CN117419751A - Time delay interference laser phase noise compensation method and device for optical frequency domain reflection - Google Patents
Time delay interference laser phase noise compensation method and device for optical frequency domain reflection Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
- G01D5/35354—Sensor working in reflection
- G01D5/35358—Sensor working in reflection using backscattering to detect the measured quantity
- G01D5/35361—Sensor working in reflection using backscattering to detect the measured quantity using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering
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- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
- G01D5/35332—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using other interferometers
Abstract
The invention discloses a time delay interference laser phase noise compensation method and device for optical frequency domain reflection, comprising the following steps: acquiring linear sweep frequency signal light based on a signal source; the sweep frequency signal light obtains a first heterodyne signal through a measurement interferometer, and the sweep frequency signal light obtains a second heterodyne signal through a reference interferometer; the first heterodyne signal and the second heterodyne signal are processed by adopting a time delay interference algorithm, so that direct compensation of laser phase noise is realized; and obtaining a strain signal based on direct compensation and reduction of the laser phase noise. The invention can realize high-precision measurement of the strain signal under the distance far exceeding the coherence length of the light source by compensating the phase noise of the laser.
Description
Technical Field
The invention relates to the technical field of distributed optical fiber sensing and laser measurement, in particular to a time delay interference laser phase noise compensation method and device for optical frequency domain reflection.
Background
The distributed optical fiber sensing and measuring technology can utilize physical mechanisms such as Rayleigh scattering, brillouin scattering and the like in the optical fiber, and sense, acquire and analyze physical quantity information and states of the optical fiber along the line by detecting the characteristics of the backward scattered light signals in the optical fiber. The Optical Frequency Domain Reflection (OFDR) technology is a typical distributed optical fiber sensing and measuring technology, and the measuring principle is based on high-coherence low-phase-noise wide-range linear sweep laser and coherent demodulation. The sensing mechanism of the OFDR on the physical quantity along the optical fiber can be further divided into an amplitude type OFDR and a phase type OFDR (phi-OFDR). The amplitude type OFDR realizes the perception of information by analyzing and comparing the correlation between measurement results at different moments by means of the statistical characteristics of the backward Rayleigh scattering amplitude. In contrast, phi-OFDR relies on the extraction of phase information of backward Rayleigh scattering signals in optical fibers, and through analysis of the phase of beat signals, accurate waveform (including frequency, amplitude and the like) information of the physical quantity to be measured can be obtained. The phase of the backward Rayleigh scattering has linear response relation with the physical quantity to be measured such as vibration and strain, so that compared with the amplitude type OFDR, the phi-OFDR has higher sensitivity and measurement accuracy, and is an important direction of the development of the OFDR technology. The invention further researches and improves the phi-OFDR technology to meet the requirements of specific fields and improve the performance and the application value.
Indeed, the generation of high coherence, low phase noise, wide range linear swept lasers faces a number of technical challenges. On the one hand, narrow linewidth lasers tend to have limited tuning performance and are more difficult to support over a wide range of sweeps. Lasers with a wide tuning range typically require a wide range of frequency sweeps to be achieved by tuning their cavity length, and their cavity stability is susceptible to poor phase noise. Meanwhile, based on the sweep laser generated by the external modulation method, the frequency sweep range is limited by the modulation bandwidth of the optical and electrical devices, and the additional modulation drive increases the cost and complexity of the system.
For this current situation, a phase noise compensation technique is required to suppress the influence and restriction of the phase noise compensation technique on the measurement performance of the system. At present, the reported laser phase noise compensation technology generally utilizes light-assisted interference to acquire phase error information, and then adopts a digital mode to carry out phase compensation on signals.
Currently, the mainstream laser phase noise compensation technology can be divided into three main methods:
1. phase noise compensation technology based on resampling: the method uses the equal phase interval points of the auxiliary interferometer signal as a sampling clock to resample the auxiliary interferometer signal, and then uses the resampled signal to perform phase noise compensation on the original measurement signal.
2. Phase noise compensated optical frequency domain reflectometer (PNC-OFDR): the method utilizes an external modulation method to generate linear sweep frequency light, and utilizes a junction-to-phase generation method on the basis of a resampling phase noise compensation technology to obtain a reference signal suitable for long-distance measurement.
3. The technology of compensating laser phase noise by a declivity filtering method comprises the following steps: the method first estimates the laser phase error using the auxiliary arm signal, and then compensates for the laser phase noise using a deskew filter.
Although the signal acquisition and processing modes of the three methods are different to a certain extent, the method is based on an auxiliary interference structure so as to acquire phase noise information of laser, and the beat frequency phase noise caused by the laser phase noise is compensated by utilizing the auxiliary interference structure, so that the influence of the laser phase noise on OFDR performance is reduced, the effective measurement distance is improved, and the theoretical spatial resolution reaching the limit of the sweep frequency range is ensured.
However, since the above methods all rely on the constructed auxiliary interference structure for the acquisition of phase noise, they face some common problems: firstly, the auxiliary interference needs long interference arm delay difference, the length is about half of the coherence length of a light source, so that an interference signal is sensitive to the environment, the stability is poor, and the actual application requirement cannot be met; secondly, the long auxiliary interference arm can only estimate the position of the optical fiber with delay close to the arm length, so that the compensation effect is uneven and the signal to noise ratio fluctuation is large. The best compensation effect is that echo signals with positions close to the length of the auxiliary interference arm, and signals deviating from the positions are poor in compensation effect; thirdly, the phase compensation method is mainly aimed at the amplitude of the backward Rayleigh scattering signal, namely, the amplitude broadening and the signal-to-noise ratio deterioration caused by laser phase noise are mainly compensated and corrected, and the exact waveform, frequency and other information of the vibration signal cannot be obtained by directly compensating the backward Rayleigh scattering phase.
According to the phi-OFDR measurement principle, the damage of direct noise such as laser phase noise, sweep nonlinearity and the like to the backward Rayleigh scattering phase is avoided, so that the existing phase noise compensation technology and method are more difficult to realize direct compensation or correction to the backward Rayleigh scattering phase, namely, direct compensation to a phase signal in the phi-OFDR is difficult to realize. Although the partial compensation technology can improve the signal to noise ratio of the phase to a certain extent through the compensation of the backward Rayleigh scattering amplitude, the partial compensation technology essentially compensates the intensity and then extracts the phase information, so that the process of realizing the compensation is complex and the effect is not obvious.
In summary, the existing laser phase noise compensation technology has limitations in terms of direct compensation of the backward rayleigh scattering phase, and faces challenges such as stability and effectiveness. Therefore, there is an urgent need to develop a laser phase noise compensation method capable of directly compensating for phase, and improving the measurement performance of the phi-OFDR system. Therefore, the invention discloses an OFDR distributed measuring device based on time delay interference and a phase noise compensation method, and the high-precision measurement of the strain signal under the distance far exceeding the coherence length of the light source can be realized by compensating the phase noise of laser.
Disclosure of Invention
The invention provides a time delay interference laser phase noise compensation method facing to light frequency domain reflection, which comprises the following steps:
acquiring sweep frequency signal light based on a signal source;
the sweep frequency signal light obtains a first heterodyne signal through a measurement interferometer, and the sweep frequency signal light obtains a second heterodyne signal through a reference interferometer;
processing the first heterodyne signal and the second heterodyne signal by adopting a time delay interference algorithm to obtain direct compensation of laser phase noise;
and obtaining a strain signal based on direct compensation and reduction of the laser phase noise.
Optionally, the process of obtaining the first heterodyne signal by the sweep frequency signal light through the measurement interferometer includes:
the sweep frequency signal light is subjected to beam splitting to obtain measuring light and reference light;
splitting the measuring light to obtain second measuring light and measuring interferometer local oscillation light;
processing the second measuring light by applying a strain signal to the set reflection point to obtain processed second measuring light;
combining the processed second measuring light with the local oscillation light of the measuring interferometer to obtain first heterodyne interference light;
and detecting the first heterodyne interference light to obtain a first heterodyne signal.
Optionally, the process of obtaining the second difference signal by the sweep frequency signal light through the reference interferometer includes:
splitting the reference light to obtain a second reference light and a reference interferometer local oscillator light;
the second reference light is processed by a reference optical fiber to obtain processed second reference light;
combining the processed second reference light and the reference interferometer local oscillation light to obtain second external differential interference light;
and detecting the second external difference interference light to obtain a second external difference signal.
Optionally, the process of obtaining direct compensation of laser phase noise includes:
obtaining the frequency corresponding to the position of the reflection point of the first heterodyne interference light and the frequency corresponding to the length of the reference optical fiber of the second heterodyne interference light based on a Fourier spectrum;
obtaining reflection point time delay and reference optical fiber time delay based on the frequency;
filtering out each reflection point signal and reference light signal by a band-pass filter based on the frequency;
obtaining the phase of the reflection point signal based on Hilbert transform;
performing time translation and combination on the reflection point time delay and the reference optical fiber time delay based on the time delay and the time delay interference algorithm to finish the compensation of the phase noise of each reflection point and obtain the phase compensation signals of each reflection point of the first heterodyne interference light;
and carrying out difference on the basis of the phases of the reflection points to obtain a delayed self-coherent signal of the strain signal to be detected.
Alternatively, the calculation formula of the phase difference of the reflection points is as follows:
Λ＝Λ 1,1 -Λ 1,2
Λ 1,1 ＝[s 1,1 (t)-s 2 (t)]-[s 1,1 (t-t 2 )-s 2 (t-t 1,1 )]＝p r (t)-p r (t-t 2 )
Λ 1,2 ＝[s 1,2 (t)-s 2 (t)]-[s 1,2 (t-t 2 )-s 2 (t-t 1,2 )]＝p r (t)-p r (t-t 2 )+p s (t)-p s (t-t 2 )
wherein, Λ represents the phase difference between two reflection points after the time delay interference laser phase noise compensation method, Λ 1,1 Representing the phase of the reflection point 1 after the time delay interference laser phase noise compensation method, Λ 1,2 Representing the phase s of the reflection point 2 after the time delay interference laser phase noise compensation method 1,1 (t) represents the phase of the reflection point 1, s extracted from the measurement path 2 (t) represents the phase extracted from the reference path, s 1,1 (t-t 2 ) Indicating time delay of the phase of the reflection point 1 extracted from the measuring path, t 2 Representing reference path time delay s 2 (t-t 1,1 ) Representing the time delay of the phase extracted from the reference path, t 1,1 Representing the time delay, p, of the reflection point 1 r (t) represents the phase variation introduced by the jitter of the fiber under test, p r (t-t 2 ) Representing the time delay of the phase change introduced by the jitter of the optical fiber s 1,2 (t) represents the phase of the reflection point 2, s extracted from the measurement path 1,2 (t-t 2 ) Representing the time delay of the phase of the reflection point 2 extracted from the measuring path, s 2 (t-t 1,2 ) Representing the time delay of the phase extracted from the reference path, t 1,2 Representing the time delay, p, of the reflection point 2 s (t)Representing the strain signal to be measured, p s (t-t 2 ) Indicating the time delay of the strain signal to be measured.
Optionally, the process of obtaining the strain signal includes:
the phase noise compensation based on the first heterodyne interference light obtains a strain signal with only environment jitter interference;
carrying out difference on the phases of the reflection points to obtain a delayed self-coherent signal of the strain signal;
and performing low-pass filtering and coefficient processing on the delayed self-coherent signal to obtain a strain signal.
The invention also discloses a time delay interference laser phase noise compensation device facing to the reflection of the optical frequency domain, which comprises: the device comprises a sweep frequency light source, a first coupler, a second coupler, a third coupler, a circulator, an optical fiber to be tested, a reference optical fiber, PZT, a fourth coupler, a fifth coupler, a first balanced photoelectric detector, a second balanced photoelectric detector, an oscilloscope and a digital signal processing module;
the sweep frequency light source is used for generating sweep frequency signal light;
the first coupler is connected with the sweep frequency light source and is used for dividing the sweep frequency signal light into measuring light and reference light;
the second coupler is connected with the first coupler and is used for dividing the measuring light into second measuring light and measuring interferometer local oscillation light;
the second coupler, the circulator, the optical fiber to be measured and the PZT are sequentially connected, wherein the circulator is used for receiving the second measuring light and outputting the second measuring light processed by the optical fiber to be measured and the PZT;
the PZT is used for applying a strain signal to be measured;
the fourth coupler is connected with the circulator and is used for combining the processed second measuring light and the local oscillation light of the measuring interferometer to obtain first heterodyne interference light;
the first balanced photoelectric detector is connected with the fourth coupler and is used for converting the optical signal of the first heterodyne interference light into an electric signal to obtain a first heterodyne signal;
the third coupler is connected with the first coupler, the reference optical fiber is connected with the third coupler, and the third coupler is connected to divide the reference light into a second reference light and a reference interferometer local oscillator light;
the fifth coupler is connected with the reference optical fiber, and is used for combining the second reference light and the reference interferometer local oscillation light to obtain second external differential interference light;
the second balanced photoelectric detector is connected with the fifth coupler and is used for converting the optical signal of the second external differential interference light into an electric signal to obtain a second external differential signal;
the oscilloscopes are connected with the first balanced photoelectric detector and the second balanced photoelectric detector, and are used for detecting and collecting beat frequency data of the first heterodyne signal and the second heterodyne signal;
the digital signal processing module is connected with the oscilloscope and is used for obtaining direct compensation of laser phase noise by adopting a time delay interference algorithm and obtaining a strain signal based on direct compensation and restoration of the laser phase noise.
Optionally, the maximum sampling frequency of the oscilloscope is 20GHz, and the number of the maximum sampling points of the dual channels is 40Mpts.
The invention has the following technical effects:
1. the invention belongs to phase direct compensation in a phase noise compensation mechanism, and unlike the prior method, the method realizes direct compensation of the phase of a laser, not just line width compensation. This means that the method can more accurately compensate the laser phase noise in terms of phase, thereby improving the accuracy of the strain signal and thus the performance of the measurement system.
2. The invention aims at improving the problem that interference signals are sensitive to environment and have poor stability. Compared with the traditional phase compensation method, a shorter and more stable optical fiber can be selected as an auxiliary interferometer. The method can reduce or eliminate the influence of environmental interference on interference signals, thereby improving the stability and the anti-interference capability of the system. This will make the compensation system more reliable and stable in a practical application scenario.
3. The invention solves the problem of uneven compensation effect in the existing method. This method can achieve a more uniform phase compensation effect than a method relying on a long interference arm delay difference. The method provides relatively consistent and accurate phase compensation regardless of the position of the echo signal, reducing phase noise.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a laser phase noise compensation method based on time delay interference in an embodiment of the invention;
FIG. 2 is a schematic diagram of a laser phase noise compensation device based on time delay interference in an embodiment of the present invention;
FIG. 3 is a comparison diagram of time domains before and after phase noise compensation in an embodiment of the present invention;
FIG. 4 is a comparison of the frequency domains before and after phase noise compensation in an embodiment of the present invention;
description of the drawings: 1. a swept frequency light source; 2. a first coupler; 3. a second coupler; 4. a third coupler; 5. a circulator; 6. an optical fiber to be measured; 7. a reference fiber; 8. PZT; 9. a fourth coupler; 10. a fifth coupler; 11. a first balanced photodetector; 12. a second balanced photodetector; 13. an oscilloscope; 14. and a digital signal processing module.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
Aiming at the defects and improvement demands of the prior art, the invention provides a laser phase noise compensation method and device based on time delay interference, and aims to realize direct high-uniformity and high-stability phase noise compensation on the phase for OFDR quasi-distributed measurement.
As shown in fig. 1, the present embodiment provides a phase noise compensation method based on time delay interference, including:
acquiring sweep frequency signal light based on a signal source: generating signal light by adopting a signal source, and generating sweep frequency laser with frequency period jitter, namely sweep frequency signal light;
the sweep frequency signal light obtains a first heterodyne signal through a measurement interferometer, and the sweep frequency signal light obtains a second heterodyne signal through a reference interferometer: the specific implementation process comprises the following steps: the sweep frequency signal light is divided into two beams by the first coupler 2, one beam is injected into an OFDR measuring loop to be used as measuring light, and the other beam is injected into a reference loop to be used as reference light; the measuring light is divided into two beams by a second coupler 3 and used as local oscillation light and measuring light of a measuring interferometer, the measuring light is injected into a port a of an circulator 5, a port b of the circulator 5 is connected with an optical fiber 6 to be measured, a port c of the circulator 5 is connected with a fourth coupler 9, two reflection points are arranged in the optical fiber, and a strain signal to be measured is added into the tail end of the optical fiber by a piezoelectric transducer 8; meanwhile, the reference light is split through a third coupler 4 to be used as local oscillation light and reference light of a reference interferometer, and the reference light passes through a high-stability delay optical fiber;
combining the measuring light of the measuring interferometer with local oscillation light to form first heterodyne interference light; combining the reference light of the reference interferometer with local oscillation light to form second external difference interference light; converting the first heterodyne signal and the second heterodyne signal into electric signals through a balance detector, and then entering a digital signal processing module;
detecting and collecting the first heterodyne interference light and the second heterodyne interference light; the frequency of two reflection points of the first heterodyne interference light and the optical fiber length of the second heterodyne interference light can be obtained on the Fourier spectrum, and the frequency corresponds to the time delay t of the two reflection points 1,1 And t 1,2 And reference fiber delay t 2 Then filtering out the signal reflection point signals of the two reflection points in the first heterodyne interference light by using an FIR filter, wherein the phase of the signal reflection point signals is s 1,1 Sum s 1,2 The method comprises the following steps: p (t) -p (t-t) 1,1 )+p r (t) and p (t) -p (t-t) 1,2 )+p r (t)+p s (t), wherein p (t) represents an error caused by phase noise, p r (t) represents phase errors due to fiber jitter, ambient temperature variation, etc., since the two reflection points are closely spaced and can be approximately equal, p s (t) represents a strain signal to be measured, applied to the second reflection point;
the first heterodyne signal and the second heterodyne signal are processed by adopting a time delay interference algorithm, so that the direct compensation of laser phase noise is realized, the strain signal is obtained based on the direct compensation and restoration of the laser phase noise, and the specific implementation process comprises the following steps: the time delay interference algorithm is adopted to respectively time shift the two reflection point signals of the second heterodyne interference light data and the first heterodyne interference light, namely, the two reflection point signals of the first heterodyne interference light data are delayed by t 2 The second differential interference light data are respectively delayed by t 1,1 And t 1,2 ；
And linearly combining the signals to obtain Λ= [ s ] 1 (t)-s 2 (t)]-[s 1 (t-t 2 )-s 2 (t-t 1 )]Wherein s is 1 Representation s 1,1 Or s 1,2 ，t 1 Representing t 1,1 Or t 1,2 The method comprises the steps of carrying out a first treatment on the surface of the Calculating the phase difference value of the two reflection points to realize the phase compensation of the first heterodyne interference light and obtain a signal p s (t)-p s (t-t 2 ) After a low-pass filter equivalent to an integrating operation and simple coefficient processing, the strain signal p can be restored s (t)；
As shown in fig. 2, the present invention further provides a phase noise compensation device based on time delay interference, including: the device comprises a sweep frequency light source 1, a first coupler 2, a second coupler 3, a third coupler 4, a fourth coupler 9, a fifth coupler 10, a circulator 5, an optical fiber 6 to be tested, a reference optical fiber 7, a PZT8, a first balanced photoelectric detector 11, a second balanced photoelectric detector 12, an oscilloscope 13 and a digital signal processing module 14;
the sweep frequency light source 1 is used for generating sweep frequency signal light; the first coupler 2 is used for dividing sweep frequency signal light into measuring light and reference light; the second coupler 3 is configured to divide the measurement light divided by the first coupler 2 into a second measurement light and a measurement interferometer local oscillation light; the third coupler 4 is configured to split the reference light split by the first coupler 2 into a second reference light and a reference interferometer local oscillation light;
the circulator 5 is positioned in an OFDR measuring path of the measuring interferometer; the optical fiber to be measured is connected with a port a of the circulator 5, a port b of the circulator 5 is connected with an optical fiber to be measured 6, a strain signal to be measured is applied by using a PZT8 (piezoelectric transducer), and a port c of the circulator 5 is connected with a fourth coupler 9; the reference optical fiber is positioned on a reference path of the reference interferometer; the fourth coupler 9 is configured to combine the second measurement light with the local oscillation light of the measurement interferometer to form a first heterodyne interference light, and detect the first heterodyne interference light by the first balanced photodetector 11; the second measuring light passes through the circulator 5 and the optical fiber 6 to be measured, then passes through a reflection point where the PZT8 applies strain, and is reflected back to the circulator 5 and output by the circulator 5; the fifth coupler 10 is configured to combine the second reference light with the reference interferometer local oscillation light to form a second differential interference light, and the second differential interference light is detected by the second balanced photodetector 12;
the oscilloscope 13 is used for detecting and collecting beat frequency data of the first heterodyne interference light and the second heterodyne interference light; the processor is used for respectively performing time shift on the second heterodyne interference light data and the two reflection point signals of the first heterodyne interference light by adopting a time delay interference algorithm, namely delaying the two reflection point signals of the first heterodyne interference light data by t 2 Second differential interference light data delayt 1,1 And t 1,2 The method comprises the steps of carrying out a first treatment on the surface of the And linearly combining the signals to obtain Λ= [ s ] 1 (t)-s 2 (t)]-[s 1 (t-t 2 )-s 2 (t-t 1 )]Wherein s is 1 Representation s 1,1 Or s 1,2 ，t 1 Representing t 1,1 Or t 1,2 ；
Calculating the phase difference value of the two reflection points to realize the phase compensation of the first heterodyne interference light data and obtain a signal p s (t)-p s (t-t 2 ) After a low-pass filter equivalent to an integrating operation and simple coefficient processing, the strain signal p can be restored s (t)；
Further, the maximum sampling frequency of the oscilloscope is 20GHz, and the number of the maximum sampling points of the dual channels is 40Mpts.
Example two
The embodiment discloses a time delay interference laser phase noise compensation method facing to light frequency domain reflection, which specifically comprises the following steps:
generating sweep frequency signal light by adopting a signal source;
the process of obtaining a first heterodyne signal by the sweep frequency signal light through the measurement interferometer and obtaining a second heterodyne signal by the sweep frequency signal light through the reference interferometer comprises the following steps:
the sweep frequency signal light is divided into two beams by the first coupler 2, one beam is injected into an OFDR measuring loop to be used as measuring light, and the other beam is injected into a reference loop to be used as reference light; the measuring light is divided into two beams by a second coupler 3 and used as local oscillation light and measuring light of a measuring interferometer, the measuring light is connected with a port a of an circulator 5, a port b of the circulator 5 is connected with an optical fiber 6 to be measured, a port c of the circulator 5 is connected with a fourth coupler 9, two reflection points are arranged in the optical fiber, and a strain signal with 5v amplitude and 2kHz frequency to be measured is added at the tail end of the optical fiber by a piezoelectric transducer 8; meanwhile, the reference light is split through a third coupler 4 to be used as local oscillation light and reference light of a reference interferometer, and the reference light passes through a high-stability delay optical fiber 7;
combining the measuring light of the measuring interferometer with local oscillation light to form first heterodyne interference light; combining the reference light of the reference interferometer with local oscillation light to form second external difference interference light; the first heterodyne signal and the second heterodyne signal are converted into electric signals through the balance detector and then enter the digital signal processing module 14;
detecting and collecting the first heterodyne interference light and the second heterodyne interference light; the frequency of two reflection points of the first heterodyne interference light and the optical fiber length of the second heterodyne interference light can be obtained on the Fourier spectrum, and the frequency corresponds to the time delay t of the two reflection points 1,1 And t 1,2 And reference fiber delay t 2 Then filtering out the signal reflection point signals of the two reflection points in the first heterodyne interference light by using an FIR filter, wherein the phase of the signal reflection point signals is s 1,1 Sum s 1,2 The method comprises the following steps: p (t) -p (t-t) 1,1 )+p r (t) and p (t) -p (t-t) 1,2 )+p r (t)+p s (t), wherein p (t) represents an error caused by phase noise, p r (t) represents phase errors due to fiber jitter, ambient temperature variation, etc., since the two reflection points are closely spaced and can be approximately equal, p s (t) represents the strain signal to be measured, in this case p s (t) is a strain signal having an amplitude of 5v and a frequency of 2 kHz;
processing the first heterodyne signal and the second heterodyne signal by adopting a time delay interference algorithm to realize direct compensation of laser phase noise; the strain signal is obtained based on direct compensation and reduction of laser phase noise, and the specific implementation process comprises the following steps: the time delay interference algorithm is adopted to respectively time shift the two reflection point signals of the second heterodyne interference light data and the first heterodyne interference light, namely, the two reflection point signals of the first heterodyne interference light data are delayed by t 2 The second differential interference light data are respectively delayed by t 1,1 And t 1,2 The method comprises the steps of carrying out a first treatment on the surface of the The signals are subjected to linear combination to obtain:
Λ 1,1 ＝[s 1,1 (t)-s 2 (t)]-[s 1,1 (t-t 2 )-s 2 (t-t 1,1 )]＝p r (t)-p r (t-t 2 )
Λ 1,2 ＝[s 1,2 (t)-s 2 (t)]-[s 1,2 (t-t 2 )-s 2 (t-t 1,2 )]＝p r (t)-p r (t-t 2 )+p s (t)-p s (t-t 2 )
calculating the phase difference value lambda of two reflection points 1,1 -Λ 1,2 The phase noise compensation of the first heterodyne interference light data can be realized to obtain a signal p s (t)-p s (t-t 2 ) The method comprises the steps of carrying out a first treatment on the surface of the The strain signal p can be restored by a low-pass filter equivalent to the integration operation and simple coefficient processing s (t) as shown in fig. 3 and 4.
The foregoing has shown and described the basic principles, principal features and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined in the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (8)
1. The time delay interference laser phase noise compensation method facing to the reflection of the optical frequency domain is characterized by comprising the following steps of:
acquiring sweep frequency signal light based on a signal source;
the sweep frequency signal light obtains a first heterodyne signal through a measurement interferometer, and the sweep frequency signal light obtains a second heterodyne signal through a reference interferometer;
processing the first heterodyne signal and the second heterodyne signal by adopting a time delay interference algorithm to realize direct compensation of laser phase noise;
and obtaining a strain signal based on direct compensation and reduction of the laser phase noise.
2. The method for compensating phase noise of time delay interference laser light facing to reflection of optical frequency domain according to claim 1, wherein the process of obtaining the first heterodyne signal by the sweep signal light through the measurement interferometer comprises:
the sweep frequency signal light is subjected to beam splitting to obtain measuring light and reference light;
splitting the measuring light to obtain second measuring light and measuring interferometer local oscillation light;
the second measuring light is processed by applying a strain signal to the set reflection point, so that the processed second measuring light is obtained;
combining the processed second measuring light with the local oscillation light of the measuring interferometer to obtain first heterodyne interference light;
and detecting the first heterodyne interference light to obtain a first heterodyne signal.
3. The method for compensating phase noise of time delay interference laser light facing to reflection of optical frequency domain according to claim 2, wherein the process of obtaining the second difference signal by the sweep signal light through the reference interferometer comprises:
splitting the reference light to obtain a second reference light and a reference interferometer local oscillator light;
the second reference light is processed by a reference optical fiber to obtain processed second reference light;
combining the processed second reference light and the reference interferometer local oscillation light to obtain second external differential interference light;
and detecting the second external difference interference light to obtain a second external difference signal.
4. The method for compensating for phase noise of time-delayed interference laser light for reflection in the optical frequency domain according to claim 3, wherein the process of obtaining direct compensation for phase noise of laser light comprises:
obtaining the corresponding frequency of the position of the reflection point of the first heterodyne interference light and the corresponding frequency of the reference optical fiber length of the second heterodyne interference light based on a Fourier spectrum;
obtaining reflection point time delay and reference optical fiber time delay based on the frequency;
filtering out each reflection point signal and reference light signal by a band-pass filter based on the frequency;
obtaining the phase of the reflection point signal based on Hilbert transform;
and performing time translation and combination on the reflection point time delay and the reference optical fiber time delay based on the time delay and the time delay interference algorithm to finish the compensation of the phase noise of each reflection point and obtain the phase compensation signal of each reflection point of the first heterodyne interference light.
5. The method for compensating phase noise of time delay interference laser light facing reflection of optical frequency domain according to claim 4, wherein the calculation formula of the phase difference of the reflection point is as follows:
Λ＝Λ 1,1 -Λ 1,2
Λ 1,1 ＝[s 1,1 (t)-s 2 (t)]-[s 1,1 (t-t 2 )-s 2 (t-t 1,1 )]＝p r (t)-p r (t-t 2 )
Λ 1,2 ＝[s 1,2 (t)-s 2 (t)]-[s 1,2 (t-t 2 )-s 2 (t-t 1,2 )]＝p r (t)-p r (t-t 2 )+p s (t)-p s (t-t 2 )
wherein, Λ represents the phase difference between two reflection points after the time delay interference laser phase noise compensation method, Λ 1,1 Representing the phase of the reflection point 1 after the time delay interference laser phase noise compensation method, Λ 1,2 Representing the phase s of the reflection point 2 after the time delay interference laser phase noise compensation method 1,1 (t) represents the phase of the reflection point 1, s extracted from the measurement path 2 (t) represents the phase extracted from the reference path, s 1,1 (t-t 2 ) Indicating time delay of the phase of the reflection point 1 extracted from the measuring path, t 2 Representing reference path time delay s 2 (t-t 1,1 ) Representing the time delay of the phase extracted from the reference path, t 1,1 Representing the time delay, p, of the reflection point 1 r (t) represents the phase variation introduced by the jitter of the fiber under test, p r (t-t 2 ) Representing the time delay of the phase change introduced by the jitter of the optical fiber s 1,2 (t) represents the phase of the reflection point 2, s extracted from the measurement path 1,2 (t-t 2 ) Representing the time delay of the phase of the reflection point 2 extracted from the measuring path, s 2 (t-t 1,2 ) Representing the time delay of the phase extracted from the reference path, t 1,2 Representing the time delay, p, of the reflection point 2 s (t) represents the strain signal to be measured, p s (t-t 2 ) Indicating the time delay of the strain signal to be measured.
6. The method for compensating for phase noise of time-delayed interference laser light for optical frequency domain reflection of claim 5, wherein the step of obtaining the strain signal comprises:
the phase noise compensation based on the first heterodyne interference light obtains a strain signal with only environment jitter interference;
carrying out difference on the phases of the reflection points to obtain a delayed self-coherent signal of the strain signal;
and performing low-pass filtering and coefficient processing on the delayed self-coherent signal to obtain a strain signal.
7. The time delay interference laser phase noise compensation device facing to the reflection of an optical frequency domain is characterized by comprising: the device comprises a sweep frequency light source (1), a first coupler (2), a second coupler (3), a third coupler (4), a circulator (5), an optical fiber to be tested (6), a reference optical fiber (7), a PZT (8), a fourth coupler (9), a fifth coupler (10), a first balance photoelectric detector (11), a second balance photoelectric detector (12), an oscilloscope (13) and a digital signal processing module (14);
the sweep frequency light source (1) is used for generating sweep frequency signal light;
the first coupler (2) is connected with the sweep frequency light source (1), and the first coupler (2) is used for dividing the sweep frequency signal light into measuring light and reference light;
the second coupler (3) is connected with the first coupler (2), and the second coupler (3) is used for dividing the measuring light into second measuring light and measuring interferometer local oscillation light;
the second coupler (3), the circulator (5), the optical fiber to be measured (6) and the PZT (8) are sequentially connected, wherein the circulator (5) is used for receiving the second measuring light and outputting the second measuring light processed by the optical fiber to be measured (6) and the PZT (8);
the PZT (8) is used for applying a strain signal to be measured;
the fourth coupler (9) is connected with the circulator (5), and the fourth coupler (9) is used for combining the processed second measuring light and the measuring interferometer local oscillation light to obtain first heterodyne interference light;
the first balanced photoelectric detector (11) is connected with the fourth coupler (9), and the first balanced photoelectric detector (11) is used for converting an optical signal of the first heterodyne interference light into an electric signal to obtain a first heterodyne signal;
the third coupler (4) is connected with the first coupler (2), the reference optical fiber (7) is connected with the third coupler (4), and the third coupler (4) is connected to divide the reference light into a second reference light and a reference interferometer local oscillation light;
the fifth coupler (10) is connected with the reference optical fiber (7), and the fifth coupler (10) is used for combining the second reference light and the reference interferometer local oscillation light to obtain second external differential interference light;
the second balanced photoelectric detector (12) is connected with the fifth coupler (10), and the second balanced photoelectric detector (12) is used for converting an optical signal of the second external differential interference light into an electric signal to obtain a second external differential signal;
the oscilloscopes (13) are connected with the first balance photoelectric detector (11) and the second balance photoelectric detector (12), and the oscilloscopes (13) are used for detecting and collecting beat frequency data of the first heterodyne signal and the second heterodyne signal;
the digital signal processing module (14) is connected with the oscilloscope (13), and the digital signal processing module (14) is used for obtaining direct compensation of laser phase noise by adopting a time delay interference algorithm and obtaining a strain signal based on direct compensation and restoration of the laser phase noise.
8. The time delay interference laser phase noise compensation device for optical frequency domain reflection according to claim 7, wherein the maximum sampling frequency of the oscilloscope (13) is 20GHz, and the number of the double-channel maximum sampling points is 40 mps.
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