.
This wavelength shift is caused by a slight change in the physical property value of the optical element with respect to the temperature. Therefore, if the minimum value of the amount of wavelength shift is brought near the middle point of the temperature range where the optical element is used, the amount of wavelength shift over the entire temperature range can be minimized, and with high accuracy An optical element that does not depend on temperature can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an optical element whose characteristics do not depend on temperature.

[0002]

2. Description of the Related Art With the recent development of high-speed communication networks, research and development for practical use of optical communication have been actively conducted. In such optical communication, it is necessary to transmit a large amount of signals at high speed, and as one of the methods, a wavelength division multiplexing method is considered to be promising. In wavelength division multiplexing, attempts have been made to increase the amount of information transmitted at a time by storing as many signals having different carrier wavelengths as possible in a narrow band.

Therefore, the wavelengths of different channels having different carrier wavelengths are very close to each other, and are used in optical communication networks to correctly transmit and receive signals of these channels having wavelengths that are close to each other. It is necessary that the characteristics of the optical filter with respect to the wavelength be stable, and a slight change in the characteristics deteriorates the quality of transmission and reception of the optical signal.

FIG. 11 is a view for explaining conventional optical filters and the problems they have. FIG. 1 shows the configuration of the solid etalon. The solid etalon is obtained by forming reflective films on both surfaces of a spacer formed of a transparent body. The reflectance of the reflective film is, for example, 90%.

When incident light is incident on such a solid etalon, multiple reflections occur between the reflection films, and a part of the light that is not reflected is output as output light. On the outgoing light side, the outgoing light emitted at each multiple reflection interferes with each other, and only light having a wavelength that satisfies the conditions for strengthening is emitted as a light beam on the outgoing light side, and light of other wavelengths is weakened. Does not form luminous flux. By detecting this light beam, light of a specific wavelength can be extracted from the incident light in which a plurality of wavelengths are superimposed. Intensity I of transmitted light emitted from etalon
When t is the intensity of incident light, I is the reflectivity of the reflective film, R is the incident angle of light, θ is the refractive index of the spacer, t is the thickness of the spacer (the interval between the reflective films), and λ is the wavelength. It is represented by the following equation (1).

It = I / (1+ (4R / (1-R) ² ) × sin (2πnt × cos θ / λ) (1) FIG. 12 shows the intensity of transmitted light of a solid etalon with respect to wavelength. (100% transmittance is 0 dB loss)
And).

As shown in FIG. 1, the solid etalon has a property of transmitting light having a wavelength satisfying a specific condition. However, when the temperature around the solid etalon rises, the characteristics of the element itself also change, and the wavelength of transmitted light shifts from a thick line to a thin line in FIG. Therefore, since the wavelength of the light received via the solid etalon on the light receiving side changes, the optical system may not work properly.

[0008] The characteristics of the solid etalon change as the temperature rises because the transparent spacer used in the solid etalon expands with temperature. When the spacer expands, the space between the reflective films of the solid etalon expands, the refractive index changes, and the optical distance that light passes during multiple reflection changes, so that the characteristics of the element itself also change. For example, when SiO ₂ is used as a spacer for a solid etalon, there is almost no change in thickness every time the temperature rises, but the change in refractive index is 10%.
Since the temperature is about ^-5, the change in the product (optical distance) of the refractive index and the thickness when the temperature rises by 10 degrees reaches 0.15 nm, which is not negligible.

To solve the above problems, Japanese Patent Laid-Open No.
No. 257567 discloses a transparent thin plate having a reflective film that reflects light on both surfaces, and a material that is different from the transparent thin plate, and is more thermally expanded than the transparent thin plate that is adhered to at least one surface of the transparent thin plate. Having a plate-like body having a large coefficient, wherein a change in the product of the thickness and the refractive index of the transparent body thin plate caused by a temperature change is caused by a change in volume caused by a temperature change of the plate-shaped body. An optical element is disclosed which is offset by deformation and in which the product of the thickness of the transparent body and the refractive index is kept approximately unchanged. In this optical element, when the transparent thin plate expands with an increase in temperature, the thickness of the transparent thin plate increases, and the refractive index changes. At the same time, the plate-shaped member closely attached to the transparent thin plate also expands. Since the thermal expansion coefficient of the plate-like body is larger than that of the transparent body thin plate, the expansion size is large, and the plate-like body expands by pulling the transparent body thin plate. Since the transparent body sheet is pulled by the plate-like body, the transparent body sheet is mechanically stretched.
Due to this mechanical stretching effect, the change in the value of the product of the thickness of the transparent thin plate and the refractive index, which has changed due to the temperature rise, is canceled out and is kept approximately unchanged. The optical distance over which the light reflected by the reflective films on both surfaces of the transparent thin plate propagates depends on the product of the thickness of the transparent thin plate and the refractive index. The characteristics of the obtained optical element are also kept unchanged. vice versa,
When the temperature decreases, the transparent thin plate shrinks, but the thickness decreases accordingly. However, the plate-like body closely contacted with the transparent thin plate contracts further than the transparent thin plate, and further contracts the transparent thin plate. This increases the thickness of the transparent sheet, and consequently, as in the case of a rise in temperature, the product of the transparent sheet thickness and the refractive index is kept approximately invariant to temperature changes. .

Further, in Japanese Patent Application Laid-Open No. 9-257567,
A quantitative principle is described in which the product of the thickness of the transparent thin plate and the refractive index is kept approximately invariant to a temperature change. The thermal expansion coefficient of the transparent thin plate is α1, and the temperature coefficient of the refractive index is n1. ,
When the Poisson's ratio is σ (σ0 = 2σ / (1−σ)), the parallel component of the refractive index distortion coefficient is P1, the vertical component is P2, and the thermal expansion coefficient of the plate is α2 (α1 <α2). The rate of change of the optical distance nt of the transparent thin plate due to the change in temperature Δ
It is assumed that (nt) / nt can be expressed by the following equation.

Δ (nt) / nt = α1 + n1− (α2−α1) × (σ0 + P1 + P2 × (1−σ0)) (2) Here, if the equation (2) becomes zero, the temperature change On the other hand, since the optical distance of the transparent thin plate does not change, by selecting a material constituting the optical element so that the equation (2) becomes approximately zero, an optical element having no characteristic change due to a temperature rise is obtained. Can be formed.

[0012]

However, the thermal expansion coefficients α1 and α2, the temperature coefficient n1 of the refractive index, etc. used in the above-mentioned prior art, equation (2) described in Japanese Patent Application Laid-Open No. 9-257567, are optical glass. Is not constant with temperature, and often increases slightly due to a rise in temperature. Therefore, the rate of change Δ (n
t) / nt is not completely constant and often slightly increases with an increase in temperature. For this reason, it is difficult to make the rate of change of the optical distance of the transparent thin plate completely zero.

Further, when the transparent thin plate is pulled by a plate having a large coefficient of thermal expansion and is mechanically stretched, if the thickness of the transparent thin plate becomes thicker than the thickness of the plate, the stretching is performed. Effect is actually reduced. In the above prior art, Japanese Patent Application Laid-Open No. Hei 9-257567, the thickness of the transparent body thin plate is required to be 1/5 or less of the thickness of the plate-like body, especially 10
Although it is considered that a ratio of 1/20 to 1/20 is preferable, even in this range, the influence of the thickness of the plate-like body and the thickness of the transparent thin plate may not be negligible. In other words, equation (2) does not take into account the influence of the thickness of the plate-shaped body or the thickness of the transparent body thin plate, so that this alone is insufficient.

[0014] As described above, the above-mentioned prior art is simply disclosed in Japanese Patent Application Laid-open No.
Even if JP-A-257567 is implemented, it is difficult to make the temperature dependence of an optical element such as a solid etalon as close to zero as possible.

An object of the present invention is to provide an optimum optical element configuration in which the temperature dependence of characteristics is as close to zero as possible.

[0016]

According to the present invention, there is provided an optical element which is adhered to at least one of both surfaces of a transparent thin plate for reflecting light therein and both sides of the transparent thin plate. And a plate having a large thermal expansion coefficient, wherein the product of the refractive index and the thickness of the transparent thin plate due to a change in temperature is minimized at a temperature approximately in the middle of the operating temperature range.

An optical element according to another aspect of the present invention is composed of a transparent thin plate having a reflection film for reflecting light on both surfaces, and a material different from the transparent thin plate, and is bonded to both surfaces of the transparent thin plate. Having a plate-like body having a larger thermal expansion coefficient than the transparent body thin plate, and a change in the product of the thickness and the refractive index of the transparent body thin plate caused by a temperature change is accompanied by a temperature change of the plate-like body. In the optical element in which the product of the thickness of the transparent body and the refractive index is kept almost unchanged, the thickness of the transparent body and the refractive index are offset. The temperature of the product is quadratic, and the temperature at which the product of the thickness of the transparent body and the refractive index is minimized in the desired temperature range is substantially at the center of the desired temperature range.

In the present invention, it is not always necessary to have a reflective film. That is, since the reflectance on the surface of the transparent thin plate is related to the ratio between the refractive index of the transparent thin plate and the refractive index of a substance in contact with the surface, even if the refractive index ratio is sufficiently large, the reflective thin film does not have a reflective film. The same effect as in the case where the reflective film is provided can be obtained.

Further, it is not always necessary to provide the plate-like body on both sides of the transparent thin plate. This is disclosed in JP-A-9-257567.
This is because, as described in the document, even if only one side is used, the tensile force due to the expansion of the plate-like body is sufficiently transmitted to the transparent thin plate, and the action of mechanically pulling the transparent thin plate is obtained.

According to the present invention, the thermal expansion coefficient and the temperature coefficient of the refractive index of the transparent thin plate or plate-like body depend on the temperature dependence.
Considering the second-order or higher effect on the temperature change of the product of the refractive index and the thickness of the transparent thin plate, the product of the refractive index and the thickness of the transparent thin plate of the actual optical element may not be completely constant. Even
The change can be minimized within the desired temperature range. Therefore, by selecting a material having an optimum physical property value that satisfies the conditions of the present invention, an actually optimum optical element can be realized.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION In the solid etalon of the present invention,
A transparent thin plate having a reflection film that reflects light on both sides, and a plate-like body that is made of a material different from the transparent thin plate and that is bonded to both surfaces of the transparent thin plate and has a larger thermal expansion coefficient than the transparent thin plate. The change in the product of the thickness of the transparent thin plate and the refractive index caused by the temperature change is offset by the deformation of the transparent thin plate due to the change in volume caused by the temperature change of the plate-like body, and the transparent body In a solid etalon in which the product of the thickness and the refractive index is kept approximately invariable, the change in the product of the thickness of the transparent body and the refractive index with temperature is quadratic, and the thickness of the transparent body in the desired temperature range is The temperature at which the product of the refractive indices is minimized is substantially at the center of the desired temperature range.

As described above, in the case of optical glass, the thermal expansion coefficients α1 and α2, the temperature coefficient n1 of the refractive index, and the like are not constant with respect to the temperature and often slightly increase with the rise in temperature. The rate of change of the optical distance nt of the body thin plate (the gradient of the temperature gradient) Δ (nt) / nt slightly increases with an increase in temperature. Therefore, in order to make Δ (nt) / nt closest to zero in the desired temperature range, it is necessary to adjust Δ (nt) / nt to become zero at the center of the desired temperature range. This is because the optical distance of the transparent thin plate, that is, the change of the product of the thickness of the transparent thin plate and the refractive index with temperature is quadratic, and the product of the thickness of the transparent thin plate and the refractive index in a desired temperature range. Is at about the center of the desired temperature range.

The reason that the temperature-dependent change in the product of the thickness of the transparent thin plate and the refractive index is quadratic means that when the function of the temperature change of the product is Taylor-expanded with temperature, the second-order term is considered. That is. And in the present invention,
This means that the position of the point at which the change up to the second-order term becomes minimum is substantially at the center of the desired temperature range. In general,
The temperature change of the product of the thickness of the transparent thin plate and the refractive index includes the second-order or higher-order term with respect to the temperature, but the higher-order term has a smaller effect on the change of the product of the actual element, An actual element is manufactured based on the knowledge that it is sufficient to consider the second-order terms in manufacturing an actual element.

In the present invention, in order to realize the above-mentioned state in the temperature range of about 0 to 85 ° C., the thermal expansion coefficient of the transparent thin plate is 5 to 7 (10 ⁻⁶ / 10) in the temperature range of 0 to 85 ° C. ° C), the temperature coefficient of the refractive index is about 3 to 5 (10 ^-6 / ° C), and the coefficient of thermal expansion of the plate is about 14 to 15 (10 ^-6 / ° C). Was.

Actually, the material of the transparent thin plate is LaC14.
(HOYA; lanthanum crown glass), and if the material of the plate is S-FPL53 (OHARA, fluorine crown glass), this state can be realized.

Further, as described above, the rate of change of the optical distance nt of the transparent thin plate is affected by the thickness of the plate-like body and the thickness of the transparent thin plate. By adjusting the thickness of the plate-like body, the temperature at which the product of the thickness of the transparent body and the refractive index is minimized in a desired temperature range can be set substantially at the center of the desired temperature range.

Further, when the above parameters are taken as described above, the thickness of the transparent thin plate is 1/7 of the thickness of the plate.
If it is below, desired characteristics can be obtained. FIG. 1 is a diagram illustrating an embodiment of the present invention.

FIG. 1 shows a transparent thin plate 10 used as a spacer of a solid etalon and reflection films 12 formed on both surfaces thereof. In the embodiment of the present invention, a plate 11 made of another material having a larger thermal expansion coefficient than the transparent thin plate 10 is bonded to the transparent thin plate 10. Thus, the transparent thin plate 10 serving as a spacer is formed.
Expansion due to heat, the thickness of the thin plate changes and the optical distance through which light passes changes, but the expansion of the plate with a large thermal expansion coefficient offsets the change in the optical distance of the transparent thin plate. It is constituted so that.

Here, the physical property value (thermal expansion coefficient, Poisson's ratio, temperature coefficient of refractive index, etc.) and thickness of the transparent thin plate 10 and the physical property value (thermal expansion coefficient, etc.) and thickness of the plate-like body 11 are shown. If properly selected, the change in the optical distance of the transparent thin plate 10 can be made approximately zero. Conventionally, a combination of the transparent body thin plate 10 and the plate-shaped body 11 was selected such that the change in the optical distance of the transparent body thin plate 10 was approximately zero in the above-described equation (2). Equation (2) is insufficient because the effect of the thickness of the plate-like body 11 and the thickness of the transparent body thin plate 10 is not taken into account. For this reason, in the present embodiment, the thickness of the transparent thin plate at each temperature was calculated using the finite element method in consideration of the shape of the solid etalon. The calculation by the finite element method uses a symmetry of the structure of the solid etalon to create a three-dimensional model of 1/8 of the actual shape, and calculates 20 × 20 × 10
= 4000 elements were calculated. The calculation of the refractive index n at each temperature is performed according to the above-described prior art (Japanese Patent Laid-Open No. 9-2).
No. 57567) and calculated using the following equation (3).

N = n0 + n1 × T-P1 (α2-α1) × T-P2 (α2-α1) × (1-σ0) × T (3) Here, the temperature change with respect to room temperature (25 ° C.) T, the refractive index of the transparent thin plate 10 at room temperature is n0, the temperature coefficient of the refractive index is n1, the thermal expansion coefficient of the transparent thin plate 10 is α1, the Poisson's ratio is σ (σ0 = 2σ / (1−σ)), and refraction is performed. The parallel component of the rate distortion coefficient was P1, the vertical component was P2, and the thermal expansion coefficient of the plate 11 was α2 (α1 <α2).

In the present embodiment, from the calculation by the finite element method, in particular, the material of the transparent thin plate is La which is an optical glass.
C14 (manufactured by HOYA) and S-FPL53 (manufactured by OHARA), which is an optical glass, were selected as the material of the plate. L
The physical property values of aC14 and S-FPL53 are as shown in Table 1,

[0032]

[Table 1]

These physical properties were used for calculation. In the present embodiment, the thickness of the transparent thin plate 10 is 65 μm,
Was 500 μm in thickness. Other shapes and dimensions are as described in FIG. That is, the shapes of the transparent thin plate 10 and the plate-shaped body 11 are 2 mm square. The adhesive for bonding the transparent thin plate 10 and the plate-like body 11 is a thermosetting two-component mixed epoxy adhesive E having a high adhesive strength.
PO-TEK353ND (Epoxy Technology)
ogy Inc. , Co., Ltd.). The reflection film 12 is a dielectric multilayer film in which Ta ₂ O ₅ and SiO ₂ are alternately stacked, and has a reflectance of about 90% in a wavelength range of 1530 nm to 1570 nm. In addition, the adhesive or the reflective film 1
2 is sufficiently thinner than the transparent thin plate 10 and the plate-like body 11, and it is confirmed by the finite element method that the optical distance of the transparent thin plate 10 is not affected by the temperature. Ignored in the calculations.

FIG. 2 shows the thickness of the transparent thin plate (LaC14) of the solid etalon obtained by using the finite element method and the formula (3).
5 shows the result of temperature change of the refractive index calculated from FIG. For comparison, FIG. 10 shows the calculation results of a transparent thin plate in the case where a plate having a large thermal expansion coefficient is not bonded. As can be seen from the figure, without the plate-like body, the thickness increases due to the thermal expansion due to the temperature rise, and the refractive index also increases. For this reason,
The optical distance which is the product of the thickness of the transparent thin plate and the refractive index is shown in FIG.
As shown in FIG. On the other hand, in the present embodiment in which the plate-like bodies are bonded,
As shown in FIG. 2, since the transparent thin plate is mechanically stretched by the plate-like body due to the temperature rise, the thickness is conversely reduced. Further, as is apparent from the equation (3), the refractive index also has a decrease due to the temperature distortion, so that the temperature gradient is reduced. For this reason, in the present embodiment, the change in the thickness of the transparent thin plate and the change in the refractive index are exactly offset, and the optical distance, which is the product of the thickness of the transparent thin plate and the refractive index, increases as shown in FIG. Change is very small. Next, the wavelength characteristic of the transmitted light of the solid etalon is calculated from the optical distance of the transparent thin plate by the equation (1), and the wavelength shift amount of the transmitted light peak depending on the temperature is shown in FIG. Here, a positive wavelength shift amount means that the wavelength of the transmitted light becomes longer. Since the transmission wavelength is proportional to the optical distance, the amount of wavelength shift due to a rise in temperature is very small in the present embodiment in which the plate is adhered, as compared with the case without the plate.

Further, FIG. 5 shows the calculated value of the wavelength shift due to temperature in the present embodiment with the wavelength range expanded, and the temperature change of the wavelength changes quadratically (approximately as a quadratic function). doing. This is because L, as shown in FIGS.
This is because the thermal expansion coefficient and the temperature coefficient of the refractive index of aC14 and S-FPL53 gradually increase with the temperature rise.

Next, FIG. 8 shows the result of calculating the wavelength shift amount by changing the thickness of the plate-like body with respect to the thickness of the transparent thin plate in the same manner. Here, the calculation was performed by changing the thickness of the transparent body thin plate without changing the thickness of the plate-shaped body. As can be seen from FIG. 8, the temperature gradient of the wavelength shift becomes positive as the thickness of the transparent thin plate with respect to the plate-like body increases. This is because, as the thickness of the transparent thin plate becomes thicker than the thickness of the plate-like body, the transparent thin plate becomes difficult to be mechanically stretched by the plate-like body having a large thermal expansion coefficient. . In order to make the temperature dependence of the wavelength characteristic close to zero as described above, it is necessary to not only select the physical properties of the material but also to optimally adjust the thickness of the plate to the thickness of the transparent thin plate. . Actually, changing the thickness of the transparent thin plate changes the half width of the transmission characteristics of the solid etalon and the width from peak to peak (free spectral range), so it is better to adjust the thickness of the plate More preferred.

In this embodiment, the plate-like body (S-FPL53)
Is 500 μm and the thickness of the transparent thin plate (LaC14) is 65 μm (about 1/7 to 1/8 of the thickness of the plate-like body). The wavelength, that is, the temperature at which the optical distance (the product of the thickness of the transparent body and the refractive index) is minimized is substantially at the center of the temperature range, and the temperature dependence of the wavelength characteristic is the smallest. In this way, considering that the change in the product of the thickness of the transparent body and the refractive index with temperature is quadratic (behaves like a quadratic function), the thickness and the refractive index of the transparent body in a desired temperature range are considered. By setting the temperature at which the product of the minimum is substantially at the center of the desired temperature range, the temperature dependence of the wavelength characteristic can be made as close as possible to zero.

Next, FIG. 9 shows the result of actually manufacturing ten solid etalons having the structure of the present embodiment and measuring the wavelength shift amount of the transmitted light peak. As can be seen from the figure, substantially the same result as the calculated value was obtained, and the wavelength shift was as small as about 0.015 nm in the temperature range of 0 to 85 ° C.

In this embodiment, LaC is used as the transparent substrate.
14 (manufactured by HOYA) and S-FPL53 (manufactured by OHARA) as the plate-like body, but other than this glass, any other glass having substantially the same physical properties can be used. For example, instead of LaC14 (made by HOYA), S-
LAL14 (manufactured by OHARA), N14 (manufactured by SCHOTT), etc. and FCD instead of S-FPL53 (manufactured by OHARA)
100 (made by HOYA) or the like can be used.

Further, even if glasses having slightly different physical properties are combined, the temperature dependence of the wavelength characteristic can be made close to zero by optimally adjusting the thickness of the plate to the thickness of the transparent thin plate. Is possible.

As described above, in the present invention, the product of the thickness of the transparent body and the refractive index is determined within a desired temperature range in consideration of the secondary change in the product of the thickness of the transparent body and the refractive index with temperature. By setting the minimum temperature to approximately the center of the desired temperature range, the temperature dependence of the wavelength characteristic is made as close to zero as possible. The invention is not limited to the embodiment.

FIG. 10 shows the results regarding the shape of the transparent thin plate obtained by the finite element method in this embodiment. When the temperature rises, the transparent thin plate 10 expands, causing a change in the refractive index. At this time, the plate-shaped body 11 having a larger thermal expansion coefficient than the transparent body thin plate 10 expands more than the transparent body thin plate 10 and pulls the transparent body thin plate 10. Thereby, the thickness of the transparent thin plate 10 is mechanically reduced, and the product of the thickness of the transparent thin plate 10 and the refractive index is kept constant.

However, in practice, the pulling force shown by the arrow in the drawing acts on the transparent thin plate 10, so that the pulling force is applied to the transparent thin plate 10 in the lateral direction around the optical element or the solid etalon. Deviates from the pulling direction. Therefore, in the peripheral portion, a sufficient force to pull the transparent body thin plate 10 cannot be obtained, and the transparent body thin plate 10 becomes thicker than other portions. As described above, since the optical distance (the product of the thickness and the refractive index) is not kept constant in the peripheral portion where the transparent thin plate 10 remains thick, it cannot be used as an optical element.

According to the calculation by the finite element method of the present embodiment, when a transparent etalon having a thickness of 60 μm and a thickness of 500 μm, respectively, of the transparent body thin plate 10 and a 2 mm square solid etalon was formed, It was found that in the range of about 1 mm square, the effect of keeping the optical distance constant was sufficiently obtained.

Therefore, when an optical element as in the present embodiment is used, the central portion of the element may be used. In the above description, it has been described that the wavelength shift behaves as a quadratic function. However, actually, higher-order effects are also reflected. However, since these higher-order effects are very small, there is no problem even if the wavelength shift amount or the product of the refractive index and the thickness of the transparent thin plate behaves as a quadratic function in practical use.
In fact, the quadratic behavior of the wavelength shift amount is a change close to the measurement limit in the current experiment, and it can be considered that there is almost no higher-order effect.

[0046]

As described above, according to the present invention,
A transparent thin plate having a reflection film that reflects light on both sides, and a plate-like body that is made of a material different from the transparent thin plate and that is bonded to both surfaces of the transparent thin plate and has a larger thermal expansion coefficient than the transparent thin plate. The change due to the product of the thickness of the transparent thin plate and the refractive index caused by the temperature change is offset by the deformation of the transparent thin plate due to the change in volume caused by the temperature change of the plate-like body, and the transparent body In a solid etalon in which the product of the thickness and the refractive index is kept approximately invariable, the change in the product of the thickness of the transparent body and the refractive index with temperature is quadratic, and the thickness of the transparent body in the desired temperature range is Since the temperature at which the product of the refractive indices is minimized is substantially at the center of the desired temperature range, it is possible to provide a solid etalon in which the temperature dependence of the wavelength characteristic is almost zero.

Alternatively, according to the present invention, a transparent thin plate that reflects light internally and a thermal expansion coefficient that is bonded to at least one of both surfaces of the transparent thin plate and that is larger than the thermal expansion coefficient of the transparent thin plate And a plate-shaped body having the following formula: wherein the product of the refractive index and the thickness of the transparent body thin plate due to a change in temperature is minimized at a temperature approximately in the middle of the operating temperature range.

According to such a solid etalon or an optical element, a change in characteristics of the element due to a change in temperature can be made almost zero, and an optical element stable against a change in temperature can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

FIG. 2 is a diagram showing a calculation result of a temperature change of a thickness and a refractive index of a transparent thin plate of a solid etalon.

FIG. 3 is a diagram showing a calculation result of a temperature change of an optical distance of a solid etalon.

FIG. 4 is a diagram illustrating a calculation result of a wavelength shift amount due to a temperature change of a solid etalon.

5 is an enlarged view of an axis of a wavelength shift amount in the calculation result of FIG. 4;

FIG. 6 is a diagram showing how the temperature coefficient of the refractive index of a transparent thin plate changes with a change in temperature.

FIG. 7 is a diagram showing a state of a temperature change of a thermal expansion coefficient of a transparent body thin plate and a plate-like body.

FIG. 8 is a diagram showing a wavelength shift amount of a solid etalon with respect to a change in a thickness of a plate-like body.

FIG. 9 is a diagram showing a change in a wavelength shift amount with respect to a temperature change of an actually manufactured solid etalon.

FIG. 10 is a view for explaining the tensile force acting on the transparent thin plate and the shape of the transparent thin plate when the temperature rises in the solid etalon of the present embodiment.

FIG. 11 is a diagram illustrating a conventional optical filter and a problem that these have.

FIG. 12 shows the intensity of transmitted light of a solid etalon with respect to wavelength.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Transparent thin plate 11 Plate-shaped body 12 Reflective film

Claims (15)

[Claims] 1. A transparent thin plate that reflects light internally, and a plate-like body adhered to at least one of both surfaces of the transparent thin plate and having a thermal expansion coefficient larger than a thermal expansion coefficient of the transparent thin plate. The product of the refractive index and the thickness of the transparent thin plate due to the temperature change,
An optical element characterized in that it is minimized at a temperature approximately in the middle of the operating temperature range. 2. The optical element according to claim 1, wherein said plate-like body is bonded to both sides of said transparent thin plate. 3. The optical element according to claim 2, wherein said transparent thin plate has a thickness of about 60 μm, and said plate-like body has a thickness of about 500 μm. 4. The optical element according to claim 1, wherein the light incident on the optical element is incident substantially at the center on one side of the transparent thin plate. 5. The method according to claim 1, wherein the product of the refractive index and the thickness of the transparent thin plate is approximated by a function up to the second order of the temperature, and the minimum point of the change in the temperature of the function is determined by the expected operating temperature range of the optical element. The optical element according to claim 1, wherein the physical property values of the transparent thin plate and the plate-like body are set so as to be approximately the intermediate temperature of the optical element. 6. A transparent thin plate having a thermal expansion coefficient of 5 to 7 (10 ⁻⁶ / ° C.) and a refractive index of 3 to 5 (10 ⁻⁶ / ° C.) in a temperature range of 0 to 85 ° C. The optical element according to claim 1, wherein a thermal expansion coefficient of the plate-like body is 14 to 15 (10 ⁻⁶ / ° C.). 7. The optical element according to claim 1, wherein a material of said transparent thin plate is lanthanum crown glass, and a material of said plate-like body is fluorine crown glass. 8. The method according to claim 8, wherein the transparent substrate is LaC14 (HO).
YA), S-LAL14 (Ohara), N14 (SC
HOTT), and S-
FPL53 (made by OHARA), FCD100 (made by HOYA)
The optical device according to claim 1, wherein any one of the following is used. 9. A temperature at which the product of the thickness of the transparent body and the refractive index is minimized in a desired temperature range by adjusting the thickness of the plate-like body with respect to the thickness of the transparent body thin plate. 2. The optical element according to claim 1, wherein the optical element is located substantially at the center of the temperature range. 10. A transparent thin plate having a reflective film for reflecting light on both sides, and a material which is made of a material different from that of the transparent thin plate, and is thermally expanded more than the transparent thin plate bonded to both surfaces of the transparent thin plate. A change in the product of the thickness of the transparent thin plate and the refractive index caused by a temperature change, and a change in the volume caused by the temperature change of the plate, the transparent thin plate having a large coefficient. Are offset by the deformation of the optical element, and the product of the thickness of the transparent body and the refractive index is kept substantially unchanged. Wherein the temperature at which the product of the thickness of the transparent body and the refractive index is minimized in a desired temperature range is substantially at the center of the desired temperature range. 11. The transparent thin plate has a coefficient of thermal expansion of 5 to 7 (10 ⁻⁶ / ° C.) and a temperature coefficient of refractive index of 3 to 5 (10 ⁻⁶ / ° C.) in a temperature range of 0 to 85 ° C. The optical element according to claim 10, wherein a thermal expansion coefficient of the plate-like body is 14 to 15 (10 ⁻⁶ / ° C.). 12. The optical element according to claim 10, wherein the material of the transparent thin plate is lanthanum crown glass, and the material of the plate is fluorine crown glass. 13. The method according to claim 13, wherein the transparent substrate is LaC14 (H
OYA), S-LAL14 (Ohara), N14 (S
CHOTT) and S
-FPL53 (made by OHARA), FCD100 (HOYA
11. The optical device according to claim 10, wherein any one of the following is used. 14. A temperature at which the product of the thickness of the transparent body and the refractive index is minimized within a desired temperature range by adjusting the thickness of the plate-like body with respect to the thickness of the transparent body thin plate. 11. The temperature range is set substantially at the center.
An optical element according to item 1. 15. The optical element according to claim 10, wherein a thickness of said transparent thin plate is not more than one seventh of a thickness of said plate-like body.