High-precision and low-noise polarization extinction type fiber optic gyroscope and method for suppressing interference spectrum modulation degree

Abstract

The present invention belongs to the field of fiber optic gyroscopes, and specifically relates to a high-precision and low-noise polarization extinction type fiber optic gyroscope and an interference spectrum modulation degree suppression method, aiming to solve the problems of noise and drift caused by the output spectrum modulation of the fiber optic sensitive loop in the existing polarization extinction fiber optic gyroscope. The present invention includes: a broadband light source, a coupler, a polarization extinction fiber optic sensitive loop, and a detector assembly, wherein the polarization extinction fiber optic sensitive loop includes a Y waveguide modulator, a first polarization maintaining fiber polarizer, a second polarization maintaining fiber polarizer, and a single-mode fiber loop. The first polarization maintaining fiber polarizer includes the first polarization maintaining tail fiber of the Y waveguide modulator and a first straight waveguide phase modulator with the same kind of polarization maintaining tail fiber. The second polarization maintaining fiber polarizer includes the second polarization maintaining tail fiber of the Y waveguide modulator and the same kind of second polarization maintaining fiber. The present invention can effectively reduce the noise and zero drift of the polarization extinction type fiber optic gyroscope, and at the same time reduce costs and improve environmental adaptability.

Description

Background Art

[0002] The depolarized fiber optic gyroscope is an interferometric fiber optic gyroscope that uses a single-mode fiber loop and a polarization-maintaining fiber depolarizer, and has the advantages of low cost, radiation resistance, and low magnetic field sensitivity. The polarization-maintaining fiber depolarizer is a key optical device in the depolarized fiber optic gyroscope. Generally, it is formed by splicing two sections of polarization-maintaining fiber with a length ratio of 1:2 at a polarization main axis angle of 45°, and the length of the shorter polarization-maintaining fiber should be greater than the decoherence length.

[0003] In a typical depolarized fiber optic gyroscope, two polarization-maintaining fiber depolarizers are placed at both ends of the single-mode fiber loop to depolarize the light beam entering the single-mode fiber loop and suppress most of the polarization errors. In 1999, B. Szafraniec et al. of Honeywell Company in the United States started from the idea of polarization state evolution, obtained its output model by deriving the transfer function of the depolarized fiber sensitive loop, and obtained the modulation spectral shape. At the same time, it was considered that as long as the polarization-maintaining fiber depolarizer has enough length, the influence of spectral modulation on the gyro performance can be ignored [1].

[0004] However, the depolarized fiber sensitive loop composed of multiple sections of polarization-maintaining fiber and a single-mode fiber loop is actually a typical Sagnac polarization interferometer. The modulation spectrum is essentially the output interference signal of the Sagnac polarization interferometer. The refractive index and length of the polarization-maintaining fiber and the single-mode fiber in the depolarized fiber sensitive loop are easily affected by the external environment and change, which will cause fluctuations in the modulation spectrum, thus causing noise and drift in the depolarized fiber optic gyroscope.

[0005] The following documents are technical background materials related to the present invention:

[0006] [1]B.Szafraniec,et al.Theory of Polarization Evolution inInterferometric Fiber-Optic Depolarized Gyros,Journal of LightwaveTechnology,1999,17(4):579-590 Summary of the Invention

[0007] In order to solve the above problems in the prior art, that is, the problem that the existing depolarized fiber optic gyroscope causes noise and drift due to the output spectral modulation of the fiber sensitive loop, the present invention provides a high-precision and low-noise depolarized fiber optic gyroscope, which includes a broadband light source, a coupler, a depolarized fiber sensitive loop, and a detector assembly. The depolarized fiber sensitive loop includes a Y-waveguide modulator, a first polarization-maintaining fiber depolarizer, a second polarization-maintaining fiber depolarizer, and a single-mode fiber loop;

[0008] The first polarization-maintaining fiber depolarizer includes a first polarization-maintaining tail fiber of a Y waveguide modulator and a first straight waveguide phase modulator; the polarization-maintaining tail fiber of the first straight waveguide phase modulator is of the same type as the first polarization-maintaining tail fiber;

[0009] The second polarization-maintaining fiber depolarizer includes a second polarization-maintaining tail fiber of a Y waveguide modulator and a second polarization-maintaining fiber; the second polarization-maintaining fiber is of the same type as the second polarization-maintaining tail fiber.

[0010] In some preferred embodiments, for the second polarization-maintaining fiber depolarizer, the second polarization-maintaining fiber can also be arranged as a second straight waveguide phase modulator; the polarization-maintaining tail fiber of the second straight waveguide phase modulator is of the same type as the second polarization-maintaining tail fiber.

[0011] In some preferred embodiments, for the first straight waveguide phase modulator or the second straight waveguide phase modulator, the high-frequency modulation signal is a sine wave, a triangular wave or other random waveforms.

[0012] In some preferred embodiments, for the high-frequency modulation signal, the signal frequency is a set multiple greater than the characteristic frequency of the depolarization fiber sensitive loop and is an even multiple of the characteristic frequency of the depolarization fiber sensitive loop, and the modulation phase amplitude is greater than π / 2.

[0013] In some preferred embodiments, for the first straight waveguide phase modulator, the two polarization-maintaining tail fibers corresponding to the chip are coupled with a polarization main axis angle of 0 degrees, the sum of the lengths of the two polarization-maintaining tail fibers is 2 times the length of the first polarization-maintaining tail fiber, and the length of the first polarization-maintaining tail fiber is greater than the depolarization length of the polarization-maintaining fiber;

[0014] For the second straight waveguide phase modulator, the two polarization-maintaining tail fibers corresponding to the chip are coupled with a polarization main axis angle of 0 degrees, the sum of the lengths of the two polarization-maintaining tail fibers is 2 times the length of the second polarization-maintaining tail fiber, and the length of the second polarization-maintaining tail fiber is greater than the depolarization length of the polarization-maintaining fiber.

[0015] On the other hand, the present invention proposes a method for suppressing the modulation degree of the interference spectrum of a high-precision and low-noise depolarized fiber optic gyroscope. When a high-frequency phase modulation signal is applied to a straight waveguide phase modulator, a time-varying birefringent phase modulation will be generated, causing the phases of various polarized light interference components in the spectral modulation factor M(λ, t) to change rapidly with time. By performing Bessel expansion analysis on M(λ, t), when the modulation frequency is much greater than the intrinsic frequency of the fiber optic loop, the time-average value of the high-frequency components that change with time in M(λ, t) will be zero. And when the modulation frequency is an even multiple of the intrinsic frequency, the difference between the clockwise and counterclockwise modulation signals generated by the fiber optic loop delay is zero, and no non-reciprocal phase shift will be introduced. At this time, the birefringent phase modulation amplitude takes a suitable value greater than π / 2, and theoretically, the terms that change with wavelength in M(λ, t) can all be made zero, that is, the output spectral modulation degree of the depolarized fiber optic sensitive loop can be made zero, reducing the noise and drift caused by the modulation spectrum.

[0016] The method for suppressing the modulation degree of the interference spectrum of the high-precision and low-noise depolarized fiber optic gyroscope specifically includes:

[0017] Step S10, applying a high-frequency modulation signal to the first straight waveguide phase modulator and / or the second straight waveguide phase modulator to generate a time-varying birefringent phase modulation, so that the phases of various polarized light interference components in the spectral modulation factor of the output spectrum of the depolarized fiber optic sensitive loop change with time;

[0018] Step S20, making the modulation phase amplitude of the high-frequency modulation signal be a value greater than π / 2, making the signal frequency be a set multiple greater than the characteristic frequency of the depolarized fiber optic sensitive loop, and being an even multiple of the characteristic frequency of the depolarized fiber optic sensitive loop, to obtain an output spectrum of the depolarized fiber optic sensitive loop with a modulation degree lower than the set threshold.

[0019] In some preferred embodiments, the output spectrum of the depolarized fiber optic sensitive loop is expressed as:

[0020]

[0021] wherein, I out (λ, t) represents the output spectrum of the depolarized fiber optic sensitive loop, λ represents the wavelength, t represents the time, and I in (λ, t) represents the input spectrum of the depolarized fiber optic sensitive loop, represents the Sagnac phase shift, and M(λ, t) represents the spectral modulation factor.

[0022] In some preferred embodiments, if the second polarization-maintaining fiber depolarizer of the high-precision low-noise polarization-demodulating fiber optic gyroscope includes the second polarization-maintaining tail fiber of the Y waveguide modulator and the second polarization-maintaining fiber, the spectral modulation factor is obtained by the first modulation method; if the second polarization-maintaining fiber depolarizer of the high-precision low-noise polarization-demodulating fiber optic gyroscope includes the second polarization-maintaining tail fiber of the Y waveguide modulator and the second straight waveguide phase modulator, the spectral modulation factor is obtained by the second modulation method.

[0023] In some preferred embodiments, when the high-frequency modulation signal is a sine wave, the method for obtaining the spectral modulation factor by the first modulation method is as follows:

[0024] M(λ, t) = 1 / 2 + 1 / 4 × sin(2θ 1s )sin(2θ 2s )cos[2π(ΔnL2 + ΔnL4) / λ + Ccos(2πf0t)] + 1 / 4 × sin(2θ 1s )sin(2θ 2s )cos[2π(ΔnL2 - ΔnL4) / λ + Ccos(2πf0t)] - 1 / 2 × cos 2 θ 1s cos 2 θ2scos[2π(ΔnL2 + ΔnL4 + Δn s L s ) / λ + Ccos(2πf0t)] - 1 / 2 × sin 2 θ 1s sin 2 θ 2s cos[2π(ΔnL2 + ΔnL4 - Δn s L s ) / λ + Ccos(2πf0t)] + 1 / 2 × cos 2 θ 1s sin 2 θ 2s cos[2π(ΔnL2 - ΔnL4 + Δn s L s ) / λ + Ccos(2πf0t)] + 1 / 2 × sin 2 θ 1s cos 2 θ 2s cos[2π(ΔnL2 - ΔnL4 - Δn s L s ) / λ + Ccos(2πf0t)]

[0025] where θ 1s is the included angle between the polarization main axis at the fusion joint of the first polarization-maintaining fiber depolarizer and the single-mode fiber loop, and θ 2sis the included angle between the polarization main axes at the fusion joint of the second polarization-maintaining fiber depolarizer and the single-mode fiber loop, Δn is the birefringence of the polarization-maintaining fiber, Δn s is the equivalent birefringence of the single-mode fiber loop, L2 is the sum of the lengths of the two polarization-maintaining pigtails of the first polarization-maintaining fiber depolarizer's first straight waveguide phase modulator, L4 is the length of the second polarization-maintaining fiber in the second polarization-maintaining fiber depolarizer, L s is the length of the single-mode fiber loop, C is the amplitude of the sine-wave modulation phase, f0 is the sine-wave modulation frequency.

[0026] In some preferred embodiments, when the high-frequency modulation signal is a sine wave, the method for obtaining the spectral modulation factor by the second modulation method is:

[0027] M(λ, t) = 1 / 2 + 1 / 4×sin(2θ 1s )sin(2θ 2s )cos[2π(ΔnL2 + ΔnL 4s ) / λ + 2Ccos(2πf0t)] + 1 / 4×sin(2θ 1s )sin(2θ 2s )cos[2π(ΔnL2 - ΔnL 4s ) / λ + 2Ccos(2πf0t)] - 1 / 2×cos 2 θ 1s cos 2 θ 2s cos[2π(ΔnL2 + ΔnL 4s + Δn s L s ) / λ + 2Ccos(2πf0t)] - 1 / 2×sin 2 θ 1s sin 2 θ 2s cos[2π(ΔnL2 + ΔnL 4s - Δn s L s ) / λ + 2Ccos(2πf0t)] + 1 / 2×cos 2 θ 1s sin 2 θ 2s cos[2π(ΔnL2 - ΔnL 4s + Δn s L s ) / λ + 2Ccos(2πf0t)] + 1 / 2×sin 2 θ 1s cos 2 θ 2s cos[2π(ΔnL2 - ΔnL 4s - Δn s Ls ) / λ + 2Ccos(2πf0t)]

[0028] where L 4s is the sum of the lengths of the two polarization-maintaining pigtails of the second straight waveguide phase modulator in the second polarization-maintaining fiber depolarizer.

[0029] Advantages of the present invention:

[0030] (1) In the high-precision and low-noise depolarized fiber optic gyroscope of the present invention, at least one polarization-maintaining fiber depolarizer is formed by fusing the polarization-maintaining pigtail of a Y-waveguide modulator and a straight waveguide phase modulator with the same type of polarization-maintaining pigtail at a polarization main axis angle of 45 degrees. By applying a high-frequency phase modulation signal to the straight waveguide phase modulator, the modulation spectrum changes rapidly over time, which can eliminate the modulation degree of the output spectrum of the depolarized fiber sensitive loop, reduce the noise and drift caused by the modulation spectrum fluctuation, achieve high precision and low noise, and can also effectively reduce the cost of the high-precision fiber optic gyroscope and improve the environmental adaptability.

[0031] (2) For the high-precision and low-noise depolarized fiber optic gyroscope of the present invention, in the case where one polarization-maintaining fiber depolarizer is formed by fusing the polarization-maintaining pigtail of a Y-waveguide modulator and a straight waveguide phase modulator with the same type of polarization-maintaining pigtail at a polarization main axis angle of 45 degrees, and two polarization-maintaining fiber depolarizers are formed by fusing the polarization-maintaining pigtail of a Y-waveguide modulator and a straight waveguide phase modulator with the same type of polarization-maintaining pigtail at a polarization main axis angle of 45 degrees, the spectral modulation factors are respectively obtained, so that the high-precision and low-noise depolarized fiber optic gyroscopes with different structures can make the modulation degree of the output spectrum of the depolarized fiber sensitive loop close to zero, and reduce the noise and drift caused by the modulation spectrum. Description of the Drawings

[0032] By reading the detailed description of the non-restrictive embodiments with reference to the following drawings, other features, objects and advantages of the present application will become more obvious:

[0033] Figure 1 is a schematic structural diagram of the first embodiment of the high-precision and low-noise depolarized fiber optic gyroscope of the present invention;

[0034] Figure 2 is a schematic structural diagram of the second embodiment of the high-precision and low-noise depolarized fiber optic gyroscope of the present invention;

[0035] Figure 3 is a schematic structural diagram of the polarization-maintaining fiber depolarizer composed of the polarization-maintaining pigtail of a Y-waveguide modulator and a straight waveguide phase modulator with the same type of polarization-maintaining pigtail in the high-precision and low-noise depolarized fiber optic gyroscope of the present invention;

[0036] Figure 4The measured spectra input into the depolarization fiber sensing loop and output from the depolarization fiber sensing loop in a high-precision depolarization fiber optic gyroscope with a 3-km-long single-mode fiber loop, which is an embodiment of the high-precision low-noise depolarization fiber optic gyroscope of the present invention;

[0037] Figure 5 The measured spectra output from the depolarization fiber sensing loop in a high-precision depolarization fiber optic gyroscope with a 3-km-long single-mode fiber loop, which is an embodiment of the high-precision low-noise depolarization fiber optic gyroscope of the present invention, after applying high-frequency phase modulation;

[0038] Figure 6 The Allan variance analysis curves of static tests before and after applying high-frequency phase modulation in a high-precision depolarization fiber optic gyroscope with a 3-km-long single-mode fiber loop, which is an embodiment of the high-precision low-noise depolarization fiber optic gyroscope of the present invention;

[0039] Explanation of reference numerals:

[0040] 1 is a broadband light source, 2 is a coupler, 3 is a depolarization fiber sensing loop, 4 is a detector assembly, 5 is a Y-waveguide modulator, 6 is a first polarization-maintaining fiber depolarizer, 7 is a second polarization-maintaining fiber depolarizer, 8 is a single-mode fiber loop, 9 is the first polarization-maintaining tail fiber of the Y-waveguide modulator, 10 is a first straight waveguide phase modulator, 11 is the second polarization-maintaining tail fiber of the Y-waveguide modulator, 12 is a second polarization-maintaining fiber, and 13 is a second straight waveguide phase modulator. Detailed implementation manners

[0041] The following further elaborates on the present application in conjunction with the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the relevant invention and do not limit the invention. Additionally, it should be noted that for the sake of description, only parts related to the relevant invention are shown in the drawings.

[0042] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The following will elaborate on the present application in detail with reference to the drawings and embodiments.

[0043] A high-precision low-noise depolarization fiber optic gyroscope of the present invention includes a broadband light source, a coupler, a depolarization fiber sensing loop, and a detector assembly. The depolarization fiber sensing loop includes a Y-waveguide modulator, a first polarization-maintaining fiber depolarizer, a second polarization-maintaining fiber depolarizer, and a single-mode fiber loop;

[0044] The first polarization-maintaining fiber depolarizer includes the first polarization-maintaining tail fiber of the Y-waveguide modulator and a first straight waveguide phase modulator; the polarization-maintaining tail fiber of the first straight waveguide phase modulator is of the same type as the first polarization-maintaining tail fiber;

[0045] The second polarization-maintaining fiber depolarizer includes a second polarization-maintaining tail fiber of the Y waveguide modulator and a second polarization-maintaining fiber; the second polarization-maintaining fiber and the second polarization-maintaining tail fiber are of the same type.

[0046] To more clearly illustrate the high-precision and low-noise depolarized fiber optic gyroscope of the present invention, each module in the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0047] The high-precision and low-noise depolarized fiber optic gyroscope according to the first embodiment of the present invention, as Figure 1 shown, is a schematic structural diagram of the first embodiment of the high-precision and low-noise depolarized fiber optic gyroscope of the present invention. The high-precision and low-noise depolarized fiber optic gyroscope includes a broad-spectrum light source 1, a coupler 2, a depolarized fiber sensing loop 3, and a detector assembly 4. The depolarized fiber sensing loop 3 includes a Y waveguide modulator 5, a first polarization-maintaining fiber depolarizer 6, a second polarization-maintaining fiber depolarizer 7, and a single-mode fiber loop 8. Each module is described in detail as follows:

[0048] The first polarization-maintaining fiber depolarizer 7 includes a first polarization-maintaining tail fiber 9 of the Y waveguide modulator and a first straight waveguide phase modulator 10. The polarization-maintaining tail fiber of the first straight waveguide phase modulator is of the same type as the first polarization-maintaining tail fiber.

[0049] The high-frequency modulation signal of the first straight waveguide phase modulator 10 is a sine wave, a triangular wave, or other random waveforms.

[0050] The high-frequency modulation signal, the signal of which is a set multiple greater than the characteristic frequency of the depolarized fiber sensing loop and is an even multiple of the characteristic frequency of the depolarized fiber sensing loop, and the modulation phase amplitude is greater than π / 2.

[0051] The first straight waveguide phase modulator 10, the two polarization-maintaining tail fibers corresponding to the chip of which are coupled at a polarization main axis angle of 0 degrees, the sum of the lengths of the two polarization-maintaining tail fibers is 2 times the length of the first polarization-maintaining tail fiber, and the length of the first polarization-maintaining tail fiber is greater than the depolarization length of the polarization-maintaining fiber.

[0052] The second polarization-maintaining fiber depolarizer 8 includes a second polarization-maintaining tail fiber 11 of the Y waveguide modulator and a second polarization-maintaining fiber 12. The second polarization-maintaining fiber and the second polarization-maintaining tail fiber are of the same type.

[0053] Under the above structure of the high-precision and low-noise depolarized fiber optic gyroscope, the method for suppressing the modulation degree of the interference spectrum includes:

[0054] Step S10, applying a high-frequency modulation signal to the first straight waveguide phase modulator to generate a time-varying birefringence phase modulation, so that the phases of various polarized light interference components in the spectral modulation factor of the output spectrum of the depolarized fiber sensing loop change with time.

[0055] The output spectrum of the depolarized fiber sensing loop is shown in Equation (1):

[0056]

[0057] Among them, I out (λ, t) represents the output spectrum of the depolarized fiber sensing loop, λ represents the wavelength, t represents the time, and I in (λ, t) represents the input spectrum of the depolarized fiber sensing loop, represents the Sagnac phase shift, and M(λ, t) represents the spectral modulation factor.

[0058] When the high-frequency modulation signal is a sine wave, the spectral modulation factor is obtained by the first modulation method, as shown in Equation (2):

[0059] M(λ, t) = 1 / 2 + 1 / 4×sin(2θ 1s )sin(2θ 2s )cos[2π(ΔnL2 + ΔnL4) / λ + Ccos(2πf0t)] + 1 / 4×sin(2θ 1s )sin(2θ 2s )cos[2π(ΔnL2 - ΔnL4) / λ + Ccos(2πf0t)] - 1 / 2×cos 2 θ 1s cos 2 θ 2s cos[2π(ΔnL2 + ΔnL4 + Δn s Ls ) / λ + Ccos(2πf0t)] - 1 / 2×sin 2 θ 1s sin 2 θ 2s cos[2π(ΔnL2 + ΔnL4 - Δn s L S ) / λ + Ccos(2πf0t)] + 1 / 2×cos 2 θ 1s sin 2 θ 2s cos[2π(ΔnL2 - ΔnL4 + Δn s L s ) / λ + Ccos(2πf0t)] + 1 / 2×sin 2 θ 1s cos 2 θ 2s cos[2π(ΔnL2 - ΔnL4 - Δn s L s ) / λ + Ccos(2πf0t)] (2)

[0060] Among them, θ 1sθ is the included angle between the polarization main axes at the fusion splice point of the first polarization-maintaining fiber depolarizer and the single-mode fiber loop. 2s Δn is the birefringence of the polarization-maintaining fiber, and Δn is the included angle between the polarization main axes at the fusion splice point of the second polarization-maintaining fiber depolarizer and the single-mode fiber loop. s is the equivalent birefringence of the single-mode fiber loop, L2 is the sum of the lengths of the two polarization-maintaining pigtails of the first straight waveguide phase modulator in the first polarization-maintaining fiber depolarizer, L4 is the length of the second polarization-maintaining fiber in the second polarization-maintaining fiber depolarizer, and L s is the length of the single-mode fiber loop, C is the amplitude of the sine-wave modulation phase, and f0 is the sine-wave modulation frequency.

[0061] Step S20: Set the modulation phase amplitude of the high-frequency modulation signal to a value greater than π / 2, set the signal frequency to a set multiple greater than the characteristic frequency of the depolarization fiber sensitive loop and an even multiple of the characteristic frequency of the depolarization fiber sensitive loop, and obtain the output spectrum of the depolarization fiber sensitive loop with a modulation degree lower than the set threshold.

[0062] The high-precision and low-noise depolarization fiber optic gyroscope according to the second embodiment of the present invention, as Figure 2 shown, is a schematic structural diagram of the second embodiment of the high-precision and low-noise depolarization fiber optic gyroscope of the present invention. The high-precision and low-noise depolarization fiber optic gyroscope includes a broadband light source 1, a coupler 2, a depolarization fiber sensitive loop 3, and a detector assembly 4. The depolarization fiber sensitive loop 3 includes a Y-waveguide modulator 5, a first polarization-maintaining fiber depolarizer 6, a second polarization-maintaining fiber depolarizer 7, and a single-mode fiber loop 8. The details of each module are described as follows:

[0063] The first polarization-maintaining fiber depolarizer 7 includes the first polarization-maintaining pigtail 9 of the Y-waveguide modulator and the first straight waveguide phase modulator 10. The polarization-maintaining pigtails of the first straight waveguide phase modulator are of the same type as the first polarization-maintaining pigtail.

[0064] The high-frequency modulation signal of the first straight waveguide phase modulator 10 is a sine wave, a triangular wave, or other random waveforms.

[0065] The high-frequency modulation signal has a signal frequency that is a set multiple greater than the characteristic frequency of the depolarization fiber sensitive loop and an even multiple of the characteristic frequency of the depolarization fiber sensitive loop, and the modulation phase amplitude is greater than π / 2.

[0066] For the first straight waveguide phase modulator 10, the two polarization-maintaining pigtails corresponding to the chip are coupled at a polarization main axis angle of 0 degrees, the sum of the lengths of the two polarization-maintaining pigtails is twice the length of the first polarization-maintaining pigtail, and the length of the first polarization-maintaining pigtail is greater than the depolarization length of the polarization-maintaining fiber.

[0067] The second polarization-maintaining fiber depolarizer 8 includes the second polarization-maintaining pigtail 11 of the Y-waveguide modulator and the second straight waveguide phase modulator 13. The polarization-maintaining pigtails of the second straight waveguide phase modulator are of the same type as the second polarization-maintaining pigtail.

[0068] The high-frequency modulation signal of the second straight waveguide phase modulator 13 is a sine wave, a triangular wave, or other random waveforms.

[0069] The high-frequency modulation signal has a signal frequency greater than a set multiple of the characteristic frequency of the fiber optic loop and is an even multiple of the characteristic frequency of the fiber optic loop, and the modulation phase amplitude is greater than π / 2.

[0070] The second straight waveguide phase modulator 13 has two polarization-maintaining pigtails corresponding to the chip coupled at a polarization main axis angle of 0 degrees, the sum of the lengths of the two polarization-maintaining pigtails is twice the length of the second polarization-maintaining pigtail, and the length of the second polarization-maintaining pigtail is greater than the depolarization length of the polarization-maintaining fiber.

[0071] Under the structure of the above-mentioned high-precision low-noise depolarization-type fiber optic gyroscope, the method for suppressing the modulation degree of the interference spectrum includes:

[0072] Step T10, applying a high-frequency modulation signal to the second straight waveguide phase modulator to generate a time-varying birefringence phase modulation, so that the phases of various polarized light interference components in the spectrum modulation factor of the output spectrum of the depolarization fiber sensitive loop change with time.

[0073] The output spectrum of the depolarization fiber sensitive loop is as shown in Equation (3):

[0074]

[0075] Among them, I out (λ, t) represents the output spectrum of the depolarization fiber sensitive loop, λ represents the wavelength, t represents the time, and I in (λ, t) represents the input spectrum of the depolarization fiber sensitive loop, represents the Sagnac phase shift, and M(λ, t) represents the spectrum modulation factor.

[0076] When the high-frequency modulation signal is a sine wave, the spectrum modulation factor is obtained through the second modulation method, as shown in Equation (4):

[0077] M(λ, t) = 1 / 2 + 1 / 4 × sin(2θ 1s )sin(2θ 2s )cos[2π(ΔnL2 + ΔnL 4s ) / λ + 2Ccos(2πf0t)] + 1 / 4 × sin(2θ 1s )sin(2θ 2s )cos[2π(ΔnL2 - ΔnL 4s ) / λ + 2Ccos(2πf0t)] - 1 / 2 × cos 2 θ 1s cos 2 θ 2scos[2π(ΔnL2+ΔnL 4s +Δn s L s ) / λ+2Ccos(2πf0t)]-1 / 2×sin 2 θ 1s sin 2 θ 2s cos[2π(ΔnL2+ΔnL 4s -Δn s L s ) / λ+2Ccos(2πf0t)]+1 / 2×cos 2 θ 1s sin 2 θ 2s cos[2π(ΔnL2-ΔnL 4s +Δn s L s ) / λ+2Ccos(2πf0t)]+1 / 2×sin 2 θ 1s cos 2 θ 2s cos[2π(ΔnL2-ΔnL 4s -Δn s L s ) / λ+2Ccos(2πf0t)] (4)

[0078] where θ 1s is the included angle between the polarization main axes at the fusion splicing point of the first polarization-maintaining fiber depolarizer and the single-mode fiber loop, θ 2s is the included angle between the polarization main axes at the fusion splicing point of the second polarization-maintaining fiber depolarizer and the single-mode fiber loop, Δn is the birefringence of the polarization-maintaining fiber, Δn s is the equivalent birefringence of the single-mode fiber loop, L2 is the sum of the lengths of the two polarization-maintaining tail fibers of the first straight waveguide phase modulator in the first polarization-maintaining fiber depolarizer, L 4s is the sum of the lengths of the two polarization-maintaining tail fibers of the second straight waveguide phase modulator in the second polarization-maintaining fiber depolarizer, L s is the length of the single-mode fiber loop, C is the phase amplitude of the sine-wave modulation, and f0 is the sine-wave modulation frequency.

[0079] Step T20: Set the modulation phase amplitude of the high-frequency modulation signal to a value greater than π / 2, set the signal frequency to a set multiple greater than the characteristic frequency of the depolarizing fiber sensitive loop and an even multiple of the characteristic frequency of the depolarizing fiber sensitive loop, and obtain the output spectrum of the depolarizing fiber sensitive loop with a modulation degree lower than the set threshold.

[0080] As Figure 3As shown in the figure, it is a schematic structural diagram of a polarization-maintaining fiber depolarizer of a high-precision and low-noise depolarized fiber optic gyroscope according to the present invention, which is composed of a polarization-maintaining tail fiber of a Y waveguide modulator and a straight waveguide phase modulator with the same type of polarization-maintaining tail fiber. The chip of the first straight waveguide phase modulator 10 (the second straight waveguide phase modulator 13 is the same as the first straight waveguide phase modulator 10) is coupled with its two sections of polarization-maintaining tail fibers at a polarization main axis angle of 0 degrees. One of the polarization-maintaining tail fibers is fused with the first polarization-maintaining tail fiber 9 of the Y waveguide modulator 5 (the second polarization-maintaining tail fiber 11 of the Y waveguide modulator 5 corresponds to the second straight waveguide phase modulator 13) at a polarization main axis angle of 45 degrees. The sum of the lengths of the two sections of polarization-maintaining tail fibers of the first straight waveguide phase modulator 10 is twice the length of the polarization-maintaining tail fiber 9 of the Y waveguide modulator 5 (the sum of the lengths of the two sections of polarization-maintaining tail fibers of the second straight waveguide phase modulator 13 is twice the length of the second polarization-maintaining tail fiber 11 of the Y waveguide modulator 5), and the lengths of both the first polarization-maintaining tail fiber 9 and the second polarization-maintaining tail fiber 11 of the Y waveguide modulator 5 are greater than the depolarization length of the polarization-maintaining fiber.

[0081] To verify the effectiveness of the technical solution of the present invention, the technical solution of the present invention is verified through experiments, and the verification process is as follows:

[0082] According to Figure 1 the structural schematic diagram, a high-precision depolarized fiber optic gyroscope is built using a 3 km long single-mode fiber loop. Preferably, a sine wave modulation signal with a frequency much higher than the intrinsic frequency of the fiber loop is applied to the straight waveguide phase modulator, and it is an even multiple of the intrinsic frequency, and the birefringence phase modulation amplitude is greater than π / 2. First, the fiber connected to the detector assembly 4 is connected to a spectrum analyzer, and the output spectrum of the depolarized fiber sensitive loop is measured using the spectrum analyzer. The spectrum before applying the high-frequency phase modulation is as Figure 4 shown, Figure 4 in which the dotted line is the original spectrum input to the depolarized fiber sensitive loop, and the solid line is the output spectrum of the depolarized fiber sensitive loop. It can be seen that there is an obvious "comb-shaped" modulation in the output spectrum of the depolarized fiber sensitive loop. After applying the high-frequency phase modulation, the output spectrum of the depolarized fiber sensitive loop is as Figure 5 shown. The spectral modulation degree at the central wavelength is reduced from 7.31 dB before modulation to 0.19 dB after modulation, which well eliminates the modulation degree of the output spectrum of the depolarized fiber sensitive loop.

[0083] Furthermore, the fiber connected to the spectrum analyzer for testing is reconnected to the detector assembly 4. After the depolarized fiber optic gyroscope is adjusted, it is statically tested for 2 hours before and after applying the high-frequency phase modulation at room temperature, and Allan variance analysis is performed. The results of the Allan variance analysis are as Figure 6 shown, Figure 6 in which the solid line is the result of the Allan variance analysis measured before applying the high-frequency phase modulation, Figure 6The dashed line in the figure is the result of the Allan variance analysis measured after applying high-frequency phase modulation. From the Allan variance curve, it can be seen that the angular random walk decreases from 5.9×10 -4 ° / √h before modulation to 2.1×10 -4 ° / √h after modulation, and the bias instability decreases from 1.1×10 -3 ° / h before modulation to 4.3×10 -4 ° / h after modulation. The experiment shows that after applying high-frequency phase modulation, both the noise and zero drift caused by the output spectrum modulation of the depolarized fiber sensitive loop are effectively suppressed, realizing a depolarized fiber optic gyroscope with high precision and low noise, effectively reducing the cost of high-precision fiber optic gyroscopes and improving the environmental adaptability.

[0084] It should be noted that the high-precision low-noise depolarized fiber optic gyroscope and the interference spectrum modulation degree suppression method provided in the above embodiments are only illustrated by dividing the above functional modules. In practical applications, the above functions can be allocated to different functional modules according to needs, that is, the modules or steps in the embodiments of the present invention can be further decomposed or combined. For example, the modules in the above embodiments can be combined into one module, or further split into multiple sub-modules to complete all or part of the functions described above. The names of the modules and steps involved in the embodiments of the present invention are only for distinguishing each module or step, and are not regarded as an improper limitation of the present invention.

[0085] An apparatus according to a third embodiment of the present invention includes:

[0086] At least one processor;

[0087] And a memory communicatively connected to at least one of the processors;

[0088] Wherein, the memory stores instructions executable by the processor, and the instructions are used to be executed by the processor to implement the interference spectrum modulation degree suppression method of the above-mentioned high-precision low-noise depolarized fiber optic gyroscope.

[0089] A computer-readable storage medium according to a fourth embodiment of the present invention stores computer instructions, and the computer instructions are used to be executed by the computer to implement the interference spectrum modulation degree suppression method of the above-mentioned high-precision low-noise depolarized fiber optic gyroscope.

[0090] Those skilled in the art of the present technology can clearly understand that for the convenience and brevity of description, the specific working processes and related descriptions of the above-mentioned storage device and processing device can refer to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0091] Those skilled in the art should be able to realize that the modules and method steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of both. The programs corresponding to the software modules and method steps can be placed in a random access memory (RAM), internal memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium well-known in the technical field. To clearly illustrate the interchangeability of electronic hardware and software, the composition and steps of each example have been generally described according to functions in the above description. Whether these functions are executed in the form of electronic hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0092] The terms "first", "second", etc. are used to distinguish similar objects, rather than to describe or represent a specific order or sequence.

[0093] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, so that a process, method, article, or device / equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent in these processes, methods, articles, or devices / equipment.

[0094] So far, the technical solution of the present invention has been described in combination with the preferred embodiments shown in the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A high-precision and low-noise depolarized fiber optic gyroscope, comprising a broadband light source, a coupler, a depolarized fiber sensing loop and a detector assembly, characterized in that, The depolarized fiber optic sensing loop includes a Y waveguide modulator, a first polarization-maintaining fiber depolarizer, a second polarization-maintaining fiber depolarizer, and a single-mode fiber loop; The first polarization-maintaining fiber depolarizer includes a first polarization-maintaining tail fiber of the Y waveguide modulator and a first straight waveguide phase modulator; the polarization-maintaining tail fiber of the first straight waveguide phase modulator is of the same type as the first polarization-maintaining tail fiber; The second polarization-maintaining fiber depolarizer includes a second polarization-maintaining tail fiber of the Y waveguide modulator and a second polarization-maintaining fiber; the second polarization-maintaining fiber is of the same type as the second polarization-maintaining tail fiber.

2. The high-precision low-noise polarization extinction type fiber optic gyroscope according to claim 1, wherein For the second polarization-maintaining fiber depolarizer, the second polarization-maintaining fiber can also be set as a second straight waveguide phase modulator; the polarization-maintaining tail fiber of the second straight waveguide phase modulator is of the same type as the second polarization-maintaining tail fiber.

3. The high-precision low-noise depolarized fiber optic gyroscope according to claim 2, characterized in that, For the first straight waveguide phase modulator or the second straight waveguide phase modulator, the high-frequency modulation signal is a sine wave, a triangular wave, or other random waveforms.

4. The high-precision low-noise polarization extinction type fiber optic gyroscope according to claim 3, wherein For the high-frequency modulation signal, the signal frequency is a set multiple greater than the characteristic frequency of the depolarized fiber optic sensing loop and is an even multiple of the characteristic frequency of the depolarized fiber optic sensing loop, and the modulation phase amplitude is greater than π / 2.

5. The high-precision and low-noise polarization extinction type fiber optic gyroscope according to claim 4, characterized in that, For the first straight waveguide phase modulator, the two polarization-maintaining tail fibers corresponding to the chip are coupled at a 0-degree polarization main axis angle, the sum of the lengths of the two polarization-maintaining tail fibers is 2 times the length of the first polarization-maintaining tail fiber, and the length of the first polarization-maintaining tail fiber is greater than the depolarization length of the polarization-maintaining fiber; For the second straight waveguide phase modulator, the two polarization-maintaining tail fibers corresponding to the chip are coupled at a 0-degree polarization main axis angle, the sum of the lengths of the two polarization-maintaining tail fibers is 2 times the length of the second polarization-maintaining tail fiber, and the length of the second polarization-maintaining tail fiber is greater than the depolarization length of the polarization-maintaining fiber.

6. A method for suppressing the modulation degree of the interference spectrum of a high-precision and low-noise polarization extinction type fiber optic gyroscope, characterized in that, The method for suppressing the modulation degree of the interference spectrum includes: Step S10, applying a high-frequency modulation signal to the first straight waveguide phase modulator and / or the second straight waveguide phase modulator to generate a time-varying birefringence phase modulation, so that the phases of various polarization interference components in the spectrum modulation factor of the output spectrum of the depolarized fiber optic sensing loop change with time; Step S20, making the modulation phase amplitude of the high-frequency modulation signal be a value greater than π / 2, making the signal frequency be a set multiple greater than the characteristic frequency of the depolarized fiber optic sensing loop and be an even multiple of the characteristic frequency of the depolarized fiber optic sensing loop, and obtaining an output spectrum of the depolarized fiber optic sensing loop with a modulation degree lower than the set threshold.

7. The method for suppressing the modulation degree of the interference spectrum of the high-precision and low-noise polarization extinction type fiber optic gyroscope according to claim 6, characterized in that The output spectrum of the depolarized fiber optic sensing loop is expressed as: Among them, I out (λ, t) represents the output spectrum of the depolarized fiber sensing loop, λ represents wavelength, t represents time, I in (λ, t) represents the input spectrum of the depolarized fiber sensing loop, represents the Sagnac phase shift, and M(λ, t) represents the spectral modulation factor.

8. The method for suppressing the modulation degree of the interference spectrum of the high-precision and low-noise polarization extinction type fiber optic gyro according to claim 7, characterized in that, If the second polarization-maintaining fiber depolarizer of the high-precision low-noise depolarized fiber optic gyro includes a second polarization-maintaining tail fiber of the Y waveguide modulator and a second polarization-maintaining fiber, then the spectrum modulation factor is obtained by the first modulation method; if the second polarization-maintaining fiber depolarizer of the high-precision low-noise depolarized fiber optic gyro includes a second polarization-maintaining tail fiber of the Y waveguide modulator and a second straight waveguide phase modulator, then the spectrum modulation factor is obtained by the second modulation method.

9. The method for suppressing the modulation degree of the interference spectrum of the high-precision low-noise polarization extinction type fiber optic gyroscope according to claim 8, characterized in that When the high-frequency modulation signal is a sine wave, the method for obtaining the spectrum modulation factor by the first modulation method is: M(λ, t) = 1 / 2 + 1 / 4 × sin(2θ 1s )sin(2θ 2s )cos[2π(ΔnL2 + ΔnL4) / λ + Ccos(2πf0t)] + 1 / 4 × sin(2θ 1s )sin(2θ 2s )cos[2π(ΔnL2 - ΔnL4) / λ + Ccos(2πf0t)] - 1 / 2 × cos 2 θ 1s cos 2 θ 2s cos[2π(ΔnL2 + ΔnL4 + Δn s L s ) / λ + Ccos(2πf0t)] - 1 / 2 × sin 2 θ 1s sin 2 θ 2s cos[2π(ΔnL2 + ΔnL4 - Δn s L s ) / λ + Ccos(2πf0t)] + 1 / 2 × cos 2 θ 1s sin 2 θ 2s cos[2π(ΔnL2 - ΔnL4 + Δn s L s ) / λ + Ccos(2πf0t)] + 1 / 2 × sin 2 θ 1s cos 2 θ 2s cos[2π(ΔnL2 - ΔnL4 - Δn s L s ) / λ + Ccos(2πf0t)] Among them, θ 1s is the included angle between the polarization main axis at the fusion joint of the first polarization-maintaining fiber depolarizer and the single-mode fiber loop, θ 2s is the included angle between the polarization main axis at the fusion joint of the second polarization-maintaining fiber depolarizer and the single-mode fiber loop, Δn is the birefringence of the polarization-maintaining fiber, Δn s is the equivalent birefringence of the single-mode fiber loop, L2 is the sum of the lengths of the two polarization-maintaining pigtails of the first straight waveguide phase modulator in the first polarization-maintaining fiber depolarizer, L4 is the length of the second polarization-maintaining fiber in the second polarization-maintaining fiber depolarizer, L s is the length of the single-mode fiber loop, C is the amplitude of the sine-wave modulation phase, and f0 is the sine-wave modulation frequency.

10. The method for suppressing the modulation degree of the interference spectrum of the high-precision low-noise polarization extinction type fiber optic gyroscope according to claim 9, characterized in that, When the high-frequency modulation signal is a sine wave, the method for obtaining the spectrum modulation factor by the second modulation method is: M(λ, t) = 1 / 2 + 1 / 4 × sin(2θ 1s )sin(2θ 2s )cos[2π(ΔnL2 + ΔnL 4s ) / λ + 2Ccos(2πf0t)] + 1 / 4 × sin(2θ 1s )sin(2θ 2s )cos[2π(ΔnL2 - ΔnL 4s ) / λ + 2Ccos(2πf0t)] - 1 / 2 × cos 2 θ 1s cos 2 θ 2s cos[2π(ΔnL2 + ΔnL 4s +Δn s L s ) / λ + 2Ccos(2πf0t)] - 1 / 2 × sin 2 θ 1s sin 2 θ 2s cos[2π(ΔnL2 + ΔnL 4s -Δn s L s ) / λ + 2Ccos(2πf0t)] + 1 / 2 × cos 2 θ 1s sin 2 θ 2s cos[2π(ΔnL2 - ΔnL 4s +Δn s L s ) / λ + 2Ccos(2πf0t)] + 1 / 2 × sin 2 θ 1s cos 2 θ 2s cos[2π(ΔnL2 - ΔnL 4s -Δn s L s ) / λ + 2Ccos(2πf0t)] Among them, L 4s is the sum of the lengths of the two polarization-maintaining pigtails of the second straight waveguide phase modulator in the second polarization-maintaining fiber depolarizer.

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