JPH01101421A - Variable interference device - Google Patents

Abstract

PURPOSE:To facilitate manufacture for relaxing the setting accuracy of components by displacing the reflection body of a Fabri Perot interferometer by a bimorph type piezoelectric element. CONSTITUTION:Reflecting films 4 are provided to light-transmissive substrates 1 and 2. The substrate 2 is fixed to a holder 6 and the substrate 1 faces the substrate 2 across spacers 3 at a specific interval. One end of the bimorph type piezoelectric element 5 is fixed to the holder 6 and the other end contacts the substrate 1. When a voltage is applied to the bimorph element to applies a force to the substrate 1, the substrate 1 curves to vary the distance between the reflecting films 4 and 4. Then the transmission wavelength of the interference meter can be varied. The displacement quantity of the bimorph element 5 is hundreds of mum, so the setting accuracy of respective components can be relaxed. The force applied to the substrate 1 is controlled and the bimorph element is used as a driving element to facilitate the manufacture of the interferometer.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a compact spectroscopic device using a Fapley-Perot interferometer.

Conventional technology> Conventionally, many spectroscopic devices using diffraction gratings have been used. This method obtains the necessary monochromatic light by mechanically rotating a diffraction grating, and while it provides high resolution, it requires high precision in positioning each optical element and also increases the size. It has the following problems. On the other hand, as another type of spectroscopic device, there is a Fapley-Bello interference device that utilizes the longitudinal effect of a piezoelectric element (the direction of the electric field and the direction of expansion and contraction are the same). The sixth factor shows this configuration. This spectroscopic device controls the distance between two opposing reflecting mirrors by expanding and contracting a longitudinal effect type piezoelectric element, and obtains the necessary monochromatic light from changes in interference characteristics.

In this structure, the interval between the two reflecting mirrors must be controlled extremely accurately, and it is not easy to control the two longitudinal effect type piezoelectric elements. However, due to black expansion of the holder due to changes in ambient temperature, the spacing between the reflectors may vary. The conventional structure described above has a major problem in the accuracy and stability of the interval control of the reflecting mirrors.

<Objective of the Invention> The present invention is based on the principle of the Fapley-Perot interferometer, and provides a compact variable interference device that can control the optical path length of the interferometer with high precision and stability and has a spectroscopic function. 0 <Example> Hereinafter, an example of the present invention will be described in detail based on the drawings. FIG. 1 is a perspective view of a variable spectrometer used to explain an embodiment of the present invention. Translucent substrates 1.2 are opposed to each other with a spacer 3 interposed therebetween at a predetermined distance. Glass, translucent ceramics, or polymer resin is used for the translucent substrate 1.2, which has a hollow structure and has a reflective film 4 formed on its opposing inner surface. The reflective film 4 is made of a metal film or a single-layer or multi-layer dielectric film. The spacer 3 and the reflective film 4 are manufactured by a thin film forming method such as a vapor deposition method, a sputtering method, or a CVD method.

Here, the basic principle of the variable interference device will be explained. Consider a case where light is incident perpendicularly to the substrate surface and there is no phase jump in the light at the reflective film 4. When the distance between the reflective films 4 is dl and the refractive index of the medium between them is kn, the Fapley-Perot interference transmittance T(λ) is expressed by the following formula and is maximized for each wavelength λm.0nd λm=−(m=L L 3...) Here, consider the case where m=1. λ at this time
1 scanning wavelength range from λa to λb (however, λb (2 people a)
)! Then, the distance d between the reflective films 4 is λa/2n≦d
When ≦λb/2n is satisfied, 0, that is, d through which light with the center wavelength λ1=2nd is transmitted, is λa/2
If you change it arbitrarily from n to λb/2n, λa
It is possible to transmit only light of an arbitrary wavelength in the wavelength range from λb to λb. For example, the scanning wavelength range t-400 to 7
If it is 50 nm, the distance d between the four reflective films is 200 nm to 8
If controlled within 75 nm, the refractive index is 0. In this case, since the space between the reflective films 4 is hollow, the refractive index is about 1. Strictly speaking, λa
Since light with a short wavelength is also transmitted, a filter that removes light with a wavelength of λa or less may be used, or a light receiving element (not shown) that is insensitive to light with a wavelength of λa or less may be used.

Here, the overall configuration will be explained. The translucent substrate 2 is fixed to a holder 6, and the bimorph 5 is placed approximately in the center of the translucent substrate 1, and the bimorph 5 is placed in contact with the translucent substrate 1 lightly, or with a very small gap between them, allowing the bimorph to move. The zero ray, which is fixed to the holder 6 at the end of the bimorph 5, passes approximately through the center of the transparent substrate 1.2 so that the bimorph 5 is not obstructed. It is necessary to provide an optical system (not shown) for this purpose. The optical system is a combination of optical fibers, lenses, light-receiving elements, etc.The bimorph 5 is constructed by cutting a notch in it so as not to obstruct the optical axis. This is a piezoelectric element that has the property of bending when a voltage is applied, by bonding two types of piezoelectric materials with different expansion and contraction directions using the electric field direction and the direction of expansion and contraction of the material being perpendicular to each other. Piezoelectric materials include ceramic materials such as barium titanate, lead titanate, lead zirconate titanate, and lead metaniobate, and polymer materials such as polyvinylidene fluoride. 0 In this case, a piezoelectric material 10 sandwiches an elastic body 11 (usually a metal plate serving as an electrode) to form a sandwich structure.0 This is then supported at one end by a support 12. The free length (effective length) of the 0 bimorph, which indicates the amount of displacement and the generated force, is 21. The width is W,
If the thickness is t and the applied voltage is V, then when the thickness of the elastic plate is sufficiently thin compared to the piezoelectric material, the amount of displacement U under no load. is expressed by the following equation.

U0=6d81(T)・v Here, dll is a piezoelectric constant, which is a constant specific to the piezoelectric material 0
Also, the generated force when the amount of displacement is 0 is F=7d3. Yl,” (1- to 3.”)-7-V
It is indicated by. Here, Y118 is the elastic constant in a certain crystal direction, and K3 is the electromechanical energy coupling coefficient 0.
Typical numerical values for lead zirconate titanate are: d =
-190X10-12 m/V.

E Y,, =6X 10 N/rri'', K3. =0
．． 3. Sufficient generated force can be obtained by appropriately selecting the shape of In the embodiment, the tip of the bimorph 5 is in contact with the transparent substrate 1, and when a voltage is applied to the bimorph, a generated force is generated, which acts on the transparent substrate 1. In response to this, the transparent substrate l is curved, and the distance d between the reflective films changes. In other words, the distance d between the reflective films can be changed by the voltage applied to the bimorph, and the interference of the interference device Characteristics can be controlled.

Figure 3 shows an example of the operation of this embodiment. When the voltage applied to the 0 bimorph is low, the load applied to the transparent substrate l is small and the distance d between the reflective films is large, so the center wavelength is at a long wavelength. As the voltage applied to the 0-bimorph through which light passes increases, the load applied to the transparent substrate 1 increases and the distance d between the reflective films decreases, so the center wavelength of the transmitted light shifts to the shorter wavelength side. 2 and 1 in the direction of the applied voltage
．． The direction of curvature is different; it can curve either upwardly or downwardly. Therefore, if the bimorph 5 and the transparent substrate 1 are bonded together and the force used to pull up the transparent substrate 1 is also used, the bimorph can be made even more compact.

The big advantage of the bimorph is that it has a large amount of displacement.

In order to curve the transparent substrate l, a very small amount of displacement of about half the transmitted wavelength is required.In this respect, it is recommended to use a laminated piezoelectric element (the amount of displacement is about several μm) that utilizes the longitudinal effect. However, this means that the positioning of the laminated piezoelectric element and the interference device requires precision on the order of μm. The amount of displacement of the bimorph is on the order of several hundred micrometers, which greatly reduces the accuracy of the positioning of each component. The interferometer is constructed in one piece, the optical path length of the interferometer is controlled by controlling the force applied to the substrate from the outside, and a bimorph is used as the driving element. It has become easier to create a variable interferometer.

FIG. 4 shows another embodiment according to the present invention. The bimorph is composed of a piezoelectric material 10 and an elastic body 11, and the piezoelectric material 10 sandwiches the elastic body 11, forming a -body structure.
Bimorphs are supported at both ends. The amount of displacement is reduced compared to the case of one end support. However, by supporting the bimorph with an elastic body and providing the elastic body with a curved part, the decrease in displacement is reduced. The advantage of supporting both ends is that the mounting accuracy of the bimorph can be ensured.The operating principle is the same as the embodiment shown in Figure 1.Another embodiment is shown in Figure 5.Bimorph 5I is a translucent substrate. It is directly fixed to the entire surface or a part of it. The force generated in response to the voltage applied to the bimorph acts on the entire transparent substrate 1, deforming the transparent substrate 1. The bimorph 5 has a hole through which the light beam passes. In this embodiment, the variable interference device can be made compact, and since the bimorph and the variable interference device are integrated, the bimorph, which was required for the holder 6 in the embodiments of FIGS. 1 and 4, can be made compact. According to the present invention, since the optical path length of the integrated Fabry-Perot interferometer is controlled by externally modifying the drive system, It can be controlled with high precision and stability, and the setting accuracy of each part can be significantly relaxed without using complicated mechanical parts.Also, since almost no current flows through the bimorph, it operates with very little power consumption. It is possible to easily create a small variable interference device with spectroscopic function.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a variable interference device showing an embodiment of the present invention. FIG. 2 is an explanatory diagram for explaining the operation of the bimorph. FIG. 3 is a characteristic diagram showing an example of the operation of the variable interference device shown in FIG. 1. FIG. 4 is a sectional view showing another embodiment of the present invention. FIG. 5 is a sectional view showing still another embodiment of the present invention. FIG. 6 is a sectional view of a conventional variable interference device. 1.2... Transparent substrate 3... Spacer 4...
Reflection - Membrane 5... Bimorph 6... Holder 10... Piezoelectric material 11... Elastic body 12...
Support 20...Longitudinal effect type piezoelectric element 2! ...Electrode 22...Holder representative Patent attorney Takeshi Sugiyama (1 other person) Whistle 1 Figure 2F55 4 (X) 9 600 70
0i 1% (nm) N3 diagram

Claims (1)

[Claims] 1. A Fabry-Perot interferometer having a cavity surrounded by two opposing reflectors and a support for supporting the reflectors, in which at least one of the reflectors is bimorph A variable interference device characterized by controlling interference characteristics by deforming it using a type piezoelectric element. 2. The variable interference device according to claim 1, wherein the bimorph piezoelectric element comprises a piezoelectric body and an elastic body, and the elastic body is curved in the thickness direction. 3. The variable interference device according to claim 1, wherein the bimorph piezoelectric element is partially or entirely coupled to at least one of the reflectors.