JPH085386A - Optical fiber gyroscope - Google Patents

Abstract

PURPOSE:To keep a gyroscope output constant even if its optical propagation characteristics have changed due to changes in ambient temperature, secular changes, or disturbances. CONSTITUTION:An LD light source 2, a first optocoupler 3, polarizer 4, a second optocoupler 5, depolarizer 6, and one terminal 7a of a single mode optical fiber coil 7 are connected sequentially-light modulator-with an optical fiber (F). A branch/insertion terminal of the second optocoupler 5 is connected to the other terminal 7b of the optical fiber coil 7 with a fiber coil (F). Interference light of CW light and CCW light of the optical fiber coil 7 is fed from the first optocoupler 3 to a photoelectric conversion circuit 9. A synchronous detector 10 detects the output of the circuit 9, extracts a component corresponding to the phase difference between the CW light and CCW light, and outputs it through an LPF 11. A light amount stabilizing circuit 16 controls an amount of light from a light source 2 to keep constant an output Sb of the circuit 9. The circuit 16 comprises a rectifier 21, LPF 14, and light source drive circuit 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber gyro, and more particularly to stabilizing gyro output.

[0002]

2. Description of the Related Art As shown in FIG. 3, a conventional optical fiber gyro 1 includes a light source 2, a first optical coupler 3, a polarizer 4 and a second optical coupler.
The optical coupler 5, the depolarizer (depolarizer) 6 and the one end 7a of the optical fiber coil 7 are sequentially connected by the optical fiber F. The branching / inserting terminal of the second optical coupler, the optical modulator 8 and the other end 7b of the optical fiber coil are connected by the optical fiber F.

The light from the light source 2 is split into two by a second optical coupler 5, and one of the split lights is incident on one end 7a of an optical fiber coil 7 via a depolarizer 6 and is, for example, CW light (clockwise light) La. From the other end 7b of the coil to the optical modulator (PZT
Modulator 8) and is modulated with, for example, a carrier of 37 KHz, and the modulated optical signal is split / branched by the second optical coupler 5.
It is input to the insertion terminal, passes through the polarizer 4, and then the first optical coupler 3
Is branched to the photoelectric conversion circuit 9 side.

On the other hand, the other branched light first branched by the optical coupler 5 is modulated by the optical modulator 8, and the modulated light enters the optical fiber coil 7 to become CCW light Lb, and one end 7a of the coil. Is output and branched by the first optical coupler 3. The lights branched by the first optical coupler 3 are CW light and CCW light.
It is a light interference light. It is known that the phase difference between CW light and CCW light corresponds to the input angular velocity. When the interference light is converted into the electric signal Sa by the photoelectric conversion circuit 9, the electric signal Sa contains a component corresponding to the phase difference. Therefore, the electric signal Sa is input to the synchronous detection circuit 10, the synchronous detection is performed by the reference signal Sr, the detection output corresponding to the phase difference is taken out, and the unnecessary wave is cut by the LPF 11 to obtain the gyro output So.

The light source 2 is a laser diode light source module in which a laser diode LD and a photodiode PD for monitoring the output light thereof are mounted. A current corresponding to the output light of the laser diode LD flows through the photodiode PD. This current is converted into a voltage by the I / V converter 12, the voltage is integrated by the integrator 13, the high frequency noise is cut by the LPF 14, and the voltage is input to the driver 15. The drive current obtained by amplifying the input current is output from the driver 15 to the laser diode LD. By the closed loop of the LD-PD-I / V converter 12-LPF 14-driver 15-LD, negative feedback control is performed so that the intensity of the output light of the LD becomes constant. That is, LD
When the amount of light is increased, the input voltage of the driver 15 increases accordingly. However, since the circuit of the driver 15 is configured so that the output current decreases conversely according to the input voltage, the negative feedback control for the LD is performed. In this way, the I / V converter 12, the integrator 13, the LPF 14, and the driver 15 constitute the light quantity stabilizing circuit 16.

The circuit configuration of the light quantity stabilizing circuit 16 is shown in FIG. The circuit adjustment is performed as follows. A strap pin 17 initially, and is opened between b, and volume R ₇ of the integrator 13 by varying, (equal to the terminal voltage of the resistor R ₁₀ (1 [Omega)) output current I _O of the driver 15 is given Set to a value.

The voltage V _{2 at} terminal a is the voltage V _{3 at} terminal b
The volume R ₂ of the I / V converter 12 is changed so as to be equal to. The voltage V _{2 at the} terminal a is equal to the current I _{1 at} PD.
Then, since V ₁ ≈0, V ₂ ≈R ₂ I ₁ . Strap between a and b of the strap terminal 17,
Form a closed loop. The diode D ₁ on the base side of the transistor Q ₁ of the driver 15 is for protecting the transistor Q ₁ by limiting the positive overvoltage to Vd≈0.7V. The capacitor C ₁ of the I / V converter 12 is for preventing oscillation.

[0008]

In the conventional optical fiber gyro, the change in ambient temperature, the change over time or the disturbance causes
Although the light quantity stabilizing circuit 16 effectively acts on the change in the light quantity of the light source 2, there is a drawback that the gyro output So changes due to the change in the characteristics of components other than the light source of the optical system.

An object of the present invention is to stabilize the gyro output So so as not to change when an arbitrary member of the optical system undergoes a change in light propagation characteristic due to a change in ambient temperature, a change over time, or a disturbance. Is.

[0010]

[Means for Solving the Problems]

(1) According to the invention of claim 1, a part of the output of the photoelectric conversion circuit is input, and a light quantity stabilizing circuit for controlling the light source is provided so that the input signal level becomes constant. (2) In the invention of claim 2, in the above item (1),
The light quantity stabilizing circuit includes a rectifying / smoothing circuit and a rectifying / smoothing circuit.
The light source driving circuit amplifies the output of the smoothing circuit and supplies a driving current to the light source.

(3) According to the invention of claim 3, in the above (2)
In the section, the light source driving circuit includes an amplifier having a function of differentially amplifying a signal and a fixed bias, and an emitter follower circuit which inputs and amplifies an output current of the amplifier and outputs a light source driving current. (4) In the invention of claim 4, in any one of the above items (1) to (3), the light source includes a laser diode as a light emitting element.

(5) According to the invention of claim 5, in the above (1)
In any one of (4) to (4), the optical fiber coil is composed of a single mode optical fiber.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is shown in FIG. 1 by giving the same reference numerals to the portions corresponding to those in FIG. In this embodiment, a part Sb of the output of the photoelectric conversion circuit 9 is input to the light quantity stabilizing circuit 16. The circuit 16 controls the light source 2 so that the input signal level becomes constant. The light quantity stabilizing circuit 16 includes a rectifying circuit 21, a smoothing LPF 14, an amplifier 22 and a driver 15. Negative feedback control is performed so that the branched output of the optical coupler 1 is constant by a closed loop composed of the light source 2-first optical coupler 3-photoelectric conversion circuit 9-light quantity stabilizing circuit 16-light source 2. The amplifier 22 and the driver 15 are collectively referred to as a light source drive circuit 23.

The output Sb of the photoelectric conversion circuit 9 depends on the light propagation characteristics of all the constituent members of the optical system from the light source 2 to the optical fiber coil 7, so that the level of the output Sb is kept constant. By controlling the light quantity of 2, the gyro output So is not affected by changes in ambient temperature of the constituent members of the optical system, changes over time, and changes in light propagation characteristics due to disturbance.

An example of the light source drive circuit 23 is shown in FIG. Do
The driver 15 is similar to the conventional circuit of FIG. Amplifier 2
2 is an auxiliary amplifier 22a on the input side, its output and a fixed via
And a differential amplifier 22b that amplifies the difference between the input and output. light source
The adjustment of the drive circuit 23 is performed as follows. Keep the fiber optic gyro active and slide it
Open between the terminals a and b of the output terminal 17₀Is predetermined
Volume R of the differential amplifier 22b ₂₇Adjust
To do.

The volume R ₂₁ of the auxiliary computing unit 22a is adjusted so that the voltage of the a terminal of the strap terminal 17 becomes equal to the voltage of the b terminal. Strap between the terminals a and b of the strap terminal 17. If the output Sb of the photoelectric conversion circuit 9 increases for some reason, the amplitude of the negative voltage at the input terminal IN of the light source drive circuit 23 increases, the voltages at the terminals a and b increase, and the point g of the differential amplifier increases. , The voltage at point h increases and the voltage at point h increases. Therefore, the base current Ib of the pnp transistor Q ₁ decreases, the emitter current I ₀ ≈h _FE I _b also decreases, and the light amount of the laser diode LD decreases. As a result, the output Sb of the photoelectric conversion circuit 9 corresponding to the interference light is reduced and returned to the original level.

[0017]

As described above, according to the present invention, the light quantity stabilizing circuit 16 controls the light source 2 so that the output of the photoelectric conversion circuit 9 becomes constant, so that the optical system changes in ambient temperature and changes over time. Alternatively, the gyro output So can be kept constant even if the light propagation characteristic changes due to disturbance.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a light source drive circuit 23 of FIG.

FIG. 3 is a block diagram of a conventional optical fiber gyro.

FIG. 4 is a circuit diagram of a light quantity stabilizing circuit 16 in FIG.

Claims (5)

[Claims] 1. A light source, a first optical coupler, a polarizer, a second optical coupler, a depolarizer, and one end of an optical fiber coil are sequentially connected by an optical fiber, and a branching / inserting terminal of the second optical coupler, an optical modulator, and The other end of the optical fiber coil is sequentially connected by an optical fiber, and the interference light of the CW light and the CCW light of the optical fiber coil is input from a branch terminal of the first optical coupler to a photoelectric conversion circuit and converted into an electric signal. Then, the converted electric signal is detected by a synchronous detection circuit, and the C which changes according to the input angular velocity is detected.
In an optical fiber gyro that obtains an electrical output corresponding to a phase difference between W light and CCW light, a part of the output of the photoelectric conversion circuit is input, and the input signal level thereof is constant, An optical fiber gyro, comprising a light quantity stabilizing circuit for controlling the light quantity of the light source. 2. The light quantity stabilizing circuit according to claim 1, comprising a rectifying / smoothing circuit and a light source driving circuit for amplifying an output of the rectifying / smoothing circuit and supplying a driving current to the light source. An optical fiber gyro characterized by. 3. The light source drive circuit according to claim 2, wherein the light source drive circuit has an amplifier having a function of differentially amplifying a signal and a fixed bias, and an output current of the amplifier is input and amplified to output a light source drive current. An optical fiber gyro characterized by comprising an emitter follower circuit for 4. The optical fiber gyro according to claim 1, wherein the light source includes a laser diode as a light emitting element. 5. The optical fiber gyro according to claim 1, wherein the optical fiber coil is composed of a single mode optical fiber.