JPS6055305A - Twin core optical fiber - Google Patents

Abstract

PURPOSE:To utilize information by light polarization to take a measurement in high-precision by forming a polarized plane maintaining SM light guide and a polarized plane nonmaintaining SM light guide in one optical fiber, and using the former for a reference and the latter as a sensor. CONSTITUTION:The optical fiber 1 has the polarized plane maintaining SM light guide 3 and polarized plane nonmaintaining SM light guide 5 in the same jacket 7. The latter SM light guide 5 consists of a core 9 and a clad 11, and the former SM light guide 3 consists of a core 13, a clad 15, and a stressed member 17 whose section is elliptic. The stressed member 17 is made of a glass material which is different in coefficient of thermal expansion from the glass materials constituting the clad 15 and jacket 7, and a stress is generated in one direction in the core by the difference in coefficient of thermal expansion to provide polarized plane maintaining property. Thus, the two SM light guides are formed in the same jacket; and one is a polarized plane maintaining type and stable against disturbance, and the other is a polarized plane nonmaintaining type and influenced easily by disturbance, so the interference between light beams passed through both light guides is utilized to take a high-sensitivity, stable measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a twin-core optical fiber used for measurement using optical interference.

[Prior art]

Conventionally, two single-mode optical fibers with the same structure are used, one of which is used as a sensor optical fiber and the other as a reference optical fiber, and light from the same light source is incident on both optical fibers from one end. Apply the disturbance to be measured, such as temperature, pressure, displacement, etc., to the optical fiber for use.
Attempts have been made to measure with high precision the change in the disturbance mentioned above by observing the interference fringes of the light emitted from both fibers at the other end.

However, in this method, the sensor optical fiber and the reference optical fiber are separate, so when measuring conditions other than the disturbance to be measured, such as pressure, the temperature, length, degree of bending, It is difficult to accurately match vibrations and other factors, and as a result, noise easily enters (there is a problem that stable measurement cannot be performed).

To improve this, the same jacket may have different characteristics (for example, the core and cladding have different refractive differences).
A twin-core optical fiber in which two single-mode (hereinafter abbreviated as 8M) optical waveguides are formed has been proposed. With such an optical fiber, the conditions for the two optical waveguides will be almost the same, but conversely, the two optical waveguides will be subject to the same disturbance, making it difficult to increase the accuracy of the disturbance to be measured. It is.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the problems of the prior art described above, it is an object of the present invention to provide a twin-core optical fiber that is highly stable and capable of performing highly accurate measurements.

[Structure of the invention]

To achieve the above object, the present invention provides a polarization-maintaining 8M optical waveguide and a non-polarization-preserving 8M optical waveguide in one optical fiber.
M optical waveguides are formed, the former is used as a reference, and the latter is used as a sensor, and highly accurate measurements are performed using information from the polarization of light.

〔Example〕

1 to 3 each show an embodiment of the present invention.

These optical fibers 1 have a polarization-maintaining 8M optical waveguide 3 and a polarization-nonmaintaining 8M optical waveguide 5 formed within the same jacket γ. Each of the non-polarization preserving 8M optical waveguides 5 is composed of a core 9 and a cladding 11, whereas the polarization preserving 8M optical waveguide 3 has a core 13, a cladding 15, and an elliptical cross section in the example shown in FIG. In the example shown in FIG. 2, the stress applying member 1T consists of a core 13, a cladding 15, and a pair of stress applying members 19 having a fan-shaped cross section, and in the example shown in FIG. It consists of a stress applying member 21). In FIG. 3, another pair of stress applying members 23 are provided to relieve the stress generated in the non-polarization preserving type 8M optical waveguide 5 located at the center and to maintain the polarization preservation property. It is something. Respective stress applying members 17, 19, 21, 23
1. It is composed of a glass material with a different coefficient of thermal expansion from the glass material constituting the cladding 15 and jacket 7, and the difference in the coefficient of thermal expansion causes stress in a certain direction in the core 13, giving it polarization preservation property. It is.

A pre-7 ohm rod for manufacturing such a twin-core optical 7-ohm < Hi, polarization preserving optical core ino and a pre-7 ohm rod for manufacturing a normal SM optical fiber are placed in the same jacket glass tube. It can be manufactured by heating and drawing after filling the gap with an appropriate glass rod.

The twin-core optical fiber of the present invention is used as shown in FIG. That is, the optical fiber 1 of the present invention is installed at a place where the disturbance to be measured is applied, and a light source 25, a lens 21, and a polarizer 29 are used at one end of the optical fiber 1.
Polarized light matching the principal' axis is incident on both SM optical waveguides, and at the other end, light exiting from both 8M optical waveguides is irradiated onto a screen 35 through a polarizer 31 and a lens 33. Then,
The plane of polarization of light passing through a polarization-maintaining 8M optical waveguide is maintained regardless of disturbances, and the plane of polarization of light passing through a non-polarization-maintaining 8M optical waveguide changes depending on the disturbance. In other words, the polarization preserving type 8M optical waveguide is used as a reference, and the non-polarization preserving type 8M optical waveguide is used as a reference.
The optical waveguide functions as a sensor.

Therefore, the interference fringes projected on the screen 35 change according to the disturbance, and by observing these interference fringes, changes in the disturbance applied to the optical fiber 1 can be measured. In particular, in this optical fiber, although the two optical waveguides are under the same conditions, the polarization preserving 8M optical waveguide is not affected by disturbances, while the non-polarization preserving 8M optical waveguide is easily affected by disturbances. A stable and highly sensitive sensor can be constructed.

In the example shown in Fig. 4, interference fringes were observed, but as shown in Fig. 5, a polarizing prism 37 and a photodetector 39 are installed at the light output end of the optical fiber 1 to detect changes in the intensity of the interference light. The measurement may be performed by doing this.

Additionally, since this optical fiber has extremely high sensitivity, it is difficult to distinguish between the sensor section and the transmission section. Therefore, it is recommended to use the light source section and the detection section as close as possible to the sensor section and to avoid disturbances at the transmission section. desirable. If the disturbance in the transmission part becomes a problem, install the optical fiber 1 of the present invention in the sensor part A as shown in FIG. It is preferable to use an optical fiber 41 having a type 8M optical waveguide.Other symbols in FIG. 6 are the same as those in FIG.

〔Effect of the invention〕

As explained above, the twin core optical fiber of the present invention is
Two 8M optical waveguides are installed in the same jacket,
One of them is polarization-preserving and stable against disturbances, and the other is polarization-preserving and susceptible to disturbances. Therefore, it is possible to utilize the interference of light that has passed through both waveguides. This makes it possible to perform extremely sensitive and stable measurements.

[Brief explanation of the drawing]

FIGS. 1 to 3 are cross-sectional views showing different embodiments of the twin-core optical fiber of the present invention, and FIGS.
Each figure is a configuration diagram showing a measurement method using the twin-core optical fiber of the present invention. 1... Twin core optical fiber, 3...
Polarization preserving single mode optical waveguide, 5...
・Polarization non-maintaining single mode optical waveguide, 7...
···Jacket. Figure 1 Figure 2 Figure 4

Claims (1)

[Claims] (1) A twin-core optical fiber characterized in that a polarization-maintaining single-mode optical waveguide and a polarization-non-maintaining single-mode optical waveguide are provided in one and the same jacket.