JPH09258116A - Variable wavelength filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the manufacture of a variable wavelength filter and to reduce the cost by laminating a transparent piezoelectric film, a reflection film and a transparent electrode and constituting an etalon with the oppositely arranged reflection film. SOLUTION: A wavelength filter 1 is constituted so that the reflection film 4 by a dielectric multilayer film is formed on a glass plate 5 as a transparent substrate, and the transparent electrode 4 is formed on the grown reflection film 4, and thereafter, the transparent piezoelectric film 2 is formed on the grown transparent electrode 3, and further, the transparent electrode 3, the reflection film 4 are laminated and formed successively on the transparent piezoelectric film 2, and the transparent electrodes 3 oppositely arranged upward/downward the transparent piezoelectric film 2 is short-circuited through a variable voltage device 6. The formed wavelength filter 1 constitutes the etalon with the oppositely arranged reflection films 4, and controls the resonator length D of the etalon with the film thickness change of the transparent piezoelectric film 2 by an applied voltage between the transparent electrodes 3. Then, incident light L1 repeats reflection between the reflection films 4 after it is made incident in the etalon, and only a resonant wavelength corresponding to the resonator length D is emitted as transmission light L2 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tunable filter based on the principle of Fabry-Perot resonator.

[0002]

2. Description of the Related Art As a filter of this type, there is a wavelength tunable filter 100 shown in FIG. This tunable filter 100 is based on the principle of Fabry-Perot resonator,
A piezo element is used to control the resonator length of the etalon.

That is, the wavelength tunable filter 100 comprises transparent glass substrates 101, 101 facing each other, and a reflecting film 1 formed on each facing surface of the transparent glass substrates 101, 101.
02 and a piezo element 103 interposed in the transparent glass substrate 101, 101.
Reference numeral 2 constitutes an etalon, and the resonator length D of this etalon is controlled by driving the piezo element 103.

According to the wavelength tunable filter 100, the incident light L ₁ is repeatedly reflected between the two reflecting films 102, 102 to obtain the transmitted light L ₂ having the resonance wavelength λ. The wavelength λ of the transmitted light L ₂ at this time is represented by the equation (1).

Λ = 2 nD / m (1) In the equation (1), n is the optical medium 10 between the reflection films 102 and 102.
The refractive index of 4, m is a natural number, and nD is the optical resonator length.

[0006]

However, in the conventional wavelength tunable filter 100, the transparent glass substrate 1 facing each other is used.
It is necessary to provide 01 and 101 with a high degree of parallelism, and since this work is performed manually, there is a problem that manufacturing is difficult and eventually cost is increased.

In addition, in the conventional tunable filter 100, it is difficult to make the piezo element 103 thin, and the resonator length D and the optical resonator length nD become large. Therefore, in order to obtain the necessary resonance wavelength λ. Increases the natural number m in equation (1). Therefore, the slope of the characteristic straight line showing the optical resonator length nD dependence of the wavelength λ of the transmitted light shown in FIG. 6 becomes small, and the conventional tunable filter 100 exhibits the characteristic straight line a, b, or c, and There is also a problem that the selection width becomes narrow and the performance is deteriorated.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide a wavelength tunable filter which is easy to manufacture, can be reduced in cost, and has a wide wavelength selection range and improved performance. It is in.

[0009]

In order to achieve the above-mentioned object, the invention according to claim 1 is a wavelength tunable filter comprising a Fabry-Perot resonator, which is laminated on both sides of a transparent piezoelectric film and arranged to face each other. Having a reflective film and a transparent electrode,
It is characterized in that the etalon is composed of the reflection films arranged to face each other, and the resonator length of the etalon is controlled by the change in film thickness of the transparent piezoelectric film depending on the voltage applied to the transparent electrodes arranged to face the etalon. There is.

Therefore, in the invention according to claim 1, the film thickness of the transparent piezoelectric film changes in proportion to the applied voltage, and the resonator length of the etalon and the optical resonator length change due to the change of the film thickness.
The wavelength of the transmitted light can be selected within this range in which the cavity length changes.

In the invention according to claim 1, since the transparent piezoelectric film, the reflective film, and the transparent electrode are laminated, and the etalon is composed of the reflective films arranged to face each other, the etalon is formed by the growth of each layer. It is formed with a high precision etalon structure, and because it does not require manual assembly, it is easy to manufacture and suitable for mass production.

Further, according to the first aspect of the invention, since the etalon is composed of a laminated body of films, the resonator length of the etalon can be designed to be small, which widens the wavelength selection width of the etalon.

According to a second aspect of the invention, there is provided the wavelength tunable filter according to the first aspect, wherein the transparent piezoelectric film, the reflective film, and the transparent electrode are laminated on a single transparent substrate. It is characterized by being.

Therefore, in the second aspect of the invention, the transparent piezoelectric film, the reflective film, and the transparent electrode are provided on one transparent substrate.
A desired etalon can be easily manufactured by sequentially forming layers in a desired order.

According to a third aspect of the invention, there is provided the wavelength tunable filter according to the second aspect, wherein the transparent electrode is formed with a connecting portion extending from the laminated portion onto the transparent substrate. It is characterized by

Therefore, in the third aspect of the invention, since the connecting portion of the transparent electrode is provided outside the laminated portion, the electrode can be easily taken out.

Further, the invention according to claim 4 is the same as claim 1.
4. The wavelength tunable filter according to any one of items 1 to 3, wherein a protective film is formed on an exposed portion of an outermost layer of a laminated portion including the transparent piezoelectric film, the reflective film, and the transparent electrode.

Therefore, in the invention described in claim 4, by covering the exposed portion with the protective film, the handling becomes easy and the resistance to external environmental change is improved.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention.
1 shows a wavelength tunable filter 1 including a Fabry-Perot resonator. The wavelength tunable filter 1 has a reflective film 4 and a transparent electrode 3 which are laminated on both sides of a transparent piezoelectric film 2 and face each other, and the reflective films 4 and 4 face each other to form an etalon. The resonator length D is controlled by the change in the film thickness of the transparent piezoelectric film 2 due to the applied voltage between the transparent electrodes 3 and 3 arranged to face each other.

Specifically, the wavelength filter 1 includes a reflection film 4 formed of a dielectric multilayer film on a glass plate 5 as a transparent substrate.
Then, a transparent electrode 3 made of, for example, an indium tin oxide film (ITO film) is formed on the grown reflective film 4, and then, for example, a barium titanate film (BaTiO ₃ film) is formed on the grown transparent electrode 3. ) Is formed on the transparent piezoelectric film 2, and the same transparent electrode 3 and the reflective film 4 are sequentially formed on the grown transparent piezoelectric film 2 and are arranged above and below the transparent piezoelectric film 2 so as to face each other. Transparent electrodes 3,3
Are short-circuited via the variable voltage device 6.

At this time, the wavelength filter 1 is preferably formed by forming a protective film 7 made of, for example, a silicon dioxide film (SiO ₂ film) on the reflective film 4 located in the outermost layer (uppermost layer in the figure). .

The wavelength filter 1 thus formed is
The reflection films 4 and 4 arranged to face each other constitute an etalon, and the resonator length D of the etalon is controlled by the change in film thickness of the transparent piezoelectric film 2 due to the applied voltage between the transparent electrodes 3 and 3. . Then, the incident light L ₁ is incident on the etalon and then repeatedly reflected between the reflection films 4 and 4, and only the resonance wavelength λ corresponding to the resonator length D is emitted as the transmitted light L ₂ .

The resonator length D changes as the film thickness of the transparent piezoelectric film 2 expands and contracts when a voltage is applied between the transparent electrodes 3 and 3. The dependency of the resonator length D on the applied voltage at this time is shown in FIG.
As shown in, the amount of change in the resonator length D and the applied voltage are in direct proportion. That is, the resonator length D is lengthened by applying a voltage, and the lengthening ratio (change amount) at this time
Increases linearly as the applied voltage increases.

Further, the wavelength λ of the transmitted light L ₂ is calculated by the above equation.
(1) Represented by λ = 2nD / m. However, n is n = D ₁ n ₁ + 2D ₂ when the film thickness and refractive index of the transparent piezoelectric film 2 are D ₁ and n _1, and the film thickness and refractive index of the transparent electrode 3 are D ₂ and n ₂ , respectively. It becomes n ₂ .

The wavelength tunable filter 1 has the formula (1)
Thus, the optical resonator length dependence of the wavelength λ of the transmitted light L ₂ shown in FIG. 6 is obtained. At this time, since the wavelength tunable filter 1 is configured as a laminated body of films, the resonator length D can be designed to be small. For example, the thickness of the transparent piezoelectric film is 1μ
m, the thickness of the transparent electrode is 1 μm, and the thickness of the reflective film is 2 μm.

Therefore, the wavelength tunable filter 1 has the same resonance wavelength λ as the conventional product by reducing the resonator length D.
The value of the natural number m in equation (1) for obtaining can be reduced. That is, in the tunable filter 1, for example, the characteristic of m ≦ 3 in FIG. 6 is obtained and the wavelength selection width A, B, or C is obtained, and the optical resonator length nD is set to the same length d.
If only changed, the wavelength selection width becomes wider than that of the conventional product having the characteristics a, b, or c.

For example, when the thickness of each layer of the laminated body is designed as described above and the transparent piezoelectric film 2 is a BaTiO ₃ film, the resonator length D is ± 20 n for an applied voltage of ± 100 V.
The optical resonator length nD is ± 40 nm (= d) because it expands and contracts by m (see FIG. 2) and the refractive index of the BaTiO ₃ film is about 2 and 3.
(See FIG. 6) As a result, the resonance wavelength λ can be selected within a range of about ± 50 nm (= A (see FIG. 6)) when the value of the natural number m in the formula (1) is 2.

As described above, the wavelength tunable filter 1 has a wide wavelength selection range and improved performance.

The wavelength tunable filter 1 includes a transparent piezoelectric film 2, a reflective film 4, and a transparent electrode 3 on one glass plate 5.
Since the etalon is composed of the reflective films 4 and 4 that are laminated and opposed to each other, the etalon is formed to have a highly precise etalon structure by forming the grown film of each layer, and it is necessary to assemble by hand. Since it is not present, it is easy to manufacture, suitable for mass production, and eventually cost reduction can be achieved.

Further, in this wavelength tunable filter 1, since the exposed portion of the outermost reflection film 4 is covered with the protective film 7, it is easy to handle and has resistance to external environmental changes due to water, acid, alkali and the like. It has been improved and can be suitably mounted.

FIG. 3 shows a tunable filter 10 as a second embodiment of the present invention.

This wavelength tunable filter 10 includes a transparent electrode 3
Is formed to have a connecting portion 3a extending from the laminated portion onto the glass plate 5, and the laminated portion has the same configuration as the wavelength tunable filter 1 described above.

Therefore, the wavelength tunable filter 10 not only exhibits the same function and effect as the wavelength tunable filter 1, but also
The electrode of the transparent electrode 3 can be easily taken out, and the manufacturing is further facilitated.

FIG. 4 shows a wavelength tunable filter 20 as a third embodiment of the present invention.

The wavelength tunable filter 20 is different from the wavelength tunable filter 1 in the laminated structure of the laminated portion, and the other structures are the same.

That is, in the laminated portion of the wavelength tunable filter 20, the reflection films 4 and 4 are formed on both sides of the transparent piezoelectric film 2 in the center, and the transparent electrodes 3 and 3 are formed further outside the reflection films 4 and 4. Further, one of the transparent electrodes 3 and 3 is formed on the glass plate 5, and the protective film 7 is formed on the other transparent electrode 3 to constitute the entire structure.

The wavelength λ of the transmitted light L ₂ of the wavelength tunable filter 20 is represented by the equation (1) λ = 2nD / m, where n is the refractive index of the transparent piezoelectric film 2.

Further, FIG. 5 shows a wavelength tunable filter 30 as a fourth embodiment of the present invention.

This wavelength tunable filter 30 is a variation example corresponding to the wavelength tunable filter 10 of the above-mentioned wavelength tunable filter 20, in which the transparent electrode 3 has a connecting portion 3a extending from the laminated portion onto the glass plate 5. Is formed.

The wavelength tunable filters 20 and 30 are
The function and effect corresponding to the wavelength tunable filters 1 and 10 described above are produced, respectively.

[0042]

As described in detail above, the present invention has the following effects.

That is, according to the first aspect of the invention, since the transparent piezoelectric film, the reflective film, and the transparent electrode are laminated, and the etalon is composed of the reflective films which are arranged facing each other, the etalon is grown in each layer. The etalon is formed with a high-precision etalon structure by film formation, and because it does not require manual assembly, it is easy to manufacture and suitable for mass production. The cavity length can be designed to be small, which widens the wavelength selection width of the etalon, which makes it easy to manufacture and reduce the cost, and also has a wide wavelength selection width and improved performance. Can be provided.

According to the second aspect of the invention, the transparent piezoelectric film, the reflective film, and the transparent electrode are provided on one transparent substrate.
A desired etalon can be manufactured by sequentially laminating and forming in accordance with a desired order, and the manufacturing is further facilitated.

Further, according to the third aspect of the invention, since the connecting portion of the transparent electrode is provided outside the laminated portion, the electrode can be easily taken out and the manufacturing is further facilitated.

Further, according to the invention described in claim 4, by covering the exposed portion with the protective film, the handling becomes easy and the resistance to the external environment change is improved. A filter can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view of a wavelength tunable filter according to a first embodiment of the present invention.

FIG. 2 is a graph showing the applied voltage dependence of the amount of change in the resonator length of the wavelength tunable filter of FIG.

FIG. 3 is a sectional view of a wavelength tunable filter as a second embodiment of the present invention.

FIG. 4 is a sectional view of a wavelength tunable filter as a third embodiment of the present invention.

FIG. 5 is a sectional view of a wavelength tunable filter according to a fourth embodiment of the present invention.

FIG. 6 is a graph showing the optical resonator length dependence of the wavelength of transmitted light that has passed through the wavelength tunable filter.

FIG. 7 is a conceptual explanatory view of a conventional wavelength tunable filter.

[Explanation of symbols]

 1, 10, 20, 30 Wavelength tunable filter 2 Transparent piezoelectric film 3 Transparent electrode 3a Connection part (transparent electrode) 4 Reflective film 5 Glass plate (transparent substrate) 7 Protective film D Resonator length

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[Procedure amendment]

[Submission date] February 14, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction contents]

For example, when the thickness of each layer of the laminated body is designed as described above and the transparent piezoelectric film 2 is a BaTiO ₃ film, the resonator length D is ± 20 n for an applied voltage of ± 100 V.
The optical resonator length nD is ± 40 nm (= d) because the BaTiO ₃ film has a refractive index of about 2.3.
(See FIG. 6) As a result, the resonance wavelength λ can be selected within a range of about ± 50 nm (= A (see FIG. 6)) when the value of the natural number m in the formula (1) is 2.

Claims (4)

[Claims] 1. A wavelength tunable filter comprising a Fabry-Perot resonator, comprising a reflective film and a transparent electrode laminated on both sides of a transparent piezoelectric film so as to be opposed to each other, and the etalon is made up of the opposed reflective film. And the resonator length of the etalon is controlled by changing the film thickness of the transparent piezoelectric film depending on the voltage applied to the transparent electrodes arranged opposite to each other. 2. The variable wavelength filter according to claim 1, wherein the transparent piezoelectric film, the reflective film, and the transparent electrode are laminated and formed on a single transparent substrate. filter. 3. The wavelength tunable filter according to claim 2, wherein the transparent electrode is formed with a connecting portion extending from the laminated portion onto the transparent substrate. Variable filter. 4. The wavelength tunable filter according to claim 1, wherein a protective film is formed on an exposed portion of an outermost layer of a laminated portion including the transparent piezoelectric film, a reflective film, and a transparent electrode. A tunable filter characterized in that