JPH0534166A - Optical fiber gyro - Google Patents

Abstract

PURPOSE:To obtain a stable gyro output in the inexpensive structure even when the double refraction of a single mode optical fiber is changed by inclining main axes of an optical diverging means and two optical fibers preserving the plane of polarization by 45 deg.. CONSTITUTION:The light reaching a connecting point 23 from a polarizer 13 through an optical fiber coupler 14 which holes the plane of polarization is a lineary-polarized light propagated through one of polarization holding axes 24x and 24y of the coupler 14. The lineary-polarized light emission enters two optical fibers 16b holding the plane of polarization at the connecting point 23 by 45 deg. to a polarization holding axis 25x. As a result of this, the linearly- polarized light is separated into two components of the same intensity of the holding axes 25x and 25y orthogonal to each other and, propagated in the fibers 16b. Even when the double refraction of a single mode optical fiber 16a is changed and a polarization holding axis thereof is changed, one is decreased when the other of the two components is increased, so that the light is constant at all times. Accordingly, the intensity of light reaching a photodetector is made constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention propagates clockwise light and counterclockwise light in an optical fiber coil, detects the phase difference between these clockwise light and counterclockwise light, and applies them to the optical fiber coil. The present invention relates to an optical fiber gyro that detects an angular velocity around a center.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional optical fiber gyro. The light from the light source 11 passes through an optical branching device 12 such as an optical fiber coupler, and further passes through a polarizer 13 to extract only a component in a predetermined polarization direction. The light from the polarizer 13 is a light such as an optical fiber coupler. The light is split into two by the branching device 14, one light of which is incident on one end of the optical fiber coil 16 as a clockwise light, and the other light passes through the optical phase modulator 17 and is counterclockwise light on the other end of the optical fiber coil 16. Is incident as.

The right-handed light and the left-handed light propagating through the optical fiber coil 16 return to the optical branching device 14 to be combined and interfere with each other, and the interfering light is extracted by the polarizer 13 only in a predetermined polarization direction. The light that has passed through the polarizer 13 is split by the optical splitter 12 and is incident on the photodetector 18, and is converted into an electrical signal corresponding to the intensity of the light. Modulation signal generator 1
The optical phase modulator 17 is driven by the periodic function from 9, for example, a sine wave signal, and the light passing therethrough is phase-modulated. The output of the photodetector 18 is synchronously detected by the synchronous detection circuit 21 by the reference signal from the modulation signal generator 19, and the detected output is output to the output terminal 22.

When the angular velocity around the axis of the optical fiber coil 16 is not applied, the phase difference between the clockwise light propagating through the optical fiber coil 16 and the counterclockwise light is zero, and the synchronous detection circuit. The output of 21 is also zero, but when an angular velocity around the axis is applied to the optical fiber coil 16, a phase difference occurs between the clockwise light and the counterclockwise light in response to this, and the synchronous detection circuit 21 The output of the polarity and level according to the direction and magnitude of the applied angular velocity is generated, and the applied angular velocity can be detected.

As described above, the optical fiber gyroscope detects the phase difference between the clockwise light and the counterclockwise light. However, the polarization state changes during propagation through the optical fiber coil 16, and the polarization direction is right angle. When there is such a component, since the optical fiber coil 16 has a small amount of birefringence, the two lights in the orthogonal polarization directions have different propagation velocities in the optical fiber coil 16 and are thus combined by the optical branching device 14. If one polarization component of the clockwise light and the other polarization component of the counterclockwise light interfere with each other, the phase difference between the clockwise light and the counterclockwise light cannot be correctly detected.

From this point of view, conventionally, it has been general to use a polarization-maintaining optical fiber for the optical fiber coil 16. In this case, the polarization states of the clockwise light and the counterclockwise light propagating through the optical fiber coil 16 are kept stable, so that the gyro performance is stable. However, since the polarization-maintaining optical fiber is expensive, there is a drawback that it is about half the total price of the optical fiber gyro.

An optical fiber gyro that solves this problem and is stable in performance has been proposed in Japanese Patent Application No. 3-158768. As shown in FIG. 3, this is composed of an inexpensive single-mode optical fiber 16a as an optical fiber coil 16 and a polarization-maintaining optical fiber 16b with extra lengths connected to both ends thereof. Due to the birefringence generated in the fiber 16a, the polarization maintaining property equivalent to that of the polarization maintaining optical fiber is provided, and the polarization maintaining optical fiber 16b is used in the extra length portion where bending does not occur to maintain the stable polarization state.

With this structure, it is possible to obtain a stable optical fiber gyro which is inexpensive and is equivalent to the case where the whole polarization plane maintaining optical fiber is used.

[0009]

However, in the optical fiber gyro shown in FIG. 3, since the birefringence generated in the single mode optical fiber 16a due to the bending stress is utilized, the coil bobbin and the single mode optical fiber 16a are used. Due to the effect of thermal stress caused by the difference in thermal expansion between the two, the birefringence generated in the single-mode optical fiber 16a is likely to change, which causes a change in polarization maintaining property in the optical fiber coil 16, that is, the polarization maintaining axis is Change, and as a result, the amount of interference light that passes through the polarizer 13 and reaches the photodetector 18 changes.
There is a problem that the output of the optical fiber gyro is likely to change.

[0010]

According to the invention of claim 1, the optical fiber coil is a single mode optical fiber,
It is composed of two polarization-maintaining single-mode optical fibers connected to both ends thereof, and utilizes the birefringence caused by bending stress of the single-mode optical fiber. At the connection point with the polarization-maintaining optical fiber, the principal axes of the polarization-maintaining optical fiber and the optical branching means are inclined by 45 ° with respect to each other.

According to the invention of claim 2, the optical fiber coil is composed of a single mode optical fiber and two polarization-maintaining optical fibers connected to both ends of the single mode optical fiber, and is generated by bending stress of the single mode optical fiber. Utilizing the birefringence, the light from the light source is incident on the optical branching means through the polarizer, and the optical branching means is constituted by the polarization-maintaining optical transmission line, and the main axes of the optical branching means and the polarizer are mutually 45 °
It is inclined.

Also in the inventions of claim 1 and claim 2, the light incident on the optical fiber coil is a component having almost the same intensity of two polarization maintaining axes of the polarization maintaining optical fiber which are orthogonal to each other. Since it propagates, the birefringence fluctuates in the part of the single mode optical fiber, and even if the polarization maintaining axis direction changes, the passing component of the orthogonal two-component polarizer is
When one decreases, the other increases and is always constant,
The intensity of the interference light does not change.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the essential parts of an optical fiber gyro according to the present invention, and the parts corresponding to those in FIG. In the present invention, as in FIG. 3, the optical fiber coil 16 is composed of a single mode optical fiber 16a and two polarization-maintaining optical fibers 16b connected to both ends thereof. In this example, a polarization maintaining optical fiber coupler is used as the optical branching device 14. The connection point 23 between the polarization-maintaining single-mode fiber coupler 14 and the two polarization-maintaining single-mode optical fibers 16b is separated, and the end face thereof is enlarged. Polarization maintaining axes 24x (X axis) and 24y
(Y axis) and the polarization maintaining axes 25x (X axis) and 25y (Y axis) orthogonal to each other at the end faces of the two polarization-maintaining single-mode fibers 16b are displaced from each other by about 45 ° about the axis. There is.

Therefore, the light that has reached the connection point 23 from the polarizer 13 through the polarization-maintaining optical fiber coupler 14 has propagated through either the polarization-maintaining axis 24x or 24y of the polarization-maintaining optical fiber coupler 14. It is linearly polarized light, and the linearly polarized light is 45 in the two polarization-maintaining optical fibers 16b at the connection point 23 with respect to the polarization maintaining axis 25x (X axis).
Incident at an angle of °. As a result, this linearly polarized light is transmitted through the polarization-maintaining optical fiber 16b through two orthogonal polarization-maintaining axes 25.
It is propagated after being divided into two components of the same intensity x and 25y. That is, the linearly polarized light of the same intensity parallel to the polarization maintaining axes 25x and 25y is incident on the polarization-maintaining optical fiber 16b. Looking at the passing components of the polarizer 13 of the light passing through the optical fiber coil 16 and further back to the polarizer 13 through the optical fiber coupler 14, the birefringence of the single mode optical fiber 16a due to thermal stress fluctuation or the like is observed. Even if the polarization maintaining axis changes (rotates) due to the change, when one of the two components increases, the other decreases and becomes constant, so that the intensity of the light reaching the photodetector 18 increases. Is constant and a stable gyro output is obtained.

At the connection point 23, fusion splicing of optical fibers is generally performed, but they may be coupled by lens coupling, optical coupling between optical fibers, or the like. An optical integrated circuit may be used as the optical branching means 14. The two polarization-maintaining optical fibers 16b are connected to the two polarization-maintaining axes 25
Since it suffices to input linearly polarized light of the same intensity parallel to x and 25y respectively, in the connection between the polarizer 13 and the optical branching means 14, for example, the polarization maintaining axis of the optical fiber on the side of the polarizer 13 and the optical branching. For example, linearly polarized light parallel to one polarization maintaining axis on the side of the polarizer 13 may be incident on the side of the optical branching means 14 by making the polarization maintaining axis of the optical fiber on the side of the means 14 side away from each other by 45 °.

[0016]

As described above, according to the present invention, the optical fiber coil 16 is composed of the single mode optical fiber coil and the two polarization maintaining optical fibers connected to both ends thereof. Can be configured inexpensively,
Moreover, since two linearly polarized light beams of the same intensity parallel to the two polarization-maintaining axes are incident on the polarization-maintaining optical fiber, the birefringence of the single-mode optical fiber 16a changes due to the temperature change. Also, stable gyro output can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part of an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional optical fiber gyro.

FIG. 3 is a block diagram showing the previously proposed optical fiber gyro.

Claims (2)

[Claims] 1. Light from a light source is distributed by a light branching means and is incident as right-handed light and left-handed light from both ends of an optical fiber coil. In the optical fiber gyro that causes interference by means, converts the intensity of the interference light into an electric signal, and detects the angular velocity applied around the center of the optical fiber coil from the electric signal, the optical fiber coil is a single mode optical fiber. And two polarization-maintaining single-mode optical fibers connected to both ends thereof, wherein the principal axes of the optical branching means and the two polarization-maintaining single-mode optical fibers are inclined by 45 ° with respect to each other. Fiber gyro. 2. Light from a light source is incident on a light splitting means through a polarizer to be distributed, and the distributed light is incident on both ends of the optical fiber coil as right-handed light and left-handed light. After propagating through the optical fiber coil, the optical branching means interferes with each other, the interference light is passed through the polarizer, and the intensity thereof is converted into an electric signal, and the electric signal is applied around the center of the optical fiber coil. In the optical fiber gyro for detecting an angular velocity, the optical fiber coil includes a single-mode optical fiber and two polarization-maintaining optical fibers connected to both ends thereof, and the optical branching unit includes a polarization-maintaining optical transmission line. An optical fiber gyro, characterized in that the principal axes of the light branching means and the polarizer are inclined by 45 ° with respect to each other.