Phase sensitive optical time domain reflectometer with high fidelity phase extraction and high response bandwidth and method of operation thereof

Abstract

The application discloses a phase-sensitive optical time domain reflectometer with high-fidelity phase extraction and high-response bandwidth and a working method thereof, and belongs to the optical technical field, to solve the problems of existing phase-sensitive optical time domain reflectometer, such as phase information extraction distortion and response bandwidth limited by sensing distance. The optical time domain reflectometer comprises a narrow-line-width light source, a fiber coupler, a first acousto-optic modulator, an erbium-doped fiber amplifier, an optical isolator, a second acousto-optic modulator, a dense wavelength division multiplexer, a circulator, a polarization controller, an optical balanced detector, a band-pass filter, a data acquisition card, a computer, an arbitrary waveform generator and the like. The application generates multi-frequency continuous light through modulation, and further modulates the multi-frequency continuous light into a multi-frequency non-uniform periodic pulse sequence to inject into a sensing optical fiber; a detection end performs real-time non-uniform periodic sampling on echo signals, and multi-frequency echo signal multiplexing realizes high-fidelity extraction of phase information. The application has flexible and controllable multiplexing frequency, high fidelity and high response bandwidth.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical technology, in particular to a phase-sensitive optical time domain reflectometer with high-fidelity phase extraction and high response bandwidth and a working method thereof. BACKGROUND

[0002] The phase-sensitive optical time domain reflectometer has high response speed of millisecond or even sub-millisecond, high sensitivity of nanostain, and is widely used in perimeter intrusion monitoring, seismic wave monitoring, structure health detection and other fields. In the phase-sensitive optical time domain reflectometer, due to the high coherence of the narrow linewidth light source, the power of the scattered light signals in the half probe pulse is superimposed and interfered with each other, the random fluctuation of the scattered signal caused by the coherent constructive and destructive interference, and the low signal-to-noise ratio of the coherent destructive position will lead to the distortion of the phase information extraction and the incorrect characterization of the monitoring signal; in the phase-sensitive optical time domain reflectometer, in order to avoid the mutual superposition of the probe light pulses, the repetition period of the probe light pulses should be greater than or equal to the time required for a single optical pulse signal to travel in the sensing optical fiber for one round trip, that is, the response bandwidth of the system is restricted by the sensing distance, according to the Nyquist sampling theorem, the maximum response bandwidth of the system is half of the repetition frequency of the probe light pulse.

[0003] Therefore, it is of great significance to extract the phase information of the phase-sensitive optical time domain reflectometer with high fidelity and to improve the response bandwidth. The high-fidelity extraction scheme mainly includes pulse modulation, special optical fiber, extraction algorithm, etc., for example: [1] adopts multiple acousto-optic modulators for multi-frequency modulation multiplexing to realize high-fidelity phase extraction; [2] adopts dual-source wavelength division multiplexing to realize high-fidelity phase extraction; [3] adopts a multimode optical fiber to multiplex signals under different modes to realize high-fidelity phase extraction. The response bandwidth is mainly improved by using a hybrid sensing system and pulse sequence frequency multiplexing, for example: [4] combines the phase-sensitive optical time domain reflectometer with a Mach-Zehnder interferometer to improve the response bandwidth; [5] adopts multi-frequency pulse sequence frequency multiplexing to improve the response bandwidth. However, the above existing schemes have too complex structure, and do not consider high-fidelity phase and response bandwidth at the same time. SUMMARY

[0004] Therefore, the present application proposes a phase-sensitive optical time domain reflectometer with high-fidelity phase extraction and high response bandwidth and a working method thereof, to solve the problems of phase information extraction distortion and response bandwidth limited by sensing distance in the existing phase-sensitive optical time domain reflectometer.

[0005] According to an aspect of the present application, a phase sensitive optical time domain reflectometer with high fidelity phase extraction and high response bandwidth is presented, which comprises a narrow linewidth light source 1, a first fiber coupler 2, a second fiber coupler 3, a first acousto-optic modulator 4, a third fiber coupler 5, a first erbium-doped fiber amplifier 6, an optical isolator 7, a second acousto-optic modulator 8, a second erbium-doped fiber amplifier 9, a first dense wavelength division multiplexer 10, a circulator 11, a sensing fiber 12, a third erbium-doped fiber amplifier 13, a second dense wavelength division multiplexer 14, a polarization controller 15, a fourth fiber coupler 16, a photoelectric balanced detector 17, a band-pass filter 18, a data acquisition card 19, a computer 20 and an arbitrary waveform generator 21;

[0006] The light signal output end of the narrow linewidth light source 1 is in communication with the light signal input end of the first optical fiber coupler 2, the two light signal output ends of the first optical fiber coupler 2 are respectively and simultaneously in communication with the No.1 light signal input end of the second optical fiber coupler 3 and the input end of the polarization controller 15, the light signal output end of the second optical fiber coupler 3 is in communication with the light signal input end of the first acousto-optic modulator 4, the light signal output end of the first acousto-optic modulator 4 is in communication with the light signal input end of the third optical fiber coupler 5, the two light signal output ends of the third optical fiber coupler 5 are respectively and simultaneously in communication with the light signal input end of the second acousto-optic modulator 8 and the light signal input end of the first erbium-doped fiber amplifier 6, the light signal output end of the first erbium-doped fiber amplifier 6 is in communication with the light signal input end of the optical isolator 7, the light signal output end of the optical isolator 7 is in communication with the No.2 light signal input end of the second optical fiber coupler 3, the light signal output end of the second acousto-optic modulator 8 is in communication with the light signal input end of the second erbium-doped fiber amplifier 9, the light signal output end of the second erbium-doped fiber amplifier 9 is in communication with the light signal input end of the first dense wavelength division multiplexer 10, the light signal output end of the first dense wavelength division multiplexer 10 is in communication with the No.1 light signal port 11-1 of the circulator 11, the No.2 light signal port 11-2 of the circulator 11 is in communication with the sensing optical fiber 12, the No.3 light signal port 11-3 of the circulator 11 is in communication with the light signal input end of the third erbium-doped fiber amplifier 13, the light signal output end of the third erbium-doped fiber amplifier 13 is in communication with the light signal input end of the second dense wavelength division multiplexer 14, the light signal input end of the fourth optical fiber coupler 16 is simultaneously in communication with the light signal output end of the polarization controller 15 and the light signal output end of the second dense wavelength division multiplexer 14, the light signal output end of the fourth optical fiber coupler 16 is in communication with the light signal input end of the photoelectric balance detector 17, the electrical signal output end of the photoelectric balance detector 17 is in communication with the electrical signal input end of the band-pass filter 18, the electrical signal output end of the band-pass filter 18 is in communication with the electrical signal input end of the data acquisition card 19, the data acquisition card 19 is connected with the computer 20, the signal output ends of the arbitrary waveform generator 21 are respectively and simultaneously in communication with the microwave signal input end of the first acousto-optic modulator 4, the microwave signal input end of the second acousto-optic modulator 8 and the trigger signal input end of the data acquisition card 19.

[0007] Further, the narrow linewidth light source 1 adopts a single-frequency narrow linewidth fiber laser, the output power is 10 dBm, and the output wavelength is 1550.12 nm.

[0008] Further, the first optical fiber coupler 2 is a 90:10 three-port coupler, the second optical fiber coupler 3 is a 50:50 three-port coupler, the third optical fiber coupler 5 is a 50:50 2×2 coupler, and the fourth optical fiber coupler 16 is a 50:50 2×2 coupler.

[0009] Further, the center frequency of the first acousto-optic modulator 4 is 100 MHz, and the working bandwidth is 120 MHz; the frequency shift of the second acousto-optic modulator 8 is -40 MHz, and the extinction ratio is 50 dB.

[0010] Further, the working waveband of the first dense wavelength division multiplexer 10 and the second dense wavelength division multiplexer 14 is 1480 and 1550.12 nm, and the attenuation bandwidth is 0.22 nm. The detection bandwidth of the photoelectric balance detector 17 is 350 MHz. The passband range of the bandpass filter 18 is 20 MHz-360 MHz.

[0011] According to another aspect of the present application, a working method of a phase-sensitive optical time domain reflectometer with high-fidelity phase extraction and high-response bandwidth is provided, which is implemented based on a phase-sensitive optical time domain reflectometer with high-fidelity phase extraction and high-response bandwidth, the phase-sensitive optical time domain reflectometer comprising a narrow-linewidth light source 1, a first fiber coupler 2, a second fiber coupler 3, a first acousto-optic modulator 4, a third fiber coupler 5, a first erbium-doped fiber amplifier 6, an optical isolator 7, a second acousto-optic modulator 8, a second erbium-doped fiber amplifier 9, a first dense wavelength division multiplexer 10, a circulator 11, a sensing optical fiber 12, a third erbium-doped fiber amplifier 13, a second dense wavelength division multiplexer 14, a polarization controller 15, a fourth fiber coupler 16, a photoelectric balance detector 17, a bandpass filter 18, a data acquisition card 19, a computer 20, and an arbitrary waveform generator 21; the working method comprises:

[0012] The continuous light output by the narrow-linewidth light source 1 is divided into two branches by the first fiber coupler 2; the continuous light of the upper branch passes through the second fiber coupler 3 and enters the first acousto-optic modulator 4 to be modulated into multi-frequency continuous light, and is divided into two paths by the third fiber coupler 5, one path of the multi-frequency continuous light is modulated into non-uniform periodic multi-frequency pulsed light by the second acousto-optic modulator 8, and a certain frequency shift is generated at the same time, and the other path of the multi-frequency continuous light is amplified by the first erbium-doped fiber amplifier 6, and then enters the first acousto-optic modulator 4 again through the optical isolator 7 and the second fiber coupler 3 to be modulated into multi-frequency light, and is also modulated into non-uniform periodic multi-frequency pulsed light by the second acousto-optic modulator 8, and a certain frequency shift is generated at the same time; through multiple modulations in a loop structure, large-bandwidth multi-frequency modulation can be realized; finally, the pulsed peak power is amplified by the second erbium-doped fiber amplifier 9, and then injected into the first dense wavelength division multiplexer 10 to filter out the spontaneous emission noise introduced by the second erbium-doped fiber amplifier 9, and finally injected into the sensing optical fiber 12 through the circulator 11; the backscattering Rayleigh scattering light signal generated in the sensing optical fiber 12 due to the non-uniform distribution of the medium refractive index is injected into the third erbium-doped fiber amplifier 13 through the circulator 11 for power amplification, and then enters the second dense wavelength division multiplexer 14 to filter out the spontaneous emission noise, and the multi-frequency modulation of the first acousto-optic modulator 4 and the chopping modulation and frequency shift of the second acousto-optic modulator 8 are controlled by the arbitrary waveform generator 21.

[0013] The continuous light of the lower branch is adjusted in polarization state by the polarization controller 15, and then is coherent frequency-mixed with the back Rayleigh scattering light filtered by the second dense wavelength division multiplexer 14 through the fourth optical fiber coupler 16, and is photoelectrically converted by the photoelectric balance detector 17. The output photoelectric current is filtered by the band-pass filter 18, and finally is non-uniformly periodically sampled by the data acquisition card 19 to record the multi-frequency mixing light signal. The computer 20 is used for data processing, high-fidelity phase extraction is realized through frequency multiplexing, and the vibration detection time is frequency-characterized by realizing non-uniform discrete Fourier transform on the high-fidelity phase information.

[0014] Further, through multiple modulations of the ring structure, the large-bandwidth multi-frequency continuous light output by the first acousto-optic modulator 4 is represented as:

[0015]

[0016] In the formula, A represents the amplitude of the continuous light output by the narrow linewidth light source 1; f c represents the frequency of the continuous light output by the narrow linewidth light source 1; M represents the modulation number; N represents the number of microwave signals; f represents the frequency interval of the microwave signals; and φ0 represents the initial phase of the continuous light output by the narrow linewidth light source 1.

[0017] The non-uniformly periodic multi-frequency pulse light output after being modulated by the second acousto-optic modulator 8 is represented as:

[0018]

[0019] In the formula, A1 is the amplitude of the optical pulse signal E P (t); rect is a rectangular function; T0 is the width of the optical pulse signal E P (t); and -Δf represents the frequency shift of the second acousto-optic modulator 8.

[0020] Then, the m pieces of frequency-mixed light signals obtained by the data acquisition card 19 through non-uniform periodic sampling are represented as:

[0021]

[0022] In the formula, T h ∈ [T, 2T], n and L respectively represent the refractive index and length of the sensing optical fiber 12, and c represents the light wave propagation speed in vacuum; B i (t) and φ i (t) respectively represent the amplitude and phase of the i-th back Rayleigh scattering light signal.

[0023] Further, the computer 20 carries out the data processing process, which comprises: for each of the m beat frequency optical signals obtained by the non-uniform period sampling of the data acquisition card 19, in the arbitrary phase extraction position interval [z1, z2] of the beat frequency optical signal, the minimum value of the amplitude information [AB i (t z1 +kT h ), AB i (t z2 +kT h )] of z1 and z2 positions is calculated, k=1, 2, 3,... is the number of non-uniform period sampling; and the beat frequency signal corresponding to the maximum value in the minimum value is phase extracted, and the extracted high-fidelity phase information is:

[0024]

[0025] The non-uniform discrete Fourier transform is performed on the high-fidelity phase information , and the frequency F(ω) of the vibration signal detected by the phase-sensitive optical time domain reflectometer can be obtained:

[0026]

[0027] In the formula, ω is the angular frequency of the base function; t n represents a time sequence.

[0028] The beneficial technical effects of the present application are:

[0029] The phase-sensitive optical time domain reflectometer with high-fidelity phase extraction and high-response bandwidth and the working method thereof can effectively realize high-fidelity extraction of phase information: according to the fact that different beat frequency signal lights have different amplitude distributions in the phase-sensitive optical time domain reflectometer, the amplitude is used as a judgment basis for multiplexing, and high-fidelity phase extraction is realized; the advantage is that the most accurate phase information can be accurately extracted on any phase extraction interval.

[0030] The phase-sensitive optical time domain reflectometer with high-fidelity phase extraction and high-response bandwidth and the working method thereof have flexible and controllable multiplexing frequency: the frequency in the optical path is controlled by the first acousto-optic modulator to be generated by the arbitrary waveform generator, the frequency interval and the number are freely programmed and flexibly controllable, and a larger modulation bandwidth can be obtained through multiple modulations of the ring junction.

[0031] The phase-sensitive optical time domain reflectometer with high fidelity phase extraction and high response bandwidth and the working method thereof have high response bandwidth: in the phase-sensitive optical time domain reflectometer, in order to avoid mutual aliasing between detection light pulses, the repetition period of the detection light pulses should be greater than or equal to the time required for a single optical pulse signal to propagate in a sensing optical fiber for one round trip, that is, the response bandwidth of the system is restricted by the sensing distance, according to the Nyquist sampling law, the maximum response bandwidth of the system is half of the repetition frequency of the detection light pulses; in the present application, non-uniform periodic modulation is used to generate detection light pulses, and non-uniform periodic sampling is performed on the beat frequency signals, so that the frequency aliasing of the detection signals is effectively avoided, that is, the limitation of the Nyquist sampling frequency on the response bandwidth is avoided.

[0032] The phase-sensitive optical time domain reflectometer with high fidelity phase extraction and high response bandwidth and the working method thereof have simple system structure: a typical frequency division multiplexing system or a wavelength division multiplexing system usually has a relatively complex structure and a high cost, in the present application, multiple microwave signals of different frequencies are loaded on a single wideband acousto-optic modulator, and non-uniform periodic pulse modulation is used, so that high fidelity phase extraction and high response bandwidth are realized, and the structure is simple. BRIEF DESCRIPTION OF DRAWINGS

[0033] The above and other objects, features and advantages of the exemplary embodiments of the present application will be more apparent from the following detailed description read in conjunction with the accompanying drawings, in which several embodiments of the present application are shown by way of example, and in which:

[0034] Figure 1 is a structural schematic diagram of the phase-sensitive optical time domain reflectometer with high fidelity phase extraction and high response bandwidth according to an embodiment of the present application;

[0035] Figure 2 is a non-uniform periodic modulation pulse light signal model in an embodiment of the present application;

[0036] Figure 3 is a non-uniform chopped optical pulse signal in an embodiment of the present application;

[0037] Figure 4 is a modulation period distribution of non-uniform periodic modulation pulse light in an embodiment of the present application;

[0038] Figure 5 is a cumulative distribution of the modulation period of non-uniform periodic modulation pulse light in an embodiment of the present application;

[0039] Figure 6 is a time domain graph of a multi-frequency beat frequency signal collected by non-uniform periodic sampling in an embodiment of the present application;

[0040] Figure 7 is a frequency domain graph of a multi-frequency beat frequency signal collected by non-uniform periodic sampling in an embodiment of the present application;

[0041] Figure 8 is the distorted phase information extracted by the conventional phase-sensitive optical time domain reflectometer.

[0042] Figure 9 is the high-fidelity phase information extracted in the embodiments of the present application. DETAILED DESCRIPTION

[0043] The principles and spirits of the present application will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are given only to enable those skilled in the art to better understand and implement the present application, and do not limit the scope of the present application in any way. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0044] In order to solve the problems of the distorted phase information extraction and the response bandwidth limited by the sensing distance of the existing phase-sensitive optical time domain reflectometer, the embodiments of the present application propose a phase-sensitive optical time domain reflectometer with high-fidelity phase extraction and high response bandwidth, as shown in the accompanying drawings. Figure 1 The phase-sensitive optical time domain reflectometer with high-fidelity phase extraction and high response bandwidth includes a narrow-linewidth light source 1, a first optical fiber coupler 2, a second optical fiber coupler 3, a first acousto-optic modulator 4, a third optical fiber coupler 5, a first erbium-doped fiber amplifier 6, an optical isolator 7, a second acousto-optic modulator 8, a second erbium-doped fiber amplifier 9, a first dense wavelength division multiplexer 10, a circulator 11, a sensing optical fiber 12, a third erbium-doped fiber amplifier 13, a second dense wavelength division multiplexer 14, a polarization controller 15, a fourth optical fiber coupler 16, an optical balanced detector 17, a band-pass filter 18, a data acquisition card 19, a computer 20 and an arbitrary waveform generator 21.

[0045] The light signal output end of the narrow line width light source 1 is communicated with the light signal input end of the first optical fiber coupler 2, the two light signal output ends of the first optical fiber coupler 2 are simultaneously communicated with the No.1 light signal input end of the second optical fiber coupler 3 and the input end of the polarization controller 15 respectively, the light signal output end of the second optical fiber coupler 3 is communicated with the light signal input end of the first acousto-optic modulator 4, the light signal output end of the first acousto-optic modulator 4 is simultaneously communicated with the light signal input end of the third optical fiber coupler 5, the two light signal output ends of the third optical fiber coupler 5 are simultaneously communicated with the light signal input end of the second acousto-optic modulator 8 and the light signal input end of the first erbium-doped fiber amplifier 6 respectively, the light signal output end of the first erbium-doped fiber amplifier 6 is communicated with the light signal input end of the optical isolator 7, the light signal output end of the optical isolator 7 is simultaneously communicated with the No.2 light signal input end of the second optical fiber coupler 3, the light signal output end of the second acousto-optic modulator 8 is simultaneously communicated with the light signal input end of the second erbium-doped fiber amplifier 9, the light signal output end of the second erbium-doped fiber amplifier 9 is communicated with the light signal input end of the first dense wavelength division multiplexer 10, the light signal output end of the first dense wavelength division multiplexer 10 is communicated with the No.1 light signal port 11-1 of the circulator 11, the No.2 light signal port 11-2 of the circulator 11 is communicated with the sensing optical fiber 12, the No.3 light signal port 11-3 of the circulator 11 is communicated with the light signal input end of the third erbium-doped fiber amplifier 13, the light signal output end of the third erbium-doped fiber amplifier 13 is communicated with the light signal input end of the second dense wavelength division multiplexer 14, the light signal input end of the fourth optical fiber coupler 16 is simultaneously communicated with the light signal output end of the polarization controller 15 and the light signal output end of the second dense wavelength division multiplexer 14, the light signal output end of the fourth optical fiber coupler 16 is communicated with the light signal input end of the photoelectric balance detector 17, the electric signal output end of the photoelectric balance detector 17 is simultaneously communicated with the electric signal input end of the band-pass filter 18, the electric signal output end of the band-pass filter 18 is communicated with the electric signal input end of the data acquisition card 19, the data acquisition card 19 is simultaneously communicated with the computer 20, the signal output end of the arbitrary waveform generator 21 is simultaneously communicated with the microwave signal input end of the first acousto-optic modulator 4, the microwave signal input end of the second acousto-optic modulator 8 and the trigger signal input end of the data acquisition card 19 respectively.

[0046] In the embodiment, preferably, the narrow linewidth light source 1 adopts a single-frequency narrow linewidth fiber laser, the output power is 10 dBm, and the output wavelength is 1550.12 nm. The first fiber coupler 2 is a 90:10 three-port coupler, the second fiber coupler 3 is a 50:50 three-port coupler, the third fiber coupler 5 is a 50:50 2x2 coupler, and the fourth fiber coupler 16 is a 50:50 2x2 coupler. The center frequency of the first acousto-optic modulator 4 is 100 MHz, and the working bandwidth is 120 MHz; the frequency shift of the second acousto-optic modulator 8 is -40 MHz, and the extinction ratio is 50 dB. The working waveband of the first dense wavelength division multiplexer 10 and the second dense wavelength division multiplexer 14 is 1480 / 1550.12 nm, and the attenuation bandwidth is 0.22 nm. The detection bandwidth of the photoelectric balance detector 17 is 350 MHz. The passband range of the band-pass filter 18 is 20 MHz-360 MHz.

[0047] Another embodiment of the present application provides a working method of a phase-sensitive optical time domain reflectometer with high-fidelity phase extraction and high-response bandwidth, the working method comprising:

[0048] The continuous light outputted by the narrow line width light source 1 is divided into two branches by the first optical fiber coupler 2; the continuous light of the upper branch passes through the second optical fiber coupler 3 and enters the first acousto-optic modulator 4 to be modulated into multi-frequency continuous light, and is divided into two paths by the third optical fiber coupler 5, one path of the multi-frequency continuous light passes through the second acousto-optic modulator 8 to be modulated into non-uniform periodic multi-frequency pulse light, and a certain frequency shift is generated at the same time, and the other path of the multi-frequency continuous light passes through the first erbium-doped fiber amplifier 6 for amplification, and then passes through the optical isolator 7 and the second optical fiber coupler 3 to enter the first acousto-optic modulator 4 again for multi-frequency modulation, and is also modulated into non-uniform periodic multi-frequency pulse light by the second acousto-optic modulator 8, and a certain frequency shift is generated at the same time, and the above-mentioned multi-frequency modulation through the ring structure can realize large bandwidth multi-frequency modulation; finally, the pulse peak power is amplified by the second erbium-doped fiber amplifier 9, and then injected into the first dense wavelength division multiplexer 10 to filter out the spontaneous emission noise introduced by the second erbium-doped fiber amplifier 9, and finally injected into the sensing optical fiber 12 through the circulator 11; the backscattering Rayleigh scattering light signal generated in the sensing optical fiber 12 due to the non-uniform distribution of the medium refractive index is injected into the third erbium-doped fiber amplifier 13 through the circulator 11 for power amplification, and then enters the second dense wavelength division multiplexer 14 to filter out the spontaneous emission noise, and the multi-frequency modulation of the first acousto-optic modulator 4 and the chopping modulation and frequency shift of the second acousto-optic modulator 8 are controlled by the arbitrary waveform generator 21; the continuous light of the lower branch is adjusted in polarization state by the polarization controller 15, and is used as the intrinsic light together with the backscattering Rayleigh scattering light filtered by the second dense wavelength division multiplexer 14 to pass through the fourth optical fiber coupler 16 for coherent beat frequency, and is converted into photoelectric current by the photoelectric balance detector 17, and the photoelectric current is filtered by the band-pass filter 18, and finally the non-uniform periodic sampling data is recorded by the data acquisition card 19, and the computer 20 is used for data processing, and high-fidelity phase extraction is realized by frequency multiplexing; at the same time, the non-uniform periodic sampling data can effectively avoid the limitation of Nyquist sampling frequency on the system response bandwidth, and the high-fidelity phase information is subjected to non-uniform discrete Fourier transform (NUDFT) to realize frequency characterization of vibration detection time.

[0049] The process of realizing large bandwidth multi-frequency modulation through the ring structure containing the first acousto-optic modulator 4 is as follows:

[0050] Since the first acousto-optic modulator 4 is a bandwidth acousto-optic modulator, it has a certain working bandwidth, and the arbitrary waveform generator 21 provides N microwave signals E1(t), E2(t), …, EN(t) with an amplitude of 1, an initial phase of 0, and frequencies of f, 2f, …, Nf respectively. N (t):

[0051]

[0052] The above N microwave signals E1(t), E2(t) … EN(t) are modulated into multi-frequency continuous light by the first acousto-optic modulator 4. N(t) is freely programmed on the arbitrary waveform generator 21 and finally synthesized into the microwave signal E(t):

[0053]

[0054] The continuous light outputted by the narrow linewidth light source 1 is set to have a frequency f c , an amplitude A, and an initial phase The continuous light is first modulated by the first acousto-optic modulator 4 into multi-frequency continuous light:

[0055]

[0056] The multi-frequency continuous light obtained by the M times of multi-frequency modulation of the ring structure is:

[0057]

[0058] The refractive index and length of the sensing optical fiber 12 are set to be n and L, the light wave propagation speed in vacuum is c, and the time required for one round trip of light wave propagation in the optical fiber is The frequency shift of the second acousto-optic modulator 8 is -Δf, and the multi-frequency continuous light E c (t) is modulated by it with a non-uniform chopping modulation with a period T Figure 2 ∈[T,2T] as shown in the following formula: h

[0059]

[0060] Wherein, A1 is the amplitude of the optical pulse signal E P (t); rect is a rectangular function; T0 is the width of the optical pulse signal E P (t). The optical pulse signal after non-uniform chopping is shown in the following formula: Figure 3 The chopping period distribution and probability density distribution are shown in the following formulas: Figure 4 5

[0061] Then, the m pieces of beat frequency optical signals obtained by non-uniform period sampling through the phase-sensitive optical time domain reflectometer with high-fidelity phase extraction and high-response bandwidth, and the data acquisition card 19 are:

[0062]

[0063] Wherein, B(t) and are the amplitude and phase of the backscattering Rayleigh scattering light signal. The single multi-frequency beat frequency signal and the spectrum are shown in the following formulas: Figure 6 7 After digital filtering processing of the m pieces of beat frequency optical signals, m×M×N pieces of beat frequency optical signals are obtained, and the optical signal at any frequency at any position z is:

[0064] ​​​​

[0065] in, f IF =f i -Δf. The optical signal at any position z at any time is:

[0066]

[0067] Where k = 1, 2, 3, ... is the number of non-uniform periodic sampling lines. Within any phase extraction position interval [z1, z2], the minimum value min[AB] of the amplitude information at positions z1 and z2 is calculated. i (t z1 +kT h ),AB i (t z2 +kT h )], Phase extraction is performed using the beat frequency signal corresponding to the maximum value among the minimum values. This frequency multiplexing method effectively achieves high-fidelity phase extraction in a phase-sensitive optical time-domain reflectometer. In summary, high-fidelity phase information can be extracted from any phase extraction position interval [z1, z2] after frequency multiplexing of the beat frequency signal sampled m times with non-uniform periods. for:

[0068]

[0069] The distortion location information extracted by a traditional phase-sensitive optical time-domain reflectometer is as follows: Figure 8 As shown, the high-fidelity location information extracted in this embodiment of the invention is as follows: Figure 9 As shown. For high-fidelity location information. The frequency F(ω) of the vibration signal detected by the phase-sensitive optical time-domain reflectometer can be obtained by performing a non-uniform discrete Fourier transform (NUDFT). The detection frequency is not limited by the Nyquist sampling rate, which avoids the problem of mutual constraint between sensing distance and system response bandwidth.

[0070]

[0071] In the formula, ω is the angular frequency of the basis function; t n Represents a time series.

[0072] The phase-sensitive optical time domain reflectometer with high-fidelity phase extraction and high-response bandwidth and the working method thereof have the advantages that high-fidelity phase information extraction is effectively realized: in the phase-sensitive optical time domain reflectometer, beat frequency signal lights of different frequencies have different amplitude distributions, and multiplexing is performed based on the amplitude as a judgment basis to realize high-fidelity phase extraction; the advantage is that the most accurate phase information can be accurately extracted on any phase extraction interval; multiplexing frequency is flexible and controllable: the frequency in the optical path is generated by the first acousto-optic modulator modulated by the arbitrary waveform generator, the frequency interval and the number are freely programmed and flexibly controllable, and greater modulation bandwidth can be obtained through multiple modulations of the ring junction; high-response bandwidth: in the phase-sensitive optical time domain reflectometer, to avoid mutual aliasing between detection light pulses, the repetition period of the detection light pulse should be greater than or equal to the time required for a single optical pulse signal to propagate in the sensing optical fiber for one round trip, that is, the response bandwidth of the system is restricted by the sensing distance, according to the Nyquist sampling theorem, the maximum response bandwidth of the system is half of the repetition frequency of the detection light pulse; the method generates detection light pulses by using non-uniform periodic modulation, and non-uniform periodic sampling is performed on the beat frequency signal, which effectively avoids the frequency aliasing of the detection signal, that is, the limitation of the Nyquist sampling frequency on the response bandwidth is avoided; simple system structure: a typical frequency division multiplexing system or a wavelength division multiplexing system usually has a complex structure and high cost, the method loads multiple microwave signals of different frequencies on a single broadband acousto-optic modulator, and non-uniform periodic pulse modulation is used, so that high-fidelity phase extraction and high-response bandwidth are realized, and the structure is simple.

[0073] While the principles and spirit of the application have been described with reference to several specific embodiments, it should be understood that the application is not limited to the disclosed specific embodiments, and the division of aspects does not mean that the features in these aspects cannot be combined for the benefit. The division is only for the convenience of expression. The present application is intended to cover various modifications and equivalent arrangements included in the spirit and scope of the appended claims.

[0074] The documents cited by the present application are as follows:

[0075] [1] M. Zabihi, Y. S. Chen, T. Zhou, et al., "Continuous fading suppression method for Phi-OTDR systems using optimum tracking over multiple probe frequencies", J. Light. Technol. 37, 3602 2019.

[0076] [2] Liu T, Li H, He T, et al., “Fading Noise Free Distributed Acoustic Sensor Assisted with Double Wavelength lasers”, Conference on Lasers and Electro- Optics. IEEE, 2020.

[0077] [3] A. E. Alekseev, V. S. Vdovenko, B. G. Gorshkov, et al. “Fading reduction in a phase optical time-domain reflectometer with multimode sensitive fiber”, Laser Phys. 26, 095101, 2016.

[0078] [4] T. Zhu, Q. He, X. Xiao, and X. Bao, “Modulated pulses based distributed vibration sensing with high frequency response and spatial resolution”, Opt. Express, 21, 2953, 2013.

[0079] [5] Z. Wang, Z. Pan, Z. Fang, and et al., “Ultra-broadband phase-sensitive optical time-domain reflectometry with a temporally sequenced multi-frequency source”, Opt. Lett., 40, 5192, 2015.

Claims

1. A method of operation of a phase sensitive optical time domain reflectometer with high fidelity phase extraction and high response bandwidth, characterized in that: The application relates to a kind of optical fiber sensing system, including narrow line width light source (1), first optical fiber coupler (2), second optical fiber coupler (3), first acousto-optic modulator (4), third optical fiber coupler (5), first erbium-doped fiber amplifier (6), optical isolator (7), second acousto-optic modulator (8), second erbium-doped fiber amplifier (9), first dense wavelength division multiplexer (10), circulator (11), sensing optical fiber (12), third erbium-doped fiber amplifier (13), second dense wavelength division multiplexer (14), polarization controller (15), fourth optical fiber coupler (16), photoelectric balance detector (17), band-pass filter (18), data acquisition card (19), computer (20) and arbitrary waveform generator (21);Wherein, The light signal output end of narrow line width light source (1) is communicated with the light signal input end of first optical fiber coupler (2), the two light signal output ends of first optical fiber coupler (2) are simultaneously communicated with the No.1 light signal input end of second optical fiber coupler (3) and the input end of polarization controller (15) respectively, the light signal output end of second optical fiber coupler (3) is communicated with the light signal input end of first acousto-optic modulator (4), the light signal output end of first acousto-optic modulator (4) is communicated with the light signal input end of third optical fiber coupler (5), the two light signal output ends of third optical fiber coupler (5) are simultaneously communicated with the light signal input end of second acousto-optic modulator (8) and first erbium-doped fiber amplifier (6) respectively, the light signal output end of first erbium-doped fiber amplifier (6) is communicated with the light signal input end of optical isolator (7), the light signal output end of optical isolator (7) is communicated with the No.2 light signal input end of second optical fiber coupler (3); The light signal output end of second acousto-optic modulator (8) is communicated with the light signal input end of second erbium-doped fiber amplifier (9), the light signal output end of second erbium-doped fiber amplifier (9) is communicated with the light signal input end of first dense wavelength division multiplexer (10), the light signal output end of first dense wavelength division multiplexer (10) is communicated with the No.1 light signal port (11-1) of circulator (11), the No.2 light signal port (11-2) of circulator (11) is communicated with sensing optical fiber (12), the No.3 light signal port (11-3) of circulator (11) is communicated with the light signal input end of third erbium-doped fiber amplifier (13), the light signal output end of third erbium-doped fiber amplifier (13) is communicated with the light signal input end of second dense wavelength division multiplexer (14); The light signal input end of fourth optical fiber coupler (16) is simultaneously communicated with the light signal output end of polarization controller (15) and the light signal output end of second dense wavelength division multiplexer (14), the light signal output end of fourth optical fiber coupler (16) is communicated with the light signal input end of photoelectric balance detector (17), the electric signal output end of photoelectric balance detector (17) is communicated with the electric signal input end of band-pass filter (18), the electric signal output end of band-pass filter (18) is communicated with the electric signal input end of data acquisition card (19), data acquisition card (19) is connected with computer (20); The signal output ends of the arbitrary waveform generator (21) are in communication with the microwave signal input end of the first acousto-optic modulator (4), the microwave signal input end of the second acousto-optic modulator (8) and the trigger signal input end of the data acquisition card (19) respectively and simultaneously; The working process of the phase-sensitive optical time domain reflectometer comprises: The continuous light output by the narrow linewidth light source (1) is divided into upper and lower branches by the first optical fiber coupler (2); the continuous light of the upper branch is modulated into multi-frequency continuous light by the first acousto-optic modulator (4) after passing through the second optical fiber coupler (3), and is divided into two paths by the third optical fiber coupler (5); one path of the multi-frequency continuous light is modulated into non-uniform periodic multi-frequency pulsed light by the second acousto-optic modulator (8) and simultaneously generates a certain frequency shift; the other path of the multi-frequency continuous light is amplified by the first erbium-doped fiber amplifier (6), and then enters the first acousto-optic modulator (4) again through the optical isolator (7) and the second optical fiber coupler (3) to be modulated into multi-frequency light, and is also modulated into non-uniform periodic multi-frequency pulsed light by the second acousto-optic modulator (8) and simultaneously generates a certain frequency shift; through multiple modulations in the ring structure, a large bandwidth multi-frequency modulation can be realized; finally, the pulsed peak power is amplified by the second erbium-doped fiber amplifier (9) and injected into the first dense wavelength division multiplexer (10) to filter out the spontaneous emission noise introduced by the second erbium-doped fiber amplifier (9), and finally injected into the sensing optical fiber (12) through the circulator (11); the backscattered Rayleigh scattering light signal generated in the sensing optical fiber (12) due to the non-uniform distribution of the medium refractive index is injected into the third erbium-doped fiber amplifier (13) through the circulator (11) for power amplification, and then enters the second dense wavelength division multiplexer (14) to filter out the spontaneous emission noise; the multi-frequency modulation of the first acousto-optic modulator (4) and the chopping modulation and frequency shift of the second acousto-optic modulator (8) are all controlled by the arbitrary waveform generator (21); The continuous light of the lower branch is adjusted in polarization state by the polarization controller (15) and then injected into the fourth optical fiber coupler (16) together with the backscattered Rayleigh scattering light filtered by the second dense wavelength division multiplexer (14) to perform coherent beat frequency, and then photoelectrically converted by the photoelectric balance detector (17); the output photoelectric current is filtered by the band-pass filter (18), and finally the non-uniform periodic sampling of the multi-frequency beat frequency light signal is recorded by the data acquisition card (19); the computer (20) is used for data processing; high-fidelity phase extraction is realized through frequency multiplexing; and the vibration detection time is characterized in frequency by performing non-uniform discrete Fourier transform on the high-fidelity phase information.

2. The method of operation of a phase sensitive optical time domain reflectometer with high fidelity phase extraction and high response bandwidth according to claim 1, characterized in that: The narrow linewidth light source (1) is a single-frequency narrow linewidth fiber laser, the output power is 10 dBm, and the output wavelength is 1550.12 nm.

3. The method of operation of a phase sensitive optical time domain reflectometer with high fidelity phase extraction and high response bandwidth according to claim 1, characterized in that: The first optical fiber coupler (2) is a 90:10 three-port coupler, the second optical fiber coupler (3) is a 50:50 three-port coupler, the third optical fiber coupler (5) is a 50:50 2x2 coupler, and the fourth optical fiber coupler (16) is a 50:50 2x2 coupler.

4. The method of operation of a phase sensitive optical time domain reflectometer with high fidelity phase extraction and high response bandwidth according to claim 1, characterized in that: The center frequency of the first acousto-optic modulator (4) is 100 MHz, and the working bandwidth is 120 MHz; the frequency shift of the second acousto-optic modulator (8) is -40 MHz, and the extinction ratio is 50 dB.

5. The method of operation of a phase sensitive optical time domain reflectometer with high fidelity phase extraction and high response bandwidth according to claim 1, characterized in that: The working wave bands of the first dense wavelength division multiplexer (10) and the second dense wavelength division multiplexer (14) are 1480 nm and 1550.12 nm, and the attenuation bandwidth is 0.22 nm.

6. The method of operation of a phase sensitive optical time domain reflectometer with high fidelity phase extraction and high response bandwidth according to claim 1, characterized in that: The detection bandwidth of the photoelectric balance detector (17) is 350 MHz.

7. The method of operation of a phase sensitive optical time domain reflectometer with high fidelity phase extraction and high response bandwidth according to claim 1, characterized in that: The passband range of the bandpass filter (18) is 20 MHz-360 MHz.

8. The method of operation of a phase sensitive optical time domain reflectometer with high fidelity phase extraction and high response bandwidth according to claim 1, characterized in that, In the working process of the phase-sensitive optical time domain reflectometer, through multiple modulations of the ring structure, the large-bandwidth multi-frequency continuous light output by the first acousto-optic modulator (4) is represented as: In the formula, A represents the amplitude of the continuous light outputted by the narrow linewidth light source (1); f c represents the frequency of the continuous light outputted by the narrow linewidth light source (1); M represents the modulation times; N represents the number of microwave signals; f represents the frequency interval of the microwave signals; and φ0 represents the initial phase of the continuous light outputted by the narrow linewidth light source (1). After being modulated by the second acousto-optic modulator (8), the non-uniform periodic multi-frequency pulse light output is represented as: wherein A1 is the optical pulse signal E P (t) ; rect is a rectangular function; To is the width of the optical pulse signal E P (t) ; -△f represents the frequency shift of the second acousto-optic modulator (8). Then, m beat frequency light signals obtained by the non-uniform periodic sampling of the data acquisition card (19) are represented as: where T h ∈ [T, 2T], n and L represent the refractive index and length of the sensing fiber (12), respectively, and c represents the speed of light in vacuum; B i (t) and φ i (t) represent the amplitude and phase of the i-th backscattered Rayleigh signal, respectively.

9. The method of operation of a phase sensitive optical time domain reflectometer with high fidelity phase extraction and high response bandwidth according to claim 8, characterized in that, The computer (20) carries out data processing process, including: for each of the m beat frequency optical signals obtained by non-uniform period sampling of the data acquisition card (19), extracting the amplitude information [AB i (t z1 +kT h ), AB i (t z2 +kT h )] at the position interval [z1, z2] at any phase of the beat frequency optical signal, and finding the minimum value of the amplitude information, k=1, 2, 3,... is the number of non-uniform period sampling; and the beat frequency signal corresponding to the maximum value in the minimum value is phase-extracted, and the extracted high-fidelity phase information is: High fidelity phase information The frequency F(ω) of the vibration signal detected by the phase-sensitive optical time-domain reflectometer can be obtained by performing a non-uniform discrete Fourier transform where ω is the basis function angular frequency; t n denotes the time series.

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