Resonator fiber-optic gyroscope for detecting angular velocity signals

Abstract

A kind of resonant fiber-optic gyroscope for detecting angular velocity signal, low coherence light is used as probe light source, the light intensity change signal caused by fiber-optic gyroscope rotation is detected using multi-beam interference phenomenon, i.e. under the action of sawtooth wave modulation signal, the periodic change frequency shift of probe light pulse is generated through Y waveguide in resonant fiber-optic gyroscope, and the corresponding photoelectric signal is obtained, the photoelectric signal is multiplied with Y waveguide driving signal and filtered to obtain the error signal with linear relationship with angular velocity, the detection of fiber-optic gyroscope rotation is realized. The light intensity change signal caused by fiber-optic gyroscope rotation is detected using multi-beam interference phenomenon of low coherence light, the structure of fiber-optic gyroscope system is significantly simplified, and high-precision measurement of rotation signal can be realized.

Description

Technical Field

[0001] This invention relates to a technology in the field of sensing, specifically a resonant fiber optic gyroscope for detecting angular velocity signals. Background Technology

[0002] Resonant fiber optic gyroscopes use fiber optic ring resonators as sensing units. Theoretically, by repeatedly cycling light through the resonator, they can achieve measurement accuracy comparable to or even higher than that of interferometric fiber optic gyroscopes using very short fiber lengths. Existing resonant fiber optic gyroscopes generally use narrow-linewidth lasers with high coherence as probe light. This introduces two problems: high-coherence lasers cause parasitic noise such as backscattering and reflection, polarization crosstalk, and nonlinear Kerr effects, severely affecting the actual measurement accuracy of resonant fiber optic gyroscopes; and resonant fiber optic gyroscope schemes based on narrow-linewidth laser sources require at least two optical frequency-locking systems to lock the laser frequency to the clockwise and counterclockwise resonance peaks of the fiber optic ring resonator, resulting in a very complex gyroscope system structure that has prevented its practical application.

[0003] The accuracy of an interferometric fiber optic gyroscope is proportional to the length of its internal fiber. Theoretically, a resonant fiber optic gyroscope can achieve the same accuracy as an interferometric fiber optic gyroscope with a longer fiber using a shorter fiber. However, existing implementations are complex, noisy, and have low accuracy. Conventional techniques and resonant fiber optic gyroscopes described in existing literature all use a highly coherent light source (also known as a narrow-linewidth laser source) as the detection source and employ at least two (often three) frequency shifters and feedback-locked control loops to measure angular velocity. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies that use highly coherent light, such as parasitic noise, by proposing a resonant fiber optic gyroscope for detecting angular velocity signals. It utilizes the multi-beam interference phenomenon of low-coherence light to detect the light intensity change signal caused by the rotation of the fiber optic gyroscope, which significantly simplifies the structure of the fiber optic gyroscope system and enables high-precision measurement of angular velocity signals.

[0005] This invention is achieved through the following technical solution:

[0006] This invention relates to a resonant fiber optic gyroscope for detecting angular velocity signals, comprising: a low-coherence broadband light source, a photodetector, a data processing unit, an optical circulator, a Y-waveguide, an optical fiber ring resonant cavity, and a circuit section, wherein: the optical signal emitted by the low-coherence broadband light source is output to the first port of the optical circulator and then to the Y-waveguide through the second port; the Y-waveguide outputs two optical modulation signals to the first and second optical couplers respectively and injects them into two opposite transmission directions in the optical fiber ring resonant cavity; the optical signals output by the optical fiber ring resonant cavity through the two optical couplers return to the Y-waveguide and are output to the photodetector from the third port of the optical circulator; the data processing unit generates two modulation signals to drive two modulation electrodes of the Y-waveguide, so that the two optical signals output by the Y-waveguide have frequency shifts of specific periods and magnitudes; the data processing unit acquires the voltage signal output by the photodetector and, using the modulation signal driving the Y-waveguide as a reference signal, performs synchronous detection on the acquired voltage signal and outputs a demodulated signal.

[0007] The aforementioned detection refers to: using low-coherence light as the detection source, and utilizing the multi-beam interference phenomenon to detect the interference signal caused by the rotation of the fiber optic gyroscope. Specifically, under the action of the Y-waveguide driving signal, the Y-waveguide in the resonant fiber optic gyroscope generates a periodic frequency shift in the detection light pulse and obtains the corresponding photoelectric signal. The photoelectric signal is multiplied with the Y-waveguide driving signal and filtered to obtain an error signal that has a linear relationship with the angular velocity, thereby realizing the detection of the rotation of the fiber optic gyroscope.

[0008] The driving signal is a waveform such as a triangular wave, a sawtooth wave, or a sine wave, preferably a sawtooth wave.

[0009] The detection includes two working modes: open-loop and closed-loop. In the open-loop mode, the frequency shifts of the two optical signals output by the Y-waveguide are the same in magnitude but opposite in direction. The magnitude of the demodulated signal is proportional to the magnitude of the angular velocity to be measured, and the sign of the demodulated signal reflects the direction of the angular velocity to be measured. After calibration, the output angular velocity signal to be measured is obtained. In the closed-loop mode, the demodulated signal is used as an error signal to control the magnitude of the frequency shift generated by the Y-waveguide on the two output optical signals, so that the demodulated signal is maintained near 0. At this time, the difference in the magnitude of the frequency shift generated by the Y-waveguide on the two output optical signals reflects the magnitude and direction of the angular velocity to be measured.

[0010] The Y-waveguide described herein has beam splitting and combining, polarization and phase modulation functions.

[0011] The modulation of optical signals by the Y-waveguide refers to applying a periodic driving signal to the Y-waveguide to cause a corresponding phase change in the optical signal. The derivative of this phase change with respect to time is the frequency change of the optical signal.

[0012] In open-loop operation, the demodulated signal that has a linear relationship with angular velocity satisfies: P out = kΩ, where: P out Ω is the output demodulated signal, k is the proportional coefficient to be calibrated, and Ω is the angular velocity to be measured.

[0013] In closed-loop operation, the error signal remains near 0. The rate of change of the ramp portion of the sawtooth wave voltage signal applied to the two output paths of the Y waveguide is V1 and V2, respectively. Then, V1 + V2 = pΩ, where p is the proportional coefficient to be calibrated and Ω is the angular velocity to be measured.

[0014] The calibration process specifically involves applying a known angular velocity Ω to the fiber optic gyroscope to be calibrated using a precision turntable, and measuring the demodulated signal P at that moment. out The voltage change rates V1 and V2 of the two input signals of the Y waveguide (open loop state) or (closed loop state) can be used to calculate the magnitudes of the proportional coefficients k (open loop state) and p (closed loop state) according to the previous formula.

[0015] The low-coherence broadband light source is preferably a broadband light source such as a superfluorescent fiber optic light source or a superluminescent light-emitting diode.

[0016] The data processing unit includes an analog-to-digital conversion module and a digital operation module. The analog-to-digital conversion module acquires the voltage signal output from the photodetector and converts it into a digital signal. The digital signal generation module generates a reference signal for synchronous demodulation and a modulation signal for driving the Y-waveguide. The digital-to-analog conversion module converts the modulation signal into an analog signal to drive the Y-waveguide. The digital operation module uses the reference signal to synchronously demodulate the digital signal obtained from the analog-to-digital conversion, generating a demodulated signal. In open-loop operation, this demodulated signal, after calibration, becomes the output signal of the gyroscope. In closed-loop operation, the amplitude or frequency of the modulation signal output from the signal generation module is controlled by the demodulated signal to adjust the frequency shift applied by the Y-waveguide to the two optical signals, ultimately locking the demodulated signal to zero.

[0017] Technical effect

[0018] This invention comprehensively solves the problems of high coherent noise, complex optical path system and control algorithm, and low measurement accuracy caused by the use of high-coherence laser light sources and multiple locked feedback loops in existing resonant gyroscopes, as well as the adverse effects of backscattering signals and nonlinear Kerr effects caused by high-coherence light sources. Compared with the prior art, this invention uses a low-coherence light source and a fiber optic ring resonant cavity to realize a resonant fiber optic gyroscope, avoiding the coherent noise caused by the use of laser light sources in traditional resonant fiber optic gyroscopes, thus improving measurement accuracy. In the experiment, navigation-level measurement accuracy was achieved for the first time using a 100-meter-long fiber optic ring. No feedback control loop is required in the open-loop operation state, and only one feedback control loop is needed in the closed-loop operation state, reducing the complexity of the system and the number of modulators. This not only reduces costs but also reduces the non-reciprocity of the system, enabling higher measurement accuracy. Attached Figure Description

[0019] Figure 1a This is a schematic diagram of the present invention;

[0020] Figure 1b Schematic diagram of a Y-waveguide;

[0021] Figure 2 The measurement results of sinusoidal angular velocity are shown in the example.

[0022] Figure 3 The Allan standard deviation of the measurement results when the example is at rest;

[0023] In the figure: 1 Low coherence broadband light source, 2 Photodetector, 3 Data processing unit, 4 Optical circulator, 5 Y waveguide, 6 Fiber optic ring, 7 First optical coupler, 8 Second optical coupler. Detailed Implementation

[0024] like Figure 1a and Figure 1bAs shown in the figure, this embodiment relates to a resonant fiber optic gyroscope based on a low-coherence light source to implement the above method. It includes: a low-coherence broadband light source 1, a photodetector 2, a data processing unit 3, an optical circulator 4, a Y-waveguide 5, an optical fiber ring 6, a first optical coupler 7, and a second optical coupler 8. The optical fiber ring 6, the first optical coupler 7, and the second optical coupler 8 constitute an optical fiber ring resonant cavity. The optical signal emitted by the low-coherence broadband light source 1 is output to the first port of the optical circulator 4 and then output to the input port of the Y-waveguide 5 through the second port. The Y-waveguide 5 has one input port a and two output ports b and c. Each output port corresponds to a phase modulation electrode. The two modulated signals output from the two output ports... Optical signals are connected to the first optical coupler 7 and the second optical coupler 8, respectively, and injected into two opposite transmission directions in the optical fiber ring 6. The optical signals output from the two optical couplers of the optical fiber ring 6 return to the Y-waveguide and are output from the third port of the optical circulator 4 to the photodetector 2. The data processing unit 3 generates two periodic sawtooth wave modulation signals, which are applied to the phase modulation electrodes of the two output ports of the Y-waveguide 5, so that the two optical signals output from the Y-waveguide 5 generate frequency shifts. At the same time, the data processing unit 3 acquires the voltage signal output by the photodetector 2, multiplies the electrical signal output by the photodetector 2 with the generated periodic sawtooth wave modulation signal, and demodulates it by low-pass filtering.

[0025] In the aforementioned fiber optic ring resonant cavity: the fiber optic ring 6 is made of a section of optical fiber wound together, and its two fiber optic ports are respectively connected to port a of the first optical coupler 7 and port a of the second optical coupler 8, and port c of the first optical coupler 7 and port c of the second optical coupler 8, thereby forming a ring resonant cavity.

[0026] Both fiber optic couplers 7 and 8 are 2×2 fiber optic couplers, wherein the coupling coefficient from port c to port d is greater than 90%, preferably 98%, and port b is left empty.

[0027] In open-loop mode, the data processing unit 3 generates two sawtooth wave modulation signals with the same period. The voltage change rates of the ramp portions of these two sawtooth waves are equal in magnitude but opposite in speed, i.e., V1 = -V2. Here, V1 is the optical path branch connected to the Y waveguide and the first coupler, i.e., the voltage change rate of the sawtooth wave voltage ramp portion on electrode b, and V2 is the optical path branch connected to the Y waveguide and the second coupler, i.e., the voltage change rate of the sawtooth wave voltage ramp portion on electrode c. The demodulated signal is the output signal of the gyroscope after calibration.

[0028] In closed-loop operation, the voltage change rates V1 and V2 of the ramp portion of the two periodic sawtooth wave modulation signals generated by the control data processing unit are adjusted in real time according to the demodulated signal, so as to apply different frequency shifts to the two optical signals, so that the demodulated signal is locked at zero value, thus completing closed-loop locking control.

[0029] Preferably, the repetition frequency of the sawtooth wave modulation signal is 21kHz, and in open-loop operation, the peak-to-peak value is equal to twice the half-wave voltage of the phase modulator in the Y-waveguide.

[0030] Preferably, the low-coherence broadband light source 1 is a superfluorescent light source based on erbium-doped fiber.

[0031] Preferably, the photodetector 2 has tunable gain and bandwidth.

[0032] The Y-waveguide 5 is a lithium niobate-based Y-waveguide modulator, which has beam splitting and combining, polarization and phase modulation functions.

[0033] The Y-waveguide 5 generates a periodic frequency shift in the probe light pulse under the action of the sawtooth wave modulation signal generated by the data processing unit 3, and simultaneously records the electrical signal output by the photodetector. In digital processing, the signal output by the photodetector is multiplied by the Y-waveguide driving signal, and then low-pass filtered to obtain the output signal.

[0034] Preferably, the data processing unit 3 includes: a field-programmable gate array module, an analog-to-digital converter, and a digital-to-analog converter.

[0035] In this embodiment, a high-precision rotary table is used to apply a sinusoidally varying angular velocity signal (frequency 0.01Hz, amplitude 10° / h) to this resonant fiber optic gyroscope. The test results are as follows: Figure 2 As shown, a well-recovered sine signal can be observed.

[0036] A static test was conducted on this resonant fiber optic gyroscope. Output data was collected for 35,000 seconds in open-loop mode, with a sampling rate of 1 point per second. Its Allan standard deviation was calculated as follows: Figure 3 As shown, the random angular walk noise of this resonant fiber optic gyroscope can be read as follows: The zero-bias instability is 0.009° / h, achieving navigation-grade accuracy.

[0037] Compared with existing technologies, the resonant fiber optic gyroscope based on a broadband light source in this embodiment achieves navigation-level testing accuracy, which is higher than that of existing resonant fiber optic gyroscopes based on narrow linewidth lasers. Moreover, its system complexity and cost are significantly reduced, making it easier to put into practical use.

[0038] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A detection method for a resonant fiber optic gyroscope used for detecting angular velocity signals, characterized in that, This resonant fiber optic gyroscope includes: a low-coherence broadband light source, a photodetector, a data processing unit including a field-programmable gate array module, an optical circulator, a Y-waveguide with beam splitting and combining, polarization, and phase modulation functions, an optical fiber ring resonant cavity, and a circuit section. Specifically: the optical signal emitted by the low-coherence broadband light source is output to the first port of the optical circulator and then to the Y-waveguide through the second port. The Y-waveguide outputs two optical modulation signals to the first and second optical couplers, respectively, and injects them into two opposite transmission directions in the optical fiber ring resonant cavity. The optical signals output from the optical fiber ring resonant cavity through the two optical couplers return to the Y-waveguide and are output to the photodetector from the third port of the optical circulator. The data processing unit generates two periodic sawtooth wave modulation signals to drive the two modulation electrodes of the Y-waveguide, giving the two optical signals output from the Y-waveguide specific period and magnitude of frequency shift. The data processing unit acquires the voltage signal output by the photodetector and, using the modulation signal driving the Y-waveguide as a reference signal, performs synchronous detection on the acquired voltage signal and outputs a demodulated signal. The data processing unit includes an analog-to-digital conversion module, a digital-to-analog conversion module, a digital signal generation module, and a digital operation module. Specifically: the analog-to-digital conversion module acquires the voltage signal output from the photodetector and converts it into a digital signal; the digital signal generation module provides a reference signal for synchronous demodulation and a modulation signal for driving the Y-waveguide; the digital-to-analog conversion module converts the modulation signal into an analog signal to drive the Y-waveguide; the digital operation module uses the reference signal to synchronously demodulate the digital signal obtained from the analog-to-digital conversion, generating a demodulated signal; in open-loop operation, this demodulated signal, after calibration, becomes the output signal of the gyroscope; in closed-loop operation, the demodulated signal is used to control the amplitude or frequency of the modulation signal output from the signal generation module, thereby adjusting the frequency shift applied by the Y-waveguide to the two optical signals, ultimately locking the demodulated signal to a value of 0. The aforementioned detection refers to: using low-coherence light as the detection source, and utilizing the multi-beam interference phenomenon to detect the light intensity change signal caused by the rotation of the resonant fiber optic gyroscope. This includes two operating modes: open-loop and closed-loop. In the open-loop mode, the frequency shifts of the two optical signals output from the Y-waveguide are of the same magnitude but opposite in direction. The magnitude of the demodulated signal is proportional to the magnitude of the angular velocity to be measured, and the sign of the demodulated signal reflects the direction of the angular velocity to be measured. After calibration, the output angular velocity signal to be measured is obtained. In the closed-loop mode, this demodulated signal is used as an error signal to control the magnitude of the frequency shift generated by the Y-waveguide on the two output optical signals, keeping the demodulated signal near 0. The difference in the magnitude of the frequency shift generated by the Y-waveguide on the two output optical signals reflects the magnitude and direction of the angular velocity to be measured. In open-loop operation, the demodulated signal has a linear relationship with the angular velocity, specifically: P out =kΩ, where: P out The output demodulated signal is given by k, which is the proportional coefficient to be calibrated, and Ω is the angular velocity to be measured. In the closed-loop working state, the error signal is maintained near 0. The rate of change of the ramp portion of the sawtooth wave voltage signal applied to the two output paths of the Y waveguide is V1 and V2, respectively. Then V1 + V2 = pΩ, where p is the proportional coefficient to be calibrated and Ω is the angular velocity to be measured. The calibration process specifically involves applying a known angular velocity Ω to the fiber optic gyroscope to be calibrated using a precision turntable, and measuring the demodulated signal P at that moment. out The voltage change rates V1 and V2 of the two input signals of the Y-waveguide can be used to calculate the magnitudes of the proportional coefficients k and p according to the previous formula.

2. The method according to claim 1, characterized in that, The low-coherence broadband light source is a super-fluorescent fiber optic light source or a super-radiative light-emitting diode broadband light source.

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