JPS6344171B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber laser gyroscope, and more particularly to an optical fiber laser gyroscope that enables minute detection of rotational angular velocity.

Conventionally, methods for detecting changes in the interference state of an optical fiber laser gyroscope using a ring interferometer 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 In method (1), in order to create fringes, the focus of the light incident condition for one rotation is shifted from the optimal coupling point, resulting in large coupling losses. Furthermore, since only a portion of the interference light is used, it is easily affected by noise, and has the disadvantage that errors occur due to positional deviations on the order of wavelengths in the optical system.

In method (2), if θ is the phase difference of the bidirectionally rotated light due to rotation, an interference light output proportional to cosθ is obtained, so the sensitivity is poor when θ is a minute amount, and even if θ changes to positive or negative, the direction of rotation is The disadvantage is that it is unknown.

Furthermore, the optical fiber used as a transmission line is a single mode fiber, but conventional single mode fibers have poor polarization preservation properties, and instability of polarization causes fluctuations in interference light.

In view of this situation, the present invention eliminates the above-mentioned drawbacks of the conventional technology, allows detection of the rotation direction, has excellent sensitivity even when the rotation angle is small, and also eliminates polarization instability in the optical fiber. did. The purpose is to provide a new optical fiber laser gyroscope.

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

First, a method for extracting bidirectionally propagating light will be explained using FIG. 1. The light source 1 is a laser, and although it would be better if an isolator was added since there would be no laser irradiation with reflected light, here a He--Ne laser was used directly. Note that when using a semiconductor laser, it is preferable to use a collimating lens. Now,
Half of the laser light emitted from the light source 1 passes through a BS (beam splitter) 3. A λ/2 plate 2 is placed in front of the BS 3 so that the laser beam enters as linearly polarized light at an angle of 45° to the direction of the PBS (polarizing beam splitter) 5 placed later.

In PBS5, S-polarized light and P-polarized light components of linearly polarized light in the 45° direction are reflected and transmitted, respectively. These lights enter the polarization-maintaining optical fiber coil 9 in opposite directions through the microlens 6, respectively, but the polarization-maintaining optical fiber coil 9
It is arranged with a 90° twist so that its intrinsic polarization axis is spatially perpendicular to the PBS 5, and is configured so that any polarized light component is incident, for example, in the long axis direction of the polarization preserving optical fiber coil 9. be.
Note that, of course, it may be placed in the short axis direction instead of the long axis direction. In this way, the clockwise propagating light (CW) propagates as P-polarized light, and when it enters PBS5 again, it enters as S-polarized light, so it is reflected toward BS3. At this time, the component PBS5 converted to the short-axis azimuth mode is transmitted, and does not reach the detector side. Therefore, it does not cause noise due to extinction ratio deterioration. Similarly, counterclockwise propagating light (CCW) propagates as S-polarized light and enters PBS5 as P-polarized light, so it is transmitted toward BS3.

Therefore, in BS3, the polarized waves of light in the CW and CCW directions can be extracted in directions such that they are spatially orthogonal.

In this way, when the polarization preserving optical fiber coil 9 does not rotate, the phase difference between CCW and CW light is equal, so the light extracted by BS3 is linearly polarized light. In this state, if the 1/4 wavelength plate 10 is placed at an orientation of 45 degrees with respect to the linearly polarized light, that is, if it is placed at an orientation that matches the orthogonal polarization axis of the linearly polarized light, the 1/4 wavelength plate 10
The output light of the four-wavelength plate 10 becomes circularly polarized light.

Now, if the polarization-maintaining optical fiber coil 9 is rotated at a rotational angular velocity Ω, a sagnac phase difference θ occurs between the P-polarized light and the S-polarized light. It is known that this θ has the following relationship with Ω.

θΩ=4πRl/λc (1) where R is the loop radius of the coil, l is the fiber length, λ is the wavelength, and C is the speed of light.

Therefore, the incident light to the quarter-wave plate 10 (P polarized light and S
The electric field vector of polarized light can be expressed by the following equation using the above θ.

ep=Acos(wt-θ) es=Acos wt...(2) However, A is a constant and w is the optical angular frequency. In other words, light is generally elliptically polarized. When the light is transmitted through the quarter-wave plate 10 in this state, a phase difference of 90° is added between the P-polarized light and the S-polarized light. Therefore, the light after passing through the quarter-wave plate 10 is expressed by the following formula.

ep′=Acos(wt−θ) es′=Acos wt …(3) After that, another PBS11 is added to the 1/4 wavelength plate 1
0, spatially orthogonal polarization components are taken out, and each light is sent to the photoelectric converter 1.
2 and 12, the respective outputs are led to a differential amplifier 13 and the outputs are observed.

The output component of PBS11 is 1/4 the direction of PBS11.
Since it is tilted at 45° to the wave plate, PBS
The transmission side output light and reflection side output light of 11 are Therefore, the photoelectric converter 1
As the light intensity received at 2 and 12, an electric signal of P ₁ =K/2A ² (1+sin θ) P ₂ =K/2A ₂ (1+sin θ) (5) can be obtained. However, k is a constant. Therefore, the output observed by the differential amplifier 13 is expressed by the following equation.

P=P ₁ -P ₂ =kA ₂ sinθ...(6) Therefore, from equation (6), when the polarization preserving optical fiber coil 9 does not rotate, the output is 0, and when it rotates, the output changes depending on the direction of rotation. It is clear that it appears with positive and negative polarities.

In fact, it is preferable to use an attenuator to adjust in advance so that the outputs of the photoelectric converters 12 are equal in a stationary state. Furthermore, by integrating the output of the differential amplifier 13, the direction from the initial state can be determined. Furthermore, P/
By performing the calculation of (P ₁ +P ₂ ), the signal is standardized and highly accurate detection is possible which is completely unaffected by fluctuations in the light source.

Note that when light is propagated between each device or element, if air is used as a medium, it is easily affected by vibrations, so the polarized light may be propagated using a polarization-maintaining optical fiber as shown by the broken line 4 in Figure 1. .

Here, the polarization-maintaining optical fiber is an optical fiber having a cross-sectional structure as shown in FIG. It has the following.

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

(1) By transmitting the emitted linearly polarized light through a quarter-wave plate, a 90° phase difference is added between the S-polarized light and the P-polarized light, so the output of the differential amplifier is proportional to sinθ. Since it is an output, the direction of rotation can be detected based on the positive or negative sign of the output.

(2) Sensitivity is greatly improved because deterioration of the extinction ratio during optical fiber propagation is not a problem.

(3) Since a polarization-maintaining optical fiber is used, the polarization plane in the optical fiber is stable.

(4) Since a differential amplifier is used, output fluctuations due to temperature characteristics of the light source or optical fiber are not a problem, and reliability is high.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the optical fiber laser according to the present invention, and FIG. 2 is a sectional view showing an example of the polarization-maintaining optical fiber used in the present invention. 1: Light source, 2: 1/2 wavelength plate, 3: BS, 4: Polarization preserving optical fiber, 5: PBS, 6: Microlens, 9: Polarization preserving optical fiber coil, 10:
1/4 wavelength plate, 11: PBS, 12: Photoelectric converter, 1
3: Differential amplifier.

Claims (1)

[Claims] 1. Linearly polarize the light from the light source, guide it to the BS (beam splitter) 3, make it incident on the polarizing beam splitter (PBS) 5 at an angle of 45 degrees, and make it enter the polarizing beam splitter (PBS) 5 on the transmission side and reflection side. Both ends of the polarization-maintaining optical fiber coil 9 are arranged so that the inherent polarization is spatially perpendicular to the polarization beam splitter 5, so that the transmission side output light and the reflection side output light are connected to the polarization-maintaining optical fiber coil 9. 9, and the phase difference of the light propagated in both directions through the polarization-maintaining optical fiber coil 9 is transferred to a differential amplifier via a quarter-wave plate 10 and a polarizing beam splitter 11. An optical fiber laser gyroscope characterized in that it is configured to detect by.