CN117527086A - Phase noise compensation method and distributed optical fiber acoustic wave sensor system - Google Patents
Phase noise compensation method and distributed optical fiber acoustic wave sensor system Download PDFInfo
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Abstract
The invention relates to a phase noise compensation method and a distributed optical fiber acoustic wave sensing system, wherein the method comprises the following steps: based on the phase noise measuring device and the signal reconstruction algorithm, respectively reconstructing the detection signals transmitted by the coherent receiving and matched filtering type sensing system and the local signals of the coherent receiver in real time; respectively carrying out phase compensation on the matched filtering kernel function and the coherent receiving signal according to the reconstructed real-time phase noise signal; and demodulating the signal based on the phase noise compensated matched filter kernel function and the coherent received signal. Compared with the prior art, the invention can completely compensate the system performance degradation problem caused by demodulation distortion caused by phase noise in the coherent receiving and matched filtering sensing system by carrying out phase noise compensation on the coherent receiving signal and the matched filtering kernel function.
Description
Technical Field
The invention relates to the technical fields of sensing technology and radar, in particular to a phase noise compensation method and a distributed optical fiber acoustic wave sensor system.
Background
The sensing technology is one of three main posts of the current information technology, and is an important bridge for the communication between the information world and the physical world. One important class of sensing technologies that is widely used includes distributed fiber optic sensors, lidar, millimeter wave radar, radio frequency radar, and the like. The method comprises the steps of utilizing a sensing system to emit detection signals (detection waves) to an optical fiber or free space, capturing signals returned to the sensing system by scattering or reflection effects of an object to be detected in the optical fiber or free space, and finally analyzing information of the object to be detected.
For the above-mentioned sensing system, the coherent receiving technology and the matched filtering technology are all important means for further improving the system performance. Coherent reception finger: and for the echo signal, firstly, interfering the echo signal with a reference signal local to the system, and then detecting the echo signal. Compared with direct detection, the coherent reception can obviously improve the signal to noise ratio of detection, and key technologies such as balanced detection, orthogonal coherent reception, polarization diversity reception and the like are further evolved. Matched filtering means: selecting a long-duration signal with good time-frequency performance to replace a narrow pulse signal with short duration as a detection wave; meanwhile, after the echo receiving is completed, based on the predicted kernel function containing the time-frequency information of the detection wave, matched filtering operation is performed to accurately recover the information of the target to be detected. The technology can effectively solve the problem that the signal to noise ratio of the system reaches the bottleneck under the common limiting factor of limited peak power of the detection signal.
The two technologies (a coherent receiving technology and a matched filtering technology) effectively improve the system performance and simultaneously have higher requirements on the ideal degree of the time-frequency characteristics of signals of all links in the system. In coherent reception, if the reference signal local to the system carries phase noise, the phase information of the signal detected after interference with the echo signal is necessarily reflected, so that the reality degree of the output signal of the receiver is affected. Matched filtering exploits the mathematical property of detecting the autocorrelation locality (pulse compression) of a wave kernel, which depends on the exact pre-designed time-frequency characteristics of the kernel. Once the time-frequency characteristic distortion is large, the effect of the matched filtering is obviously reduced, and even the effect is the opposite. Thus, in coherent reception and matched filtering sensing systems, it is generally desirable that the phase noise level of each functional unit in the system be as low as possible.
When the level of phase noise within the sensing system is limited by technical factors or cost, if it is desired to break through the system performance bottleneck, a phase noise compensation technique needs to be introduced. However, taking into account the phase noise introduced by coherent reception and the phase distortion suffered by matched filtering, the phase distortion occurs in both the receiver and transmitter parts of the system, respectively. The process between transmitting and receiving, namely the process of interaction between the detection wave and the target to be detected and echo generation, is extremely complex, such as the situation that the position of the target is unknown, a plurality of targets with different echo intensities are overlapped, and even the whole process of the optical fiber in the distributed optical fiber sensing system is regarded as the target to be detected.
Therefore, it is very challenging to design a phase noise compensation method that can cover all cases completely. In addition, the design of the phase noise compensation method also faces the problems of compatibility with a specific demodulation algorithm, the calculated amount of signal processing and the like.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a phase noise compensation method and a distributed optical fiber acoustic wave sensor system, which can completely compensate the system performance degradation problem caused by demodulation distortion caused by phase noise in a coherent receiving and matched filtering type sensing system by carrying out phase noise compensation on a coherent receiving signal and a matched filtering kernel function.
The aim of the invention can be achieved by the following technical scheme:
according to a first aspect of the present invention, there is provided a phase noise compensation method for a coherent reception and matched filtering type sensing system, the method comprising:
based on the phase noise measuring device and the signal reconstruction algorithm, respectively carrying out real-time phase noise signal reconstruction on the detection signals transmitted by the coherent receiving and matched filtering type sensing system and the local signals of the coherent receiver;
respectively carrying out phase compensation on the matched filtering kernel function and the coherent receiving signal according to the reconstructed real-time phase noise signal; and
and carrying out signal demodulation based on the phase noise compensated matched filtering kernel function and the coherent received signal.
Preferably, the reconstruction process of the real-time phase noise signal is to convert an observable electrical signal into phase information of an input signal, specifically: and calculating an absolute phase signal in real time according to the phase noise signal output by the phase noise measuring device, and subtracting a preset ideal phase signal to obtain a reconstructed real-time phase noise signal.
Preferably, when the phase noise of the detection signal transmitted by the coherent receiving and matched filtering type sensing system is the same as the phase noise source or main source of the local signal of the coherent receiver, the same phase noise measuring device can be used for phase noise reconstruction; when the source or main source of phase noise of the detection signal transmitted by the coherent receiving and matched filtering type sensing system is different from that of the local signal of the coherent receiver, the phase noise is reconstructed by using different phase noise measuring devices.
Preferably, the signal demodulation is performed based on the phase compensated matched filtering kernel function and the coherent received signal, specifically: and performing cross-correlation operation on the phase noise compensated matched filtering kernel function and the coherent receiving signal to obtain a demodulation signal after phase noise compensation.
Preferably, the coherent received signal and the real-time phase noise signal are converted into corresponding complex signals by using hilbert transform of a digital domain before reconstruction.
Preferably, the phase noise compensated coherent received signal expression is:
wherein S (t) is an analysis signal of the coherent received signal before phase noise compensation, exp [. Cndot.]Representing a complex-valued natural logarithmic function,is a real-time phase noise function of the local signal of the coherent receiver.
Preferably, the phase noise compensated matched filter kernel expression is:
wherein k (t) is a matched filter kernel function before phase noise compensation, exp [. Cndot.]Representing a complex-valued natural logarithmic function,as a function of the real-time phase noise of the probe signal.
According to a second aspect of the present invention there is provided a coherent reception and matched filtering sensing system, the system comprising:
a coherent light source for outputting a continuous laser light disturbed by phase noise;
the first beam splitter is used for splitting continuous laser output by the coherent light source;
the optical modulation unit is used for modulating the laser after the light splitting of the first light splitter to generate detection light;
the optical circulator is used for injecting the detection light output by the optical modulation unit into the sensing optical fiber to be detected and receiving the back scattered light returned by the sensing optical fiber;
the coherent receiver is used for beating frequency according to the local light injected into the local port of the coherent receiver by the second optical splitter and the back scattered light entering the signal port of the coherent receiver to generate a coherent receiving signal;
the second beam splitter is used for splitting the output of the first beam splitter;
the phase noise measuring device is used for measuring a real-time phase noise signal corresponding to the local signal of the coherent receiver and a real-time phase noise signal of the detection light;
the phase compensation output unit is used for carrying out phase noise compensation and signal demodulation by adopting the method of claim 1 according to the coherent receiving signal output by the coherent receiver and the real-time phase noise signal output by the phase noise measuring device, so as to obtain the response of the sensing optical fiber after the phase noise compensation.
Preferably, the phase noise measuring device comprises a beam splitter, a delay fiber, a 90-degree optical bridge, a first balanced photoelectric detector and a second balanced photoelectric detector;
and the laser output by the second optical splitter is directly input to the 90-degree optical bridge through the optical splitter, the laser output by the second optical splitter is input to the 90-degree optical bridge after passing through the delay optical fiber, and the output of the 90-degree optical bridge is respectively input to a first balanced photoelectric detector and a second balanced photoelectric detector to measure a real-time phase noise signal corresponding to a local signal of the coherent receiver.
Preferably, the real-time phase noise signal corresponding to the local signal of the coherent receiver corresponds to the analytic signal expression:
wherein I is i (t)、I q (t) outputting an I-path phase noise differential signal of a coherent light source for the first balanced photoelectric detector and a Q-path phase noise differential signal for the second balanced photoelectric detector respectively, ρ 3 Represents the intensity scaling factor, E, introduced by the phase noise measuring device corresponding to the optical path 0 Vector intensity, omega of photoelectric field output by coherent light source 0 For the angular frequency of the light source, τ A To delay the self time of the optical fiber N (t) is the phase noise term of the coherent light source; Δφ N And (t) is the phase difference of the coherent light source and self-delay, which is the optical path difference introduced by the delay optical fiber.
Compared with the prior art, the invention has the following advantages:
1) The method of the invention carries out phase noise compensation on the coherent receiving signal and the matched filtering kernel function in parallel, thereby being capable of completely compensating demodulation distortion caused by phase noise in the coherent receiving and matched filtering sensing system and further causing the problem of system performance degradation.
2) The method does not depend on any assumption or estimation of the state of the target to be detected, does not need to change other steps of a demodulation algorithm, has small calculated amount and has good universality.
Drawings
FIG. 1 is a flow chart of a phase noise compensation method of the present invention;
fig. 2 is a schematic diagram of a phase noise compensation method in an embodiment
FIG. 3 is a schematic diagram of a distributed fiber optic acoustic wave sensor system with phase noise compensation according to an embodiment of the present invention;
FIG. 4 is a diagram showing an internal structure of a phase noise measuring apparatus in a system according to an embodiment of the present invention;
FIG. 5 is a diagram showing the practical effect of a distributed optical fiber acoustic wave sensor with phase noise compensation according to an embodiment of the present invention;
reference numerals: 1-a coherent light source; 2-a first beam splitter; a 3-light modulation unit; a 4-light circulator; 5-sensing optical fibers; 6-a first beam splitter; 7-a coherent receiver; the device comprises an 8-phase noise measuring device, an 81-beam splitter, an 82-delay optical fiber, an 83-90-degree optical bridge, an 84-first balance photoelectric detector and an 85-second balance photoelectric detector; 9-phase compensation output unit.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
Examples
The present embodiment provides a phase noise compensation method for a coherent receiving and matched filtering type sensing system, as shown in fig. 1, the method includes:
based on the phase noise measuring device and the signal reconstruction algorithm, respectively reconstructing the detection signals transmitted by the coherent receiving and matched filtering type sensing system and the local signals of the coherent receiver in real time;
respectively carrying out phase compensation on the matched filtering kernel function and the coherent receiving signal according to the reconstructed real-time phase noise signal;
and performing cross-correlation operation on the phase noise compensated matched filtering kernel function and the coherent receiving signal, and analyzing the related information of the target to be detected of the sensing system by using a matched filtering technology to obtain a demodulation signal after phase noise compensation.
The reconstruction process of the real-time phase noise signal is a process of converting an observable electric signal into phase information of an input signal, and specifically comprises the following steps: and calculating an absolute phase signal in real time according to the phase noise signal output by the phase noise measuring device, and subtracting a preset ideal phase signal to obtain a reconstructed real-time phase noise signal.
The coherent receiving and matched filtering type sensing system in the embodiment refers to a sensing system such as a distributed optical fiber sensor, a laser radar, a millimeter wave radar, a radio frequency radar and the like which utilize a coherent receiving technology to improve the receiving performance of echo signals and utilize a matched filtering technology to realize pulse compression and introduce additional signal-to-noise ratio gain.
Further, when the phase noise of the detection signal transmitted by the coherent receiving and matched filtering type sensing system is the same as the phase noise source or main source of the local signal of the coherent receiver, the same phase noise measuring device can be used for reconstructing the phase noise, and at the moment; when the source or main source of phase noise of the detection signal transmitted by the coherent receiving and matched filtering type sensing system is different from that of the local signal of the coherent receiver, the phase noise is reconstructed by using different phase noise measuring devices.
It should be noted that, in this embodiment, the digital domain hilbert transform is adopted to convert the coherent received signal and the real-time phase noise signal into corresponding complex signals before the reconstruction is performed, so as to perform the analysis processing.
The kernel function of matched filtering demodulation refers to a complex-valued function which is designed in advance and has good time-frequency characteristics and is used for modulating a detection signal transmitted by a generating system, and the complex-valued function is marked as k (t). The echo signal refers to a complex value signal which is reflected or scattered by an object to be detected of the sensing system, thus carrying information thereof, and is acquired by a coherent receiver and is marked as S (t).
Phase noise compensated matched filter kernel function k A The expression (t) is:
wherein k (t) is a matched filter kernel function before phase noise compensation, exp [. Cndot.]Representing a complex-valued natural logarithmic function,the phase of k (t) is modified for the real-time phase noise function of the probe signal.
Phase noise compensated coherent received signal S A The expression (t) is:
wherein S (t) is a coherent received signal before phase noise compensation, exp [. Cndot.]Representing a complex-valued natural logarithmic function,the phase of S (t) is modified for a real-time phase noise function of the local signal of the coherent receiver.
Next, this embodiment provides a distributed optical fiber acoustic wave sensing system with phase noise compensation, which adopts coherent receiving and matched filtering techniques, as shown in fig. 3, and includes:
a coherent light source 1 for outputting a continuous laser light disturbed by phase noise;
a first beam splitter 2 for splitting the continuous laser light output from the coherent light source 1;
an optical modulation unit 3 for modulating the laser beam split by the first beam splitter 2 to generate a detection pulse light;
the optical circulator 4 is used for injecting the detection pulse light output by the optical modulation unit 3 into the sensing optical fiber 5 to be detected and receiving back scattered light returned by the sensing optical fiber 5;
the coherent receiver 7 is configured to beat frequencies according to the local light injected into the local port of the coherent receiver 7 by the second optical splitter 6 and the back-scattered light entering the signal port of the coherent receiver 7, and generate a coherent reception signal;
a second beam splitter 6 for splitting the output of the first beam splitter 2;
a phase noise measuring device 8 for measuring a real-time phase noise signal corresponding to the local signal of the coherent receiver 7 and a real-time phase noise signal of the probe light;
the phase compensation output unit 9 is configured to perform phase noise compensation and signal demodulation according to the coherent received signal output by the coherent receiver 7 and the real-time phase noise signal output by the phase noise measurement device 8 by using the above method, so as to obtain the response of the sensing optical fiber 5 after phase noise compensation.
As can be seen from fig. 2, the second optical splitter 2 and the phase noise measuring device 8 in this embodiment are both auxiliary devices for compensating phase noise, and the rest are all necessary functional units of the long-distance distributed optical fiber acoustic wave sensor.
The phase noise measuring device 8 may be an auxiliary interferometer, which mainly takes the internal physical signal of the system as input, and converts the phase information thereof into an observable electrical signal in real time and outputs the observable electrical signal.
Because the detection signal transmitted by the system and the local signal of the coherent receiver have the main sources of phase noise of the coherent light source, the reconstruction of the real-time phase noise signal is realized by adopting the same phase noise measuring device 8. It should be noted that unlike in a typical radar system, the echo signal of interest is generated by reflection from only a single target, and for a distributed fiber acoustic wave sensor, each position of the sensing fiber generates an echo due to the backward Rayleigh scattering effect and is superimposed back to the sensing system; this allows the effectiveness of the method of the invention to be completely verified.
Next, each part of the system of the present embodiment will be described in detail.
The coherent light source 1 outputs a continuous laser light disturbed by phase noise, and in this embodiment, the line width of the coherent light source is 100kHz, the center wavelength is 1550nm, the output power is 13dBm, and the output optical field vector can be expressed as:
wherein E is 0 Vector intensity, omega of photoelectric field output by coherent light source 0 Is the angular frequency of the light source phi N (t) is the phase noise term of the coherent light source. The output of the coherent light source 1 is connected to the input of the first beam splitter 2.
In this embodiment, the optical modulation unit 3 selects an acousto-optic modulator, an input end of the optical modulation unit is connected to a first output end of the first light splitting period 2, and after the optical modulation unit modulates the optical modulation, a detection pulse light for detecting the sensing optical fiber 5 is generated, and an electric field of the detection pulse light is expressed as:
wherein ρ is 1 Light intensity scaling factor, E, introduced for the corresponding light path 0 The vector intensity omega of the photoelectric field output by the coherent light source 1 0 Is the angular frequency of the light source phi N (t) is the phase noise term of the coherent light source 1; k (t) is a radio frequency signal for driving the acousto-optic modulator and is also a kernel function required in the demodulation process, so that k (t) =expi [ phi ] is satisfied k (t)]Wherein phi is k (t) is a phase term of the kernel function.
The output port of the acousto-optic modulator is connected with the first port of the optical circulator 4, and is injected into the sensing optical fiber 5 through the second port of the optical circulator 4, and the excited back Rayleigh scattered light signal is expressed as:
wherein v is g For group velocity of light in sensing fiber, T M For the duration of the kernel function, τ is the integral variable, and R represents the response of the sensing fiber, i.e., the target parameter that needs to be measured in this embodiment. Rayleigh backscattering back to the second port of optical circulator 4 and out the third port of optical circulator 4; the third port of the optical circulator 4 is connected to a signal port of a coherent receiver 7.
The second output end of the first optical splitter 2 is connected to the second optical splitter 6, the output end of the second optical splitter is connected to the local port of the coherent receiver 7, and the local light injected into the local port of the coherent receiver 7 and the back scattered light entering the signal port of the coherent receiver 7 are subjected to beat frequency to generate a coherent receiving signal, which is expressed as:
wherein ρ is 2 The intensity scaling factor is introduced for the part of the optical path from the first optical splitter to the coherent receiver, re represents the real part of the complex signal, and R is the response of the sensing optical fiber under the receiving bandwidth;
after entering the digital signal processing unit 9, the coherent received signal is converted into an analytic signal, namely a first digital signal:
wherein,is a convolution operator, k N (t) is a kernel function perturbed by phase noise of the light source, satisfying k N (t)＝k(t)expi[φ N (t)]。
As shown in fig. 4, the phase noise measuring device 8 includes a beam splitter 81, a delay fiber 82, a 90-degree optical bridge 83, a first balanced photodetector 84, and a second balanced photodetector 85. The device is an orthogonal coherent receiver. In this embodiment, the length of the delay fiber is 20 meters, corresponding toDelay amount tau A And approximately 100ns. In the phase noise measuring unit, the first balanced photoelectric detector and the second balanced photoelectric detector respectively output an I path and a Q path of a differential signal for measuring the phase noise of the coherent light source, which are phase differencesThe corresponding analytic signal, i.e., the second digital signal, can be expressed as:
wherein ρ is 3 Represents the intensity scaling factor, Δφ, introduced in the phase noise measurement device 8 in response to the optical path N (t) the optical path difference introduced by the delay optical fiber corresponds to the phase difference between the coherent light source and the self delay, and the delta phi is satisfied N (t)＝φ N (t)-φ N (t-τ A )，τ A Is the self-delay of the delay fiber.
In this embodiment, the first digital signal and the second digital signal are sent to the phase compensation output unit 9 for performing the phase noise compensation operation.
1) And reconstructing the second digital signal to restore the phase noise of the coherent light source.
Taking the argument for the second digital signal S (t):
Δφ A (t)＝Arg[S(t)]＝ω res τ A +φ N (t)-φ N (t-τ A )
wherein Arg {.cndot } represents taking principal value of argument, ω, for plural numbers res τ A Is a residual phase term, the value of which is related to the instantaneous frequency of the coherent light source and the length of the delay fiber in the phase noise measuring device (8);
for delta phi A (t) performing a one-step integration operation to obtain a reconstructed light source phase noise, i.e., a third digital signal:
2) After the third digital signal is obtained, compensating the phase noise item introduced by the local light in the beat frequency process in the first digital signalObtaining a fourth digital signal:
it is known that the phase noise term in the fourth signal, which is introduced by the beat process in the local light, has been eliminated.
3) By multiplying the reconstructed phase noise term, i.e. the third digital signal, with the used kernel function, a new reconstructed kernel function, i.e. the fifth digital signal, is obtained:
4) Performing cross-correlation operation on the fourth digital signal and the fifth digital signal to obtain the response of the sensing optical fiber after phase noise compensation, namely a sixth digital signal:
wherein x is A (t) is an autocorrelation function of the fifth digital signal, since the kernel function k (t) is a broad spectrum signal, x A (t) the width in the time domain is inversely proportional to the bandwidth of k (t), so that R is obtained after phase noise compensation pnc Can be approximately regarded as the response of the sensing medium and no longer contain the phase noise term phi N (t). For the sixth digital signal R pnc And converting to obtain strain distribution information of all positions on the sensing optical fiber.
FIG. 5 givesAnd the distribution curve of the strain resolution along with the distance in the demodulation result of the distributed optical fiber acoustic wave sensor in the embodiment is obtained before and after phase noise compensation, and the smaller the value of the strain resolution is, the better the system performance is. As can be seen from FIG. 5, after the phase noise compensation method of the present invention is used, the strain resolution can be still achieved at the end of the 50km sensing fiberThis result demonstrates the effectiveness of the method of the present invention.
While the invention has been described with reference to certain preferred embodiments, it will be understood by those skilled in the art that various changes and substitutions of equivalents may be made and equivalents will be apparent to those skilled in the art without departing from the scope of the invention. Therefore, the protection scope of the invention is subject to the protection scope of the claims.
Claims (10)
1. A method for compensating phase noise for a coherent reception and matched filtering type sensing system, the method comprising:
based on the phase noise measuring device and the signal reconstruction algorithm, respectively reconstructing the detection signals transmitted by the coherent receiving and matched filtering type sensing system and the local signals of the coherent receiver in real time;
respectively carrying out phase compensation on the matched filtering kernel function and the coherent receiving signal according to the reconstructed real-time phase noise signal; and
and carrying out signal demodulation based on the phase noise compensated matched filtering kernel function and the coherent received signal.
2. The method for compensating phase noise of coherent receiving and matched filtering type sensing system according to claim 1, wherein the reconstruction process of the real-time phase noise signal is a process of converting an observable electrical signal into phase information of an input signal, specifically: and calculating an absolute phase signal in real time according to the phase noise signal output by the phase noise measuring device, and subtracting a preset ideal phase signal to obtain a reconstructed real-time phase noise signal.
3. The method for compensating phase noise of a coherent reception and matched filtering type sensing system according to claim 1, wherein when phase noise of a detection signal transmitted by the coherent reception and matched filtering type sensing system is the same as a phase noise source or a main source of a local signal of a coherent receiver, the same phase noise measuring device is used for phase noise reconstruction; when the source or main source of phase noise of the detection signal transmitted by the coherent receiving and matched filtering type sensing system is different from that of the local signal of the coherent receiver, the phase noise is reconstructed by using different phase noise measuring devices.
4. The method for compensating phase noise of a coherent receiving and matched filtering type sensing system according to claim 1, wherein the signal demodulation is performed based on the matched filtering kernel function after phase compensation and the coherent receiving signal, specifically: and performing cross-correlation operation on the phase noise compensated matched filtering kernel function and the coherent receiving signal to obtain a demodulation signal after phase noise compensation.
5. The method for compensating phase noise of a coherent receiving and matched filtering type sensing system according to claim 1, wherein the coherent receiving signal and the real-time phase noise signal are converted into corresponding complex signals by using hilbert transform of a digital domain before reconstruction, and are analyzed.
6. The method for compensating phase noise of coherent receiving and matched filtering type sensing system according to claim 5, wherein the phase noise compensated coherent receiving signal expression is:
wherein S (t) is an analysis signal of the coherent received signal before phase noise compensation, exp [. Cndot.]Representing a complex-valued natural logarithmic function,is a real-time phase noise function of the local signal of the coherent receiver.
7. The method for compensating phase noise in a coherent reception and matched filter sensing system of claim 5, wherein the phase noise compensated matched filter kernel expression is:
wherein k (t) is a matched filter kernel function before phase noise compensation, exp [. Cndot.]Representing a complex-valued natural logarithmic function,as a function of the real-time phase noise of the probe signal.
8. A distributed fiber optic acoustic wave sensing system, the system comprising:
a coherent light source (1) for outputting a continuous laser light disturbed by phase noise;
a first beam splitter (2) for splitting the continuous laser beam output from the coherent light source (1);
the optical modulation unit (3) is used for modulating the laser after being split by the first beam splitter (2) to generate detection light;
the optical circulator (4) is used for injecting the detection light output by the optical modulation unit (3) into the sensing optical fiber (5) to be detected and receiving the back scattered light returned by the sensing optical fiber (5);
a coherent receiver (7) for generating a coherent reception signal according to beat frequency of the local light injected into the local port of the coherent receiver (7) by the second optical splitter (6) and the back-scattered light entering the signal port of the coherent receiver (7);
a second beam splitter (6) for splitting the output of the first beam splitter (2);
a phase noise measuring device (8) for measuring a real-time phase noise signal corresponding to a local signal of the coherent receiver (7) and a real-time phase noise signal of the probe light;
a phase compensation output unit (9) for performing phase noise compensation and signal demodulation according to the coherent received signal output by the coherent receiver (7) and the real-time phase noise signal output by the phase noise measurement device (8) by adopting the method of claim 1, so as to obtain the response of the sensing optical fiber (5) after phase noise compensation.
9. The system according to claim 8, characterized in that the phase noise measuring device (8) comprises a beam splitter (81), a delay fiber (82), a 90 degree optical bridge (83), a first balanced photodetector (84) and a second balanced photodetector (85);
the laser output by the second optical splitter (6) is directly input to the 90-degree optical bridge (83) through the optical splitter (81), the laser output by the second optical splitter is input to the 90-degree optical bridge (83) after passing through the delay optical fiber (82), and the output of the 90-degree optical bridge (83) is respectively input to the first balance photoelectric detector (84) and the second balance photoelectric detector (85) to measure real-time phase noise signals corresponding to local signals of the coherent receiver (7).
10. The system according to claim 9, wherein the real-time phase noise signal corresponding to the local signal of the coherent receiver (7) has a resolved signal expression:
wherein I is i (t)、I 1 (t) are respectively the first balanced photoelectric probesThe detector (84) outputs an I-path phase noise differential signal of the coherent light source, the second balanced photodetector (85) outputs a Q-path phase noise differential signal, ρ 3 Represents the intensity scaling factor, E, introduced by the phase noise measuring device (8) in correspondence with the optical path 0 The vector intensity omega of the photoelectric field output by the coherent light source (1) 0 For the angular frequency of the light source, τ A To delay the self time of the optical fiber N (t) is the phase noise term of the coherent light source (1); Δφ N And (t) is the phase difference of the coherent light source and self-delay, which is the optical path difference introduced by the delay optical fiber (82).
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