Fiber-optic gyroscope frequency characteristic test method based on CORDIC algorithm

Abstract

The invention relates to a sensor testing method, in particular to a fiber-optic gyroscope frequency characteristic testing method based on a CORDIC algorithm, and solves the technical problems that a traditional method for testing the frequency characteristic of a fiber-optic gyroscope through an angular vibration table has limitation and cannot meet the full-band testing requirement of the fiber-optic gyroscope. The method comprises the following steps: S1, determining the number of discrete points required by a sinusoidal signal in a period in a CORDIC algorithm and a rotation angle between every two discrete points; s2, generating a sinusoidal signal in a digital signal processor of the fiber-optic gyroscope; s3, obtaining an output sinusoidal signal; s4, superposing the output sinusoidal signal to a modulation square wave of the Y waveguide of the fiber-optic gyroscope; and S5, changing the number of discrete points in the digital signal processor, and collecting the response angular rate of the fiber-optic gyroscope until the amplitude of the response angular rate is reduced to 0.707 times of the amplitude of the target sinusoidal signal in the S1 and the corresponding frequency range is the bandwidth of the fiber-optic gyroscope, thereby completing the fiber-optic gyroscope frequency characteristic test based on the CORDIC algorithm.

Description

Technical Field

[0001] The present invention relates to a sensor testing method, and particularly to a method for testing the frequency characteristics of a fiber optic gyroscope based on the CORDIC algorithm. Background Art

[0002] A fiber optic gyroscope (FOG) is a core device of a fiber optic strapdown inertial navigation system. It can measure the angular motion of a carrier relative to inertial space and has the advantages of being all-solid-state, high-precision, fast startup speed, long service life, etc., and is widely used in inertial fields such as navigation and positioning. As Figure 1 shown, the fiber optic gyroscope includes optical devices and a digital processing circuit 6, where the optical devices include a light source 1, a photodetector 2, a coupler 3, a Y waveguide 4, and an optical fiber loop 5, and the digital processing circuit 6 includes a pre-amplification circuit 61, an A / D converter 62, a digital signal processor 63 (FPGA), a D / A converter 64, a post-amplification circuit 65, and a data output port 66.

[0003] The frequency characteristic is an important factor affecting the dynamic performance of a closed-loop fiber optic gyroscope and is an important indicator for measuring the angular velocity tracking ability and anti-interference ability of the fiber optic gyroscope. The bandwidth of the fiber optic gyroscope is crucial for its fast response ability. Therefore, accurately testing the frequency characteristics of the fiber optic gyroscope is an important part of the performance testing of the fiber optic gyroscope. The traditional method for measuring the frequency characteristics of a fiber optic gyroscope is to use an angular vibration table for testing. However, this measurement method has certain limitations. On the one hand, the bandwidth of a closed-loop fiber optic gyroscope is usually as high as several thousand Hz. However, the output frequency of a general angular vibration table does not exceed several hundred Hz, and the bandwidth range of the fiber optic gyroscope significantly exceeds the output range of the angular vibration table. The traditional angular vibration table testing method cannot meet the full-band testing requirements of the fiber optic gyroscope. On the other hand, the angular vibration table testing method is more suitable for a fiber optic gyroscope that has been assembled and adjusted. If the test results are not ideal, it is relatively difficult to change its parameter design. Summary of the Invention

[0004] The purpose of the present invention is to solve the technical problem that the traditional method for testing the frequency characteristics of a fiber optic gyroscope using an angular vibration table has limitations and cannot meet the full-band testing requirements of the fiber optic gyroscope, and to provide a method for testing the frequency characteristics of a fiber optic gyroscope based on the CORDIC algorithm.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A method for testing the frequency characteristics of a fiber optic gyroscope based on the CORDIC algorithm, characterized in that it includes the following steps:

[0007] S1. Input the frequency and amplitude of the target sine signal into the digital signal processor of the fiber optic gyroscope, and determine the number of discrete points required for the sine signal within one period in the CORDIC algorithm and the rotation angle between every two discrete points;

[0008] S2. Generate a sine signal in the digital signal processor of the fiber optic gyroscope according to the rotation angle;

[0009] S3. Calculate the amplitude of the sine signal generated in S2 and input it into the digital signal processor to obtain the output sine signal;

[0010] S4. Superimpose the output sine signal onto the modulation square wave of the Y waveguide of the fiber optic gyroscope;

[0011] S5. Place the fiber optic gyroscope statically on the vibration isolation table, change the number of discrete points in the digital signal processor to realize the frequency change of the output sine signal, collect the response angular rate of the fiber optic gyroscope until the amplitude of the response angular rate is reduced to 0.707 times the amplitude of the target sine signal in S1, and the corresponding frequency range is the bandwidth of the fiber optic gyroscope, thus completing the frequency characteristic test of the fiber optic gyroscope based on the CORDIC algorithm.

[0012] Further, S1 is specifically as follows:

[0013] 1.1. According to the time for light to transmit one circle in the entire fiber loop of the fiber optic gyroscope, calculate the period τ of each discrete point through the following formula:

[0014] τ = n eff L / c

[0015] In the formula, n eff is the effective refractive index of the optical fiber, L is the length of the fiber loop, and c is the speed of light in vacuum;

[0016] 1.2. Input the frequency f m and amplitude of the sine signal into the digital signal processor of the fiber optic gyroscope, and then calculate the number of discrete points n required to generate a sine signal with one period in the CORDIC algorithm according to the frequency f m :

[0017] n = 1 / f m τ;

[0019] 1.3. Since the phase change sum of n discrete points is equal to the phase change value 2π of one period of the sine signal, therefore, the rotation angle θ between every two adjacent discrete points:

[0020] θ = 2π / n

[0021] In the formula, 2π is the phase change value of one period of the sine signal.

[0022] Further, S2 is specifically as follows:

[0023] 2.1. From any coordinate point (x0, y0), after rotating counterclockwise by an angle θ around the origin O of the coordinates, it reaches the coordinate point (x N , y N ). Then the coordinate relationship between (x0, y0) and (x N , y N ) is:

[0024]

[0025] 2.2. Express the coordinate relationship obtained in step 2.1 as a vector, and the rotation formula can be obtained as:

[0026]

[0027] 2.3. Divide the rotation angle θ obtained in step 1.3 into G rotation angles θ i , i = 0, 1, 2,..., G; According to the CORDIC algorithm, the rotation angle θ i needs to satisfy the following relationship:

[0028] tanθ i = 2 -i

[0029] Then according to step 2.2, the process of each rotation is:

[0030]

[0031] In the formula: di is the rotation direction. When di takes the value of 1, it means counterclockwise rotation. When di takes the value of -1, it means clockwise rotation; tanθ i and cosθ i can be obtained by calculating in the shift register of the digital signal processor;

[0032] 2.4. Through G rotations, the sum of the rotation angles ∑d i θ i infinitely approaches the rotation angle θ. According to step 2.3, the process from any coordinate point (x0, y0) to the coordinate point (x N , y N ) is:

[0033]

[0034] 2.5. Store the value of cosθ i in the lookup table of the digital signal processor in advance. In the digital signal processor, the sine signal φ m (t) can be calculated by the CORDIC algorithm as:

[0035] φ m\(\varphi(t)=\varphi_0\sin(2\pi ft)\) m t

[0036] Where \(t\) is time and \(\varphi_0\) is the amplitude of the sine signal.

[0037] Further, S3 is specifically as follows:

[0038] 3.1. Express the relationship between the Sagnac phase difference \(\varphi\) and the rotation angular rate \(\Omega\) in the fiber optic gyroscope as:

[0039]

[0040] Then, the scale factor \(K\) of the fiber optic gyroscope s is denoted as:

[0041]

[0042] Where \(D\) is the diameter of the fiber optic loop and \(\lambda\) is the light source wavelength;

[0043] 3.2. Express the relationship between the maximum angular rate \(\Omega\) output by the fiber optic gyroscope π and the corresponding phase difference \(\pi\) as:

[0044]

[0045] 3.3. Convert the digital signal output by the digital signal processor into an analog signal through a D / A converter and output it. According to step 3.2, the analog amplitude \(A_1\) of the demodulated sine signal can be obtained:

[0046]

[0047] Where \(M\) is the number of bits of the D / A converter and \(2\) M is the full-scale quantity size of the \(M\)-bit D / A converter;

[0048] 3.4. According to the Sagnac effect, the phase difference \(\Delta\varphi\) between the two beams of light propagating in the clockwise and counterclockwise directions in the fiber optic loop m (t) is:

[0049] \(\Delta\varphi\) m (t)=\(\varphi\) m (t)-\(\varphi\) m (t - \(\tau\));

[0051] 3.5. Substitute the sine signal \(\varphi\) m (t)=\(\varphi_0\sin(2\pi ft)\) m obtained in step 2.5 into the phase difference \(\Delta\varphi\) m (t)=\(\varphi\) m (t)-\(\varphi\) m(t - τ), calculate the actual amplitude A2 of the sine signal as follows:

[0052] A2 = 2φ0sin(πf m τ);

[0054] 3.6. Calculate the amplitude φ0 of the sine signal based on the simulated amplitude A1 obtained in step 3.3 and the actual amplitude A2 obtained in step 3.5:

[0055]

[0056] 3.7. Substitute the amplitude φ0 of the sine signal obtained in step 3.6 into the sine signal φ m (t) = φ0sin(2πf m t) to calculate the output sine signal of the digital signal processor.

[0057] Furthermore, S4 is specifically as follows:

[0058] 4.1. Apply a bias phase of π / 2 to the fiber optic loop through the Y waveguide to obtain the modulation square wave φ b (t) of the fiber optic gyro Y waveguide:

[0059]

[0060] where m is the value of the τ period, m = 0, 1, 2,...;

[0061] 4.2. Superimpose the output sine signal obtained in step 3.7 on the modulation square wave φ b (t) of the fiber optic gyro Y waveguide to obtain the feedback signal φ(t):

[0062] φ(t) = φ b (t) + φ m (t);

[0064] 4.3. Apply the feedback signal φ(t) to the Y waveguide of the fiber optic gyro to perform phase modulation on the optical wave of the fiber optic gyro.

[0065] Furthermore, S5 is specifically as follows:

[0066] 5.1. Place the fiber optic gyrostatically on the vibration isolation table, change the number of discrete points n in the digital signal processor to achieve a change in the sine signal frequency, collect the response angular rate of the fiber optic gyro through the upper computer test software, and record the amplitude A of the output response angular rate of the fiber optic gyro;

[0067] 5.2. Repeat step 5.1 until the amplitude A of the output response angular rate of the fiber optic gyro is reduced to 0.707 times the input amplitude of the target sine signal in step 1.2, and the corresponding frequency range is the bandwidth Δf of the fiber optic gyro3dB , the frequency characteristic test of the fiber optic gyroscope based on the CORDIC algorithm is completed.

[0068] Advantages of the present invention:

[0069] 1. The method of the present invention generates an output sine signal inside the digital signal processor of the fiber optic gyroscope through the CORDIC algorithm, and superimposing this output sine signal on the modulation square wave of the Y waveguide will generate a sine phase modulation on the optical signal in the optical fiber, thereby generating a sine or cosine-varying phase difference, which is equivalent to applying a sine or cosine-varying angular rate to the fiber optic gyroscope. Without an external input angular rate signal, by changing the frequency of the input sine signal and testing the output response of the fiber optic gyroscope, the frequency characteristics of the fiber optic gyroscope within the full frequency band can be obtained.

[0070] 2. The method of the present invention solves the limitations of the traditional angular vibration table measurement method, improves the test frequency range, and reduces the test cost and difficulty.

[0071] 3. The sine signal generated by the method of the present invention greatly reduces the resource consumption inside the digital signal processor.

[0072] 4. The method of the present invention can complete the frequency characteristic test of the fiber optic gyroscope without using an additional test device before assembling the fiber optic gyroscope, which is convenient for timely changing the design parameters of the fiber optic gyroscope and improves the designability of the fiber optic gyroscope.

[0073] 5. The method of the present invention provides an efficient, accurate and convenient test method for the frequency characteristic test of the full frequency band of the fiber optic gyroscope, and provides an effective method for studying the frequency characteristics of the fiber optic gyroscope. Description of the Drawings

[0074] Figure 1 is a schematic structural diagram of the fiber optic gyroscope;

[0075] Appendix Figure 1 Marking description of:

[0076] 1 - Light source, 2 - Photoelectric detector, 3 - Coupler, 4 - Y waveguide, 5 - Fiber optic loop, 6 - Digital processing circuit, 61 - Preamplifier circuit, 62 - A / D converter, 63 - Digital signal processor, 64 - D / A converter, 65 - Post-amplifier circuit, 66 - Data output port;

[0077] Figure 2 is a simulation schematic diagram of the output sine signal in the embodiment of the method for testing the frequency characteristics of a fiber optic gyroscope based on the CORDIC algorithm of the present invention;

[0078] Figure 3This is a simulation schematic diagram after the superposition of a sine signal and a Y waveguide modulation square wave in an embodiment of a method for testing the frequency characteristics of an optical fiber gyroscope based on the CORDIC algorithm of the present invention;

[0079] Figure 4 is Figure 3 a partially enlarged schematic diagram. Specific implementation manner

[0080] A method for testing the frequency characteristics of an optical fiber gyroscope based on the CORDIC algorithm includes the following steps:

[0081] S1. Input the frequency and amplitude of the target sine signal into the digital signal processor 63 of the optical fiber gyroscope, and determine the number of discrete points required for the sine signal within one period in the CORDIC algorithm and the rotation angle between every two discrete points;

[0082] The sine signal generated in the digital signal processor 63 consists of multiple discrete points. Since the principle of the optical fiber gyroscope is to obtain the rotational speed difference by demodulating the phase difference between the forward light and the backward light in the optical fiber loop 5, it is necessary to ensure that the duration of each discrete point is the time for light to transmit one circle in the entire optical fiber loop 5.

[0083] 1.1. According to the time for light to transmit one circle in the entire optical fiber loop 5 of the optical fiber gyroscope, calculate the period τ of each discrete point through the following formula:

[0084] τ = n eff L / c

[0085] In the formula, n eff is the effective refractive index of the optical fiber, L is the length of the optical fiber loop 5, and c is the speed of light in vacuum;

[0086] 1.2. Input the frequency f m and amplitude of the sine signal into the digital signal processor 63 of the optical fiber gyroscope, and then input the frequency f m of the sine signal into the digital signal processor 63 of the optical fiber gyroscope, and calculate the number of discrete points n required to generate a sine signal with one period in the CORDIC (Coordinate Rotation Digital Computer) algorithm:

[0087] n = 1 / f m τ;

[0089] 1.3. Since the sum of the phase changes of n discrete points is equal to the phase change value 2π of a sine signal with one period, the rotation angle θ between every two adjacent discrete points is:

[0090] θ = 2π / n

[0091] where 2π is the phase change value of one period of the sine signal;

[0092] S2. Generate a sine signal in the digital signal processor 63 of the fiber optic gyro according to the number of discrete points n obtained in step 1.2 and the rotation angle θ obtained in step 1.3;

[0093] 2.1. Rotate counterclockwise by an angle θ around the coordinate origin O from any coordinate point (x0, y0) to reach the coordinate point (x N , y N ). Then the coordinate relationship between (x0, y0) and (x N , y N ) is:

[0094]

[0095] 2.2. Express the coordinate relationship obtained in step 2.1 as a vector, and the rotation formula can be obtained as:

[0096]

[0097] 2.3. Divide the rotation angle θ obtained in step 1.3 into G rotation angles θ i , i = 0, 1, 2,..., G; According to the CORDIC algorithm, the rotation angle θ i needs to satisfy the following relationship:

[0098] tanθ i = 2 -i

[0099] Then according to step 2.2, each rotation process is:

[0100]

[0101] where: di is the rotation direction. When di takes the value of 1, it means counterclockwise rotation; when di takes the value of -1, it means clockwise rotation; tanθ i and cosθ i can be obtained by calculating in the shift register in the digital signal processor 63;

[0102] 2.4. Through G rotations, the sum of the rotation angles ∑d i θ i infinitely approaches the rotation angle θ. According to step 2.3, the process of rotating from any coordinate point (x0, y0) to the coordinate point (x N , y N ) is:

[0103]

[0104] 2.5. The process of rotating to the coordinate point (x N , y N ) from any coordinate point (x0, y0) generates a sine signal φ m (t) in the digital signal processor 63 of the fiber optic gyroscope:

[0105] φ m (t) = φ0sin(2πf m t)

[0106] In the formula, t is time and φ0 is the amplitude of the sine signal;

[0107] Since the rotation angle θ i is a series of fixed known angles, the values of cosθ i can be pre-stored in the look-up table of the digital signal processor 63, and the generation of the sine signal is obtained by calculation through the look-up table and the shift register in the digital signal processor 63;

[0108] S3. Calculate the amplitude of the sine signal generated in S2 and input it into the digital signal processor 63 to obtain the output sine signal;

[0109] 3.1. Express the relationship between the Sagnac phase difference φ and the rotation angular rate Ω in the fiber optic gyroscope as:

[0110]

[0111] Then the scale factor K s of the fiber optic gyroscope is denoted as:

[0112]

[0113] In the formula, D is the diameter of the optical fiber loop 5 and λ is the wavelength of the light source 1;

[0114] 3.2. Express the relationship between the maximum angular rate Ω π output by the fiber optic gyroscope and its corresponding phase difference π (i.e., the phase π of the first-order interference fringe) as:

[0115]

[0116] 3.3. Convert the digital signal output from the digital signal processor 63 into an analog signal through the D / A converter 64. Then, any angular rate Ω of the fiber optic gyroscope can be expressed as:

[0117]

[0118] Therefore, the analog amplitude A1 of the sine angular rate output can be obtained from the above formula:

[0119]

[0120] Wherein, M is the number of bits of the D / A converter 64, and 2 M is the full-scale quantity size of the M-bit D / A converter 64;

[0121] 3.4. Due to the Sagnac effect, the phase difference Δφ m (t) between the two beams of light propagating in the clockwise and counterclockwise directions in the optical fiber loop 5 is:

[0122] Δφ m (t) = φ m (t) - φ m (t - τ);

[0124] 3.5. Add the sine signal obtained in step 2.5 to the digital demodulation of the fiber optic gyroscope, which is equivalent to applying a sine phase modulation to the gyro Y waveguide 4, that is, substitute the sine signal φ m (t) = φ0sin(2πf m t) obtained in step 2.5 into the phase difference Δφ m (t) = φ m (t) - φ m (t - τ) obtained in step 3.4, and calculate the actual amplitude A2 of the sine angular rate output:

[0125] Δφ m (t) = φ m (t) - φ m (t - τ) = 2φ0sin(πf m τ)cos(2πf m t - πf m τ)

[0126] A2 = 2φ0sin(πf m τ);

[0128] 3.6. Calculate the amplitude φ0 of the sine signal according to the analog amplitude A1 obtained in step 3.3 and the actual amplitude A2 obtained in step 3.5:

[0129]

[0130] 3.7. Substitute the amplitude φ0 of the sine signal obtained in step 3.6 into the sine signal φ m (t) = φ0sin(2πf m t) obtained in step 2.5, and calculate the output sine signal that the digital signal processor 63 needs to generate.

[0131] S4. Apply the output sine signal obtained in step 3.7 to the modulation square wave of the fiber optic gyro Y waveguide 4 to obtain the response angular rate of the fiber optic gyroscope, specifically:

[0132] 4.1. To improve the sensitivity of the fiber optic gyroscope, a bias phase of π / 2 is applied to the fiber optic loop 5 through the Y waveguide 4, and the modulation square wave φ b (t) of the Y waveguide 4 of the fiber optic gyroscope can be obtained:

[0133]

[0134] where m is the value of the τ period, m = 0, 1, 2, …;

[0135] 4.2. The output sine signal obtained in step 3.7 is superimposed on the modulation square wave φ b (t) of the Y waveguide 4 of the fiber optic gyroscope, and the feedback signal φ(t) can be obtained:

[0136] φ(t) = φ b (t) + φ m (t);

[0138] 4.3. The feedback signal φ(t) is applied to the Y waveguide 4 of the fiber optic gyroscope to perform phase modulation on the light wave of the fiber optic gyroscope;

[0139] S5. The fiber optic gyroscope is placed statically on the vibration isolation table. The number of discrete points is changed in the digital signal processor 63 to realize the frequency change of the output sine signal, and the response angular rate of the fiber optic gyroscope is collected until the amplitude of the response angular rate is reduced to 0.707 times the amplitude of the target sine signal in S1. The corresponding frequency range is the bandwidth Δf of the fiber optic gyroscope 3dB , and the frequency characteristic test of the fiber optic gyroscope based on the CORDIC algorithm is completed. Specifically:

[0140] 5.1. The fiber optic gyroscope is placed statically on the vibration isolation table. The number of discrete points n is changed in the digital signal processor 63 to realize the frequency change of the sine signal. The response angular rate of the fiber optic gyroscope is collected through the upper computer test software, and the amplitude A and frequency of the output response angular rate of the fiber optic gyroscope are recorded;

[0141] 5.2. Repeat step 5.1 until the amplitude A of the output response angular rate of the fiber optic gyroscope is reduced to 0.707 times the input amplitude of the target sine signal in step 1.2. The corresponding frequency range is the bandwidth Δf 3dB of the fiber optic gyroscope, and the frequency characteristic test of the fiber optic gyroscope based on the CORDIC algorithm is completed.

[0142] The following details the method for testing the frequency characteristics of the fiber optic gyroscope based on the CORDIC algorithm of the present invention through specific embodiments.

[0143] Input the frequency and amplitude of the target sine signal into the digital signal processor 63 of the fiber optic gyroscope, and determine the number of discrete points required for the sine signal within one period and the rotation angle between every two discrete points; for a fiber optic gyroscope with a fiber optic ring 5 having a length of 2000 m and an equivalent diameter of 60 mm, and using an ASE light source 1 with a wavelength of 1560 nm, if the input signal is a sine angular rate with a frequency of 200 Hz and an amplitude of 1° / s, the parameters of its equivalent sine signal are as follows:

[0144] From the parameters of the fiber optic gyroscope, it can be known that the transit time τ of the fiber optic gyroscope is 9.8 μs, and the time duration of each sampling point of the sine signal is 9.8 μs, then the number of points n within one period of the sine signal is 510; if the fiber optic gyroscope uses a 16-bit D / A converter 64, then the amplitude φ0 of the sine signal that can be obtained is 23794.

[0145] Generate the corresponding output sine signal through the CORDIC algorithm in the digital signal processor 63 inside the fiber optic gyroscope:

[0146] Define the correction factor P in the CORDIC algorithm as:

[0147]

[0148] Then the process from the coordinate point (x0, y0) to the coordinate point (x N , y N ) can be expressed as:

[0149]

[0150] When the number of rotations G ≥ 16, the correction factor P ≈ 0.6073. Therefore, the correction factor P can be written as a fixed value of 0.6073 into the digital signal processor 63;

[0151] To ensure that the number of rotations G is sufficient to make the sum of the rotation angles ∑d i θ i approximate the rotation angle θ, and at the same time reduce the resource consumption in the digital signal processor 63, a 16-stage pipeline can be used to implement the iteration of the number of rotations in the CORDIC operation. Since the correction factor in each stage of the pipeline is a constant, the total correction factor P can be multiplied at the last stage of the 16-stage pipeline. The operation formula for each stage of the pipeline can be simplified as follows:

[0152]

[0153] Among them, Z i represents the remaining unrotated angle after i rotations. When i is 15, the remaining unrotated angle approaches 0.

[0154] Since the rotation angle θ for each timei It is necessary to satisfy tanθ i = 2 -i , so the rotation angles of the 16-stage pipeline can be pre-stored in the look-up table, and the operation can be completed through the shift register; since the demodulation period of the fiber optic gyroscope is 2τ, the time duration of each sampling point of the sine signal is set to τ, and the simulation waveform diagram of generating the sine signal using the CORDIC algorithm is shown in Figure 2 ; The generated output sine signal is superimposed on the π / 2 modulation square wave of the Y waveguide 4, and the simulation waveform diagram after superimposition is shown in Figure 3 , Figure 4 .

Claims

1. A method for testing the frequency characteristics of an optical fiber gyroscope based on the CORDIC algorithm, characterized in that It includes the following steps: S1. Input the frequency and amplitude of the target sine signal into the digital signal processor (63) of the fiber optic gyroscope, and determine the number of discrete points required for the sine signal within one period in the CORDIC algorithm and the rotation angle between every two discrete points; S2. Generate a sine signal in the digital signal processor (63) of the fiber optic gyroscope according to the rotation angle; S3. Calculate the amplitude of the sine signal generated in S2 and input it into the digital signal processor (63) to obtain the output sine signal; S4. Superimpose the output sine signal on the modulation square wave of the Y waveguide (4) of the fiber optic gyroscope; S5. Place the fiber optic gyroscope statically on the vibration isolation table, change the number of discrete points in the digital signal processor (63) to realize the frequency change of the output sine signal, collect the response angular rate of the fiber optic gyroscope until the amplitude of the response angular rate decreases to 0.707 times the amplitude of the target sine signal in S1, and the corresponding frequency range is the bandwidth of the fiber optic gyroscope, thus completing the frequency characteristic test of the fiber optic gyroscope based on the CORDIC algorithm.

2. The fiber optic gyroscope frequency characteristic testing method based on the CORDIC algorithm according to claim 1, wherein Specifically, S1 is as follows: 1.

1. According to the time for light to transmit one circle in the entire fiber loop (5) of the fiber optic gyroscope, calculate the period τ of each discrete point through the following formula: τ = n eff L / c where n eff is the effective refractive index of the optical fiber, L is the length of the optical fiber loop (5), and c is the speed of light in vacuum; 1.

2. Input the frequency f and amplitude of the sine signal into the digital signal processor (63) of the fiber optic gyroscope, and then calculate the number of discrete points n required to generate a sine signal for one period in the CORDIC algorithm according to the frequency f: m and amplitude, and then according to the frequency f m calculate the number of discrete points n required to generate a sine signal for one period in the CORDIC algorithm: n = 1 / f m τ; 1.

3. Since the sum of the phase changes of n discrete points is equal to the phase change value 2π of one period of the sine signal, the rotation angle θ between every two adjacent discrete points is: θ = 2π / n In the formula, 2π is the phase change value of one period of the sine signal.

3. The method for testing the frequency characteristics of an optical fiber gyroscope based on the CORDIC algorithm according to claim 2, wherein Specifically, S2 is as follows: 2.

1. Rotating counterclockwise by an angle θ around the origin O from any coordinate point (x0, y0) to reach the coordinate point (x N , y N ), then the coordinate relationship between (x0, y0) and (x N , y N ) is as follows: 2.

2. Represent the coordinate relation formula obtained in step 2.1 as a vector, and the rotation formula can be obtained as: 2.

3. Divide the rotation angle θ obtained in step 1.3 into G rotation angles θ i , where i = 0, 1, 2, …, G; According to the CORDIC algorithm, the rotation angle θ i should satisfy the following relationship: tanθ i = 2 -i Then, according to step 2.2, each rotation process is as follows: Where: di is the rotation direction. When the value of di is 1, it represents counterclockwise rotation; when the value of di is -1, it represents clockwise rotation; tanθ i and cosθ i can be obtained by calculation through the shift register in the digital signal processor (63); 2.

4. Make the sum of the rotation angles equal to ∑d after G rotations i θ i Approach the rotation angle θ infinitely. According to step 2.3, the process from any coordinate point (x0, y0) to the coordinate point (x N , y N ) is as follows: 2.

5. Store the value of cosθ i in the lookup table of the digital signal processor (63) in advance, and the sine signal φ m (t) can be calculated by the CORDIC algorithm in the digital signal processor (63) as follows: φ m (t) = φ0sin(2πf m t) In the formula, t is the time, and φ0 is the amplitude of the sine signal.

4. The method for testing the frequency characteristics of an optical fiber gyroscope based on the CORDIC algorithm according to claim 3, wherein Specifically, S3 is as follows: 3.

1. Express the relationship between the Sagnac phase difference φ and the rotation angular rate Ω in the fiber optic gyroscope as: Then the scale factor K of the fiber optic gyroscope s is denoted as: In the formula, D is the diameter of the fiber loop (5), and λ is the wavelength of the light source (1); 3.

2. Represent the relationship between the maximum angular rate Ω output by the fiber optic gyroscope π and its corresponding phase difference π as: 3.

3. Convert the output digital signal in the digital signal processor (63) into an analog signal through the D / A converter (64) and output it. According to step 3.2, the analog amplitude A1 of the demodulated sine signal can be obtained: Where M is the number of bits of the D / A converter (64), and 2 M is the full-scale quantity magnitude of the M-bit D / A converter (64); 3.

4. According to the Sagnac effect, the phase difference Δφ between the two beams of light propagating in the clockwise and counterclockwise directions respectively in the optical fiber loop (5) m (t) is as follows: Δφ m (t) = φ m (t) - φ m (t - τ); 3.

5. Substitute the sine signal φ m (t) = φ0sin(2πf m t) obtained in step 2.5 into the phase difference Δφ m (t) = φ m (t) - φ m (t - τ) obtained in step 3.4, and calculate the actual amplitude A2 of the sine signal as follows: A2 = 2φ0sin(πf m τ); 3.

6. Calculate the amplitude φ0 of the sine signal according to the analog amplitude A1 obtained in step 3.3 and the actual amplitude A2 obtained in step 3.5; 3.

7. Substitute the amplitude φ0 of the sine signal obtained in step 3.6 into the sine signal φ obtained in step 2.5 m (t) = φ0 sin(2πf m t), and calculate the output sine signal of the digital signal processor (63).

5. The method for testing the frequency characteristics of an optical fiber gyroscope based on the CORDIC algorithm according to claim 4, wherein Specifically, S4 is as follows: 4.

1. By applying a bias phase of π / 2 to the fiber optic loop (5) through the Y waveguide (4), the modulation square wave φ b (t) of the fiber optic gyro Y waveguide (4) can be obtained: In the formula, m is the value of the τ period, m = 0, 1, 2,...; 4.

2. Superimpose the output sine signal obtained in step 3.7 onto the modulation square wave φ b (t) of the fiber optic gyro Y waveguide (4) to obtain the feedback signal φ(t): φ(t) = φ b (t) + φ m (t); 4.

3. Apply the feedback signal φ(t) to the Y waveguide (4) of the fiber optic gyroscope to perform phase modulation on the light wave of the fiber optic gyroscope.

6. The method for testing the frequency characteristics of an optical fiber gyroscope based on the CORDIC algorithm according to claim 5, wherein Specifically, S5 is as follows: 5.

1. Place the fiber optic gyroscope statically on the vibration isolation table, change the number of discrete points n in the digital signal processor (63) to realize the change of the sine signal frequency, collect the response angular rate of the fiber optic gyroscope through the upper computer test software, and record the amplitude A of the output response angular rate of the fiber optic gyroscope. 5.

2. Repeat step 5.1 until the amplitude A of the output response angular rate of the fiber optic gyroscope is reduced to 0.707 times the amplitude of the target sine signal input in step 1.2, and the corresponding frequency range is the bandwidth Δf of the fiber optic gyroscope 3dB , and complete the frequency characteristic test of the fiber optic gyroscope based on the CORDIC algorithm.

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