WO2016121880A1 - Temperature compensating element and light sensor system - Google Patents

Abstract

The purpose of the present invention is to provide a temperature compensating element and a light sensor system whereby temperature compensation can be effectively performed. The temperature compensating element according to an embodiment of the present invention is provided with a stress imparting part. The stress imparting part applies an anisotropic stress to an optical fiber in accordance with a temperature change in an external device optically connected to the optical fiber.

Description

Temperature compensation element and optical sensor system

Embodiments described herein relate generally to a temperature compensation element and an optical sensor system.

An optical sensor that measures a magnetic field or current using light such as a laser has temperature characteristics due to temperature dependency of a sensor fiber or the like, and an error occurs in a measurement result depending on temperature.
Therefore, a method has been proposed in which a temperature compensation element is used to apply a stress corresponding to the temperature to the sensor fiber to control the temperature characteristic of the sensor fiber to cancel the temperature characteristic of the optical sensor itself.
However, conventionally, the temperature compensation element has a problem that it cannot effectively apply non-uniform stress to the sensor fiber.

JP 2010-96761 A JP 2005-517961 A JP 2002-529709 A JP 2012-68107 A

An object of the present invention is to provide a temperature compensation element and an optical sensor system that can effectively perform temperature compensation in order to solve the above-described problems.

According to the embodiment, the temperature compensation element includes a stress applying portion. The stress applying unit applies anisotropic stress to the optical fiber according to a temperature change of an external device optically connected to the optical fiber.

FIG. 1 is a cross-sectional view in the light propagation direction of the temperature compensation element according to the first embodiment. 2A is a cross-sectional view of an example of a polarization maintaining fiber along line AA in FIG. FIG. 2B is a cross-sectional view of another example of the polarization maintaining fiber along the line AA in FIG. FIG. 3A is a cross-sectional view of an example of a temperature compensation element along line BB in FIG. FIG. 3B is a cross-sectional view of another example of the temperature compensation element taken along line BB in FIG. FIG. 4 is a cross-sectional view in the light propagation direction of the temperature compensation element according to the second embodiment. FIG. 5A is a cross-sectional view of an example of a temperature compensation element along line AA in FIG. FIG. 5B is a cross-sectional view of another example of the temperature compensation element along line AA in FIG. FIG. 6 is a cross-sectional view of an example of a temperature compensation element according to the third embodiment. FIG. 7A is a cross-sectional view of an example of a temperature compensation element according to the fourth embodiment. FIG. 7B is a cross-sectional view of another example of the temperature compensation element according to the fourth embodiment. FIG. 8 is a diagram illustrating a configuration example of the temperature compensation element according to the fifth embodiment. FIG. 9 is a diagram illustrating a configuration example of a Sagnac interference type optical sensor system according to the sixth embodiment. FIG. 10 is a diagram illustrating an example of the temperature characteristics of the sensor unit and the temperature characteristics of the temperature compensation element according to the sixth embodiment. FIG. 11 is a diagram illustrating an example of temperature characteristics of the Sagnac interference type optical sensor system according to the sixth embodiment.

Hereinafter, a temperature compensation element and an optical sensor system according to an embodiment will be described in detail with reference to the drawings.
(First embodiment)
The temperature compensation element according to the first embodiment will be described. FIG. 1 is a cross-sectional view in the light propagation direction of the temperature compensation element according to the first embodiment. As shown in FIG. 1, the temperature compensation element 1 includes a polarization maintaining fiber 2, a protective layer 3 that covers the polarization maintaining fiber 2, a stress applying layer 4 that applies stress to the polarization maintaining fiber 2, and the like. .

The polarization maintaining fiber 2 is covered with a protective layer 3 on the outer periphery. The protective layer 3 covers not only the periphery of the temperature compensation element 1 but also the entire polarization plane holding fiber 2 extending from both ends of the temperature compensation element 1. The protective layer 3 has a function of protecting the polarization maintaining fiber 2 from the external environment. For example, the protective layer 3 prevents light from the outside from entering the inside of the polarization maintaining fiber 2 and prevents noise from being generated in the light passing through the polarization maintaining fiber 2. Further, the protective layer 3 prevents moisture, dust, and the like from adhering to the polarization-maintaining fiber 2 and prevents the polarization-maintaining fiber 2 from corroding. The protective layer 3 is made of UV curable resin or acrylic resin, and has a thickness of about 30 to 40 μm. The material and structure of the protective layer 3 are not limited to a specific configuration.

The stress applying layer (stress applying portion) 4 is composed of the metal thin film layer 5 and covers a part of the polarization-maintaining fiber 2. The polarization-maintaining fiber 2 is not covered with the protective layer 3 in a predetermined section in the light propagation direction. The metal thin film layer 5 covers the polarization maintaining fiber 2 in a section not covered by the protective layer 3. Further, as shown in FIG. 1, the metal thin film layer 5 may also cover a portion covered with the protective layer 3 beyond the section.

Most of the metal thin film layer 5 is in direct contact with the polarization-maintaining fiber 2. Thereby, the metal thin film layer 5 can apply stress to the polarization plane holding fiber 2 without interposing the protective layer 3, and can effectively apply stress to the polarization plane holding fiber 2. In addition, since most of the metal thin film layer 5 is in direct contact with the polarization-maintaining fiber 2, the metal thin-film layer 5 can apply a finer stress to the polarization-maintaining fiber 2, and can be more accurately biased. Stress can be applied to the wavefront holding fiber 2. The stress applied to the polarization plane holding fiber 2 will be described in detail later.

Next, the polarization plane maintaining fiber 2 will be described.
FIG. 2 shows cross-sectional views of two examples of polarization maintaining fiber 2 along line AA in FIG.
As shown in FIG. 2, the polarization-maintaining fiber 2 covers the periphery of the core 11, the polarization-plane holding portions 12 a and 12 b adjacent to the core 11, and the core 11 and the polarization-plane holding portions 12 a and b at the center. It has a clad 13 and the like. Further, as described above, the polarization-maintaining fiber 2 is covered with the protective layer 3.

The polarization-maintaining fiber 2 is a stress-applied polarization-maintaining fiber such as a panda-type polarization-maintaining fiber (FIG. 2A) and a bow-tie polarization-maintaining fiber (FIG. 2B). As shown in FIG. 2A, in the panda-type polarization plane holding fiber, the polarization plane holding section 12 that applies stress to the core 11 has a circular cross section. Further, as shown in FIG. 2B, in the bow-tie polarization plane holding fiber, the polarization plane holding section 12 has a trapezoidal cross section. The polarization plane holding unit 12 of the bow tie type polarization plane holding fiber is installed such that the trapezoidal short side faces the core 11. Which form the polarization-maintaining fiber 2 takes is determined by the use and installation location of the polarization-maintaining fiber 2.

The core 11 (optical fiber) is a light passage section through which light such as a laser generated from a sensor or light such as a laser generated from a signal processor passes. The core 11 is located at the center of the polarization-maintaining fiber 2. The core 11 has two birefringence axes (in FIG. 2, a Y axis (Fast Axis) and an X axis (Slow Axis)). Since the core 11 has two birefringence axes, two linearly polarized lights can pass through the core 11 while being constrained by the respective birefringence axes.

The polarization plane holding unit 12 a is installed inside the polarization plane holding fiber 2 in parallel with the core 11. The polarization plane holding unit 12a is installed at a predetermined distance from the core 11. Further, the polarization plane holding unit 12b is installed inside the polarization plane holding fiber 2 in parallel with the core 11 on the opposite side of the polarization plane holding unit 12a. The polarization plane holding portions 12 a and b have a function of adjusting stress generated in the core 11. For example, the polarization plane holding units 12a and 12b apply stress to the core 11, and hold the polarization plane of linearly polarized light that passes through the core 11 while being constrained by the birefringence axis.

The clad 13 is formed in a cylindrical shape so as to fix the core 11 and the polarization plane holding portions 12a and 12b at predetermined positions. The clad 13 may apply stress to the core 11 similarly to the polarization plane holding portions 12a and 12b.
The structure of the polarization-maintaining fiber 2 is the same in any part of the polarization-maintaining fiber 2.
The configuration of the polarization-maintaining fiber 2 is not limited to a specific configuration.

Next, the stress applying layer 4 will be described.
The stress applying layer 4 has a function of applying stress to a part of the polarization-maintaining fiber 2. The stress applying layer 4 expands or contracts according to the temperature change of the stress applying layer 4 itself, and applies a stress to the polarization plane holding fiber 2. That is, the stress applying layer 4 applies a stress corresponding to the temperature to the polarization plane holding fiber 2. When the stress applying layer 4 applies stress to the polarization-maintaining fiber 2, stress is applied to the core 11 installed in the polarization-maintaining fiber 2. When stress is applied to the core 11, the core 11 is distorted, and the optical characteristics such as the extinction ratio or crosstalk of the core 11 change. As the optical characteristics of the core 11 change, the phase of propagating light passing through the core 11 changes.

On the other hand, an optical sensor that measures a magnetic field or an electric current has a temperature characteristic, and a phase change occurs in light propagating through the sensor according to a temperature change, resulting in an error in the measurement result. For example, when the phase of light generated from the optical sensor advances as the temperature rises, an error occurs in the measurement result as the phase advances.

The stress applying layer 4 covering a part of the polarization-maintaining fiber 2 extending from the optical sensor changes the optical characteristics of the polarization-maintaining fiber 2 so as to cancel out an error caused by the optical sensor.
For example, in the above example, the stress applying layer 4 applies stress to the polarization-maintaining fiber 2 so that an optical characteristic is generated such that the phase of propagating light passing through the core 11 is delayed as the temperature rises. Thereby, the phase change caused by the temperature change of the optical sensor and the phase change caused by the temperature change of the temperature compensation element 1 cancel each other, and the optical sensor measures the object without being affected by the ambient temperature. Can do.

FIG. 3 shows cross-sectional views of two examples of temperature compensating elements along line BB in FIG.
As shown in FIG. 3, the metal thin film layer 5 constituting the stress applying layer 4 covers the polarization plane holding fiber 2.
The stress applying layer 4 is configured so that the stress applied to the polarization-maintaining fiber 2 is not uniformly generated on the outer periphery of the polarization-maintaining fiber 2 (is generated anisotropically). Since the stress applied to the polarization plane holding fiber 2 is anisotropically generated on the outer periphery, the core 11 is more effectively distorted unevenly, and the refractive index and extinction ratio of the core 11 or optical characteristics such as crosstalk are reduced. The change becomes noticeable.

For example, the stress applying layer 4 is composed of a metal thin film layer 5 composed of metal or the like. The metal constituting the metal thin film layer 5 is a metal having a known and stable characteristic such as a coefficient of thermal expansion such as nickel, gold, or aluminum, but is not limited to a specific type of metal. The metal thin film layer 5 is formed such that a cross section perpendicular to the light propagation direction is non-circular such as an ellipse or a rectangle. The stress resulting from the expansion or contraction of the metal thin film layer 5 having a non-circular cross section is generated anisotropically in the polarization-maintaining fiber 2. As a result, the core 11 in the polarization-maintaining fiber 2 is effectively distorted unevenly, and the change in optical characteristics with respect to the temperature change of the core 11 becomes remarkable.

FIG. 3A is a cross-sectional view of an example of a temperature compensation element taken along line BB in FIG. In the example shown in FIG. 3A, the metal thin film layer 5 has an elliptical shape extending in the y-axis direction. For example, when the metal thin film layer 5 expands due to a temperature rise, the stress generated by the expansion is applied in the direction of crushing the polarization plane holding fiber 2. Further, the stress generated in the y-axis direction of the polarization-maintaining fiber 2 is larger than the stress generated in the x-axis direction. Therefore, the polarization-maintaining fiber 2 is crushed by a greater stress from the y-axis direction and is distorted more significantly in the y-axis direction. As described above, in the example shown in FIG. 3A, when a temperature change occurs, the stress generated in the metal thin film layer 5 is anisotropically generated in the polarization-maintaining fiber 2, and changes with respect to the temperature change of the core 11. The change in optical characteristics becomes remarkable.

Further, the metal thin film layer 5 constituting the stress applying layer 4 may be formed so that the central portion of the metal thin film layer 5 and the polarization plane holding fiber 2 are displaced. In this case, the metal thin film layer 5 may be circular. Such stress resulting from the expansion or contraction of the metal thin film layer 5 is anisotropically generated in the polarization-maintaining fiber 2. As a result, the core 11 in the polarization-maintaining fiber 2 is effectively distorted, and the change in optical characteristics with respect to the temperature change of the core 11 becomes remarkable.

FIG. 3B is a cross-sectional view of another example of the temperature compensation element taken along line BB in FIG. In the example shown in FIG. 3 (B), the metal thin film layer 5 is formed so that the cross section perpendicular to the light propagation direction is circular, but the polarization-maintaining fiber 2 is displaced from the center of the metal thin film layer 5. Yes. For example, when the metal thin film layer 5 expands due to a temperature rise, the stress applied to the core 11 of the polarization-maintaining fiber 2 from the direction opposite to the x-axis direction (from right to left in FIG. 3B) It is larger than the stress applied from the direction. Accordingly, the core 11 of the polarization-maintaining fiber 2 is applied with a greater stress from the opposite direction to the x-axis direction and is well and significantly distorted in the x-axis direction. As described above, in the example shown in FIG. 3B, when a temperature change occurs, the stress generated by the metal thin film layer 5 is anisotropically generated in the polarization-maintaining fiber 2, and changes with respect to the temperature change of the core 11. The change in optical characteristics becomes remarkable.

Next, the direction in which stress is applied will be described.
The polarization plane holding fiber 2 holds the plane of polarization by the difference between the light propagation constants of the two birefringence axes. In addition, the light propagation constant of the birefringence axis changes significantly by applying a stress in the direction along the birefringence axis of the polarization-maintaining fiber 2. Therefore, the difference between the light propagation constants of both birefringence axes is effectively changed by applying a stress in a direction along one of the birefringence axes.
As a result, the optical characteristics such as the extinction ratio or crosstalk of the polarization-maintaining fiber 2 change more significantly with respect to stress. When it is necessary to change the temperature change of the optical characteristics of the polarization-maintaining fiber 2 more remarkably, the stress applying layer 4 has the direction of the stress applied to the polarization-maintaining fiber 2 as one birefringence axis. It is formed to be parallel.

On the other hand, when the magnitude of the stress applied to each birefringence axis is approximate, the difference in the light propagation constant of the birefringence axis does not change much, and the extinction ratio or crosstalk of the polarization-maintaining fiber 2 or the like The optical characteristics of the film change slowly. For example, when stress is applied between both birefringence axes (that is, an angle around 45 degrees from both birefringence axes), the magnitude of the stress generated in both birefringence axis directions approximates, The difference in the light propagation constant changes slowly. As a result, the optical characteristics such as the extinction ratio or crosstalk of the polarization-maintaining fiber 2 change gently with respect to temperature changes.
When it is necessary to change the temperature change of the optical characteristics of the polarization-maintaining fiber 2 gently, the stress applying layer 4 is formed so that the magnitude of the stress applied to the polarization-maintaining fiber 2 is approximated. The

Since the metal thin film layer 5 is bonded to the polarization plane holding fiber 2, when the metal thin film layer 5 expands or contracts due to a temperature change, the longitudinal load stress (stress generated in the light propagation direction) is also applied to the polarization plane holding fiber 2. Applied. When longitudinal load stress is applied, the polarization-maintaining fiber 2 extends or contracts in the light propagation direction. This also changes the optical characteristics such as the extinction ratio or crosstalk of the polarization-maintaining fiber 2.

As described above, the amount of change in optical characteristics such as the extinction ratio or crosstalk of the polarization-maintaining fiber 2 varies depending on the intensity and direction of the stress applied to the polarization-maintaining fiber 2. The material, shape, or direction of the metal thin film layer 5 is determined so that the metal thin film layer 5 has a temperature change of an optical characteristic that cancels a temperature characteristic of a sensor that compensates the temperature, and is limited to a specific configuration. It is not a thing.

Next, a method for forming the metal thin film layer 5 will be described.
The metal thin film layer 5 is formed by electrolytic plating or metal vapor deposition. For example, the protective layer 3 in the section where the stress applying layer 4 of the polarization-maintaining fiber 2 is formed is removed. The portions other than the section are masked. In this state, the metal thin film layer 5 is formed by performing electrolytic plating or metal vapor deposition on the section where the stress applying layer 4 of the polarization-maintaining fiber 2 is formed.
Further, in order to form the metal thin film layer 5 so that the cross section of the metal thin film layer 5 is non-circular, or to form the metal thin film layer so that the polarization plane maintaining fiber 2 is displaced from the center of the metal thin film layer 5. In addition, a process step such as adjustment of the direction and strength of the electric field, adjustment of the plating time or deposition time in the electroplating or metal deposition, or axis rotation with respect to the direction of the electric field of the polarization plane holding fiber 2 or the direction of metal deposition is performed alone or It is done in combination. Further, the thickness of the metal thin film layer 5 is also adjusted by a similar process.

Further, the metal thin film layer 5 may be formed so that the cross-sectional view of the metal thin film layer 5 has a predetermined shape by processing after being formed concentrically on the stress applying layer 4 of the polarization maintaining fiber 2. For example, the metal thin film layer 5 may be formed so that a cross-sectional view of the metal thin film layer 5 has a predetermined shape by file or etching.
In addition, the formation method of the metal thin film layer 5 should just be a method which can process the metal thin film layer 5 to a predetermined | prescribed shape, and is not limited to a specific formation method.

The temperature compensation element configured as described above can apply a non-uniform stress to the core. Therefore, the temperature compensation element can change the optical characteristics of the core more significantly according to the temperature change.
(Second Embodiment)
A temperature compensation element 1 according to the second embodiment will be described. FIG. 4 is a cross-sectional view in the light propagation direction of the temperature compensation element according to the second embodiment.
The second embodiment is different from the first embodiment in that the stress applying layer 4 includes a ferrule 6 and a wax material 7 in addition to the metal thin film layer 5. Therefore, about the point other than this, the same code | symbol as 1st Embodiment is attached | subjected and the detailed description is abbreviate | omitted.

FIG. 5 shows cross-sectional views of two examples of temperature compensation elements along line AA in FIG.
As shown in FIG. 5, the stress applying layer 4 includes a metal thin film layer 5, a ferrule 6 covering the outer periphery of the metal thin film layer 5, and a brazing material 7 that bonds the metal thin film layer 5 and the ferrule 6. Have

The metal thin film layer 5 is the same as in the first embodiment. FIG. 5A is a cross-sectional view of an example of a temperature compensation element in which the metal thin film layer 5 shown in FIG. FIG. 5B is a cross-sectional view of an example of a temperature compensation element in which the metal thin film layer 5 shown in FIG. 3B is covered with a ferrule 6.

The ferrule 6 has a function of fixing the polarization-maintaining fiber 2 when the polarization-maintaining fiber 2 is inserted into a connector or the like. The ferrule 6 has a cylindrical shape, and covers the metal thin film layer 5 so that the center portion of the ferrule 6 and the center portion of the polarization-maintaining fiber 2 coincide.
That is, the polarization-maintaining fiber 2 and the ferrule 6 are positioned concentrically. Since the polarization-maintaining fiber 2 and the ferrule 6 are positioned concentrically, when the ferrule 6 is inserted into a connector or the like, the propagation axis of the light passing through the polarization-maintaining fiber 2 is the same as the connection destination fiber. Match. As a result, optical transmission loss in connector connection is reduced.

The ferrule 6 is a substance having a known and stable temperature characteristic such as a coefficient of thermal expansion such as, for example, an Fe-Ni invar alloy or a kovar alloy, but is not limited to a specific type of metal. The ferrule 6 may be formed in a cylindrical shape by injection molding or machining. The manufacturing method of the ferrule 6 is not limited to a specific method.

The metal thin film layer 5 and the ferrule 6 are bonded by a wax material 7. The brazing material 7 fills the space between the metal thin film layer 5 and the ferrule 6 without a gap, and fixes the ferrule 6 to the metal thin film layer 5 so that the polarization-maintaining fiber 2 and the ferrule 6 are positioned concentrically. . The wax material 7 is a substance having a known and stable temperature characteristic such as a coefficient of thermal expansion, such as Sn—Pb eutectic solder, an alloy of tin / silver / copper, or an alloy of tin / bismuth. However, the present invention is not limited to these metals.

The temperature compensating element 1 has a structure in which different types of metals having known and stable thermal expansion coefficients are covered in multiple layers. As a result, the temperature compensation element 1 can stably apply stress to the polarization-maintaining fiber 2 according to the temperature. Further, the temperature compensation element 1 can apply stress to the polarization-maintaining fiber 2 with higher accuracy by a combination of metals. Furthermore, the temperature compensation element 1 can apply a larger stress to the polarization-maintaining fiber 2 by a combination of metals. The temperature compensation element 1 can control the optical characteristics such as the extinction ratio or crosstalk of the polarization-maintaining fiber 2 in more detail and widely by adjusting the type, thickness, and shape of the metal.

For example, it is assumed that the ferrule 6 is a substance having a thermal expansion coefficient smaller than that of the metal thin film layer 5. In this case, the ferrule 6 does not expand or contract more than the metal thin film layer 5 even if the temperature changes. Since the metal thin film layer 5 is fixed to the ferrule 6, even when a temperature change occurs, the metal thin film layer 5 is unlikely to expand or contract in the vertical direction (light propagation direction). As a result, the stress applying layer 4 suppresses the longitudinal load stress from being applied to the polarization plane holding fiber 2.

Also, the polarization maintaining fiber 2 has optical characteristics such as extinction ratio or crosstalk when a lateral load stress (stress generated perpendicular to the light propagation direction) occurs rather than a longitudinal load stress. The change is small.
Therefore, the stress applying layer 4 can suppress the longitudinal load stress that greatly changes the optical characteristics. As a result, the stress applying layer 4 can control the change in the optical characteristics more finely.

The temperature compensation element configured as described above can finely control the optical identification of the core. In addition, the temperature compensation element can apply a stronger stress to the core, and the change in the optical characteristics of the core can be made more remarkable.
(Third embodiment)
A third embodiment will be described. FIG. 6 is a cross-sectional view perpendicular to the light propagation direction of the temperature compensation element according to the third embodiment. That is, FIG. 6 is a cross-sectional view of the temperature compensation element along a line corresponding to the line AA in FIG.

The third embodiment differs from the first embodiment in that the temperature compensation element 1 is formed of a plurality of flat plates and the like. Therefore, about the point other than this, the same code | symbol as 1st Embodiment is attached | subjected and the detailed description is abbreviate | omitted.

As shown in FIG. 6, the temperature compensating element 1 is provided between the flat plate 21 that holds the polarization plane holding fiber 2 from the upper side, the flat plate 22 that holds the polarization plane holding fiber 2 from the lower side, and the flat plates 21 and 22. Spacer 23, flat plates 21 and 22, adjustment bolt 25 penetrating spacer 23, nut 26 attached to the tip of adjustment bolt 25 protruding from flat plate 22, provided between adjustment bolt 25 and flat plate 21 The spring 24, the washer 27 installed between the adjustment bolt 25 and the spring 24, and the washer 28 installed between the spring 24 and the flat plate 21 are included. The spacer 23a, the adjusting bolt 25a, the nut 26a, the spring 24a, and the washers 27a and 28a are installed at one end (right side in the example of FIG. 6) of the flat plates 21 and 22 in the width direction (x-axis direction of FIG. 6). The Further, the spacer 23b, the adjusting bolt 25b, the nut 26b, the spring 24b, and the washers 27b and 28b are the other ends in the width direction (x-axis direction in FIG. 6) of the flat plates 21 and 22 (left side in the example of FIG. 6). Installed. The components installed at both ends of the flat plates 21 and 22 have the same configuration.

The plane plates 21 and 22 are rectangular members having a predetermined thickness, a predetermined width, and a predetermined length. Further, the flat plates 21 and 22 have substantially the same size and shape. The widths of the flat plates 21 and 22 (that is, the size in the x-axis direction in FIG. 6) may be any width that can sandwich the polarization-maintaining fiber 2 and wider than the diameter of the polarization-maintaining fiber 2. . The width, length (that is, the size in the light propagation direction), and thickness (that is, the size in the y-axis direction in FIG. 6) of the flat plates 21 and 22 depend on the temperature compensation configuration required for the temperature compensation element 1. It is determined and is not limited to a specific configuration. The flat plates 21 and 22 are metal plates having known and stable characteristics such as a coefficient of thermal expansion, but are not limited to specific materials.

The flat plates 21 and 22 are installed so as to sandwich the polarization-maintaining fiber 2 from above and below in parallel. The flat plates 21 and 22 are installed in the region of the polarization-maintaining fiber 2 that is not covered by the protective layer 3. Thereby, the flat plates 21 and 22 can apply stress to the polarization-maintaining fiber 2 without interposing the protective layer 3. The flat plates 21 and 22 may sandwich part of the region of the polarization-maintaining fiber 2 that is covered with the protective layer 3.

Stress is applied to the flat plates 21 and 22 from the springs 24a and 24b and the adjusting bolts 25a and 24b in the direction in which the flat plates 21 and 22 approach each other. The flat plates 21 and 22 apply the stress applied by the springs 24 a and 24 b and the adjusting bolts 25 a and 25 b to the polarization-maintaining fiber 2.

The spacer 23a is sandwiched along the right end of the flat plates 21 and 22 in the width direction. That is, the spacer 23 a is linearly installed at the right end of the flat plates 21 and 22 from one end to the other end in the light propagation direction of the flat plates 21 and 22. The spacer 23a is a metal or an elastic body, but is not limited to a specific substance or shape. The spacer 23 a prevents the polarization plane holding fiber 2 from being damaged by the pressure applied by the flat plates 21 and 22 to the polarization plane holding fiber 2.

The thickness of the spacer 23a (the size in the y-axis direction in FIG. 6) is slightly smaller than the diameter of the polarization-maintaining fiber 2. As a result, the flat plates 21 and 22 are less likely to apply stress to the spacer 23 a, and can effectively apply stress to the polarization-maintaining fiber 2.
Further, when the polarization-maintaining fiber 2 is crushed to a predetermined width, the stress applied by the flat plates 21 and 22 is applied to the spacer 23a. As a result, it is possible to prevent the polarization-maintaining fiber 2 from being crushed and damaged from a predetermined width. The spacer 23b has the same configuration.

The adjusting bolt 25a passes through the flat plate 21, the spacer 23a, and the flat plate 22, and protrudes downward from the flat plate 22. The adjustment bolt 25a has a nut 26a attached to the protruding end. Washers 27 a and 28 a are provided between the head of the adjustment bolt 25 a and the flat plate 21. The spring 24a is installed between the washers 27a and 28a. The adjustment bolt 25a, the washers 27a and 28a and the center of the spring 24a are passed through, and the washers 27a, 28a and the spring 24a are fixed. The spring 24 is installed between the washers 27a and 28a in a contracted state, and constantly applies stress to the flat plate 21 by the repulsive force of the spring 24a.

The spring 24a is formed of an elastic body having a temperature characteristic in which a spring constant or an elastic coefficient changes according to a temperature change. The spring 24a is, for example, a metal alloy spring, a metal alloy leaf spring, or a spring spring made of ceramic, but is not limited to a specific type of elastic body.
The spring 24b, the adjusting bolt 25b, and the washers 27b and 28b have the same configuration.

Next, the stress applied to the polarization plane holding fiber 2 will be described.
The spring 24a is contracted by the adjusting bolt 25a. Therefore, the repulsive force of the spring 24a is adjusted by tightening or loosening the adjustment bolt 25a.
For example, when the adjusting bolt 25a is tightened, the spring 24a is contracted and the repulsive force of the spring 24a is increased. Conversely, when the adjustment bolt 25a is loosened, the spring 24a is extended and the repulsive force of the spring 24a is weakened. Similarly, the repulsive force of the spring 24b is adjusted by tightening or loosening the adjusting bolt 25b. Therefore, the stress applied to the polarization plane holding fiber 2 is adjusted by adjusting the adjustment bolt 25a to adjust the repulsive force of the spring 24a, and adjusting the adjustment bolt 25b to adjust the repulsive force of the spring 24b. .

As described above, the springs 24a and 24b are made of an elastic body having a temperature characteristic in which a spring constant or an elastic coefficient changes according to a temperature change. Therefore, when a temperature change occurs, the spring constants or elastic coefficients of the springs 24a and b change, and the repulsive force of the springs 24a and b changes. Therefore, when the temperature changes, the stress applied to the polarization plane holding fiber 2 also changes. Therefore, the stress applied to the polarization-maintaining fiber 2 can have temperature dependence.

The temperature compensation element 1 may sandwich the polarization plane holding fiber 2 so that the stress applied by the flat plates 21 and 22 is applied along the two birefringence axes of the core 11. In this case, the temperature compensation element 1 can change the optical characteristics such as the extinction ratio or the crosstalk of the polarization-maintaining fiber 2 more remarkably with respect to the temperature change.

As described above, by adjusting the repulsive force of the springs 24a and 24b and the direction of the polarization-maintaining fiber 2, the amount of change of the optical characteristics such as the extinction ratio or crosstalk of the polarization-maintaining fiber 2 with respect to the temperature change can be changed. Can be controlled. Further, unlike the first and second embodiments, in the present embodiment, the temperature compensation element 1 can apply stress from only one surface of the polarization-maintaining fiber 2. Thereby, the temperature compensation element 1 can apply stress in a specific direction more remarkably.

The temperature compensation element 1 does not have to be provided with the spring 24. That is, the flat plates 21 and 22 are directly fixed by the adjusting bolt 25 and the nut 26 with the spacer 23 interposed therebetween. In this case, the temperature compensation element 1 can apply a stress corresponding to the temperature change to the polarization plane holding fiber 2 due to the difference in thermal expansion coefficient between the flat plates 21 and 22, the spacer 23, and the adjusting bolt 25.

Further, the temperature compensating element 1 does not need to be provided with the adjusting bolt 25 and the nut 26. That is, the flat plates 21 and 22 may be bonded with the spacer 23 interposed therebetween. For example, the bonding method of the flat plates 21 and 22 and the spacer 23 includes mechanical fitting bonding, bonding with an adhesive, or bonding by welding or welding, but is not limited to a specific method. In this case, the temperature compensation element 1 can apply a stress corresponding to the temperature change to the polarization plane holding fiber 2 due to the difference in thermal expansion coefficient between the flat plates 21 and 22 and the spacer 23.

Further, the temperature compensation element 1 according to the present embodiment may apply stress to the polarization plane holding fiber 2 covered with the protective layer 3. In this case, the stress applied to the polarization-maintaining fiber 2 is applied to the polarization-maintaining fiber 2 through the protective layer 3.

Further, the number of adjustment bolts and springs included in the temperature compensation element 1 according to the present embodiment is not limited to a specific number.
The space formed by the flat plates 21 and 22, the spacer 23a and the polarization-maintaining fiber 2 and the space formed by the flat plates 21 and 22, the spacer 23b and the polarization-maintaining fiber 2 are filled with silicon rubber or the like. It may be filled with an agent.

The temperature compensation element configured as described above can apply stress to the core from one direction. As a result, the temperature compensation element can crush the core in a specific direction and control the change in optical characteristics of the core more precisely.
(Fourth embodiment)
A fourth embodiment will be described. FIG. 7A is a cross-sectional view perpendicular to the light propagation direction of the temperature compensation element according to the fourth embodiment.
The fourth embodiment differs from the third embodiment in that the flat plate 22 according to the third embodiment is replaced with a V-groove plate 31 having a V-shaped groove. Therefore, about the point other than this, the same code | symbol as 3rd Embodiment is attached | subjected and the detailed description is abbreviate | omitted.

As shown in FIG. 7A, the temperature compensation element 1 includes a flat plate 21 that holds the polarization plane holding fiber 2 from the upper side, a V-groove plate 31 that holds the polarization plane holding fiber 2 from the lower side, the flat plate 21, and the V groove. Spacer 23 provided between plates 31, flat plate 21, V groove plate 31, adjustment bolt 25 penetrating spacer 23, nut 26 attached to the tip of adjustment bolt 25 protruding from V groove plate 31, adjustment bolt A spring 24 provided between the adjustment bolt 25 and the flat plate 21, a washer 27 provided between the adjustment bolt 25 and the spring 24, and a washer 28 provided between the adjustment bolt 25 and the flat plate 21. Have.

The V-groove plate 31 is formed with substantially the same width and length as the flat plate 21. The V-groove plate 31 is formed to a thickness capable of forming a V-shaped groove. The V-groove plate 31 has a V-shaped groove at the center in the width direction (the x-axis direction in FIG. 7A). The V-shaped groove provided in the V-groove plate is linearly formed from one end to the other end of the V-groove plate 31 in the light propagation direction. A V-shaped groove provided in the V-groove plate is installed to accommodate the polarization-maintaining fiber 2. The angle and depth of the V-shaped groove are determined by the diameter of the polarization-maintaining fiber 2 and the content of temperature compensation, but are not limited to a specific configuration.

Further, the V-groove plate 31 is a metal plate having known and stable characteristics such as a coefficient of thermal expansion, but is not limited to a specific substance. The method for forming the V-shaped groove may be a general excavation process or a casting process for forming the V-groove plate 31 situation, and is not limited to a specific method.

The temperature compensation element 1 sandwiches the polarization-maintaining fiber 2 so as to be accommodated in a V-shaped groove formed in the V-groove plate 31. This prevents the polarization-maintaining fiber 2 from shifting in the width direction between the flat plate 21 and the V-groove plate 31. Further, the plane plate 21 and the V-groove plate 31 can stably apply an anisotropic stress to the polarization plane holding fiber 2. Further, by adjusting the shape of the V-shaped groove, the angle of the stress applied to the polarization-maintaining fiber 2 is stably controlled.

Note that the V-shaped groove does not have to be completely V-shaped. For example, a structure in which the V-shaped tip is a flat surface may be used. FIG. 7B shows an example in which a groove having a V-shaped tip having a flat surface is formed in the V-groove plate. FIG. 7B is a cross-sectional view perpendicular to the light propagation direction of the temperature compensation element 1. For simplification, FIG. 7B shows the flat plate 21, the spacer 23, and the V-groove plate 31 without the adjustment bolt 25, the spring 24, the nut 26, and the washers 27 and 28.

As shown in FIG. 7B, the V-shaped groove formed in the V-groove plate 31 has a flat tip. Since the plane portion is not in contact with the polarization-maintaining fiber 2, the same effect as that obtained when the polarization-maintaining fiber 2 is accommodated in the V-shaped groove can be obtained. By forming the tip of the V-shaped groove on a flat surface, the thickness of the V-groove plate 31 can be reduced.

In addition, as shown in FIG. 7B, when the angle of the V-shaped groove is 60 degrees, the polarization plane holding fiber 2 includes the flat plate 21, one surface of the V-shaped groove, and the other surface of the V-shaped groove. Stress isotropically applied at an angle of 120 degrees. Therefore, in this case, changes in optical characteristics such as the extinction ratio or crosstalk of the polarization-maintaining fiber 2 due to temperature changes are unlikely to occur. For this reason, when the change in the optical characteristics of the core 11 needs to be remarkable, the V-shaped groove formed in the V-groove plate 31 does not have a value of the angle of the V-shaped groove around 60 degrees. It is desirable to be formed as follows.

The temperature compensation element 1 may sandwich the polarization plane holding fiber 2 so that the stress applied by the flat plate 21 and the V-groove plate 31 is applied along the two birefringence axes of the core 11. In this case, the temperature compensation element 1 can change the optical characteristics such as the extinction ratio or the crosstalk of the polarization-maintaining fiber 2 more remarkably with respect to the temperature change.
Further, the temperature compensation element 1 according to the present embodiment may apply stress to the polarization-maintaining fiber 2 covered with the protective layer 3. In this case, the stress applied to the polarization-maintaining fiber 2 is applied to the polarization-maintaining fiber 2 through the protective layer 3.
Further, the number of adjustment bolts and springs included in the temperature compensation element 1 according to the present embodiment is not limited to a specific number.
The space formed by the flat plate 21, the V-groove plate 31, the spacer 23a, and the polarization-maintaining fiber 2 and the space formed by the flat plate 21, the V-groove plate 31, the spacer 23b, and the polarization-maintaining fiber 2 are as follows. It may be filled with a filler such as silicon rubber.

The temperature compensation element configured as described above can prevent the core from rotating or moving. As a result, the temperature compensation element can stably apply stress to the core and can stably perform temperature compensation.
(Fifth embodiment)
A fifth embodiment will be described. In the fifth embodiment, the temperature compensation element 1 is obtained by connecting a plurality of temperature compensation elements described in the first to fourth embodiments in series. FIG. 8 is a diagram schematically showing an example of the temperature compensation element 1 according to the present embodiment. As shown in FIG. 8, the temperature compensation element 1 includes temperature compensation elements 1a, 1b, and 1c.

Each temperature compensation element 1a, 1b, and 1c is one of the temperature compensation elements described in the first to fourth embodiments. Each of the temperature compensation elements 1a, 1b, and 1c may be any of the temperature compensation elements described in the first to fourth embodiments, may be the same temperature compensation element, or may have a different structure. But you can. Each temperature compensation element 1a, 1b and 1c is not limited to a specific combination.

The temperature compensation elements 1a, 1b, and 1c are connected to each other by fusion-bonding of polarization plane holding fibers of the temperature compensation element, connector connection, optical coupling through a lens, or the like. Note that. The connection method of each temperature compensation element 1a, 1b, and 1c is not limited to a specific method.

In FIG. 8, the temperature compensation element 1 has three temperature compensation elements, but may have two, four or more temperature compensation elements. The temperature compensation element 1 may have at least two temperature compensation elements.

The temperature compensation element 1 has complicated temperature characteristics by superimposing the temperature characteristics of the individual temperature compensation elements. Therefore, the temperature compensation element 1 can have a temperature characteristic that cannot be realized with one temperature compensation element.

The temperature compensation element configured as described above can realize more complicated temperature compensation. As a result, the temperature compensation element can realize temperature compensation that is difficult or impossible to achieve with one temperature compensation element.
(Sixth embodiment)
Next, a sixth embodiment will be described. FIG. 9 is a diagram schematically illustrating a configuration example of a Sagnac interference type optical sensor system (optical sensor system) according to the sixth embodiment. The Sagnac interference type optical sensor according to the sixth embodiment includes any one of the temperature compensation elements according to the first to fifth embodiments.

As shown in FIG. 9, the Sagnac interference type optical sensor system 10 includes a signal processing unit 40, a polarization plane holding fiber unit 60, a sensor unit 70, and the like. The Sagnac interference type optical sensor system 10 measures a current passing through the electric wire 74 in the sensor unit 70. The Sagnac interferometric optical sensor system 10 can measure a current of several kiloamperes passing through the electric wire 74, for example. The Sagnac interference type optical sensor system 10 may be installed in a substation or the like, and may measure a current passing through a transformer or the like. In addition, the place where the Sagnac interference type optical sensor system 10 is installed and the measurement target are not limited to a specific configuration.

The signal processing unit 40 has a function of supplying light (measurement light) such as a measurement laser to the sensor unit 70 and a function of receiving measurement light (reflected light) reflected by the sensor unit 70. Further, the signal processing unit 40 has a function of measuring a current passing through the electric wire 74 based on the reflected light received from the sensor unit 70.
As shown in FIG. 9, the signal processing unit 40 includes a light source driving circuit 41, a light source 42, a fiber coupler 43, an optical filter 44, a phase modulator driving circuit 45, a phase modulator 46, a detector 47, a synchronous detection circuit 48, An arithmetic circuit 49 and a surplus coil 50 are included.

The light source driving circuit 41 has a function of stably supplying a current to the light source 42. The light source drive circuit 41 is electrically connected to the light source 42. Further, the light source driving circuit 41 may have a function of controlling the intensity, frequency, phase, and the like of light emitted from the light source 42.
The light source 42 emits measurement light according to the current supplied from the light source driving circuit 41. The light source 42 is optically connected to the fiber coupler 43 through an optical fiber (for example, a polarization-maintaining fiber). The light source 42 supplies measurement light to the fiber coupler 43 through an optical fiber. The light source 42 is an LED or the like, but is not limited to a specific configuration.

The fiber coupler 43 has a function of collecting two lights into one light or separating one light into two lights. The fiber coupler 43 is optically connected to the light source 42, the optical filter 44, and the detector 47 through an optical fiber. The fiber coupler 43 supplies the measurement light emitted from the light source 42 to the optical filter 44 and supplies the reflected light supplied from the optical filter 44 to the detector 47.

The optical filter 44 has a function of converting light having a specific property (for example, linearly polarized light). The optical filter 44 is optically connected to the fiber coupler 43 and the phase modulator 46 through an optical fiber. The optical filter 44 filters measurement light supplied from the fiber coupler 43 to the phase modulator 46 and filters reflected light supplied from the phase modulator 46 to the fiber coupler 43. For example, the optical filter 44 serves to remove noise generated in the measurement light and the reflected light.

The phase modulator driving circuit 45 has a function of controlling the phase modulator 46 using a control signal and controlling the phase of light passing through the phase modulator 46. The phase modulator driving circuit 45 is electrically connected to the phase modulator 46 and the synchronous detection circuit 48. The phase modulator driving circuit 45 can control the phase of light passing through the phase modulator 46 based on an external signal. In the present embodiment, the phase modulator driving circuit 45 controls the phase of light passing through the phase modulator 46 based on the signal from the synchronous detection circuit 48.
The phase modulator 46 modulates the phase or frequency of light passing through the phase modulator 46 based on a control signal from the phase modulator driving circuit 45.

The detector 47 has a function of converting the supplied light into an electrical signal and outputting it. The detector 47 is optically connected to the fiber coupler 43 by an optical fiber or the like, and is electrically connected to the synchronous detection circuit 48. The detector 47 is supplied with the reflected light from the fiber coupler 43, converts the supplied reflected light into an electric signal, and supplies it to the synchronous detection circuit 48.

The synchronous detection circuit 48 has a function of supplying a signal for controlling the phase to the phase modulator driving circuit 45. The synchronous detection circuit 48 has a function of extracting a signal having a specific phase from the electrical signal transmitted from the detector 47. The synchronous detection circuit 48 is electrically connected to the detector 47 and the phase modulator drive circuit 45. The synchronous detection circuit 48 controls the phase of the measurement light to a specific phase via the phase modulator driving circuit. The synchronous detection circuit 48 extracts a signal having the same phase as that of the measurement light from the electrical signal transmitted from the detector 47. Thereby, the synchronous detection circuit 48 can extract an electrical signal for the reflected light having the same phase as the measurement light. The synchronous detection circuit 48 supplies the extracted electrical signal to the arithmetic circuit 49.

The arithmetic circuit 49 calculates the current passing through the electric wire 74 based on the electric signal supplied from the synchronous detection circuit 48. The arithmetic circuit 49 is electrically connected to the synchronous detection circuit 48. The arithmetic circuit 49 may be a dedicated circuit, a PC, or the like. The arithmetic circuit 49 transmits information indicating the calculated current to the outside.

The surplus coil 50 is an optical fiber that supplies the measurement light supplied through the phase modulator 46 to the polarization plane holding fiber unit 60 and supplies the reflected light supplied through the polarization plane holding fiber unit 60 to the phase modulator 46. is there.

The polarization-maintaining fiber unit 60 has a function of canceling the change in optical characteristics with respect to the temperature change of the sensor unit 70. As shown in FIG. 9, the polarization-maintaining fiber unit 60 includes a temperature compensation element 1, a light transmission fiber 61 that optically connects the signal processing unit 40 and the temperature compensation element 1, and the temperature compensation element 1 and the sensor unit 70. And the like.

The light transmission fiber 61 supplies the measurement light supplied through the signal processing unit 40 to the temperature compensation element 1 and supplies the reflected light supplied through the temperature compensation element 1 to the signal processing unit 40. The light transmission fiber 62 supplies the measurement light supplied through the temperature compensation element 1 to the sensor unit 70 and supplies the reflected light supplied through the sensor unit 70 to the temperature compensation element 1.

The temperature compensation element 1 is installed to cancel the change in the optical characteristics with respect to the temperature change of the sensor unit 70. The temperature compensation element 1 is installed in the vicinity of the sensor unit 70 so that the temperature of the temperature compensation element 1 matches the temperature of the sensor unit 70. When a temperature change occurs in the sensor unit 70, the temperature compensation element 1 causes an optical characteristic change (phase change) opposite to the optical characteristic change of the sensor unit 70 to occur in the core of the polarization-maintaining fiber unit 60. .

The temperature compensation element 1 is a temperature compensation element shown in any one of the first to fifth embodiments. The configuration of the temperature compensation element 1 is determined according to the change in optical characteristics with respect to the temperature change of the sensor unit 70, and is not limited to a specific configuration.

The sensor unit 70 causes a change in characteristics due to the current flowing through the electric wire 74 with respect to the light passing therethrough. For example, the sensor unit 70 has a function of causing the measurement light and the reflected light to generate a Faraday phase difference resulting from a current passing through the electric wire 74. As shown in FIG. 9, the sensor unit 70 includes a quarter-wave plate 71, a sensor fiber 72 disposed so as to surround the electric wire 74 from the quarter-wave plate 71, and a mirror 73 provided at the tip of the sensor fiber 72. Etc.

The quarter-wave plate 71 has two birefringence axes and has a function of shifting the phase of light passing through each birefringence axis by π / 2. The quarter-wave plate 71 is installed at the introduction port of the sensor unit 70. The quarter wavelength plate 71 has a function of converting linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light.

The sensor fiber 72 is an optical fiber connected to the quarter wavelength plate 71. The sensor fiber 72 is installed so as to surround the electric wire 74 through which a current to be measured flows. The sensor fiber 72 has a function of causing the measurement light and the reflected light to generate a Faraday phase difference caused by the magnetic field of the current flowing through the electric wire 74.

The mirror 73 is installed at the tip of the sensor fiber 72. The mirror 73 has a function of reflecting the measurement light supplied through the sensor fiber 72 and supplying the reflected light to the sensor fiber 72.
A current measured by the Sagnac interferometric optical sensor system 10 flows through the electric wire 74.

Next, an operation example of the Sagnac interference type optical sensor system 10 will be described.
Here, it is assumed that the current measured by the Sagnac interference optical sensor system 10 flows through the electric wire 74.

The light source drive circuit 41 supplies power to the light source 42. The light source 42 supplies measurement light such as a laser to the fiber coupler 43 through an optical fiber by the electric power from the light source driving circuit 41. The measurement light supplied from the light source 42 passes through the fiber coupler 43 and the optical filter 44 and is supplied to the phase modulator 46.

The phase modulator 46 is controlled by the phase modulator driving circuit 45 and controls the phase of the measurement light passing therethrough. That is, the synchronous detection circuit 48 sends a control signal for setting the measurement light to a predetermined phase or frequency to the phase modulator driving circuit 45. The phase modulator driving circuit 45 controls the phase modulator 46 based on the received control signal. As a result, the measurement light that has passed through the phase modulator 46 has a predetermined phase or frequency.

The measurement light that has passed through the phase modulator 46 passes through the extra length coil 50 and the light transmission fiber 61 of the polarization plane holding fiber portion 60 and is supplied to the temperature compensation element 1. When supplied to the temperature compensation element 1, characteristics such as the phase of the measurement light change depending on optical characteristics such as an extinction ratio or crosstalk of the temperature compensation element 1.

The measurement light that has passed through the temperature compensation element 1 passes through the light transmission fiber 62 and is supplied to the quarter wavelength plate 71 of the sensor unit 70. The phase of the measuring light is adjusted by the quarter wavelength plate 71 and passes through the sensor fiber 72. A Faraday phase difference is generated in the phase of the measurement light passing through the sensor fiber 72 due to the current passing through the electric wire 74.

The measurement light that has passed through the sensor fiber 72 is reflected by the mirror 73 and passes through the sensor fiber 72 again. The measurement light (reflected light) reflected by the mirror 73 includes a sensor fiber 72, a quarter wavelength plate 71, a light transmission fiber 62, a temperature compensation element 1, a light transmission fiber 61, a surplus coil 50, a phase modulator 46, and an optical. The light passes through the filter 44 and the fiber coupler 43 and is supplied to the detector 47.

When the reflected light is supplied to the detector 47, the detector 47 converts the reflected light into an electric signal and sends it to the synchronous detection circuit 48.
When receiving the electrical signal from the detector 47, the synchronous detection circuit 48 extracts the electrical signal generated from the reflected light from the received electrical signal. That is, the synchronous detection circuit 48 extracts a signal having the same phase or frequency of the measurement light from the received electrical signal. As a result, the synchronous detection circuit 48 can extract an electric signal generated from the reflected light without being interfered by noise. The detector 47 sends the extracted electrical signal to the arithmetic circuit 49.

The arithmetic circuit 49 receives an electrical signal from the detector 47. When the electric signal is received from the detector 47, the arithmetic circuit 49 calculates the Faraday phase difference caused by the current passing through the electric wire 74 from the received electric signal. When the Faraday phase difference is calculated, the arithmetic circuit 49 calculates the current flowing through the electric wire 74 from the calculated Faraday phase difference. Note that the method of calculating the current flowing through the electric wire 74 based on the received electrical signal by the arithmetic circuit 49 is not limited to a specific method.

FIG. 10 is a diagram illustrating an example of the temperature characteristics of the sensor unit 70 and the temperature characteristics of the temperature compensation element 1 according to the sixth embodiment.
In the diagram shown in FIG. 10, the x-axis is the sensor temperature and the y-axis is the ratio error. As shown in FIG. 10, the ratio error of the sensor unit 70 increases substantially linearly as the temperature of the sensor unit 70 increases. For example, when the temperature of the sensor unit 70 is −30 ° C., the ratio error of the sensor unit 70 is about −0.15%. When the temperature of the sensor unit 70 is 5 ° C., the ratio error of the sensor unit 70 is almost 0%. Furthermore, when the temperature of the sensor unit 70 is 30 ° C., the ratio error of the sensor unit 70 is about 0.1%.

Conversely, as the temperature of the sensor unit 70 increases, the ratio error of the temperature compensation element 1 decreases almost linearly. For example, when the temperature of the sensor unit 70 is −30 ° C., the ratio error of the temperature compensation element 1 is about 0.15%. When the temperature of the sensor unit 70 is 5 ° C., the ratio error of the temperature compensation element 1 is almost 0%. Further, when the temperature of the sensor unit 70 is 30 ° C., the ratio error of the temperature compensation element 1 is about −0.1%.

As shown in FIG. 10, the temperature compensation element 1 has a temperature characteristic opposite to the temperature characteristic of the sensor unit 70, and the temperature characteristic of the sensor unit 70 is canceled by the temperature compensation element 1.

FIG. 11 is a diagram illustrating an example of temperature characteristics of the Sagnac interference optical sensor system 10 according to the sixth embodiment.
The temperature characteristic of the Sagnac interference type optical sensor system 10 is determined by adding the temperature characteristic of the sensor unit 70 and the temperature characteristic of the temperature compensation element 1. That is, the Sagnac interference optical sensor system 10 can cancel the temperature characteristic of the sensor unit 70 using the temperature characteristic of the temperature compensation element 1.

As shown in FIG. 11, the ratio error of the Sagnac interferometric optical sensor system 10 is approximately 0% regardless of the temperature of the sensor unit 70. As described above, the temperature characteristic of the temperature compensation element 1 is opposite to the temperature characteristic of the sensor unit 70. Therefore, the temperature characteristic of the Sagnac interference type optical sensor system 10 changes at about 0% regardless of the temperature of the sensor unit 70.

The polarization-maintaining fiber unit 60 may perform temperature compensation for the signal processing unit 40.
In this case, the polarization-maintaining fiber unit 60 is installed so that the temperature of the temperature compensation element 1 matches the temperature of the signal processing unit 40. Further, the Sagnac interference type optical sensor system may include a temperature compensation element 1 for the signal processing unit 40 and a temperature compensation element 1 for the sensor unit 70.

The Sagnac interference type optical sensor system as described above can cancel the change in the optical characteristic with respect to the temperature change of the sensor unit by the temperature compensation element 1. As a result, the Sagnac interferometric optical sensor system can accurately measure current even when a temperature change occurs. In addition, the Sagnac interference type optical sensor system can be configured more easily than a system that corrects the current measurement result based on the temperature of the sensor unit measured using a thermometer or the like.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... Temperature compensation element, 1a thru | or c ... Temperature compensation element, 2 ... Polarization surface holding fiber, 3 ... Protective layer, 4 ... Stress application layer (stress application part), 5 ... Metal thin film layer, 6 ... Ferrule, 7 ... Wax Material: 11 ... Core, 12 ... Polarization plane holding section, 21 and 22 ... Planar plate, 23a and b ... Spacer, 24a and b ... Spring, 31 ... V groove plate, 40 ... Signal processing section, 60 ... Polarization plane holding fiber Part, 70 ... sensor part, 72 ... fiber sensor, 73 ... mirror.

Claims (14)

1. A temperature compensation element that performs temperature compensation on an optical fiber that propagates light,
   A stress applying unit that applies anisotropic stress to the optical fiber in accordance with a temperature change of an external device optically connected to the optical fiber;
   A temperature compensation element comprising:
2. The stress applying part is a stress applying layer that covers the optical fiber.
   The temperature compensation element according to claim 1.
3. The stress applying part is a stress applying layer that applies stress generated by thermal expansion of the stress applying part anisotropically to the optical fiber.
   The temperature compensation element according to claim 1 or 2.
4. The stress applying part is composed of a plurality of substances having different coefficients of thermal expansion.
   The temperature compensation element according to any one of claims 1 to 3.
5. The stress applying part has a structure in which a plurality of concentric substances are stacked.
   The temperature compensation element according to claim 4.
6. The stress applying part is made of metal.
   The temperature compensation element according to any one of claims 1 to 5.
7. The stress applying portion is composed of two flat plates installed in parallel, and has a structure in which the optical fiber is sandwiched between the two flat plates.
   The temperature compensation element according to claim 1.
8. The stress applying unit provides an elastic body on at least one of the flat plates, and applies stress to the flat plate by a repulsive force of the elastic bodies.
   The temperature compensation element according to claim 7.
9. The elastic body is a spring;
   The temperature compensation element according to claim 8.
10. The temperature compensation element according to any one of claims 7 to 9, wherein the stress applying unit includes a spacer between the two flat plates.
11. The stress applying part includes a groove for fixing the optical fiber on an inner surface of at least one of the flat plates.
    The temperature compensation element according to any one of claims 7 to 10.
12. The temperature compensation element according to any one of claims 1 to 11, wherein the stress applying unit applies a strong stress to the birefringence axis of the optical fiber.
13. A temperature compensation element in which a plurality of temperature compensation elements according to any one of claims 1 to 12 are optically connected.
14. An optical sensor system comprising a sensor unit, a signal processing unit, and a polarization plane holding fiber unit,
    The polarization-maintaining fiber part is
    An optical fiber that optically connects the sensor unit and the signal processing unit;
    A stress applying unit that applies anisotropic stress to the optical fiber in accordance with a temperature change of an external device optically connected to the optical fiber;
    Comprising a temperature compensation element comprising
    Optical sensor system.

Images