JPS62121311A - Optical fiber gyro - Google Patents

Abstract

PURPOSE:To non-polarize a light beam which is propagated through an optical fiber loop, and to suppress an output drift by providing a means for non- polarizing the light beam, between the first and the second distributing means for distributing the light beam. CONSTITUTION:The light beam from a single mode fiber 11 is divided into two by an optical directional coupler 12, and propagated to a single mode fiber 13 and a signal mode fiber 14. The single mode fiber 14 side becomes a resistive terminal 15. Subsequently, the light beam from a light source 10 is propagated through the mode fiber 13 in a state that it remains emitted and polarized, and led to a non-polarizing device 16, and non-polarized after having passed through side device. Also, an output light beam of the non- polarizing device 16 passes through an optical directional coupler 20 once before reaching an optical fiber loop 24, but since its number of times is small, there is scarcely a chance by which a degree of non-polarization is disturbed. In this way, a drift of a detection output is reduced remarkably comparing with a conventional case, and even at a minute angular velocity, a measurement can be executed with a high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical fiber gyro that detects the angular velocity of a rotating body by detecting interference waves (il-waves) of light propagating in opposite directions through a fiber loop.

[Technical background of the invention and its problems]

In controlling moving objects such as aircraft and ships, it is essential to accurately know the rotation angle information of the object, and a rate sensor that detects the rotation angle speed plays an important role in the control device. .

Conventionally, a mechanical gyro that utilizes the inertia of a rotating body has been used as a rate sensor, but in recent years Sagnac
Optical sensors that utilize this effect have been developed and are thought to become the mainstream rate sensors in the future. Among these optical rate sensors, the optical 7-eye gyro uses an optical fiber loop as an optical path, propagates light around both sides of the loop, and detects the rate (angular velocity) from the interference light.It is highly accurate and compact. , research and development will become more active due to the i=J potential for lower prices.

In this optical 7-eye camera, rate detection 2 is performed by detecting a minute optical phase difference due to the Sagnac effect, but is the change in the polarization state that occurs within the optical fiber the optical phase error due to birefringence? This causes a drift in the detection output and a variation in the scale factor.

In order to eliminate this problem, conventional methods (7) use a constant IJli wave (polarization preserving) fiber to remove single-wave fluctuations (a) use a polarizer and a polarization adjustment element to only produce a single polarization component. A method has been proposed in which the light source section is completely non-polarized, the polarization plane of the light passing through the fiber is randomly set, and the error meter is canceled. Figure 3 shows the configuration of a phase modulation optical gyro with a non-polarized light source (methods mentioned above).The light from the sterile light generator (or non-polarized light source) (1) is non-polarized. guided by the optical fiber (2), and connected to the optical directional coupler (
3) is divided into two. One of the two divided lights passes through the non-glue mode fiber (4) and is supplied to the optical power directional coupler (5). The optical directional coupler (5) splits the light from the non-gle mode fiber (4) into two and supplies it to both ends of the non-dal mode loose optical fiber (6).

The light propagated in both the right and left directions of the original fiber loop (6) is circularly coupled by a phase changer (7-way optical power directional coupler 15) before or after passing through the loop.

The recombined source is a single mode fiber (4).

The phase modulator (7), which passes through the optical directional coupler (3) and is guided to the optical output device (8), converts the original fiber-passing light into a frequency fO.
The phase is modulated periodically. The detection signal of the photodetector (8) includes a modulation frequency that reads the Sagnac phase difference Δφ component and its higher-order components, and the signal processing circuit 19) detects the phase difference Δφ expressed by each frequency component, It converts into f signal and outputs it.

In this method, the effects of polarization state changes are separated by using a single non-IJTi element for loop propagation light, but this is done by making the light source non-polarized or at the light source itself or immediately after it. At this time, the directional coupler L3J, (5) is due to manufacturing defects, and the original characteristic is that the 1 element passes through the optical power directional coupler twice from the light source and becomes the light 7 eye paluse. In the meantime, the 'ipA polarization; the polarization is distorted, which causes the above-mentioned output error.

On the other hand, in the method (7) above, it is difficult to manufacture a directional coupler using a polarization constant fiber, and the problem is that the polarization plane is insufficiently maintained using only a polarization constant fiber, and (a) The method described above has disadvantages such as the large number of necessary components and clutter in order to realize the plane of polarization.

[Aspect of the invention]

Is the present invention related to the above J? It was done with consideration, and it is a simple +
An object of the present invention is to provide an optical fiber gyro that can suppress output drift by unpolarizing light propagating through an optical fiber loop with S configuration.

[Summary of the invention]

The optical fiber gyro according to the present invention uses light in the path from the light source to the optical fiber gyro. 1st to distribute. Second
A means for depolarizing the principal is provided between the distributing means, thereby reducing the number of times the light from the light source passes through the distributing means, thereby reducing the unpolarized likelihood. The ability to reduce the output drift is to increase the number of guns to six.

[Embodiments of the invention]

Hereinafter, an embodiment of the original fiber gyro according to the present invention will be described with reference to FIGS. 1 and 2.

As the light source t10), a light source having a wide spectral width and a direction of incidence into a single mode fiber with excellent directivity, such as a superluminescent diode, can be used. The reason for using a light source with a wide spectral width is that the wider the spectral width of the propagating light, the more it is possible to reduce output noise due to interference between signal light and return light due to Rayleigh scattering within the fiber, and output drift due to the Kerr effect.

In addition, let M be the origin point where the unpolarized likelihood function B, which will be described later, becomes a town.

Light from the beam tl(l is coupled into a single mode fiber υ).

The light from the non-gle mode fiber 10+ is split into two by the optical power directional coupling 6112 and sent to the single mode fiber Become. light source u
The light emitted from O is polarized and propagates through the single mode fiber ti3n, and is guided to the non-polarizer i1Q, and after passing through, it becomes non-polarized. (Two wires are coupled in series so that the polarization preserving surfaces are at an angle of 45 degrees to each other, and the propagating light is made non-polarized.For this configuration, see, for example, the Institute of Electronics and Communication Engineers Technical Research Report 0QE.
83-42 (IEICE Technical Report Vol. 83NO, 90P, 73
~P, 78. Association Law Rokuden Communication Society July 26, 1983
(Published on the same day). According to Bandai, there are four non-polarizers that consist of only fibers in the propagation optical path. You can set it up. The light depolarized by the depolarizer ue is guided to the single mode fiber α power and propagated through the optical directional coupler 1A (i = i) to the non-gle mode fiber Qυ and the single 7-domain fiber 4. Mode fiber laser I) K-coupled light is composed of a non-glue mode fiber and wound around a drum device L! After propagating clockwise through the optical fiber loop 1241r, the phase modulator (
C) and periodically ((phase modulated).

After the light coupled to the non-glued fiber 124 is phase modulated by a phase modulator 125), it is transferred to the optical fiber loop t.
14J counterclockwise (V).

The fiber is loose (the light propagated in opposite directions through the two fibers is re-coupled). The 07 dal mode fiber is exclusively coupled to the directional coupler lA; the 20 side is a non-reflection termination.

The unpolarized light propagated through the non-gle mode fiber is guided to the photodetector via the optical directional coupler and the non-gle mode fiber. The photodetector fj detects interference 6y of the original signal, converts it into electric signal 1g, and outputs it. The output signal of this photodetector (to) is converted into an angular velocity signal in a signal processing section, and the angular velocity is detected.

In the fiber gyro shown in FIG. 1, a non-polarizer is disposed between the optical directional coupler U and the optical directional coupler 121.

In this +J4 B■, the unpolarized light is connected to the optical directional coupler between the reeds leading to the original fiber loose (to).
Since the light passes through only once, the degree to which the original degree of non-polarization becomes low F is small.

In other words, the light introduced into the depolarizer t161 is the original polarized light, and the 4K light that passes through the optical directional coupler u4 is
Even if it is subjected to kiln movement with ITF optical characteristics, the light is made non-polarized without any effect. The output light of the depolarizer +l[i passes through the t-fiber loop (the original directionality combiner -1?) once before reaching the circle, but this number of times is less than in the case of Fig. 2, so the light There is little opportunity for the degree of non-polarization to be disturbed.As a result, as shown in Figure 2 (station building with zero input angular velocity), the drift of the detection output (actual q) is lower than in the conventional case (e[). Even if the angular velocity is extremely small, the consistency is determined to be less than 100%.

The non-polarizer may be made of a constant polarization fiber as described above, or may be made of a non-polarizer of the Lyot type in a birefringent crystal mold. When using a split-wave fiber, the optical propagation path can be made entirely of fibers, resulting in less loss in the optical test and simpler grooves.0 When using a birefringent crystal, the axis alignment required for a polarization-controlled fiber is 4. Although it is Chichi, there is a slight loss of Moto Sumire.

Of course, it is also possible to use a 'jt source that does not have 1M elementality and outputs 9 r as the light source JOI, and in this case, as described above, by arranging a light control device, the light is propagated through the original fiber loop. Drift to increase the luminosity r of light? can be reduced.

In addition, optical fiber loops 24) and phase modulation API
'25), when a polarization constant fiber is used, the change in mi is reduced by less than t, which is OT.

〔Effect of the invention〕

As explained above, according to the optical fiber gyro according to the present invention, output drift can be suppressed with a simple structure, and measurement precision can be improved.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining an embodiment of the optical fiber gyro according to the present invention, FIG. 2 is a diagram for explaining the four characteristics of the optical fiber gyro according to the present invention, and FIG. 3 is a diagram for explaining a conventional original fiber gyro. 0 LILJ...Light source, (13,l:'tJ...Optical force tropic coupler, 4...Non-likelihood generator,; 24J...Original fiber loose, ■...Phase modulator, 1291...・Light/direction device, C
→...Signal processing section. Agent Patent attorney Nori Chika Ken Yudo Take Hana Kikuo Kinu? figure

Claims (1)

[Claims] A light source that outputs light and a first light source that distributes the light from this light source.
a distributing means for distributing light from one of the first distributing means, a means for outputting light having a lower degree of polarization than the output light, and a second distributing means for distributing the light from the first distributing means; It includes an optical fiber loop to which the output light of the second distribution means is supplied and the light propagates in opposite directions, and a photodetector that detects interference light of the lights propagated in opposite directions through the optical fiber loop. Hikari Fuaibagairo.