A design method for closed-loop fiber optic gyroscope with low noise and high bandwidth

Abstract

The present invention belongs to a method for improving the performance of a fiber optic gyroscope, and in particular, relates to a design method for a closed-loop fiber optic gyroscope with low noise and high bandwidth. By modeling a closed-loop fiber optic gyroscope control system, calculating the expressions of the closed-loop fiber optic gyroscope bandwidth and noise, theoretically analyzing the common influencing factors of bandwidth and noise, and then increasing the influencing factors that are positively correlated with the bandwidth and negatively correlated with the noise, the purpose of increasing the fiber optic gyroscope bandwidth while reducing noise is achieved. The present invention provides a practical solution for broadening the application scope of fiber optic gyroscopes, and helps to improve the comprehensive performance of closed-loop fiber optic gyroscopes.

Description

Technical Field

[0001] The invention belongs to a method for improving the performance of a fiber optic gyroscope, and in particular relates to a design method for a closed-loop fiber optic gyroscope with low noise and high bandwidth. Background Art

[0002] As a new generation of optical inertial instruments, fiber optic gyroscopes are fully solid-state, fast start-up, light weight, long life, and low cost. They are widely used in various fields such as sea, land, air, and space. Bandwidth and noise are important technical indicators of fiber optic gyroscopes. Bandwidth reflects the ability of fiber optic gyroscopes to track input angular velocity and suppress interference signals, and noise determines the control accuracy of the gyro system. In actual engineering applications, the two are interrelated. Therefore, it is necessary to balance the relationship between the two according to the specific requirements of the control system, solve the conflict between the tracking speed and control accuracy of the fiber optic gyroscope, and seek the optimal solution.

[0003] Depending on the application requirements, the requirements of fiber optic gyroscopes for bandwidth and noise are also different. At present, the research related to the bandwidth of fiber optic gyroscopes is mainly focused on bandwidth size control. In order to correctly reflect the input information, the closed-loop bandwidth of the discrete system selected in general engineering applications should be greater than the system working bandwidth. When the bandwidth of the fiber optic gyroscope is too low, it will attenuate the high-frequency information, which may lead to incomplete representation of the carrier angular motion signal, resulting in larger attitude errors and navigation errors. However, high-bandwidth gyroscopes have less attenuation for high-frequency vibration signals, so they are prone to introduce high-frequency noise in high-frequency vibration environments.

[0004] Noise is another important indicator of the fiber optic gyroscope. It is an important factor affecting the zero bias stability and random walk coefficient of the fiber optic gyroscope. Zero bias stability is usually defined as the standard deviation of the gyroscope output angular rate under a certain average time (such as 10s, 100s), which is determined by the drift and noise of the output signal. When the drift caused by environmental changes is greatly suppressed, the noise level becomes the main factor affecting the accuracy of the gyroscope. The random noise in the fiber optic gyroscope includes optical path noise, circuit noise, control system noise, etc. Only by suppressing these noises can the purpose of reducing the gyroscope random walk coefficient and improving the gyroscope accuracy be achieved.

[0005] The main factors that determine the bandwidth of the fiber optic gyroscope are the signal forward channel gain and the feedback loop gain. The signal forward channel gain is proportional to the light source power, optical path loss, detector responsivity and other factors, which also affect the noise of the fiber optic gyroscope. Therefore, in engineering applications, it is necessary to conduct a comprehensive analysis and calculation of the fiber optic gyroscope's indicators to find the optimal solution. At present, the bandwidth improvement of the existing closed-loop fiber optic gyroscope mainly relies on increasing the closed-loop loop gain. Therefore, while increasing the bandwidth, the control noise will increase, the zero-bias stability of the closed-loop fiber optic gyroscope will be reduced, and the improvement of the comprehensive performance of the fiber optic gyroscope will be limited. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a design method for a closed-loop fiber optic gyroscope with low noise and high bandwidth. The common influencing factors of the bandwidth and noise of the closed-loop fiber optic gyroscope are theoretically analyzed, that is, the influencing factors that are positively correlated with the bandwidth and negatively correlated with the noise. By increasing the related factors, the purpose of reducing noise while increasing the bandwidth of the fiber optic gyroscope is achieved.

[0007] The present invention includes the following technical solutions:

[0008] A method for designing a closed-loop fiber optic gyroscope with low noise and high bandwidth, characterized in that it specifically comprises the following steps:

[0009] Step 1: Establish a control model of a closed-loop fiber optic gyroscope;

[0010] Step 2: Simplify the model obtained in step 1 and calculate the transfer function of the closed-loop system;

[0011] Step 3: Calculate the bandwidth and noise of the closed-loop fiber optic gyroscope according to the simplified control model obtained in step 2;

[0012] Step 4: Analyze the expressions of bandwidth and noise obtained in step 3 to determine the factors affecting bandwidth and noise;

[0013] Step 5: Adjust the common influencing factors of bandwidth and noise in step 4 to achieve the purpose of increasing the bandwidth of the fiber optic gyroscope while reducing the noise.

[0014] Furthermore, the control model of the closed-loop fiber optic gyroscope in step 1 is modeled by approximating each module as a proportional link, and then multiplying each link according to the working principle of the closed-loop fiber optic gyroscope.

[0015] Furthermore, the step of establishing the control model of the closed-loop fiber optic gyroscope specifically includes:

[0016] Step 1-1: Establish the Sagnac effect module;

[0017] According to the Sagnac effect, the angular velocity sensed by the gyroscope is linearly related to the two interfering beams, so it can be regarded as a proportional link, and the proportional coefficient K is s for:

[0018]

[0019] In the formula, K s is the proportionality coefficient between the gyro angular velocity and the Sagnac phase shift; L is the length of the fiber ring; D is the average diameter of the fiber ring; λ is the central wavelength of the light source; c is the speed of light in vacuum;

[0020] Step 1-2: Establish a photoelectric detection module;

[0021] The working principle of the photodetector is essentially to use a photodiode to convert the light signal into a current signal, and then pass the current signal through the transimpedance R f Converted into a voltage signal, this module can be regarded as a proportional link, the proportional coefficient K d for:

[0022] K d =η·R f

[0023] In the formula, K d is the proportional coefficient between the light intensity signal and the detector output voltage; η is the photoelectric conversion efficiency of the detector; R f is the transimpedance;

[0024] Step 1-3: Establish the preamplifier module;

[0025] The voltage signal converted from light intensity is a weak signal and needs to be amplified before subsequent processing. The preamplifier circuit is also a proportional link, and its proportional coefficient is K. q ;

[0026] Step 1-4: Establish A / D sampling module;

[0027] The A / D sampling, quantization and modulation link can be regarded as a proportional link and a delay link. -1 , proportionality coefficient K A / D The analog / digital conversion coefficient is set as U1 after preamplification and the digital signal after A / D conversion is D d , then its proportionality coefficient K A / D for:

[0028]

[0029] Step 1-5: Establish digital demodulation module;

[0030] The system uses the difference ΔP between the positive and negative half-cycles of the square wave when demodulating the signal:

[0031] ΔP=2P0K L sin(φ s +φ f )sin(φ b )

[0032] Where, P0 is the output power of the light source; K L is the loss of the optical signal in the entire optical path; φ s is the Sagnac phase shift; φ f is the feedback phase; φ b is the bias phase;

[0033] In general, φ s +φ f It is a small amount, so when performing conventional dynamic analysis, the module can be simplified into a nonlinear sinusoidal link for calculation, that is, ΔP≈2P0K L sin(φ b ), so the demodulation coefficient K jt for:

[0034] K jt =2P0K L sin(φ b )

[0035] Step 1-6: Build the digital controller module;

[0036] The process of signal demodulation is to sample the gyro signals of the positive half cycle of the square wave and the negative half cycle of the square wave respectively, then subtract the negative half cycle signal from the positive half cycle signal, and add up the results to get the gyro output. p express;

[0037] Step 1-7: Establish a step wave generation module;

[0038] The signal output by the digital controller is accumulated again to obtain a step wave. Therefore, the step wave generation module can be regarded as an integral link, which is expressed as 1 / (1-z -1 );

[0039] Step 1-8: Establish system circuit delay module;

[0040] The system circuit delay module can use a first-order lag link z -1 express;

[0041] Step 1-9: Establish D / A conversion, post-amplification, and phase modulation modules;

[0042] The D / A converter converts the step wave quantization signal into an analog voltage signal with a conversion coefficient of K. D / A ;

[0043] The post-amplifier amplifies the voltage signal with a magnification factor of K. b ;

[0044] The phase modulator converts the voltage signal into a non-reciprocal phase difference signal useful for the optical path, and the modulation coefficient is K. m .

[0045] Furthermore, the transfer function of the closed-loop system of the simplified control model in step 2 is:

[0046]

[0047] In the formula, is the feedback channel gain, where N D / A is the number of bits of the D / A converter; is the time constant of the system, where τ is the discrete time of the fiber gyroscope, G = 2K jt K A / D K q K L R f ηP0sin(Δφ b )·K s is the forward channel gain, K = K p is the proportional control coefficient.

[0048] Furthermore, in step 3:

[0049] The bandwidth expression of fiber optic gyroscope is:

[0050]

[0051] The total optical path noise reaching the detector is:

[0052]

[0053] In the formula,

[0054] is the noise current caused by the light source intensity noise, where η is the detector responsivity, P is the light intensity reaching the detector, Δf is the counting bandwidth, λ is the light wavelength, and Δλ is the spectrum width;

[0055] is the detector shot noise, where e is the electron charge, i dark is the dark current of the detector;

[0056] is the detector thermal noise, where k is the Boltzmann constant, R is the amplifier transimpedance, and T is the thermodynamic temperature.

[0057] Furthermore, the factors affecting bandwidth and noise in step 4 are specifically:

[0058] The bandwidth of the fiber optic gyroscope is positively correlated with the light source output power, detector responsivity, forward channel gain and proportional control coefficient, and is negatively correlated with the optical path loss, system discrete time and the number of bits of the D / A converter.

[0059] The optical path noise of the fiber optic gyroscope is negatively correlated with the output power of the light source and the responsivity of the detector.

[0060] Furthermore, the common influencing factors of bandwidth and noise in step 5 are light source output power and detector responsivity.

[0061] Furthermore, the step 5 specifically includes: increasing the light source output power and the detector responsivity.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] The bandwidth improvement of the existing closed-loop fiber optic gyroscope mainly relies on increasing the closed-loop loop gain. Therefore, while increasing the bandwidth, the control noise will increase and the zero-bias stability of the closed-loop fiber optic gyroscope will be reduced. The present invention proposes a low-noise and high-bandwidth closed-loop fiber optic gyroscope design method, which can increase the bandwidth of the closed-loop fiber optic gyroscope while reducing the noise, providing a practical solution for broadening the application scope of the fiber optic gyroscope and helping to improve the comprehensive performance of the closed-loop fiber optic gyroscope. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The drawings described below are only an example of the present invention. A person skilled in the art can obtain other drawings based on these drawings without creative work.

[0065] Figure 1 It is a closed-loop fiber optic gyro control model;

[0066] Figure 2 This is a simplified control model of a closed-loop fiber optic gyroscope. DETAILED DESCRIPTION

[0067] The embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

[0068] See attached Figure 1 and 2 The present invention provides a method for designing a closed-loop fiber optic gyroscope with low noise and high bandwidth, which specifically comprises the following steps:

[0069] Step 1: Establish a control model of a closed-loop fiber optic gyroscope.

[0070] At present, the control model of the closed-loop fiber optic gyroscope is modeled by approximating each module as a proportional link, and then multiplying each link according to the working principle of the closed-loop fiber optic gyroscope. The specific implementation steps are:

[0071] Step 1-1: Establish the Sagnac effect module;

[0072] According to the Sagnac effect, the angular velocity sensed by the gyroscope is linearly related to the two interfering beams, so it can be regarded as a proportional link, and the proportional coefficient K is s for:

[0073]

[0074] In the formula, K sis the proportionality coefficient between the Sagnac phase shift and the gyro angular velocity; L is the length of the fiber ring; D is the average diameter of the fiber ring; λ is the central wavelength of the light source; c is the speed of light in vacuum;

[0075] At this time, the Sagnac phase shift is Δφ s for:

[0076]

[0077] Where Ω is the gyro angular velocity.

[0078] Step 1-2: Establish a photoelectric detection module;

[0079] The working principle of the photodetector is essentially to use a photodiode to convert the light signal into a current signal, and then pass the current signal through the transimpedance R f Converted into a voltage signal, this module can be regarded as a proportional link, the proportional coefficient K d for:

[0080] K d =η·R f

[0081] In the formula, K d is the proportional coefficient between the light intensity signal and the detector output voltage; η is the photoelectric conversion efficiency of the detector; R f is the transimpedance.

[0082] Step 1-3: Establish the preamplifier module;

[0083] The voltage signal converted from light intensity is a weak signal and needs to be amplified before subsequent processing. The preamplifier circuit is also a proportional link, and its proportional coefficient is K. q .

[0084] Step 1-4: Establish A / D sampling module;

[0085] In actual use, in order to take into account the requirements of sampling speed and sampling accuracy, an A / D conversion chip with a suitable number of bits should be selected. Its main function is to quantize the amplified analog voltage signal. Considering that there is still a certain delay time in the sampling process, the A / D sampling quantization and modulation link can be regarded as a proportional link and a delay link. -1 , proportionality coefficient K A / D It is the analog / digital conversion coefficient. Assume that the voltage signal after preamplification is U1 and the digital signal after A / D conversion is D d , then its proportionality coefficient K A / D for:

[0086]

[0087] Step 1-5: Establish digital demodulation module;

[0088] For a fiber optic gyroscope using square wave bias modulation, the signal output by the interferometer in the positive half cycle of the square wave is:

[0089]

[0090] The signal output by the interferometer in the negative half cycle of the square wave is:

[0091]

[0092] When the system performs signal demodulation, it uses the difference ΔP between the positive half-cycle and the negative half-cycle of the square wave. After calculation, we can get:

[0093] ΔP=2P0K L sin(φ s +φ f )sin(φ b )

[0094] Where, P0 is the output power of the light source; K L is the loss of the optical signal in the entire optical path; φ s is the Sagnac phase shift; φ f is the feedback phase; φ b is the bias phase;

[0095] In general, φ s +φ f It is a small amount, so when performing conventional dynamic analysis, the module can be simplified into a nonlinear sinusoidal link for calculation, that is, ΔP≈2P0K L sin(φ b ), so the demodulation coefficient K jt for:

[0096] K jt =2P0K L sin(φ b )

[0097] Step 1-6: Build the digital controller module;

[0098] The process of signal demodulation is to sample the gyro signals of the positive half cycle of the square wave and the negative half cycle of the square wave respectively, then subtract the negative half cycle signal from the positive half cycle signal, and add up the results to get the gyro output. p express.

[0099] Step 1-7: Establish a step wave generation module;

[0100] The signal output by the digital controller is accumulated again to obtain a step wave. Therefore, the step wave generation module can be regarded as an integral link, which is expressed as 1 / (1-z -1 ).

[0101] Step 1-8: Establish system circuit delay module;

[0102] The system circuit delay module can use a first-order lag link z -1 express.

[0103] Step 1-9: Establish D / A conversion, post-amplification, and phase modulation modules;

[0104] The D / A converter converts the step wave quantization signal into an analog voltage signal with a conversion coefficient of K. D / A ;

[0105] The post-amplifier amplifies the voltage signal with a magnification factor of K. b ;

[0106] The phase modulator converts the voltage signal into a non-reciprocal phase difference signal useful for the optical path, and the modulation coefficient is K. m .

[0107] After the modules are established in the above steps 1-1 to 1-9, the system is implemented as follows Figure 1 Closed loop control is shown.

[0108] Step 2: Simplify the model obtained in step 1 and calculate the transfer function of the closed-loop system.

[0109] After simplifying the model established in step 1, we can obtain Figure 2 The simplified control model is shown. It can be seen from the simplified control model that the digital closed-loop fiber optic gyroscope system is a typical first-order system, and the transfer function of the system is:

[0110]

[0111] Where, Y(z) is the transfer function of the system; W(z) is the input signal; G is the forward channel gain; K is the proportional control coefficient; M is the feedback channel gain;

[0112] The transfer function of the closed-loop system is calculated as:

[0113]

[0114] In the formula, is the time constant of the system, and τ is the discrete time of the fiber gyroscope.

[0115] Step 3: Calculate the bandwidth and noise of the closed-loop FOG based on the simplified control model.

[0116] Since the gyro closed-loop system is a typical first-order system, the -3dB bandwidth calculation formula is:

[0117]

[0118] Since the forward channel gain G = 2K jt K A / D K q K L R f ηP0sin(Δφ b )·K s is the open-loop scaling factor of the fiber gyroscope; feedback channel gain is the inverse of the closed-loop system scale factor, where N D / A is the number of bits of the D / A converter; the proportional control coefficient K = K p ; The bandwidth expression of fiber optic gyroscope can be expanded as:

[0119]

[0120] The noise of the fiber optic gyro control system can be approximately equivalent to a band-limited white noise and a slowly changing linear link, namely zero drift. It is a typical underdamped second-order system. Under the action of white noise, the output performance of the system is expressed by the equivalent noise bandwidth.

[0121] The influence of the angular rate of the control platform on the gyro control noise can be approximately expressed as:

[0122]

[0123] Where G0(jω) is the influence of the angular velocity of the control platform on the gyro control noise; n is the test frequency; jω is the system response frequency; ξ is the equivalent damping coefficient.

[0124] Let s = jω, then:

[0125]

[0126] The transfer function of the control noise to the system angle output is obtained as:

[0127]

[0128] The mean square error of the output angles is:

[0129]

[0130] Therefore, the influence of fiber optic gyro control noise on the system angular velocity and angle output is mainly caused by the gyro bandwidth ω gyr0 , test frequency ω nIt is determined by the combined effect of the three factors: and the equivalent damping coefficient ξ. Under the same noise level, the wider the gyro bandwidth, the greater the control noise. Therefore, it is necessary to control the noise source. The main noise generated in this process is the optical path noise. The total optical path noise reaching the detector is:

[0131]

[0132] In the formula,

[0133] is the noise current caused by the light source intensity noise, where η is the detector responsivity, P is the light intensity reaching the detector, Δf is the counting bandwidth, λ is the light wavelength, and Δλ is the spectrum width;

[0134] is the detector shot noise, where e is the electron charge, i dark is the dark current of the detector;

[0135] is the detector thermal noise, where k is the Boltzmann constant, R is the amplifier transimpedance, and T is the thermodynamic temperature.

[0136] Considering the sensitivity of the fiber optic gyroscope is the modulation phase, is the feedback phase shift, then the relationship between the random walk coefficient RWC and the signal-to-noise ratio SNR can be expressed as:

[0137]

[0138] Step 4: Analyze the expressions of bandwidth and noise to determine the factors affecting bandwidth and noise.

[0139] From the analysis of the expressions of bandwidth and noise in step 3, it can be seen that the bandwidth of the fiber optic gyroscope is positively correlated with the output power of the light source, the responsivity of the detector, the forward channel gain and the proportional control coefficient, and is negatively correlated with the optical path loss, the system discrete time and the number of bits of the D / A converter; the optical path noise of the fiber optic gyroscope is negatively correlated with the output power of the light source and the responsivity of the detector.

[0140] Step 5: Adjust the common influencing factors of bandwidth and noise in step 4 to achieve the purpose of increasing the bandwidth of the fiber optic gyroscope while reducing the noise.

[0141] In step 4, because the light source output power and the detector responsivity are both positively correlated with the bandwidth and negatively correlated with the noise, increasing the light source output power and the detector responsivity can increase the bandwidth of the fiber optic gyroscope while reducing the noise level.

[0142] The present invention establishes a control model of a closed-loop fiber optic gyroscope based on its working principle, calculates its bandwidth and noise, and analyzes their influencing factors. By increasing the influencing factors that are positively correlated with the bandwidth and negatively correlated with the noise, the design of a low-noise and high-bandwidth closed-loop fiber optic gyroscope is achieved, providing a practical solution for broadening the application range of the fiber optic gyroscope.

Claims

1. A design method for a low-noise, high-bandwidth closed-loop fiber optic gyroscope, characterized in that: The specific steps include: Step 1: Establish a control model of a closed-loop fiber optic gyroscope; Step 2: Simplify the model obtained in step 1 and calculate the transfer function of the closed-loop system; Step 3: Calculate the bandwidth and noise of the closed-loop fiber optic gyroscope according to the simplified control model obtained in step 2; Step 4: Analyze the expressions of bandwidth and noise obtained in step 3 to determine the factors affecting bandwidth and noise; Step 5: Adjust the common influencing factors of bandwidth and noise in step 4 to achieve the purpose of increasing the bandwidth of the fiber optic gyroscope while reducing the noise.

2. A method for designing a low-noise, high-bandwidth closed-loop fiber gyroscope as claimed in claim 1, characterized in that: The control model of the closed-loop fiber optic gyroscope in step 1 is modeled by approximating each module as a proportional link, and then multiplying each link according to the working principle of the closed-loop fiber optic gyroscope.

3. A method for designing a low-noise, high-bandwidth closed-loop fiber gyroscope according to claim 1 or 2, characterized in that: The steps of establishing the control model of the closed-loop fiber optic gyroscope specifically include: Step 1-1: Establish the Sagnac effect module; According to the Sagnac effect, the angular velocity sensed by the gyroscope is linearly related to the two interfering beams, so it can be regarded as a proportional link, and the proportional coefficient K s for: In the formula, K s is the proportionality coefficient between the gyro angular velocity and the Sagnac phase shift; L is the length of the fiber ring; D is the average diameter of the fiber ring; λ is the central wavelength of the light source; c is the speed of light in vacuum; Step 1-2: Establish a photoelectric detection module; The working principle of the photodetector is essentially to use a photodiode to convert the light signal into a current signal, and then pass the current signal through the transimpedance R f Converted into a voltage signal, this module can be regarded as a proportional link, the proportional coefficient K d for: K d =η·R f In the formula, K d is the proportional coefficient between the light intensity signal and the detector output voltage; η is the photoelectric conversion efficiency of the detector; R f is the transimpedance; Step 1-3: Establish the preamplifier module; The voltage signal converted from light intensity is a weak signal and needs to be amplified before subsequent processing. The preamplifier circuit is also a proportional link, and its proportional coefficient is K. q ; Step 1-4: Establish A / D sampling module; The A / D sampling, quantization and modulation link can be regarded as a proportional link and a delay link. -1 , proportionality coefficient K A / D The analog / digital conversion coefficient is set as U1 after preamplification and the digital signal after A / D conversion is D d , then its proportionality coefficient K A / D for: Step 1-5: Establish digital demodulation module; The system uses the difference ΔP between the positive and negative half-cycles of the square wave when demodulating the signal: ΔP=2P0K L sin(φ s +φ f )sin(φ b ) Where, P0 is the output power of the light source; K L is the loss of the optical signal in the entire optical path; φ s is the Sagnac phase shift; φ f is the feedback phase; φ b is the bias phase; In general, φ s +φ f It is a small amount, so when performing conventional dynamic analysis, the module can be simplified into a nonlinear sinusoidal link for calculation, that is, ΔP≈2P0K L sin(φ b ), so the demodulation coefficient K jt for: K jt =2P0K L sin(φ b ) Step 1-6: Build the digital controller module; The process of signal demodulation is to sample the gyro signals of the positive half cycle of the square wave and the negative half cycle of the square wave respectively, then subtract the negative half cycle signal from the positive half cycle signal, and add up the results to get the gyro output. p express; Step 1-7: Establish a step wave generation module; The signal output by the digital controller is accumulated again to obtain a step wave. Therefore, the step wave generation module can be regarded as an integral link, which is expressed as 1 / (1-z -1 ); Step 1-8: Establish system circuit delay module; The system circuit delay module can use a first-order lag link z -1 express; Step 1-9: Establish D / A conversion, post-amplification, and phase modulation modules; The D / A converter converts the step wave quantization signal into an analog voltage signal with a conversion coefficient of K. D / A ; The post-amplifier amplifies the voltage signal with a magnification factor of K. b ; The phase modulator converts the voltage signal into a non-reciprocal phase difference signal useful for the optical path, and the modulation coefficient is K. m .

4. A method for designing a low-noise, high-bandwidth closed-loop fiber gyroscope as claimed in claim 1, characterized in that: The transfer function of the closed-loop system of the simplified control model in step 2 is: In the formula, is the feedback channel gain, where N D / A is the number of bits of the D / A converter; is the time constant of the system, where τ is the discrete time of the fiber gyroscope, G = 2K jt K A / D K q K L R f ηP0sin(Δφ b )·K s is the forward channel gain, K = K p is the proportional control coefficient.

5. The method for designing a low-noise, high-bandwidth closed-loop fiber gyroscope according to claim 1, characterized in that: In step 3: The bandwidth expression of fiber optic gyroscope is: The total optical path noise reaching the detector is: In the formula, is the noise current caused by the light source intensity noise, where η is the detector responsivity, P is the light intensity reaching the detector, Δf is the counting bandwidth, λ is the light wavelength, and Δλ is the spectrum width; is the detector shot noise, where e is the electron charge, i dark is the dark current of the detector; is the detector thermal noise, where k is the Boltzmann constant, R is the amplifier transimpedance, and T is the thermodynamic temperature.

6. A method for designing a low-noise, high-bandwidth closed-loop fiber gyroscope as claimed in claim 1, characterized in that: The factors affecting bandwidth and noise in step 4 are specifically: The bandwidth of the fiber optic gyroscope is positively correlated with the light source output power, detector responsivity, forward channel gain and proportional control coefficient, and is negatively correlated with the optical path loss, system discrete time and the number of bits of the D / A converter. The optical path noise of the fiber optic gyroscope is negatively correlated with the output power of the light source and the responsivity of the detector.

7. The method for designing a low-noise, high-bandwidth closed-loop fiber gyroscope according to claim 1, characterized in that: The common influencing factors of bandwidth and noise in step 5 are light source output power and detector responsivity.

8. The method for designing a low-noise, high-bandwidth closed-loop fiber gyroscope according to claim 1, characterized in that: The step 5 specifically includes: increasing the light source output power and the detector responsivity.

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