Optical frequency domain reflectometry time delay interferometry laser phase noise compensation method and device

Abstract

The application discloses a time delay interference laser phase noise compensation method and device for optical frequency domain reflection, and comprises the following steps: obtaining a linear sweep signal light based on a signal source; obtaining a first heterodyne signal through a measurement interferometer, and obtaining a second heterodyne signal through a reference interferometer; and processing the first heterodyne signal and the second heterodyne signal by using a time delay interference algorithm, so that direct compensation of laser phase noise is realized; and obtaining a strain signal based on the direct compensation of the laser phase noise. Through compensation of the laser phase noise, high-precision measurement of the strain signal can be realized at a distance far beyond the coherence length of the light source.

Description

Method and apparatus for time-delay interferometric laser phase noise compensation for optical frequency domain reflection Technical Field

[0001] This invention relates to the field of distributed fiber optic sensing and laser measurement technology, and in particular to a method and apparatus for compensating phase noise of time-delayed interferometric lasers for optical frequency domain reflection. Background Technology

[0002] Distributed fiber optic sensing and measurement technology utilizes physical mechanisms such as Rayleigh scattering and Brillouin scattering in optical fibers to sense, acquire, and analyze physical quantities and their states along the fiber by detecting the characteristics of backscattered light signals. Optical frequency domain reflectometry (OFDR) is a typical distributed fiber optic sensing and measurement technology. Its measurement principle is based on high coherence, low phase noise, wide-range linear sweep laser and coherent demodulation. Based on the sensing mechanism of physical quantities along the fiber, OFDR can be further divided into amplitude-based OFDR and phase-based OFDR (φ-OFDR). Amplitude-based OFDR relies on the statistical characteristics of the backscattered Rayleigh amplitude and senses information by analyzing and comparing the correlation between measurement results at different times. In contrast, φ-OFDR relies on extracting the phase information of the backscattered Rayleigh signal in the fiber. By analyzing the phase of the beat frequency signal, it can obtain the exact waveform (including its frequency and amplitude) information of the measured physical quantity. Benefiting from the linear response between the phase of backscattered Rayleigh scattering and measured physical quantities such as vibration and strain, φ-OFDR exhibits higher sensitivity and measurement accuracy compared to amplitude-type OFDR, making it an important direction for OFDR technology development. This invention further delves into and improves φ-OFDR technology to meet the needs of specific fields and enhance its performance and application value.

[0003] In reality, generating wide-range linear frequency-sweeping lasers with high coherence and low phase noise faces numerous technical challenges. On one hand, narrow-linewidth lasers often have limited tuning performance, making it difficult to support wide-range frequency sweeps. Lasers with wider tuning ranges typically require tuning their cavity length to achieve large-range frequency sweeps, which can affect the stability of the resonant cavity, resulting in poor phase noise. Furthermore, frequency-sweeping lasers generated based on external modulation methods have their frequency sweep range limited by the modulation bandwidth of optical and electronic devices, and the additional modulation drive increases the system's cost and complexity.

[0004] To address this situation, phase noise compensation techniques are needed to suppress its impact on and limitations on system measurement performance. Currently, reported laser phase noise compensation techniques typically utilize optically assisted interferometry to obtain phase error information, and then use digital methods to perform phase compensation on the signal.

[0005] Currently, mainstream laser phase noise compensation techniques can be divided into three main methods:

[0006] 1. Phase noise compensation technique based on resampling: This method uses the equal phase interval points of the auxiliary interferometer signal as the sampling clock to resample the auxiliary interferometer signal, and then uses the resampled signal to compensate for the phase noise of the original measurement signal.

[0007] 2. Phase noise compensated optical frequency domain reflectometer (PNC-OFDR): This method uses external modulation to generate linear sweep frequency light. Based on resampling phase noise compensation technology, it uses a phase generation method to obtain a reference signal suitable for long-distance measurement.

[0008] 3. Deskew filtering method for compensating laser phase noise: This method first uses the auxiliary arm signal to estimate the laser phase error, and then uses a deskew filter to compensate for the laser phase noise.

[0009] Although the signal acquisition and processing methods of the above three methods are somewhat different, they all rely on the constructed auxiliary interference structure to obtain the phase noise information of the laser, and then use it to compensate for the beat frequency phase noise caused by the laser phase noise, thereby reducing the impact of laser phase noise on OFDR performance, improving the effective measurement distance, and ensuring that the theoretical spatial resolution limited by the sweep frequency range is achieved.

[0010] However, since the acquisition of phase noise by the above methods all depend on the constructed auxiliary interferometric structure, they face some common problems: First, the auxiliary interferometer requires a long interferometer arm delay difference, with a length approximately half the coherence length of the light source, resulting in interference signals that are sensitive to the environment and have poor stability, failing to meet practical application requirements; Second, using a long auxiliary interferometer arm can only estimate the fiber position with a delay close to its arm length, leading to uneven compensation effects and large signal-to-noise ratio fluctuations. The best compensation effect is achieved for echo signals located close to the length of the auxiliary interferometer arm, while the compensation effect is poor for signals deviating from this position; Third, the above phase compensation methods mainly target the amplitude of the backscattered Rayleigh signal, that is, they mainly compensate and correct for the amplitude broadening and signal-to-noise ratio degradation caused by laser phase noise, and they cannot directly compensate for the phase of backscattered Rayleigh, thus failing to obtain the exact waveform and frequency information of the vibration signal.

[0011] Based on the measurement principle of φ-OFDR, direct noise such as laser phase noise and sweep frequency nonlinearity damages the backscattered Rayleigh phase. Therefore, existing phase noise compensation techniques and methods are difficult to directly compensate or correct for the backscattered Rayleigh phase, meaning it is difficult to achieve direct compensation of the phase signal in φ-OFDR. Although some compensation techniques can improve the phase signal-to-noise ratio to some extent by compensating for the backscattered Rayleigh amplitude, they essentially compensate for the intensity before extracting the phase information, resulting in a complex compensation process and limited effectiveness.

[0012] In summary, existing laser phase noise compensation techniques have limitations in directly compensating for the backscattered Rayleigh phase, facing challenges in stability and effectiveness. Therefore, there is an urgent need to research a laser phase noise compensation method capable of directly compensating for the phase, thereby improving the measurement performance of φ-OFDR systems. This patent presents an OFDR distributed measurement device and phase noise compensation method based on time-delay interferometry. By compensating for laser phase noise, high-precision measurement of strain signals can be achieved at distances far exceeding the coherence length of the light source. Summary of the Invention

[0013] This invention provides a time-delay interferometric laser phase noise compensation method for optical frequency domain reflection, comprising:

[0014] Obtain the swept frequency signal light based on the signal source;

[0015] The swept frequency signal light is passed through a measurement interferometer to obtain a first heterodyne signal, and the swept frequency signal light is passed through a reference interferometer to obtain a second heterodyne signal;

[0016] The first heterodyne signal and the second heterodyne signal are processed by a time-delay interferometry algorithm to obtain direct compensation for laser phase noise;

[0017] The strain signal is obtained by directly compensating for and restoring the laser phase noise.

[0018] Optionally, the process of obtaining the first heterodyne signal from the swept frequency signal light via a measurement interferometer includes:

[0019] The swept frequency signal light is split into measurement light and reference light;

[0020] The measurement beam is split into a second measurement beam and the local oscillator beam of the measurement interferometer;

[0021] The second measuring light is processed by applying a strain signal to the set reflection point to obtain the processed second measuring light;

[0022] The processed second measuring beam and the local oscillator beam of the measuring interferometer are combined to obtain the first heterodyne interference beam;

[0023] The first heterodyne signal is obtained by detecting the first heterodyne interference light.

[0024] Optionally, the process of obtaining the second heterodyne signal from the swept frequency signal light via a reference interferometer includes:

[0025] The reference beam is split to obtain a second reference beam and a reference interferometer local oscillator beam;

[0026] The second reference light is processed by the reference fiber to obtain the processed second reference light;

[0027] The processed second reference beam and the local oscillator beam of the reference interferometer are combined to obtain the second heterodyne interference beam;

[0028] The second heterodyne signal is obtained by detecting the second heterodyne interference light.

[0029] Optionally, the process of obtaining direct compensation for laser phase noise includes:

[0030] The frequency corresponding to the reflection point of the first heterodyne interference light and the frequency corresponding to the reference fiber length of the second heterodyne interference light are obtained based on the Fourier spectrum.

[0031] The reflection point delay and the reference fiber delay are obtained based on the frequency.

[0032] Based on the frequency, the signals at each reflection point and the reference light signal are filtered out using a bandpass filter;

[0033] The phase of the signal at the reflection point is obtained based on the Hilbert transform;

[0034] Based on the time delay and time delay interference algorithm, the time delay of the reflection point and the time delay of the reference fiber are time-shifted and combined to complete the phase noise compensation of each reflection point and obtain the phase compensation signal of each reflection point of the first heterodyne interference light.

[0035] Based on the phase difference of each reflection point, the delayed autocoherent signal of the strain signal to be measured is obtained.

[0036] Optionally, the formula for calculating the phase difference of the reflection points is as follows:

[0037] Λ=Λ 1,1 -Λ 1,2

[0038] Λ 1,1 =[s 1,1 [(t)-s2(t)]-[s 1,1 (t-t2)-s2(tt 1,1 )]=p r (t)-p r (t-t2)

[0039] Λ 1,2 =[s 1,2 [(t)-s2(t)]-[s 1,2 (t-t2)-s2(tt 1,2 )]=p r (t)-p r (t-t2)+p s (t)-ps (t-t2)

[0040] In the formula, Λ represents the phase difference between two reflection points after the time-delayed interferometric laser phase noise compensation method. 1,1 Λ represents the phase of reflection point 1 after the time-delayed interferometric laser phase noise compensation method. 1,2 This represents the phase of reflection point 2 after the time-delayed interferometric laser phase noise compensation method, s. 1,1 s(t) represents the phase extracted from reflection point 1 from the measurement path, and s2(t) represents the phase extracted from the reference path. 1,1 (t-t2) represents the time delay of the phase of reflection point 1 extracted from the measurement path, t2 represents the time delay of the reference path, and s2(tt) 1,1 ) indicates a time delay applied to the phase extracted from the reference path, t 1,1 p represents the time delay at reflection point 1. r (t) represents the phase change introduced by the jitter of the fiber under test, p r (t-t2) represents the time delay applied to the phase change introduced by fiber jitter, s 1,2 (t) represents the phase of reflection point 2 extracted from the measurement path, s 1,2 (t-t2) represents the time delay applied to the phase of reflection point 2 extracted from the measurement path, s2(tt 1,2 ) indicates a time delay applied to the phase extracted from the reference path, t 1,2 p represents the time delay at reflection point 2. s (t) represents the strain signal to be measured, p s (t-t2) represents the time delay of the strain signal to be measured.

[0041] Optionally, the process of obtaining the strain signal includes:

[0042] Based on the phase noise compensation of the first heterodyne interference light, a strain signal with only environmental jitter interference is obtained;

[0043] The delayed autocoherent signal of the strain signal is obtained by differentially analyzing the phase of each reflection point.

[0044] The strain signal is obtained by performing low-pass filtering and coefficient processing on the delayed autocoherent signal.

[0045] The present invention also discloses a time-delay interferometric laser phase noise compensation device for optical frequency domain reflection, comprising: a swept frequency light source, a first coupler, a second coupler, a third coupler, a circulator, an optical fiber under test, a reference optical fiber, a PZT, a fourth coupler, a fifth coupler, a first balanced photodetector, a second balanced photodetector, an oscilloscope, and a digital signal processing module.

[0046] The frequency sweep light source is used to generate frequency sweep signal light;

[0047] The first coupler is connected to the swept frequency light source, and the first coupler is used to split the swept frequency signal light into measurement light and reference light;

[0048] The second coupler is connected to the first coupler, and the second coupler is used to split the measurement light into a second measurement light and a measurement interferometer local oscillator light;

[0049] The second coupler, circulator, fiber under test and PZT are connected in sequence, wherein the circulator is used to receive the second measurement light and output the second measurement light processed by the fiber under test and PZT;

[0050] The PZT is used to apply the strain signal to be measured.

[0051] The fourth coupler is connected to the circulator, and the fourth coupler is used to combine the processed second measurement light and the local oscillator light of the measurement interferometer to obtain the first heterodyne interference light;

[0052] The first balanced photodetector is connected to the fourth coupler. The first balanced photodetector is used to convert the optical signal of the first heterodyne interference light into an electrical signal to obtain the first heterodyne signal.

[0053] The third coupler is connected to the first coupler, and the reference fiber is connected to the third coupler. The third coupler is used to split the reference light into a second reference light and a reference interferometer local oscillator light.

[0054] The fifth coupler is connected to the reference fiber, and the fifth coupler is used to combine the second reference light and the local oscillator light of the reference interferometer to obtain the second heterodyne interference light;

[0055] The second balanced photodetector is connected to the fifth coupler. The second balanced photodetector is used to convert the optical signal of the second heterodyne interference light into an electrical signal to obtain the second heterodyne signal.

[0056] The oscilloscopes are connected to the first balanced photodetector and the second balanced photodetector, and the oscilloscopes are used to detect and acquire the beat frequency data of the first heterodyne signal and the second heterodyne signal;

[0057] The digital signal processing module is connected to the oscilloscope and is used to obtain direct compensation for laser phase noise using a time-delay interferometry algorithm, and to obtain the strain signal based on the direct compensation for laser phase noise.

[0058] Optionally, the oscilloscope has a maximum sampling frequency of 20 GHz and a maximum sampling point count of 40 Mpts for dual channels.

[0059] The present invention has the following technical effects:

[0060] 1. This invention employs a direct phase compensation mechanism in phase noise compensation, unlike existing methods. This method achieves direct compensation of the laser phase, not just linewidth compensation. This means that the method can more accurately compensate for laser phase noise, thereby improving the accuracy of the strain signal and ultimately enhancing the performance of the measurement system.

[0061] 2. This invention addresses the issues of interference signals' sensitivity to the environment and poor stability. Compared to traditional phase compensation methods, shorter and more stable optical fibers can be used as auxiliary interferometers. This method can reduce or eliminate the impact of environmental interference on the interference signal, thereby improving the system's stability and anti-interference capability. This will make the compensation system more reliable and stable in practical applications.

[0062] 3. This invention solves the problem of uneven compensation effect in existing methods. Compared with methods that rely on the delay difference of long interferometer arms, this method can achieve a more uniform phase compensation effect. Regardless of the position deviation of the echo signal, this method can provide relatively consistent and accurate phase compensation, reducing phase noise. Attached Figure Description

[0063] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0064] Figure 1 is a flowchart of a laser phase noise compensation method based on time delay interference in an embodiment of the present invention;

[0065] Figure 2 is a schematic diagram of a laser phase noise compensation device based on time delay interference in an embodiment of the present invention;

[0066] Figure 3 is a time-domain comparison diagram before and after phase noise compensation in an embodiment of the present invention;

[0067] Figure 4 is a comparison diagram of the frequency domain before and after phase noise compensation in an embodiment of the present invention;

[0068] Figure descriptions: 1. Sweep frequency light source; 2. First coupler; 3. Second coupler; 4. Third coupler; 5. Circulator; 6. Fiber under test; 7. Reference fiber; 8. PZT; 9. Fourth coupler; 10. Fifth coupler; 11. First balanced photodetector; 12. Second balanced photodetector; 13. Oscilloscope; 14. Digital signal processing module. Detailed Implementation

[0069] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0070] Example 1

[0071] To address the shortcomings and improvement needs of existing technologies, this invention provides a laser phase noise compensation method and apparatus based on time-delay interferometry, with the aim of achieving direct, highly uniform, and stable phase noise compensation for OFDR quasi-distributed measurements.

[0072] As shown in Figure 1, this embodiment provides a phase noise compensation method based on time-delay interference, including:

[0073] Frequency sweep signal light is obtained based on a signal source: a signal source is used to generate signal light, which generates a frequency sweep laser with periodic frequency jitter, i.e., frequency sweep signal light;

[0074] The swept frequency signal light is used to obtain a first heterodyne signal via a measurement interferometer, and a second heterodyne signal via a reference interferometer. The specific implementation process includes: the swept frequency signal light is split into two beams via a first coupler 2; one beam is injected into the OFDR measurement loop as the measurement light, and the other beam is injected into the reference loop as the reference light; the measurement light is split into two beams via a second coupler 3, serving as the local oscillator light and the measurement light of the measurement interferometer; the measurement light is injected into port a of circulator 5; port b of circulator 5 is connected to the fiber under test 6; port c of circulator 5 is connected to a fourth coupler 9; two reflection points are set in the fiber, and a piezoelectric transducer 8 is used to add the strain signal to be measured at the end of the fiber; simultaneously, the reference light is split into beams via a third coupler 4, serving as the local oscillator light and the reference light of the reference interferometer; the reference light passes through a high-stability delay fiber.

[0075] The measuring light of the measuring interferometer is combined with the local oscillator light to form a first heterodyne interference beam; the reference light of the reference interferometer is combined with the local oscillator light to form a second heterodyne interference beam; the beams are then converted into electrical signals, namely the first heterodyne signal and the second heterodyne signal, by a balanced detector, and then enter the digital signal processing module.

[0076] The first and second heterodyne interference beams are detected and collected. The frequencies of the two reflection points of the first heterodyne interference beam and the fiber length of the second heterodyne interference beam can be obtained from the Fourier spectrum. The frequencies corresponding to the two reflection points are time delays t. 1,1 and t 1,2 The reference fiber delay is t2, and then an FIR filter is used to filter out the signals from the two reflection points in the first heterodyne interference light. The phase of the reflection point signal is s. 1,1 and s 1,2 That is: p(t) - p(tt) 1,1 )+p r (t) and p(t)-p(tt) 1,2 )+p r (t)+p s (t), where p(t) represents the error caused by phase noise, p r (t) represents the phase error caused by fiber jitter, ambient temperature changes, etc. Because the two reflection points are close to each other, they can be approximated as equal. s (t) represents the strain signal to be measured, applied to the second reflection point;

[0077] A time-delay interferometry algorithm is used to process the first and second heterodyne signals to directly compensate for laser phase noise. Based on this direct compensation, the strain signal is reconstructed. The specific implementation process includes: using the time-delay interferometry algorithm, the data of the second heterodyne interferometer and the two reflection point signals of the first heterodyne interferometer are time-shifted respectively. Specifically, the two reflection point signals of the first heterodyne interferometer are delayed by t2, and the second heterodyne interferometer data are delayed by t... 1,1 and t 1,2 ;

[0078] Linearly combining the above signals yields Λ=[s1(t)-s2(t)]-[s1(t-t2)-s2(t-t1)], where s1 represents s 1,1 or s 1,2 t1 represents t 1,1 or t 1,2 By calculating the phase difference between the two reflection points, phase compensation for the first heterodyne interference light can be achieved, yielding signal p. s (t)-p s (t-t2), after passing through a low-pass filter equivalent to an integration operation and simple coefficient processing, the strain signal p can be reconstructed. s (t);

[0079] As shown in Figure 2, the present invention also provides a phase noise compensation device based on time delay interference, comprising: a swept 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 under test 6, a reference optical fiber 7, a PZT 8, a first balanced photodetector 11, a second balanced photodetector 12, an oscilloscope 13, and a digital signal processing module 14.

[0080] The frequency sweep light source 1 is used to generate frequency sweep signal light; the first coupler 2 is used to split the frequency sweep signal light into measurement light and reference light; the second coupler 3 is used to split the measurement light split by the first coupler 2 into a second measurement light and a measurement interferometer local oscillator light; the third coupler 4 is used to split the reference light split by the first coupler 2 into a second reference light and a reference interferometer local oscillator light.

[0081] The circulator 5 is located in the OFDR measurement path of the measuring interferometer; the fiber under test is connected to port a of the circulator 5, port b of the circulator 5 is connected to the fiber under test 6, and a strain signal to be measured is applied by a PZT8 (piezoelectric transducer); port c of the circulator 5 is connected to the fourth coupler 9; the reference fiber is located in the reference path of the reference interferometer; the fourth coupler 9 is used to combine the second measuring light with the local oscillator light of the measuring interferometer to form a first heterodyne interference light, which is detected by the first balanced photodetector 11; the second measuring light passes through the circulator 5 and the fiber under test 6, then passes through the reflection point where the strain is applied by the PZT8, and is reflected back to the circulator 5 and output by the circulator 5; the fifth coupler 10 is used to combine the second reference light with the local oscillator light of the reference interferometer to form a second heterodyne interference light, which is detected by the second balanced photodetector 12;

[0082] The oscilloscope 13 is used to detect and acquire the beat frequency data of the first heterodyne interference light and the second heterodyne interference light; the processor is used to employ a time-delay interference algorithm to time-shift the data of the second heterodyne interference light and the two reflection point signals of the first heterodyne interference light respectively, that is, the two reflection point signals of the first heterodyne interference light data are delayed by t2, and the data of the second heterodyne interference light are delayed by t... 1,1 and t 1,2 Linearly combining the above signals yields Λ=[s1(t)-s2(t)]-[s1(t-t2)-s2(t-t1)], where s1 represents s 1,1 or s 1,2 t1 represents t 1,1 or t 1,2 ;

[0083] By calculating the phase difference between the two reflection points, phase compensation of the first heterodyne interference light data can be achieved, yielding signal p. s (t)-p s(t-t2), after passing through a low-pass filter equivalent to an integration operation and simple coefficient processing, the strain signal p can be reconstructed. s (t);

[0084] Furthermore, the oscilloscope has a maximum sampling frequency of 20 GHz and a maximum sampling point count of 40 Mpts for dual channels.

[0085] Example 2

[0086] This embodiment discloses a time-delay interferometric laser phase noise compensation method for optical frequency domain reflection, specifically including the following:

[0087] A single signal source is used to generate a frequency-sweeping signal light;

[0088] The process of obtaining the first heterodyne signal from the swept frequency signal light via a measurement interferometer, and obtaining the second heterodyne signal from the swept frequency signal light via a reference interferometer, includes:

[0089] The swept-frequency signal light is split into two beams by the first coupler 2. One beam is injected into the OFDR measurement loop as the measurement light, and the other beam is injected into the reference loop as the reference light. The measurement light is split into two beams by the second coupler 3, serving as the local oscillator light and the measurement light of the measurement interferometer. The measurement light is connected to port a of circulator 5, port b of circulator 5 is connected to the fiber under test 6, and port c of circulator 5 is connected to the fourth coupler 9. Two reflection points are set in the fiber, and a strain signal with an amplitude of 5V and a frequency of 2kHz is added to the end of the fiber using a piezoelectric transducer 8. At the same time, the reference light is split into beams by the third coupler 4, serving as the local oscillator light and the reference light of the reference interferometer. The reference light passes through a high-stability delay fiber 7.

[0090] The measuring light of the measuring interferometer is combined with the local oscillator light to form a first heterodyne interference light; the reference light of the reference interferometer is combined with the local oscillator light to form a second heterodyne interference light; the light is converted into electrical signals, namely the first heterodyne signal and the second heterodyne signal, by a balanced detector, and then enters the digital signal processing module 14.

[0091] The first and second heterodyne interference beams are detected and collected. The frequencies of the two reflection points of the first heterodyne interference beam and the fiber length of the second heterodyne interference beam can be obtained from the Fourier spectrum. The frequencies corresponding to the two reflection points are time delays t. 1,1 and t 1,2 The reference fiber delay is t2, and then an FIR filter is used to filter out the signals from the two reflection points in the first heterodyne interference light. The phase of the reflection point signal is s. 1,1 and s 1,2 That is: p(t) - p(tt) 1,1 )+p r (t) and p(t)-p(tt) 1,2 )+pr (t)+p s (t), where p(t) represents the error caused by phase noise, p r (t) represents the phase error caused by fiber jitter, ambient temperature changes, etc. Because the two reflection points are close to each other, they can be approximated as equal. s (t) represents the strain signal to be measured, in this example p s (t) represents a strain signal with an amplitude of 5V and a frequency of 2kHz;

[0092] A time-delay interferometry algorithm is used to process the first and second heterodyne signals to directly compensate for laser phase noise. Based on this direct compensation, the strain signal is reconstructed. The specific implementation process includes: using the time-delay interferometry algorithm, the data of the second heterodyne interferometer and the two reflection point signals of the first heterodyne interferometer are time-shifted respectively. Specifically, the two reflection point signals of the first heterodyne interferometer are delayed by t2, and the second heterodyne interferometer data are delayed by t... 1,1 and t 1,2 Linear combination of the above signals yields:

[0093] Λ 1,1 =[s 1,1 [(t)-s2(t)]-[s 1,1 (t-t2)-s2(tt 1,1 )]=p r (t)-p r (t-t2)

[0094] Λ 1,2 =[s 1,2 [(t)-s2(t)]-[s 1,2 (t-t2)-s2(tt 1,2 )]=p r (t)-p r (t-t2)+p s (t)-p s (t-t2)

[0095] Calculate the phase difference Λ between the two reflection points. 1,1 -Λ 1,2 This allows for phase noise compensation of the first heterodyne interferometric optical data, resulting in signal p. s (t)-p s (t-t2); after passing through a low-pass filter equivalent to an integration operation and simple coefficient processing, the strain signal p can be reconstructed. s (t), as shown in Figures 3 and 4.

[0096] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A time-delay interferometric laser phase noise compensation method for optical frequency domain reflection, characterized in that, include: Obtain the swept frequency signal light based on the signal source; The swept frequency signal light is passed through a measurement interferometer to obtain a first heterodyne signal, and the swept frequency signal light is passed through a reference interferometer to obtain a second heterodyne signal; A time-delay interferometry algorithm is used to process the first heterodyne signal and the second heterodyne signal to achieve direct compensation for laser phase noise; The strain signal is obtained by directly compensating for and restoring the laser phase noise. The process of obtaining a first heterodyne signal from the swept frequency signal light via a measurement interferometer includes: splitting the swept frequency signal light into a measurement light and a reference light; splitting the measurement light into a second measurement light and a measurement interferometer local oscillator light; processing the second measurement light by applying a strain signal to a set reflection point to obtain a processed second measurement light; combining the processed second measurement light and the measurement interferometer local oscillator light to obtain a first heterodyne interference light; and detecting the first heterodyne interference light to obtain a first heterodyne signal. The process of obtaining a second heterodyne signal from the swept frequency signal light via a reference interferometer includes: splitting the reference light into a second reference light and a reference interferometer local oscillator light; processing the second reference light via a reference fiber to obtain a processed second reference light; and combining the processed second reference light with the reference interferometer local oscillator light. The beam is combined to obtain a second heterodyne interference beam; the second heterodyne interference beam is detected to obtain a second heterodyne signal; the process of obtaining direct compensation for laser phase noise includes: obtaining the corresponding frequency of the reflection point of the first heterodyne interference beam and the corresponding frequency of the reference fiber length of the second heterodyne interference beam based on the Fourier spectrum; obtaining the reflection point delay and the reference fiber delay based on the frequencies; filtering out the signals of each reflection point and the reference light signal based on the frequencies using a bandpass filter; obtaining the phase of the reflection point signal based on the Hilbert transform; performing time shifting and combining the reflection point delay and the reference fiber delay based on the time delay and time delay interference algorithm to complete the phase noise compensation of each reflection point, and obtaining the phase compensation signal of each reflection point of the first heterodyne interference beam; the formula for calculating the phase difference of the reflection point is as follows: In the formula, This represents the phase difference between two reflection points after the time-delayed interferometric laser phase noise compensation method. This represents the phase of reflection point 1 after the time-delayed interferometric laser phase noise compensation method. This represents the phase of reflection point 2 after the time-delayed interferometric laser phase noise compensation method. This indicates the phase of reflection point 1 extracted from the measurement path. This represents the phase extracted from the reference path. This indicates that the phase of reflection point 1 extracted from the measurement path is subject to a time delay. Indicates the reference path time delay. This indicates that the phase extracted from the reference path is subject to a time delay. This represents the time delay at reflection point 1. This represents the phase change introduced by the jitter of the fiber under test. This indicates a time delay applied to the phase change introduced by fiber jitter. This indicates the phase of reflection point 2 extracted from the measurement path. This indicates that the phase of reflection point 2 extracted from the measurement path is subject to a time delay. This indicates that the phase extracted from the reference path is subject to a time delay. This indicates the time delay at reflection point 2. Indicates the strain signal to be measured. This indicates the time delay of the strain signal to be measured.

2. The time-delay interferometric laser phase noise compensation method for optical frequency domain reflection according to claim 1, characterized in that, The process of obtaining the strain signal includes: obtaining a strain signal with only environmental jitter interference based on phase noise compensation of the first heterodyne interference light; obtaining a delayed self-coherent signal of the strain signal by differential calculation based on the phase of each reflection point; and obtaining the strain signal by low-pass filtering and coefficient processing of the delayed self-coherent signal.

3. A time-delay interferometric laser phase noise compensation device for optical frequency domain reflection, characterized in that, The apparatus for implementing the method as described in any one of claims 1-2 comprises: a swept-frequency light source (1), a first coupler (2), a second coupler (3), a third coupler (4), a circulator (5), an optical fiber under test (6), a reference optical fiber (7), a PZT (8), a fourth coupler (9), a fifth coupler (10), a first balanced photodetector (11), a second balanced photodetector (12), an oscilloscope (13), and a digital signal processing module (14); wherein the swept-frequency light source (1) is used to generate swept-frequency signal light; the first coupler (2) is connected to the swept-frequency light source (1), and the first coupler (2) is used to divide the swept-frequency signal light into measurement light and reference light; the second... Coupler (3) is connected to the first coupler (2), and the second coupler (3) is used to split the measurement light into a second measurement light and a measurement interferometer local oscillator light; the second coupler (3), circulator (5), fiber under test (6) and PZT (8) are connected in sequence, wherein the circulator (5) is used to receive the second measurement light and output the second measurement light processed by the fiber under test (6) and the PZT (8); the PZT (8) is used to apply the strain signal to be measured; the fourth coupler (9) is connected to the circulator (5), and the fourth coupler (9) is used to combine the processed second measurement light and the measurement interferometer local oscillator light to obtain the first heterodyne interference light; The first balanced photodetector (11) is connected to the fourth coupler (9). The first balanced photodetector (11) is used to convert the optical signal of the first heterodyne interference light into an electrical signal to obtain the first heterodyne signal. The third coupler (4) is connected to the first coupler (2). The reference fiber (7) is connected to the third coupler (4). The third coupler (4) is used to split the reference light into a second reference light and a reference interferometer local oscillator light. The fifth coupler (10) is connected to the reference fiber (7). The fifth coupler (10) is used to combine the second reference light and the reference interferometer local oscillator light to obtain the second heterodyne interference light. The second balanced photodetector ( 12) Connected to the fifth coupler (10), the second balanced photodetector (12) is used to convert the optical signal of the second heterodyne interference light into an electrical signal to obtain the second heterodyne signal; the oscilloscope (13) is connected to the first balanced photodetector (11) and the second balanced photodetector (12), and the oscilloscope (13) is used to detect and collect the beat frequency data of the first heterodyne signal and the second heterodyne signal; the digital signal processing module (14) is connected to the oscilloscope (13), and the digital signal processing module (14) is used to obtain the direct compensation of the laser phase noise by using the time delay interference algorithm, and obtain the strain signal based on the direct compensation of the laser phase noise.

4. The time-delay interferometric laser phase noise compensation device for optical frequency domain reflection according to claim 3, characterized in that, The oscilloscope (13) has a maximum sampling frequency of 20 GHz and a maximum number of sampling points of 40 Mpts for dual channels.

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