Resonant optical gyroscope signal detection method based on optical switch

Abstract

The invention relates to a resonant optical gyroscope signal detection method based on an optical switch. The resonant optical gyroscope signal detection method comprises the following steps: step 1, adopting a narrow linewidth laser as a light source; 2, the split light field enters a lithium niobate phase modulator A and a phase modulator B to be modulated by a triangular wave voltage signal, the light field subjected to phase modulation is coupled in opposite directions to enter a waveguide resonant cavity, and a photoelectric detector A and a photoelectric detector B are used at the output end of the resonant cavity to obtain a voltage signal; and voltage signals obtained by the photoelectric detector A and the photoelectric detector B are accessed to a lock-in amplifier. 3, arranging an optical switch A between the waveguide resonant cavity and the photoelectric detector A; and an optical switch b is arranged between the waveguide resonant cavity and the photoelectric detector B, so that the detection of a gyro signal is completed. The interference of polarization noise can be reduced, and the resonant frequency locking precision and the angular velocity detection sensitivity of the gyroscope are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of resonant integrated optical gyroscopes, and relates to a resonant optical gyroscope signal detection method, in particular to a resonant optical gyroscope signal detection method based on an optical switch. BACKGROUND

[0002] The resonant optical gyroscope uses a modulation demodulation method for angular velocity sensing. In the absence of noise interference, the gyroscope output is basically an ideal symmetrical resonance curve. When the laser frequency is locked at the resonance frequency position, the light intensity corresponding to the left and right frequency shift points after signal modulation is equal, and the peak-to-peak value of the square wave signal used for demodulation is 0, which can be used to represent that the system is in a stationary state.

[0003] However, due to the existence of polarization noise and back scattering noise in the optical path, the symmetry of the original output curve is destroyed, thereby affecting the original modulation demodulation signal detection method. The specific calculation of the output spectrum line containing polarization noise shows that due to the existence of the secondary polarization mode spectrum line, the resonance curve on one side of the main polarization mode is obviously deformed, and the curves on both sides are no longer symmetric about the center of the resonance frequency point. At this time, if the laser frequency is locked at the resonance frequency point and the left and right equal distance frequency shift is generated under the action of signal modulation, the two light intensities corresponding to the output are obviously different, and a square wave error signal with a peak-to-peak value of 0 is generated.

[0004] Therefore, from the perspective of signal processing, due to the existence of noise, the asymmetry of the spectrum line will cause the commonly used phase modulation spectrum method to still generate a non-0 error feedback signal, resulting in a frequency locking error of the system and interfering with the locking of the resonance frequency point of the system.

[0005] In addition, due to the deformation and distortion of the spectrum line, the slope size and linearity of the linear working interval of the demodulation curve will decrease, thereby reducing the sensitivity of the angular velocity detection of the system.

[0006] Therefore, the present application designs a resonant optical gyroscope signal detection method based on an optical switch for the spectrum line containing noise to reduce the interference of the polarization noise.

[0007] Through retrieval, no existing technical disclosure documents similar to the present application have been found. SUMMARY

[0008] The present application aims to overcome the shortcomings of the prior art, and provides a resonant optical gyroscope signal detection method based on an optical switch, which can reduce the interference of the polarization noise and improve the resonance frequency locking precision and angular velocity detection sensitivity of the gyroscope.

[0009] The present application solves the practical problems by adopting the following technical solutions:

[0010] A resonant optical gyroscope signal detection method based on optical switch, comprising the following steps:

[0011] Step 1, a narrow linewidth laser is used as a light source, the wavelength of the output light field is 1550nm, and the light field is divided into two after passing through an isolator and a beam splitter;

[0012] Step 2, the split light field enters the lithium niobate phase modulator A and the phase modulator B to be modulated by a triangular wave voltage signal, the modulated light field is coupled into the waveguide resonant cavity from opposite directions, and the voltage signal is obtained from the output end of the resonant cavity using two photodetectors A and photodetector B; the voltage signals obtained by the two photodetectors A and photodetector B are connected to a lock-in amplifier, and the synchronous demodulation of the modulated signal is realized by means of a same frequency reference signal, so as to obtain the clockwise and counterclockwise demodulation signals; the demodulation signal generated by the clockwise CW loop is used as an error signal to complete laser frequency locking through a PI controller, so that the output frequency of the laser always keeps consistent with the resonant frequency of the CW direction; at the same time, the change of the counterclockwise CCW demodulation signal is used as the sensing quantity of the gyroscope system, and is directly output to the detection equipment by the lock-in amplifier, so as to complete the gyroscope angular velocity sensing based on the modulation and demodulation technology;

[0013] Step 3, an optical switch A is arranged between the waveguide resonant cavity and the photodetector A, and an optical switch B is arranged between the waveguide resonant cavity and the photodetector B, so as to complete the detection of the gyroscope signal;

[0014] Moreover, the specific method of step 2 is:

[0015] The split light field enters the lithium niobate phase modulator A and the phase modulator B, and is modulated by a triangular wave, and the frequency of the triangular wave voltage signal is set to f tri , and the peak-to-peak value is 2V0;

[0016] The specific expression of the triangular wave function V tri (t) is as follows:

[0017]

[0018] The triangular wave voltage signal makes the phase change of the light field when passing through the phase modulator:

[0019]

[0020] Wherein, V π is the half-wave voltage, which represents the voltage signal size corresponding to the phase change of the light field passing through the waveguide phase modulator by π, and the voltage signals of different amplitudes can be quantified by V π ;

[0021] A modulation factor M1 is defined, which is proportional to the amplitude of the applied signal:

[0022]

[0023] The above triangular wave modulation voltage signal is brought into the gyro spectrum line calculation to obtain the final output spectrum line of the modulated light field. Since the phase derivative is the frequency, the frequency argument of the output light intensity contains the frequency shift term f(t) generated by the triangular wave modulation, where q represents the transmission coefficient of the light field in the waveguide ring after one round of transmission, p describes the resonance depth of the output spectrum line, r is the waveguide resonant cavity loss coefficient in the gyro, and FSR is the free spectral range;

[0024]

[0025] In the upper half cycle of the triangular wave signal modulation, the frequency shift amount f(t) is equal to 2f tri , indicating that the frequency of the laser is shifted to the right; in the lower half cycle of the triangular wave signal modulation, the frequency shift amount is -2f tri , and the frequency of the laser is shifted to the left accordingly. Therefore, the output expressions of the light intensity in one triangular wave modulation period are formula (5) and (6), respectively.

[0026]

[0027] When the frequency of the laser is exactly the resonance frequency point, since the ideal output spectrum line is symmetrical on both sides, the output light intensity I R in one triangular wave modulation period is equal to I L ; when there is a certain frequency detuning amount, the output light intensity I R when the frequency is shifted to the right is obviously not equal to the output light intensity I L when the frequency is shifted to the left, and at this time the light field output is a peak-to-peak non-zero square wave signal. Therefore, the peak-to-peak value of the output waveform in a period can be obtained in experiments to obtain the demodulation signal, which can provide an error feedback signal for system frequency locking and angular velocity sensing.

[0028] Moreover, the specific steps of step 3 include:

[0029] (1) Before the light field enters the detector A and the detector B, two waveguide optical switch devices are additionally used between the waveguide resonant cavity exit position and the photodetector to adjust the correspondence between the clockwise and counterclockwise exiting light field and the two photodetectors. The light switching direction of the output end is switched by applying a corresponding control voltage signal to the light switch A and the light switch B.

[0030] The modulation frequency of the triangular wave is set to f tri , the period is T tri , and the switching frequency of the optical switch is set to twice the frequency of the triangular wave modulation signal. Therefore, the frequency shift amount of the light field in the entire triangular wave period is:

[0031]

[0032] (2) In the time range of 0 to , the voltage signal controls the output terminal ① in the optical switch A to be on, and the output terminal ④ in the optical switch B to be on;

[0033] Based on the above circuit, the frequency f of the light field output by the laser is locked in the clockwise direction in the waveguide resonant cavity through the detector A, the phase-locked module and the PI control, while the frequency f+2f tri corresponding to the light intensity is output through the detector B and the demodulation module, which is used for angular velocity sensing;

[0034] The output light intensity P1 in the time range of 0 to is calculated, and the expression is as follows:

[0035]

[0036] (3) In the time range of to , the voltage signal is changed to switch the light transmission direction of the two optical switches, at this time the output terminal ② in the optical switch A is on, and the output terminal ③ in the optical switch B is on; at this time the laser frequency is locked in the counterclockwise light field direction in the resonant cavity, while the clockwise light field passes through the detector B to output the light intensity corresponding to the frequency f+2f tri ; when the system rotates, the spectral lines in the clockwise and counterclockwise directions produce a frequency shift Δf;

[0037] The output light intensity P2 in the time range of to is calculated, and the expression is as follows:

[0038]

[0039] In the lower half cycle of the triangular wave signal modulation, the switching process of the optical switch is the same as that in the upper half cycle;

[0040] (4) In the time range of to , the output terminal ① in the optical switch A and the output terminal ④ in the optical switch B are on, at this time the laser frequency is re-locked in the clockwise direction in the resonant cavity; however, due to the frequency shift of the laser caused by the lower half cycle triangular wave signal modulation, the amount of frequency shift is -2f tri , at this time the detector B outputs the light intensity corresponding to the frequency f-2f tri in the counterclockwise direction spectrum, and the expression of the output light intensity corresponding to P3 is obtained

[0041]

[0042] (5) In to T tri The time, light switch A output end ② and light switch B output end ③ are turned on, and the laser frequency is locked to the resonant frequency of the waveguide resonant cavity in the counterclockwise direction, and the detector B output clockwise spectrum line frequency f-2f tri Corresponding to the light intensity;

[0043] Substitute the frequency mismatch Δf caused by rotation and the frequency shift -2f in the spectrum formula tri , the output light intensity expression corresponding to P4 can be obtained:

[0044]

[0045] Thus, the size of the four output light intensities in the triangular wave modulation period can be obtained, and the output voltage signal waveform is similar to the conventional triangular wave modulation output, which is a square wave signal.

[0046] The advantages and beneficial effects of the present application are:

[0047] The present application proposes a resonant optical gyroscope signal detection method based on an optical switch, which is a signal processing method for optimizing the output spectrum of the gyroscope by introducing an optical switch structure into the resonant optical gyroscope. Based on the original triangular wave modulation demodulation of the gyroscope signal, the data extraction points are increased in the cycle by increasing the optical switch, the data on one side of the clockwise and counterclockwise spectrum is effectively extracted for signal demodulation, the influence of the spectrum deformation caused by polarization noise is reduced, and the sensing accuracy of the gyroscope is improved. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 (a) is the output spectrum line diagram of the gyro signal modulation and demodulation of the present application - static state;

[0049] Figure 1 (b) is the output spectrum line diagram of the gyro signal modulation and demodulation of the present application - rotating state;

[0050] Figure 2 is a schematic diagram of the resonant optical gyroscope system of the present application;

[0051] Figure 3 (a) is the output light intensity of the upper half cycle detector of the present application ;

[0052] Figure 3 (b) is the output light intensity of the upper half cycle detector of the present application ;

[0053] Figure 4 (a) is the output light intensity of the lower half cycle detector of the present application

[0054] Figure 4(b) is the output light intensity of the lower half cycle detector of the present application

[0055] Reference signs:

[0056] 1. light source; 2. isolator; 3. phase modulator A; 4. phase modulator B; 5. waveguide resonator; 6. optical switch A; 7. optical switch B; 8. photodetector A; 9. photodetector B; DETAILED DESCRIPTION

[0057] The embodiments of the present application are further described below in conjunction with the accompanying drawings:

[0058] The present application designs a resonant optical gyroscope signal detection method based on optical switch, which effectively extracts spectral line data by introducing optical structure and reduces the interference of polarization noise.

[0059] Step 1: a narrow linewidth laser is used as a light source, the wavelength of the output light field is 1550nm, after passing through an isolator and a beam splitter, the light field is divided into two parts;

[0060] The working principle of step 1 is:

[0061] The resonant optical gyroscope usually uses a signal detection method of modulation and demodulation. When the system rotates, the clockwise and counterclockwise spectral lines produce a certain frequency shift in opposite directions, and the frequency shift is detected to perceive the angular velocity information. According to the experimental test process, it is very difficult to directly detect the change of light intensity caused by the frequency shift of the resonance point to perceive the angular velocity. For the THZ order of light field frequency, the frequency shift caused by small angular velocity rotation may be less than 1HZ, and the change of light intensity caused by sagnac effect is usually a very weak signal, so modulation and demodulation technology is often used in experiments to amplify the weak signal and improve the signal-to-noise ratio of the system.

[0062] The resonant optical gyroscope experimentally uses a narrow linewidth laser as a light source, the wavelength of the output light field is 1550nm, after passing through an isolator and a beam splitter, the light field is divided into two parts.

[0063] Step 2, the split light field enters into the lithium niobate phase modulator A and phase modulator B is modulated by a triangular wave voltage signal, the phase modulated light field is coupled into the waveguide resonant cavity from the opposite direction respectively, and the voltage signal is obtained from the photoelectric detector A and photoelectric detector B at the resonant cavity output end; the voltage signals obtained by the two photoelectric detectors A and photoelectric detector B are connected to the lock-in amplifier, and the synchronous demodulation of the modulated signal is realized by means of the same frequency reference signal, so that the clockwise and counterclockwise demodulation signals are obtained; the demodulation signal generated by the clockwise CW loop is taken as the error signal to complete the laser frequency locking through the PI controller, so that the output frequency of the laser always keeps consistent with the resonant frequency of the CW direction; at the same time, the change of the counterclockwise CCW demodulation signal is taken as the sensing quantity of the gyro system, which is directly output to the detection equipment by the lock-in amplifier, so that the gyro angular velocity sensing is completed based on the modulation and demodulation technology;

[0064] The specific method of step 2 is:

[0065] The split light field enters into the lithium niobate phase modulator A and phase modulator B, and is modulated by a triangular wave, and the frequency of the triangular wave voltage signal is set to f tri , and the peak-to-peak value is 2V0;

[0066] The specific expression of the triangular wave function V tri (t) is as follows:

[0067]

[0068] The triangular wave voltage signal makes the phase change of the light field when passing through the phase modulator:

[0069]

[0070] Wherein, V π is the half-wave voltage, which represents the voltage signal size corresponding to the phase change of the light field after passing through the waveguide phase modulator, and the voltage signal of different amplitude can be quantified by V π to change the phase;

[0071] Define the modulation factor M1, which is proportional to the amplitude of the applied signal:

[0072]

[0073] The triangular wave modulation voltage signal is brought into the gyro spectrum line calculation, and the final output spectrum line of the modulated light field is obtained. Since the phase derivative is the frequency, the frequency argument of the output light intensity contains the frequency shift term f(t) generated by the triangular wave modulation, wherein q represents the transmission coefficient of the light field in the waveguide ring after one round of transmission, p describes the resonance depth of the output spectrum line, r is the waveguide resonant cavity loss coefficient in the gyro, and FSR is the free spectral range;

[0074]

[0075] In the upper half cycle of the triangular wave signal modulation, the frequency shift amount f(t) is equal to 2f tri , which indicates that the frequency of the laser is shifted to the right. In the lower half cycle of the triangular wave signal modulation, the frequency shift amount is -2f tri , and the frequency of the laser is shifted to the left. Therefore, the output expressions of the light intensity in one triangular wave modulation cycle are formula (5) and formula (6).

[0076]

[0077] When the frequency of the laser is exactly the resonance frequency point, since the ideal output spectrum line is symmetrical on both sides, the output light intensity I R in one triangular wave modulation cycle is equal to I L . When there is a certain frequency detuning amount, the output light intensity I R when the frequency is shifted to the right is obviously not equal to the output light intensity I L when the frequency is shifted to the left, and at this time the light field output is a peak-to-peak non-zero square wave signal. Therefore, the peak-to-peak value of the output waveform in a cycle can be obtained by experiment, which can provide an error feedback signal of system frequency locking and angular velocity sensing.

[0078] The working principle of step 2 is as follows:

[0079] The split light field enters the lithium niobate phase modulator and is modulated by the voltage signal. The phase-modulated light field is coupled into the waveguide resonant cavity from opposite directions, and the resonant spectrum lines in the clockwise CW direction and the counterclockwise CCW direction are obtained by using two photodetectors at the output end of the resonant cavity. Finally, the converted voltage signal is connected to the phase-locked amplifier, and the synchronous demodulation of the modulated signal is realized by means of the same frequency reference signal, so that the clockwise and counterclockwise demodulation spectrum lines are obtained.

[0080] From Figure 1 (a) and Figure 1(b) The middle region of the demodulation curve is linear, and when the system is in a static state, the demodulation signal output is 0, and the angular velocity information of the external environment can be linearly perceived when rotating. The specific angular velocity sensing process is that the demodulation spectrum line generated by the clockwise (CW) loop is taken as an error signal to complete laser frequency locking through a PI controller, so that the output frequency of the laser always maintains consistency with the resonant frequency in the CW direction. At the same time, the change of the counterclockwise (CCW) demodulation signal is taken as the sensing quantity of the gyro system, and is directly output to the detection equipment by the phase-locked amplifier, so as to complete the detection of the signal and the angular velocity sensing based on the modulation and demodulation technology.

[0081] Step 3, setting an optical switch A between the waveguide resonant cavity and the photodetector A; setting an optical switch B between the waveguide resonant cavity and the photodetector B, thereby completing the detection of the gyro signal;

[0082] The specific steps of the step 3 include:

[0083] (1) Before the light field enters the detector A and the detector B, two waveguide optical switch devices are additionally used between the waveguide resonant cavity exit position and the photodetector, to adjust the correspondence between the clockwise and counterclockwise exiting light field and the two photodetectors. By applying a corresponding control voltage signal to the optical switch A and the optical switch B, the light transmission direction of the output end is switched;

[0084] The modulation frequency of the triangular wave is set to f tri , the period is T tri , and the switching frequency of the optical switch is set to twice the frequency of the triangular wave modulation signal; then the frequency shift amount of the light field in the entire triangular wave period is:

[0085]

[0086] (2) In the range of time 0 to , the voltage signal controls the output end ① of the optical switch A to be conductive, and the output end ④ of the optical switch B to be conductive. Based on the above circuit, the light field frequency f output by the laser passes through the detector A, the phase-locked module and the PI control to be locked in the clockwise direction of the waveguide resonant cavity. The output frequency f+2f tri corresponding to the light intensity of the counterclockwise loop passes through the detector B and the demodulation module to output a signal for angular velocity sensing.

[0087] The output light intensity P1 in the time range of 0 to is calculated, and the expression is as follows:

[0088]

[0089] (3) In the range of to Within a certain time, the voltage signal is changed to switch the light transmission direction of the two optical switches. At this time, the output terminal ② of optical switch A is turned on, and the output terminal ③ of optical switch B is turned on. At this time, the laser frequency is locked in the counterclockwise direction of the light field in the resonant cavity, while the clockwise light field outputs the frequency f+2f through detector B. tri When the system rotates, the spectral lines in the clockwise and counterclockwise directions produce a frequency shift Δf. Figure 3 (a) and Figure 3 (b) shows the output light intensity of detector B at different times during the first half cycle of the triangle wave modulation.

[0090] calculate arrive The output light intensity P2 within a certain time period is expressed as follows:

[0091]

[0092] In the second half cycle of the triangle wave signal modulation, the switching process of the optical switch is the same as that in the first half cycle.

[0093] (4) arrive During the time, the output terminal ① of optical switch A and the output terminal ④ of optical switch B are connected, and the laser frequency is re-locked in the clockwise direction of the resonant cavity. However, due to the modulation of the triangle wave signal in the second half cycle, the frequency shift of the laser is -2f tri At this time, the photodetector B outputs the frequency f-2f in the counterclockwise spectrum line. tri The corresponding light intensity can be obtained by expressing the output light intensity of P3.

[0094]

[0095] (5) to T tri During the time, the output terminal ② of optical switch A and the output terminal ③ of optical switch B are connected, and the laser frequency is locked to the counterclockwise resonant frequency of the waveguide resonant cavity. At the same time, the detector B outputs the clockwise spectral line frequency f-2f tri The corresponding light intensity; Similarly, when the system has a certain angular velocity, the output light intensity of the two-stage detector B is shown as follows: Figure 4 (a) and Figure 4 (b) Substitute the frequency detuning Δf and the frequency shift -2f caused by rotation into the spectrum formula. tri , the output light intensity expression corresponding to P4 can be obtained:

[0096]

[0097] From this, we can obtain the magnitude of the four output light intensities within the triangle wave modulation period. The output voltage signal waveform is similar to the traditional triangle wave modulation output, which is a square wave signal.

[0098] The working principle of the step 3 is:

[0099] Based on the polarization noise will destroy the output spectrum line symmetry, the system lock and angular velocity sensor. Below in the above resonant optical gyroscope signal detection, increase the optical switch device, extract a side signal data demodulation to reduce the secondary polarization mode spectrum line influence. Figure 2 For the optimized system schematic diagram, the laser light field after phase modulation, also from clockwise and counterclockwise direction into the waveguide resonant cavity.

[0100] Before the light field into the detector, in the resonant cavity emission position and photodetector between the additional use of two waveguide optical switch (optical switch) device, in order to adjust the clockwise and counterclockwise emission of light field and two photodetector corresponding relationship. By applying the corresponding control voltage signal to the optical switch, to switch its output end of the light direction. Set the modulation frequency of the triangular wave is f tri , the period is T tri , the switching frequency of optical switch is set to 2 times the frequency of the triangular wave modulation signal. Then in the whole triangular wave cycle, the frequency of the light field is;

[0101]

[0102] In the time is 0 to , the voltage signal control optical switch A in the output end ① conductive, optical switch B in the output end ④ conductive. Based on the above circuit, then the laser output light field frequency f through the detector A, phase locked loop module and PI control lock in the waveguide resonant cavity clockwise direction. And counterclockwise loop output frequency f+2f tri corresponding light intensity, and through the detector B and demodulation module output signal, for angular velocity sensor. In to time, change the voltage signal to switch the light direction of two optical switch, at this time the output end ② of optical switch A is conductive, and the output end ③ of optical switch B is conductive. At this time the laser frequency is locked in the resonant cavity counterclockwise light field direction, and the clockwise direction of light field through the detector B output frequency f+2f tri corresponding light intensity. In the system rotation, the clockwise and counterclockwise direction of the spectrum line produces frequency shift Δf, Figure 3 then shows the output light intensity of detector B at different time in the upper half cycle of the triangular wave modulation. The specific calculation of the output light intensity P1 in 0 to , and the output light intensity P2 in to , the expression is as follows:

[0103]

[0104] In the second half cycle of the triangle wave signal modulation, the switching process of the optical switch is the same as that in the first half cycle. arrive During the time, the output terminal ① of optical switch A and the output terminal ④ of optical switch B are connected, and the laser frequency is re-locked in the clockwise direction of the resonant cavity. However, due to the modulation of the triangle wave signal in the second half cycle, the frequency shift of the laser is -2f tri At this time, the photodetector B outputs the frequency f-2f in the counterclockwise spectrum line. tri The corresponding light intensity. to T tri During the time, the output terminal ② of optical switch A and the output terminal ③ of optical switch B are connected, and the laser frequency is locked to the counterclockwise resonant frequency of the waveguide resonant cavity. At the same time, the detector B outputs the clockwise spectral line frequency f-2f tri Similarly, when the system has a certain angular velocity, the output light intensity of the two-stage detector B is as follows: Figure 4 Substitute the frequency detuning amount Δf and the frequency shift amount -2f caused by rotation into the spectrum formula. tri , the specific output light intensity expression corresponding to P3 and P4 can be obtained:

[0105]

[0106] From this, we can deduce the magnitude of the four output light intensities within the triangle wave modulation cycle. The output voltage signal waveform is similar to the traditional triangle wave modulation output, which is a square wave signal. The difference is that the output signal extraction data within the entire cycle is increased by additionally applying an optical switch. By sampling the square wave data of the upper half cycle P1 and P2 or the square wave data of the lower half cycle P3 and P4, the system's demodulated output spectrum can be obtained and used for angular velocity sensing. Due to the interference of polarization noise, when the distance between the two resonance valleys is close, the actual output spectrum will inevitably produce obvious distortion on one side, while the other side of the curve is less affected. Therefore, selectively sampling the data on one side (such as P1 and P2 data) for signal demodulation can significantly reduce the interference caused by polarization noise.

[0107] The working principle of the present invention is:

[0108] Resonant optical gyros use modulation and demodulation for angular velocity sensing. Ideally, the gyro output is a symmetrical resonant curve. When the laser frequency is locked at the resonant frequency, the demodulated square wave signal's peak-to-peak value is zero, indicating a stationary state. However, polarization noise in the optical path disrupts the symmetry of the output curve, causing the commonly used phase modulation spectrum method to generate a non-zero error feedback signal even when the system is at the resonant frequency. This results in frequency lock errors, disrupting the resonant frequency lock, and reducing angular velocity detection sensitivity.

[0109] To this end, the application provides a resonant optical gyroscope signal detection method based on an optical switch, aiming to effectively reduce polarization noise interference and improve the resonant frequency locking accuracy and angular velocity detection sensitivity of the gyroscope.

[0110] Specifically, the demodulation spectrum corresponding to the one-side detection method after using the optical switch is calculated, and the variation trend of the two demodulation methods in the linear working interval under the same temperature condition is compared. The phase interval between the two polarization modes is 0.005π. Due to the interference of polarization noise on one side of the original spectrum, the demodulation amplitude and linearity of the frequency detuning greater than 0 interval are obviously smaller than the detuning less than 0 interval during the demodulation process using the traditional method. When the one-side detection method is used, the demodulation amplitude of the spectrum is basically symmetrical about the center of the resonance point, and the linearity is also obviously improved. Further calculation of the curve slope of the traditional detection method and the one-side detection method near the center frequency point is k d1 and k d2 The slope ratio of the two is about 1.078.

[0111] In addition to analyzing the optimization and improvement of the linearity of the spectrum by the one-side detection method, the demodulation square wave error amplitude of the traditional detection method and the one-side detection method under triangular wave modulation is calculated. When the laser frequency is fixed at the resonance frequency position, the output square wave amplitude is 0 in the ideal case, and the actual polarization noise and other factors cause the system to output a non-zero demodulation signal, which brings frequency locking error to the system. When ΔβL=0.005π, the square wave amplitude corresponding to the one-side detection method can be reduced to 0.018 of the original.

[0112] In summary, within a certain temperature range, by applying an optical switch to the gyro system for one-side signal detection, the square wave error amplitude of the demodulation output at the resonance frequency position can be reduced, which is beneficial to improve the frequency locking accuracy of the system. The linearity of the demodulation curve is obviously improved and optimized, which improves the sensitivity of the angular velocity sensor of the system.

[0113] The innovation of the application lies in:

[0114] 1. A narrow linewidth laser is used as a light source to output a light field with a wavelength of 1550nm; the modulated light field is coupled into the waveguide resonant cavity from the opposite direction, and two photodetectors are used to obtain the clockwise and counterclockwise resonant spectrum at the output end of the resonant cavity, and the converted voltage signals are connected to a phase-locked amplifier for synchronous demodulation;

[0115] A triangular wave with a frequency of f tri and a peak-to-peak value of 2V0 is used for signal modulation, and two waveguide optical switches are arranged between the resonant cavity exit position and the photodetector, and the switching frequency of the optical switch is twice the frequency of the triangular wave modulation signal.

[0116] 2. In the triangular wave modulation period, by controlling the light switch light direction, alternately locking the laser frequency in the clockwise or counterclockwise direction of the resonant frequency, and making the other side of the optical field produce a frequency shift of ±2f tri , selectively sampling the output data of a certain half cycle (upper half cycle or lower half cycle) in the triangular wave modulation period for signal demodulation, so as to reduce the polarization noise interference.

[0117] 3. By comparing the demodulation square wave error amplitudes of the two signal detection methods under different temperature conditions, the square wave error amplitude corresponding to the optimized signal detection method can be reduced to 0.018 of the original.

[0118] It should be emphasized that the embodiments described in the present application are illustrative rather than restrictive, and therefore the present application includes but is not limited to the embodiments described in the specific embodiments, and any other embodiments derived by those skilled in the art according to the technical solutions of the present application also belong to the scope of protection of the present application.

Claims

1. A resonator optical gyroscope signal detection method based on an optical switch, characterized by: It comprises the following steps: Step 1, using a narrow linewidth laser as a light source, the wavelength of the output light field is 1550nm, after the isolator and the beam splitter, the light field is divided into two parts; Step 2, the split light field enters the lithium niobate phase modulator A and phase modulator B and is modulated by a triangular wave voltage signal, the modulated light field is coupled into the waveguide resonant cavity from the opposite direction, and the voltage signal is obtained from the output end of the resonant cavity using two photodetectors A and photodetector B; the voltage signals obtained by the two photodetectors A and photodetector B are connected to the phase-locked amplifier, and the synchronous demodulation of the modulated signal is realized by means of the same frequency reference signal, so as to obtain the clockwise and counterclockwise demodulation signals; the demodulation signal generated by the clockwise CW loop is used as an error signal to complete the laser frequency locking through the PI controller, so that the output frequency of the laser always keeps consistent with the resonant frequency of the CW direction; at the same time, the change of the counterclockwise CCW demodulation signal is used as the sensing quantity of the gyro system, which is directly output to the detection equipment, so as to complete the gyro angular velocity sensing based on the modulation and demodulation technology; Step 3, an optical switch A is arranged between the waveguide resonant cavity and the photodetector A; an optical switch b is arranged between the waveguide resonant cavity and the photodetector B, thereby completing the detection of the gyro signal.

2. The signal detection method of the resonator optical gyroscope based on the optical switch according to claim 1, characterized in that: The specific method of step 2 is: The split light field enters into the lithium niobate phase modulator A and the phase modulator B, signal modulation is carried out using a triangular wave, the frequency of the triangular wave voltage signal is set as f tri , and the peak-peak value is 2V0. Triangular wave form function V tri The specific expression of (t) is as follows: The triangular wave voltage signal applied makes the phase change of the light field when passing through the phase modulator: Among them, V π V is the half-wave voltage, which means the voltage signal size corresponding to the phase change of π after the light field passes through the waveguide phase modulator. Voltage signals of different amplitudes can be represented by V π to quantify the phase change; Define the modulation factor M1, which is proportional to the amplitude of the applied signal: The triangular wave modulation voltage signal is brought into the gyro spectrum calculation, and the final output spectrum of the modulated light field is obtained. Since the phase derivative is the frequency, the frequency argument of the output light intensity contains the frequency shift term f(t) generated by the triangular wave modulation, wherein q represents the transmission coefficient of the light field in the waveguide ring after one round of transmission, p describes the resonance depth of the output spectrum, r is the waveguide resonant cavity loss coefficient in the gyro, and FSR is the free spectral range; In the upper half cycle of the triangular wave signal modulation, the frequency shift f(t) equals to 2f tri , which means the frequency of the laser is shifted to the right; in the lower half cycle of the triangular wave signal modulation, the frequency shift f(t) equals to -2f tri , which means the frequency of the laser is shifted to the left, therefore, the output expression of the light intensity in a triangular wave modulation cycle is respectively formula (5) and (6); When the frequency of the laser is exactly the resonance frequency point, due to the symmetry of the ideal output spectrum on both sides, the output light intensity I R is equal to I L ; while when there is a certain frequency detuning, the output light intensity I R right shift is obviously not equal to the corresponding light intensity I L left shift, at this time the light field output is a peak-to-peak non-zero square wave signal; therefore, the peak-to-peak value of the output waveform in the cycle can be obtained by collecting the demodulation signal in the experiment, which can provide the error feedback signal of the system frequency locking and angular velocity sensing.

3. The signal detection method of the resonator optical gyroscope based on the optical switch according to claim 1, characterized in that: The specific steps of step 3 include: (1) Before the light field enters the detector A and the detector B, two waveguide optical switch devices are additionally used between the waveguide resonant cavity exit position and the photodetector, to adjust the corresponding relationship between the clockwise and counterclockwise output light field and the two photodetectors. By applying corresponding control voltage signals to the optical switch A and the optical switch B, the light transmission direction of the output end is switched; The modulation frequency of the triangular wave is set as f tri , the period is T tri , the switching frequency of the optical switch is set as twice the frequency of the triangular wave modulation signal; the frequency shift of the optical field in the whole triangular wave period is: (2) in the range of time from 0 to the voltage signal controls the output terminal 1 in the optical switch A to be on, and the output terminal 4 in the optical switch B to be on; Based on the above circuit, the frequency f of the light field output by the laser is locked in the clockwise direction in the waveguide resonant cavity through the detector A, the phase-locked module and the PI control; while the counterclockwise circuit outputs the frequency f+2f tri The corresponding light intensity is output through the detector B and the demodulation module, and the signal is used for angular velocity sensing. The output light intensity P1 within the time period from 0 to is expressed as follows: (3) in the time interval from the voltage signal is changed to switch the light direction of the two optical switches, at this time the output end ② of the optical switch A is turned on, and the output end ③ of the optical switch B is turned on; at this time, the laser frequency is locked in the counterclockwise light field direction in the resonant cavity, and the clockwise light field passes through the detector B to output the frequency f+2f tri corresponding to the light intensity; when the system rotates, the spectral lines in the clockwise and counterclockwise directions produce a frequency shift Δf; Computing To The output light intensity P2 size within the time, expression as follows: In the lower half cycle of the triangular wave signal modulation, the switching process of the optical switch is the same as that in the upper half cycle; (4) In the time interval from to the output terminal ① of the optical switch A is connected to the output terminal ④ of the optical switch B, at this time the laser frequency is relocked in the clockwise direction of the resonant cavity; but due to the modulation of the lower half cycle triangular wave signal, the frequency shift of the laser is -2f tri , at this time the photoelectric detector B outputs the corresponding light intensity of the frequency f-2f tri in the counterclockwise direction spectrum, and the corresponding output light intensity expression of P3 can be obtained (5) In the time interval from T tri to T tri , the output end ② of the optical switch A and the output end ③ of the optical switch B are connected, the laser frequency is locked to the resonant frequency of the waveguide resonant cavity in the counterclockwise direction, and the output of the detector B corresponds to the light intensity of the spectrum line frequency f-2f Substitute the frequency detuning Δf and the frequency shift -2f caused by rotation into the formula of the spectral line tri The expression of the output light intensity corresponding to P4 can be obtained. Thus, four output light intensity sizes in the triangular wave modulation period can be obtained, and the output voltage signal waveform is similar to the traditional triangular wave modulation output, which is a square wave signal.

Images