Method for inhibiting relative intensity noise of closed-loop dual-channel fiber-optic gyroscope

Abstract

The invention discloses a method for suppressing relative intensity noise of a closed-loop dual-channel fiber-optic gyroscope. The method comprises the following steps: 1) taking two closed-loop Sagnac interferometers as two channels of a closed-loop fiber-optic gyroscope; one light source is used for driving the two closed-loop Sagnac interferometers, and a square wave bias signal and a step wave signal are applied to each channel at the same time; wherein the step wave signals applied to the two channels are the same, and the square wave bias signals applied to the two channels are opposite in phase; 2) calculating a Sagnac phase phi S detected by the closed-loop fiber-optic gyroscope according to a feedback phase phi F of a first closed loop in the closed-loop fiber-optic gyroscope; and 3) calculating error signals Vr1 and Vr2 of a second closed loop in the closed-loop fiber-optic gyroscope, sending the error signals Vr1 and Vr2 to the integrator for feedback control, and calibrating feedback coefficients GM1 and GM2 of the first closed loop, so that the feedback phases of the two channels are the same, and the phase modulation depths are the same. According to the invention, the sensitivity of the closed-loop fiber-optic gyroscope is greatly improved.

Description

Technical Field

[0001] This invention relates to a closed-loop demodulation method for dual-channel fiber optic gyroscopes based on four-state square waves to suppress relative intensity noise. This method can be used to improve the measurement sensitivity of fiber optic gyroscopes and is of great value for the application of fiber optic gyroscopes in inertial navigation, seismology, and geological exploration. Background Technology

[0002] Fiber optic gyroscopes employ two main solution methods: open-loop and closed-loop. Closed-loop solutions, due to their linear response and other characteristics, are widely used in fiber optic gyroscopes. Their overall system structure can be simplified as follows: Figure 1 As shown, where φ S The detected Sagnac phase has a total phase of φ = φ S +φ F +φ b .

[0003] In the closed-loop scheme, a square wave bias signal V1 and a stepped wave signal V2 are simultaneously applied through the Y-waveguide, thereby generating a bias phase φ in the phase term of the optical signal. b (t) and feedback phase φ F (t), the waveforms of the two are as follows: Figure 2 , Figure 3 As shown; where the phase bias is generally generated using a four-state square wave with a period of T = 2τ, τ is the transit time of the fiber loop, and φ B The modulation depth is used. The stepped wave signal employs... Figure 3 The waveform shown in (a) is a stepped wave generated using an accumulator, and the height difference between adjacent steps is denoted as V. F When the accumulated value reaches its maximum, it will automatically overflow and reset, and the resulting feedback phase is as follows: Figure 3 As shown in (b), the feedback phase generated at the non-reset point is φ F The reset point is φ F -2π.

[0004] After this closed-loop scheme, including the Sagnac phase φ S The interference light signal, after photoelectric conversion, can be written as V p (t), which is also a signal with period T = 2τ, contains four states, and can be written as follows, where G p This is the equivalent gain coefficient.

[0005]

[0006] Signal V p The four voltage states mentioned above (t) are used for subsequent digital demodulation, and the demodulation process yields the error signal V. e As shown in the following formula:

[0007] Ve =(V A +V B )-(V C +V D ) = 4G p I0sinφ B sin(φ S +φ F )

[0008] Because V e ∝sin(φ S +φ F This can be used as an error signal for subsequent feedback control systems. When the feedback is stable, V e When the value is controlled to be near 0, then φ is obtained. S +φ F →0, based on the feedback phase φ F The input Sagnac phase φ can be calculated. S .

[0009] Relative intensity noise (RIN) affects V e The signal-to-noise ratio (SNR) affects the accuracy of the closed-loop solution. Considering the white noise characteristics of RIN and V... p The four voltage states of (t) are taken from different time periods, therefore the noise n corresponding to these four states is... A n B n C n D They are irrelevant, therefore V e noise V N The combined effect of noise from four states:

[0010]

[0011] Therefore V e The signal-to-noise ratio R can be expressed as follows, where σ is the noise level n. A n B n C n D Standard deviation

[0012]

[0013] The signal-to-noise ratio of the error signal is related to the modulation depth, and as the feedback stabilizes, i.e., φ... S +φ F →0, the signal-to-noise ratio will decrease, which will affect the application of closed-loop solution in gyroscopes. Summary of the Invention

[0014] In view of the problems existing in the prior art, the purpose of this invention is to provide a method for suppressing relative intensity noise in closed-loop fiber optic gyroscopes and improve the sensitivity of closed-loop fiber optic gyroscopes.

[0015] The technical solution of this invention is as follows:

[0016] A method for suppressing relative intensity noise in a closed-loop dual-channel fiber optic gyroscope, comprising the following steps:

[0017] 1) Use two closed-loop Sagnac interferometers as two channels of a closed-loop fiber optic gyroscope; drive the two closed-loop Sagnac interferometers with a light source, and simultaneously apply a square wave bias signal and a step wave signal to each channel; wherein the step wave signals applied to the two channels are the same, and the square wave bias signals applied to the two channels are out of phase.

[0018] 2) Based on the feedback phase φ of the first closed loop in the closed-loop fiber optic gyroscope F Calculate the Sagnac phase φ detected by the closed-loop fiber optic gyroscope S ;

[0019] 3) Calculate the error signal V of the second closed loop in the closed-loop fiber optic gyroscope. r1 V r2 It is then fed into an integrator for feedback control, thereby calibrating the feedback coefficient G of the first closed loop. M1 G M2 This ensures that the feedback phases and phase modulation depths of the two channels are the same.

[0020] Furthermore, the four bias phases within one cycle of the first channel are -φ. B -φ B +2π, φ B φ B -2π, the four bias phases of the second channel within one cycle are opposite to those of the first channel; φ B This represents the modulation depth of the square wave bias signal.

[0021] Furthermore, the error signal of the first closed loop G p I0 is the equivalent gain coefficient, and I0 is the light intensity of the light source

[0022] Furthermore, the error signal V of the second closed loop r1 =-4G p I0sin∈πsin((1+∈)φ B V r2 =4G p I0sin∈πsin((1+∈)φ B ); among which, calibration G M1 and G M2 This helps to ensure the feedback phase φF The accuracy of G is denoted by ∈, which is the inaccuracy factor. p I0 is the equivalent gain coefficient, and I0 is the light intensity of the light source

[0023] This invention utilizes a single light source to drive two closed-loop Sagnac interferometers, which serve as two channels of a closed-loop fiber optic gyroscope, and their input Sagnac phase φ is... S Consistent.

[0024] A square wave bias signal and a stepped wave signal are simultaneously applied to two channels, respectively. The stepped wave signals are identical, but the square wave bias signals of the two channels are out of phase, i.e., the resulting bias phases φ are respectively... b1 (t)=-φ b2 (t)=φ b (t), such as Figure 4 As shown, the feedback phase φ F (t) and the above Figure 1 The analysis is the same for single-channel fiber optic gyroscopes.

[0025] After undergoing light intensity detection, photoelectric conversion, and subsequent operational amplifiers, the two sets of signals are processed by a joint algorithm. The specific solution scheme of this invention is shown below. This invention also includes a first closed loop and a second closed loop.

[0026] The interference light signals from the two channels, after photoelectric conversion, can be written as follows:

[0027] V p1 (t)=G p I0[1+cos(φ S +φ F +φ b1 )]

[0028] V p2 (t)=G p I0[1+cos(φ S +φ F +φ b2 )]

[0029] Both are signals with a period of T = 2τ, and both contain four states. Within one period of one channel, the four bias phases are -φ... B -φ B +2π, φ B , φ B -2π. The four bias phases of the two channels within one cycle are opposite to those of the one channel. The four states of the one channel are: V A1 V B1 V C1 V D1 The two channels have four states: V A2 V B2 VC2 V D2 After processing by the joint algorithm, the error signal of the first closed loop is obtained:

[0030]

[0031] After considering the effect of RIN, due to the correlation of noise, the noise of the two channels at the same time (A, B, C, D) is the same. After processing by the joint algorithm, the noise can be written as:

[0032]

[0033] The corresponding signal-to-noise ratio of the error signal is:

[0034]

[0035] As can be seen, in the dual-channel fiber optic gyroscope closed-loop solution of the present invention, the signal-to-noise ratio of the error signal is only related to the size of RIN and not to the modulation depth. At the same time, the signal-to-noise ratio will not decrease as the feedback stabilizes. This shows that the present invention can maintain a high signal-to-noise ratio during the solution process.

[0036] Meanwhile, this invention addresses the φ caused by temperature drift, etc. B The changes construct a second closed loop. This is primarily used to monitor the feedback coefficient G of the first closed loop. M .

[0037] Due to fluctuations in the modulation coefficient caused by reset errors or temperature changes, the feedback coefficient is now out of sync. ∈ is the inaccuracy factor, and ∈ is much less than 1; therefore, the bias phase and feedback phase are also correspondingly inaccurate:

[0038]

[0039] Calculate V at this time r1 and V r2 As the error signal of the second closed loop:

[0040] V r1 =(V A1 -V B1 )+(V C1 -V D1 ) = -4G p I0sin∈πsin((1+∈)φ B )

[0041] V r2 =(V A2 -V B2 )+(V C2 -V D2 ) = 4G pI0sin∈πsin((1+∈)φ B )

[0042] The two error signals from the second closed loop are fed into the integrator for feedback control. The first closed loop adjusts the feedback phase φ. F Make φ S =-φ F The second closed loop adjusts the feedback coefficient G of the two channels by controlling the operational amplifier gain or the analog-to-digital converter reference voltage. M1 G M2 This ensures that the feedback phases in the two channels are consistent and the modulation depths are equal.

[0043] Compared with the prior art, the positive effects of the present invention are as follows:

[0044] The overall device employs a dual-channel fiber optic Sagnac interferometer. By jointly processing the signals from the two channels, a new first closed-loop error signal is constructed, which effectively improves the signal-to-noise ratio compared to existing methods. Furthermore, this invention constructs a second closed loop to address the limitations of the first closed loop, generating a new error signal to regulate and stabilize the feedback coefficients of the two channels. Attached Figure Description

[0045] Figure 1 This is a diagram of a closed-loop system.

[0046] Figure 2 Phase offset φ for four-state square wave b Waveform diagram.

[0047] Figure 3 The stepped wave signal and its corresponding feedback phase φ F Waveform diagram;

[0048] (a) Step wave signal voltage waveform diagram, (b) Feedback phase waveform diagram.

[0049] Figure 4 For dual-channel four-state square wave phase bias φ b Waveform diagram.

[0050] Figure 5 This is a flowchart of the dual-channel closed-loop solution scheme. Detailed Implementation

[0051] The following is based on Figure 5 The present invention will now be described in further detail.

[0052] The specific process of this invention is as follows: Figure 5 As shown, after sensing the angular velocity Ω input, the two channels are modulated in opposite phases through their respective Y-waveguides, applying opposite four-state square wave phase biases, and superimposed with the same feedback phase φ. FAfter photoelectric conversion and subsequent equivalent amplification, the signals from the two channels are jointly processed to obtain the error signal of the first closed loop. To ensure the stability of the closed-loop solution, a second closed-loop monitoring mechanism was introduced to address changes in the feedback coefficients caused by reset errors. The error signal V of the second closed loop was obtained by processing the signals from both channels separately. r1 V r2 It is fed into an integrator for feedback control to adjust the first closed-loop feedback coefficient G of the two channels. M1 G M2 This ensures the stability of feedback and bias.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for suppressing relative intensity noise in a closed-loop dual-channel fiber optic gyroscope, comprising the following steps: 1) Use two closed-loop Sagnac interferometers as two channels of a closed-loop fiber optic gyroscope; Two closed-loop Sagnac interferometers are driven by a single light source, and a square wave bias signal and a step wave signal are simultaneously applied to each channel; wherein the step wave signals applied to the two channels are the same, and the square wave bias signals applied to the two channels are out of phase; 2) Based on the feedback phase φ of the first closed loop in the closed-loop fiber optic gyroscope F Calculate the Sagnac phase φ detected by the closed-loop fiber optic gyroscope S ; 3) Calculate the error signal V of the second closed loop in the closed-loop fiber optic gyroscope. r1 V r2 It is then fed into an integrator for feedback control to calibrate the feedback coefficient G of the first closed loop. M1 G M2 This ensures that the feedback phases and phase modulation depths of the two channels are the same.

2. The method according to claim 1, characterized in that, The four bias phases within one cycle of the first channel are -φ, respectively. B -φ B +2π, φ B φ B -2π, the four bias phases of the second channel within one cycle are opposite to those of the first channel; φ B This represents the modulation depth of the square wave bias signal.

3. The method according to claim 2, characterized in that, Error signal of the first closed loop G p I0 is the equivalent gain coefficient, and I0 is the light intensity of the light source.

4. The method according to claim 2, characterized in that, The error signal V of the second closed loop r1 =-4G p I0sin∈πsin((1+∈)φ B V r2 =4G p I0sin∈πsin((1+∈)φ B ); among which, calibration G M1 and G M2 This helps to ensure the feedback phase φ F The accuracy of G is denoted by ∈, which is the inaccuracy factor. p I0 is the equivalent gain coefficient, and I0 is the light intensity of the light source.

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