JPH04198904A - Optical fiber coil - Google Patents

Abstract

PURPOSE:To make output drift small by a simple constitution and to accomplish very stable temperature characteristic by winding an optical fiber symmetrically to an optical fiber coil in the radial direction and the center axis direction of the optical fiber coil and also arranging a polarization cancelling device in the center part of a sensing coil. CONSTITUTION:The optical fiber 1 having desired length is wound on bubbins 11 and 12 for the same length from both ends to be divided into two and the optical fiber is wound to a bubbin 3 for a fiber coil. The optical fiber is wound in such a way that the optical fibers which are mutually in an equal distance from a center part are nearly at the same positions in the radial direction of the coil, and further it is wound to be symmetrical with the center axis. After fusing and splicing the fiber type polarization cancelling device 5 between the incident ends 13 and 14 of two optical fibers, it is housed inside the bubbin 3. Thus, a temperature difference between the optical fibers 1 wound round to the respective layers of the coil is reduced and a phase error in an optical interference output signal is made extremely small, then detection sensitivity is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an optical fiber coil for a sensor, in which a portion used as a sensing loop is wound into a coil shape.

Conventional technology Since the past, optical fiber sensors have been used as sensors for a variety of applications, as they have advantages such as high sensitivity, small size, light weight, and good environmental resistance. It's coming. For example, in an optical fiber gyroscope for detecting the rotational angular velocity of a moving body, an optical fiber is wound into a coil to increase the area surrounded by the fiber in order to improve sensitivity. However, it is well known that when an optical fiber is wound into a coil in multiple layers, the temperature of each part of the optical fiber will be different from each other, resulting in a decrease in measurement accuracy. It is being

In order to reduce the influence of such temperature differences, various methods have been proposed for winding the optical fiber symmetrically around the sensing coil. FIGS. 3 and 4 show symmetric windings for temperature compensation of a conventional optical fiber coil. In the figure, 1 is an optical fiber, 2
3 is the central portion of the optical fiber, 3 is the coil bobbin, and 4 is the central axis direction of the sensing coil. As shown in Figures 3 and 4, winding into a coil is started from the middle part 2 of the entire length of the optical fiber 1, and both optical fibers are alternately coiled with the winding start as a reference for each layer or every two layers. ing. Specifically, after winding optical fibers of a desired length onto two rewinding bobbins so that they have the same length, these bobbins are used as a supply side, and each layer is A symmetrically wound optical fiber coil is produced by replacing the supply-side coils. In addition, the optical fiber used is a polarization-maintaining fiber capable of maintaining the input polarization direction.

Problems to be Solved by the Invention However, in the above-mentioned wound optical fiber coil, the manufacturing process of the coil is extremely complicated.
There were problems in that the time required to manufacture the coil increased and only the manufacturing yield did not improve. In addition, since the optical fiber is wound by skipping one or two layers, the optical fiber becomes twisted and distorted, deteriorating the optical propagation characteristics, and the optical fiber itself is easily damaged. At the same time, it also had the following problem. In addition, the desired optical fiber had to be divided into two parts without being cut into lengths equal to the two bobbins, which required a manufacturing process for rewinding the fiber. Furthermore, optical fibers use polarization-maintaining fibers, and the cost of fiber coils is extremely high, and the productivity of the coils is extremely low.

The present invention solves these conventional problems, and provides an optical fiber coil that has a simple configuration, extremely small output drift, and extremely stable temperature characteristics, and also provides an optical fiber that can be easily mass-produced. We also provide coils at the same time.

In one step to solve the problem, the optical fiber coil of the present invention is such that the optical fibers constituting the optical fiber coil are arranged such that the portions equidistant from each other from the center in the longitudinal direction are arranged such that in the radial direction of the optical fiber/z+ coil, The coils are wound so that the coils are at the same position and are symmetrical about the center of the coil in the central axis direction as well. Furthermore, in order to reduce the fluctuation factors of the plane of polarization when using a normal single mode fiber as an optical fiber, a fiber-type depolarizer (depolarizer) is installed in the center of the coil.
It is located. In addition, a material with excellent thermal conductivity is used as the material for the bobbin around which the optical fiber is wound.

Function In the optical fiber coil according to the present invention, with the above-described configuration, it is possible to reduce the temperature difference between the optical fibers/X4 wound in each layer of the coil in response to changes in ambient temperature. , it becomes possible to make the phase error in the optical interference output signal extremely small. Furthermore, by inserting a fiber-type depolarization device to deal with variations in the plane of polarization in the optical fiber, it is possible to extremely reduce variations in light propagation characteristics and improve detection sensitivity. . Furthermore, since the method for manufacturing this optical fiber coil is symmetrical with respect to the central axis direction of the optical fiber coil, it is possible to change the rotation direction of the fiber coil after winding one side of the fiber. Instead, it is possible to create an optical fiber coil for a fiber loop by simply inverting the fiber coil. In other words, it is possible to simplify the fiber coil manufacturing process.
It is also possible to reduce the cost of fiber coils at the same time.

EXAMPLE Hereinafter, an example of the present invention will be briefly described with reference to the drawings. FIG. 1 is a diagram showing a method for manufacturing an optical fiber coil in an embodiment of the present invention, and FIG. 2 is a cross-sectional view of the optical fiber coil. First, the manufactured optical fiber 1 of desired length is inserted into the rewinding bobbin 1 from both ends thereof.
1. Roll up the same length as in 12 and divide it into two. (1st
Figure a) Next, the coil input end 13 is inserted into the fiber coil bobbin 3 through the rewinding bobbin 11, and the optical fiber begins to be wound as shown in FIG. After winding the rewinding bobbin 11, the optical fiber is wound around the fiber coil bobbin 3 from the rewinding bobbin 12 by the same operation.

(Figure 1b) The optical fibers should be wound so that they are at the same distance from the center or at approximately the same position in the radial direction of the coil, and also with respect to the central axis. Wrap it symmetrically. Furthermore, a fiber type depolarizer (depolarizer) 5 is placed between the input ends 13 and 14 of the two optical fibers inserted inside the fiber coil bobbin 3, and the depolarizer 5 is placed in the center of the optical fibers. After fusion splicing as shown in FIG. 2, it is stored inside the fiber coil bobbin 3 along the inner wall. (Fig. 1C) In this optical fiber coil manufacturing method, the fiber can be symmetrically wound around the optical fiber coil 3 by simply replacing the rewinding bobbins 11 and 12, so the fiber coil manufacturing process is simplified. is very simple and can be produced in a short time. The vicinity of the center of the optical fiber and the detailed winding of the stratum corneum are as follows:
It looks like the cross-sectional view in the figure. In this example,
Kovar material is used as the material for the bobbin of the optical fiber coil.
Although stainless steel or the like was used, other materials may be used as long as they have good thermal conductivity. In addition, as the optical fiber 1, a normal single mode fiber is used, but
It goes without saying that the coil of the sensing fiber loop may be configured using a polarization maintaining fiber. Note that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

Effects of the Invention As described above, according to the present invention, the optical fiber is wound symmetrically around the optical fiber coil in the radial direction and central axis direction, and in addition, the sensing coil A depolarizer is placed in the center of the optical fiber to control the plane of polarization, and since the optical fiber coil is made of a highly thermally conductive material, it is resistant to changes in ambient temperature. It is possible to stably provide a sensing optical fiber coil that can provide stable optical interference output at a low price, and is extremely effective in practice.

[Brief explanation of the drawing]

FIG. 1 is a procedure diagram showing a method for symmetrically winding an optical fiber coil in an embodiment of the present invention, FIG. 2 is a cross-sectional view of an optical fiber coil manufactured by the same method, and FIGS. 3 and 4 are conventional FIG. 2 is a cross-sectional view of a symmetrical winding of an optical fiber. DESCRIPTION OF SYMBOLS 1... Optical fiber, 2... Middle part of fiber, 3...
... Fiber coil, 4... Central axis of the coil, 5...
- Fiber type depolarization device, 11.12... Rewinding bobbin, 13.14... Coil input end of optical fiber. Name of agent: Patent attorney Akira Okaji and two others Figure 1 Figure 2 Figure 6

Claims (3)

[Claims] (1) The total length of the optical fiber is divided into sections (a) and (b).
An optical fiber coil characterized in that it is equally divided into two sections, and an optical fiber type depolarization device is disposed in the center of the sections (a) and (b). (2) The optical fiber coil according to claim 1, wherein a material having high thermal conductivity is used as a material of the bobbin around which the optical fiber is wound. (3) The optical fiber coil according to claim 1, wherein a single mode optical fiber is used as the optical fiber.