JPH08313268A - Interference type optical gyro - Google Patents

Abstract

PURPOSE: To provide a gyro having high measurement accuracy in a simple structure by a constitution wherein a light entering from a light source and propagating in a sensing loop is allowed to enter the sensing loop again after it is amplified by an optical amplifier. CONSTITUTION: When a light enters a directional coupler 3 via a directional coupler 5 and an isolator 4, it is divided into two divided lights incident on a sensing loop 1 and a phase modulator 2, respectively. In the loop 1, two divided lights are propagated in the directions different from each other and interfered with each other to enter the coupler 3 again. While the light incident on the coupler 3 is divided two divisional lights, the light emitted to a side of an isolator is shut off. The light entering a directional coupler 6 is further divided and one part is amplified by an amplifier 7, then it is incident on the loop 1 again via the isolator 4 and coupler 3. The other part divided by the coupler 6 is detected by a photodetector 9 to be photoelectrically converted and inputted to an electronic circuit 10, thereby detecting an angle velocity of the light incident on the loop 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interference type optical gyro for detecting an angular velocity of an aircraft, a ship or the like.

[0002]

2. Description of the Related Art A gyroscope was used to detect the posture and position of an aircraft or a ship. This gyroscope is based on the principle that when the top is rotated, the top itself tries to keep the direction of its rotation axis constant. However, there is a problem that it is consumed due to friction between the rotating shaft of the top and the bearing, and it is expensive because the manufacturing requires high precision.

Therefore, an optical fiber gyro that does not use mechanical elements has been widely used.

There are mainly two types of optical fiber gyros.
One is an interference fiber gyroscope (hereinafter referred to as “IF
OG ”. ), And the other is a resonant fiber gyroscope (hereinafter referred to as “R-FOG”).

The R-FOG is a highly accurate ring resonator,
It is composed of a light source and an optical detector, and measures the angular velocity by detecting the difference between the resonance points of the CW wave (light traveling in the clockwise direction) and the CCW wave (light traveling in the counterclockwise direction). ing.

The I-FOG uses a low-coherence light source as a light source, divides the light into two by a directional coupler, and then enters both ends of a sensing loop to obtain a gyro signal from the interference light obtained. Some of them are simple in configuration, cheap in price, and practical, and are used not only in aircraft and ships, but also in navigation systems for vehicles and earthquake prediction systems. There are two types of I-FOG, an open loop type and a closed loop type.

[0007]

By the way, I-FOG
Although it is necessary to lengthen the fiber loop length in order to improve the resolution of, the device becomes larger and the price becomes higher accordingly. Further, the open-loop type optical fiber gyro has a lower dynamic range than the closed-loop type optical fiber gyro, and there is a problem that a large angular velocity cannot be measured.

On the other hand, in the R-FOG, while the optical fiber length is short and the angular velocity can be measured with high accuracy, the whole measuring system is complicated and the price is high. Moreover, in the R-FOG, there is a problem that an error is induced by the Kerr effect and scattered light.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide an interference type optical gyro having a simple structure and high measurement accuracy.

[0010]

In order to achieve the above object, the present invention provides a light source, a first directional coupler that splits light from the light source into two, and a light that is split into two. A sensing loop that interferes with light that enters from both ends and propagates in opposite directions, a phase modulator that is provided at one end of the sensing loop, an optical detector that receives the interference light from the sensing loop, and an optical detector. In an interferometric optical gyro having an electronic circuit for detecting an angular velocity from a gyro signal from a measuring instrument, a second directional coupler provided between a light source and a first directional coupler, and a first direction A third directional coupler provided between the directional coupler and the photodetector, and light emitted from the sensing loop provided between the second directional coupler and the third directional coupler. And then re-injects into the first directional coupler and It is obtained and an optical amplifier using the optical feedback loop.

According to the present invention, a light source, a first directional coupler that splits light from the light source into two, and light that is split into two and is incident from both ends and propagates in mutually opposite directions. For sensing, a phase modulator provided at one end of the sensing loop, an optical detector for receiving interference light from the sensing loop, and an electronic circuit for detecting an angular velocity from a gyro signal from the optical detector. And a second directional coupler provided between the light source and the first directional coupler, and between the first directional coupler and the photodetector. A third directional coupler provided, and a first directional coupler provided between the second directional coupler and the third directional coupler and amplifying light emitted from the sensing loop. For optical feedback to the sensing loop via Those having an amplifier and, polarizer disposed through the fourth directional coupler between the first directional coupler and the sensing loop.

In addition to the above configuration, the present invention may use a light source that emits spontaneous emission light of an Er-doped optical fiber as the light source.

In addition to the above configuration, in the present invention, the electronic circuit may detect the angular velocity based on the deviation on the time axis of the output pulse of the gyro signal that occurs when the angular velocity is input to the sensing loop (open. Loop method).

In addition to the above configuration, in the present invention, the output pulse of the modulation voltage applied by the electronic circuit to the phase modulator is always maximum with respect to the output pulse of the gyro signal generated when the angular velocity is input to the sensing loop. The feedback control may be performed as described above, and the angular velocity may be detected from the feedback amount (closed loop method).

[0015]

According to the above structure, the light propagating in the sensing loop after being incident from the light source is amplified by the optical amplifier and then is incident again in the sensing loop, whereby the first directional coupler and the sensing loop are connected. Since the optical path of the Sagnac loop consisting of is used multiple times, high resolution can be obtained even if the optical fiber length is relatively short. That is, the output signal of the photodetector is a pulse, and the pulse width of this pulse is short, so that the measurement accuracy is high. The shortness of the pulse width, that is, the sharpness of the pulse is determined by the gain of the optical amplifier and the loss of the optical path. Since a low coherence light source is used as the light source, there is no error induced by the Kerr effect and scattered light, and the cost can be kept low. In the case of the closed loop type, the resolution is further improved,
The angular velocity can be measured with high accuracy.

[0016]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a conceptual diagram showing an embodiment of an interference type optical gyro of the present invention.

In the figure, reference numeral 1 is a sensing loop, and a phase modulator 2 is connected to one end (upper end in the drawing) of the sensing loop. The other end of the sensing loop 1 and the phase modulator 2
Is connected to one input / output terminal of the first directional coupler 3. One of the other input / output terminals of the first directional coupler 3 is connected to one of the other input / output terminals of the second directional coupler 5 via the isolator 4 and the third directional coupler 6 Is connected to one of the input / output terminals. An optical amplifier composed of an Er-doped optical fiber (hereinafter referred to as "EDFA") is provided between one of the other input / output terminals of the second directional coupler 5 and one of the other input / output terminals of the third directional coupler 6. 7) is connected. A light source 8 of low coherence is connected to the rest of the other input / output terminal of the second directional coupler 5,
An optical detector 9 is connected to the rest of the other input / output ends of the directional coupler 6. The output of the photodetector 9 is the electronic circuit 10
And the output of the electronic circuit 10 is input to the phase modulator 2.

Next, the operation of the embodiment will be described.

When the light from the light source 8 enters the first directional coupler 3 through the second directional coupler 5 and the isolator 4, the light is branched into two, and one end and the phase of the sensing loop 1 are detected. The light enters the modulator 2. In the sensing loop 1, the lights propagate in opposite directions, interfere with each other, and enter the first directional coupler 3 again. The light incident on the first directional coupler 3 is split into two, but the light emitted to the isolator 4 side is blocked there, and the third directional coupler 6
The light incident on is further split into two. One of the lights branched by the third directional coupler 6 enters the optical amplifier 7 and is amplified. The light amplified by the optical amplifier 7 enters the sensing loop 1 again via the second directional coupler 5, the isolator 4, and the first directional coupler 3.

On the other hand, the other light branched by the third directional coupler 6 is received by the photodetector 9. The light received by the photodetector 9 is photoelectrically converted into a pulse and input to the electronic circuit 10. The electronic circuit 10 detects the angular velocity input to the sensing loop 1 from the pulse from the photodetector 9.

Here, if the entire loop propagation time of the light propagating in the sensing loop 1 and the modulation frequency of the phase modulator match, the positions on the waveform time axis match, and the output signal P
_TOTAL (t) has a sharp pulse-like waveform as shown in FIG.

FIGS. 6 and 7 are diagrams showing an interference signal group circulating in the sensing loop 1 and a total sum thereof.

In the figure, P1 (t), P2 (t), P
3 (t) ... are interference signals of the first round, the second round, and the third round, respectively, and P _TOTAL (t) is the sum of them (where ωτ = 2nπ, n = 1, 2, 3). …).

On the other hand, when ω and the propagation time are not synchronized, as shown in FIG. 7, P1 (t), P2 (t), P2
The waveform positions of 3 (t) ... Do not coincide, and P _TOTAL (t) does not become a sharp pulse.

Next, a theoretical analysis will be tried.

The first circulating interference signal P1 (t) (without optical feedback, the output signal of a normal I-FOG is the same) is given by the equation (1).

[0028]

## EQU1 ## P ₁ (t) = K [1 + ν cos (φ _s + φ _e c
os (ω _m t))] where ν is an interference constant, k is a photoelectric conversion constant, ω _m is a phase modulator frequency, and φ _e is an effective phase modulation degree.

The effective phase modulation degree φ _e is given by the equation (2).

[0030]

Φ _e = 2φ _m sin (πω _m τ _s ) where τ _s = L / C, L is the length of the sensing loop, φ
_m is the phase amplitude of the phase modulator, and φ _s is the Sagnac phase due to rotation (when the sensing loop inputs the angular velocity).

The Sagnac phase φ _s is expressed by the equation (3).

[0032]

Φ _s = 4πRLΩ / (λ ₀ c) where Ω is the angular velocity, R is the length of the Sagnac loop, and λ ₀
Is the central wavelength of the light source, and c is the speed of light in a vacuum.

The second circulating interference signal P ₂ (t) is a signal representing the result of passing through the optical feedback loop and is expressed by the equation (4).

[0034]

## EQU00004 ## P ₂ (t) = AKK '[1 + ν cos (φ _s +
φ _e cos (ω _m t−ω _m τ))] × [1 + ν cos (φ
_s + φ _e cos (ω _m t))] The third circular interference signal P ₃ (t) is expressed by the equation (5).

[0035]

## EQU00005 ## P ₃ (t) = AKK '[1 + ν cos (φ _s +
_{φ e cos (ω m t-} 2ω m τ))] × [1 + νcos
(φ _s + φ _e cos (ω _mt −ω _m τ))] × [1 + νc
os (φ _s + φ _e cos (ω _mt ))] where A is the gain of the EDFA and K ′ is a constant due to the feedback coupler and optical circuit loss. The gyro signal of the optical gyro is the sum of P ₁ (t), P ₂ (t), P ₃ (t) ...

[0036]

[ _Equation 6] P _TOTAL (t) = P ₁ (t) + P ₂ (t) + P
₃ (t) + ... If ωτ = 2nπ is satisfied in the equation (6), this condition can be realized by appropriately adjusting the frequency of the phase modulator. In this case, the expression 6 is expressed by the following expression 7.

[0037]

(7) P _TOTAL (t) = K [1 + ν cos (φ _s + φ
_e cos (ω _m τ))] / {1-AK ′ [1 + ν cos
(φ _s + φ _e cos (ω _m t))]} Since the gyro signal is a pulse, the peak position of the output pulse is determined by the equation 8 (the equation 7 is differentiated by t).

[0038]

Equation 8] _P'TOTAL (t) = 0 Therefore equation (9) is obtained.

[0039]

## EQU9 ## Kν sin (φ _s + φ _e cos ω _m t) = 0 and the equation 10 is obtained.

[0040]

Φ _s + φ _e cos ω _m t = 2nπ Equation 10 is determined by the Sagnac phase φ _s and the degree of phase modulation. Therefore, when the Sagnac phase φ _s changes, the pulse position of the gyro signal moves. The angular velocity can be measured by utilizing such a relationship.

There are two methods for detecting the gyro signal of the optical gyro: the open loop method and the closed loop method.

A principle diagram of the open loop method is shown in FIG.

In the figure, the solid line shows the gyro signal when the optical gyro is not rotating. When the optical gyro rotates, the gyro signal moves as shown by the broken line. The angular velocity of rotation can be measured by the amount of movement of these pulses. The open loop method is a method of measuring the angular velocity of rotation by the moving amount of a pulse. The mathematical formula is calculated below.

First, when there is no rotation, φ _s = 0 and n = 1. Expression 11 is obtained from Expression 10.

[0045]

Φ _e0 cos ωmt ₀ = 2π where φ _e0 and t ₀ are the degree of phase modulation and the position of the peak of the output pulse in the stationary state. φ _e0 and t ₀ are measurable quantities.

On the other hand, when there is rotation, the pulse of the gyro signal of the optical gyro moves. From FIG. 4, the amount of movement of the pulse of the gyro signal is Δt, and the input angular velocity Ω is expressed by the equation 12 from the equations 3, 10, and 11.

[0047]

Ω = λ ₀ cφ _e0 sin (ω _m t) / 4πRL Next, the closed loop method will be described.

From the above analysis, it can be seen that two quantities, the Sagnac phase and the degree of phase modulation, cause a shift of the gyro signal on the time axis. The present purpose is to adjust the appropriate phase modulation amount to compensate the Sagnac phase. When the phase modulator and Sagnac phase are completely canceled, the gyro output pulse is stationary on the time axis. Here, the principle of the closed loop method is shown in FIG.

Since the Sagnac phase is canceled by the phase modulator, it is necessary to control the feedback modulation voltage applied to the phase modulator. The angular velocity can be detected from the feedback amount. From the equations (10) and (11), the Sagnac phase is represented by the equation (13).

[0050]

Φs = (φ _e0 −φ _e ) cos ω _m t ₀ Here, φ _e is the degree of phase modulation when there is rotation, and is an amount that can be measured by the feedback amount of the electronic circuit.

From the above, it can be seen that the gyro signal of the interference type optical gyro of this embodiment is a sharp pulse. If the pulse of the gyro signal is sharp, the angular velocity detection accuracy increases. The sharpness of the pulse can be adjusted by the gain of the EDFA. In the closed loop, the detection point is the peak position of the pulse of the gyro signal, and the detection accuracy is higher than that of the I-FOG (the detection point is the zero point position of the output waveform).

FIG. 2 is a conceptual diagram of another embodiment of the interference type optical gyro of the present invention.

The difference from the embodiment shown in FIG. 1 is that a polarizer 12 is provided between the first directional coupler 3 and the sensing loop 1 via a fourth directional coupler 11. Is.

The light emitted from the light source 8 enters the polarizer 12 via the second directional coupler 5, the isolator 4 and the first directional coupler 3. The light from the light source 8 is the polarizer 12
When passing through, only light of a predetermined polarization direction passes and enters the fourth directional coupler 11. Fourth directional coupler 11
The light that is incident on is split into two and is incident on one end of the sensing loop 1 and the phase modulator 2. The lights that have entered the sensing loop 1 propagate in opposite directions, interfere with each other, and are combined again by the fourth directional coupler 11 and then enter the first directional coupler 3 through the polarizer 12. . The light incident on the first directional coupler 3 is split into two by the third directional coupler 6. One of the branched lights is amplified by an optical amplifier 7, and then passes through a second directional coupler 5, an isolator 4, a first directional coupler 3, a polarizer 12 and a fourth directional coupler 11. The other light that is propagated to the sensing loop 1 again and branched is received by the photodetector 9. Since the polarization directions of the light received by the photodetector 9 are aligned, the pulse of the gyro signal becomes sharp, and highly accurate angular velocity measurement is performed. That is, since the polarizer 12 is provided between the first directional coupler 3 and the sensing loop 1, the polarization of the light propagating in the sensing loop 1 is aligned, and the angular velocity measurement accuracy is improved.

FIG. 3 is a conceptual diagram showing another embodiment of the interference type optical gyro of the present invention.

The difference from the embodiment shown in FIG. 2 is that spontaneous emission light of an Er-doped optical fiber is used as a light source.

The light emitted from the pumping light source 13 enters the WDM (wavelength division multiplex) coupler 14 and the Er-doped optical fiber 15. When the excitation light is incident on the Er-doped optical fiber 15, the light is amplified and spontaneous emission light having a wide spectral width is generated. This spontaneous emission light enters the sensing loop 1 via the second directional coupler 5, the isolator 4, the first directional coupler 3, the polarizer 12 and the fourth directional coupler 11. Therefore, light having a wide spectrum width and having uniform polarization directions propagates in the sensing loop 1, so that the angular velocity measurement with a wide dynamic range and high accuracy is performed.

[0058]

In summary, according to the present invention, the following excellent effects are exhibited.

(1) By amplifying the light emitted from the sensing loop and then performing optical feedback to the sensing loop again, an interference type optical gyro having a simple structure and high measurement accuracy can be realized.

(2) When a polarizer is provided between the first directional coupler and the sensing loop, the polarization directions of light propagating in the sensing loop are aligned, so that more accurate angular velocity measurement can be performed. it can.

(3) When spontaneous emission light is used as the light source, the spectrum of the light propagating in the sensing loop is widened, and the dynamic range is expanded.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an embodiment of an interference type optical gyro of the present invention.

FIG. 2 is a conceptual diagram of another embodiment of the interference type optical gyro of the present invention.

FIG. 3 is a conceptual diagram showing another embodiment of the interference type optical gyro of the present invention.

FIG. 4 is a diagram showing the principle of the open loop method.

FIG. 5 is a diagram showing the principle of the closed loop method.

FIG. 6 is a diagram showing a group of interference signals circulating in a sensing loop and a total sum thereof.

FIG. 7 is a diagram showing a group of interference signals circulating in a sensing loop and a total sum thereof.

[Explanation of symbols]

 1 Sensing Loop 2 Phase Modulator 3 First Directional Coupler 6 Third Directional Coupler 7 Optical Amplifier 8 Light Source 9 Optical Detector 10 Electronic Circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Kajioka 5-1-1 Hidaka-cho, Hitachi-shi, Ibaraki Hitachi Cable Co., Ltd. Hidaka factory

Claims (5)

[Claims] 1. A light source, a first directional coupler that splits the light from the light source into two, and interference of light that is split into two and is propagated in opposite directions. Sensing loop, a phase modulator provided at one end of the sensing loop, an optical detector that receives the interference light from the sensing loop, and an electronic circuit that detects the angular velocity from the gyro signal from the optical detector. In the interferometric optical gyro having, a second directional coupler provided between the light source and the first directional coupler, and provided between the first directional coupler and the optical detector. The third directional coupler, and the light emitted from the sensing loop, which is provided between the second directional coupler and the third directional coupler, is amplified and then returned to the first directional coupler. An optical amplifier that is incident and provides optical feedback to the sensing loop An interferometric optical gyro characterized by having. 2. A light source, a first directional coupler that splits light from the light source into two, and interference between lights that are split into two and are propagated in opposite directions. Sensing loop, a phase modulator provided at one end of the sensing loop, an optical detector that receives the interference light from the sensing loop, and an electronic circuit that detects the angular velocity from the gyro signal from the optical detector. In the interferometric optical gyro having, a second directional coupler provided between the light source and the first directional coupler, and provided between the first directional coupler and the optical detector. And a third directional coupler, which is provided between the second directional coupler and the third directional coupler, amplifies light emitted from the sensing loop, and then passes through the first directional coupler. And an optical amplifier for optical feedback to the sensing loop And a polarizer provided between the first directional coupler and the sensing loop via a fourth directional coupler, the interferometric optical gyro. 3. The interference type optical gyro according to claim 1, wherein a light source that emits spontaneous emission light of an Er-doped optical fiber is used as the light source. 4. The interference type according to claim 1, wherein the electronic circuit detects the angular velocity based on a deviation on the time axis of an output pulse of a gyro signal generated when the angular velocity is input to the sensing loop. Optical gyro. 5. The electronic circuit feeds back a modulation voltage applied to a phase modulator to an output pulse of a gyro signal generated when an angular velocity is input to the sensing loop so that the output pulse is always maximized. The interference type optical gyro according to claim 1 or 2, wherein the angular velocity is detected based on the feedback amount while the control is performed.