JPS6344173B2 - - Google Patents

Description

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

Conventionally, in an optical fiber laser gyroscope 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 the optical fiber can be broadly classified into the following two methods.

(1) Method for detecting changes in interference fringes (2) Method for detecting changes in interference light intensity Among these methods, method (1) removes the focus of the incident condition of one of the lights from the optimal coupling point to create fringe, so coupling loss is reduced. Moreover, since only a part of the interference light is used, the S/N ratio is not sufficient, and furthermore, a large error occurs due to a positional shift of the optical system on the order of a wavelength.

In method (2), if θ is the phase difference of the bidirectionally propagating light due to rotation, an interference light output proportional to cos θ can be obtained, but when θ is a minute amount, the detection sensitivity is poor and the direction of rotation cannot be detected. It was hot. 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.

In view of this situation, the present invention provides an optical fiber laser gyroscope that is capable of detecting the direction of rotation and has good detection sensitivity and S/N ratio when the phase difference of propagating light due to rotation is minute. The purpose is to

An embodiment of the configuration of the present invention will be specifically described below with reference to the drawings.

In the figure, 6 is a polarization-maintaining optical fiber configured in a coil shape, and 4 is a beam splitter.

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 linearly polarized light is split into transmitted light and reflected light by the beam splitter 4, one of them passes through the Faraday element 5, and the other does not pass through the Faraday element 5. The light is incident on the polarization axis, for example, along the long axis direction. Of course, the light may be incident in the short axis direction.

In order to do this, the Faraday element 5 is configured to rotate the plane of polarization by 45 degrees, and both end faces of the polarization preserving optical fiber 6 are shaped to have a relative spatial polarization orientation difference of 45 degrees. ing.

As a result, the linearly polarized light propagating clockwise (CW) through the coiled polarization-preserving optical fiber 6 and the linearly polarized light propagating counterclockwise (CCW) are spatially polarized when extracted again by the beam splitter 4. It becomes orthogonal to . Therefore, since the polarization planes of the CW and CCW signal lights (propagating 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 coiled polarization-maintaining optical fiber 6 is again guided to the quarter-wave plate 7 by the beam splitter 4. The fast axis or slow axis of the quarter-wave plate 7 is the CW emitted from the optical fiber.
Or set equal to the direction of CCW linearly polarized light. Therefore, a 90° phase bias is added between the CW propagating light and the CCW propagating light.

In the case of this embodiment, when θ=0, that is, when it is stationary, linearly polarized light enters the quarter-wave plate 7, so
Circularly polarized light is emitted. Further, when θ≠0, that is, when the light is rotating, elliptically polarized light is emitted.

The light emitted from the 1/4 wavelength plate 7 is
The transmitted light and reflected light of the polarized beam splitter 8 are guided to a polarized beam splitter 8 installed at an angle of 45 degrees, and the transmitted light and reflected light of the polarized beam splitter 8 are converted into electric signals by photoelectric converters 9, and these two outputs are differentially connected. By performing differential amplification with the amplifier 10, the polarization state, that is, θ can be determined.

In the conventional configuration, the output could only be obtained as a signal proportional to cos θ, but in the present invention, since the 1/4 wavelength plate 7 is inserted, it is possible to extract a signal proportional to sin θ. . That is, this is because the transmitted light and reflected light outputs of the polarizing beam splitter 8 can be proportional to (1+sin θ) and (1−sin θ), respectively.

In addition, in the configuration shown in this figure, a new beam splitter is inserted between the beam splitter 4 and the 1/4 wavelength plate 7, and the split light is used to extract a signal proportional to cos θ, so that θ is ±90 If the detection range is configured to be used when the temperature exceeds .degree., it is possible to significantly expand the detection range.

As explained above, the optical fiber laser gyroscope of the present invention has the following remarkable effects.

(1) Since a signal proportional to sin θ can be detected, the direction of rotation can be detected, and the detection sensitivity is good even when θ is small.

(2) There is almost no interference between the signal light and the backscattered light, so the S/N ratio is good.

(3) Since a polarization-maintaining optical fiber is used, the polarization plane of the propagating light is stable and the accuracy is high.

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

[Brief explanation of drawings]

The figure is an explanatory diagram showing one embodiment of the present invention. 1: Laser light source, 2: Polarizer, 3: 1/2 wavelength plate,
4: Beam splitter, 5: Faraday element,
6: Coiled polarization-maintaining optical fiber, 7: 1/4 wavelength plate, 8: Polarizing beam splitter, 9: Photoelectric converter, 10: Differential amplifier.

Claims (1)

[Claims] 1 Linearly polarized light is split into transmitted light and reflected light by a beam splitter 4, and one of the split linearly polarized lights is passed through a Faraday element 5 that rotates the plane of polarization by 45 degrees, and the other is split without going through a Faraday element. A coiled polarization-maintaining optical fiber 6, which has a relative spatial polarization orientation difference of 45 degrees on both end faces, is incident on one of its unique polarization axes from both ends, and the phase difference between the two emitted lights is calculated by calculating the phase difference between the linearly polarized light. It is guided to a polarizing beam splitter 8 via a quarter-wave plate 7 arranged with its fast axis or slow axis aligned with the azimuth.
An optical fiber laser gyroscope characterized in that the phase difference between the linearly polarized light is detected from the differential output between the transmitted light and the reflected light of the polarized beam splitter 9.