CN102788595A - Optical fiber gyroscope frequency characteristic elevating method and device based on Faraday effect - Google Patents

Abstract

The invention discloses an optical fiber gyroscope frequency characteristic evaluation device based on the Faraday effect. The excitation current source includes a signal generator, a conversion amplifier circuit and a current coil. Sensitive optical path includes light source, circulator, Y waveguide phase modulator, polarization beam splitter, polarization maintaining fiber ring, λ/4 wave plate, sensing fiber, mirror and detector; analog fiber optic gyroscope signal processing detection circuit includes pre- Amplifying circuit, A/D conversion circuit, digital signal processing unit, the first D/A conversion circuit, the second D/A conversion circuit and lock-in amplifier; The Faraday effect that the present invention applies is to adopt sinusoidal current to excite sensitive optical circuit to produce, wherein The sinusoidal signal used as the excitation signal can achieve high-frequency output, which solves the problem of limited output frequency of the excitation signal for the frequency characteristic test of the fiber optic gyroscope, so it can realize high-bandwidth evaluation.

Description

Method and device for evaluating frequency characteristics of fiber optic gyroscope based on Faraday effect

technical field

The invention relates to a method and device for evaluating the frequency characteristics of an optical fiber gyroscope based on the Faraday effect, and belongs to the technical field of inertia.

Background technique

Fiber optic gyro is a new type of fiber optic rotation sensor that has emerged with the rapid development of fiber optic technology. Because of its phase modulation sensing method with extremely high sensitivity, compactness and high mechanical strength, it will become a popular choice in many fields such as aerospace, aviation, and navigation. The most promising inertial component, as an important inertial sensor, measures the angular velocity of the carrier and is the core component of the inertial system, which determines the performance of the entire inertial system to a considerable extent.

Fiber optic gyro is a new type of angular velocity sensor based on the Sagnac effect. It has the advantages of an all-solid-state structure without rotating parts, large dynamic range, large bandwidth, low power consumption, shock resistance, small size, no startup process, and long life.

With the successful application of medium and low-precision fiber optic gyroscopes in recent years and the improvement of the performance of optical devices, the development of high-precision fiber optic gyroscopes for inertial navigation systems has become a development trend. The testing method of fiber optic gyroscope restricts the improvement of the accuracy of fiber optic gyroscope to a certain extent. The dynamic characteristics of the fiber optic gyroscope is an important performance index to characterize its reliability and environmental adaptability. Its quality directly determines the application range of the gyroscope. Among them, the frequency characteristic analysis is an important part of the dynamic characteristics.

Digital closed-loop fiber optic gyroscope is the main solution of medium and high precision fiber optic gyroscope, which represents the research direction at home and abroad. In order to improve the reliability and environmental adaptability of the fiber optic gyroscope and improve the tracking characteristics of the closed loop, the researchers of the fiber optic gyroscope have been working hard to improve the dynamic characteristics by improving the control algorithm of the closed loop feedback. increase.

The traditional test method of dynamic characteristics of fiber optic gyroscope is to measure the step response curve and frequency response curve of the gyroscope with mechanical equipment such as sudden stop table and angular vibration table. When the angular vibration table is used to test the bandwidth of the gyroscope, the angular vibration table moves at a sinusoidal alternating angular rate, which can provide angular rates of different frequencies and amplitudes. The fiber optic gyroscope accepts sinusoidal signal input of different frequencies, records the corresponding input angular vibration amplitude and phase, and measures the amplitude and phase of the fiber optic gyroscope output signal to obtain the frequency characteristics of the fiber optic gyroscope.

Since the general angular vibration table is designed for mechanical gyroscopes, the output angular vibration frequency is generally only about 200Hz to 300Hz. At present, the maximum operating frequency range of the most advanced angular vibration table in China can only reach 500Hz, but the bandwidth of the fiber optic gyroscope is far away. Far more than 500Hz, far from meeting the requirements of digital closed-loop fiber optic gyroscope dynamic characteristics test.

The hardware-in-the-loop simulation test scheme is to add a disturbance signal to the fiber optic ring of the fiber optic gyroscope, and use the time difference between the two beams of counter-propagating light to pass through the disturbance, and the difference is a delay time τ, thereby generating a phase difference, which replaces the Sagnac caused by the input angular velocity. Phase difference, change the frequency of the disturbance signal and then measure the frequency characteristics.

The following are specific implementation plans:

调制。Using PZT to apply modulation signal to realize frequency characteristic evaluation scheme: According to the working principle of fiber optic gyro, a PZT element is introduced into the gyro fiber optic ring, and a sinusoidal angular rate is simulated by applying a sinusoidal modulation of a certain frequency to the PZT, so as to measure the optical fiber The amplitude-frequency response curve of the gyro determines its bandwidth. Its structure principle diagram like chart 1 shows. The working principle of the closed-loop fiber optic gyroscope: the light emitted by the SLD light source is polarized by the polarizer after passing through a coupler, becomes linearly polarized light and enters the Y-waveguide phase modulator, where it is phase-modulated. The two beams of light passing through the fiber ring interfere, and finally, the light carrying phase information enters the Pin detector through the coupler. The preamplifier circuit amplifies and filters the voltage signal to be measured output by the PIN/FET, and the analog signal enters the A/D conversion circuit for discrete and quantization, and converts it into a digital signal, which is input to the digital signal processing unit for demodulation operation, signal processing When the unit accumulates the demodulation results to form a ladder wave, it outputs a square wave signal superimposed on the digital ladder wave, and the superimposed signal is applied to the Y waveguide phase modulator after D/A conversion to realize closed-loop feedback and

modulation.

According to the working principle of the above closed-loop fiber optic gyroscope, a PZT element is introduced into the fiber optic ring of the gyroscope, and a sinusoidal modulation is realized by applying a sinusoidal voltage signal of a certain frequency to the PZT to simulate a sinusoidally changing angular rate, thereby measuring the amplitude and frequency of the fiber optic gyroscope response curve to determine its bandwidth.

调制。Through the integrated optical modulator to realize the digital dynamic test method to measure the bandwidth scheme: using the principle of fiber optic gyroscope closed-loop detection, superimpose the required signal on the feedback ladder wave, and replace it with the phase difference between the two beams of light caused by the ladder wave Enter the Sagnac phase difference caused by the angular velocity. It has successively proposed three schemes of adding step signal, sinusoidal signal, and pseudo-random signal as external signals on the feedback ladder wave. In addition, a pseudo-random signal is added to the feedback ladder wave as an external signal, and then the correlation identification method is used to correlate the digital closed-loop output signal after wavelet filtering with the pseudo-random signal to obtain the impulse response of the gyroscope closed-loop loop, and then through Fourier The amplitude-frequency characteristics and phase-frequency characteristics of the gyroscope are obtained through leaf transformation. The structure is shown in Figure 2. The working principle of the closed-loop fiber optic gyroscope: the light emitted by the SLD light source is polarized by the polarizer after passing through a coupler, becomes linearly polarized light and enters the Y-waveguide phase modulator, where it is phase-modulated. The two beams of light passing through the fiber ring interfere, and finally, the light carrying phase information enters the Pin detector through the coupler. The preamplifier circuit amplifies and filters the voltage signal to be measured output by the PIN/FET, and the analog signal enters the A/D conversion circuit for discrete and quantization, and converts it into a digital signal, which is input to the digital signal processing unit for demodulation operation, signal processing When the unit accumulates the demodulation results to form a ladder wave, it outputs a square wave signal superimposed on the digital ladder wave, and the superimposed signal is applied to the Y waveguide phase modulator after D/A conversion to realize closed-loop feedback and

modulation.

According to the working principle of the closed-loop fiber optic gyroscope above, the gyroscope bandwidth is obtained by judging the gyroscope demodulation output signal according to the amplitude by superimposing the sinusoidal signal on the fiber optic gyroscope feedback ladder wave for equivalent external input angular velocity.

The key to the hardware-in-the-loop simulation test scheme is that the time difference between two beams of counter-propagating light passing through the disturbance is the delay time τ, but the delay time τ is generally very small, only on the order of μs. When measuring low frequencies, the added external signal frequency is small , the change is relatively slow, and the change is not obvious within the time of μs. Due to the reciprocity of the optical fiber gyro optical path, the disturbance at low frequencies has no obvious change in the phase, which can only be improved by increasing the amplitude of the disturbance. Therefore, in It is not easy to measure the frequency characteristics of the equivalent input in the low frequency band.

Contents of the invention

The purpose of the present invention is to solve the above problems, and propose a device and method for evaluating the frequency characteristics of a fiber optic gyroscope based on the Faraday effect. This device can measure the frequency characteristics in the full bandwidth of the fiber optic gyroscope, and provide verification means for the research on the closed-loop control of the fiber optic gyroscope. . In addition, the closed-loop bandwidth of the fiber optic gyroscope that has been finalized can be obtained, which provides a basis for the scope of application of the fiber optic gyroscope's environmental adaptability.

A device for evaluating the frequency characteristics of a fiber optic gyroscope based on the Faraday effect, including an excitation current source, a sensitive optical path, and an analog fiber optic gyroscope signal processing and detection circuit;

The excitation current source includes a signal generator, a conversion amplifier circuit and a current coil; the signal generator generates an alternating current signal, and the alternating current signal is output to the conversion amplifier circuit, and the conversion amplifier circuit performs AC amplification on the alternating current signal, and then converts the alternating current signal to The current is output to the current coil, and the current coil is wound on the sensing fiber of the sensitive optical path. The alternating current is passed through the current coil, and the generated magnetic field causes the sensing fiber in the sensitive optical path to induce the Faraday effect, and the signal is transmitted by the excitation current source. into the sensitive optical path; after the alternating current output by the conversion amplifier circuit passes through a sampling resistor, a sampling voltage is obtained, and the sampling voltage is output to the reference port of the lock-in amplifier;

Sensitive optical path includes light source, circulator, Y waveguide phase modulator, polarization beam splitter, polarization maintaining fiber ring, λ/4 wave plate, sensing fiber, mirror and detector; Entering the Y-waveguide phase modulator, polarized into linearly polarized light at the Y-waveguide phase modulator and then subjected to phase modulation, the modulated polarized light is output to the polarization beam splitter, and the polarized light is coupled by two pigtails of the polarization beam splitter Finally, it is injected into the polarization-maintaining fiber ring, and the polarized light is transmitted along the X-axis and Y-axis of the polarization-maintaining fiber ring respectively. After entering the λ/4 wave plate, in the λ/4 wave plate, the polarized light becomes left-handed and right-handed respectively. When the circularly polarized light enters the sensing fiber, the phase of the two circularly polarized lights changes (F=2VNI), where F is the Faraday effect phase difference, V is the Verdet constant, N is the number of turns of the winding wire, and I is the current size. The two beams of circularly polarized light are transmitted at different speeds and output to the reflector. After being reflected at the mirror surface of the mirror, the polarization modes of the two beams of circularly polarized light are exchanged, and then pass through the sensing fiber again, so that the two beams of circularly polarized light generate Phase doubled (2F=4VNI); the two beams of circularly polarized light pass through the λ/4 wave plate again, and then return to linearly polarized light, and then the two beams of linearly polarized light interfere; the light carrying phase information enters the detector from the circulator, The detector converts the optical signal into a voltage signal and outputs it to the preamplifier circuit;

调制，同时，数字信号处理单元还将解调的结果输出至第二D/A转换电路，第二D/A转换电路将数字解调结果转换为模拟解调结果，输出至锁相放大器的信号通道端口进行测量，锁相放大器测量幅值与相位差大小，实现了频率特性评估。The analog fiber optic gyroscope signal processing and detection circuit includes a preamplifier circuit, an A/D conversion circuit, a digital signal processing unit, a first D/A conversion circuit, a second D/A conversion circuit and a lock-in amplifier; the preamplifier circuit is capable of detecting The voltage signal to be measured output by the device is amplified and filtered, and then output to the A/D conversion circuit. The A/D conversion circuit discretizes and quantifies the analog voltage signal to be measured, converts it into a digital voltage signal to be measured, and outputs it to the digital signal processing Unit, the digital signal processing unit subtracts the digital signals in two adjacent delay times for demodulation, and accumulates the demodulation results as a ladder wave, and at the same time, superimposes a square wave signal on the ladder wave to obtain a superimposed signal , the superimposed signal is input into the first D/A conversion circuit, and the first D/A conversion circuit converts the digital superimposed signal into an analog superimposed signal, and outputs it to the Y waveguide phase modulator to realize closed-loop feedback and

Modulation, at the same time, the digital signal processing unit also outputs the demodulation result to the second D/A conversion circuit, and the second D/A conversion circuit converts the digital demodulation result into an analog demodulation result, and outputs the signal to the lock-in amplifier The channel port is used for measurement, and the lock-in amplifier measures the amplitude and phase difference to realize frequency characteristic evaluation.

A method for evaluating the frequency characteristics of an optical fiber gyroscope based on the Faraday effect, comprising the following steps:

Step 1: The light emitted by the light source enters the Y-waveguide phase modulator after passing through a circulator, and is modulated into linearly polarized light at the Y-waveguide phase modulator to be phase-modulated; the polarized light is coupled by two pigtails of the polarization beam splitter Inject into the polarization-maintaining fiber ring, transmit along the X-axis and Y-axis of the polarization-maintaining fiber respectively, after passing through the λ/4 wave plate, they become left-handed and right-handed circularly polarized light respectively, and enter the sensing fiber; due to the exciting alternating current A magnetic field is generated, and the Faraday magneto-optical effect is generated in the sensing fiber, so that the phase of the two circularly polarized lights changes, (F=2VNI, where F is the Faraday effect phase difference, V is the Verdet constant, and N is the winding wire The number of turns, I is the magnitude of the current, two beams of circularly polarized light are transmitted at different speeds, after being reflected at the mirror, the polarization modes of the two beams of circularly polarized light are exchanged, and then pass through the sensing fiber again, and experience the Faraday effect to make The phase of the two beams of light is doubled, 2F=4VNI, after the two beams of light pass through the λ/4 wave plate again, they return to linearly polarized light, and then the two beams of linearly polarized light interfere; finally, the light carrying the phase information enters through the circulator Detector, the light returning to the detector only carries the non-reciprocal phase difference due to the Faraday effect;

Step 2: The pre-amplification circuit amplifies and filters the voltage signal to be measured output by the photodetector, and the analog signal enters the A/D conversion circuit for discrete and quantization, and converts it into a digital signal, which is input to the digital signal processing unit for demodulation operation , the signal processing unit accumulates the demodulation results to form a staircase wave, and at the same time outputs a square wave signal superimposed on the digital staircase wave, and the superimposed signal is converted by the first D/A conversion circuit and applied to the Y waveguide phase modulator to realize closed-loop feedback and ±π/2 modulation; at the same time, the signal processing unit outputs the output of the demodulation result after conversion by the second D/A conversion circuit, and enters the signal channel port of the lock-in amplifier for measurement; uses the lock-in amplifier to measure the signal amplitude and phase The size of the difference, changing the frequency of the excitation current signal to achieve frequency characteristic evaluation.

The advantages of the present invention are:

(1) The Faraday effect applied in the present invention is generated by using a sinusoidal current to excite the sensitive optical path, wherein the sinusoidal signal as the excitation signal can realize high-frequency output, which solves the problem that the output frequency of the excitation signal for the frequency characteristic test of the fiber optic gyroscope is limited, so it can be Enables high-bandwidth evaluation;

(2) This device uses a sensing optical path that is sensitive to the Faraday effect, which can better generate the Faraday effect for sensitive currents and improve the signal-to-noise ratio of sensitive signals;

(3) The circuit of this device simulates the signal detection circuit of the fiber optic gyroscope, which can simulate the fiber optic gyroscope by adjusting the forward gain and feedback gain in the device, so as to realize the accurate evaluation of the frequency characteristics;

(4) Four fiber optic rings of different lengths are installed in the device, and the fiber rings can be connected by jumpers, so that the frequency characteristics of fiber optic gyroscopes with different lengths of fiber rings can be evaluated, which increases the applicability of the evaluation device ;

(5) The evaluation method of this device is a lock-in amplifier, which can accurately evaluate the bandwidth of the fiber optic gyroscope.

Description of drawings

Fig. 1 is the semi-physical simulation schematic diagram utilizing PZT in the background technology;

Fig. 2 is the schematic diagram of the hardware-in-the-loop simulation utilizing the integrated optical modulator in the background technology;

Fig. 3 is a structural schematic diagram of the present invention.

In the picture:

1-Excitation current source 2-Sensitive optical path 3-Analog fiber optic gyroscope signal processing detection circuit

101-Signal Generator 102-Converting and Amplifying Circuit 103-Current Coil

201-SLD light source 202-Circulator

204-Y waveguide phase modulator 205-Polarization beam splitter 206-Polarization maintaining fiber ring

207-λ/4 wave plate 208-Sensing fiber 209-Reflector

210-Detector

301-Pre-amplification circuit 302-A/D conversion circuit 303-Digital signal processing unit

304-First D/A conversion circuit 305-Second D/A conversion circuit 306-Lock-in amplifier

Detailed ways

The present invention will be further described in detail with reference to the accompanying drawings and embodiments.

The present invention is a Faraday effect-based fiber optic gyroscope frequency characteristic evaluation device, as shown in FIG.

The excitation current source 1 provides the excitation signal for the device, and realizes the frequency sweep by changing the frequency of the excitation signal, and completes the evaluation of the frequency characteristics. The excitation current source 1 includes a signal generator 101 , a conversion amplifier circuit 102 and a current coil 103 .

The excitation current source 1 adopts triode AC conversion and amplification. The basic principle of amplification is: when the input signal is 0, the amplification circuit is working in the amplification state, and has a suitable DC operating point. When an AC signal is added to the amplifying circuit, the base current will change accordingly on the basis of the original DC, and the change of the base current will cause the collector current to change in β (β is the AC magnification) to realize current amplification. . In order to meet the above requirements for high AC output and long-time work, and to eliminate crossover distortion, a push-pull triode-to-tube amplification form with complementary and symmetrical dual power supplies is used to realize the two push-pull triodes respectively in the positive phase of the sinusoidal signal. Amplify in the negative period, which solves the problem of crossover distortion.

The signal generator 101 generates an alternating current signal, the frequency of the alternating current signal can be adjusted by the signal generator 101, and the alternating current signal is output to the conversion and amplification circuit 102, and the conversion and amplification circuit 102 performs AC amplification on the alternating current signal, and then The alternating current is output to the current coil 103, and the current coil 103 is wound on the sensing optical fiber 208 of the sensitive optical path 2, and the alternating current is passed into the current coil 103, and the generated magnetic field causes the sensing optical fiber 208 in the sensitive optical path 2 to induce the Faraday effect , to realize the transmission of the signal from the excitation current source to the sensitive optical circuit. After the alternating current output by the conversion amplifier circuit 102 passes through a sampling resistor, a sampling voltage is obtained, and the sampling voltage is output to the reference port of the lock-in amplifier 305 .

Sensitive optical path 2 includes SLD light source 201, circulator 202, Y waveguide phase modulator 204, polarization beam splitter 205, polarization maintaining fiber ring 206, λ/4 wave plate 207, sensing fiber 208, mirror 209, detector 210 .

The SLD light source 201 emits light, and the light enters the Y-waveguide phase modulator 204 after passing through a single-mode circulator 202, and is polarized into linearly polarized light at the Y-waveguide phase modulator 204 and then subjected to phase modulation, and the modulated polarized light is output to Polarization beam splitter 205, the polarized light is coupled by the two pigtails of the polarization beam splitter 205, and injected into the polarization maintaining fiber ring 206, and the polarized light is respectively transmitted along the X axis and Y axis of the polarization maintaining fiber ring 206, and enters λ/4 After the wave plate 207, in the λ/4 wave plate 207, the polarized light becomes left-handed and right-handed circularly polarized light respectively, and enters the sensing fiber 208, and a magnetic field is generated in the sensing fiber 208 due to the excitation of the alternating current. The Faraday magneto-optic effect changes the phase of the two beams of circularly polarized light (F=2VNI, where F is the phase difference of the Faraday effect, V is the Verdet constant, N is the number of turns of the winding wire, and I is the magnitude of the current). The beams of circularly polarized light are transmitted at different speeds, output to the reflector 209, after being reflected on the mirror surface of the reflector 209, the polarization modes of the two beams of circularly polarized light are exchanged, pass through the sensing fiber 208 again, and experience the Faraday effect, Double the phase produced by the two circularly polarized lights (2F=4VNI). After the two beams of circularly polarized light pass through the λ/4 wave plate 207 again, they return to linearly polarized light, and then the two beams of linearly polarized light interfere. Finally, the light carrying phase information enters the detector 210 from the single-mode circulator 202, and the detector 210 converts the optical signal into a voltage signal and outputs it to the preamplifier circuit 301. passed to the circuit.

The polarization-maintaining optical fiber ring 206 is provided with 4 optical fiber rings of different lengths, which are 570m, 350m, 100m and 200m respectively. The polarization beam splitter 205 and the λ/4 wave plate 207 are connected to form a polarization maintaining fiber ring 206, so that the frequency characteristics of the fiber optic gyroscope with different lengths of fiber rings can be evaluated, which increases the applicability of the evaluation device.

The analog fiber optic gyroscope signal processing detection circuit 3 includes a preamplifier circuit 301, an A/D conversion circuit 302, a digital signal processing unit 303, a first D/A conversion circuit 304, a second D/A conversion circuit 305 and a lock-in amplifier 306 .

调制，同时，数字信号处理单元303还将解调的结果输出至第二D/A转换电路305，第二D/A转换电路305将数字解调结果转换为模拟解调结果，输出至锁相放大器306的信号通道端口进行测量，锁相放大器306测量幅值与相位差大小，进而实现了频率特性评估。The preamplifier circuit 301 amplifies and filters the voltage signal to be measured output by the detector 210, and then outputs it to the A/D conversion circuit 302, and the A/D conversion circuit 302 discretizes and quantizes the analog voltage signal to be measured, and converts it into a digital The voltage signal to be measured is output to the digital signal processing unit 303, and the digital signal processing unit 303 subtracts and demodulates the digital signals within two adjacent delay times, and accumulates the demodulation results to form a ladder wave. At the same time, The square wave signal is superimposed on the ladder wave to obtain a superimposed signal, and the superimposed signal is input to the first D/A conversion circuit 304, and the first D/A conversion circuit 304 converts the digital superimposed signal into an analog superimposed signal, and outputs it to the Y waveguide phase modulator 204, to achieve closed-loop feedback and

Modulation, at the same time, the digital signal processing unit 303 also outputs the demodulated result to the second D/A conversion circuit 305, and the second D/A conversion circuit 305 converts the digital demodulation result into an analog demodulation result, and outputs it to the phase-locked The signal channel port of the amplifier 306 is used for measurement, and the lock-in amplifier 306 measures the amplitude and phase difference, thereby realizing frequency characteristic evaluation.

The connection between the excitation current source 1 and the sensitive optical path 2 is realized by winding the coil on the sensing fiber 208 , and the connection between the sensitive optical path 2 and the detection circuit 3 for analog fiber optic gyro signal processing is realized through the photodetector 210 .

The present invention adopts frequency-adjustable alternating current to excite the magnetosensitive optical circuit to generate Faraday effect, and the phase difference generated by Faraday effect replaces the phase difference of Sagnac effect, because the alternating sinusoidal current can realize high-frequency output, by detecting the phase difference of Faraday effect The frequency characteristics evaluation test in the low frequency and high frequency bands can be realized, especially the evaluation in the high frequency band, which solves the shortcomings of the traditional method of limited frequency evaluation and the insignificant response of the hardware-in-the-loop simulation scheme in the low frequency band.

The invention can measure the frequency characteristic of the fiber optic gyroscope, and also can measure the bandwidth of the gyroscope. Its significance: 1. Through the research of the project, it can provide verification means for the research of the closed-loop control algorithm of the fiber optic gyroscope. 2. Through the evaluation and testing of the algorithm, the closed-loop bandwidth of the fiber optic gyroscope that has been finalized can be obtained, which provides a basis for the scope of application of the fiber optic gyroscope's environmental adaptability.

The present invention is a kind of fiber optic gyroscope frequency characteristic evaluation method based on Faraday effect, comprises the following several steps:

Step 1: The light emitted by the SLD light source 1 is polarized by the fiber polarizer 203 after passing through a single-mode circulator 202, becomes linearly polarized light and enters the Y-waveguide phase modulator 204, and is subjected to a phase at the Y-waveguide phase modulator 204. modulation. The polarized light is coupled by the two pigtails of the polarization beam splitter 205 and injected into the polarization maintaining fiber ring 206, respectively transmitted along the X-axis and Y-axis of the polarization-maintaining fiber, and becomes left-handed and right-handed after passing through the λ/4 wave plate 207 The circularly polarized light rotates and enters the sensing fiber 208. Because the excitation alternating current generates a magnetic field, the Faraday magneto-optical effect is produced in the sensing fiber 208, so that the phase of the two beams of circularly polarized light changes (F=2VNI, where F is the Faraday effect phase difference, V is the Verdet constant, N is the number of turns of the winding wire, and I is the magnitude of the current) and is transmitted at different speeds. After being reflected at the reflector 209, the polarization modes of the two beams of circularly polarized light are exchanged, pass through the sensing fiber 208 again, and experience Faraday The effect doubles the phase of the two beams of light (2F=4VNI, where F is the Faraday effect phase difference, V is the Verdet constant, N is the number of turns of the winding wire, and I is the magnitude of the current). After the two beams of light pass through the λ/4 wave plate 207 again, they return to linearly polarized light, and then the two beams of linearly polarized light interfere. Finally, the light carrying the phase information enters the detector 210 from the single-mode circulator 202 . Since the two beams of light that interfered have passed through the X-axis and Y-axis of the polarization-maintaining fiber and the left-handed and right-handed modes of the sensing fiber during the optical transmission process, there is only a slight difference in time, so they return to the detector The light at 210 only carries the non-reciprocal phase difference due to the Faraday effect.

Step 2: The pre-amplification circuit 301 amplifies and filters the voltage signal to be measured output by the photodetector 210, and the analog signal enters the A/D conversion circuit 302 for discrete and quantization, and converts it into a digital signal to be input to the digital signal processing unit 303 For demodulation operation, the signal processing unit 303 accumulates the demodulation results to form a step wave, and at the same time outputs a square wave signal superimposed on the digital step wave, and the superimposed signal is applied to the Y waveguide phase after being converted by the first D/A conversion circuit 304 Closed-loop feedback and ±π/2 modulation are implemented on the modulator 204 . At the same time, the signal processing unit 303 converts the output of the demodulation result through the second D/A conversion circuit 305 and then enters the test port of the lock-in amplifier 306 for measurement. The lock-in amplifier 305 is used to measure the signal amplitude and phase difference, and the excitation current signal is changed to realize frequency characteristic evaluation.

Claims (5)

1. A fiber optic gyroscope frequency characteristic evaluation device based on Faraday effect, is characterized in that, comprises excitation current source, sensitive optical circuit and analog fiber optic gyroscope signal processing detection circuit; The excitation current source includes a signal generator, a conversion amplifier circuit and a current coil; the signal generator generates an alternating current signal, and the alternating current signal is output to the conversion amplifier circuit, and the conversion amplifier circuit performs AC amplification on the alternating current signal, and then converts the alternating current signal to The current is output to the current coil, and the current coil is wound on the sensing fiber of the sensitive optical path. The alternating current is passed through the current coil, and the generated magnetic field causes the sensing fiber in the sensitive optical path to induce the Faraday effect, and the signal is transmitted by the excitation current source. into the sensitive optical path; after the alternating current output by the conversion amplifier circuit passes through a sampling resistor, a sampling voltage is obtained, and the sampling voltage is output to the reference port of the lock-in amplifier; Sensitive optical path includes light source, circulator, Y waveguide phase modulator, polarization beam splitter, polarization maintaining fiber ring, λ/4 wave plate, sensing fiber, mirror and detector; Entering the Y-waveguide phase modulator, polarized into linearly polarized light at the Y-waveguide phase modulator and then subjected to phase modulation, the modulated polarized light is output to the polarization beam splitter, and the polarized light is coupled by two pigtails of the polarization beam splitter Finally, it is injected into the polarization-maintaining fiber ring, and the polarized light is transmitted along the X-axis and Y-axis of the polarization-maintaining fiber ring respectively. After entering the λ/4 wave plate, the polarized light becomes left-handed and right-handed in the λ/4 wave plate. When the circularly polarized light enters the sensing fiber, the phase of the two circularly polarized lights changes, F=2VNI, where F is the Faraday effect phase difference, V is the Verdet constant, N is the number of turns of the winding wire, and I is the current , the two beams of circularly polarized light are transmitted at different speeds, output to the mirror, after being reflected at the mirror surface, the polarization modes of the two beams of circularly polarized light are exchanged, and then pass through the sensing fiber again, so that the two beams of circularly polarized light The generated phase doubles 2F=4VNI; the two beams of circularly polarized light pass through the λ/4 wave plate again, and then return to linearly polarized light, and then the two beams of linearly polarized light interfere; the light carrying phase information enters the detector from the circulator, and is detected The device realizes the conversion from optical signal to voltage signal and outputs it to the preamplifier circuit; The analog fiber optic gyroscope signal processing and detection circuit includes a preamplifier circuit, an A/D conversion circuit, a digital signal processing unit, a first D/A conversion circuit, a second D/A conversion circuit and a lock-in amplifier; the preamplifier circuit is capable of detecting The voltage signal to be measured output by the device is amplified and filtered, and then output to the A/D conversion circuit. The A/D conversion circuit discretizes and quantifies the analog voltage signal to be measured, converts it into a digital voltage signal to be measured, and outputs it to the digital signal processing Unit, the digital signal processing unit subtracts the digital signals in two adjacent delay times for demodulation, and accumulates the demodulation results as a ladder wave, and at the same time, superimposes a square wave signal on the ladder wave to obtain a superimposed signal , the superimposed signal is input into the first D/A conversion circuit, and the first D/A conversion circuit converts the digital superimposed signal into an analog superimposed signal, and outputs it to the Y waveguide phase modulator to realize closed-loop feedback and

Modulation, at the same time, the digital signal processing unit also outputs the demodulation result to the second D/A conversion circuit, and the second D/A conversion circuit converts the digital demodulation result into an analog demodulation result, and outputs the signal to the lock-in amplifier The channel port is used for measurement, and the lock-in amplifier measures the amplitude and phase difference to realize frequency characteristic evaluation. 2. a kind of fiber optic gyroscope frequency characteristic evaluation device based on Faraday effect according to claim 1, is characterized in that, the frequency of alternating current signal is regulated by signal generator. 3. a kind of fiber optic gyroscope frequency characteristic evaluation device based on Faraday effect according to claim 1, is characterized in that, described light source is SLD light source. 4. a kind of fiber optic gyroscope frequency characteristic evaluation device based on Faraday effect according to claim 1, is characterized in that, is provided with the fiber optic ring of 4 different lengths in described polarization-maintaining fiber ring, is respectively 570m, 350m, 100m and 200m, when you need to use one of the lengths of the optical ring, connect the selected optical ring to the polarization beam splitter and the λ/4 wave plate through jumpers to form a polarization-maintaining optical fiber ring. 5. A method for evaluating the frequency characteristics of an optical fiber gyroscope based on the Faraday effect, comprising the following steps: Step 1: The light emitted by the light source enters the Y-waveguide phase modulator after passing through a circulator, and is modulated into linearly polarized light at the Y-waveguide phase modulator to be phase-modulated; the polarized light is coupled by two pigtails of the polarization beam splitter Inject into the polarization-maintaining fiber ring, transmit along the X-axis and Y-axis of the polarization-maintaining fiber respectively, after passing through the λ/4 wave plate, they become left-handed and right-handed circularly polarized light respectively, and enter the sensing fiber; due to the exciting alternating current A magnetic field is generated, and the Faraday magneto-optical effect is generated in the sensing fiber, so that the phase of the two circularly polarized lights changes, F=2VNI, where F is the Faraday effect phase difference, V is the Verdet constant, and N is the turn of the winding wire Number, I is the magnitude of the current, and it is transmitted at different speeds. After being reflected at the mirror, the polarization modes of the two circularly polarized lights are exchanged, and they pass through the sensing fiber again, and experience the Faraday effect to make the phase of the two beams of light Double, 2F=4VNI, after the two beams of light pass through the λ/4 wave plate again, they return to linearly polarized light, and then the two beams of linearly polarized light interfere; finally, the light carrying phase information enters the detector from the circulator and returns to the detector The light only carries the non-reciprocal phase difference due to the Faraday effect; Step 2: The pre-amplification circuit amplifies and filters the voltage signal to be measured output by the photodetector, and the analog signal enters the A/D conversion circuit for discrete and quantization, and converts it into a digital signal, which is input to the digital signal processing unit for demodulation operation , the signal processing unit accumulates the demodulation results to form a staircase wave, and at the same time outputs a square wave signal superimposed on the digital staircase wave, and the superimposed signal is converted by the first D/A conversion circuit and applied to the Y waveguide phase modulator to realize closed-loop feedback and ±π/2 modulation; at the same time, the signal processing unit outputs the demodulation result after being converted by the second D/A conversion circuit, and then enters the test port of the lock-in amplifier for measurement; uses the lock-in amplifier to measure the signal amplitude and phase difference The size of the excitation current signal is changed to realize the evaluation of the frequency characteristics.

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