JP4296974B2 - Fabry-Perot tunable filter and multi-channel Fabry-Perot tunable filter - Google Patents

Description

  The present invention relates to a Fabry-Perot tunable filter and a multi-channel Fabry-Perot tunable filter.

  The Fabry-Perot filter includes two flat half mirrors and has a configuration in which main surfaces of the two half mirrors are arranged in parallel to each other. The Fabry-Perot filter is a filter that can select light of an arbitrary wavelength from light of a plurality of wavelengths by using reflection and interference by the two half mirrors. The Fabry-Perot tunable filter is a tunable filter that can select the wavelength of output light by changing the interval between two half mirrors. Various mechanisms for adjusting the distance between the two half mirrors have been proposed.

  Japanese Examined Patent Publication No. 7-86591 discloses an optical fiber type Fabry-Perot resonator in which a piezoelectric element is disposed around an optical fiber, and multilayer reflectors are disposed at both ends of the optical fiber. In this optical fiber type Fabry-Perot resonator, a voltage is applied to the piezoelectric element so that the piezoelectric element is expanded and contracted to change the distance between the multilayer film reflecting mirrors disposed at both ends of the optical fiber. At this time, as the piezoelectric element expands and contracts, the optical fiber disposed inside the piezoelectric element also expands and contracts.

  Japanese Patent Laid-Open No. 5-72035 discloses an optical fiber type Fabry-Perot resonator in which an optical fiber divided into three is disposed inside and this optical fiber is connected to a piezoelectric element through a ferrule. The reflecting mirror is disposed on the end face of the optical fiber. In this optical fiber type Fabry-Perot resonator, the piezoelectric element expands and contracts when a voltage is applied to the piezoelectric element. As the piezoelectric element expands and contracts, the distance between the reflecting mirrors is adjusted by moving the optical fiber fixed through the ferrule.

  Japanese Patent Application Laid-Open No. 2000-162516 discloses a Fabry-Perot resonator including a micromachine having a diaphragm or a piezoelectric element. A micromachine having a diaphragm is formed such that a half mirror is directly disposed on the diaphragm and the distance between the half mirrors is adjusted by driving the diaphragm.

  A micromachine having a piezoelectric element includes a transparent plate on which one half mirror is fixed among half mirrors that are separated from each other and a main body on which the other half mirror is fixed. The transparent plate and the main body are fixed via a piezoelectric element. In this micromachine, the distance between the half mirrors facing each other is determined by the length of the piezoelectric element. As the piezoelectric element expands and contracts, the distance between the two fixing members fixing the two half mirrors is adjusted. This micromachine is formed so that the distance between the half mirrors is adjusted as the distance between the two fixing members is adjusted.

JP-A-5-72035 discloses a Fabry-Perot resonator using an optical fiber core expanded by thermal diffusion in addition to the mechanism for adjusting the distance between the half mirrors. Yes. In the Fabry-Perot resonator, it is disclosed that the connection loss in the gap between the optical fibers is improved, and high finesse and low loss can be realized.
Japanese Patent Publication No.7-86591 JP-A-5-72035 JP 2000-162516 A

  The Fabry-Perot tunable filter disclosed in Patent Document 1 or Patent Document 2 described above has a configuration in which the optical fiber itself is expanded or contracted or moved by a piezoelectric element. For this reason, there has been a problem that the optical fiber is easily deteriorated or broken. That is, there is a problem that the durability and reliability of the device are insufficient.

  In the Fabry-Perot tunable filter disclosed in Patent Document 1 or Patent Document 2, an optical fiber having a half mirror on at least one end face is driven by an actuator connected to the outside of the optical fiber. Therefore, there is a problem that it is difficult to maintain the parallelism between the half mirrors in driving the actuator. Furthermore, in these Fabry-Perot type tunable filters, it is necessary to arrange an actuator made of a piezoelectric element all around the optical fiber in order to maintain parallelism, and complicated processing of hollowing out the piezoelectric material is necessary. There was a problem.

  In the Fabry-Perot tunable filter disclosed in Patent Document 3 described above, a filter having a diaphragm type micromachine has a problem that the driving voltage becomes high because the diaphragm is driven by static electricity. There is also a problem that the switching speed is slow. For those equipped with a piezoelectric element type micromachine, even if the distance between the half mirrors can be changed, the displacement of the distance between the half mirrors cannot be increased, and the wavelength selection range is narrow and impractical. There was a problem.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems. A Fabry-Perot wavelength tunable filter and a multi-channel Fabry-Perot wavelength tunable filter with high device reliability and low optical loss are provided. The purpose is to provide.

In order to achieve the above object, a Fabry-Perot tunable filter according to the present invention includes a first actuator having a first half mirror disposed at an end thereof, and the first half mirror via a space. And a second half mirror disposed so that the main surfaces are parallel to each other. The first actuator is formed of a light-transmitting piezoelectric material, the first actuator has an internal electrode for extending and contracting the first actuator, and the internal electrode is configured to transmit light to the first actuator. The first half mirror is formed so as to pass through the inside of one actuator. By adopting this configuration, it is possible to provide a Fabry-Perot tunable filter with high device reliability and low optical loss.

Upper SL internal electrode includes a plurality of plate electrodes main surface is arranged perpendicular to the direction in which the light travels, the plate electrode is arranged such that each of the main surfaces parallel to each other Has been. The plate electrode will have a opening for passing the light. The opening may be formed such that the area gradually decreases along the direction in which the light travels. By adopting this configuration, the effect of condensing the light can be further increased, and the light loss can be further reduced.

Upper Symbol plate electrodes along the direction in which the light travels, or may be formed so that the distance therebetween decreases gradually. By adopting this configuration, the effect of condensing the light can be further increased, and the light loss can be further reduced.

  Preferably in the above invention, the piezoelectric material includes a ceramic piezoelectric material, and the ceramic piezoelectric material is oriented along a specific crystal axis. More preferably, the piezoelectric material contains PLZT, and the PLZT is oriented so that the degree of orientation is 80% or more along the light traveling direction. By adopting this configuration, the light transmittance of the piezoelectric material can be improved and the light loss can be further reduced.

  Preferably, in the above invention, the second half mirror includes a second actuator disposed at an end, and the second actuator has a main surface of the second half mirror in the light traveling direction. It is formed so that it may translate along. By adopting this configuration, it is possible to adjust the distance between the first half mirror and the second half mirror with a low voltage.

  In order to achieve the above object, a multi-channel Fabry-Perot tunable filter according to the present invention includes a plurality of the Fabry-Perot tunable filters described above, and the plurality of Fabry-Perot tunable filters are integrally held. . By adopting this configuration, it is possible to provide a multi-channel Fabry-Perot tunable filter with high device reliability and low optical loss.

  According to the present invention, it is possible to provide a Fabry-Perot tunable filter and a multi-channel Fabry-Perot tunable filter with high device reliability and low optical loss.

(Embodiment 1)
(Constitution)
A Fabry-Perot tunable filter according to the first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic cross-sectional view of a first Fabry-Perot tunable filter according to the present embodiment. An inner cylinder part 23 is formed inside the outer cylinder part 22. The outer cylinder part 22 and the inner cylinder part 23 are formed in a cylindrical shape, and are arranged coaxially with each other. Inside the inner cylinder portion 23, a half mirror 1 as a first half mirror and a half mirror 2 as a second half mirror are formed. The first actuator includes a piezoelectric ceramic 11, flat plate electrodes 7 and 8, and external electrodes 3 and 4, and the second actuator includes a piezoelectric ceramic 12, flat plate electrodes 9 and 10, and external electrodes 5 and 6.

The piezoelectric ceramic 11 and the piezoelectric ceramic 12 are made of a piezoelectric material. The piezoelectric ceramics 11 and 12 have translucency. The piezoelectric ceramic in the present embodiment is made of PLZT. In particular, PLZT in the present embodiment uses a composition having a composition of (Pb _0.91 La _0.09 ) (Zr _0.53 Ti _0.47 ) O ₃ , but is not limited to this composition. The piezoelectric ceramics 11 and 12 are formed in a columnar shape along the inner wall of the inner cylinder portion 23.

  An optical fiber 13 is connected to one end face of the piezoelectric ceramic 11, and the half mirror 1 is disposed on the other end face of the piezoelectric ceramic 11. Similarly, the optical fiber 14 is connected to one end face of the piezoelectric ceramic 12, and the half mirror 2 is disposed on the other end face of the piezoelectric ceramic 12. The half mirror 1 and the half mirror 2 are formed so that the planar shape is circular. In the present embodiment, the half mirrors 1 and 2 are mirrors formed so that the reflectance is 95 to 99%, and are formed by a method such as vapor deposition.

  The piezoelectric ceramic 11 and the piezoelectric ceramic 12 are arranged so that the main surfaces of the half mirror 1 and the half mirror 2 are parallel to each other. The half mirror 1 and the half mirror 2 are arranged so that the main surfaces are parallel to each other with a high accuracy of about 1 or less, which is several tens of wavelengths of light. The optical fibers 13 and 14, the piezoelectric ceramics 11 and 12, and the half mirrors 1 and 2 are formed so as to be coaxial. The piezoelectric ceramic 11 has flat electrodes 7 and 8 and external electrodes 3 and 4 as internal electrodes, and the piezoelectric ceramic 12 has flat electrodes 9 and 10 and external electrodes 5 and 6 as internal electrodes. Yes. The piezoelectric ceramic 12 has a configuration that is symmetrical to the piezoelectric ceramic 11. The configurations of the plate electrodes 9 and 10 and the external electrodes 5 and 6 with respect to the piezoelectric ceramic 12 are formed to be symmetric with the configurations of the plate electrodes 7 and 8 and the external electrodes 3 and 4 in the piezoelectric ceramic 11.

  The piezoelectric ceramics 11 and 12 are formed to be able to expand and contract in the direction in which light travels when a voltage is applied between the flat plate electrode 7 and the flat plate electrode 8. In FIG. 1, light enters in the direction indicated by arrow 41 and exits in the direction indicated by arrow 42. Piezoelectric ceramics 11 and 12 in the present embodiment are formed to expand and contract along the extending direction of optical fibers 13 and 14. That is, the distance between the main surface of the half mirror 1 and the main surface of the half mirror 2 can be changed while maintaining a parallel state.

  A spacer may be disposed between the piezoelectric ceramic 11 and the piezoelectric ceramic 12.

  FIG. 2 shows an enlarged cross-sectional view of the piezoelectric ceramic 11 portion. The piezoelectric ceramic 11 in the present embodiment is formed in a cylindrical shape by laminating 20 layers of flat plate-like PLZT having a thickness of 10 μm. The laminated piezoelectric ceramics 11 are formed so that a cylindrical shape has a diameter of 2 mm and a thickness of 0.2 mm.

  In addition, the PLZT as the piezoelectric ceramic in the present embodiment is polarized so that it is c-axis oriented with a degree of orientation of 80% or more in a direction parallel to the incident direction of light and domain oriented in the parallel direction. Has been processed. Furthermore, the piezoelectric ceramic in the present embodiment has an electro-optic effect (Pockels effect) and is formed so as to collect light along the direction in which light travels.

  An outer electrode 3 and an outer electrode 4 are formed on the outer periphery of the piezoelectric ceramic 11. A plate electrode 7 as an internal electrode is formed inside the piezoelectric ceramic 11 so as to be electrically connected to the external electrode 3. A plate electrode 8 is formed inside the piezoelectric ceramic 11 so as to be electrically connected to the external electrode 4. The plate electrodes 7 and 8 are formed so as to go inward from the external electrodes 3 and 4. The external electrode 3 and the external electrode 4 are electrically independent from each other. The plate electrode 7 and the plate electrode 8 are electrically independent from each other. The flat plate electrode 7 and the flat plate electrode 8 are formed on the boundary surfaces of the stacked layers of PLZT.

  The plate electrodes 7 and 8 are arranged so that their main surfaces are parallel to each other. An arrow 43 indicates the direction in which light enters, and an arrow 44 indicates the direction in which light is emitted. The plate electrode 7 and the plate electrode 8 are arranged such that the main surface is perpendicular to the direction in which light travels. The plate electrodes 7 and the plate electrodes 8 are alternately arranged along the direction in which light travels, and are formed so that the distance between them is constant.

  FIG. 3 is a cross-sectional view taken along the line III-III in FIG. The external electrode 3 and the external electrode 4 are formed on a part of the outer peripheral portion of the piezoelectric ceramic 11. The plate electrodes 7 and 8 are formed so as to have a circular planar shape, and have protruding portions for electrical connection with the external electrodes 3 and 4. The plate electrodes 7 and 8 have an opening 39 on the central axis of the piezoelectric ceramic 11. The opening 39 is formed so that the planar shape is circular, and the center of this circle is formed so as to be coaxial with the central axis of the piezoelectric ceramic 11. The opening 39 is a portion that is cut out to allow light to pass through. The opening 39 in the present embodiment is formed to have a diameter of about 0.2 mm.

  The plate electrodes 7 and 8 in the present embodiment are formed using Pt as a material. The material of the internal electrode is not particularly limited to Pt, and any material having conductivity may be used. For example, Pd—Ag may be used as a material. Moreover, although the Ag electrode is used for the external electrodes 3 and 4 in this Embodiment, it is not restricted to this form in particular, What is necessary is just conductive.

  In FIG. 2, the openings formed in the plate electrodes 7 and 8 are formed coaxially with each other. That is, the plate electrodes 7 and 8 are formed such that an optical path 35 is formed inside the piezoelectric ceramic 11 and light passes through the inside of the piezoelectric ceramic 11 and reaches the first half mirror.

  FIG. 4 is a schematic cross-sectional view of a second Fabry-Perot tunable filter according to the present embodiment. The outer cylindrical portion 22 and the inner cylindrical portion 23 are formed, and the piezoelectric ceramic 11 is disposed, as in the first Fabry-Perot tunable filter.

  In the second Fabry-Perot tunable filter, the second actuator is not connected to the half mirror 2, and a rod lens 24 is formed instead of the second actuator. No internal electrode or the like is formed inside the rod lens 24 and does not expand or contract. The half mirror 2 is fixed without translation. The rod lens 24 is formed so that light passing through the half mirror 2 is condensed toward the optical fiber 14.

  As described above, the second Fabry-Perot tunable filter is formed so as to adjust the distance between the half mirrors only by the first actuator. Other configurations are the same as those of the first Fabry-Perot tunable filter.

  The actuator in the present invention can be manufactured by a known technique. For example, a ceramic main material is temporarily fired and then processed into a sheet shape. Next, internal electrodes are formed on the surface of the sheet-like ceramic and fired in a laminated state. Next, after the laminated and integrated ceramics are heat-treated and crystallized, further polarization treatment is performed. Finally, it can be manufactured by a method such as attaching an external electrode.

(Action / Effect)
In FIG. 1, light enters through the optical fiber 13 as indicated by an arrow 41. Since the piezoelectric ceramic 11 is made of a translucent piezoelectric material, light passes through the piezoelectric ceramic 11. At this time, as shown in FIGS. 2 and 3, the light enters the half mirror 1 through the opening 39 formed in the plate electrodes 7 and 8.

The incident light is transmitted and interfered by the half mirror 1 and the half mirror 2, and only the selected light is emitted through the piezoelectric ceramic 12 and the optical fiber 14 as indicated by an arrow 42. For example, the incident light includes light having four wavelengths of λ ₁ , λ ₂ , λ ₃ , and λ ₄ , and the emitted light can be only light of λ ₁ .

  In the first Fabry-Perot tunable filter, when changing the wavelength of light to be selected, the distance between the half mirror 1 and the half mirror 2 is changed. In the first Fabry-Perot tunable filter according to this embodiment, the distance between the two half mirrors 1 and 2 is changed by the expansion and contraction of the piezoelectric ceramic 11 and the piezoelectric ceramic 12.

  When a voltage is applied between the external electrode 3 and the external electrode 4, the piezoelectric ceramic 11 is expanded or contracted by generating an electric field inside the piezoelectric material sandwiched between the flat plate electrode 7 and the flat plate electrode 8. To do. The piezoelectric ceramic 11 expands and contracts along the inner wall of the inner cylinder portion 23.

  Thus, by applying a voltage to the external electrode 3 and the external electrode 4, the piezoelectric ceramic 11 itself through which light passes is expanded and contracted in the axial direction. As a result, the half mirror 1 can be translated in the axial direction of the piezoelectric ceramic 11 and the distance between the half mirror 1 and the half mirror 2 can be changed.

  Similarly, in the piezoelectric ceramic 12, by applying a voltage between the external electrode 5 and the external electrode 6, an electric field is generated between the plate electrode 9 and the plate electrode 10, and the piezoelectric ceramic 12 expands and contracts. As a result, the half mirror 2 is translated in the axial direction of the piezoelectric ceramic 12, and the distance between the half mirror 1 and the half mirror 2 can be adjusted. Thus, the Fabry-Perot tunable filter according to the present invention is formed so that light passes through the actuator.

  The first actuator is formed of a translucent piezoelectric material, an internal electrode for expanding and contracting the actuator is formed, and light incident on the internal electrode passes through the inside of the actuator and reaches the first half mirror. By being formed in this way, the optical fiber itself can be configured not to move at all such as expansion and contraction, and the optical fiber can be prevented from being damaged. As a result, a Fabry-Perot tunable filter with high device reliability can be provided. In addition, since incident light passes through a transmissive piezoelectric material, the piezoelectric material can have a lens effect and light loss can be reduced.

  Furthermore, the Fabry-Perot tunable filter according to the present invention can drive the actuator with a low voltage and can increase the switching speed. For example, in a Fabry-Perot type tunable filter including a diaphragm type micromachine disclosed in the aforementioned Japanese Patent Laid-Open No. 2000-162516, a voltage of about 20 to 150 V is required for driving, and the switching speed is about 1 ms. On the other hand, the Fabry-Perot tunable filter in this embodiment can be driven at about 10 V and has a switching speed of about 0.1 ms.

  In the first Fabry-Perot tunable filter in the present embodiment, each piezoelectric ceramic is connected to two half mirrors. That is, a second actuator is formed in addition to the first actuator. The second actuator is formed such that the main surface of the second half mirror moves along the light traveling direction. By adopting this configuration, the distance between the first half mirror and the second half mirror can be adjusted with a low voltage. For example, in the second Fabry-Perot tunable filter shown in FIG. 4, if the same one as the first actuator is formed on the second half mirror side, the same displacement amount can be adjusted with about a half voltage. Can do. Moreover, the displacement amount of the distance between half mirrors can be increased.

  The piezoelectric material in the present embodiment includes a ceramic piezoelectric material, and the ceramic piezoelectric material is oriented along a specific crystal axis. By adopting this configuration, the translucency of the ceramic piezoelectric material can be improved. In the present embodiment, the ceramic piezoelectric material includes PLZT, and the PLZT is formed so as to be oriented in the c-axis along the direction in which light travels. By adopting this configuration, the light transmittance of PLZT itself can be improved. For example, ordinary PLZT is oriented to a maximum of about 75 to 80% by polarization treatment, but if this PLZT is oriented 90% in the c-axis direction, the transmittance of PLZT itself is improved from 88% to 95%. (This translucency is calculated when the PLZT thickness is 0.2 mm, the wavelength of incident light is 1.5 μm, and an antireflection film is formed on the surface). Thus, the light loss can be reduced by improving the light transmittance of PLZT.

  The ceramic piezoelectric material is not particularly limited to PLZT, and may be, for example, PBZT (a composite oxide of Pb, Bi, Zr and Ti having a rhombohedral crystal structure).

  In the second Fabry-Perot tunable filter shown in FIG. 4, an actuator for changing the distance between the half mirrors is formed only on the first half mirror side. That is, in FIG. 4, the half mirror 2 as the second half mirror is fixed to the rod lens 24 and does not move. On the other hand, in the half mirror 1 as the first half mirror, when a voltage is applied between the external electrode 3 and the external electrode 4, the piezoelectric ceramic 11 expands and contracts in the axial direction so as to move in parallel. Is formed.

  Thus, the configuration of the Fabry-Perot tunable filter can be simplified by providing a configuration in which the distance between the half mirrors is adjusted only by the first actuator.

  The performance of the optical filter is determined by finesse (F). In general, finesse is shown as a function of half mirror reflectivity and mirror parallelism. However, since it is more difficult to increase the parallelism between mirrors than to increase the reflectivity of the half mirror, finesse is dominated by the parallelism between mirrors. The Fabry-Perot tunable filter according to the present invention has an effect that the parallelism between the half mirrors is difficult to shift because the optical member itself through which light passes expands and contracts. Therefore, finesse can be improved. Further, since the processing accuracy can be easily increased, finesse can be easily increased. Furthermore, in addition to easy processing accuracy, productivity is improved because assembly is easy. Thus, the Fabry-Perot tunable filter according to the present invention is also suitable for mass production.

  The flat plate electrode as the internal electrode in the present embodiment has a structure having an opening in a circular flat plate, but is not particularly limited to this form, and can apply a voltage between the piezoelectric materials and transmit light to the inside of the piezoelectric material. What is necessary is just to be formed so that it may pass. For example, many rectangular plate electrodes may be formed so as to surround the optical path. Moreover, in this Embodiment, although the piezoelectric material is formed in the column shape, it is not restricted to this form in particular, For example, you may form in the shape of a prism.

(Embodiment 2)
(Constitution)
A Fabry-Perot type tunable filter according to the second embodiment of the present invention will be described with reference to FIGS. The Fabry-Perot type tunable filter according to the present embodiment includes an outer cylinder part and an inner cylinder part, and the piezoelectric ceramic expands and contracts along the inner cylinder part, similar to the Fabry-Perot type tunable filter according to the first embodiment. is there. The Fabry-Perot tunable filter according to the present embodiment is different from the Fabry-Perot tunable filter according to the first embodiment in the configuration of internal electrodes formed inside the piezoelectric ceramic.

  FIG. 5 is a schematic cross-sectional view for explaining a piezoelectric ceramic portion as an actuator in the first Fabry-Perot tunable filter according to the present embodiment.

  In the first Fabry-Perot tunable filter according to the present embodiment, the half mirror 1 and the half mirror 2 are formed so that the main surfaces face each other, and the piezoelectric ceramic 11 is connected to the half mirror 1. A piezoelectric ceramic 12 is connected to the half mirror 2. An optical fiber 13 is connected to the piezoelectric ceramic 11, and an optical fiber 14 is connected to the piezoelectric ceramic 12. Light enters in the direction indicated by arrow 41 and exits in the direction indicated by arrow 42.

  The internal electrode of the first Fabry-Perot tunable filter in the present embodiment includes a flat plate electrode 17 and a flat plate electrode 18 arranged so that the main surface is perpendicular to the direction in which light travels. The plate electrode 17 and the plate electrode 18 are arranged so that their main surfaces are parallel to each other. The plate electrodes 17 and 18 are alternately arranged along the direction in which light travels.

  The plate electrodes 17 and 18 are arranged so that the distance between them is constant. The plate electrodes 17 and 18 are formed so that the cross-sectional area of the optical path passing through the inside of the piezoelectric ceramic 11 gradually decreases. In FIG. 5, the area (size) of the opening formed in the flat plate electrode 17 and the flat plate electrode 18 is formed so as to decrease toward the right side of the drawing.

  FIG. 6 is an explanatory diagram of the optical path in the piezoelectric ceramic 11. The optical path 36 through which light passes through the piezoelectric ceramic 11 is determined by the shape of the opening formed in the internal electrode. In FIG. 6, light enters from one end face of the piezoelectric ceramic 11 as indicated by an arrow 45. The opening of the plate electrode in the present embodiment is formed so that the planar shape is circular, and the size of the opening of the plate electrode is formed so as to gradually decrease along the light traveling direction. Therefore, as shown in FIG. 6, the cross section of the optical path 36 is formed in a circular shape, and the cross sectional area of the optical path 36 becomes smaller as the light travels.

  Similarly, in the piezoelectric ceramic 12, the plate electrode 19 and the plate electrode 20 are formed so that the opening gradually becomes smaller along the direction in which light travels. In the present embodiment, the openings formed in the plate electrodes 17 to 20 are formed so that the maximum diameter is 0.2 mm and the minimum diameter is 0.06 mm. The openings of the plate electrodes 19 and 20 in the present embodiment are formed coaxially with the piezoelectric ceramics 11 and 12 having a cylindrical shape and two half mirrors having a circular planar shape.

  FIG. 7 is an explanatory diagram of the second Fabry-Perot tunable filter according to the present embodiment. FIG. 7 is a schematic cross-sectional view for explaining a piezoelectric ceramic portion as an actuator in the second Fabry-Perot tunable filter according to the present embodiment.

  In the second Fabry-Perot tunable filter, the outer tube portion and the inner tube portion are provided, and two piezoelectric ceramics are disposed in the inner tube portion. The same as the variable filter.

  The second Fabry-Perot tunable filter includes flat plate electrodes 27 to 30 as internal electrodes. The flat plate electrode 27 and the flat plate electrode 28 are formed in the piezoelectric ceramic 11 so that the interval between the flat plate electrode 27 and the flat plate electrode 28 gradually decreases along the direction in which light travels. The plate electrodes 29 and 30 are formed in the piezoelectric ceramic 12 so that the distance between them is gradually reduced along the direction in which light travels. In the present embodiment, the gap between the electrodes is formed to be 20 μm on the wide side and 10 μm on the narrow side.

  The piezoelectric ceramic 11 and the piezoelectric ceramic 12 are formed in a cylindrical shape. The plate electrodes 27 to 30 have openings having a circular planar shape, and are formed so that the centers of the circles of the openings are coaxial with the piezoelectric ceramics 11 and 12. That is, the optical path for light to pass through the inside of the piezoelectric ceramics 11 and 12 is formed to be cylindrical. The half mirror 1 and the half mirror 2 are formed so as to have a circular planar shape, and are arranged so as to be coaxial with the piezoelectric ceramics 11 and 12.

  Since the configuration other than the above is the same as that of the first Fabry-Perot tunable filter in the first embodiment, description thereof will not be repeated here.

(Action / Effect)
The first Fabry-Perot tunable filter according to the present embodiment shown in FIGS. 5 and 6 is formed so that the area of the opening of the plate electrode gradually decreases along the direction in which light travels. Yes. By adopting this configuration, it is possible to condense using the electro-optic effect (Pockels effect) of the translucent piezoelectric ceramic, and to significantly reduce the optical loss. The Pockels effect is an effect that changes the refractive index when an electric field is applied, and is given by the following equation.

n = n ₀ −n ₀ ³ × r ₃₃ × E / 2 (1)
Here, n is the refractive index, n ₀ is the refractive index when the electric field is 0, r ₃₃ is the primary electro-optic coefficient (value determined by the substance), and E is the electric field strength.

  In the first Fabry-Perot tunable filter, the electric field strength inside the piezoelectric ceramic is increased by gradually decreasing the diameter of the opening formed in the flat plate electrode as the internal electrode. For this reason, the refractive index of the piezoelectric ceramic itself is locally reduced, and light can be collected.

  In FIG. 6, light can be condensed as indicated by an arrow 46. As a result, optical loss can be greatly reduced. Similarly, the light passing through the half mirror 2 can be condensed toward the optical fiber 14 inside the piezoelectric ceramic 12, and the optical loss can be greatly reduced. That is, loss due to light diffusion can be made extremely small.

  As described above, the Fabry-Perot tunable filter according to the present invention can add a lens effect peculiar to the internal electrode, and can greatly reduce the optical loss.

  In the second Fabry-Perot tunable filter shown in FIG. 7, the distance between the flat plate electrode 27 and the flat plate electrode 28 is formed so as to gradually decrease along the direction in which light travels. Also by adopting this configuration, the electric field strength inside the piezoelectric ceramic can be increased along the direction in which the light travels, and the light can be condensed by the Pockels effect.

  In FIG. 7, as indicated by an arrow 47, light travels from the portion of the piezoelectric ceramic 11 as the distance between the plate electrode 27 and the plate electrode 28 increases from the portion where the space between the plate electrode 27 and the plate electrode 28 decreases. Gather on the axis. Similarly, in the piezoelectric ceramic 12, the light passing through the half mirror 2 toward the optical fiber 14 is collected. As a result, optical loss can be greatly reduced.

  In order to confirm the effect in the present embodiment, a comparative test was performed between the first Fabry-Perot tunable filter in the first embodiment and the Fabry-Perot tunable filter in the present embodiment. First, a first Fabry-Perot tunable filter according to Embodiment 1 in which light loss due to diffusion is about 45% was prepared. As a result of adopting the configuration of the present embodiment for this tunable filter, the optical loss due to diffusion is 6% in the first Fabry-Perot tunable filter in the present embodiment, and the second Fabry-Perot wavelength. In the variable filter, it could be 13%. Thus, in this embodiment, light loss due to diffusion can be significantly reduced.

  Since other operations and effects are the same as those in the first embodiment, description thereof will not be repeated here.

(Embodiment 3)
(Constitution)
A multi-channel Fabry-Perot tunable filter according to the present invention will be described with reference to FIG. FIG. 8 is a schematic perspective view of the multi-channel Fabry-Perot tunable filter according to the present embodiment.

  The multi-channel Fabro lipper type tunable filter according to the present embodiment includes any one of the Fabry-Perot type tunable filters of the first and second embodiments. In the present embodiment, nine Fabry-Perot type tunable filters are provided, and are fixed integrally by holding bodies 25 and 26.

  The holding body 25 and the holding body 26 are formed in a rectangular parallelepiped shape, and are formed so that their main surfaces face each other in parallel. A first actuator having a half mirror 31 as a first half mirror is fixed to the holder 25, and a first mirror having a half mirror 32 as a second half mirror is formed on the holder 26. 2 actuators and the like are fixed. For example, in the Fabry-Perot tunable filter in FIG. 1, the inner cylindrical portion is divided between the first half mirror and the second half mirror, and each divided inner cylindrical portion is the holding body 25 or the holding body. 26 is provided. The holding body 25 and the holding body 26 are inserted into an outer cylinder portion (not shown) and fixed.

  The half mirror 31 is disposed at the end of the holding body 25 so that the light of the corresponding optical fiber 17 enters. The half mirror 32 has a main surface parallel to the main surface of the corresponding half mirror 31, and is arranged coaxially with the half mirror 31. The optical fiber 18 is arranged so that light from the corresponding half mirror 32 can be emitted.

  The multi-channel Fabry-Perot tunable filter according to the present embodiment is formed such that an actuator is individually formed for each half mirror 31, and each actuator can be driven independently. That is, each Fabry-Perot tunable filter is formed so that the distance between the half mirror 31 and the half mirror 32 can be individually adjusted.

  Other configurations are the same as those in the first and second embodiments, and thus description thereof will not be repeated here.

(Action / Effect)
The multi-channel Fabry-Perot tunable filter according to the present embodiment includes a plurality of Fabry-Perot tunable filters according to the first or second embodiment and is multi-channeled.

  As shown in FIG. 8, the light incident in the direction of the arrow 50 is filtered through one Fabry-Perot tunable filter, and is emitted in the direction of the arrow 51 through the corresponding optical fiber. In addition, as shown by an arrow 48, incident light is filtered through another Fabry-Perot tunable filter different from the one Fabry-Perot tunable filter, and passes through a corresponding optical fiber. As shown in FIG.

  Since the multi-channel Fabry-Perot type tunable filter according to the present embodiment is formed so that each actuator can be individually driven, a large number of light can be individually filtered.

  As described above, the present invention is applied to a multi-channel Fabry-Perot tunable filter by providing a plurality of Fabry-Perot tunable filters and a plurality of the Fabry-Perot tunable filters integrally held. Can be applied. As a result, it is possible to provide a multi-channel Fabry-Perot tunable filter with high device reliability and low optical loss.

  In the present embodiment, the plurality of Fabry-Perot wavelength tunable filters are held by a rectangular parallelepiped holding body. However, the present invention is not limited to this configuration, and a plurality of Fabry-Perot wavelength tunable filters are held individually. That's fine.

  Other operations and effects are the same as those of the Fabry-Perot tunable filter according to the first or second embodiment, and thus description thereof will not be repeated here.

  In addition, the said embodiment disclosed this time is an illustration in all the points, Comprising: It is not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and includes all modifications within the scope and meaning equivalent to the terms of the claims.

3 is a schematic cross-sectional view of a first Fabry-Perot tunable filter according to Embodiment 1. FIG. 3 is an enlarged cross-sectional view of a piezoelectric ceramic portion of the first Fabry-Perot tunable filter according to Embodiment 1. FIG. 3 is an enlarged cross-sectional view of a piezoelectric ceramic of a first Fabry-Perot tunable filter in Embodiment 1. FIG. FIG. 4 is a schematic cross-sectional view of a second Fabry-Perot tunable filter in the first embodiment. 6 is a schematic cross-sectional view of a part of a first Fabry-Perot tunable filter according to Embodiment 2. FIG. 6 is an explanatory diagram of a Pockels effect of a first Fabry-Perot tunable filter according to Embodiment 2. FIG. 6 is a schematic cross-sectional view of a part of a second Fabry-Perot tunable filter in Embodiment 2. FIG. FIG. 10 is a schematic perspective view of a multi-channel Fabry-Perot tunable filter according to Embodiment 3.

Explanation of symbols

  1, 2, 31, 32 Half mirror, 3-6 External electrode, 7-10, 17-20, 27-30 Flat plate electrode, 11, 12 Piezoelectric ceramic, 13, 14, 17, 18 Optical fiber, 22 Outer cylinder , 23 inner cylinder part, 24 rod lens, 25, 26 holder, 35, 36 optical path, 39 opening part, 41-51 arrow.

Claims (7)

A first actuator having a first half mirror disposed at an end;
A second half mirror disposed apart from the first half mirror via a space and disposed such that main surfaces thereof are parallel to each other;
The first actuator is formed of a translucent piezoelectric material,
The first actuator has an internal electrode for expanding and contracting the first actuator,
The internal electrode is formed so that light passes through the inside of the first actuator and reaches the first half mirror ,
The internal electrode includes a plurality of plate electrodes arranged such that the main surface is perpendicular to the direction in which the light travels,
The plate electrodes are arranged such that their main surfaces are parallel to each other,
The flat plate electrode is a Fabry-Perot tunable filter having an opening for allowing the light to pass therethrough . Prior Symbol opening, along the direction in which light travels, the area is formed so as to gradually become smaller, the Fabry-Perot type tunable filter according to claim 1. Before Symbol plate electrodes along the direction in which the light travels, is formed so that the distance therebetween gradually decreases, the Fabry-Perot type tunable filter according to claim 1 or 2. The piezoelectric material includes a ceramic piezoelectric material,
The Fabry-Perot tunable filter according to any one of claims 1 to 3, wherein the ceramic piezoelectric material is oriented along a specific crystal axis. The ceramic piezoelectric material includes PLZT,
5. The Fabry-Perot tunable filter according to claim 4, wherein the PLZT is oriented along a light traveling direction and an orientation degree of 80% or more. The second half mirror includes a second actuator disposed at an end;
6. The Fabry-Perot type wavelength according to claim 1, wherein the second actuator is formed such that a main surface of the second half mirror moves in parallel along a traveling direction of the light. Variable filter. A plurality of Fabry-Perot tunable filters according to any one of claims 1 to 6,
A multi-channel Fabry-Perot tunable filter in which a plurality of the Fabry-Perot tunable filters are integrally held.

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