JP2013200300A - Micro diameter three-axis electric field sensor and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in which reduction in dimensions of an optical sensor is desired, but the reduction therein confronts pains-taking difficulty in terms of machining for allowing for exhibition of desired performance.SOLUTION: The micro diameter three-axis electric field sensor contains: a detection element; two pieces of prisms; a wavelength plate; three pieces of optical fiber collimators; and a holding tool. The detection element is a hexahedron of an electro-optical effect crystal. Each of two pieces of prisms has one surface of each orthogonal surface optically bonded to an adjacent surface of the detection element. To one surface of the wavelength plate, an adjacent surface to the adjacent surfaces bonded to the prism of the detection element is optically bonded and other orthogonal surfaces of the prism are optically bonded, and to other surface of the wavelength plate, the holding tool holding the optical fiber collimators is optically bonded.

Description

  The present invention relates to a micro-diameter three-axis electric field sensor, which has good reproducibility and enables stable production.

  The direction of the electric field at which the electro-optic effect electric field sensor has the maximum sensitivity is determined by the crystal plane orientation of the electro-optic effect crystal, the crystal optical axis of the quartz plate used as the wavelength plate, and the direction of linearly polarized light incident from the optical fiber. It is possible to design whether to have maximum sensitivity in the traveling direction (z direction) of light incident on the electro-optic effect crystal or maximum sensitivity in two orthogonal directions (x direction, y direction) (see FIG. 11). .

  When this is used, the electric field strength in the three directions x, y, and z can be measured with one crystal chip. Since the electric field is a vector quantity, if the components in the three axial directions of x, y, and z orthogonal to each other can be measured, the electric field strength at that point can be accurately known by vector synthesis. Moreover, the spatial resolution to measure is never small.

  The electro-optic effect crystal used for detection belongs to a group III-V compound semiconductor such as GaAs, for example, has a crystal structure called a zinc blende structure, and has a cleavage property on six surfaces orthogonal to each other. Therefore, it is considered that a relatively beautiful surface can be provided to form a cube or a rectangular parallelepiped. The same applies to II-VI group compound semiconductors such as ZnTe (zinc telluride) and CdTe (cadmium telluride).

If the electric field sensor chip can be assembled in the form shown in FIGS. 9 and 10, a triaxial electric field sensor in which bundled fibers are combined in one direction can be realized. In this minute diameter triaxial electric field sensor, wave plates 3d, 3e, and 3f are optically bonded to three surfaces that are different in direction of the detection element 1 and are orthogonal to each other. The prisms 2e and 2f are optically bonded to the two wave plates 3e and 3f so that the orthogonal surfaces are in the same direction. The optical fiber collimators 4e, 4d, 4f are optically bonded to the orthogonal surfaces of the wave plate 3d and the prisms 2e, 2f. The light propagating through the optical fiber collimator 4d is incident on the upper surface of the detection element 1 through the wave plate 3d. The light propagating through the optical fiber collimator 4e enters the side surface of the detection element 1 through the prism 2e and the wave plate 3e. The light propagating through the optical fiber collimator 4f enters the side surface of the detection element 1 through the prism 2f and the wave plate 3f. That is, since the light propagating through the different optical fiber collimators 4d, 4e, and 4f has different directions and is incident on three orthogonal surfaces, it is possible to simultaneously measure the triaxial electric field.
However, the micro-diameter three-axis electric field sensor in this case is very difficult to manufacture because it has a large number of parts and many adhesion points.

JP 2007-57324 A JP2011-238863A

The invention described in Patent Document 1 has the following description in paragraph 0022.
The optical sensor 5 includes a ferrule 51 that guides the polarization maintaining fiber 4 to a predetermined position, a collimator lens 52 that shapes light emitted from the polarization maintaining fiber 4 guided by the ferrule 51 into parallel light, and a collimator lens 52. A Faraday rotator 53 that rotates the light that has passed through, and an electro-optic crystal that changes the polarization state of the light according to the electric field to be measured. The light emitted from the Faraday rotator 53 is incident thereon, and the dielectric reflection film 541 on the opposite side is incident. And an electro-optic crystal 54 that is reflected by and emitted to the Faraday rotator 53. The electro-optic crystal 54 does not have optical rotation, and a dielectric reflection film 542 is formed on the Faraday rotator 53 side.
Patent Document 1 discloses the structure of a small-diameter electric field sensor that detects an electric field in a unidirectional direction. Even if this description and FIG. 2 are referred to, the configuration of the optical sensor 5 is detected by the prism proposed in the present invention. The light incident structure from the side surface of the element is not seen, and it is unclear how much improvement has been made for miniaturization.

  Patent Document 2 was previously published by the applicant of the present patent application and relates to a light modulation degree control circuit for detecting an electro-optic effect electromagnetic field by an optical heterodyne method. A small diameter triaxial electric field sensor is desired.

(Claim 1) A small-diameter triaxial electric field sensor according to the present invention includes a detection element, two prisms, a wave plate, three optical fiber collimators, and a holding jig. The detection element is a hexahedron of an optical crystal having an electro-optic effect. In each of the two prisms, one of the orthogonal surfaces is optically bonded to an adjacent surface of the detection element. One surface of the wave plate is optically bonded to an adjacent surface to which the prism of the detection element is bonded, and another orthogonal surface of the prism is optically bonded to the other surface of the wave plate. The holding jig holding the fiber collimator is optically bonded to the surface.

As an optical crystal having an electro-optic effect, for example, a compound semiconductor crystal such as ZnTe crystal, CdTe, and GaAs, LiNiO ₃ (lithium niobate), and an organic compound optical crystal called DAST can be employed.

  The two prisms can be made of, for example, quartz glass, and are optically bonded to the detection element with an adhesive such as an ultraviolet curable resin. The wave plate uses a birefringent crystal such as quartz to generate a phase difference. The shape is, for example, a rectangular plate, and the detection element and the two prisms are optically bonded to one surface with an adhesive such as an ultraviolet curable resin.

  The holding jig is made of, for example, glass, and is optically bonded to the surface of the wave plate opposite to the surface to which the detection element or the like is bonded while holding the three optical fiber collimators.

The light that has propagated through the three optical fiber collimators passes through the wave plate and enters the detection element, but the different lights enter from three orthogonal surfaces in different directions and face each other. Since the light is reflected on the surface and returned to the optical fiber collimator, the electric field strength in three orthogonal axes can be measured. That is, the light propagating through each of the different optical fiber collimators is transmitted through the wave plate, and one of them directly enters one of the adjacent surfaces of the detection element (the surface to which the wave plate is bonded) and remains. The two are refracted by the prism and are incident on the adjacent surfaces of the detection element which are orthogonal to each other.
Since the three optical fiber collimators can be bundled in parallel, the sensor itself is very small.

(Claim 2) The detection element may be one obtained by cutting out a specified plane orientation with respect to a specific orientation of a ZnTe crystal called a crystal face and mirror-polishing six faces.
In this way, the detection element can be easily manufactured, and a high quality element can be provided.

(Claim 3) The optical fiber collimator preferably has a GRIN lens fused to the tip of the polarization maintaining fiber. The polarization maintaining fiber is also called a birefringent fiber, and is designed to intentionally have a large birefringence so that random fluctuations of the birefringence do not significantly change the polarization of light. Bowtie fibers, elliptical jacket fibers, and the like can be used.
A GRIN lens (Graded Index lens) is an optical element that functions as a lens by having a refractive index distribution from the center to the radial direction, and the refractive index distribution is preferably a square distribution or a distribution close to a square distribution.
The holding jig is made of glass and has insertion holes for inserting the three optical fiber collimators in parallel and separately, and the polarization maintaining fiber is aligned with the polarization direction with an optical adhesive. It may be fitted via.
If it carries out like this, relative positioning of each polarization-maintaining fiber is easy, and the attachment with respect to a wavelength plate can also be performed easily.

(Claim 4) The length of each side of the detection element may be 0.5 to 1.5 mm.
In this way, the detection element is sufficiently small and the electric field can be easily measured.

(Claim 5) The area and the shape of one surface of the wave plate may be equal to the sum and the shape of the bonding area of the detection element and the two prisms bonded to the one surface.
In this way, the sensor can be made sufficiently small and the optical action is good.

(Claim 6) One prism of the two prisms is a small prism whose orthogonal side length is equal to the length of one side of the detection element, and the other prism has a length of the orthogonal side. A large prism that is twice the length of the orthogonal side of the one prism may be used.
In this way, the detection element and one prism can be aligned and bonded to the orthogonal plane of the other prism, and light emitted from one of the three optical fiber collimators can pass through the prism without passing through the prism. The light emitted from the other one from the adjacent surface is reflected by the other prism, and the light emitted from the remaining one from the surface adjacent to the adjacent surface of the detection element is reflected by one prism and detected. The light can enter the adjacent surface of the element from the adjacent surface, and accurate measurement can be performed by maintaining the detection element, the wave plate, the two prisms, and the polarization maintaining fiber in a predetermined positional relationship.

(Claim 7) A reflective coating may be applied to the surface in contact with the space of the detection element and the reflective surfaces of the two prisms.
In this case, by applying the reflective coating, a large amount of light returns from the detection element to the optical fiber collimator, and measurement can be performed accurately and stably.

(8) In the manufacturing method of the micro-diameter triaxial electric field sensor according to the present invention, after the detection element and the two prisms are optically bonded to one surface of the wave plate, the holding jig of the wave plate is bonded. Reflective coating is applied to parts other than the surface to be covered.
Masking must be performed on the surface not provided with the reflective coating. However, in the case of a small optical component, the masking operation is very difficult and the cost is increased. If the detection element and the two prisms are optically bonded to the one surface of the wave plate, masking may be performed only on the opposite surface of the wave plate to which the detection element or the like is bonded. Will be very easy.
Further, the reflective coating may be performed after bonding the detection element, the two prisms, and the holding jig to the wave plate.

(Claim 1) According to the micro-diameter triaxial electric field sensor of the present invention, it is possible to easily form an electric field sensor maintaining a predetermined positional relationship, and sufficiently cope with fine measurement.

  According to the second aspect, the detection element can be easily manufactured, and a high-quality detection element can be provided.

  According to the third aspect, the relative positioning of each polarization-maintaining fiber is easy, and the attachment to the wave plate can be facilitated.

  According to the fourth aspect, the detection element is sufficiently small, and the measurement of the electric field is facilitated.

  According to the fifth aspect, the sensor can be made sufficiently small, and the optical action is also good.

  According to the sixth aspect of the present invention, the detection element and the one prism can be aligned and bonded to the orthogonal plane of the other prism, and the detection element, the wave plate, the two prisms, and the polarization maintaining fiber are kept in a predetermined positional relationship. This enables accurate measurement.

  According to the seventh aspect, by applying the reflective coating, a large amount of light returns from the detection element to the optical fiber collimator, and the measurement can be performed accurately and stably.

  According to the method of manufacturing the micro-diameter triaxial electric field sensor of the present invention according to the eighth aspect, the masking operation of the portion where the coating is not applied becomes very simple.

It is a perspective view shown in the state which decomposed | disassembled the specific example of the micro diameter triaxial electric field sensor concerning this invention. It is a perspective view of a state where a detection element and two prisms are optically bonded. It is a perspective view of a state where a detection element, two prisms, and a wave plate are optically bonded. It is a perspective view of the holding jig holding the optical fiber collimator. It is a partially cutaway side view of a specific example of a small diameter triaxial electric field sensor. It is a front-end | tip part perspective view of a micro diameter triaxial electric field sensor specific example. It is a side view of an optical fiber collimator. It is a partially cutaway side view of a state where a glass capillary is attached to an optical fiber collimator. It is a perspective view shown in the state which decomposed | disassembled another specific example of the micro diameter triaxial electric field sensor of a comparative example. FIG. 10 is a perspective view of the sensor in FIG. 9 during assembly. It is explanatory drawing of the detection axis (direction) of the electric field with respect to a detection element.

  1 to 6, 1 is a detection element, 2a is one prism, 2b is the other prism, 3 is a wave plate, 4a, 4b, 4c are optical fiber collimators, and 5 is a holding jig. The detection element 1 is a hexahedron of zinc telluride (ZnTe) crystal.

  The detection element 1 was a cube, and was cut out in a specified plane orientation with respect to a specific orientation of a ZnTe crystal called a crystal plane, and six surfaces were mirror-polished.

  The other prism 2b is composed of two orthogonal surfaces 2b1 and 2b2 which are orthogonal to each other, a reflecting surface 21b which is an inclined surface, and two side surfaces which form a triangle, and the orthogonal surfaces 2b1 and 2b2 and the reflecting surface 21b each have an angle of 45 °. It has become. One prism 2a has a shape obtained by dividing the other prism 2b into two in the longitudinal direction. When one side of the detection element 1 is 1 mm, the orthogonal surfaces 2b1 and 2b2 are 2 mm × 1 mm each, and the reflecting surface 21b is 2 mm × about 1.4 mm. The length of the orthogonal side L2 formed by intersecting the orthogonal surfaces 2b1 and 2b2 is 2 mm.

  Similarly to the above, when one side of the detection element is 1 mm, one surface 3a of the wave plate 3 is a square having a side of 2 mm, and the detection element 1 and the two prisms 2a and 2b are optically bonded. Therefore, the area and shape of one surface 3a of the wave plate 3 are equal to the sum and shape of the bonding areas of the detection element 1 and the two prisms 2a and 2b bonded to the one surface.

The light propagating through the different optical fiber collimators 4a, 4b, and 4c is appropriately polarized by the wave plate 3, and one of the lights 4c is incident on the adjacent surface 1c of the detection element 1 as it is, One piece 4b enters the adjacent surface 1b of the detection element 1 through the other prism 2b, and the remaining one piece 4a enters the adjacent surface 1a of the detection element 1 through one prism 2a.
That is, since the light propagating through the different optical fiber collimators 4a, 4b, and 4c has different directions and is incident on three orthogonal surfaces, it is possible to simultaneously measure three-axis electric fields.

(Claim 2) The detection element 1 is cut out in a specified plane orientation with respect to a specific orientation of a ZnTe crystal called a crystal plane, and six faces are mirror-polished.
In this case, the detection element 1 can be easily manufactured and a high-quality one can be provided.

(Claim 3) As shown in FIG. 7, the optical fiber collimator is obtained by peeling off the outer coating 44 and the inner coating 43 at the tip of the polarization maintaining fiber 41 and fusing the GRIN lens 42 to the fiber end face. The outer diameter of the fiber and GRIN lens is 125 μm.
As shown in FIG. 8, a cylindrical glass capillary 52 is attached and fixed to the portion where the coating of the polarization maintaining fiber 41 is removed for reinforcement. Further, a square glass capillary 51 is mounted thereon and fixed with an adhesive 6. As will be described later, the glass capillary 51 is a component of the holder 5, has a square cross section with a side of 0.5 to 1.5 mm, and has an insertion hole with a diameter of 360 μm in the longitudinal direction.
Next, as shown in FIG. 4, the four glass capillaries 51 are bonded together to form the holding jig 5. The holding jig 5 has four holes. Of these, only three optical fiber collimators 4a, 4b, and 4c are inserted, so three insertion holes for the holding jig are formed. It only has to be. Three optical fiber collimators 4a, 4b, and 4c are respectively fixed to the three insertion holes 5a, 5b, and 5c of the holding jig 5 by optical bonding with their polarization directions aligned in advance. As shown in FIGS. 5 and 6, the holding jig 5 is optically bonded to the other surface 3 b of the wave plate 3.
In this case, the relative positioning of the optical fiber collimators 4a, 4b, and 4c is easy, and the optical fiber collimators 4a, 4b, and 4c can be easily attached to the wave plate 3, and the detection element 1, the two prisms 2a and 2b, the wave plate 3, and the optical fiber collimator. 4a, 4b, 4c can be configured in a predetermined positional relationship, and accurate measurement is possible.

(Claim 4) The length of each side of the detection element 1 is 0.5 to 1.5 mm.
In this case, the detection element 1 can be made small, and the electric field can be easily measured.

(Claim 5) The area and shape of one surface 3a of the wave plate 3 are equal to the sum and shape of the bonding area of the detection element 1 bonded to the one surface 3a and the two prisms 2a and 2b.
In this case, the sensor can be made small and the optical action is also good.

(Claim 6) Of the two prisms, one prism 2a is a small prism whose orthogonal side length L1 is equal to the length L1 of one side of the detection element 1, and the other prism 2b is orthogonal. The side length L2 is a large prism that is twice the length L1 of the orthogonal side of one prism 2a.
In this case, the detection element 1 and the small prism 2b can be aligned and bonded to the orthogonal surface 2b1 of the other prism 2b. In this way, the light guided to the optical fiber collimator 4c is reflected as it is from the adjacent surface 1c of the detection element 1 and the light guided to the optical fiber collimator 4b is reflected by the other prism 2b. The optical fiber collimator 4a is reflected from one of the prisms 2a from the adjacent surface 1b and enters the detecting device 1 from the adjacent surface 1a of the detecting device 1, so that the detecting device, the wave plate, the two prisms, the light The fiber collimator can be configured in a predetermined positional relationship, and accurate measurement is possible.

(Claim 7) A reflective coating C is applied to the surface in contact with the space of the detection element 1 and the reflective surfaces 21a and 21b of the two prisms 2a and 2b. As shown in FIG. 3, after the detection element 1 and the two prisms 2a and 2b are bonded to one surface 3a of the wave plate 3, a reflective coating C can be applied.
In this case, by applying the reflective coating C, a large amount of light returns from the detection element 1 to the optical fiber collimator, and measurement can be performed accurately and stably.

(Claim 8) After the detection element 1 and the two prisms 2a and 2b are optically bonded to one surface 3a of the wave plate 3, the light is reflected on a portion other than the other surface 3b to which the holding jig 5 of the wave plate 3 is bonded. Coating C is applied. The reflection coating C may be applied to the surface in contact with the space of the detection element 1 and the reflection surfaces 21a and 21b of the two prisms, but all the portions other than the portion to which the holding jig 5 of the wave plate 3 is bonded. It may be coated on the part.
Therefore, it is sufficient to perform masking only on the other surface 3b to which the holding jig 5 of the wave plate 3 is bonded, and the masking operation becomes extremely easy.
Also, as shown in FIG. 6, the reflective coating can be applied after the assembly of the tip of the sensor is completed. In this case, coating can be performed with little masking.

DESCRIPTION OF SYMBOLS 1 Detection element 2a One prism 21a Reflecting surface 2a1 Orthogonal surface 2a2 Orthogonal surface 2b Other prism 21b Reflecting surface 2b1 Orthogonal surface 2b2 Orthogonal surface 2e Prism 2f Prism 3 Wave plate 3d Wave plate 3e Wave plate 3f Wave plate 4 Optical fiber collimator 4a Optical fiber collimator 4b Optical fiber collimator 4c Optical fiber collimator 4d Optical fiber collimator 4e Optical fiber collimator 4f Optical fiber collimator 41 Polarization maintaining fiber 42 GRIN lens 43 Inner coating 44 Outer coating 5 Holding jig 51 Glass capillary 52 Glass capillary 6 Adhesive 7 Linearly polarized light

Claims (8)

Including a detection element, two prisms, a wave plate, three optical fiber collimators and a holding jig,
The detection element is a hexahedron of an electro-optic effect crystal,
In each of the two prisms, one of the orthogonal surfaces is optically bonded to an adjacent surface of the detection element,
The one surface of the wave plate is optically bonded to the adjacent surface to which the prism of the detection element is bonded, and the other orthogonal surface of the prism is optically bonded,
A micro-diameter three-axis electric field sensor, wherein the holding jig holding the optical fiber collimator is optically bonded to the other surface of the wave plate.   2. The micro-diameter triaxial electric field sensor according to claim 1, wherein the detection element is cut out in a specified plane orientation with respect to a specific orientation of a ZnTe crystal called a crystal plane, and six surfaces are mirror-polished. The optical fiber collimator has a GRIN lens fused to the tip of a polarization maintaining fiber,
The holding jig is made of glass and includes insertion holes for inserting the three optical fiber collimators in parallel and separately, and the polarization maintaining fiber is aligned with the polarization direction so that an optical adhesive is attached to the insertion hole. The micro-diameter three-axis electric field sensor according to claim 1 or 2, wherein the sensor is fitted through a gap.
  The micro-diameter triaxial electric field sensor according to any one of claims 1 to 3, wherein a length of each side of the detection element is about 0.5 to 1.5 mm.   The area and shape of the one surface of the wave plate are equal to the sum and shape of the bonding area of the detection element and the two prisms bonded to the one surface. 3. A micro-diameter triaxial electric field sensor described in 1.   One prism of the two prisms is a small prism whose orthogonal side length is equal to the length of one side of the detection element, and the other prism has a length of the orthogonal side of the one prism. The micro-diameter triaxial electric field sensor according to any one of claims 1 to 5, which is a large prism that is twice the length of the orthogonal side.   The micro-diameter triaxial electric field sensor according to any one of claims 1 to 6, wherein a reflective coating is applied to a surface in contact with the space of the detection element and a reflective surface of the two prisms.   2. The optical element is bonded to one surface of the wave plate, and then a reflective coating is applied to a portion of the wave plate other than the surface to which the holding jig is bonded. 8. A manufacturing method of the micro-diameter triaxial electric field sensor according to 7.

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