Matching interference type fiber bragg grating sensor based on complete random binary sequence

Abstract

The invention provides a matching interference type fiber bragg grating sensor based on a completely random binary sequence. The matching interference type fiber bragg grating sensor comprises a laser pulse generation unit, a phase modulation unit and a sensing unit, the laser pulse generation unit is used for generating laser pulses; the phase modulation unit is connected with the laser pulse generation unit, and the phase modulation unit applies different modulation sequences to each laser pulse and modulates the phase of the laser pulse into a completely randomly distributed phase so as to reduce the self-coherence of the laser pulse; and laser pulses generated by the laser pulse generation unit are input into the sensing unit after passing through the phase modulation unit. According to the method, the Rayleigh scattering noise of the matched interference type fiber grating sensor is efficiently suppressed by means of signal phase modulation and demodulation, and an important technical support is provided for accelerating and promoting the engineering practical process of the matched interference type fiber grating sensor.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber optic sensing and signal processing, and particularly to a matching interference type fiber Bragg grating sensor based on a completely random binary sequence. Background Art

[0002] Matching interference type fiber optic sensors have extremely important application prospects in future underwater aquaculture, marine resource exploration and other fields due to many advantages such as high acoustic pressure sensitivity, large dynamic range, and easy large-scale arraying. The underwater wet-end structure of the matching interference type fiber optic sensor based on fiber Bragg grating requires no additional devices except for the fiber Bragg grating, and a highly integrated sensing array structure can be realized on a single fiber. Due to its significant advantages in reliability, large-scale and miniaturization, the matching interference type sensor based on fiber Bragg grating has become a research hotspot in various fields such as marine ranches, underwater environment monitoring and seabed resource exploration in recent years.

[0003] After decades of development, the fiber optic sensor system based on fiber Bragg grating has overcome a series of problems from basic theory to practical application. With the in-depth research, the matching interference type fiber optic sensor has entered the application stage in several fields. However, in the process of promoting practical application, the basic scientific problems originating from the optical physics level but ignored in laboratory research have become new technical bottlenecks in system application. One of the important problems is the Rayleigh scattering effect in the matching interference type fiber optic sensor. Rayleigh scattering will accumulate with the increase of the fiber transmission distance, which will in turn cause problems such as increased noise, limited multiplexing scale and transmission distance. The key to solving this problem lies in solving the contradiction between the narrow linewidth of high-monochromaticity laser and low coherence. The traditional methods for suppressing Rayleigh scattering include changing the coherence length of the light source or adding transmission fibers by means of a circulator and an isolator. However, the negative effects brought by these two methods are also obvious. The former will increase the background noise, and the latter will increase the complexity of the hydrophone and reduce the overall reliability, which is not suitable for large-scale sensing. Therefore, it is urgent to study a matching interference type fiber Bragg grating sensor that does not increase the background noise and system complexity and has no negative effects at all. Summary of the Invention

[0004] In view of the defects existing in the prior art, the present invention provides a matching interference type fiber Bragg grating sensor based on a completely random binary sequence.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: The present invention provides a matching interference type fiber Bragg grating sensor based on a completely random binary sequence, including a matching interference type fiber Bragg grating sensor, and the matching interference type fiber Bragg grating sensor includes a laser pulse generating unit, a phase modulation unit, and a sensing unit; The laser pulse generating unit is used to generate laser pulses; the phase modulation unit is connected to the laser pulse generating unit, and the phase modulation unit applies different modulation sequences to each laser pulse, modulating the phase of the laser pulse into a completely randomly distributed phase to reduce the self-coherence of the laser pulse; The laser pulses generated by the laser pulse generating unit are input to the sensing unit after passing through the phase modulation unit.

[0006] Further, the laser pulse generating unit includes a laser light source and an acousto-optic fiber modulator; the laser emitted by the laser light source is modulated into pulsed laser by the acousto-optic fiber modulator.

[0007] Further, the phase modulation unit includes an optical fiber phase modulator, a completely random binary sequence generating unit, a high-speed arbitrary waveform generator, and a phase modulator driver; The completely random binary sequence generating unit is used to generate a completely random binary sequence and input the completely random binary sequence to the high-speed arbitrary waveform generator. The high-speed arbitrary waveform generator generates high and low levels with completely random distribution according to the completely random binary sequence. The high and low levels with completely random distribution are input to the phase modulator driver, and the phase modulator driver modulates the optical fiber phase modulator, so that the phase of the laser pulse is modulated into a completely randomly distributed phase according to the distribution law of the high and low levels.

[0008] Further, the sensing unit includes a circulator and a sensing channel; the sensing channel is composed of a fiber grating and a sensing optical fiber.

[0009] Further, the completely random binary sequence is a binary sequence with completely random distribution containing 0 and 1, or the completely random binary sequence is a sequence with completely random distribution containing -1 and 1.

[0010] Further, the matched interference fiber grating sensor includes an optical fiber matched interferometer, and the optical fiber matched interferometer is connected in the optical path between the phase modulation unit and the sensing unit.

[0011] Further, the optical fiber matched interferometer includes a first optical fiber coupler, a first transmission arm, a second transmission arm, a second optical fiber coupler, and a delay optical fiber; the laser input to the optical fiber matched interferometer is divided into two beams by the first optical fiber coupler. One beam is transmitted to the second optical fiber coupler through the first transmission arm, and the delay optical fiber is connected to the first transmission arm. The other beam is transmitted to the second optical fiber coupler through the second transmission arm. The two pulsed laser beams with a certain time interval formed are combined and output by the second optical fiber coupler.

[0012] Further, the matched interference fiber grating sensor includes an optical fiber amplifier, and the optical fiber amplifier is connected in the optical path between the phase modulation unit and the sensing unit for amplifying the power of the pulsed laser.

[0013] Further, the sensing unit includes a backward light detection unit, and the backward light detection unit is connected to the circulator.

[0014] Further, a polarization switch is further included, and the pulsed laser output by the phase modulation unit is transmitted to the sensing unit after passing through the polarization switch; The polarization switching frequency of the polarization switch is 1 / 4 of that of the fiber optic acousto-optic modulator; when the previous pulse of the pulse pair output by the fiber optic coupler completely passes through the polarization switch, the polarization switch changes its polarization state once. Let the output polarization state of the first pulse pair be XX, the polarization state of the second pulse pair is XY, the polarization state of the third pulse pair is YY, the polarization state of the fourth pulse pair is YX, the polarization state of the fifth pulse pair is XX... and so on. Due to the presence of the polarization switch, the polarization states of the laser pulse pairs output to the fiber grating in the sensing channel are XX, XY, YY, YX, XX, XY, YY, YX, XX... in turn. Every four polarization states form a cycle. The polarization states of the backward light of the sensing channel transmitted to the pulse pairs of the backward light detection unit through the circulator are also XX, XY, YY, YX, XX... After collecting the pulse pairs of the four polarization states, a polarization synthesis algorithm is used for demodulation, which can effectively solve the signal disturbance caused by polarization random perturbation.

[0015] Compared with the prior art, the beneficial technical effects of the present invention are as follows: The matching interference type fiber grating sensor based on a completely random binary sequence provided by the present invention starts from the physical essence of light waves, and realizes the efficient suppression of Rayleigh scattering noise of the matching interference type fiber grating sensor through the means of signal phase modulation and demodulation, providing an important technical support for accelerating the engineering practicalization process of the matching interference type fiber sensor.

[0016] Specifically, by applying different modulation sequences to each laser pulse through the phase modulation unit, the phase of the laser pulse is modulated into a phase with a completely random distribution to reduce the self-coherence of the laser pulse, thereby suppressing the influence of Rayleigh scattering on the interference signal. The phases of the pulsed lasers are in a completely random distribution, so the cross-correlation coefficients between different pulses are very small, and thus the interference effect generated by Rayleigh scattering is also very weak. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0018] Figure 1 Schematic diagram of a matching interferometric fiber Bragg grating sensor based on a completely random binary sequence provided for Example 1; Figure 2 Schematic diagram of a matching interferometric fiber Bragg grating sensor based on a completely random binary sequence provided for Example 2; Figure 3 Schematic diagram of a matching interferometric fiber Bragg grating sensor based on a completely random binary sequence provided for Example 3; Figure 4 Schematic diagram of a matching interferometric fiber Bragg grating sensor based on a completely random binary sequence provided for Example 4; Figure 5 Schematic diagram of a matching interferometric fiber Bragg grating sensor based on a completely random binary sequence provided for Example 5; Figure 6 Schematic diagram of a matching interferometric fiber Bragg grating sensor based on a completely random binary sequence provided for Example 6; Figure 7 Relative amplitude diagram after phase modulation by a random binary sequence provided for an example; Figure 8 Relative intensity diagram of the light wave after phase modulation provided for an example; Figure 9 Power spectral density diagram after random binary phase modulation provided for an example; Figure 10 Schematic diagram of the autocorrelation function of a completely random binary sequence provided for an example; Figure 11 Schematic diagram of the cross-correlation function between two different completely random binary sequences provided for an example; Figure 12 Comparison diagram of the background phase noise before and after the technology of combining the polarization switching technology and the pseudo-random code in the matching interferometric fiber Bragg grating sensor provided for an example; Figure 13 Comparison diagram of the matching interferometric fiber Bragg grating sensor without pseudo-random code modulation, using the same set of pseudo-random codes for modulation of four polarization states, and using pseudo-random codes with different sorting methods for modulation of four polarizers respectively under the condition of a 10-km link length provided for an example.

[0019] Annotation of the attached figure: 1. Laser pulse generation unit; 101. Laser light source; 102. Fiber acousto-optic modulator; 103. Fiber acousto-optic modulator driver; 2. Phase modulation unit; 201. Fiber phase modulator; 202. Completely random binary sequence generation unit; 203. High-speed arbitrary waveform generator; 204. Phase modulator driver; 3. Sensing unit; 310. Sensing channel; 311. Fiber Bragg grating; 312. Sensing grating; 301. Circulator 4. Fiber optic matching interferometer; 401. First fiber optic coupler; 402. First transmission arm; 403. Second transmission arm; 404. Second fiber optic coupler; 405. Delay fiber 5. Retroreflection detection unit 6. Transmission link 7. Data acquisition card 8. Computer 9. Polarization switch 10. Attenuator 11. Piezoelectric ceramic Specific implementation mode

[0020] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0021] Refer to Figure 1 , Embodiment 1 provides a matching interference type fiber Bragg grating sensor based on a completely random binary sequence, including a matching interference type fiber Bragg grating sensor, and the matching interference type fiber Bragg grating sensor includes a laser pulse generation unit 1, a phase modulation unit 2, and a sensing unit 3; The laser pulse generation unit 1 is used to generate laser pulses; the phase modulation unit 2 is connected to the laser pulse generation unit 1, and the phase modulation unit 2 applies different modulation sequences to each laser pulse, modulating the phase of the laser pulse into a completely randomly distributed phase to reduce the self-coherence of the laser pulse; The laser pulses generated by the laser pulse generation unit 1 are input into the sensing unit 3 after passing through the phase modulation unit.

[0022] Refer to Figure 2 , Embodiment 2 provides a matching interference type fiber Bragg grating sensor based on a completely random binary sequence, including a matching interference type fiber Bragg grating sensor, and the matching interference type fiber Bragg grating sensor includes a laser pulse generation unit 1, a phase modulation unit 2, and a sensing unit 3; The laser pulse generation unit 1 is used to generate laser pulses; the phase modulation unit 2 is connected to the laser pulse generation unit 1, and the phase modulation unit 2 applies different modulation sequences to each laser pulse, modulating the phase of the laser pulse into a completely randomly distributed phase to reduce the self-coherence of the laser pulse; The laser pulse generated by the laser pulse generating unit 1 is input into the sensing unit 3 after passing through the phase modulation unit.

[0023] The laser pulse generating unit 1 includes a laser light source 101 and an acousto-optic fiber modulator 102; the laser emitted by the laser light source 101 is modulated into pulsed laser by the acousto-optic fiber modulator 102.

[0024] The phase modulation unit 2 includes an optical fiber phase modulator 201, a completely random binary sequence generating unit 202, a high-speed arbitrary waveform generator 203, and a phase modulator driver 204; The completely random binary sequence generating unit 202 is used to generate a completely random binary sequence, and input the completely random binary sequence into the high-speed arbitrary waveform generator 203. The high-speed arbitrary waveform generator 203 generates high and low levels with a completely random distribution according to the completely random binary sequence. The high and low levels with a completely random distribution are input into the phase modulator driver 204, and the phase modulator 204 drives and modulates the optical fiber phase modulator 201, so that the phase of the laser pulse is modulated into a completely random distribution according to the distribution law of the high and low levels.

[0025] Refer to Figure 7 , since the phase of the pulsed light wave output by the laser light source 101 is continuous before phase modulation, once a completely random distribution of high and low levels is applied to the phase modulator 201, the phase of the laser light wave will be modulated according to the distribution law of the levels, and the magnitude of the phase change is related to the response of the phase modulator 201 to the applied level. Ideally, the amplitude of the high and low levels just makes the phase of the optical fiber pulse change by π.

[0026] Refer to Figure 8 , different completely random binary sequences generate different numbers of level sequences, and the frequency of the high-speed arbitrary waveform generator 203 can be set to adjust the duration of each chip. Setting the frequency of the high-speed arbitrary waveform generator 203 can modulate the length of each optical wave segment.

[0027] The sensing unit 3 includes a circulator 301 and a sensing channel 310; the sensing channel 310 is composed of an optical fiber grating 311 and a sensing optical fiber 312.

[0028] It further includes a fiber optic matching interferometer 4, and the fiber optic matching interferometer 4 is connected in the optical path between the phase modulation unit 2 and the sensing unit 3. Specifically, the fiber optic matching interferometer 4 includes a first fiber optic coupler 401, a first transmission arm 402, a second transmission arm 403, a second fiber optic coupler 404, and a delay fiber 405; the laser input to the fiber optic matching interferometer 4 is divided into two beams by the first fiber optic coupler 401, one of which is transmitted to the second fiber optic coupler 404 through the first transmission arm 402, and the delay fiber 405 is connected to the first transmission arm 402, and the other is transmitted to the second fiber optic coupler 404 through the second transmission arm 403, and the two pulsed lasers with a certain time interval formed are combined and output by the second fiber optic coupler 404.

[0029] Generally, the optical path from the circulator 301 to the sensing channel 310 in the matching interference type fiber optic grating sensor is called the transmission link 6. In a large-scale fiber optic sensing system, the transmission link 6 often reaches dozens or even hundreds of kilometers. When the optical pulse passes through the optical fiber of this part of the link, the back-end Rayleigh scattering generated, because Rayleigh scattering is elastic scattering, its wavelength is the same as the wavelength of the pulsed laser that causes Rayleigh scattering, and the Rayleigh scattering caused by each pulse will accumulate and will interfere with the reflected interference light to produce an interference effect.

[0030] Referring to Figure 3 , compared with the embodiment 2, the matching interference type fiber optic grating sensor provided by the embodiment 3, the sensing unit 3 includes a backward light detection unit 5, and the backward light detection unit 5 is connected to the circulator 301. The photodetector of the backward light detection unit 5 will capture the interference generated by the above interference effect, and become the Rayleigh scattering phase noise of the interference signal.

[0031] Since the wavelength of the backward transmitted Rayleigh scattering noise is the same as that of the returned interference signal, that is, it can cause interference, the present invention applies different modulation sequences to each laser pulse through the phase modulation unit, modulates the phase of the laser pulse into a completely random distribution of phases, makes the phase continuity of the laser pulse be randomly modulated, and the phase continuity of the Rayleigh scattering light caused by the laser pulse is also disrupted into a completely random distribution in the forward and backward directions to reduce the self-coherence of the laser pulse.

[0032] The completely random binary sequence is a binary sequence with a completely random distribution containing 0 and 1, or the completely random binary sequence is a sequence with a completely random distribution containing -1 and 1. The binary sequence is an absolute random sequence, and the elements in the sequence are unknown and cannot be regenerated and replicated; at the same time, the autocorrelation or cross-correlation function characteristics of the completely random binary sequence have mathematical statistical characteristics similar to Gaussian white noise.

[0033] In one embodiment, a binary random sequence of {-1, 1} with 1000 numbers is generated using the random function: {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 1,1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 1, 1, 1, 1, 1, 1,1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 1, 1, 1,1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 1, 1, 1, 1, 1, 1,1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 1,1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1}, Referring to Figure 10 , which is the autocorrelation function of the sequence. It can be seen from the figure that there is only one peak at the zero point of the abscissa, that is, there is a maximum value when the two sequences completely overlap. Any misalignment will cause the autocorrelation function of the sequence to drop sharply. Therefore, modulating each pulse according to the same completely random sequence can reduce the Rayleigh scattering effect.

[0034] Since the Rayleigh scattering interference effect is related to the correlation coefficient between pulses, when different pulses are modulated with different completely random binary sequences, the cross-correlation function between two pulses can be further reduced compared with modulating with the same completely random binary sequence, thereby further reducing the Rayleigh scattering effect. Referring to Figure 11 , which is the cross-correlation function between any two different completely random binary sequences. It can be seen from the figure that after using different completely random binary sequences for different pulses, the peak value at the zero point of the abscissa is also greatly reduced. Theoretically, the number of arrangement methods of completely random binary sequences is close to infinitely many.

[0035] Referring to Figure 4, compared with Embodiment 3, the matching interference type fiber grating sensor based on a completely random binary sequence provided by Embodiment 4 has the completely random binary sequence output by the completely random binary sequence generation unit generated by a computer 8; a piezoelectric ceramic 11 is provided on the second transmission arm 403; and a data acquisition card 7 is further included. The data acquisition card 7 is respectively connected to a high-speed arbitrary waveform generator 203, a computer 8, a backward light detection unit 5, and a fiber acousto-optic modulator driver 103. The data acquisition card 7 can generate a high-frequency sine signal and output it to the piezoelectric ceramic 11 to realize carrier modulation of the phase of the light beam transmitted by the second transmission arm 403; the data acquisition card 7 can also generate a pulse signal and output it to the fiber acousto-optic modulator driver 103 to modulate the fiber acousto-optic modulator 102; the data acquisition card 7 can generate a trigger signal to trigger the high-speed arbitrary waveform generator 203 to generate a completely random signal. After receiving the trigger signal sent by the data acquisition card 7, the high-speed arbitrary waveform generator 203 starts to output a corresponding voltage waveform according to the characteristics of the completely random binary sequence. The output voltage waveform is transmitted to the phase modulator driver 204, and then the fiber phase modulator 201 is driven by the phase modulator driver 203 to generate a phase jump. There is a fixed time interval between the signal sent by the data acquisition card 7 to the fiber acousto-optic modulator driver 103 and the trigger signal output to the high-speed arbitrary waveform generator 203, and the specific time interval is determined according to the response delay of the high-speed arbitrary waveform generator 203.

[0036] Referring to Figure 5 , compared with Embodiment 4, the matching interference type fiber grating sensor based on a completely random binary sequence provided by Embodiment 5 further includes a polarization switch 9. The laser pulse generated by the phase modulation unit 2 passes through the polarization switch 9 and then is input into the transmission link 6 through the circulator 301, is transmitted to the sensing channel 310 through the transmission link 6, and the backward light of the sensing channel 310 is transmitted to the backward light detection unit 5 through the circulator 301. In this embodiment, the polarization switch 9 is connected to the optical path between the second fiber coupler 404 and the circulator 301 and is connected to the data acquisition card 7. Other structures and designs in Embodiment 5 can be the same as those in Embodiment 4.

[0037] The polarization switch 9 has a polarization switching frequency that is 1 / 4 of that of the fiber acousto-optic modulator 102; when the previous pulse of the pulse pair output by the fiber coupler completely passes through the polarization switch 9, the polarization switch 9 changes its polarization state once. Let the output polarization state of the first pulse pair be XX, the polarization state of the second pulse pair be XY, the polarization state of the third pulse pair be YY, the polarization state of the fourth pulse pair be YX, the polarization state of the fifth pulse pair be XX, and so on. By analogy, due to the presence of the polarization switch 9, the polarization states of the laser pulse pairs output to the fiber grating 311 in the sensing channel are XX, XY, YY, YX, XX, XY, YY, YX, XX... in sequence. Every four polarization states form a cycle. The polarization states of the return light of the sensing channel 310 transmitted to the pulse pair of the return light detection unit 5 via the circulator 301 are also XX, XY, YY, YX, XX... After collecting the pulse pairs of the four polarization states, a polarization synthesis algorithm is used for demodulation, which can effectively solve the signal perturbation caused by polarization random perturbation.

[0038] In this embodiment, to organically combine the pseudo-random code technology and the polarization switching technology, a set of completely random binary sequences needs to be prepared for each polarization state. The pseudo-random code sequences of the fiber grating-based sensor need at least four different sets of completely random binary sequences to prevent the increase in phase noise caused by the coincidence of random phases between different polarization states.

[0039] In this embodiment, it is necessary to precisely control the trigger delay between the fiber acousto-optic modulator 102 and the fiber polarization switch 9 to ensure that after the previous pulse of the pulse pair output by the second fiber coupler 404 completely passes through the polarization switch 9, the polarization switch 9 switches to an orthogonal polarization state.

[0040] In a specific embodiment, as Figure 5 shown, the output wavelength of its laser light source 101 is 1539.77 nm, the modulation frequency of the fiber acousto-optic modulator 102 is 250 kHz, the width of a single chip of the pseudo-random code sequence generated by the high-speed arbitrary waveform generator 203 is 2.4 ns, and the peak-to-peak voltage output by the phase modulator driver 204 is 5.5 V. A delay coil is provided on the first transmission arm 402, the fiber time delay of the delay coil is 500 ns, the round-trip time delay of the sensing fiber between adjacent fiber gratings is 500 ns, and the switching frequency of the polarization switch 9 is 62.5 kHz. When the previous pulse of the pulse pair output by the fiber coupler completely passes through the polarization switch 9, the polarization switch 9 changes its polarization state once. Let the output polarization state of the first pulse pair be XX, the polarization state of the second pulse pair be XY, the polarization state of the third pulse pair be YY, the polarization state of the fourth pulse pair be YX, the polarization state of the fifth pulse pair be XX, and so on. By analogy. A set of pseudo-random codes corresponding to each polarization state is as follows: The pseudo-random code corresponding to the XX polarization state is: {-1, 1, 1, 1, 1, 1, -1, 1, 1, -1, 1, 1, 1, -1, 1, 1, -1, -1, 1, 1, -1, -1, -1, 1, -1, 1, -1, 1, -1, 1, -1, 1, 1, -1, -1,1, -1, -1, -1, -1, -1, 1, -1, 1, 1, -1, -1, 1, -1, 1, 1, 1, -1, 1, -1, -1, -1, 1, 1, 1, 1, -1, 1, 1, -1, -1, -1, 1, 1, -1, 1, 1, 1, -1, -1, -1, 1, 1, -1,-1, -1, -1, 1, 1, -1, 1, 1, 1, -1, 1, -1, 1, -1, 1, 1, -1, 1, -1, -1, -1, 1,1, -1, -1, -1, 1, 1, -1, 1, -1, -1, 1, 1, 1, -1, -1, -1, -1, -1, 1, 1, -1, 1,1, 1, -1, -1, -1, -1, 1, -1, 1, 1, 1, -1, -1, 1, -1, 1, -1, 1, 1, -1, -1, -1,-1, 1, 1, -1, -1, -1, 1, 1, 1, 1, 1, -1, 1, -1, -1, 1, -1, 1, -1, -1, 1, -1,1, -1, 1, 1, -1, -1, -1, 1, -1, -1, -1, 1, -1, 1, -1, -1, 1, -1, 1, -1, -1,1, 1, 1, -1, -1, 1, 1, -1, -1, 1, 1, 1, -1, -1, 1, -1, 1, -1, -1, 1, -1, 1,1, -1, -1, -1, -1, 1, 1, -1, -1, -1, 1, 1, 1, 1, 1, -1, 1, -1, -1, -1, -1, -1, 1, 1, -1, -1, -1, -1, -1, -1, 1, -1, -1, -1, 1, 1, 1, 1, 1, 1, -1, 1, 1, -1, 1, -1, -1, -1, -1, 1, 1, -1, -1, -1, 1, 1, -1, -1, 1, 1, 1, -1, 1, 1, -1,-1, 1, -1, -1, 1, 1, 1, 1, 1,-1, -1, -1, -1, 1, -1, -1, -1, 1, 1, 1, 1, 1,1, -1, 1, 1, -1, -1, 1, 1, -1, 1, 1, -1, -1, -1, -1, -1, -1, -1, 1, -1, -1, -1, -1, -1, -1, 1, -1, 1, -1, -1, 1, -1, -1, 1, -1, 1, 1, 1, 1, 1, 1, 1, 1, -1, 1, 1, -1, 1, -1, 1, 1, 1, 1, 1, -1, 1, -1, 1, 1, 1, -1, 1, -1, 1, -1, 1,1, 1, -1, -1, 1, 1, 1, 1, -1, 1, -1, 1, 1, -1, 1, -1, 1, -1, -1, -1, -1, 1, -1, -1, -1, -1, -1, 1, 1, -1, -1, -1, -1, -1, 1, -1, -1, 1, 1, -1, 1, -1, -1,1, 1, 1, -1, -1, 1, -1, -1, 1, -1, 1, -1, -1, -1, -1, 1, 1, -1, -1, -1, -1,1, -1, 1, 1, 1, -1, -1, 1, -1, -1, 1, 1, -1, -1, -1, 1, 1, -1, 1, 1, -1, 1, -1, 1, 1, -1, -1, 1, 1, 1, 1, 1, 1, -1, -1, -1, 1, 1, -1, 1, -1, 1, -1, 1, 1,1, -1, -1, 1, -1, -1, -1, 1, -1, 1, -1, -1, 1, 1, -1, -1, -1, 1, -1, 1, -1,1, -1, -1, -1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, 1, 1, -1, 1, -1, -1, -1, -1,1, -1, 1, -1, 1, -1, 1, 1, 1, 1, 1, 1, -1, -1, 1, -1, -1, -1, 1, -1, 1, 1, 1,-1, -1, 1, -1, -1, -1, -1, 1, 1, -1, -1, -1, 1, 1, -1, -1, 1, 1, 1, -1, -1,1, -1, -1, -1, 1, 1, 1, -1, -1, -1, -1, -1,1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1, 1, 1, -1, -1, 1, -1, -1, -1, -1, 1, 1, -1, 1, 1, -1, 1, -1, -1, -1, 1, 1, 1, 1, 1, -1, -1, -1, -1, 1, -1, 1, -1, -1, 1, -1, 1, -1, 1, -1, 1, -1, 1, -1, -1, -1, 1, -1, -1, 1, 1, -1, 1, 1, -1, 1, -1, -1, 1, 1, -1, 1, 1, -1, -1, -1, -1, 1, -1, 1, 1, 1, -1, 1, 1, -1, -1, -1, 1, 1, -1, -1, 1, 1, -1,-1, 1, 1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, 1, 1, -1, 1, -1, 1,1, -1, -1, 1, -1, -1, 1, -1, -1, -1, 1, 1, 1, -1, 1, -1, 1, 1, -1, 1, 1, 1, -1, -1, 1, -1, -1, 1, -1, 1, 1, 1, -1, 1, -1, 1, 1, -1, 1, 1, -1, -1, 1, -1, -1, -1, 1, 1, -1, 1, 1, -1, -1, -1, 1, -1, 1, -1, -1, 1, 1, -1, 1, -1, 1, 1,1, 1, 1, -1, 1, 1, 1, -1, -1, -1, -1, -1, -1, 1, 1, -1, 1, 1, 1, 1, 1, -1, 1,-1, -1, 1, -1, -1, -1, 1, 1, 1, 1, 1, 1, -1, 1, 1, -1, -1, 1, -1, 1, -1, 1, -1, 1, 1, -1, -1, 1, -1, -1, 1, -1, 1, 1, -1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1, 1, 1, 1, 1, -1, -1, -1, 1, -1, 1, 1, 1, -1, 1, -1, -1, 1, 1, -1, 1, -1, -1, -1, -1, -1, 1, -1, 1, -1, -1, 1, -1, -1, 1,1, 1, 1, -1, 1, -1, 1, -1,-1, 1, 1, -1, -1, 1, -1, -1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, 1, -1, -1, -1, 1,-1, -1, 1, 1, -1, -1, -1, -1, 1, 1, 1, 1, -1, 1, -1, 1, 1, -1, -1, -1, 1, -1,-1, -1, -1, -1, 1, -1, 1, -1, 1, -1, -1, 1, 1, 1, -1, 1, -1, -1, -1, -1, -1,-1, -1, -1, -1, 1, 1, -1, 1, 1, 1, -1, -1, 1, 1, -1, -1, 1, 1, 1, -1, 1, 1, -1, -1, -1, 1, -1, -1, 1, 1, -1, -1, 1, -1, 1, -1, 1, 1, 1, -1, 1, 1, 1, -1,1, 1, -1, 1, -1, 1, -1, -1, -1, 1, -1, -1, 1, 1, -1, 1, 1, -1, 1, -1, 1, -1}, The pseudo-random code corresponding to the XY polarization state is: {-1, 1, -1, 1, 1, -1, -1, 1, -1, 1, -1, -1, -1, 1, -1, -1, 1, 1, 1, -1, -1, 1, -1, -1, 1, 1, -1, 1, -1, 1, -1, -1, 1, -1, -1, 1, -1, -1, -1, -1, -1, -1, 1, 1, -1, -1, 1, 1, 1, 1, -1, 1, -1, -1, -1, 1, -1, 1, 1, -1, 1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, -1, 1, 1, -1, -1, -1, 1, 1, 1, 1, -1, 1, 1, -1, 1, -1, -1, -1, 1, 1, 1, -1, -1, -1, -1, 1, -1, -1, 1, -1, -1, 1, 1, 1, 1, 1, 1, -1, -1, 1, 1, 1, 1, -1, -1, -1, -1, 1, -1, 1, 1, 1, -1, 1, -1, -1, 1, 1, -1, 1, -1, 1, -1, -1, -1, 1, 1, 1, 1, 1, -1, 1, -1, 1, -1, 1, 1, -1, 1, -1, -1, 1, 1, 1, -1, -1, -1, -1, 1, 1, -1, 1, 1, 1, 1, -1, -1, 1, -1, 1, 1, -1, 1, -1, -1, 1, -1, -1, -1, -1, 1, 1, -1, 1, 1, 1, 1, -1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 1, -1, 1, -1, -1, 1, 1, 1, 1, 1, 1, 1, -1, -1, 1, -1, 1, -1, -1, -1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, 1, 1, -1, 1, -1, -1, 1, 1, 1, 1, 1, 1, -1, -1, 1, -1, -1, -1, 1, 1, 1, 1, 1, 1, -1, 1, -1, -1, -1, 1, 1, 1, -1, 1, 1, -1, -1, 1, 1}-1, -1, -1, 1, -1, 1, 1, -1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, 1, -1, 1, 1, -1, -1, -1, 1, -1, 1, -1, -1, 1, 1, 1, -1, -1, 1, 1, -1, -1, -1, 1, -1, -1, -1, -1, -1, -1, -1, -1, 1, -1, 1, -1, -1, 1,1, -1, -1, -1, 1, 1, 1, -1, 1, 1, -1, 1, -1, 1, 1, 1, -1, 1, -1, 1, 1, 1, -1,-1, -1, 1, 1, -1, 1, -1, -1, -1, 1, 1, 1, -1, -1, -1, -1, 1, -1, -1, 1, -1,1, 1, 1, -1, 1, 1, 1, -1, 1, -1, 1, 1, -1, 1, -1, 1, -1, 1, 1, 1, -1, -1, 1,1, -1, -1, 1, 1, -1, 1, 1, 1, -1, -1, -1, 1, -1, 1, -1, -1, 1, 1, 1, -1, -1,-1, 1, 1, 1, 1, 1, 1, -1, -1, 1, 1, -1, -1, -1, -1, -1, 1, -1, -1, 1, -1, -1,-1, -1, -1, 1, -1, 1, 1, 1, 1, 1, 1, -1, 1, -1, -1, -1, -1, -1, 1, -1, 1, 1,1, -1, -1, -1, 1, -1, -1, -1, 1, 1, 1, -1, 1, -1, -1, 1, -1, 1, 1, -1, -1, -1, -1, 1, -1, 1, -1, 1, -1, -1, -1, -1, -1, 1, -1, -1, 1, -1, -1, -1, -1, 1,-1, 1, 1, -1, -1, 1, -1, -1, -1, 1, 1, -1, 1, -1, -1, 1, -1, -1, -1, 1, -1,1, -1, -1, 1, -1, 1, 1, 1, 1, -1, -1, -1, 1, -1, 1, -1, -1, 1, 1, 1, -1, -1,-1, 1, 1, 1, 1, 1, -1, 1, 1, 1, 1, -1, 1,-1, 1, 1, -1, 1, -1, 1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, 1, -1, -1, 1, -1, -1, -1, -1, 1, -1, 1, -1, -1, -1, -1, 1, -1, 1, -1, -1, 1, -1, 1, 1, -1, -1, -1, 1, -1, -1, 1, 1, -1, 1, -1, 1,1, 1, -1, -1, 1, 1, -1, -1, -1, -1, -1, -1, -1, 1, 1, 1, -1, 1, -1, -1, 1, 1,-1, -1, -1, -1, -1, -1, -1, 1, 1, -1, 1, -1, 1, 1, -1, -1, -1, 1, -1, 1, 1,1, -1, -1, -1, 1, -1, -1, 1, 1, -1, 1, -1, -1, 1, 1, 1, -1, -1, 1, 1, -1, 1,-1, -1, 1, -1, 1, -1, -1, -1, -1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, 1, -1, 1,-1, 1, 1, -1, 1, -1, -1, 1, -1, -1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, 1, 1, -1, 1, -1, 1, 1, -1, 1, 1, -1, -1, 1, 1, 1, -1, -1, 1, 1, -1, 1, 1, 1, -1, -1,-1, -1, -1, 1, -1, -1, 1, 1, -1, 1, 1, 1, -1, -1, -1, -1, -1, -1, 1, -1, -1,1, -1, -1, 1, 1, -1, 1, -1, 1, 1, -1, -1, -1, -1, -1, 1, 1, -1, 1, -1, 1, 1,1, -1, 1, -1, -1, -1, 1, -1, -1, -1, 1, 1, 1, 1, -1, -1, 1, -1, 1, 1, -1, -1,-1, 1, 1, -1, 1, -1, 1, 1, -1, -1, 1, 1, 1, -1, -1, 1, 1, -1, 1, 1, -1, -1, -1, -1, -1, 1, -1, 1, 1, -1, 1, 1, -1, 1, -1, 1,-1, -1, 1, 1, 1, 1, -1, 1, -1, -1, -1, 1, 1, 1, 1, 1, -1, -1, -1, 1, -1, 1, -1, -1, -1, -1, 1, 1, 1, 1,1, 1, -1, -1, -1, -1, -1, -1, -1, 1, -1, -1, -1, -1, 1, -1, -1, 1, -1, -1, -1, 1, -1, -1, 1, -1, 1, 1, -1, 1, 1, 1, 1, 1, -1, -1, 1, 1, 1, -1, 1, -1, 1,1, 1, -1, 1, 1, -1, -1, -1, 1, 1, -1, 1, -1, -1, -1, -1, 1, -1, -1, 1, 1, -1,1, -1, 1, 1, -1, -1, 1, 1, -1, -1, -1, 1, 1, 1, -1, -1, 1, -1, -1, -1, 1, -1,-1, 1, 1, 1, -1, 1, 1, 1, -1, 1, -1, 1, 1, -1, -1, -1, -1, -1, 1, -1, 1, 1,1, 1}, The pseudo-random code corresponding to the YY polarization state is: {-1, 1, 1, 1, 1, 1, 1, -1, -1, 1, -1, 1, -1, 1, -1, 1, -1, 1, -1, -1, 1, -1, -1, 1, -1, 1, 1, 1, 1, -1, -1, -1, 1, -1, -1, -1, -1, -1, -1, -1, 1, 1, -1, -1, -1, -1, -1, 1, 1, -1, 1, -1, -1, -1, 1, 1, 1, -1, -1, -1, -1, 1, -1, -1, 1, -1, -1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, -1, -1, 1, -1, 1, 1, 1, 1, -1, 1, 1, -1, -1, -1, -1, -1, 1, 1, -1, 1, -1, -1, 1, -1, -1, -1, -1, 1, -1, 1, 1, -1, -1, 1, -1, 1, 1, -1, 1, -1, 1, -1, 1, -1, 1, 1, 1, 1, 1, -1, -1, -1, 1, -1, -1, 1, 1, -1, 1, -1, -1, -1, -1, -1, -1, -1, 1, 1, -1, 1, 1, 1, 1, 1, -1, 1, 1, -1, -1, 1, -1, -1, 1, -1, -1, -1, -1, 1, -1, 1, 1, -1, 1, -1, 1, -1, 1, 1, -1, -1, 1, 1, 1, 1, -1, 1, -1, 1, -1, 1, 1, 1, 1, -1, 1, 1, 1, -1, 1, -1, -1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, 1, 1, -1, -1, -1, -1, 1, 1, 1, 1, 1, -1, -1, -1, 1, 1, -1, -1, -1, 1, 1, 1, -1, 1, 1, -1, 1, 1, -1, -1, -1, 1, -1, 1, -1, -1, 1, 1, 1, 1, 1, 1, -1, 1, -1, -1, -1, 1, 1, 1, 1, 1, 1, 1, 1, -1, 1, -1, 1, 1, -1, 1, 1, 1, -1, 1, 1, 1, -1, -1, -1, -1, -1, -1, 1}-1, 1, -1, 1, 1, 1, 1, 1, -1, 1, -1, 1, 1, -1, -1,-1, 1, 1, 1, -1, -1, -1, -1, -1, -1, 1, -1, 1, 1, -1, -1, 1, 1, -1, 1, 1, 1,1, -1, 1, 1, -1, -1, 1, 1, 1, 1, 1, -1, -1, -1, -1, 1, 1, -1, -1, -1, 1, -1,1, -1, 1, 1, -1, -1, -1, -1, -1, -1, 1, -1, 1, 1, 1, 1, 1, 1, 1, -1, 1, 1, 1,1, -1, 1, 1, 1, 1, -1, 1, 1, -1, 1, -1, -1, 1, 1, -1, 1, -1, -1, -1, -1, -1,-1, -1, -1, 1, 1, -1, -1, -1, -1, 1, -1, 1, -1, 1, 1, 1, 1, 1, 1, -1, 1, -1,-1, -1, -1, -1, -1, -1, -1, 1, 1, 1, -1, 1, 1, 1, -1, 1, -1, 1, 1, 1, -1, 1,1, 1, -1, -1, -1, -1, -1, -1, 1, 1, -1, 1, 1, 1, -1, 1, -1, 1, 1, -1, 1, 1, -1, -1, -1, -1, -1, 1, -1, 1, -1, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1,1, -1, -1, 1, 1, -1, -1, -1, -1, -1, -1, -1, 1, 1, 1, -1, -1, -1, -1, -1, 1,-1, -1, 1, -1, -1, -1, -1, 1, 1, -1, 1, -1, 1, 1, -1, -1, 1, -1, -1, -1, -1,1, 1, 1, -1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, 1, -1, 1, -1, -1, 1, 1, 1, 1,-1, -1, -1, -1, 1, 1, -1, -1, -1, 1, -1, 1, -1, 1, 1, 1, -1, -1, 1, 1, -1, 1,1, 1, 1, 1, -1, -1, 1, -1, -1, 1,-1, 1, -1, 1, 1, -1, -1, 1, -1, 1, 1, -1,1, 1, 1, 1, 1, -1, 1, 1, 1, 1, 1, 1, -1, 1, -1, -1, -1, -1, 1, -1, 1, 1, 1,1, -1, -1, 1, -1, -1, -1, 1, -1, 1, -1, -1, -1, -1, 1, 1, -1, 1, -1, -1, 1,1, 1, -1, 1, 1, 1, 1, -1, -1, 1, -1, -1, -1, 1, 1, 1, 1, 1, 1, -1, -1, 1, 1,1, 1, 1, -1, -1, 1, -1, 1, 1, -1, -1, 1, 1, 1, 1, -1, 1, -1, 1, 1, 1, -1, 1,1, -1, -1, 1, 1, 1, 1, 1, -1, 1, 1, -1, -1, 1, -1, -1, 1, 1, 1, -1, 1, -1, 1,-1, 1, 1, -1, -1, 1, -1, 1, 1, 1, 1, 1, 1, -1, -1, 1, -1, 1, -1, 1, 1, -1, -1, -1, -1, 1, 1, -1, -1, 1, -1, 1, -1, 1, -1, 1, -1, -1, 1, 1, -1, 1, -1, 1,1, 1, -1, 1, 1, -1, -1, -1, -1, 1, -1, 1, 1, -1, 1, -1, 1, -1, 1, -1, 1, -1,-1, -1, 1, 1, 1, 1, -1, 1, -1, -1, 1, -1, 1, -1, 1, 1, -1, -1, 1, -1, -1, -1,-1, -1, 1, 1, 1, -1, -1, 1, -1, -1, 1, 1, -1, 1, -1, 1, 1, -1, 1, 1, -1, -1,-1, -1, 1, 1, -1, 1, -1, 1, -1, -1, 1, 1, 1, -1, 1, -1, 1, 1, -1, 1, 1, -1, -1, -1, 1, 1, 1, -1, -1, 1, 1, 1, 1, 1, -1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1,1, 1, -1, 1, -1, -1, -1, -1, -1, -1, 1, 1, 1,1, -1, -1, 1, -1, 1, 1, -1, 1,-1, 1, 1, -1, -1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, 1, 1, 1, -1, 1, -1, 1,-1, 1, 1, -1, 1, -1, -1, 1, -1, -1, -1, 1, 1, 1, -1, -1, 1, -1, -1, -1, -1,1, 1, -1, -1, -1, -1, 1, -1, 1, -1, -1, 1, 1, -1, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1, 1, -1, 1, 1, -1, 1, 1, 1, -1, -1, -1, -1, -1, 1, -1, -1, -1, -1,1, -1, -1, -1, 1, -1, 1, 1, -1, 1, -1, 1, 1, 1, -1, -1, -1, 1, 1, 1, -1, 1,1, -1, 1, -1, 1, 1, -1, 1, 1, -1, -1, 1, -1, 1, 1, -1}, The pseudo-random code corresponding to the YX polarization state is: {1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1, 1, 1, 1, -1, 1, 1, -1, 1, -1, 1, -1, 1, -1, 1, -1, 1, -1, -1, 1, -1, 1, 1, 1, 1, -1, -1, -1, 1, 1, -1, 1, 1, -1, -1, -1, 1, 1, -1, 1, -1, 1, 1, 1, 1, -1, 1, -1, -1, 1, -1, -1, 1, -1, 1, -1, -1, 1, 1, -1, -1, -1, 1, -1, -1, 1, 1, 1, -1, 1, 1, 1, 1, -1, 1, -1, -1, -1, -1, -1, 1, 1, -1, -1, -1, -1, -1, -1, 1, 1, 1, -1, -1, -1, 1, 1, 1, -1, -1, -1, 1, 1, -1, -1, -1, 1, 1, 1, 1, -1, -1, -1, 1, -1, -1, -1, 1, 1, -1, 1, 1, 1, -1, 1, 1, -1, -1, -1, 1, -1, -1, -1, -1, 1, -1, 1, -1, -1, -1, -1, 1, 1, -1, 1, -1, 1, -1, 1, -1, 1, -1, -1, -1, 1, -1, 1, -1, -1, 1, -1, -1, -1, 1, 1, -1, -1, 1, -1, 1, -1, -1, 1, 1, -1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1, 1, -1, 1, 1, 1, -1, 1, -1, -1, 1, 1, -1, 1, -1, 1, -1, 1, 1, 1, -1, 1, -1, 1, 1, -1, -1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, 1, 1, 1, 1, 1, -1, -1, 1, -1, -1, 1, -1, 1, -1, 1, -1, 1, 1, -1, -1, -1, 1, 1, -1, 1, 1, 1, -1, 1, -1, 1, 1, -1, -1, -1, 1, -1, 1, -1, -1, 1, 1, 1, 1, -1, -1, 1, -1, 1, -1, 1,1, -1, -1, 1, -1, -1, -1, 1, -1, -1, 1, -1, -1, -1, -1, 1, 1, 1, -1, -1, 1, -1, -1, -1, -1, 1, -1, 1, -1, -1, -1, 1, 1, 1, -1,-1, -1, -1, -1, 1, -1, 1, 1, -1, 1, -1, -1, -1, 1, 1, 1, -1, 1, -1, 1, 1, 1,-1, -1, 1, 1, -1, -1, -1, 1, -1, -1, 1, -1, -1, 1, 1, 1, -1, -1, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 1, -1, -1, 1, 1, -1, -1, -1, -1, 1, -1, -1, 1,1, -1, 1, 1, 1, 1, -1, 1, -1, -1, -1, -1, -1, 1, 1, -1, 1, -1, -1, 1, -1, 1,1, 1, -1, -1, 1, -1, 1, -1, 1, 1, -1, 1, 1, 1, -1, -1, 1, -1, -1, 1, 1, 1, 1,-1, -1, -1, 1, 1, 1, 1, 1, -1, -1, 1, -1, -1, 1, -1, -1, -1, 1, -1, -1, -1,1, -1, -1, -1, -1, -1, 1, 1, 1, 1, 1, -1, 1, 1, 1, 1, -1, -1, -1, 1, -1, -1,1, -1, 1, 1, -1, 1, 1, -1, -1, 1, -1, -1, 1, -1, 1, -1, -1, -1, -1, 1, -1, 1,-1, 1, -1, 1, -1, 1, 1, 1, -1, -1, 1, 1, -1, -1, -1, 1, 1, -1, 1, 1, -1, -1,-1, -1, 1, -1, -1, 1, 1, -1, 1, 1, 1, -1, 1, -1, 1, -1, -1, -1, -1, -1, -1,1, 1, 1, -1, 1, -1, 1, -1, -1, 1, -1, 1, 1, 1, -1, -1, -1, 1, 1, 1, 1, 1, 1,1, -1, 1, 1, 1, 1, 1, -1, -1, -1, -1,-1, -1, 1, -1, 1, 1, -1, 1, -1, 1, 1, -1, 1, 1, -1, 1, -1, 1, -1, 1, 1, -1, 1, -1, 1, 1, -1, 1, -1, -1, 1, -1, 1, 1,-1, -1, -1, 1, -1, 1, -1, 1, 1, -1, -1, 1, -1, 1, 1, 1, -1, 1, 1, 1, 1, 1, 1,1, -1, -1, -1, -1, 1, -1, -1, -1, -1, 1, -1, -1, -1, -1, 1, -1, 1, 1, -1, 1,1, -1, 1, -1, 1, -1, -1, 1, -1, -1, -1, -1, -1, 1, 1, 1, 1, -1, 1, -1, 1, -1,1, -1, 1, -1, -1, -1, -1, 1, -1, 1, -1, 1, -1, -1, 1, 1, 1, 1, 1, 1, -1, 1, -1, -1, 1, -1, -1, 1, -1, -1, -1, 1, 1, -1, -1, -1, 1, -1, -1, -1, 1, 1, 1, -1, -1, -1, 1, 1, 1, 1, 1, -1, 1, 1, 1, -1, -1, -1, 1, -1, 1, 1, -1, -1, 1, 1,-1, -1, 1, 1, -1, 1, -1, -1, -1, -1, 1, 1, -1, -1, -1, -1, 1, -1, 1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, -1, 1, 1, 1, 1, -1, -1, -1, 1, 1, -1, 1, -1,-1, -1, 1, -1, -1, 1, -1, 1, 1, 1, 1, 1, 1, -1, 1, 1, 1, -1, 1, -1, 1, -1, -1, 1, -1, 1, 1, 1, -1, 1, -1, 1, -1, 1, -1, 1, -1, -1, -1, 1, 1, -1, 1, -1, -1, 1, -1, 1, -1, 1, 1, 1, 1, -1, -1, 1, -1, 1, -1, 1, 1, -1, -1, 1, 1, 1, 1,-1, 1, -1, 1, -1, 1, 1, -1, -1, 1, -1, -1,1, 1, 1, 1, 1, 1, -1, 1, -1, 1, 1,-1, -1, -1, 1, -1, -1, 1, 1, 1, -1, -1, -1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, 1, 1, -1, -1, 1, -1, 1, 1, -1, 1, 1, 1, -1, 1, 1, -1, 1, 1, 1, -1, -1, -1,-1, 1, 1, -1, -1, -1, -1, -1, -1, -1, 1, -1, 1, -1, -1, 1, -1, 1, 1, -1, 1,1, 1, -1, 1, -1, 1, 1, -1, 1, 1, -1, -1, -1, 1, 1, -1, -1, -1, 1, 1, 1, -1, -1, 1, 1, 1, -1, 1, 1, 1, 1, -1, 1, -1, -1, -1, -1, 1, -1, -1, -1, -1, 1,-1, 1, 1, -1, -1, -1, 1, -1, 1, -1, 1, -1, -1, -1, 1, 1, 1, 1, -1, 1, 1, -1}.

[0041] Based on the above settings in this embodiment, the changes in the background phase noise before and after the technology that combines polarization switching technology and pseudo-random code are started are as follows Figure 12 shown. Before starting the technology that combines polarization switching technology and pseudo-random code, the background phase noise of the system is close to -60 dB@1kHz. After starting the technology that combines polarization switching technology and pseudo-random code, the background phase noise of the system is reduced by about 20 dB.

[0042] Figure 13 is a comparison diagram of the matching interferometric fiber grating sensor under the condition of a 10-kilometer link length without pseudo-random code modulation, using the same set of pseudo-random codes for modulation of four polarization states, and using pseudo-random codes with different sorting methods for four polarizers respectively. Refer to Figure 13 It can be seen that under the condition of a 10-kilometer transmission distance, the background noise suppression effects of not using pseudo-random code modulation, using the same pseudo-random code for modulation of four polarization states (XX, XY, YY, YX), and using different pseudo-random codes for modulation of four polarization states are compared. Among them, in the first case, without pseudo-random code modulation, based on Figure 4 the structure in, where Figure 4However, the computer 8 does not generate a pseudo-random code sequence and provide it to the high-speed arbitrary waveform generator 203, that is, the matched interferometric fiber grating sensor does not use pseudo-random code modulation. In the second case, the same set of pseudo-random code modulation is used for the four polarization states. Based on Figure 3 the structure in, the computer 8 generates a pseudo-random code sequence {-1, 1} sequence and imports it into the high-speed arbitrary waveform generator 203. The high-speed arbitrary waveform generator 203 will output corresponding waveforms according to the pseudo-random code sequence input by the computer 8. By connecting the fiber optic phase modulator 201 to the matched interferometric fiber grating sensor system to adjust the phase of the laser pulse, the self-coherence of the laser pulse is changed, thereby suppressing the influence of Rayleigh scattering on the interference signal. The third case is to add a polarization switch 9 in the structure shown in Figure 4 , and its structure is as shown in Figure 5 , and different sorting methods of pseudo-random code modulation are used for the four polarizers respectively. Specifically, the pseudo-random codes corresponding to the XX polarization state, the pseudo-random codes corresponding to the XY polarization state, the pseudo-random codes corresponding to the YX polarization state, and the pseudo-random codes corresponding to the YY polarization state adopt the specific forms provided above, which will not be elaborated here. In the three cases, except for the different choices of whether to perform pseudo-random code modulation and whether to organically combine the pseudo-random code modulation technology and the polarization suppression technology, the selection and conditions of other devices are exactly the same. Under the condition of a 10-kilometer link length, the effects of the schemes of not performing pseudo-random code modulation on the matched interferometric fiber grating sensor, using the same set of pseudo-random code modulation for the four polarization states, and using different sorting methods of pseudo-random code modulation for the four polarizers are compared. The results are as shown in Figure 13 . It can be seen from Figure 13 that when the same pseudo-random code is used for modulation of the four polarization states, not only the suppression effect is not as good as that when different pseudo-random codes are used for modulation of the four polarization states, but also virtual signals appear in the demodulation results.

[0043] Referring to Figure 6 , compared with Embodiment 5, the matched interferometric fiber grating sensor based on a completely random binary sequence provided in Embodiment 6 is a multi-sensing channel multiplexing structure. Except for the increase in the number of sensing channels 310, the rest of the structure remains the same as that of the single-channel sensor. Specifically, the sensing channel 310 is a single-channel fiber grating type sensing channel, multiple time-division channel fiber grating type sensing channels, or multiple wavelength-division channel fiber grating type sensing channels. Multiple time-division channels mean that laser pulses of the same wavelength can realize sensing of multiple channels, and each channel is arranged in sequence in time. Wavelength division multiplexing means that different wavelengths of pulses are used for sensing, and each wavelength is transmitted to one or more channels, and each channel only acts on one wavelength.

[0044] Referring to Figure 9, In one embodiment, experiments verified that in the case of 10 km link transmission, due to the existence of Rayleigh scattering, the background noise of the system was close to -62 dB@1kHz. In the experiment, the optical transmission from the laser light source 101 to the fiber coupler was all based on single-mode polarization-maintaining fiber. In this experiment, the modulation frequency of the fiber acousto-optic modulator 102 was 250 kHz, the output frequency of the high-speed arbitrary waveform generator 203 was 312.5 kHz, the output duration of a single value in the completely random sequence was 2.4 ns, the peak-to-peak voltage output after being driven by the phase modulator 204 was 5.5 V, and the round-trip time delay of the sensing fiber between the fiber gratings 311 was 500 ns. After starting the pseudo-random code modulation, the background noise of the system was reduced to -80 dB@1kHz. The suppression of Rayleigh scattering exceeded 15 dB.

[0045] Matters not described in this invention are well-known techniques.

[0046] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0047] The above-described embodiments merely represent several implementation manners of this application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of this application, several modifications and improvements can still be made, and these all belong to the protection scope of this application. Therefore, the protection scope of this application should be subject to the appended claims.

[0048] The above is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A matching interference type fiber Bragg grating sensor based on a completely random binary sequence, characterized in that Including a matched interference fiber Bragg grating sensor, the matched interference fiber Bragg grating sensor includes a laser pulse generating unit, a phase modulation unit, and a sensing unit; The laser pulse generating unit is used to generate laser pulses; the phase modulation unit is connected to the laser pulse generating unit, and the phase modulation unit applies different modulation sequences to each laser pulse, modulating the phase of the laser pulse into a completely randomly distributed phase to reduce the self-coherence of the laser pulse; The laser pulses generated by the laser pulse generating unit are input into the sensing unit after passing through the phase modulation unit.

2. The matching interference type fiber grating sensor based on a completely random binary sequence according to claim 1, characterized in that, The laser pulse generating unit includes a laser light source and an acousto-optic fiber modulator; the laser emitted by the laser light source is modulated into pulsed laser by the acousto-optic fiber modulator.

3. The matching interference type fiber grating sensor based on a completely random binary sequence according to claim 1, characterized in that, The phase modulation unit includes an optical fiber phase modulator, a completely random binary sequence generating unit, a high-speed arbitrary waveform generator, and a phase modulator driver; The completely random binary sequence generating unit is used to generate a completely random binary sequence and input the completely random binary sequence into the high-speed arbitrary waveform generator. The high-speed arbitrary waveform generator generates high and low levels with completely random distribution according to the completely random binary sequence, and the high and low levels with completely random distribution are input into the phase modulator driver. The phase modulator driver modulates the optical fiber phase modulator to modulate the phase of the laser pulse into a completely randomly distributed phase according to the distribution law of the high and low levels.

4. The matching interference type fiber grating sensor based on a completely random binary sequence according to claim 1, wherein The sensing unit includes a circulator and a sensing channel; the sensing channel is composed of a fiber Bragg grating and a sensing optical fiber.

5. The matching interference type fiber grating sensor based on a completely random binary sequence according to claim 3, characterized in that, The completely random binary sequence is a binary sequence with completely random distribution containing 0 and 1, or the completely random binary sequence is a sequence with completely random distribution containing -1 and 1.

6. The matching interference type fiber grating sensor based on a completely random binary sequence according to claim 1, wherein, The matched interference fiber Bragg grating sensor includes an optical fiber matched interferometer, and the optical fiber matched interferometer is connected in the optical path between the phase modulation unit and the sensing unit.

7. The matching interference type fiber grating sensor based on a completely random binary sequence according to claim 6, characterized in that, The optical fiber matched interferometer includes a first optical fiber coupler, a first transmission arm, a second transmission arm, a second optical fiber coupler, and a delay optical fiber; the laser input into the optical fiber matched interferometer is divided into two beams by the first optical fiber coupler. One beam is transmitted to the second optical fiber coupler through the first transmission arm, and a delay optical fiber is connected to the first transmission arm. The other beam is transmitted to the second optical fiber coupler through the second transmission arm. The two pulsed lasers with a certain time interval formed are combined and output by the second optical fiber coupler.

8. The matching interference type fiber grating sensor based on a completely random binary sequence according to claim 1, characterized in that, The matched interference fiber Bragg grating sensor includes an optical fiber amplifier, and the optical fiber amplifier is connected in the optical path between the phase modulation unit and the sensing unit for amplifying the power of the pulsed laser.

9. The matching interference type fiber grating sensor based on a completely random binary sequence according to claim 4, wherein The sensing unit includes a backward light detection unit, and the backward light detection unit is connected to the circulator.

10. The matching interference type fiber grating sensor based on a completely random binary sequence according to any one of claims 1 to 9, characterized in that, It also includes a polarization switch, and the pulsed laser output by the phase modulation unit is transmitted to the sensing unit after passing through the polarization switch; The polarization switch has a polarization switching frequency that is 1 / 4 of that of the acousto-optic modulator; when the previous pulse of the output pulse pair of the fiber coupler completely passes through the polarization switch, the polarization switch changes its polarization state once. Let the output polarization state of the first pulse pair be XX, the polarization state of the second pulse pair be XY, the polarization state of the third pulse pair be YY, the polarization state of the fourth pulse pair be YX, the polarization state of the fifth pulse pair be XX, and so on. By analogy, due to the presence of the polarization switch, the polarization states of the laser pulse pairs output to the fiber grating in the sensing channel are XX, XY, YY, YX, XX, XY, YY, YX, XX... in sequence. Every four polarization states form a cycle. The polarization states of the return light of the sensing channel transmitted to the pulse pairs of the return light detection unit via the circulator are also XX, XY, YY, YX, XX... After collecting the pulse pairs of the four polarization states, a polarization synthesis algorithm is used for demodulation, which can effectively solve the signal perturbation caused by polarization random perturbation.

Images