JPH07167931A - Optical fiber sensor device - Google Patents

Abstract

PURPOSE:To provide an optical fiber sensor device excellent in practical application, in which complex refraction of optical fiber is small, by furnishing a circumferential groove at the periphery of a non-magnetic ring-shaped member, and winding a twined optical fiber on resilient pieces fastened into the groove. CONSTITUTION:To wind an optical fiber 1 in loop form, a groove 7 for insertion of the optical fiber 1 is furnished at the peripheral surface of a bobbin 5 as a, non-magnetic ring-shaped member. To the bottom of this groove 7, resilient pieces 6 are adhered at even intervals circumferentially. The optical fiber 1 is twined and inserted into this groove 7 while given a controlled tension. Because therein the optical fiber 1 lifts the resilient pieces 6 a little, the twine of the fiber is held by the friction of their contacting surfaces involving a repulsive force. The roles of the resilient pieces 6 are to separate the optical fiber 1 from the groove 7, absorb and relieve the tensile stress in the optical fiber 1 produced thermal expansion and contraction, and prevent generation of detrimental stresses resulting from the fiber touching the groove 7 which is hard.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber sensor such as a magnetic measuring device using an optical fiber.

[0002]

2. Description of the Related Art In a magnetic measuring device using the Faraday effect, when a single mode optical fiber is twisted, it is possible to cancel the birefringence that occurs when it is processed into a loop. By suppressing the birefringence, the effect of eliminating the factor of the measurement error can be obtained, and therefore, the twist is widely used in the production of the optical fiber sensor. The principle of holding the twist of the twisted fiber is to fix the connector 2 and the fiber 1 at both ends of the optical fiber 1 with an adhesive 3 as shown in FIG.

Optical fiber sensor 4 of magnetic measuring device
Is formed into a loop by winding the optical fiber 1 a plurality of times along the bobbin 5 which is a non-magnetic annular member as shown in FIG. Place this loop so that it surrounds the current-carrying conductor.
When linearly polarized light enters the optical fiber 1, the plane of polarization is rotated in proportion to the magnetic field due to the Faraday effect. By calculating this rotation angle, the magnetic field generated by the conductor is measured. Since the rotation of the polarization plane is measured, the disorder of the polarization causes a measurement error. The extinction ratio is one measure of the degree of polarization disorder, and is indicated by the ratio of circularly polarized light / non-polarized light component to linearly polarized light. In general, an anisotropic medium has two optical axes with different refractive indexes, which is called birefringence. An optically isotropic medium such as glass also becomes anisotropic when stress is applied to generate birefringence. This birefringence is a main factor that deteriorates the extinction ratio of the medium, and thus affects the measurement accuracy of the measuring device.

[0004]

However, the above-described optical fiber sensor has the following problems to be solved. That is, although the optical fiber is twisted in order to eliminate the birefringence, it is necessary to fix the fiber in order to maintain this twist. When an optical fiber is fixed with an adhesive, stress is generated and birefringence occurs. Figure 6
In the conventional embodiment shown in FIGS. 7 to 7, since the optical fiber is fixed to the bobbin with the adhesive, the shrinkage that occurs when the adhesive cures causes a stress on the bonding interface. In the magnetic measurement device applying the Faraday effect, an increase in birefringence causes a measurement error, which is a problem. Furthermore, when comparing the degree of thermal expansion and contraction due to temperature, a single-mode quartz optical fiber is a linear expansion coefficient of 0.4 × 10 ^-6, the bobbin (eg: Al or insulator) is twenty-three to sixty × 10 ^{- 6.} Adhesives (eg silicones) have a large coefficient difference of 300 × 10 ^-6 , so
When the temperature becomes high, thermal expansion causes excessive tensile stress to the optical fiber. This stress causes an increase in birefringence, eliminates the twisting effect, and in the worst case, there is a risk of cracking the optical fiber. On the other hand, when the optical fiber is wound, if the twisted optical fiber is not always applied with a certain amount of tension and held, the optical fiber is entangled and the optical fiber is broken, so that the tension is more likely to work.

The present invention has been proposed to solve the above-mentioned problems of the prior art, and its object is to provide a practical optical fiber sensor device having a small birefringence of the optical fiber. .

[0006]

According to the present invention, a groove portion is provided in a circumferential direction of an outer peripheral surface of a non-magnetic annular member, and a twisted optical fiber is wound on an elastic member fixed to the groove portion with a predetermined tension. It is characterized by

[0007]

By holding the twisted optical fiber on the elastic member, the large stress generated at the interface between the conventional optical fiber and the adhesive can be avoided and birefringence can be suppressed. Further, the elastic member on the annular member absorbs the generation of the tensile stress applied to the optical fiber due to the thermal expansion of the optical fiber and the annular member having different expansion coefficients by the flexible elastic deformation force. Therefore, an optical fiber sensor device having small birefringence and being practical can be constructed.

[0008]

EXAMPLE An example of the present invention will be described in detail below.
FIG. 1 is a partially enlarged cross-sectional view of the insertion groove 7 of the optical fiber 1 provided on the outer peripheral surface of the bobbin 5 of the non-magnetic annular member for winding the optical fiber 1 in a loop shape in parallel with the central axis of the bobbin radius R. It is a figure. An elastic piece 6 is provided on the bottom of the groove 7.
Are bonded in an evenly divided arrangement on the circumference as shown in FIG. In this embodiment, an RTV having heat resistance and flexibility
Silicone was used for the elastic piece 6. Next, the twisted optical fiber 1 is inserted into the groove portion 7 while applying a controlled tension. At this time, since the optical fiber 1 pushes down the elastic piece 6 a little, the twist of the optical fiber 1 is held by mutual contact surface friction accompanied by repulsive force. The role of the elastic piece 6 is to separate the optical fiber 1 from the bottom of the groove portion 7 to absorb and eliminate the tensile stress to the optical fiber 1 caused by thermal expansion / contraction, and for the optical fiber 1 to touch the hard groove portion 7. To prevent the generation of harmful stress. Therefore, it is necessary to select an appropriate number of the elastic pieces 6 and the width in the groove direction depending on the size of the bobbin radius R. As an example, R =
When the trial calculation is performed under the conditions of 200 mm, temperature difference = 50 ° C, the expansion difference is about 4 mm per turn, and the radius change is about 0.6 mm. Therefore, the thickness of the elastic piece 6 measured from the bottom of the groove 7 is 0.6 mm.
The thickness and shape are selected so that a large stress is not generated in the optical fiber 1 even if the above is applied and 0.6 mm is compressed. This prevents tensile stress from being applied to the optical fiber 1.

According to this method, since the optical fiber 1 is held without being adhered, there is no fear of generating stress at the joint interface between the fiber and the adhesive unlike the conventional example. As described above, if the optical fiber 1 is not stressed, the birefringence can be suppressed to a small value, and a practical optical fiber sensor device for measurement can be obtained.

FIG. 3 shows another embodiment, in which the groove portion 7 is formed.
It shows how the groove cover 8 is attached from above,
The elastic piece 6'is also adhered to the groove cover 8 side, and the optical fiber 1 is pressed and fixed from above. This is an example in which the optical fiber 1 is prevented from loosening and fraying due to the negative temperature difference. FIGS. 4 to 5 show schematic views of the shape of the groove cover 8. In addition to this, an embodiment in combination with the existing technology, such as a configuration in which the cross-sectional shape of the groove is changed, an example in which the groove is formed of a material corresponding to the elastic body piece 6, an example in which the slip prevention process is changed to the elastic body piece 6, Can be considered.

[0011]

As described above, according to the present invention, it is possible to provide a practical optical fiber sensor device having a small birefringence.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of an optical fiber sensor according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an example of an overview of the optical fiber sensor according to FIG.

FIG. 3 is a sectional view of a main part of an optical fiber sensor according to another embodiment of the present invention.

FIG. 4 is a schematic view of an example of mounting the groove cover according to FIG.

FIG. 5 is a detailed illustration of a groove cover.

FIG. 6 is a schematic view showing an example of conventional twist holding of an optical fiber.

FIG. 7 is a block diagram of a conventional optical fiber sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical fiber 2 ... Connector 3 ... Adhesive 4 ... Optical fiber sensor 5 ... Bobbin 6,6 '... Elastic piece 7 ... Groove part R ... Bobbin radius 8 ... Groove cover

Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical indication location G02B 26/08 Z (72) Inventor Kiyotoshi Terai 2-1, Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Stock Company Toshiba Corporation Hamakawasaki Plant (72) Inventor Masao Takahashi 2-1, Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Stock Company Toshiba Hamakawasaki Plant (72) Inventor Keiko Niwa 2-1-1, Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Company Toshiba Hamakawasaki factory

Claims (5)

[Claims] 1. An optical fiber sensor device comprising a non-magnetic annular member provided with a groove portion in the circumferential direction of the outer peripheral surface thereof, and a twisted optical fiber wound on an elastic member fixed to the groove portion with a predetermined tension. 2. The optical fiber sensor device according to claim 1, wherein a groove cover having an elastic member for pressing and fixing the optical fiber is attached to the upper portion of the optical fiber. 3. The optical fiber sensor device according to claim 1, wherein the elastic member is silicon rubber. 4. The optical fiber sensor device according to claim 1, wherein the elastic member is not adhered to the optical fiber. 5. The elastic member has a thickness capable of absorbing tensile stress applied to the optical fiber due to a difference in thermal expansion coefficient between the annular member and the optical fiber.
2. The optical fiber sensor device according to 2 above.