JPH0248640A - Fabry-perot type optical filter - Google Patents

Abstract

PURPOSE:To miniaturize and stabilize the above filter by changing the refractive index of a parallel flat plate of a dielectric material which is integrally formed via transparent electrodes. CONSTITUTION:High-reflectivity mirrors 2, 5 are provided on both surfaces of the parallel flat plate 1 made of the dielectric material which is an electrooptic effect crystal and the transparent electrodes 4, 5 are provided on the outer side thereof, by which the optical filter is constituted. The index ellipsoid of the flat plate 1 changes and the refractive index of the flat plate 1 changes according to an electric field when the electric field is impressed to the flat plate by applying a voltage to the electrodes 4, 5. The Fabry-Perot type optical filter which is miniaturized and is stabilized is obtd. by this constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a Fabry-Perot optical filter that can vary the wavelength of transmission.

<Prior Art> One example of a conventional 7-application-Perot optical filter is one in which mirrors are formed on two opposing surfaces of a parallel flat glass plate. In this type of Fabry-Perot optical filter,
The medium between the mirrors is glass, and the refractive index and spacing between the mirrors cannot be changed by electrical control.
It is difficult to vary its transmission wavelength.

Another example of a conventional Fabry-Perot optical filter is to arrange two mirrors parallel to each other on a common surface, and then change the distance between the mirrors using a screw or piezo fine adjustment device. , which can vary the passing wavelength. Although this type of Fabry-Perot optical filter can vary the wavelength it passes, since the mirror is a separate component, its alignment is easily lost due to the influence of vibrations or Since the dimensions are relatively large, there is a problem in that it cannot be constructed in a compact size.

<Problem to be solved by the invention> In the first example of the conventional Fabry-Perot type optical filter,
Since the intermirror medium in which the two mirrors are integrally formed is glass, it is difficult to electrically control and change the refractive index and spacing between the mirrors, and it is not possible to vary the passing wavelength.

In the second example of the conventional Fabry-Perot optical filter, two individual mirrors are arranged facing each other in parallel, and the position of one of the mirrors is moved by a fine adjustment device to adjust the distance between the mirrors. It changes the wavelength of the light passing through it.

However, the seven alignments of the mirror are easily distorted by the influence of temperature, vibration, etc., and the fine movement device is relatively large in size, so it cannot be made compact.

As described above, in the conventional 7-application Perot optical filter, there are problems in that the passing wavelength cannot be made variable or the device becomes large and unstable.

The present invention is based on the above-mentioned conventional technology, and is based on a Fabry vessel that is small, stable, and whose passing wavelength can be varied by electrical control.
The purpose of the present invention is to provide a shaped optical filter.

Means for Solving the Problems> The configuration of the present invention to achieve the above object is to configure a resonant circuit by arranging two high reflectivity mirrors facing each other in parallel, and to In a Fabry-Perot optical filter, which passes only the light with a wavelength that satisfies the resonance condition out of the light that is almost perpendicularly incident on either side, and blocks the light with the remaining wavelengths, when an electric field is applied, the refractive index changes. The present invention is characterized in that a dielectric parallel plate having a changing electro-optical effect is inserted between the mirrors, and transparent electrodes are formed on opposing surfaces of the dielectric parallel plate.

Effect> The resonance conditions of a resonant circuit constituted by two high-reflectance mirrors change depending on the refractive index of the medium between the mirrors. Therefore, if a current is passed between the transparent electrodes and an electric field is applied to the dielectric parallel plates to change the refractive index, the resonance conditions change and the wavelength transmitted also changes.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

An embodiment of the present invention is shown in the drawings. As shown in the figure, high reflectance mirrors 2 and 3 are formed on both sides of a dielectric parallel plate having an electro-optic effect (hereinafter referred to as an electro-optic effect crystal) 1, and transparent electrodes 4 and 5 are further formed on the outside thereof. It is formed. The electro-optic effect crystal 1 has an electro-optic effect in which a refractive index ellipsoid changes and its refractive index changes when an electric field is applied. For example, lithium niobate (LiNbO3)
and lithium tantalate (LiTa03) are known. The transparent electrodes 4 and 5 are made of tin-doped indium oxide (
Sn-doped In, 03) is -numerical. Furthermore, mirror 2
．． When 3 is a metal thin film miller, this can be used as an electrode and the transparent electrodes 4 and 5 can be omitted. As the mirrors 2 and 3, in addition to metal thin film mirrors, a dielectric multilayer mirror formed by laminating a plurality of dielectric films having different refractive indexes may also be used. A dielectric multilayer mirror is practically more advantageous in terms of reflectance and light absorption characteristics.

Resonance conditions for the Fabry-Perot optical filter with the above configuration:
Yo, the wavelength λ in a vacuum. When the light enters the Fabry-Perot optical filter almost perpendicularly and makes one round trip between the mirrors 2 and 3, the phase change is equal to an integer (m) times 2π. In other words, the wavelength of light that satisfies the resonance conditions. 2° is expressed by the following equation.

λ = 2nd/m where n is the refractive index of the electro-optic effect crystal, and d is the thickness of the electro-optic effect crystal.

Therefore, by applying an electric field E between the transparent electrodes 4 and 5 and changing the refractive index n of the electro-optic effect crystal, the resonance condition changes and the passing wavelength λ is changed. , , will change.

Here, to explain how the refractive index n of the electro-optic effect crystal 1 changes depending on the electric field E applied between the transparent electrodes 4 and 5, in the Fabry-Bello type optical filter of this embodiment, the optical The vertical electrode configuration has the same direction as the traveling direction of E and the direction of application of the electric field E, and the polarization state of the incident light is not numerically determined to be a special state.
Consideration is given so that the characteristics of the Fabry-Bello type optical filter do not depend on the polarization state of the incident light. When such conditions are given, the electro-optic effect crystal 1 has a tetragonal system.
and <411111>, trigonal <3> and <3
11II1>, hexagonal crystal system 6> and 61i> are suitable, and the mirrors 2, 3 and the transparent electrode 81i4.5 are formed.Three faces of the electro-optic effect crystal 1 are suitable. Here, the parentheses 〈 〉 indicate the crystal point group. In these cases, the refractive index n of the electro-optic effect crystal 1 changes by the following change Δn due to the electric field E applied between the transparent electrodes 4° and 50°.

Δn = no γ13E/2 Here, no represents the refractive index for ordinary rays, a, and 3 represent the Pockels coefficient. Therefore, the passing wavelength λ. Pl is the electric field E applied between the transparent electrodes 4°5 as shown in the formula below.
can be varied by controlling.

λ. ,,=2 (n0+n03713E/2)d/m
<Effects of the Invention> As described above in detail based on the examples, in the present invention, an electric field is applied to a dielectric parallel plate to change its refractive index by the electro-optic effect. Therefore, it has become possible to electrically control the passing wavelength by changing the resonance conditions of a resonant circuit composed of two mirrors.

Furthermore, moving the mirror eliminates the need for a fine movement device, resulting in a smaller size and higher stability.

[Brief explanation of the drawing]

The drawing is a structural diagram of a Fabry-Bello optical filter according to an embodiment of the present invention. In the drawings, 1 is an electro-optic effect crystal, 2.3 is a mirror 4.5 is a transparent electrode. Patent applicant: Agent of Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] A resonant circuit is constructed by arranging two high-reflectance mirrors facing each other in parallel, and only the light with a wavelength that satisfies the resonance condition among the light that is almost perpendicularly incident on one of the mirrors is generated. In a Fabry-Perot optical filter that allows light of the remaining wavelengths to pass through, a dielectric parallel plate having an electro-optical effect in which the refractive index changes when an electric field is applied is inserted between the mirrors, and the dielectric A Fabry-Perot optical filter characterized in that transparent electrodes are formed on opposite surfaces of body-parallel plates.