Method and device for measuring transit time of optical fiber ring of optical fiber gyroscope

Abstract

The invention provides a fiber-optic gyroscope transit time measuring method which comprises the following steps: generating a square wave bias modulation signal and a triangular wave modulation signal, and superposing to generate a special modulation signal; a special modulation signal is applied to a Y waveguide phase modulator through a D / A converter and an amplification circuit, phase modulation is performed on two beams of light in a light path, and interference occurs in the Y waveguide phase modulator after the light subjected to phase modulation is propagated for a circle in an optical fiber ring; the interference light returns to the coupler, and a light intensity signal is converted into an analog voltage signal through a detector; demodulating the signals of the rising half-cycle detector and the falling half-cycle detector of the triangular wave signal to obtain an optical fiber ring transit time error delta t; the square wave bias modulation signal period is adjusted, and when the error is zero, half of the square wave bias modulation signal period is the fiber loop transit time. According to the invention, high-precision detection of the transit time of the optical fiber ring can be realized only by adjusting FPGA software, and online closed-loop control of the control period of the gyroscope is realized while the angular rate measurement function of the optical fiber gyroscope is not influenced.

Description

Technical Field

[0001] The invention relates to the technical field of fiber optic gyroscope applications, and in particular to a method for measuring fiber transit time of a fiber optic gyroscope. Background Art

[0002] The fiber ring is a sensitive element in the fiber optic gyroscope. Based on the Sagnac effect, two beams of light transmitted in opposite directions in the fiber ring will produce a phase difference under the angular velocity input. The angular velocity can be measured by detecting the Sagnac phase difference. The time it takes for light to transmit one circle in the fiber ring is called the transit time τ. The transit time is an important parameter of the fiber ring. The control period of the gyroscope needs to be as consistent as possible with the transit time of the fiber ring. When the two are inconsistent, the performance of the fiber optic gyroscope will be affected, resulting in a decrease in the zero bias and threshold indicators of the fiber optic gyroscope.

[0003] The traditional method of measuring the transit time of a fiber optic loop is to apply square wave modulation and take the minimum value of the peak width of the interference comb wave signal. However, since the modulation signal is not an ideal square wave, there are limited rise times and fall times in the signal. When the square wave modulation period is near the transit time, the comb wave peak width does not change significantly, and the precise transit time cannot be measured. There are also some other measurement methods for the transit time of a fiber optic loop, such as the use of asymmetric square waves and sinusoidal wave modulation. These methods have a certain effect on improving the accuracy of the transit time test, but the modulation waveform used is inconsistent with the conventional fiber optic gyroscope closed-loop modulation waveform, which will affect the normal signal processing of the fiber optic gyroscope, making it impossible to measure the transit time of the fiber optic loop without affecting the angular velocity measurement. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a method for measuring the transit time of an optical fiber ring of an optical fiber gyroscope, which effectively improves the detection accuracy of the optical fiber ring transit time; the specific steps of the method are as follows:

[0005] S1, generate a square wave bias modulation signal and a triangle wave modulation signal, and superimpose the square wave bias modulation signal and the triangle wave modulation signal

[0006] The period of the square wave bias modulation signal is T;

[0007] The high half cycle and low half cycle time of the square wave bias modulation signal are equal, both are T hf , where T hf Close to the transit time of the fiber ring to be tested τ, T hf The difference with τ is the fiber ring transit time error Δt;

[0008] The period of the triangular wave modulation signal is T tri , T tri Less than T hf ;

[0009] The rise time and fall time of the triangle wave modulation signal are equal, which is T tri / 2;

[0010] The delay time of the rising edge or falling edge of the triangle wave modulation signal relative to the square wave bias modulation signal is the same;

[0011] A complete triangle wave signal is superimposed in the high half cycle and the low half cycle of the square wave bias modulation signal;

[0012] The above-mentioned superimposed modulation signal is a dedicated modulation signal;

[0013] The period of the dedicated modulation signal is the same as the period of the square wave bias modulation signal, both of which are T.

[0014] S2. Apply the dedicated modulation signal to the Y-waveguide phase modulator after passing through a D / A converter and an amplifier circuit, so as to phase modulate the two light beams transmitted clockwise and counterclockwise along the optical fiber ring in the optical path. After the phase modulated light propagates in the optical fiber ring for one circle, interference occurs in the Y-waveguide phase modulator.

[0015] S3, the interference light returns to the coupler and converts the light intensity information signal into an analog voltage signal through the detector, wherein the light intensity information signal includes the Sagnac phase difference information of the fiber optic gyroscope and the Δt described in step S1;

[0016] By demodulating the detector signals of the rising half cycle and the falling half cycle of the triangle wave signal, an error signal of the fiber loop transit time and half the period of the dedicated modulation signal is obtained.

[0017] S4. Determine the polarity and size of the error Δt and adjust the period of the square wave bias modulation signal

[0018] If the error Δt is 0, then half of the period of the square wave bias modulation signal is the transit time of the optical fiber ring;

[0019] If the error Δt is not zero, the period of the square wave bias modulation signal is adjusted until the error Δt is zero.

[0020] S5. The above S1 to S4 continue to work, and the period of the square wave bias modulation signal is kept equal to the fiber loop transit time.

[0021] The dedicated modulation signal is generated by the internal logic of the FPGA processor, and its digital signal sequence is output in sequence according to the clock cycle, and an analog modulation signal is generated through a D / A converter and an amplifier circuit;

[0022] The period adjustment of the dedicated modulation signal can be achieved by adjusting the length of the digital signal sequence inside the FPGA;

[0023] The period adjustment of the dedicated modulation signal is achieved by adjusting the length of the digital quantity signal sequence inside the FPGA processor;

[0024] The period of the dedicated modulation signal is achieved by adjusting the clock frequency through a phase-locked loop inside the FPGA processor or a digital frequency synthesizer outside the FPGA processor;

[0025] The special modulation signal superimposes a triangular wave signal on the optical fiber square wave bias modulation signal; the half period T of the square wave bias modulation signal is set hf Close to the transit time τ of the fiber loop to be tested, the half period T of the square wave bias modulation signal hf The difference between τ and Δt is set; the modulated triangular wave signal is set to an isosceles triangle shape, that is, the rising time is equal to the falling time, and the triangular wave modulation signal period T tri Less than half period T of square wave bias modulation signal hf At the same time, the delay time of the rising edge or falling edge of the triangle wave relative to the square wave bias modulation signal is the same;

[0026] The error Δt between half of the period T / 2 of the special modulation signal and the transit time τ of the optical fiber loop to be measured affects the interference phase of the rising and falling segments of the triangular wave, causing the interference light intensity to change within the corresponding time;

[0027] The fiber ring transit time error is reflected in the interference light intensity signal, and the specific form is as follows:

[0028] The high level part of the square wave bias modulation signal in the special modulation signal is A, the low level part is B, and the corresponding triangle wave rising period time is T Au , T Bu The falling period is T Ad , T Bd The corresponding time output interference light intensity is I Au ,I Bu ,I Ad ,I Bd , then the interference light intensity error signal ΔI=I caused by the error Δt between the transit time of the optical fiber ring and the modulation signal period Au –I Ad =I Bd –I Bu ; When Δt is small enough, it is approximately considered that ΔI is proportional to Δt;

[0029] The method theoretically has no effect on the closed-loop detection signal of the fiber optic gyroscope, and can be used alone to design a fiber optic ring transit time measurement device, or can be added as an independent function to the closed-loop control loop of the fiber optic gyroscope to realize online detection of the control cycle of the fiber optic gyroscope and continuous closed-loop tracking;

[0030] A device for measuring the transit time of an optical fiber ring of an optical fiber gyroscope, the device comprising a light source, a coupler, a Y-waveguide modulator, an optical fiber ring to be measured, a detector, a preamplifier circuit, an A / D converter, an FPGA processor, a D / A converter, and an amplifier circuit;

[0031] The light emitted by the light source is divided into two beams of light with equal intensity in the Y-waveguide modulator through the coupler; the two beams of light with equal intensity return to the Y-waveguide modulator to interfere after relatively propagating one circle in the optical fiber ring to be tested; the interference light propagates to the detector through the coupler, and the light intensity signal is converted into an analog voltage signal; the analog voltage signal is amplified by the preamplifier circuit, converted into a digital quantity by the A / D converter, and then input into the FPGA processor, and the optical fiber ring transit time error is solved inside the FPGA processor, and the control cycle closed-loop control is completed; a digital modulation signal is generated according to the control cycle, converted into an analog modulation signal by the D / A converter and the amplifier circuit, and applied to the Y-waveguide modulator to complete phase modulation.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) There is no need to modify the existing digital closed-loop fiber optic gyroscope optical path and circuit. Only the FPGA software needs to be adjusted to realize the fiber loop transit time detection.

[0034] (2) Through triangular wave modulation, the time error is converted into the difference of output voltage within the triangular wave modulation range, avoiding the influence of non-ideal rising and falling edges of square wave modulation; at the same time, the detection resolution is independent of the sampling frequency, and there is no need to use special high-speed or ultra-high-speed sampling devices.

[0035] (3) The special modulation signal of the present invention makes the fiber loop transit time error and the closed-loop fiber optic gyroscope Sagnac effect phase difference independent of each other, and the two operate simultaneously in the fiber optic gyroscope as independent control loops, thereby realizing online closed-loop control of the fiber optic gyroscope control cycle.

[0036] (4) The fiber ring transit time detection method can be extended to the fiber optic gyroscope with four-state wave modulation by simple modification. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a control loop diagram of the fiber optic gyroscope transit time measurement method of the present invention.

[0038] Figure 2 It is a system schematic diagram of the fiber optic gyroscope transit time measurement method of the present invention.

[0039] Figure 3 The modulation waveform applied to the Y-waveguide modulator in the fiber optic gyroscope transit time measurement method of the present invention.

[0040] Figure 4 This is a schematic diagram of the detector output voltage signal when there is no angular rate input in the fiber optic gyroscope transit time measurement method of the present invention and the fiber optic ring transit time is greater than half of the modulation signal period.

[0041] Figure 5 This is a schematic diagram of the detector output voltage signal when there is no angular rate input in the fiber optic gyroscope transit time measurement method of the present invention and the fiber optic ring transit time is less than half of the modulation signal period.

[0042] Figure 6 This is a schematic diagram of the detector output voltage signal when there is no angular rate input in the fiber optic gyroscope transit time measurement method of the present invention and the fiber optic ring transit time is equal to half of the modulation signal period.

[0043] Figure 7 It is a schematic diagram of the detector output voltage signal when the fiber optic gyroscope transit time measurement method of the present invention has an angular velocity input and the fiber optic ring transit time is equal to half of the modulation signal period.

[0044] Specific implementation methods

[0045] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0046] A device for measuring the transit time of an optical fiber ring of an optical fiber gyroscope, the device comprising a light source, a coupler, a Y waveguide modulator, an optical fiber ring to be measured, a detector, a preamplifier circuit, an A / D converter, an FPGA processor, a D / A converter, and an amplifier circuit. Figure 2 As shown;

[0047] The light emitted by the light source is divided into two beams of light with equal intensity in the Y-waveguide modulator through the coupler; the two beams of light with equal intensity are relatively propagated in the optical fiber ring to be tested for one cycle, and then return to the Y-waveguide modulator to interfere; the interference light is propagated to the detector through the coupler, and the light intensity signal is converted into an analog voltage signal; the analog voltage signal is amplified by the preamplifier circuit, converted into a digital quantity by the A / D converter, and then input into the FPGA processor, and the optical fiber ring transit time error is solved inside the FPGA processor, and the control cycle closed-loop control is completed; a digital modulation signal is generated according to the control cycle, converted into an analog modulation signal by the D / A converter and the amplifier circuit, and applied to the Y-waveguide modulator to complete phase modulation;

[0048] like Figure 1 As shown, a method for measuring the transit time of an optical fiber ring of an optical fiber gyroscope effectively improves the detection accuracy of the transit time of the optical fiber ring, generates a special modulation signal in an FPGA processor according to a preset digital sequence, and applies it to the Y waveguide modulator to complete phase modulation; the two beams of light after phase modulation propagate one circle in the optical fiber ring to be measured, return to the Y waveguide modulator to interfere, and the interfered optical signal is input into the detector; the detector outputs an error signal, performs error demodulation in the FPGA processor, and corrects the modulation signal period according to the result of the error demodulation, so that the error signal gradually decreases; when the error signal is 0, the half period of the special modulation signal is equal to the transit time of the optical fiber ring, and the accurate transit time of the optical fiber ring can be obtained; the specific steps of the method are as follows:

[0049] S1, generate a square wave bias modulation signal and a triangle wave modulation signal, and superimpose the square wave bias modulation signal and the triangle wave modulation signal

[0050] The period of the square wave bias modulation signal is T;

[0051] The high half cycle and low half cycle time of the square wave bias modulation signal are equal, both are T hf , where T hf Close to the transit time of the fiber ring to be tested τ, T hf The difference with τ is the fiber ring transit time error Δt;

[0052] The period of the triangular wave modulation signal is T tri , T tri Less than T hf ;

[0053] The rise time and fall time of the triangle wave modulation signal are equal, which is T tri / 2;

[0054] The delay time of the rising edge or falling edge of the triangle wave modulation signal relative to the square wave bias modulation signal is the same;

[0055] A complete triangle wave signal is superimposed in the high half cycle and the low half cycle of the square wave bias modulation signal;

[0056] The above-mentioned superimposed modulation signal is a dedicated modulation signal;

[0057] The period of the dedicated modulation signal is the same as the period of the square wave bias modulation signal, both of which are T.

[0058] S2. Apply the dedicated modulation signal to the Y-waveguide phase modulator after passing through a D / A converter and an amplifier circuit, so as to phase modulate the two light beams transmitted clockwise and counterclockwise along the optical fiber ring in the optical path. After the phase modulated light propagates in the optical fiber ring for one circle, interference occurs in the Y-waveguide phase modulator.

[0059] S3, the interference light returns to the coupler and converts the light intensity information signal into an analog voltage signal through the detector, wherein the light intensity information signal includes the Sagnac phase difference information of the fiber optic gyroscope and the Δt described in step S1;

[0060] By demodulating the detector signals of the rising half cycle and the falling half cycle of the triangle wave signal, an error signal of the fiber loop transit time and half the period of the dedicated modulation signal is obtained.

[0061] S4. Determine the polarity and size of the error Δt and adjust the period of the square wave bias modulation signal

[0062] If the error Δt is 0, then half of the period of the square wave bias modulation signal is the transit time of the optical fiber ring;

[0063] If the error Δt is not 0, the period of the square wave bias modulation signal is adjusted until the error is 0.

[0064] S5. The above S1 to S4 continue to work, and the period of the square wave bias modulation signal is kept equal to the fiber loop transit time.

[0065] The dedicated modulation signal is generated by the internal logic of the FPGA processor, and its digital signal sequence is output in sequence according to the clock cycle, and an analog modulation signal is generated through a D / A converter and an amplifier circuit;

[0066] The period adjustment of the dedicated modulation signal can be achieved by adjusting the length of the digital signal sequence inside the FPGA;

[0067] The period adjustment of the dedicated modulation signal is achieved by adjusting the length of the digital quantity signal sequence inside the FPGA processor;

[0068] The period of the dedicated modulation signal is achieved by adjusting the clock frequency through a phase-locked loop inside the FPGA processor or a digital frequency synthesizer outside the FPGA processor;

[0069] The special modulation signal superimposes a triangular wave signal on the optical fiber square wave bias modulation signal; the half period T of the square wave bias modulation signal is set hf Close to the transit time τ of the fiber loop to be tested, the half period T of the square wave bias modulation signal hf The difference between τ and Δt is set; the modulated triangular wave signal is set to an isosceles triangle shape, that is, the rising time is equal to the falling time, and the triangular wave modulation signal period T triLess than half period T of square wave bias modulation signal hf At the same time, the delay time of the rising edge or falling edge of the triangle wave relative to the square wave bias modulation signal is the same;

[0070] The error Δt between half of the period T / 2 of the special modulation signal and the transit time τ of the optical fiber loop to be measured affects the interference phase of the rising and falling segments of the triangular wave, causing the interference light intensity to change within the corresponding time;

[0071] The fiber ring transit time error is reflected in the interference light intensity signal, and the specific form is as follows:

[0072] The high level part of the square wave bias modulation signal in the special modulation signal is A, the low level part is B, and the corresponding triangle wave rising period time is T Au , T Bu The falling period is T Ad , T Bd The corresponding time output interference light intensity is I Au ,I Bu ,I Ad ,I Bd , then the interference light intensity error signal ΔI=I caused by the error Δt between the transit time of the optical fiber ring and the modulation signal period Au –I Ad =I Bd –I Bu ; When Δt is small enough, it is approximately considered that ΔI is proportional to Δt;

[0073] The method theoretically has no effect on the closed-loop detection signal of the fiber optic gyroscope, and can be used alone to design a fiber optic ring transit time measurement device, or can be added as an independent function to the closed-loop control loop of the fiber optic gyroscope to realize online detection of the control cycle of the fiber optic gyroscope and continuous closed-loop tracking;

[0074] The dedicated modulation signal is composed of the square wave bias modulation signal and the triangle wave modulation signal, and digital superposition is completed in the FPGA. The duty cycle of the square wave bias modulation signal is 50%, wherein the half cycle of the output high voltage is A, the half cycle of the output low voltage is B, the modulation signal cycle is T, and the two half cycles are both T / 2; the triangle wave modulation signal is an isosceles triangle with a cycle of T tri , the time positions of the triangle wave modulation signal in the two half cycles of A and B are exactly the same, satisfying:

[0075] V AH =V BH , T A1 =T B1 , T Au =T Ad =T Bu =T Bd =T tri / 2, such as Figure 3 shown;

[0076] The modulation phase applied by the modulation signal of the present invention to the two beams of light propagating relatively in the optical fiber loop through the Y waveguide modulator will be described below for the modulation phases of the two beams of light and the output signal of the detector in different cases;

[0077] Assume that the transit time of the optical fiber loop is τ and the period of the dedicated modulation signal is T, and define Δt = τ - T / 2;

[0078] As Figure 4 shown is the schematic diagram of the detector output voltage signal when there is no angular rate input and Δt > 0;

[0079] As Figure 5 shown is the schematic diagram of the detector output voltage signal when there is no angular rate input and Δt < 0;

[0080] As Figure 6 shown is the schematic diagram of the detector output voltage signal when there is no angular rate input and Δt = 0;

[0081] After the dedicated modulation signal is applied to the Y waveguide modulator, a phase modulation with a period of T is applied to the two beams of light propagating in opposite directions in the optical fiber loop. After the two beams of light propagate one week in the optical fiber loop, interference occurs. When interference occurs, there is a delay of τ in the modulation phase shift of the two beams of light;

[0082] When τ > T / 2 or τ < T / 2, that is, when Δt > 0 or Δt < 0, the phase difference between the two beams of light in the rising and falling segments of the triangular wave is not equal, the interference light intensity changes, and an error signal similar to a square wave will appear at the detector output; taking Δt as a variable, this error quantity is an odd function of Δt. Especially when Δt is small enough, this error quantity can be approximately considered proportional to Δt; when Δt = 0, the detector output error quantity is also 0, and at this time the detector output is the traditional closed-loop fiber optic gyro comb wave;

[0083] The interference light intensity error signal is amplified by the preamplifier circuit and then converted into a digital quantity by the A / D converter. By increasing the sampling frequency, the signal-to-noise ratio can be improved by the method of multi-point sampling and accumulation within a specified time period; the FPGA selects the data corresponding to the time for error calculation;

[0084] Inside the FPGA, the sampled data in different time periods can be used to calculate the digital time error by simple accumulation and smoothing and taking the relative difference. This value is proportional to Δt; according to this error quantity, the modulation signal period is corrected until Δt = 0; that is, the closed-loop tracking of the optical fiber loop transit time is realized. At this time, the modulation signal period is equal to twice the optical fiber loop transit time, that is, T / 2 = τ;

[0085] The modulation signal period T can be corrected by using a variety of means; the modulation signal period T can be corrected by adjusting the length of the digital signal sequence, changing the internal phase-locked loop of the FPGA, or adjusting the clock frequency by using the external digital frequency synthesizer of the FPGA.

[0086] Figure 7 Schematic diagram of the detector output voltage signal when Δt = 0 with angular rate input;

[0087] It can be seen that the Sagnac phase difference caused by the angular rate input is expressed as the voltage difference between time periods A and B in the detector output; it is easy to see that the detector output error caused by the time error is demodulated separately within the two time periods A and B, and the angular rate signal has no effect on it; at the same time, after the modulation signal cycle completes the closed-loop tracking, the voltage error caused by the time error within the two time periods A and B is 0, which will not affect the angular rate measurement; that is to say, the time error control loop and the angular rate measurement loop work independently at the same time, and do not affect each other.

[0088] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention using the above disclosed contents without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the contents of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for measuring the transit time of an optical fiber ring of an optical fiber gyroscope, characterized in that: The specific steps of the method are as follows: S1, generate a square wave bias modulation signal and a triangle wave modulation signal, and superimpose the square wave bias modulation signal and the triangle wave modulation signal The period of the square wave bias modulation signal is T; The high half cycle and low half cycle time of the square wave bias modulation signal are equal, both are T hf , where T hf Close to the transit time of the fiber ring to be tested τ, T hf The difference with τ is the fiber ring transit time error Δt; The period of the triangular wave modulation signal is T tri , T tri Less than T hf ; The rise time and fall time of the triangle wave modulation signal are equal, which is T tri / 2; The delay time of the rising edge or falling edge of the triangle wave modulation signal relative to the square wave bias modulation signal is the same; A complete triangle wave signal is superimposed in the high half cycle and the low half cycle of the square wave bias modulation signal; The above-mentioned superimposed modulation signal is a dedicated modulation signal; The period of the dedicated modulation signal is the same as the period of the square wave bias modulation signal, both of which are T; S2, applying the dedicated modulation signal to the Y-waveguide phase modulator after passing through a D / A converter and an amplifier circuit, so as to phase modulate the two light beams transmitted clockwise and counterclockwise along the optical fiber ring in the optical path, and the phase-modulated light interferes in the Y-waveguide phase modulator after propagating one circle in the optical fiber ring; S3, the interference light returns to the coupler and converts the light intensity information signal into an analog voltage signal through the detector, wherein the light intensity information signal includes the Sagnac phase difference information of the fiber optic gyroscope and the Δt described in step S1; By demodulating the detector signals of the rising half cycle and the falling half cycle of the triangle wave signal, an error signal of the fiber loop transit time and half the period of the special modulation signal is obtained; S4. Determine the polarity and size of the error Δt and adjust the period of the square wave bias modulation signal If the error Δt is 0, then half of the period of the square wave bias modulation signal is the transit time of the optical fiber ring; If the error Δt is not 0, adjusting the period of the square wave bias modulation signal until the error is 0; S5. The above S1 to S4 continue to work, and the period of the square wave bias modulation signal is kept equal to the fiber loop transit time.

2. The method for measuring the transit time of an optical fiber gyroscope optical fiber ring according to claim 1, characterized in that: The dedicated modulation signal is generated by the internal logic of the FPGA processor, and its digital signal sequence is output in sequence according to the clock cycle, and an analog modulation signal is generated through a D / A converter and an amplifier circuit.

3. The method for measuring the transit time of an optical fiber ring of an optical fiber gyroscope according to claim 1, characterized in that: The period adjustment of the dedicated modulation signal can be achieved by adjusting the length of the digital signal sequence inside the FPGA.

4. The method for measuring the transit time of an optical fiber gyroscope optical fiber ring according to claim 1, characterized in that: The period adjustment of the dedicated modulation signal is achieved by adjusting the length of the digital quantity signal sequence inside the FPGA processor.

5. The method for measuring the transit time of an optical fiber gyroscope optical fiber ring according to claim 1, characterized in that: The period of the dedicated modulation signal is achieved by adjusting the clock frequency through a phase-locked loop inside the FPGA processor or a digital frequency synthesizer outside the FPGA processor.

6. The method for measuring the transit time of an optical fiber ring of an optical fiber gyroscope according to claim 1, characterized in that: The special modulation signal superimposes a triangular wave signal on the optical fiber square wave bias modulation signal; the half period T of the square wave bias modulation signal is set hf Close to the transit time τ of the fiber loop to be tested, the half period T of the square wave bias modulation signal hf The difference between τ and Δt is set; the modulated triangular wave signal is set to an isosceles triangle shape, that is, the rising time is equal to the falling time, and the triangular wave modulation signal period T tri Less than half period T of square wave bias modulation signal hf At the same time, the delay time of the rising edge or falling edge of the triangle wave relative to the square wave bias modulation signal is the same.

7. A method for measuring the transit time of an optical fiber ring of an optical fiber gyroscope according to claim 1, characterized in that: The error Δt between half of the period T / 2 of the special modulation signal and the transit time τ of the optical fiber loop to be measured affects the interference phase of the rising and falling segments of the triangle wave, causing the interference light intensity to change within the corresponding time.

8. The method for measuring the transit time of an optical fiber ring of an optical fiber gyroscope according to claim 1, characterized in that: The fiber loop transit time error Δt is reflected in the interference light intensity signal, and the specific form is as follows: The high level part of the square wave bias modulation signal in the special modulation signal is A, the low level part is B, and the corresponding triangle wave rising period time is T Au , T Bu The falling period is T Ad , T Bd The corresponding time output interference light intensity is I Au ,I Bu ,I Ad ,I Bd , then the interference light intensity error signal ΔI=I caused by the error Δt between the transit time of the optical fiber ring and the modulation signal period Au -I Ad =I Bd -I Bu .

9. A device for measuring the transit time of an optical fiber ring of an optical fiber gyroscope, used to implement the method for measuring the transit time of an optical fiber ring of an optical fiber gyroscope as claimed in any one of claims 1 to 8, characterized in that: The device comprises a light source, a coupler, a Y-waveguide modulator, an optical fiber ring to be tested, a detector, a preamplifier circuit, an A / D converter, an FPGA processor, a D / A converter, and an amplifier circuit; The light emitted by the light source is divided into two beams of light with equal intensity in the Y-waveguide modulator through the coupler; the two beams of light with equal intensity return to the Y-waveguide modulator to interfere after relatively propagating one circle in the optical fiber ring to be tested; the interference light propagates to the detector through the coupler, and the light intensity signal is converted into an analog voltage signal; the analog voltage signal is amplified by the preamplifier circuit, converted into a digital quantity by the A / D converter, and then input into the FPGA processor, and the optical fiber ring transit time error is solved inside the FPGA processor, and the control cycle closed-loop control is completed; a digital modulation signal is generated according to the control cycle, converted into an analog modulation signal by the D / A converter and the amplifier circuit, and applied to the Y-waveguide modulator to complete phase modulation.

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