JPH0721415B2 - Rotational angular velocity detector - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an optical fiber gyro, and more particularly to a rotational angular velocity detector suitable for an automobile or the like in which environmental changes such as temperature are remarkable.

[Background of the Invention]

A rotation angle detector such as a gyro is used for the navigation system of a mobile body, but a rotation angular velocity detector using an optical fiber loop, a so-called optical fiber gyro is widely adopted for the navigation system of an automobile. .

FIG. 5 shows an example of the optical fiber gyro. This optical fiber gyro is disclosed in, for example, U.S. Pat. No. 4,410,275, which includes a semiconductor laser 1, optical fiber directional couplers 2, 4, an optical fiber polarizer 3, an optical fiber phase modulator 5, and an optical fiber. It is composed of a loop 6, a photodetector 7, a drive circuit 8, an oscillator 9, and a synchronous detector 10.

The semiconductor laser 1 functions as a light source that generates light with a uniform phase.

The optical fiber directional couplers 2 and 4 perform branching and coupling of light and correspond to a branching and coupling of light using a half mirror. The reason why two optical fiber directional couplers are used here is that when light is branched and combined by one optical fiber directional coupler, a certain phase shift occurs, so that two optical fiber directional couplers are used. This is to cancel this phase shift.

The optical fiber polarizer 3 plays a role of a filter that allows only a unidirectional polarization plane to pass, because the light propagating in the optical fiber changes its vibration plane, that is, the polarization plane due to disturbance.

The optical fiber phase modulator 5 applies phase modulation to the light propagating in the optical fiber.

The optical fiber loop 6 is a sensing portion that detects the rotational angular velocity.

The photodetector 7 functions to convert an optical signal into an electric signal.

The drive circuit 8 functions to drive the semiconductor laser 1 to emit light stably.

The oscillator 9 is for driving the optical fiber phase modulator 5, and has a function of outputting a signal having a constant amplitude and frequency.

The synchronous detector 10 takes out only the phase modulation signal component from the signal taken out by the photodetector 7 and functions to improve the sensitivity.

When an angular velocity is applied to the optical fiber loop 6, an angular velocity signal is obtained from the synchronous detector 10 according to the angular velocity, and the optical fiber loop 6 operates as a rotational angular velocity detector.

By the way, according to the conventional optical fiber gyro, since the optical phase modulator 5 is used and the angular velocity signal can be taken out by the synchronous detector 10, there is an advantage that it operates with high sensitivity, but on the other hand, optical However, there is a problem that various components are easily affected by environmental changes and lack stability.

In particular, the optical fiber phase modulator is "Optics Letters, Vol. g
As disclosed in "yroscope with polarization-holding fiber", the temperature coefficient is large and the change in characteristics due to temperature change is remarkable.

Therefore, the optical fiber gyro using the conventional optical phase modulator has a drawback that it is difficult to put it into practical use in a place where the environment changes drastically such as an automobile.

[Object of the Invention]

It is an object of the present invention to provide a rotational angular velocity detector which is capable of sufficiently stable operation in spite of the above-mentioned drawbacks of the prior art and which can be sufficiently applied despite changes in the environment, and which is also sufficiently applicable to automobiles and the like.

[Outline of Invention]

In order to achieve this object, the present invention provides an optical path for characteristic detection in an optical phase modulator of an optical fiber gyro, detects a characteristic change of the optical phase modulator by this, and corrects according to this detection result. It is characterized by the point.

Example of Invention

Hereinafter, the rotational angular velocity detector according to the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 shows an embodiment of the present invention. In the figure, 11 and 12 are optical fiber directional couplers, 13 is a photodetector, 14 is a detecting optical fiber, 15 is a reference optical fiber, and 16 is a control. Circuits, which together constitute an optical fiber type interferometer.

Reference numeral 50 is an optical fiber phase modulator, the details of which are shown in FIG. 2, and the cylindrical electrostrictive element 17 made of an electrostrictive material is used.
Is a part of the optical fiber loop 6 and the optical fiber 60 (first
The optical path for optical modulation) and the optical fiber for detection 14 (second optical path for optical modulation) are wound under the same conditions. Electrostrictive element 17 is provided with electrodes on the inner and outer peripheral surfaces of the cylinder, and when an AC signal from oscillator 9 is applied to this,
The outer diameter of the electrostrictive element 17 changes according to the voltage and the polarity, and the length of the optical fiber 60 expands and contracts in response to this, and as a result, phase modulation is given to the light propagating through the optical fiber 60. become. This is the same in the case of the optical fiber phase modulator 5 in the conventional example of FIG. However, in the optical fiber phase modulator 50 in this embodiment, the detection optical fiber 14 is further wound around the electrostrictive element 17, and the light propagating through the optical fiber 14 also has an optical fiber 60.
The same phase change as that of the light propagating through the optical fiber is provided. Therefore, the optical fiber phase modulator 50 constitutes the phase modulating means having the first and second optical paths for phase modulation. Become.

The structure of the part for detecting the angular velocity other than the part forming the optical fiber type interferometer is the same as that of the conventional example shown in FIG. 5, and the optical fiber directional coupling is provided between the semiconductor laser 1 and the optical fiber loop 6. The optical device 2 (first optical branching / coupling means) and the optical fiber directional coupler 4 (second optical branching / coupling means) are arranged in series, and the optical path divided by the optical fiber directional coupler 4 is divided into two. The optical fiber loop 6 is connected to one end and the other end, respectively, and the return light from the optical fiber loop 6 is coupled by the optical fiber directional coupler 4 and branched by the optical fiber directional coupler 2 to be a photodetector. The optical fiber loop type optical rotational angular velocity detector of the phase modulation system is adapted to detect the rotational angular velocity by detecting the rotational angular velocity in 7.

Next, the operation of this embodiment will be described.

The light emitted from the semiconductor laser 1 is split into two by an optical fiber directional coupler 2, one of which is used for angular velocity detection and the other of which is used for the above-mentioned optical fiber interferometer.

It is taken out by the optical fiber directional coupler 2 and is also the coupler.
The light introduced into 11 is further split into two, one of which is transmitted through the detecting optical fiber 14 of the optical fiber phase modulator 50 to the optical fiber directional coupler 12 and the other of which is the reference light. It is transmitted to the directional coupler 12 through the fiber 15.
Then, the two lights that have passed through these two optical paths are combined by the directional coupler 12, enter the photodetector 13 as interference light, and are converted into an electric signal here, and are converted into a control circuit. Supplied to 16.

FIG. 3 shows details of the control circuit 16.

The control circuit 16 is composed of a preamplifier 18, an AGC (automatic gain adjustment circuit) 19, a phase comparator 20, a low-pass filter 21, and a DC amplifier 22, and oscillates the phase of the signal p supplied from the photodetector 13. It serves to generate a DC voltage dc corresponding to the phase difference of the signal ck supplied from the signal 9 compared with the phase.

Since the signal p from the photodetector 13 is an interference light due to the light propagated through the detection optical fiber 14 and the light propagated through the reference light optical fiber 15, its intensity is for detection. The optical fiber 14 fluctuates at the same frequency as the phase modulation signal received by the optical fiber phase modulator 50, that is, the signal ck from the oscillator 9.

Accordingly, when the phase comparator 20 compares the phases of the signals ck and p, the comparison result represents the average value of the phase deviation received by the optical fiber phase modulator 50 by the light propagated through the detecting optical fiber 14. That is, this is obtained as the voltage value of the DC voltage dc.

As shown in FIG. 2, this DC voltage dc is supplied as a DC bias voltage to the electrostrictive element 17 of the optical fiber phase modulator 50, whereby the phase deviation given by the phase modulator 50 is supplied. The average value of the place is controlled.

Therefore, it is now assumed that the characteristics of the optical fiber phase modulator 50 have changed due to changes in the ambient temperature. Then, the DC voltage dc changes in response to this, and this acts to cancel the characteristic change of the optical fiber phase modulator 50. As a result, the feedback control works, and eventually the characteristic change due to temperature change is suppressed. A constant phase characteristic is always maintained.

Therefore, according to this embodiment, even if the phase characteristic of the optical fiber phase modulator 50 is about to change due to temperature change or the like,
Since the feedback control in the direction of canceling it is applied and the characteristics of the optical fiber phase modulator 50 are always kept constant, the influence of the temperature change on the angular velocity detection is suppressed sufficiently small, and the accurate angular velocity detection is always performed. You can

Further, according to this embodiment, since the optical fiber interferometer method is used for detecting the characteristic change of the optical fiber phase modulator 50, the detection can be performed with high sensitivity only by adding a lightweight and small optical system. Has the effect.

By the way, the present invention is also applicable to an optical waveguide type optical gyroscope, and one example thereof is shown in FIG.

In the embodiment shown in FIG. 4, the entire structure is formed on a crystal substrate. In the drawing, 23 is a waveguide type light emitting device, 24, 26, 32, 3
3 is a waveguide type branch coupling element, 25 is a polarization filter, 27 is a waveguide type phase modulator, 28 is a mode filter, 29 and 30 are connection ends of optical fiber loops, 31 and 34 are waveguide type light receiving elements, Reference numeral 35 is a detection waveguide, and 36 is a reference light waveguide.

An optical fiber loop is connected to the connection ends 29 and 30, and the light emitting element 23, the phase modulator 27, and the light receiving elements 31 and 34 are respectively connected to the drive circuit 8, the oscillator 9, and the synchronizing circuit as in the case of the embodiment of FIG. If the detector 10 and the control circuit 16 are connected, the same operation as in the embodiment of FIG. 1 can be achieved and the same effect can be obtained.

Here, since the constituent elements of each part of such an optical waveguide type may be known ones, a detailed description thereof will be omitted. In particular, regarding the waveguide type phase modulator 27, for example, “S.P. I-E Volume 157. Laser Inertial Rotation Sensor 1978 “Integrated Optics Aposible Solicilation Forefront Huawei Gyroscope”
M. Papillon and Sea. Pushe "(SPIE
Vol.157 Laser InertiaI Rotation Sensor 1978
"Integrated Optics A Possible Solution For
The Fiber Gyroscope "M.Papuchon and C.Puech)
The detailed description is omitted here.

In the embodiment of FIG. 4, the waveguide type phase modulator 27 (there are two) constitutes the optical phase modulating means, and the waveguide type branch coupling element 26 to the connecting end 30 are provided.
That is, the waveguides up to 1 form the first optical path for phase modulation, and the detecting waveguide 35 forms the second optical path for phase modulation.

〔The invention's effect〕

As described above, according to the present invention, the influence of temperature change can be sufficiently suppressed, and therefore, except for the drawbacks of the prior art, it can be sufficiently put into practical use even in a place where the environment changes drastically such as an automobile, and always achieve good accuracy. It is possible to easily provide the rotation angular velocity detector that operates originally.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a rotational angular velocity detector according to the present invention, FIG. 2 is an explanatory view showing an embodiment of an optical fiber phase modulator according to the present invention, and FIG. 3 is also a control according to the present invention. FIG. 4 is a block diagram showing an embodiment of the circuit, FIG. 4 is a constitutional view showing another embodiment of the present invention, and FIG. 5 is a constitutional view showing a conventional example of the rotational angular velocity detector. 1 ... Semiconductor laser, 2,4,11,12 ... Optical fiber directional coupler, 3 ... Optical fiber polarizer, 6 ... Optical fiber loop, 7,13 ... Photodetector, 8 ... Drive Circuit, 9 ... Oscillator, 10 ... Synchronous detector, 14 ... Detection optical fiber, 15 ...
… Optical fiber for reference light, 16 …… Control circuit, 50 …… Optical fiber phase modulator.

Claims (1)

[Claims] 1. A first and a second optical branching / coupling means arranged in series between a light source and an optical fiber loop, wherein the optical paths divided by the second optical branching / coupling means are respectively connected to one of the optical fiber loops. The rotation angular velocity is detected by connecting to the other end, coupling the return light from the optical fiber loop with the second optical branching / coupling means, and branching and detecting with the first optical branching / coupling means. In the optical fiber loop type optical rotation angular velocity detector of the phase modulation system, the first and second phase modulation optical paths are provided, and the first phase modulation optical path is divided by the second optical branching / coupling means. Is disposed in one of the optical paths, and the second optical path for optical modulation is the first optical path.
Optical phase modulating means arranged in the optical path branched from the light source by the optical branching and coupling means, and the second optical modulation optical path of the optical phase modulating means branched from the light source by the first optical branching and coupling means. And a control circuit means for supplying a correction signal to the optical phase modulation means in accordance with the detection result of the light detection means, and the characteristics of the optical phase modulation means. A rotational angular velocity detector characterized in that changes are automatically corrected.