A brillouin optical time domain analyzer based on pseudo-random sequences

Abstract

The application relates to a Brillouin optical time domain analyzer based on a pseudo-random sequence, wherein continuous laser generated by a laser is divided into two branches by an optical coupler, and the two branches are respectively incident into a pumping branch and a detection branch; a signal generating circuit module generates a radio frequency signal of a pseudo-random sequence to drive the pumping branch, and generates a continuous radio frequency signal with Brillouin frequency shift to drive the detection branch; unipolar pseudo-random sequence coded laser generated by the pumping branch and single sideband detection light generated by the detection branch are respectively incident into a sensing optical fiber to be detected; the detection light and the pseudo-random sequence coded laser are transmitted in opposite directions in the sensing optical fiber and interact to generate stimulated Brillouin scattering signals; the detection light is swept, the coding detection and decoding steps are repeated after each frequency adjustment, and a Brillouin gain spectrum is constructed. Compared with the prior art, the Brillouin scattering signal SNR and detection efficiency are significantly improved under the premise of not affecting the spatial resolution and detection time, and efficient sensing of medium and long distance distributed temperature / strain is realized.

Description

Technical Field

[0001] This invention relates to the field of optical measurement and sensing technology, and in particular to a Brillouin optical time-domain analyzer system based on pseudo-random sequences. Background Technology

[0002] Brillouin optical time-domain analyzers (OTD-A) are an important branch of distributed fiber optic sensing technology, capable of providing strain or temperature sensing capabilities for dense arrays, and have been widely used in structural health monitoring, perimeter security, and other fields. This technology is based on the stimulated Brillouin scattering effect of optical fibers, achieving sensing through changes in the Brillouin frequency shift caused by strain / temperature. However, in practical long-distance sensing applications, environmental noise and the fixed loss of the sensing fiber (approximately 0.2 dB / km) significantly reduce the signal-to-noise ratio at the far end, making it difficult to effectively detect the measured parameters. Therefore, improving the signal-to-noise ratio of the Brillouin sensing signal has become a key issue in engineering practice.

[0003] In traditional solutions, increasing the input optical power is one way to improve the signal-to-noise ratio (SNR). However, in Brillouin optical time-domain analyzers, the peak power of both the pulsed pump light and the continuous probe light is limited by fiber nonlinear effects such as modulation instability and nonlocality, making it difficult to further increase their peak power. Furthermore, while increasing the pulse width can improve the SNR, it reduces spatial resolution, making it difficult to meet the requirements of high-precision applications and limiting the development of this technology.

[0004] Pulse coding is an effective method to improve the signal-to-noise ratio (SNR) without changing the spatial resolution and detection duration. Based on the linear superposition principle, this technique involves delaying and superimposing a series of single-pulse responses, and then using a specific decoding scheme to recover the fiber's time-domain response. Its hardware implementation is simple, and the demodulation algorithm typically involves only routine computations. For example, the scheme disclosed in Chinese patent application CN201610044101.8. Currently, complementary Golay coding, simplex coding, and cyclic cyclolic coding schemes have been applied in Brillouin optical time-domain analyzers, but they still have limitations: complementary Golay coding and simplex coding require additional computational overhead and memory consumption, limiting their implementation efficiency; cyclic cyclolic coding leads to baseline fluctuations and increased noise, making it difficult to effectively improve the SNR; while high-performance genetic optimization coding schemes have advantages in resisting coding distortion and demodulation rate, they rely on distributed genetic optimization search algorithms, which are computationally intensive and slow, resulting in poor compatibility with Brillouin optical time-domain analyzers. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art, such as high computational overhead and memory consumption and low signal-to-noise ratio, and to provide a Brillouin optical time-domain analyzer based on pseudo-random sequences.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A Brillouin optical time-domain analyzer based on pseudo-random sequences includes: a continuous laser, an optical coupler, a signal generation circuit module, a pump branch, a detection branch, a sensing fiber under test, and a signal acquisition circuit.

[0008] The optical coupler splits the continuous laser generated by the continuous laser into two branches, which are respectively incident on the pump branch and the detector branch.

[0009] The signal generation circuit module generates a pseudo-random sequence of radio frequency signals to drive the pump branch, and generates a continuous radio frequency signal with Brillouin frequency shift to drive the detection branch.

[0010] The pump branch generates a unipolar pseudo-random sequence encoded laser and incident it onto the first port of the sensing fiber under test; the probe branch generates a single-sideband probe light with frequency shift and incident it onto the second port of the sensing fiber under test; the probe light and the pseudo-random sequence encoded laser in the sensing fiber propagate towards each other and interact to generate a stimulated Brillouin scattering signal.

[0011] The signal acquisition circuit samples the stimulated Brillouin scattering signal and decodes it to obtain the fiber time-domain response at the current frequency.

[0012] The signal generation circuit module sweeps the radio frequency signal driving the detection branch and repeats the encoding detection and decoding steps after each frequency adjustment to construct the Brillouin gain spectrum.

[0013] As a preferred technical solution, the pump branch includes an optical intensity modulator and a polarization controller;

[0014] The light intensity modulator generates a unipolar pseudo-random sequence encoded laser and incident it onto the input of the polarization controller;

[0015] The polarization controller modulates the polarization of the unipolar pseudo-random sequence encoded laser to make its polarization state non-orthogonal to that of the continuous probe light, and then incident the polarization-modulated random sequence encoded laser onto the sensing fiber under test.

[0016] As a preferred technical solution, the detection branch includes a light intensity modulation and control unit;

[0017] The light intensity modulation and control unit shifts the frequency of the input continuous laser based on the frequency of the radio frequency signal driven by the detection branch provided by the generation circuit module.

[0018] As a preferred technical solution, the optical intensity modulation and control unit includes an IQ modulator and an optical filter;

[0019] The Q modulator is used to perform single-sideband modulation on the incident continuous laser, and the frequency offset is determined by the frequency of the RF signal driving the detection branch provided by the signal generation circuit module; the optical filter is used to suppress sidebands and noise.

[0020] As a preferred technical solution, the signal generation circuit module has two independent output channels and one synchronous trigger channel, including an arbitrary waveform generator and a signal generator.

[0021] The arbitrary waveform generator generates a pseudo-random sequence encoded waveform, which is used as a radio frequency signal to drive the optical intensity modulator to generate a pseudo-random sequence encoded laser; the frequency of the radio frequency signal of the pseudo-random sequence is consistent with the frequency shift of the optical intensity modulator.

[0022] The signal generator outputs a continuous radio frequency signal with Brillouin frequency shift to drive the optical intensity modulation control unit, and performs frequency sweeping on the output radio frequency signal.

[0023] As a preferred technical solution, the light intensity modulator is an acousto-optic modulator; the signal generation circuit module includes an arbitrary waveform generator and an acousto-optic driver that matches the acousto-optic modulator;

[0024] A switching signal is provided by an arbitrary waveform generator and input to the acousto-optic driver. The acousto-optic driver generates a pseudo-random sequence of radio frequency signals to drive the acousto-optic modulator.

[0025] As a preferred technical solution, the length of the sequence periodic column of the pseudo-random sequence radio frequency signal generated by the signal generation circuit module is more than twice the length of the optical fiber under test.

[0026] As a preferred technical solution, the signal acquisition circuit includes an optical circulator, a photodetector, a high-speed digital acquisition card, and a computer.

[0027] The optical circulator is a single-mode circulator. Its first port is connected to the output of the pump branch, the second port is connected to the sensing fiber under test, and the third port is connected to the photodetector. Pseudo-random sequence encoded laser is introduced through the first port, enters the sensing fiber under test through the second port and interacts with the continuous light, and the stimulated Brillouin scattering signal generated by the sensing fiber under test is input to the photodetector through the third port.

[0028] The photodetector converts the stimulated Brillouin scattering light signal into an electrical signal and transmits it to the high-speed digital acquisition card.

[0029] The computer decodes the collected stimulated Brillouin scattering signal to obtain the fiber time-domain response at the current frequency.

[0030] The signal acquisition circuit samples the stimulated Brillouin scattering signal for a period exceeding three times the length of the pseudo-random sequence.

[0031] As a preferred technical solution, the computer decodes the acquired stimulated Brillouin scattering signal, as follows:

[0032] The stimulated Brillouin scattering signal is sliced, and after discarding the first and last segments, the remaining segments are accumulated and averaged to obtain the intensity superimposed Brillouin encoded scattering response.

[0033] The elements of the unipolar pseudo-random sequence signal are bipolar switched and cross-correlated with the intensity-superimposed Brillouin coded scattering response to obtain the fiber time-domain response at the current detection frequency.

[0034] As a preferred technical solution, the signal generator in the signal generation circuit module performs frequency sweeping, and repeats the encoding detection and decoding steps after each frequency adjustment; obtains the Brillouin gain spectrum of the sensing fiber under test based on the fiber time-domain response at different frequencies, and obtains the Brillouin frequency shift of the sensing fiber under test by searching for the peak value through Lorentz fitting, and determines the temperature / strain application amount based on the change in Brillouin frequency shift.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1) This invention proposes a Brillouin optical time-domain analyzer system based on pseudo-random sequences. A pseudo-random sequence with a high duty cycle is used as the pump source. Utilizing the high autocorrelation and low cross-correlation characteristics of the pseudo-random sequence-encoded laser, signals can be effectively distinguished while reducing interference, further ensuring the system's anti-interference capability and signal recovery accuracy. This scheme significantly improves the signal-to-noise ratio of the Brillouin scattering signal without affecting the sensing spatial resolution and detection time, thereby achieving efficient detection of temperature / strain at medium to long distances.

[0037] 2) Compared to traditional encoding methods, the pseudo-random sequence used in this invention requires only a small amount of hardware resources to quickly generate long-period sequences, featuring simple structure and high generation efficiency. Furthermore, the unipolar pseudo-random sequence in this invention only requires a single sequence to complete the detection process, and the receiving end can achieve signal recovery through cross-correlation operations of the bipolar corresponding sequences. This mechanism not only significantly shortens the signal detection time but also significantly improves the system demodulation efficiency.

[0038] 3) The high duty cycle m-sequence used in this invention is superior to the traditional L-bit Golay coding in terms of coding gain performance, which enables the receiver to obtain a higher signal-to-noise ratio. It can not only enhance the intensity of the Brillouin scattering signal, but also effectively suppress noise interference, thereby improving the system's anti-noise performance and signal detection reliability. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the structure of the Brillouin optical time-domain analyzer based on pseudo-random sequences of the present invention;

[0040] Figure 2 This is a schematic diagram of the structure of a Brillouin optical time-domain analyzer based on pseudo-random sequences in one embodiment of the present invention;

[0041] Figure 3 The figure shows the actual effect test results of the embodiment of the present invention;

[0042] The numbers in the diagram indicate: 1. Continuous laser, 2. Optical coupler, 3. Signal generation circuit module, 4. Optical intensity modulator, 5. Optical intensity modulation control unit, 6. Polarization controller, 7. Sensor fiber under test, 8. Signal acquisition circuit. Detailed Implementation

[0043] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0044] Example 1

[0045] A Brillouin optical time-domain analyzer system based on pseudo-random sequences is presented. Pseudo-random sequences are approximately random sequences generated by deterministic algorithms, characterized by high autocorrelation and low cross-correlation. Their autocorrelation function peaks at zero delay and rapidly decreases to near zero at non-zero delay; the cross-correlation between different sequences is extremely low, allowing them to be used simultaneously in the same system with minimal mutual interference. These characteristics enable pseudo-random sequences to effectively distinguish signals while reducing interference, making them highly suitable for use in conjunction with a Brillouin optical time-domain analyzer.

[0046] like Figure 1As shown, the system includes a continuous laser 1, an optical coupler 2, a signal generation circuit module 3, an optical intensity modulator 4, a polarization controller 6, an optical intensity modulation control unit 5, a sensing fiber under test 7, and a signal acquisition circuit 8. First, the continuous laser 1 generates laser light. After passing through the optical coupler 2, the laser light splits into two branches: a pump light and a continuous probe light. The pump light, after passing through the optical intensity modulator 4 driven by the signal generation circuit module 3, is converted into a pseudo-random sequence encoded laser with intensity modulation. The polarization state of the encoded laser is changed by the polarization controller 6. The continuous probe light, after passing through the optical intensity modulation control unit 5 driven by the signal generation circuit module 3, is converted into a single-sideband modulated light with frequency shift. The single-sideband modulated light is injected into the sensing fiber under test 7 and interacts with the pseudo-random sequence encoded laser traveling in the opposite direction to generate a Brillouin scattering signal. The Brillouin scattering signal is received by the signal acquisition circuit 8, and a specific demodulation algorithm is used to recover the fiber's time-domain response at the current detection frequency. By sweeping the frequency of the probe light driving signal from the signal generation circuit module 3, a Brillouin gain spectrum can be constructed, thereby achieving effective long-distance temperature / strain sensing.

[0047] This invention uses pseudo-random sequences instead of traditional single pulses for sensing and detection, enabling efficient monitoring of temperature / strain in distributed long-distance sensing optical fibers without sacrificing sensing accuracy or detection time. The high duty cycle pseudo-random sequences in this device significantly reduce the high light intensity pressure required for stimulated Brillouin scattering, improving the system's stability and practicality. It can be used as a high-performance monitoring system in fields such as structural health monitoring and perimeter security, and has significant engineering application value.

[0048] like Figure 2The illustration shows one specific embodiment of the present invention. In this embodiment, the Brillouin optical time-domain analyzer comprises: a continuous laser 1 generating laser light that is incident on the input end of an optical coupler 2; the optical coupler 2 splits the laser light into two branches, a pump branch and a probe branch, which are respectively incident on the optical input ends of an optical intensity modulator 4 and an optical intensity modulation control unit 5; a signal generation circuit module 3 generates a pseudo-random sequence radio frequency signal and a continuous radio frequency signal with Brillouin frequency shift, the former being input to the optical intensity modulator 4 and the latter to the optical intensity modulation control unit 5. The pump branch generates a pseudo-random sequence encoded laser light through the optical intensity modulator 4 and inputs it to the input end of a polarization controller 6; the polarization controller 6 performs polarization modulation on the pseudo-random sequence encoded laser light and inputs it to the sensing fiber 7 under test. The probe branch performs single-sideband modulation on the probe laser light through the optical intensity modulation control unit 5 and incident the modulated continuous probe light onto the sensing fiber 7 under test. In the sensing fiber 7, the probe light and the pseudo-random sequence encoded laser light propagate towards each other and interact to generate a stimulated Brillouin scattering signal. The signal acquisition circuit 8 samples and decodes the scattered signal to recover the fiber time domain response at the current frequency; the continuous probe light driving signal provided by the signal generation circuit module 3 is used to sweep the frequency, and the above encoding, detection and decoding steps are repeated after each frequency adjustment, so as to realize the construction of the Brillouin gain spectrum, thereby enabling effective long-distance temperature / strain sensing.

[0049] The continuous laser 1 is a narrow linewidth single-frequency laser with a nominal output frequency of 1550.12nm, an output linewidth of less than 3kHz, and an output power of 50mW.

[0050] Optical coupler 2 distributes the intensity of the optical power output by the continuous laser according to the splitting ratio parameter. In this embodiment, a polarization-maintaining optical coupler is selected, with a nominal splitting ratio of 20:80. The 20% end is incident on the optical intensity modulation and control unit 5 as continuous probe light, and the 80% end is incident on the optical intensity modulator 4 as pulse pump light.

[0051] The optical intensity modulator 4 uses a 1550nm fiber acousto-optic modulator with a nominal acousto-optic crystal frequency shift of 200MHz, an extinction ratio greater than 50dB, and an insertion loss of less than 3dB.

[0052] The pump light driving signal provided by signal generation circuit module 3 is a pseudo-random sequence code, where the sequence period is related to the sensing fiber 7 under test, and the sequence length must be more than twice the length of the sensing fiber 7 under test. The frequency of the provided probe light driving signal must be close to the Brillouin frequency shift of the sensing fiber 7 under test, and combined with frequency sweeping, the Brillouin gain spectrum can be constructed. Specifically, signal generation circuit module 3 includes an arbitrary waveform generator and a signal generator, with two independent output channels and one synchronous trigger channel. The arbitrary waveform generator outputs the generated pseudo-random sequence code waveform through one of the independent output channels, and uses it as an RF signal to drive the acousto-optic modulator to generate pseudo-random sequence code laser. To ensure the normal operation of the acousto-optic modulator, the RF signal frequency of the pseudo-random sequence waveform provided by the arbitrary waveform generator must be consistent with the frequency shift of the acousto-optic modulator. In addition, an acousto-optic driver matching the acousto-optic modulator can be selected, which is nominally capable of outputting an RF signal with a stability better than 100ppm when using a digital modulation signal input. Since the pseudo-random sequence encoded waveform used in this system is essentially a digital intensity modulated pulse sequence, a switching signal can be provided by an arbitrary waveform generator and input to the acousto-optic driver, which then generates an RF signal for the acousto-optic modulator. The former of the two driving schemes is simpler in hardware, while the latter is more convenient to operate, and both produce the same effect. The pseudo-random sequence uses a 10th-order m-sequence (1023 symbols), with each symbol lasting 40ns (corresponding to a 4m spatial resolution), a return-to-zero code modulation duty cycle of 8% (symbol period 500ns), and a single sequence period of 500ns * 1023 = 511500ns, which is slightly longer than the round-trip time of light in the optical fiber 7 of the sensor under test. The signal generator has a nominal signal frequency range of 8-12GHz, an upper limit of output level of 16dBm, and a frequency accuracy of 0.01Hz. The signal generator outputs a continuous radio frequency signal with Brillouin frequency shift through another independent output channel to drive the optical intensity modulation control unit 5. The frequency of the continuous radio frequency signal is about 10.8GHz, which is close to the Brillouin frequency shift of the sensing fiber 7 under test.

[0053] The optical intensity modulation control unit 5 includes an IQ modulator and an optical filter. The IQ modulator has a nominal modulation bandwidth covering 8-12 GHz and an insertion loss of less than 6 dB. The optical filter has a nominal optical wave range of 1530 nm-1610 nm, a filtering bandwidth of 0.08 nm-4 nm, and an insertion loss of less than 3 dB. The IQ modulator performs single-sideband modulation on the incident continuous probe light, with a carrier rejection ratio exceeding 25 dB. The frequency offset is determined by the frequency of the continuous drive signal provided by the signal generation circuit module 3. The optical filter is used to further suppress sidebands and noise, and its filtering bandwidth is selected as 0.08 nm.

[0054] The polarization controller 6 uses an optical polarizer with a nominal modulation operating range of over 100nm@1550nm, an output polarization degree of less than 5%, and an average polarization mode dispersion of less than 0.05ps. The polarizer modulates the polarization state of the input pseudo-random sequence encoded laser to ensure that it is not orthogonal to the polarization state of the continuous probe light; otherwise, the stimulated Brillouin scattering signal cannot be excited normally.

[0055] The sensing fiber under test 7 is a G.652.D single-mode fiber with a nominal sensing distance of about 50.4 km and a transmission loss of less than 0.2 dB / km@1550 nm. The pseudo-random sequence encoded laser and the continuous probe light travel in opposite directions and their polarization states are not orthogonal. They interact within the single-mode fiber to produce stimulated Brillouin scattering.

[0056] The signal acquisition circuit 8 mainly includes an optical circulator, a photodetector, a high-speed digital acquisition card, and a computer. First, the optical circulator is a single-mode circulator, serving as a link guiding element. Port 1 receives a pseudo-random sequence encoded laser light, which enters the fiber optic cable 7 under test via port 2 and interacts with the continuous light. Port 3 inputs the stimulated Brillouin scattering signal generated by this interaction into the photodetector. The photodetector is an InGaAs type photodetector with a nominal 3dB bandwidth of DC-200MHz and a cross-group gain of 10kV / W@1550nm. The photodetector converts the stimulated Brillouin scattering light signal into an electrical signal and transmits it to the high-speed digital acquisition card. The high-speed digital acquisition card is a programmable high-speed acquisition card with a nominal analog bandwidth of 400MHz and a sampling rate of 1GS / s@16-bit resolution. The sampling period of the stimulated Brillouin scattering signal in the signal acquisition circuit 8 needs to be more than three times the length of the pseudo-random sequence to ensure distortion-free decoding. The trigger period of the high-speed acquisition card is 511.5µs, and the acquisition time at a single frequency is 400ms. Subsequent decoding operations: Using a sequence period of 511.5 μs as the time unit, the 400 ms Brillouin signal is sliced. After discarding the first and last segments, the remaining segments are cumulatively averaged to obtain the intensity-superimposed Brillouin coded scattering response. Then, each element (containing only 0 and 1) of the unipolar 10th-order m-sequence signal is multiplied by 2-1 to achieve bipolar switching, and cross-correlation is performed with the intensity-superimposed Brillouin coded scattering response to obtain the fiber time-domain response at the current detection frequency.

[0057] The signal generator in signal generation circuit module 3 performs frequency sweeping, with a sweeping range of 10.78GHz-10.88GHz and a sweeping step size of 1MHz (i.e., 100 frequency conversions). After each frequency adjustment, the above encoding detection and decoding steps are repeated, with a total detection time of 400ms*100=40s. The Brillouin gain spectrum of the fiber under test can be directly obtained based on the fiber time-domain response at different frequencies, and the Brillouin frequency shift of the fiber under test can be obtained by searching for the peak value through Lorentz fitting. When external temperature / strain is applied to the fiber under test, the Brillouin frequency shift changes linearly. The amount of temperature / strain applied can be determined by the change in Brillouin frequency shift, realizing long-distance distributed temperature / strain sensing.

[0058] Compared to traditional Golay coding, the pseudo-random sequence coding scheme used in this invention differs significantly in its generation method and modulation / demodulation approach. Golay coding, as a conventional error-correcting code, typically generates a pair of sequences using matrix expansion. In this invention, the m-sequence can be generated by an arbitrary waveform generator providing a switching signal, which is then input to an acousto-optic driver to generate a radio frequency signal. This requires minimal hardware resources for rapid generation of long-period sequences, resulting in a simple structure and high generation efficiency. At the modulation / demodulation end, Golay coding typically requires converting bipolar dual sequences into unipolar quad sequences and injecting them sequentially into the sensing link. After receiving the respective sensing signals, difference and cross-correlation operations are performed. In this invention, however, the m-sequence only requires a single sequence to complete the detection process. The receiving end can recover the signal through cross-correlation operations of the corresponding bipolar sequences. This mechanism not only significantly shortens the signal detection time but also significantly improves the system demodulation efficiency. Furthermore, the L-bit m-sequence used in this invention has better coding gain performance than the traditional L-bit Golay coding. The theoretical coding gain of this invention is (L+1) / 2√L, while that of the latter is √L / 2. This advantage enables the receiver to obtain a higher signal-to-noise ratio, thereby effectively improving the system's noise immunity and signal detection reliability.

[0059] The Brillouin optical time-domain analyzer system scheme based on pseudo-random sequences in this embodiment of the invention. Figure 3 First, a comparison of the fiber time-domain responses of the traditional single-pulse system and the pseudo-random sequence system at the Brillouin shift is presented. Figure 3 (a) This demonstrates that the pseudo-random sequence provides a stable coding gain for the Brillouin optical time-domain analyzer, resulting in a higher signal-to-noise ratio for the stimulated scattering signal. To verify the sensing capability of this system, hotspot events of 30.1℃, 42.6℃, and 52.1℃ were applied to the end of the fiber under test. At these temperatures, the Brillouin frequency shift of the fiber under test was linearly shifted, and the shift amount was linearly mapped to the temperature change, as shown in the figure below. Figure 3 As shown in (b); at the same time... Figure 3(b) The rising edge of the heating zone from 10% to 90% confirms that the spatial resolution of this system is approximately 4.4 m, which is close to the duration of a single symbol in a pseudo-random sequence of 40 ns; the horizontal axis of the image represents the distance of the optical fiber to be tested. Figure 3 In (a), the vertical axis represents the normalized Brillouin gain. Figure 3 (b) The vertical axis represents the Brillouin frequency shift.

[0060] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A Brillouin optical time-domain analyzer based on pseudo-random sequences, characterized in that, include: Continuous laser (1), optical coupler (2), signal generation circuit module (3), pump branch, detection branch, sensor fiber under test (7), and signal acquisition circuit (8); The optical coupler (2) splits the continuous laser generated by the continuous laser (1) into two branches, which are respectively incident on the pump branch and the probe branch; The pump branch includes an intensity modulator (4) and a polarization controller (6); the intensity modulator (4) generates a unipolar pseudo-random sequence encoded laser and incident it onto the input of the polarization controller (6); the polarization controller (6) polarizes the unipolar pseudo-random sequence encoded laser so that its polarization state is non-orthogonal to that of the continuous probe light, and incidents the polarization-modulated random sequence encoded laser onto the sensing fiber (7) under test; the probe branch includes an intensity modulation control unit (5); the intensity modulation control unit (5) shifts the frequency of the input continuous laser based on the frequency of the probe branch drive radio frequency signal provided by the generation circuit module (3); The signal generation circuit module (3) generates a pseudo-random sequence of radio frequency signals to drive the pump branch and generates a continuous radio frequency signal with Brillouin frequency shift to drive the detection branch. The signal generation circuit module (3) has two independent output channels and one synchronous trigger channel, including an arbitrary waveform generator and a signal generator. The arbitrary waveform generator generates a pseudo-random sequence encoded waveform, which is used as a radio frequency signal to drive the optical intensity modulator (4) to generate a pseudo-random sequence encoded laser; the frequency of the radio frequency signal of the pseudo-random sequence is consistent with the frequency shift of the optical intensity modulator (4); The signal generator outputs a continuous radio frequency signal with Brillouin frequency shift to drive the optical intensity modulation control unit (5), and performs frequency sweeping on the output radio frequency signal; The pump branch generates a unipolar pseudo-random sequence encoded laser and is incident on the first port of the sensing fiber (7) under test; the probe branch generates a single-sideband probe light with frequency offset and is incident on the second port of the sensing fiber (7) under test; the probe light and the pseudo-random sequence encoded laser in the sensing fiber (7) are transmitted in opposite directions and interact to generate a stimulated Brillouin scattering signal. The signal acquisition circuit (8) samples the stimulated Brillouin scattering signal and decodes it to obtain the fiber time domain response at the current frequency. The signal generation circuit module (3) sweeps the radio frequency signal of the driving detection branch and repeats the encoding detection and decoding steps after each frequency adjustment to construct the Brillouin gain spectrum; The signal acquisition circuit (8) includes an optical circulator, a photodetector, a high-speed digital acquisition card, and a computer; The optical circulator is a single-mode circulator, with its first port connected to the output of the pump branch, its second port connected to the optical fiber under test (7), and its third port connected to the photodetector. The pseudo-random sequence encoded laser is introduced through the first port, enters the sensing fiber (7) under test through the second port and interacts with the continuous light, and the stimulated Brillouin scattering signal generated by the sensing fiber (7) under test is input to the photodetector through the third port. The photodetector converts the stimulated Brillouin scattering light signal into an electrical signal and transmits it to the high-speed digital acquisition card. The computer decodes the acquired stimulated Brillouin scattering signal: it slices the stimulated Brillouin scattering signal, discards the first and last segments, and performs cumulative averaging on the remaining segments to obtain the intensity-superimposed Brillouin coded scattering response; it then performs bipolar switching on each element of the unipolar pseudo-random sequence signal and cross-correlates it with the intensity-superimposed Brillouin coded scattering response to obtain the fiber time-domain response at the current detection frequency.

2. The Brillouin optical time-domain analyzer based on pseudo-random sequences according to claim 1, characterized in that, The light intensity modulation control unit (5) includes an IQ modulator and an optical filter; The Q modulator is used to perform single-sideband modulation on the incident continuous laser, and the frequency offset is determined by the frequency of the detection branch driving radio frequency signal provided by the signal generation circuit module (3); the optical filter is used to suppress sidebands and noise.

3. The Brillouin optical time-domain analyzer based on pseudo-random sequences according to claim 1, characterized in that, The light intensity modulator (4) is an acousto-optic modulator; the signal generation circuit module (3) includes an arbitrary waveform generator and an acousto-optic driver that matches the acousto-optic modulator. A switching signal is provided by an arbitrary waveform generator and input to the acousto-optic driver. The acousto-optic driver generates a pseudo-random sequence of radio frequency signals to drive the acousto-optic modulator.

4. A Brillouin optical time-domain analyzer based on pseudo-random sequences according to claim 1, characterized in that, The length of the sequence periodic column of the pseudo-random sequence radio frequency signal generated by the signal generation circuit module (3) is more than twice the length of the optical fiber under test (7).

5. A Brillouin optical time-domain analyzer based on pseudo-random sequences according to claim 1, characterized in that, The signal acquisition circuit (8) samples the stimulated Brillouin scattering signal for a period exceeding three times the length of the pseudo-random sequence.

6. A Brillouin optical time-domain analyzer based on pseudo-random sequences according to claim 1, characterized in that, The signal generator in the signal generation circuit module (3) performs frequency sweeping. After each frequency adjustment, the encoding detection and decoding steps are repeated. The Brillouin gain spectrum of the sensing fiber under test is obtained according to the fiber time-domain response at different frequencies. The peak value is searched by Lorentz fitting to obtain the Brillouin frequency shift of the sensing fiber under test. The temperature / strain application amount is determined based on the change in Brillouin frequency shift.

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