CN114719955B - Coherent fading noise suppression method in distributed optical fiber measurement of optical frequency domain reflectometer - Google Patents
Coherent fading noise suppression method in distributed optical fiber measurement of optical frequency domain reflectometer Download PDFInfo
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- CN114719955B CN114719955B CN202210399592.3A CN202210399592A CN114719955B CN 114719955 B CN114719955 B CN 114719955B CN 202210399592 A CN202210399592 A CN 202210399592A CN 114719955 B CN114719955 B CN 114719955B
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- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
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Abstract
The invention discloses a coherent fading noise suppression method in distributed optical fiber measurement of an optical frequency domain reflectometer, which comprises the following steps: the laser generates linear sweep-frequency laser with high coherence under the feedback control of the optical phase-locked loop module; the linear sweep laser with high coherence is divided into two parts by a first polarization maintaining coupler, one part of light with higher energy enters a second polarization maintaining coupler to be divided into two paths of optical signals, one path of optical signal generates N paths of echo signals, and the N paths of reference signals divided by the other path of optical signal generate interference by a third polarization maintaining coupler, and the optical signals are combined to generate an optical beat signal; converting the combined optical beat signal into an electric signal through a balanced receiver; acquiring electrical signal data by using a synchronous acquisition card, and converting the electrical signal data into a digital signal; carrying out vector weighted average processing on the digital signal to obtain a measurement signal with suppressed coherent fading noise; the method effectively inhibits coherent fading noise and improves the optical fiber distributed vibration measurement capability based on optical frequency domain reflectometer phase demodulation.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to a coherent fading noise suppression method in distributed optical fiber measurement of an optical frequency domain reflectometer.
Background
The distributed optical fiber measurement technology based on Optical Frequency Domain Reflectometer (OFDR) phase measurement is a distributed real-time sensing system with space distribution positioning and time change sensing, and can realize continuous measurement of field space distribution of physical quantity along an optical fiber; the distributed measurement and sensing capability with long distance, high resolution, high sensitivity and high precision is a core technical index of the system; the method has wide application prospect and practical value in a plurality of fields such as hydrology monitoring, earthquake early warning, aerospace, smart cities and the like, relating to industrial manufacturing, national defense construction and civil safety.
In the prior art, due to the randomness of the rayleigh scattering signal, large random fluctuation can occur in the coherent superposition in the coherent demodulation process, so that coherent fading noise is generated; the existence of the mechanism seriously influences the accuracy of phase measurement, thereby limiting the performance of distributed optical fiber measurement; currently, there are two main types of approaches to this problem.
One method is to use a weak reflection optical fiber grating array manufactured by etching or an optical fiber processed by ultraviolet exposure and the like as a sensing optical fiber to directly improve the intensity of optical echo, thereby improving the signal-to-noise ratio and reducing the influence of noise and crosstalk on the phase of an echo signal; such methods are completely limited by the performance specifications of the grating array or the processed fiber, such as reflectivity, distribution of the grating array or the processing points, and the like.
The other method is to carry out vector weighted average on echo signals with non-correlation so as to achieve the purpose of suppressing coherent fading noise; measuring by using the characteristics of Rayleigh scattering and the wavelength of the detection light and adopting sweep light sources with different frequencies or dividing a sweep light source into a plurality of sub-sweep frequency bands with different initial frequencies in the data processing process so as to obtain a plurality of groups of Rayleigh echo signals with different amplitude statistical characteristics for vector addition; such methods require sacrificing system complexity or spatial resolution, limiting system performance.
Therefore, how to obtain the capabilities of long-distance, high-sensitivity distributed vibration positioning and amplitude measurement by suppressing the phase noise caused by coherent fading without sacrificing the high spatial resolution capability of the original OFDR system has become a technical problem to be solved by those skilled in the art.
Disclosure of Invention
In view of the above problems, the present invention provides a method for suppressing coherent fading noise in distributed optical fiber measurement of an optical frequency domain reflectometer, which at least solves some of the above technical problems, and suppresses phase noise caused by coherent fading by performing vector weighted averaging on an echo signal and a local oscillator optical signal, thereby improving the optical fiber distributed vibration measurement capability of phase demodulation of the optical frequency domain reflectometer; the method comprises the following steps:
s1, a laser generates linear sweep-frequency laser with high coherence under the feedback control of an optical phase-locked loop module;
s2, dividing the high-coherence linear sweep laser into two parts through a first polarization maintaining coupler, enabling a part of light with higher energy to enter a second polarization maintaining coupler to be divided into two paths of optical signals, enabling one path of optical signals to generate N paths of echo signals, dividing the other path of optical signals into N paths of reference signals, enabling the two paths of optical signals to generate interference through a third polarization maintaining coupler, and combining the beams to generate an optical beat signal;
s4, collecting the electric signal data by using a synchronous acquisition card, and converting the electric signal data into a digital signal;
and S5, carrying out vector weighted average processing on the digital signal to obtain a measurement signal with suppressed coherent fading noise.
Preferably, the method further comprises:
and S6, performing time domain and frequency domain processing analysis on the measurement signal with the suppressed coherent fading noise, resolving phase information of the signal, and obtaining a vibration signal applied to the multi-core optical fiber to be detected.
Preferably, the step S1 specifically includes:
s11, dividing an optical signal output by a laser into two parts of optical signals with non-uniform energy through a first polarization maintaining coupler;
s12, inputting a part with lower energy into a Mach-Zehnder interferometer, and outputting an interference optical signal by the Mach-Zehnder interferometer to enter an optical phase-locked loop module;
s13, suppressing sweep frequency nonlinear noise and phase frequency noise of the laser through an optical phase-locked loop module, and generating a phase-locked control signal;
and S14, combining the phase locking control signal and the sweep frequency signal, and performing feedback control on the laser to generate high-coherence linear sweep frequency laser.
Preferably, the step S2 specifically includes:
s21, enabling high-coherence linear sweep frequency laser to pass through a first polarization maintaining coupler, and enabling a part of light with higher energy to enter a second polarization maintaining coupler; dividing the two optical signals into two paths of optical signals with non-uniform energy through the second polarization maintaining coupler; one path of optical signal with higher energy is taken as a measuring path; one path of optical signal with lower energy is used as a reference path;
s22, the measuring optical signals are equally divided into N measuring optical signals through a first 1 xN coupler and enter N non-polarization-maintaining circulators, and the N non-polarization-maintaining circulators are connected with the multi-core fiber to be measured to obtain N Rayleigh echo signals with independent statistical characteristics; meanwhile, the reference path optical signal is equally divided into N paths of reference optical signals through a second 1 xN coupler;
s23, the N non-polarization-maintaining circulators are respectively connected with N independent polarization controllers, and the polarization states of the N paths of Rayleigh echo signals are adjusted;
and S24, interfering the adjusted N paths of Rayleigh echo signals and the N paths of reference optical signals through N third polarization-maintaining couplers, and combining the beams to generate N paths of optical beat signals.
Preferably, in step S1; the first polarization-maintaining coupler divides an optical signal output by the laser into two optical signals according to a power division ratio of 99.5.
Preferably, in step S2; and the second polarization-maintaining coupler divides the optical signal into two paths according to the power distribution proportion of 80.
Preferably, in step S2; the third polarization-maintaining coupler is of a 2 × 2 type, and inputs the optical beat signal generated by beam combination into the balanced receiver according to a power distribution ratio of 50.
Preferably, in the step S1; the laser is a wavelength tunable narrow linewidth laser.
Compared with the prior art, the invention has the beneficial effects that at least: the invention is based on the distributed optical fiber measuring capability of the optical frequency domain reflectometer, two arms of an interference structure are divided into N parts, phase vector weighted average of a plurality of non-correlated Rayleigh scattering light and local oscillator light beat frequency signals in a multi-core optical fiber is adopted, coherent fading noise is effectively inhibited, further, the vibration information applied to the multi-core optical fiber is obtained by demodulating the phase of the signals after the vector weighted average, and the long-distance and high-sensitivity distributed vibration positioning and amplitude measuring capability is obtained under the condition of not sacrificing the high spatial resolution capability of an original system.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
FIG. 1 is a flow chart of a coherent fading noise suppression method in distributed optical fiber measurement of an optical frequency domain reflectometer according to the present invention;
fig. 2 is a schematic structural diagram of a coherent fading noise suppression system in distributed optical fiber measurement according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a signal processing flow according to an embodiment of the present invention;
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
As shown in fig. 1, an embodiment of the present invention provides a coherent fading noise suppression method in distributed optical fiber measurement of an optical frequency domain reflectometer, including the following steps:
s1, a laser generates linear sweep-frequency laser with high coherence under the feedback control of an optical phase-locked loop module;
s2, dividing the high-coherence linear sweep laser into two parts through a first polarization maintaining coupler, enabling a part of light with higher energy to enter a second polarization maintaining coupler to be divided into two paths of optical signals, enabling one path of optical signals to generate N paths of echo signals, dividing the other path of optical signals into N paths of reference signals, enabling the two paths of optical signals to generate interference through a third polarization maintaining coupler, and combining the beams to generate an optical beat signal;
s3, converting the combined optical beat signal into an electric signal through a balance receiver;
s4, acquiring the electric signal data by using a synchronous acquisition card, and converting the electric signal data into a digital signal;
and S5, carrying out vector weighted average processing on the digital signals to obtain measurement signals with suppressed coherent fading noise.
And S6, performing time domain and frequency domain processing analysis on the measurement signal with the suppressed coherent fading noise, and resolving phase information of the signal to obtain a vibration signal applied to the multi-core fiber to be measured.
The above steps are described in detail below, and the overall method of the embodiment of the present invention is as follows:
in step S1, as shown in fig. 2, a wavelength tunable narrow linewidth laser is preferably used as a light source to output a light signal; an optical signal output by the laser is divided into two parts of optical signals with non-uniform energy through a first polarization maintaining coupler; according to the power distribution proportion of 99.5, the first polarization-preserving coupler inputs a part of optical signals accounting for 0.5% of energy into the Mach-Zehnder interferometer, and the Mach-Zehnder interferometer outputs interference optical signals to enter the optical phase-locked loop module; suppressing the sweep frequency nonlinear noise and the phase frequency noise of the laser by an optical phase-locked loop module to generate a phase-locked control signal; and combining the phase-locked control signal with the frequency sweeping signal generated by the frequency sweeping signal generator, and performing feedback control on the laser to generate high-coherence linear frequency sweeping laser.
In the step S2, the linear sweep laser with high coherence passes through the first polarization maintaining coupler, and light accounting for 99.5% of energy enters the second polarization maintaining coupler; the second polarization-maintaining coupler divides the two optical signals into two paths of non-uniform energy through the second polarization-maintaining coupler according to the power distribution proportion of 80; one path of optical signal with 80% energy is used as a measuring path; one path of optical signal with 20% energy is used as a reference path;
as shown in fig. 2, the measurement optical signals are equally divided into N paths of measurement optical signals by the first 1 × N coupler and enter N non-polarization-maintaining circulators, common ports of the N non-polarization-maintaining circulators are connected to input ports of the multicore fiber to be measured, the signals are sent into N fiber cores of the multicore fiber associated with the external physical quantity, N paths of rayleigh echo signals with independent statistical characteristics are obtained by utilizing the independence of each core of the multicore fiber, and the N paths of measurement optical signals are output through output ports of the N non-polarization-maintaining circulators; meanwhile, the reference path optical signal is equally divided into N paths of reference optical signals through a second 1 xN coupler;
as shown in fig. 2, the N non-polarization-maintaining circulators are respectively connected to N independent polarization controllers, and the polarization controllers adjust the polarization states of the N rayleigh echo signals; interfering the adjusted N paths of Rayleigh echo signals and N paths of reference light signals through N third polarization maintaining couplers, and combining beams to generate N paths of optical beat signals; the third polarization-maintaining coupler adopts a 2 x 2 type and inputs the optical beat signals generated by beam combination into N balanced receivers according to the power distribution proportion of 50.
In step S3, the balanced receivers preferably have a bandwidth of DC-100MHz, and receive the bundled optical beat signals through N balanced receivers and perform photoelectric conversion, as shown in fig. 3, to convert the optical beat signals into N electrical signals.
In step S4, as shown in fig. 2 and 3, N paths of electrical signal data are acquired by using N paths of synchronous acquisition cards, and the acquired N paths of electrical signals are converted into digital signals.
In step S5, as shown in fig. 3, vector-weighted averaging processing is performed on the digital signal to obtain a measurement signal with coherent fading noise suppressed.
In step S6, as shown in fig. 3, time domain and frequency domain processing analysis is performed on the measurement signal with the coherent fading noise suppressed, phase information of the signal is resolved, a field space distribution condition of the physical quantity along the optical fiber is obtained, a vibration signal applied to the multi-core optical fiber to be measured is obtained, and distributed optical fiber sensing and measurement are achieved.
The method for suppressing coherent fading noise in distributed optical fiber measurement of the optical frequency domain reflectometer uses a multi-core optical fiber as a sensing optical fiber, effectively suppresses phase noise caused by coherent fading by carrying out weighted averaging on a plurality of uncorrelated Rayleigh scattering light and local oscillator light beat frequency signals in the multi-core optical fiber, and further obtains vibration information applied to the multi-core optical fiber by demodulating the phase of the signals after the weighted averaging, thereby improving the vibration measurement capability of the distributed optical fiber of the optical frequency domain reflectometer, obtaining the capabilities of long-distance and high-sensitivity distributed vibration positioning and amplitude measurement without sacrificing the high spatial resolution of the original system, and being capable of realizing continuous measurement of the field spatial distribution of physical quantities along the optical fiber.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (6)
1. The coherent fading noise suppression method in the distributed optical fiber measurement of the optical frequency domain reflectometer is characterized by comprising the following steps of:
s1, a laser generates linear sweep-frequency laser with high coherence under the feedback control of an optical phase-locked loop module;
s2, the high-coherence linear frequency sweeping laser is divided into two parts through a first polarization maintaining coupler, one part of light with higher energy enters a second polarization maintaining coupler to be divided into two paths of optical signals, one path of optical signal generates N paths of echo signals, the other path of optical signal is divided into N paths of reference signals, interference occurs through a third polarization maintaining coupler, and beam combination is carried out to generate a light beat signal;
s3, converting the combined optical beat signals into electric signals through a balance receiver;
s4, acquiring the electric signals by using a synchronous acquisition card, and converting the electric signals into digital signals;
s5, carrying out vector weighted average processing on the digital signal to obtain a measurement signal with suppressed coherent fading noise;
the step S1 specifically includes:
s11, dividing an optical signal output by a laser into two parts of optical signals with non-uniform energy through a first polarization maintaining coupler;
s12, inputting a part with lower energy into a Mach-Zehnder interferometer, and outputting an interference optical signal by the Mach-Zehnder interferometer to enter an optical phase-locked loop module;
s13, suppressing sweep frequency nonlinear noise and phase frequency noise of the laser through an optical phase-locked loop module, and generating a phase-locked control signal;
s14, combining the phase-locked control signal and the sweep frequency signal, and performing feedback control on a laser to generate high-coherence linear sweep frequency laser;
the step S2 specifically includes:
s21, enabling the high-coherence linear sweep frequency laser to pass through a first polarization maintaining coupler, and enabling a part of light with higher energy to enter a second polarization maintaining coupler; dividing the two optical signals into two paths of optical signals with non-uniform energy through the second polarization maintaining coupler; one path of optical signal with higher energy is taken as a measuring path; one path of optical signal with lower energy is used as a reference path;
s22, the measuring path optical signals are equally divided into N measuring optical signals through a first 1 xN coupler and enter N non-polarization-preserving circulators, and the N non-polarization-preserving circulators are connected with the multi-core optical fiber to be measured to obtain N Rayleigh echo signals with independent statistical characteristics; meanwhile, the reference path optical signals are equally divided into N paths of reference optical signals through a second 1 xN coupler;
s23, connecting the N non-polarization-maintaining circulators with N independent polarization controllers respectively, and adjusting the polarization states of the N paths of Rayleigh echo signals;
and S24, interfering the adjusted N paths of Rayleigh echo signals and the N paths of reference optical signals through N third polarization-maintaining couplers, and combining to generate N paths of optical beat signals.
2. The method for coherent fading noise suppression in optical frequency domain reflectometry distributed fiber optic measurements as in claim 1 further comprising:
and S6, performing time domain and frequency domain processing analysis on the measurement signal with the suppressed coherent fading noise, and resolving phase information of the signal to obtain a vibration signal applied to the multi-core fiber to be measured.
3. The method for suppressing coherent fading noise in distributed fiber measurement by optical frequency domain reflectometer as in claim 1, wherein in said step S1; the first polarization-maintaining coupler divides an optical signal output by the laser into two optical signals according to a power division ratio of 99.5.
4. The method for suppressing coherent fading noise in distributed fiber measurement by optical frequency domain reflectometer as in claim 1, wherein in said step S2; and the second polarization-maintaining coupler divides the optical signal into two paths according to the power distribution proportion of 80.
5. The method for suppressing coherent fading noise in distributed optical fiber measurement by optical frequency domain reflectometer as in claim 1, wherein in said step S2; the third polarization-maintaining coupler is of a 2 × 2 type, and inputs the optical beat signal generated by beam combination into the balanced receiver according to a power distribution ratio of 50.
6. The method for suppressing coherent fading noise in distributed optical fiber measurement by optical frequency domain reflectometer as in claim 1, wherein in said step S1; the laser is a narrow linewidth laser with tunable wavelength.
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| CN102322880B (en) * | 2011-08-18 | 2013-06-05 | 天津大学 | Polarization sensitive distributive optical frequency domain reflection disturbance sensor and demodulation method |
| EP2860498B1 (en) * | 2013-10-09 | 2017-12-06 | Optoplan AS | Processing data from a distributed fibre-optic interferometric sensor system |
| CN106052842B (en) * | 2016-08-05 | 2022-03-15 | 上海交通大学 | Distributed optical fiber vibration sensing system capable of eliminating fading noise and demodulation method thereof |
| US11959799B2 (en) * | 2018-08-08 | 2024-04-16 | Aselsan Elektronik Sanayi Ve Ticaret Anonim Sirketi | Extinction ratio free phase sensitive optical time domain reflectometry based distributed acoustic sensing system |
| CN110132397B (en) * | 2019-05-09 | 2021-03-19 | 南京大学 | Method for reducing dead zone probability in phi-OTDR system based on space division multiplexing |
| CN112747815B (en) * | 2021-01-06 | 2024-02-02 | 苏州光格科技股份有限公司 | Coherent fading noise suppression method in distributed optical fiber acoustic wave sensing system |
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| WO2016011431A1 (en) * | 2014-07-17 | 2016-01-21 | Halliburton Energy Services, Inc. | Noise removal for distributed acoustic sensing data |
| CN105067103A (en) * | 2015-08-31 | 2015-11-18 | 上海交通大学 | Vibration detection device and method based on optical frequency domain reflectometer |
| CN113237431A (en) * | 2021-05-06 | 2021-08-10 | 山东大学 | Measurement method for improving distributed spatial resolution of OFDR system |
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