阅读说明：本技术 高阶相位调制瑞利botda温度/应变测量方法及装置 (High-order phase modulation Rayleigh BOTDA temperature/strain measurement method and device ) 是由 李永倩 王磊 刘艳蕊 于 2019-10-25 设计创作，主要内容包括：高阶相位调制瑞利BOTDA温度/应变测量方法及其测量装置,利用任意波形发生器驱动的相位调制器对脉冲基底光和脉冲信号光进行高阶相位调制,经过高阶相位调制的脉冲基底光在传感光纤中产生的不同相位关系的背向瑞利散射光作为探测光与每一个对应的同步相位高阶相位调制脉冲泵浦光发生受激布里渊散射作用,作用后携带传感信息不同相位关系的探测光经光电检测器检测和数据采集卡采集后传入计算机进行解调和处理。该方法将高阶相位调制技术引入到瑞利布里渊光时域分析系统中,不仅可以有效抑制相干瑞利噪声,提高系统的信噪比和测量精度,而且能够延长传感距离,减少测量所需时间。(The method comprises the steps of carrying out high-order phase modulation on pulse base light and pulse signal light by utilizing a phase modulator driven by an arbitrary waveform generator, using backward Rayleigh scattering light with different phase relations generated in a sensing optical fiber by the pulse base light subjected to the high-order phase modulation as detection light to generate stimulated Brillouin scattering effect with each corresponding synchronous phase high-order phase modulation pulse pumping light, detecting the detection light carrying sensing information with different phase relations by a photoelectric detector and acquiring the detection light by a data acquisition card, and transmitting the detection light to a computer for demodulation and processing. According to the method, a high-order phase modulation technology is introduced into a Rayleigh Brillouin optical time domain analysis system, so that coherent Rayleigh noise can be effectively inhibited, the signal-to-noise ratio and the measurement precision of the system are improved, the sensing distance can be prolonged, and the time required by measurement is shortened.)

1. A Rayleigh BOTDA temperature/strain measurement method based on high-order phase modulation is characterized in that,

the method is characterized in that a phase modulator driven by an arbitrary waveform generator is used for carrying out high-order phase modulation on pulse substrate light and pulse signal light, Rayleigh scattering light generated by the pulse substrate light with different phase relations is used as detection light to generate stimulated Brillouin scattering effect with each corresponding synchronous phase high-order phase modulation pulse pumping light, and the Rayleigh detection light with different phase relations after the stimulated Brillouin scattering effect is generated is subjected to superposition averaging to suppress coherent Rayleigh noise, so that high signal-to-noise ratio and high-precision temperature/strain measurement is realized.

2. A Rayleigh BOTDA temperature/strain measurement method based on high-order phase modulation is characterized in that,

continuous light output by a narrow linewidth Laser (LD) is input into a synthesized optical signal module through a polarization maintaining coupler (PCO), a lower branch of the synthesized optical signal module generates high-order phase modulation pulse substrate light with different phases through a Microwave Signal Source (MSS) and a Phase Modulator (PM), an upper branch generates required synchronous phase high-order phase modulation pulse pump light synchronous with the phase of the pulse substrate light through a pulse signal source (PSG) and the phase modulator, and the superposed and synthesized optical signal is incident into a sensing optical fiber, the backward Rayleigh scattering light with different phase relations generated in the sensing optical fiber by the pulse substrate light after the high-order phase modulation is used as probe light to generate stimulated Brillouin scattering effect with each corresponding synchronous phase high-order phase modulation pulse pumping light, and the probe light with different phase relations of the sensing information after the stimulated Brillouin scattering effect is detected by a Photoelectric Detector (PD) and collected by a data acquisition card (DAQ) and then is transmitted into a Computer (COM) for demodulation and processing.

3. The method according to claim 2, wherein the computer performs demodulation by extracting the probe light carrying stimulated brillouin scattering information with different phase relationships in each repetition period to perform superposition averaging so as to suppress coherent rayleigh noise; the computer carries out processing, namely reconstructing data demodulated by different microwave modulation frequencies to obtain a Brillouin gain spectrum, obtaining the distribution of Brillouin frequency shift along the optical fiber through Lorentz fitting, and realizing the distributed sensing of temperature or strain by utilizing the linear relation of the Brillouin frequency shift, the temperature and the strain.

4. The Rayleigh BOTDA temperature/strain measurement method based on high-order phase modulation as claimed in claim 2, wherein backward Rayleigh scattering light with different phase relationships generated in the sensing fiber by the pulse base light after the high-order phase modulation is used as probe light to generate stimulated Brillouin scattering effect with each corresponding synchronous phase high-order phase modulation pulse pumping light, and the probe light with different phase relationships carrying sensing information after the stimulated Brillouin scattering effect is expressed as

In the formula, E_RThe intensity of the probe light, H, is the back Rayleigh scattering produced in the fiber by the Stokes light_SBS(v, z) is the transfer function of stimulated brillouin scattering, where v is the microwave scanning frequency and z is the optical pulse propagation distance.

5. The method as claimed in claim 2, wherein the data acquisition card collects the detected data and sends the collected data to the computer for demodulation and processing, the computer separates and extracts the collected data, then performs the superposition averaging on the detected light with different phase relations to suppress the coherent rayleigh noise, and the signal after the superposition averaging is expressed as

The demodulated signals with different microwave modulation frequencies are reconstructed to obtain a Brillouin gain spectrum, the distribution of Brillouin frequency shift along the optical fiber is obtained through Lorentz fitting, and the temperature or strain distributed sensing is realized by utilizing the linear relation of the Brillouin frequency shift, the temperature and the strain.

6. A measuring device for the Rayleigh BOTDA temperature/strain measuring method based on the high-order phase modulation according to any one of claims 2 to 5, characterized in that the measuring device comprises a narrow-linewidth Laser (LD), a polarization maintaining coupler (PCO), a synthetic optical signal module consisting of a pulse signal source (PSG), a first electro-optical modulator (EOM1), a first phase modulator (PM1), a first erbium-doped fiber amplifier (EDFA1), a first grating filter (GF1), a first polarization controller (PC1), a Microwave Signal Source (MSS), a second electro-optical modulator (EOM2), a second erbium-doped fiber amplifier (EDFA2), a second grating filter (GF2), a second phase modulator (PM2), an Arbitrary Waveform Generator (AWG), a second polarization controller (PC2) and an optical Coupler (CO), an Optical Circulator (OC), a Polarization Scrambler (PS), a sensing Fiber (FU), and a sensing fiber (T), The device comprises a third erbium-doped fiber amplifier (EDFA3), an Optical Filter (OF), a Photoelectric Detector (PD), a data acquisition card (DAQ) and a Computer (COM), wherein the synthetic optical signal module comprises a high-order phase modulation module consisting OF a Phase Modulator (PM), an Arbitrary Waveform Generator (AWG) and a pulse signal source (PSG); the narrow-linewidth Laser (LD) outputs two paths of continuous light through a polarization maintaining coupler (PCO), the upper-branch continuous light sequentially passes through a first electro-optic modulator (EOM1) driven by a pulse signal source (PSG), a first phase modulator (PM1) driven by an Arbitrary Waveform Generator (AWG), a first erbium-doped fiber amplifier (EDFA1), a first grating filter (GF1) and a first polarization controller (PC1) and then is connected with a first input light port of a light Coupler (CO), the lower branch sequentially passes through a second electro-optic modulator (EOM2) driven by a Microwave Signal Source (MSS), a second erbium-doped fiber amplifier (EDFA2), a second grating filter (GF2), a second phase modulator (PM2) driven by an Arbitrary Waveform Generator (AWG) and a second polarization controller (PC2) and then is connected with a second input light port of the light Coupler (CO), and the optical coupler of the light Coupler (CO) is connected with a first output light port of the light ring (OC), the second optical port OF the Optical Circulator (OC) is connected with the sensing optical Fiber (FUT) after passing through the Polarization Scrambler (PS), and the third optical port OF the Optical Circulator (OC) is connected with the Computer (COM) through a third erbium-doped fiber amplifier (EDFA3), an Optical Filter (OF), a Photoelectric Detector (PD) and a data acquisition card (DAQ) in sequence.

7. The Rayleigh BOTDA temperature/strain measurement device based on the high-order phase modulation of claim 6, wherein the synthesized optical signal module is composed of a pulse signal source (PSG), a first electro-optical modulator (EOM1), a first phase modulator (PM1), a first erbium-doped fiber amplifier (EDFA1), a first grating filter (GF1), a first polarization controller (PC1), a Microwave Signal Source (MSS), a second erbium-doped fiber amplifier (EDFA2), a second grating filter (GF2), a second phase modulator (PM2), an Arbitrary Waveform Generator (AWG), a second polarization controller (PC2) and an optical Coupler (CO), the first electro-optical modulator (EOM1) driven by the pulse signal source (PSG) performs pulse modulation on the upper branch optical signal output by the polarization maintaining coupler (PCO), and the modulated pulse signal light enters the high-order phase modulation module for synchronous phase modulation, amplifying by a first erbium-doped fiber amplifier (EDFA1) and filtering by a first grating filter (GF1)After noise removal, the output center frequency is v₀The sensing pulse light of (1); the second electro-optical modulator (EOM2) driven by the Microwave Signal Source (MSS) performs double-sideband modulation of carrier suppression on the lower branch optical signal output by the polarization maintaining coupler (PCO), and the output frequency component is v₀±v_mThe microwave of (1) wherein v is₀Is the center frequency, v, of a narrow linewidth Laser (LD)_mThe microwave signal source is a drive frequency which can be adjusted near Brillouin frequency shift of the sensing fiber, pulse substrate light which is subjected to microwave modulation enters a high-order phase modulation module for high-order phase modulation after being amplified by a second erbium-doped fiber amplifier (EDFA2) and noise is filtered by a second grating filter (GF2), and output pulse substrate signals with different phase relations and upper-branch synchronous phase sensing pulse light are subjected to polarization adjustment and then are superposed and synthesized in an optical Coupler (CO).

8. The Rayleigh BOTDA temperature/strain measurement device based on the high-order phase modulation of claim 6, wherein the high-order phase modulation module is composed of a Phase Modulator (PM), an Arbitrary Waveform Generator (AWG) and a pulse signal source (PSG), the Arbitrary Waveform Generator (AWG) drives the Phase Modulator (PM) to perform the high-order phase modulation on the pulse substrate light and the pulse signal light, and the pulse substrate continuous optical signal and the pulse optical signal with different phase relationships are generated.

9. The higher-order phase modulation based rayleigh BOTDA temperature/strain measurement device of claim 8 wherein the Arbitrary Waveform Generator (AWG) drive has amplitude v₁～v_NN is the order of modulation, and the duration of each amplitude is equal to the repetition period t of the pulse signal light_lengthThe synchronous trigger signal generated by the pulse signal source (PSG) is used for synchronously triggering the Arbitrary Waveform Generator (AWG) to ensure that the pulse substrate light and the pulse signal light correspond to each other and keep the phase synchronization so as to maximize the stimulated Brillouin scattering effect generated by the pulse substrate light and the pulse signal light, and the synchronous trigger time is the repetition period t of the pulse signal light_lengthTo ensure that only one pulse light is transmitted in the optical fiber in each different phase period。

Technical Field

The invention relates to the technical field of measurement, in particular to a high-order phase modulation Rayleigh BOTDA temperature/strain measurement method and a measurement device thereof.

Background

Brillouin Optical Time Domain Analysis (BOTDA) sensing technology is taken as a novel distributed sensing technology, has become a research hotspot at home and abroad in the field of current Optical fiber sensing application by virtue of the advantages of high detection signal intensity, high measurement precision, wide dynamic range, long sensing distance and the like, and is widely applied to the fields of equipment fault detection and positioning, oil and gas pipeline safety condition monitoring, large-scale structure health detection, geological disaster monitoring and early warning and the like.

The conventional BOTDA measurement principle is to inject pulsed pump light and continuous probe light into two ends of an optical fiber respectively, the two beams of light propagate in the optical fiber in opposite directions, and when the two beams of light meet and the frequency difference of the two beams of light is in the Brillouin gain spectrum range, the pulsed pump light transfers energy to the continuous probe light through Stimulated Brillouin Scattering (SBS). By scanning the frequency of the continuous probe light, the probe light power at different optical fiber positions changing along with the frequency can be obtained at the pumping end, so that a reconstructed Brillouin gain spectrum can be obtained, and the distribution of Brillouin frequency shift along the optical fiber can be obtained through Lorentz fitting. And realizing distributed sensing of temperature or strain by utilizing the linear relation between the Brillouin frequency shift and the environmental temperature and strain. However, the conventional BOTDA system with double-end incidence has a complex structure and high implementation cost, is not suitable for some practical application occasions, and cannot normally operate once an optical fiber is broken due to environmental or human reasons.

In 2011, q.cui et al propose a single-ended BOTDA system based on rayleigh scattering, which utilizes a radio frequency port of a microwave signal source modulation electro-optical modulator and a direct current bias port of a pulse signal source modulation electro-optical modulator to generate a composite signal of a sensing pulse and a backward rayleigh scattering light generated by a microwave modulation pulse substrate, and the two signals generate SBS action in an optical fiber, thereby realizing single-ended, single-light-source, and nondestructive measurement. The single-ended BOTDA distributed sensor based on Rayleigh scattering greatly overcomes the defect of double-end incidence of the traditional BOTDA, but because the detection light which has SBS action with the pulse pump light is Rayleigh scattering light generated in the optical fiber by microwave modulation continuous light, the power of the detection light is small, and the detection light is seriously influenced by coherent Rayleigh noise, the system has the problems of small signal, large noise, low signal-to-noise ratio, poor measurement precision and the like, and the coherent Rayleigh noise cannot be filtered simply by signal superposition averaging or adding a filter. Therefore, there is an urgent need for a method and a device for measuring rayleigh BOTDA temperature/strain, which can effectively suppress coherent rayleigh noise and improve the signal-to-noise ratio and measurement accuracy of the system.

Disclosure of Invention

The invention mainly aims to provide a Rayleigh BOTDA temperature/strain measurement method based on high-order phase modulation and a measurement device thereof aiming at the defects of the prior art so as to inhibit the influence of coherent Rayleigh noise on the system performance, improve the signal-to-noise ratio of the system and improve the measurement precision.

Therefore, the invention discloses the following technical scheme:

a Rayleigh BOTDA temperature/strain measurement method based on high-order phase modulation is characterized in that high-order phase modulation is carried out on pulse base light and pulse signal light through a phase modulator driven by an arbitrary waveform generator, Rayleigh scattering light generated by the pulse base light with different phase relations serves as detection light to generate stimulated Brillouin scattering effect with each corresponding synchronous phase high-order phase modulation pulse pumping light, and the Rayleigh detection light with different phase relations after the stimulated Brillouin scattering effect is generated is subjected to superposition averaging to suppress coherent Rayleigh noise, so that high-signal-to-noise ratio and high-precision temperature/strain measurement is achieved.

The method is characterized in that continuous light output by a narrow linewidth laser is input to a synthesized optical signal module through a polarization-maintaining coupler, a lower branch of the synthesized optical signal module generates high-order phase modulation pulse base light with different phases through a microwave signal source and a phase modulator, an upper branch of the synthesized optical signal module generates required synchronous phase high-order phase modulation pulse pumping light synchronous with the phase of the pulse base light through a pulse signal source and the phase modulator, the superposed and synthesized optical signal is incident into a sensing optical fiber, backward Rayleigh scattering light with different phase relations generated in the sensing optical fiber by the pulse base light with the high-order phase modulation is used as detection light to generate stimulated brillouin scattering effect with each corresponding synchronous phase high-order phase modulation pulse pumping light, and the detection light with different phase relations of sensing information after action is transmitted into a computer for Brillouin scattering after being detected by a photoelectric detector and collected by a data collection card And (4) demodulating and processing.

Further, preferably, in the rayleigh BOTDA temperature/strain measurement method based on high-order phase modulation, the computer demodulation is to extract the probe light carrying the stimulated brillouin scattering information with different phase relationships in the repetition period to perform superposition averaging so as to suppress coherent rayleigh noise; the computer processing comprises the steps of reconstructing data after the detection light of different microwave modulation frequencies is demodulated to obtain a Brillouin gain spectrum, obtaining the distribution of Brillouin frequency shift along the optical fiber through Lorentz fitting, and realizing the distributed sensing of the temperature or the strain by utilizing the linear relation of the Brillouin frequency shift, the temperature and the strain.

Further, preferably, backward rayleigh scattering light with different phase relationships generated in the sensing fiber by the pulse substrate light subjected to the higher-order phase modulation is used as detection light to generate stimulated brillouin scattering effect with each corresponding synchronous phase higher-order phase modulation pulse pumping light, and the detection light with different phase relationships carrying sensing information after the stimulated brillouin scattering effect is expressed as

In the formula, E_RThe intensity of the probe light, H, is the back Rayleigh scattering produced in the fiber by the Stokes light_SBS(v, z) is the transfer function of stimulated brillouin scattering, where v is the microwave scanning frequency and z is the optical pulse propagation distance.

Further, preferably, when the data acquisition card acquires the detected data and sends the acquired data to the computer for demodulation and processing, the computer separates and extracts the acquired data, then performs superposition averaging on the detection light with different phase relationships to suppress coherent rayleigh noise, and a signal after the superposition averaging is represented as

The demodulated signals with different microwave modulation frequencies are reconstructed to obtain a Brillouin gain spectrum, the distribution of Brillouin frequency shift along the optical fiber is obtained through Lorentz fitting, and the temperature or strain distributed sensing is realized by utilizing the linear relation of the Brillouin frequency shift, the temperature and the strain.

The invention also discloses a Rayleigh BOTDA temperature/strain measuring device based on the high-order phase modulation, which comprises a narrow-linewidth laser, a polarization-maintaining coupler, a pulse signal source, a first electro-optical modulator, a first phase modulator, a first erbium-doped fiber amplifier, a first grating filter, a first polarization controller, a microwave signal source, a second electro-optical modulator, a second erbium-doped fiber amplifier and a second grating filter, a composite optical signal module (comprising a high-order phase modulation module consisting of the phase modulator, the arbitrary waveform generator and a pulse signal source), an optical circulator, a polarization scrambler, a sensing optical fiber, a third erbium-doped optical fiber amplifier, an optical filter, a photoelectric detector, a data acquisition card and a computer, wherein the composite optical signal module consists of the second phase modulator, the arbitrary waveform generator, the second polarization controller and the optical coupler. The narrow linewidth laser outputs two paths of continuous light through a polarization maintaining coupler, the upper path of the continuous light sequentially passes through a first electro-optical modulator driven by a pulse signal source, a first phase modulator driven by an arbitrary waveform generator, a first erbium-doped optical fiber amplifier, a first grating filter and a first polarization controller and then is connected with a first input light port of the optical coupler, and the lower path of the continuous light sequentially passes through a second electro-optical modulator driven by a microwave signal source and a second erbium-doped optical fiber amplifier, the second grating filter, the second phase modulator driven by the random waveform generator and the second polarization controller are connected with the second input optical port of the optical coupler, the output optical port of the optical coupler is connected with the first optical port of the optical circulator, the second optical port of the optical circulator is connected with the sensing optical fiber after passing through the polarization scrambler, and the third optical port of the optical circulator is sequentially connected with the computer through the third erbium-doped optical fiber amplifier, the optical filter, the photoelectric detector and the data acquisition card.

Preferably, in the rayleigh BOTDA temperature/strain measuring device based on high-order phase modulation, the synthesized optical signal module includes a pulse signal source, a first electro-optical modulator, and a first phaseThe pulse signal source driven first electro-optical modulator carries out pulse modulation on an upper branch optical signal output by the polarization-maintaining coupler, the modulated pulse signal light enters a high-order phase modulation module for high-order synchronous phase modulation, and the output center frequency is v after the pulse signal light is amplified by the first erbium-doped optical fiber amplifier and noise is filtered by the first grating filter₀The sensing pulse light of (1); the second electro-optical modulator driven by the microwave signal source performs double-sideband modulation for inhibiting carrier on the lower branch optical signal output by the polarization maintaining coupler, and the output frequency component is v₀±v_mThe microwave of (1) wherein v is₀Is the center frequency, v, of a narrow linewidth laser_mThe microwave signal source is the drive frequency adjustable near the Brillouin frequency shift of the sensing optical fiber, the pulse substrate light modulated by microwave enters a high-order phase modulation module for high-order phase modulation after being amplified by a second erbium-doped optical fiber amplifier and noise is filtered by a second grating filter, and the output pulse substrate signal with different phase relations and the upper-branch synchronous phase sensing pulse light are superposed and synthesized in an optical coupler after being subjected to polarization adjustment.

Preferably, in the rayleigh BOTDA temperature/strain measurement apparatus based on high-order phase modulation, the high-order phase modulation module is composed of a phase modulator, an arbitrary waveform generator and a pulse signal source, and the arbitrary waveform generator drives the phase modulator to perform high-order phase modulation on the pulse substrate light and the pulse signal light, so as to generate the pulse substrate continuous optical signal and the pulse optical signal with different phase relationships.

Wherein preferably, the amplitude of the drive of the arbitrary waveform generator is v₁～v_NN is the order of modulation, and the duration of each amplitude is equal to the repetition period t of the pulse signal light_lengthThe synchronous trigger signal generated by the pulse signal source is used for synchronously triggering the arbitrary waveform generator to enable the pulse base light and the pulseThe signal lights are corresponding and the phases are kept synchronous so as to maximize the stimulated Brillouin scattering effect of the signal lights and the phase, and the synchronous triggering time is the repetition period t of the pulse signal light_lengthTo ensure that only one pulse light is transmitted in the optical fiber in each different phase period.

According to the invention, a high-order phase modulation technology is introduced into a Rayleigh Brillouin optical time domain analysis system, and the influence of coherent Rayleigh noise on the system is reduced by utilizing the superposition average of Rayleigh scattering probe light with different phase relations generated by modulation. The method not only can effectively inhibit coherent Rayleigh noise and improve the signal-to-noise ratio and the measurement precision of the system, but also can prolong the sensing distance and reduce the measurement time.

The present invention will be further explained with reference to the accompanying drawings.

Drawings

FIG. 1 is a schematic diagram of the composition of the measuring apparatus of the present invention;

FIG. 2 is a schematic diagram of a phase modulator;

FIG. 3 is a graphical illustration of phase change of a phase modulator versus amplitude of a drive signal;

FIG. 4 is a schematic diagram of the drive signals for an arbitrary waveform generator;

fig. 5 is a schematic diagram of a composite optical signal composed of the pulse signal light and the pulse base light.

The reference numerals in the figures denote: LD, narrow linewidth laser, PCO, polarization maintaining coupler, PSG, pulse signal source, EOM1, first electro-optical modulator, PM1, first phase modulator, EDFA1, first erbium-doped fiber amplifier, GF1, first grating filter, PC1, first polarization controller, MSS, microwave signal source, EOM2, second electro-optical modulator, EDFA2, second erbium-doped fiber amplifier, GF2, second grating filter, AWG, arbitrary waveform generator, PM2, second phase modulator, PC2, second polarization controller, CO, optical coupler, OC, optical circulator, PS, polarization scrambler, FUT, sensing fiber, EDFA3, third erbium-doped fiber amplifier, OF, optical filter, PD, photoelectric detector, DAQ, data acquisition card, COM, and computer.

The notation used herein: v. of₀Is the output frequency, v, of a narrow linewidth laser_mDrive frequency, v, adjustable for microwave signal source near Brillouin frequency shift of sensing fiber₁～v_NFor the driving amplitude of an arbitrary waveform generator, N being the order of modulation, V_πIs the half-wave voltage of the phase modulator, V is the amplitude of the modulation signal input by the radio frequency end of the phase modulator,for phase change of the optical carrier, E_in(t) is the input light wave field of the phase modulator, E_out(t) is the output light wave field of the phase modulator, E₀For the amplitude, omega, of the input light wave field₀For the angular frequency of the input light wave field, t_lengthA time parameter, E, equal to or greater than the propagation time of the pulsed signal light over the length of the sensing fiber₁(t) intensity of the pulsed pump light with time, E₂(t) intensity of higher-order phase-modulated pulsed-substrate light with time, E₁Amplitude of the pulsed pump light, E₂Modulating the amplitude, t, of pulsed background light for higher order phases₁Is the starting time of the pulsed pump light, t₂T is the end time of the pulse pump light, t is the propagation time of the light pulse, J₁(C) Is a first order bessel function, C is a modulation index,n different phases, E, generated for higher order phase modulation_RThe intensity of the probe light, H, is the back Rayleigh scattering produced in the fiber by the Stokes light_SBS(v, z) is the transfer function of SBS, v is the microwave scanning frequency and z is the light pulse propagation distance.

Detailed Description

The invention will be further explained with reference to the drawings.

The invention utilizes a Rayleigh BOTDA system based on a high-order phase modulation technology to perform high-order phase modulation on pulse base light and pulse signal light through a phase modulator driven by an arbitrary waveform generator, Rayleigh scattered light generated by the pulse base light with different phase relations is used as detection light to perform SBS action with each corresponding synchronous phase high-order phase modulation pulse pumping light, and the Rayleigh detection light with different phase relations after the SBS action is performed with superposition averaging to inhibit coherent Rayleigh noise, thereby realizing high signal-to-noise ratio and high-precision temperature/strain measurement.

Referring to fig. 1, the system of the present invention is composed and operated as follows:

the narrow-linewidth laser LD outputs two paths of continuous light through a polarization maintaining coupler PCO and enters a synthesized light signal module, wherein the upper branch is subjected to pulse modulation by a first electro-optical modulator EOM1 driven by a pulse signal source PSG, the modulated pulse signal light enters a high-order phase modulation module, and the first phase modulator PM1 driven by an arbitrary waveform generator AWG is subjected to high-order phase modulation to generate a signal with the frequency v₀The synchronous phase high-order phase modulation pulse signal light is Amplified by a first erbium-doped fiber amplifier EDFA1, and After Spontaneous Emission (ASE) noise is filtered by a first grating filter GF1, the polarization state of the Amplified Spontaneous Emission (ASE) noise is adjusted by a first polarization controller PC1, and then the Amplified Spontaneous Emission (ASE) noise enters a light coupler CO; the lower branch circuit is firstly subjected to double-sideband modulation of suppressed carrier by a second electro-optical modulator EOM2 driven by a microwave signal source MSS, and the output frequency is v₀±v_mThe microwave modulation pulse substrate light is amplified by a second erbium-doped fiber amplifier EDFA2, spontaneous radiation noise is filtered by a second grating filter GF2, the microwave modulation pulse substrate light enters a high-order phase modulation module, and the second phase modulator PM2 driven by an arbitrary waveform generator AWG performs high-order phase modulation with the driving amplitude v₁～v_NA drive period equal to a repetition period t of the pulse signal light_lengthThe synchronous signal generated by the pulse signal source PSG is used for synchronizing the AWG, so that the pulse substrate light and the pulse signal light correspond to each other and keep the phase synchronization, the stimulated Brillouin scattering effect generated by the pulse substrate light and the pulse signal light is maximized, and the synchronous triggering time is the repetition period t of the pulse signal light_lengthSo as to ensure that only one pulse light is transmitted in the optical fiber in each different phase period, and finally the polarization state of the pulse light is adjusted by the second polarization controller PC2 and then the pulse light is input into the optical coupler CO. Upper branchThe synchronous phase high-order phase modulation pulse signal light and the pulse substrate light OF the lower branch circuit after high-order modulation are superposed and synthesized by an optical coupler CO and then enter a polarization scrambler PS through an optical circulator OC, the polarization scrambler PS scrambles the polarization state OF the synthesized light signal and then enters a sensing optical fiber FUT, backward Rayleigh scattering light with different phase relations generated by 1-order sidebands OF the pulse substrate is used as detection light and generates stimulated Brillouin scattering action with corresponding sensing pulse light used as pumping light, the detection light after the stimulated Brillouin scattering action (namely carrying sensing information) is input to a third erbium-doped optical fiber amplifier EDFA3 through the optical circulator OC to be amplified, then the upper sidebands OF the detection light are filtered by an optical filter OF, then the detection light is directly detected by a photoelectric detector PD and then data acquisition is carried out by a data acquisition card DAQ, and the acquired data is input to a computer COM for demodulation and processing.

The coherent Rayleigh noise in a Rayleigh BOTDA system is inhibited by using high-order phase modulation, the principle is that the amplitude-phase correlation is utilized, namely, an interference signal in a certain phase can be eliminated by superposing a signal with a phase difference of 180 degrees, and pulse substrate Rayleigh scattering detection light with different phase relations generated by the high-order phase modulation can eliminate a coherent fading phase point with a phase difference of 180 degrees by superposition averaging, so that the influence of the coherent Rayleigh noise on the system performance is inhibited.

Schematic structure of phase modulator as shown in fig. 2, when an optical signal passes through an electro-optic crystal of the phase modulator, the phase of the optical wave is modulated. Assuming that the amplitude of the modulation signal input from the radio frequency end of the phase modulator is V, the phase of the optical carrier changesIs composed ofWherein, V_πThe phase variation versus amplitude of the driving signal for a half-wave voltage of PM is shown in fig. 3, and thus phase modulation can be performed by modulating the amplitude of the radio frequency input. Suppose the input light wave field of PM is E_in(t)＝E₀cos(ω₀t)，E₀For input of light wave fieldsAmplitude, omega₀For the angular frequency of the input light wave field, the output light wave field can be expressed as PM modulated

The driving signal generated by the arbitrary waveform generator in the higher-order phase modulation module is shown in fig. 4, and the amplitude is v₁～v_NN is the order of modulation, and the duration of each amplitude is equal to the repetition period t of the pulse signal light_lengthThe synchronous trigger signal generated by the pulse signal source is used for synchronously triggering the arbitrary waveform generator to ensure that the pulse substrate light and the pulse signal light correspond to each other and keep the phases synchronous so as to maximize the stimulated Brillouin scattering effect generated by the pulse substrate light and the pulse signal light, and the synchronous trigger time is the repetition period t of the pulse signal light_lengthTo ensure that only one pulse light is transmitted in the optical fiber in each different phase period.

The composite optical signal composed of the pulse signal light and the pulse substrate light in the composite optical signal module is shown in fig. 5, and the output optical field thereof can be represented as

In the formula, E₁(t) intensity of pumping pulse light with time, E₂(t) intensity of higher-order phase-modulated pulsed-substrate light with time, E₁Amplitude of the pulsed pump light, E₂Modulating the amplitude, t, of pulsed background light for higher order phases₁Is the starting time of the pulsed pump light, t₂T is the end time of the pulse pump light, t is the propagation time of the light pulse, J₁(C) Is a first order bessel function, C is a modulation index,n different phases generated for high-order phase modulation range from 0 pi to 2 pi.

Since the modulation performance deterioration of the first electro-optical modulator EOM1, the second electro-optical modulator EOM2, the first phase modulator PM1, and the second phase modulator PM2 all change the state of the system, which affects the noise reduction effect, and further reduces the system performance, both the electro-optical modulator and the phase modulator used need to be high-performance modulators with high extinction ratio and high stability. The AWG needs a precise and stable signal to drive the phase modulator to ensure a precise and stable phase modulation effect, so the AWG is also a high-precision and high-stability AWG.

The polarization state of the light is adjusted by the first polarization controller PC1 and the second polarization controller PC2 to ensure that the polarization fading of the pulse signal light and the pulse substrate light is minimum when the optical coupler is superposed and synthesized, and the polarization scrambler PS is used for scrambling the polarization states of the probe light, the pump light and the scattered probe light after SBS action, so as to effectively reduce the influence of polarization noise.

The microwave signal source MSS carries out double-sideband modulation for inhibiting carrier waves on the second electro-optic modulator, so that the non-local effect can be effectively reduced, and the sensing distance is prolonged. The optical filter OF is used for filtering the upper sideband OF the probe light scattered back by the circulator after SBS (the reserved frequency is v)₀-v_mStokes probe light) to form a brillouin gain spectrum.

The backward Rayleigh scattering light with different phase relations generated in the sensing optical fiber by the pulse substrate light after the high-order phase modulation is taken as the detection light to generate the stimulated Brillouin scattering effect with each corresponding synchronous phase high-order phase modulation pulse pumping light, and the detection light with different phase relations of the sensing information after the SBS effect is generated can be expressed as the detection light with different phase relations

In the formula, E_RThe intensity of the probe light, H, is the back Rayleigh scattering produced in the fiber by the Stokes light_SBS(v, z) is the transfer function of SBS, where v is the microwave scanning frequency and z is the light pulse propagation distance.

The data acquisition card DAQ acquires data detected by PD and sends the data to the computer for demodulation and processing, the computer separates and extracts the acquired data, then the detection light with different phase relations is subjected to superposition averaging to inhibit coherent Rayleigh noise, and a signal after the superposition averaging can be expressed as

The demodulated signals with different microwave modulation frequencies are reconstructed to obtain a Brillouin gain spectrum, the distribution of Brillouin frequency shift along the optical fiber is obtained through Lorentz fitting, and the temperature or strain distributed sensing is realized by utilizing the linear relation of the Brillouin frequency shift, the temperature and the strain.

The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solution of the present invention by those skilled in the art should fall within the protection scope defined by the claims of the present invention without departing from the spirit of the present invention.