JPH02147908A - Fiber-optic gyroscope - Google Patents

Abstract

PURPOSE:To achieve a smaller size of the apparatus along with a higher measuring accuracy by picking up and combining light with specified wavelengths, the one turning clockwise and the other turning counterclockwise within an optical fiber loop, with a photocoupler to detect a difference between frequencies corresponding to the wavelengths. CONSTITUTION:In fiber-optic gyroscope which comprises a progressive wave type amplifier 10 and an optical fiber loop 20, as a signal gain of a ring laser becomes larger than a transmission loss of the loop, a laser oscillation occurs and light turning clockwise containing a wavelength lambda1 and light turning counterclockwise containing a wavelength lambda2 are generated within the optical fiber loop 20. Moreover, light with wavelengths lambda1 and lambda2 generated are picked up with a first photocoupler 21, combined with a second coupler 22 and then, supplied to a beat frequency detector 23. Then, a difference is determined between frequencies nu1 and nu2 with the detector 23 respectively corresponding to the wavelengths lambda1 and lambda2 and a beat frequency DELTAf is outputted. In addition, a temperature change of the progressive wave type optical amplifier is suppressed to stabilize an oscillation frequency of the ring laser.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an optical fiber gyro with an active structure that detects angular velocity using an optical fiber, and is used in inertial navigation systems of aircraft and ships. It is.

(Conventional technology) Conventionally, the technology in this field is as described in "
There was one described in "Optical Fiber Sensor" 1st Edition (Sho 61-7-30), Ohmsha, P, 212-213.

Optical gyroscopes for detecting rotational angular velocity relative to inertial space include active configurations in which the optical loop for detecting rotation itself is a laser oscillator, and passive configurations such as Sagnac's interferometers in which the light source is outside the sensing loop. There is a structure.

The feature of the active optical gyro is that it detects the difference in oscillation frequency between clockwise light and counterclockwise light (this is called the beat frequency), and measures the rotational speed from the magnitude of the beat frequency. An example of this configuration is shown in FIG.

FIG. 2 is a block diagram of an active optical gyro using a conventional He--Ne gas laser type ring laser.

This optical gyro has a structure in which two reflecting mirrors 1.2, one semi-transparent mirror 3, and three He-Ne gas laser tubes 4, 5.6 are arranged in a triangular shape, and the light rotates clockwise. P1 and counterclockwise light P2 can be generated.

When the light gyro is stationary, both lights PL and P
The two oscillation frequencies are the same. However, when the optical gyroscope rotates clockwise at a predetermined angular velocity ω as shown by the arrow in Figure 2 within a plane that includes the optical path, the time it takes to reach the same point on the optical path progresses clockwise. Light P1 is long,
The light traveling counterclockwise is short. Therefore, the light P1. ．．
This is the same as if the length of the laser resonator of P2 is different, and the two lights PL and P2 will oscillate at different frequencies. This difference in oscillation frequency, that is, Be I frequency Δ
f is proportional to the angular velocity ω at which the optical gyro rotates. Therefore, if the lights P1 and P2 in both directions are extracted from the semi-transparent mirror 3 and interfered with each other, and the beat frequency Δf is measured, the angular velocity ω
can be detected. The rotation angle is then determined by integrating the angular velocity ω over time.

This type of active optical gyro has higher measurement sensitivity than passive optical gyros, and is also used for flying objects such as airplanes.

(Problems to be Solved by the Invention) However, the optical gyro having the above configuration has the following problems.

(2) Since the He--Ne gas laser tubes 4, 5, and 6 are used, they generate a large amount of heat, which increases the temperature fluctuation of the optical gyro. Furthermore, since the optical path medium is a gas, the refractive index is likely to fluctuate. Therefore, there was a risk that the beat frequency would fluctuate and the measurement accuracy would deteriorate.

(2) Since He--Ne gas laser tubes 4, 5, and 6 are used, there are problems in that the device becomes larger, heavier, consumes more power, and becomes more expensive.

The present invention provides an optical fiber gyro that solves the problems of the prior art, including reduced measurement accuracy, increased size, increased weight, increased power consumption, and increased cost.

(Means for Solving the Problems) In order to solve the above problems, the invention of claim 1 provides an optical fiber gyro having an active structure, which has at least a traveling wave optical amplifier and an optical fiber loop, and has a single wave a ring laser that generates clockwise light including a long or multiple wavelengths λ1 and counterclockwise light including a single wavelength (or multiple wavelengths) λ2;
a first optical coupler that takes out the lights of wavelengths λ1 and λ2 in the optical fiber loop; a second optical coupler that combines the wavelengths λ1 and λ2; It is composed of a beat frequency detector that detects the difference between frequencies ν1 and ν2 (Sh1-Sh2) corresponding to wavelengths λ1 and ^2, respectively.

In the invention of claim 2, claim 1. The optical fiber gyro is provided with temperature control means for suppressing temperature fluctuations of the traveling wave optical amplifier.

(Function) According to the invention of claim 1, since the optical fiber gyro is configured as described above, the ring laser oscillates when the signal gain becomes larger than the transmission loss of the loop, and the right laser beam having the wavelength ^1 is generated. Circular light and counterclockwise light having a wavelength ^2 are generated in the optical fiber loop. Its wavelength λ1. λ2 is the first. The signal is taken out of the loop by a second optical coupler, multiplexed by a second optical coupler, and then supplied to a beat frequency detector. Beat frequency detector has wavelength λ1
The difference between frequencies ν1 and ν2 corresponding to λ2 and λ2 is calculated. Since this difference is proportional to the angular velocity, the angular velocity of the fiber optic gyro can be determined6.Then, traveling wave optical amplifiers and optical fiber loops improve measurement accuracy due to low power consumption and small temperature fluctuations, and improve the accuracy of the equipment. Small, lightweight,
It works to reduce costs.

The temperature control means according to the second aspect functions to suppress temperature fluctuations of the traveling wave optical amplifier, stabilize the oscillation frequency of the ring laser, and further improve measurement accuracy.

Therefore, the above problem can be solved.

(Embodiment) FIG. 1 is a block diagram of an optical fiber gyro showing an embodiment of the present invention.

This optical fiber gyro has a traveling wave optical amplifier 10 manufactured by, for example, coating (adhering) an antireflection film on both ends of a semiconductor element. The loops 20 are connected to form a ring laser. A first optical coupler 21 for optical branching is inserted into the optical fiber loop 20, and a second optical coupler for optical multiplexing is inserted on the output side of the first optical coupler 21.
A beat frequency detector 23 is connected to the optical coupler 22 and the output side thereof.

Here, the first optical coupler 21 connects the optical fiber loop 2
Wavelength at 0^1 (=C/ν1, where C is the speed of light,
ν1 is the clockwise light pH including the frequency) and the wavelength λ2 (
-C/ν2, where C is the speed of light and ν2 is the frequency), out of the counterclockwise light P12, it has a function of extracting light with wavelengths λ1 and λ2. The second optical coupler 22 has a function of combining the extracted lights of wavelengths λ1 and λ2. Furthermore, the beat frequency detector 23 inputs the output of the second optical coupler 22 and detects the difference between the frequencies ν1 and ν2 corresponding to the wavelengths λ1 and λ2 (Sh1-Sh2), that is, the beat frequency Δf. It is composed of a light receiving element and the like.

FIG. 3 is a diagram showing an example of the configuration of the traveling wave optical amplifier 10 in FIG. 1.

This optical amplifier 10 is modularized and has a traveling wave optical amplifying element 11 in which both end faces of a semiconductor laser are coated with an antireflection film, and the optical amplifying element 11 functions as a temperature control means. It is fixed on the element (thermionic cooling element) 12. A temperature sensor 13 such as a thermistor for detecting the temperature of the optical amplification cable 11 is fixed on the Peltier element 12 . Although not shown, a control circuit for driving and controlling the Vertier element 12 based on the output of the temperature sensor 13 is connected outside the module. Further, on both sides of the optical amplifying element 1-1, spherical lens fibers 20a and 20b whose tips are processed into a spherical shape are arranged, and the spherical lens fibers 20a and 20b are placed on the Peltier element 1-2 with solder 14 or the like. is fixed. The tip lens fibers 20a and 20b are the optical fiber loop 2
Connected to 0.

The operation of the optical fiber gyro configured as follows will now be described.

When power is applied to the optical fiber gyro, light is emitted from both ends of the optical amplifying element 11 in the optical amplifier 10 shown in FIG. Light P1. emitted from the right end of the optical amplification element 11. 1 is the spherical lens fiber 20a, and the optical fiber loop 2 in FIG.
0 and the optical coupler 21 to the tip spherical lens fiber 20.
b, and efficiently enters the light amplifying cable 11. The clockwise light pH is optically amplified in the process of passing through the optical amplifying element 11, is emitted from the right end of the optical amplifying element 11, and is efficiently transmitted to the conical lens fiber 20a.

Similarly, the light PL2 emitted from the left end of the optical amplification element 11 is transmitted through the tip lens fiber 20b, the optical fiber loop 20, and the first
The light enters from the right end of the optical amplification cable 11 via the optical coupler 21 and the spherical lens fiber 20a, is optically amplified in the optical amplification element 11, and is emitted from the left end. In this way, the optical amplifier 10 adjusts the clockwise light pH and the counterclockwise light PL2.
Optical amplification is performed independently for both.

Then, when the signal gain of the ring laser becomes larger than the transmission loss of the loop, the ring laser oscillates, producing clockwise light with wavelength λ1 (-C/ν1) and light with wavelength λ
2 (-C/v2) is generated in the optical fiber loop 20.

The generated lights of wavelengths λ1 and λ2 are transferred to the first optical coupler 2.
1, multiplexed by a second optical coupler 22, and then supplied to a beat frequency detector 23. The beat frequency detector 23 determines the difference between the frequencies ν1 and ν2 corresponding to the wavelengths λ1 and λ2 (Sh1-Sh2), and outputs the beat frequency Δf.

When the optical fiber gyro is stationary, the wavelength λ1 of the clockwise light pH and the wavelength λ2 of the counterclockwise light PL2 are equal, so the beat frequencies Δf of the two light pHs and P12 are not detected. However, when the optical fiber gyro rotates clockwise at an angular velocity ω, as indicated by the arrow in FIG. 1, for example, the oscillation wavelengths λ1 and λ2 become different due to the Sagnac effect. Since there is a proportional relationship between the magnitude of the angular angle ω and the beat frequency Δf (-shi1-shi2), the beat frequency detector 23 detects the beat frequency Δf.
By detecting f, it is possible to know the angular velocity ω. Also,
The rotation angle is determined by integrating the angular velocity ω over time.

This embodiment has the following advantages.

<a> Since the traveling wave optical amplifier 10 is used as the optical amplifier, it consumes less power and generates less heat compared to those using conventional gas lasers, so the temperature fluctuation of the optical amplifier 10 itself is is very small. Moreover, it also has the advantages of small size, light weight, and low cost.

(b) Since the optical fiber loop 20 is used as the light guide path, there is very little variation in the optical path length due to temperature fluctuations or mechanical vibrations compared to conventional ones, so high measurement accuracy can be obtained.

(c) Temperature fluctuations in the optical amplification element 11 can be easily controlled to about 0.001° C. using the Peltier element 12, thereby further reducing fluctuations in the beat frequency Δf and further improving measurement accuracy. Can be done.

Note that the present invention is not limited to the illustrated embodiment, and the traveling wave optical amplifier 10 may be configured with something other than that shown in FIG. 3, or the Peltier element 12 provided in the traveling wave optical amplifier 10 may be replaced. Various modifications are possible, such as providing other temperature control means. Further, in the above embodiment, a single wavelength λ1. λ2
As explained in , even if they have multiple wavelengths, the beat frequency detector 23 takes the frequency difference (Shi 1 - Shi 2), so the wavelengths of clockwise light and counterclockwise light cancel each other out. Almost the same actions and effects as in the above embodiment can be obtained.

(Effect of the invention) As explained in detail above, according to the invention of claim 1,
Since the ring laser is configured with a traveling wave optical amplifier and an optical fiber loop, it consumes less power and generates less heat, resulting in very small temperature fluctuations. Furthermore, since an optical fiber loop is used as the light guide path, there is very little variation in the optical path length due to temperature fluctuations or mechanical vibrations.

Therefore, an active optical gyro that is small, lightweight, low power consumption, low cost, and has high measurement accuracy can be obtained.

Further, in the invention of claim 2, since the temperature control means is provided, temperature fluctuations in the traveling wave optical amplifier are reduced, the oscillation frequency of the ring laser is stabilized, and measurement accuracy is further improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical fiber gyro showing an embodiment of the present invention, FIG. 2 is a block diagram of a conventional optical gyro, and FIG. 3 is a block diagram of a traveling wave optical amplifier shown in FIG. 10... Traveling wave optical amplifier, 11...
Optical amplification element, 12... Peltier element, 13...
...Temperature sensor, 20...Optical fiber loop, 21.22...1st. second optical coupler, 2
3...Beat frequency detector.

Claims (2)

[Claims] 1. It has a traveling wave optical amplifier and an optical fiber loop,
a ring laser that generates clockwise light having a wavelength λ1 and counterclockwise light having a wavelength λ2; a first optical coupler that extracts light having wavelengths λ1 and λ2 in the optical fiber loop; a second optical coupler that combines the wavelengths λ1 and λ2, and inputs the output of the second optical coupler to combine the wavelengths λ1 and λ.
The difference between frequencies ν1 and ν2 (ν1−
An optical fiber gyro comprising: a beat frequency detector for detecting ν2). 2. 2. The optical fiber gyro according to claim 1, further comprising temperature control means for suppressing temperature fluctuations of said traveling wave optical amplifier.