JPS58198713A - Optical Fiber Valley The Gyro - Google Patents

Abstract

PURPOSE:To improve the detection sensitivity, by branching a linearly polarized light to a transmitted light and a reflected light and allowing these lights to pass through a coil-shaped polarization plane preserving optical fiber and detecting the phase difference between both lights through a 1/4 wavelength plate. CONSTITUTION:The light from a laser light source 1 is linearly polarized completely by a polarizer 2 and has the direction adjusted optionally by a 1/2 wavelength plate 3 and is branched by a beam splitter 4. When the light is branched to the transmitted light and the reflected light by the beam splitter 4, one is incident to one intrinsic polarization axis from one end of a coil-shaped polarization plane preserving optical fiber 6 through a Farrady element 5, and the other is incident to said intrinsic polarization axis from the other end of said fiber 6 without passing the element 5. Lights propagated to the polarization plane preserving optical fiber are led to a 1/4 wavelength plate 7 by the beam splitter 4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber laser gyro.

Conventionally, in an optical fiber laser gyro using a multi-thickness wound optical fiber in the optical path of a ring interferometer, methods for detecting the phase difference of bidirectionally propagating light within an optical fiber can be broadly classified into the following two methods.

(1) Interference fringe change detection method. (2 interference light intensity change detection method.

Among these methods, (1) has a large coupling loss because the focal point of the incident condition of one light is removed from the optimal coupling point to create fringes, and the S/N ratio is low because only a part of the interference light is used. However, there was a drawback that the optical system was not sufficiently accurate, and a large error occurred due to the positional shift of the optical system on the order of a wavelength.

In method (2), the phase difference of bidirectional propagating light due to rotation is Δ
If θ is used, an interference light output proportional to COS Δθ can be obtained, but when Δθ is a minute amount, the detection sensitivity is poor and the direction of rotation cannot be detected.

Furthermore, since the optical fiber used as the transmission line was a normal single mode optical fiber, stable phase detection was not possible.

On the other hand, methods using optical phase and frequency modulators have also been proposed, but these methods are insufficient in terms of reliability and cost. There is also a so-called orthogonal polarization method in which orthogonal polarization modes within an optical fiber are assigned to bidirectionally propagating light, but this method is not sufficient because it is affected by changes in the length of the optical fiber due to temperature.

Furthermore, in the conventional method, the signal light and the backscattered light within the optical fiber cause interference, which becomes a noise source and causes poor detection sensitivity.

In view of this situation, the present invention makes it possible to detect the direction of rotation when the phase difference of propagating light due to rotation is minute.
The purpose is to provide an optical fiber laser gyro with good detection sensitivity, and its gist is that linearly polarized light is split into transmitted light and reflected light by a beam splitter, and one of the split lights is 45° polarized. A Faraday element that gives rotation, and the other light enters one characteristic polarization axis of a coiled polarization-maintaining optical fiber from both ends without going through a Faraday element, and the phase difference between the two emitted lights is measured by a quarter-wave plate. This is due to the fact that it is configured to be detected through the .

The configuration of the present invention will be specifically explained with reference to the drawings showing one embodiment.

In the figure, 6 is a coiled polarization maintaining optical fiber, and 4 is a beam splitter.

1. Light from a laser light source 1 is completely linearly polarized by a polarizer 2, its direction is arbitrarily adjusted by a 1/2 wavelength plate 3, and then split by a beam splitter 4.

When the transmitted light and the reflected light are split by the beam splitter 4, one of them passes through the Faraday element 5 and the other does not pass through the coiled polarization-maintaining optical fiber 6, and each enters one unique polarization axis from both ends. be done.

The Faraday element 5 rotates polarized light by 45°, and both end faces of the polarization-maintaining optical fiber 6 are shaped to have a relative spatial polarization orientation difference of 45°.

As a result, the light propagating in the clockwise (CW) direction and the light propagating in the counterclockwise direction (CCW) in the coiled polarization maintaining optical fiber 6 become spatially orthogonal. Therefore, since the polarization planes of the CW and CCW signal lights and the backscattered lights are spatially orthogonal, the interference is low and the S/N ratio is good.

In this way, the light propagated through the polarization-maintaining optical fiber is again guided to the quarter-wave plate 7 by the beam splitter 4.

The quarter-wave plate 7 is arranged so that its fast axis is located in a direction forming an angle of 45° with the spatially orthogonal direction. The transmitted light from this 1/4 wavelength plate 7 is 1/2△
It becomes linearly polarized light with an orientation of O.

When this light Δθ=0, that is, when it is stationary, the analyzer 9
is installed so as to be in the extinction state, and when Δθ˜0, that is, when it is rotating, the extinction state is maintained by controlling the current flowing through the coil surrounding the Faraday element 8. 10 is a photoelectric conversion element, and 11 is a current control circuit.

In this way, the phase difference Δθ is determined from the control current, and the output at this time becomes proportional to sin Δθ.

Alternatively, without using the Faraday element 8, the output light from the 1/4 wavelength plate 7 is directly received by the analyzer 9, and by mechanically rotating the analyzer 9, the phase difference is calculated from the rotation angle. Δθ may also be determined. However, the method using the Faraday element 8 allows the zero-order method to be used, and the dynamic range of the detection range can be expanded.

The optical fiber layer 4-1 gyro of the present invention as explained above has the following remarkable effects.

(Since a signal proportional to ll sin Δθ can be detected, the direction of rotation can be detected, and the detection sensitivity is good even when the phase difference of propagating light due to the rotational angular velocity is minute.

(2) Since the polarization of the signal light and the backscattered light are orthogonal,
There is little interference, the S/N ratio is good, and the detection sensation is good.

(3) Since the m-wavefront preserving optical fiber is used, the polarization plane of the propagating light is stable and the detection sensitivity is good.

Note that the polarization-maintaining optical fiber herein is an optical fiber that has a unique polarization axis and has the property of preserving the polarization plane.

(4) Since no phase modulator or frequency modulator is particularly required, it is inexpensive and highly reliable.

Note that it is desirable that a condensing or collimating lens is attached to the end face of the optical fiber.

[Brief explanation of drawings]

The figure is an explanatory diagram showing one embodiment of the present invention. 1: Light source, 2: Polarizer, 3: 1/2 wavelength plate, 4: Beam splitter, 5: Fluorub element, 6: Polarization maintaining optical fiber, 7: 1/4 wavelength plate, 8: Faraday element, 9 :
Analyzer, 10: Photoelectric conversion element, 11: Current control circuit. Agent Patent Attorney Fujio Sato 7- 7-I-Ko

Claims (1)

[Claims] The linearly polarized light is split into transmitted light and reflected light by the beam splitter 4, and one of the split lights is passed through a Faraday element 5 that rotates the polarization by 45 degrees, and the other is sent through a coil-shaped polarization plane preserving device without going through a Faraday element. An optical fiber laser gyro characterized in that the optical fiber laser gyro is configured so that the light is incident on one characteristic polarization axis of an optical fiber 6 from both ends, and the phase difference between the two emitted lights is detected via a quarter-wave plate 7.