CN114112004B - Method for electronic polarization adjustment and polarization state monitoring of optical fiber sensing system - Google Patents
Method for electronic polarization adjustment and polarization state monitoring of optical fiber sensing system Download PDFInfo
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- 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 provides a method for electronic polarization adjustment and polarization state monitoring of an optical fiber sensing system, which comprises the following steps: modulation signal generation, interference signal transmission and electronic polarization adjustment and polarization state monitoring. The invention reflects the polarization fading condition by generating a high-frequency modulation signal which is different from the environmental interference on the frequency spectrum and analyzing and identifying the phase difference of the two paths of modulation vibration interference signals or indirectly reflecting the index of the phase difference of the two paths of signals. The invention can be applied to the occasions with large environmental noise, particularly effectively solves the problems of monitoring and adjusting the system polarization state of the long-distance optical fiber sensing vibration system, overcomes the defect of large interference of environmental background noise, and ensures that the long-distance optical fiber vibration detection system is feasible in technical and engineering application because the installation position of the polarization controller is on the side of the sensing host.
Description
Technical Field
The invention relates to the technical field of communication, in particular to a method for electronic polarization adjustment and polarization state monitoring of an optical fiber sensing system.
Background
With the development of optical fiber technology, optical fiber sensing technology is widely applied to various fields. The dual-M-Z (Mach-Zehnder ) interferometer is commonly used in the fields of optical fiber perimeter security, long-distance submarine cable vibration monitoring and the like due to the high sensitivity characteristic. Because the polarization characteristic of the single-mode fiber is easily interfered by external environment factors, the light source is divided into 2 paths of light beams after passing through the initial 1-to-2 coupler, and the polarization state is random when the 2 paths of light beams reach the subsequent 1-to-2 coupler for combining. In an extreme case, when the polarization states of the two beams of light are orthogonal to each other, the two beams of light will not form interference, and the detector will not detect the interference signal. At this time, the system has serious false alarm and missing report phenomena. In order to overcome this phenomenon, the system needs to have a corresponding offset device.
Working principle of the double MZ ring:
the light source is divided into 2 paths through C1;
clockwise: (light source enters the sensor arm through C2, then goes to C3, then goes through the conductive arm to PD 1)
In the counterclockwise direction: (light source goes through conducting arm into C3, through sensing arm to C2, and then into PD 2).
If a vibration event occurs between the sensing arms between C2 and C3, the signals received by PD1 and PD2 will have a phase difference. That is, there is a certain correspondence between the phase difference and the vibration position. And the software can deduce the occurrence position of the specific vibration event according to the phase difference.
C1 is a 1 in 2 optical coupler; c2 and C3 are 2 in 2 optical couplers. The dual MZ rings typically include 3 or 4 cores. Wherein the 2 core between C2 and C3 is simply referred to as the sensing arm; c3 and PD 1; the core between C1 and C3 is simply referred to as the conducting arm.
The prior solution places one polarization controller on each of the 2 reference arms of the dual MZ ring (i.e., between C2 and C3); by utilizing the current modulation characteristic of the semiconductor laser, the bias current of the semiconductor laser is artificially changed, and a disturbance is made at the starting end of the MZ ring to enable the double MZ ring to form interference. Interference signals of 2 paths of signals (clockwise and anticlockwise) are synchronously acquired by the receiving detection boards PD1 and PD2, and the system forms a Lissajous figure by using the 2 paths of signals. And the algorithm obtains the phase difference of the 2 paths of signals by an ellipse fitting method based on the Lissajous figure.
Ideally, the lissajous figure would be a straight line with the phase difference of the 2 signals being 0. When polarization fading exists (namely the Lissajous figure is not a straight line, and the phase difference of the 2 paths of signals is not 0), the system MCU optimally adjusts the polarization states of the 2 polarization controllers through a certain search algorithm. After the polarization states of the 2 reference arms of the double MZ ring are adjusted in place, the polarization state of the system is also in an ideal state with minimal polarization fading.
The prior scheme has the following defects:
(1) 2 electronic polarization controllers are required. It is expensive.
(2) The polarization controller needs to be placed in the range of the passive sensing module, and needs to be externally supplied with power.
(3) When the environmental noise is large, the Lissajous figures formed by receiving 2 paths of signals are disordered and are not an ideal straight line any more, but are irregular shapes formed by combining scattered points. The difficulty of calculating the phase difference of the 2-path signals by an ellipse fitting method is high.
Disclosure of Invention
The invention provides a method for electronic polarization adjustment and polarization state monitoring of an optical fiber sensing system, which aims to solve the problem that the existing double-M-Z interferometer cannot be applied to occasions with large environmental noise. The invention can be applied to the occasions with large environmental noise, particularly effectively solves the problems of monitoring and adjusting the system polarization state of the long-distance optical fiber sensing vibration system, overcomes the defect of large interference of environmental background noise, and ensures that the long-distance optical fiber vibration detection system is feasible in technical and engineering application because the installation position of the polarization controller is on the side of the sensing host.
The invention provides a method for electronic polarization adjustment and polarization state monitoring of an optical fiber sensing system, which comprises the following steps: the method comprises the following steps:
s1, generating a modulation signal: the signal generator generates a modulation signal to modulate the laser source and applies the modulated optical signal to the polarization controller, the modulation signal is a CW dot frequency signal, and the modulation signal is used for distinguishing from the environmental background noise;
s2, interference signal transmission: the polarization controller outputs the optical signal to the passive sensing module and generates a two-way interference signal to be output to the receiving detector, the receiving detector receives the two-way interference signal and converts the two-way interference signal into two-way electric signals to be output to the signal processing device, and the laser source, the passive sensing module and the receiving detector are a double MZ interference system;
s3, monitoring the polarization state: the signal processing device analyzes the electric signals to obtain frequency spectrum signals corresponding to the modulation signals, phase difference or cross correlation coefficient of the frequency spectrum signals is calculated to obtain polarization state of the optical fiber sensing system, and the polarization state is used for analyzing to obtain position and mode characteristic results;
s4, electronic deviation adjustment: and the MCU detects the polarization state and adjusts the polarization controller according to the phase difference or the cross correlation coefficient so as to enable the optical fiber sensing system to be in a stable state.
In the method for electronically adjusting the polarization and monitoring the polarization state of the optical fiber sensing system according to the present invention, as a preferred mode, step S2 includes:
s21, outputting the optical signal to a passive sensing module by the polarization controller;
s22, a first optical splitter coupler in the passive sensing module receives optical signals and respectively outputs the optical signals to a second optical splitter coupler and a third optical splitter coupler, the second optical splitter coupler converts the optical signals into interference signals through a sensing arm and outputs the interference signals to the third optical splitter coupler and outputs the interference signals to a first photoelectric detection plate of a receiving detector through a conducting arm to generate clockwise electric signals, and the third optical splitter coupler outputs the optical signals output by the first optical splitter coupler through the conducting arm to the sensing arm to convert the interference signals and outputs the interference signals to a second photoelectric detection plate of the receiving detector through the second optical splitter coupler to generate counterclockwise electric signals.
According to the method for electronic polarization adjustment and polarization state monitoring of the optical fiber sensing system, as a preferred mode, the sensing arm is an optical fiber between the second optical splitter and the third optical splitter, and the conducting arm comprises an optical fiber between the first optical splitter and the third optical splitter, an optical fiber between the third optical splitter and a first photoelectric detection plate.
The invention relates to a method for electronic polarization adjustment and polarization state monitoring of an optical fiber sensing system.
The invention relates to a method for electronic polarization adjustment and polarization state monitoring of an optical fiber sensing system.
As a preferred mode, in step S3, the method for calculating the phase difference includes: the signal processing device acquires at least more than 2 clockwise electrical signals and anticlockwise electrical signals, then performs FFT spectrum analysis to obtain clockwise spectrum signals and anticlockwise spectrum signals corresponding to the modulation signals, and calculates difference values of the clockwise spectrum signals and the anticlockwise spectrum signals to obtain phase differences;
in step S4, it is determined whether the phase difference is zero, and if so, the polarization fading of the optical fiber sensing system is small, and electronic polarization adjustment is not needed; if not, the polarization fading of the optical fiber sensing system is large, and the electronic polarization adjustment is carried out by adjusting the polarization controller.
As a preferred mode, in step S3, the method for calculating the cross-correlation coefficient includes: the signal processing device collects at least more than 2 clockwise electric signals and anticlockwise electric signals, then carries out band-pass filtering to filter out environmental background noise, and then carries out correlation operation on the clockwise electric signals and the anticlockwise electric signals to obtain cross correlation coefficients;
in step S4, judging whether the cross correlation coefficient is close to 1, if yes, the polarization fading of the optical fiber sensing system is small, and electronic deviation adjustment is not needed; if not, the polarization fading of the optical fiber sensing system is large, and the electronic polarization adjustment is carried out by adjusting the polarization controller.
According to the method for electronic polarization adjustment and polarization state monitoring of the optical fiber sensing system, as a preferred mode, the laser source is a modulatable laser source.
The invention relates to a method for electronic polarization adjustment and polarization state monitoring of an optical fiber sensing system, which is used as a preferred mode, the optical fiber sensing system further comprises a PZT phase modulator electrically connected with the output end of a laser source and the output end of a signal generator, and the output end of the PZT phase modulator is electrically connected with the input end of a polarization controller;
in step S1, the signal generator generates a modulation signal to modulate the PZT phase modulator at the rear end of the laser source and applies the modulated optical signal to the polarization controller.
According to the method for electronic polarization adjustment and polarization state monitoring of the optical fiber sensing system, as a preferred mode, a modulation signal is a sine wave signal or a square wave signal, and the frequency of the modulation signal is 30 kHz.
The working process of the invention is as follows:
the system only uses one electronic polarization controller and is arranged behind the laser source; in the system, 1 PZT phase modulator is added between a laser source and a polarization controller, or a laser source with a modulation function is adopted; the system generates a high-frequency (such as 30 kHz) sine wave or square wave signal as a modulation signal, and applies the modulation signal to a PZT phase modulator or a modulatable laser source; the interference signals received by the detection boards PD1 and PD2 include vibration interference signals corresponding to the modulation frequency (e.g., 30 kHz) position. The system selects a frequency spectrum part signal corresponding to the 30kHz vibration modulation signal in the interference signal by a software method. (since the modulated signal is higher in frequency and easily distinguished from environmental interference), the system calculates the phase difference of the 2-way signal or a variable (e.g., cross-correlation coefficient) that can reflect the phase difference. If the phase difference is 0 or the cross-correlation coefficient is close to 1, it means that the polarization fading is small. The system periodically monitors the polarization state of the dual MZ interferometric system. If the polarization fading is large, the state of the polarization controller is adjusted periodically or actively, and finally the polarization state of the system is in an ideal state.
The software identifies the polarization state of the 2-way signal by the following two methods.
Signals of a plurality of points are collected by the high-speed ADC for FFT spectrum analysis, FFT values corresponding to 30kHz frequency spectrums are found, and phase differences of 2 paths of signals are directly calculated.
The high-speed ADC is used for collecting signals of a plurality of points, firstly, band-pass is conducted, environmental background noise is filtered, then, cross-correlation operation is conducted on two paths of signals, and cross-correlation coefficients are obtained.
The invention relates to the generation of an interference signal which is spectrally distinguished from environmental disturbances by means of a PZT phase modulator. Some semiconductor lasers have a modulation function, and the same effect can be achieved by giving a similar high frequency signal (30 kHz) to the semiconductor laser. The modulatable semiconductor laser is equivalent to a laser source + PZT phase modulator function.
The invention is applied to the occasions with large environmental noise (especially long distance), a system hardware scheme, a PZT phase modulator and a polarization controller or a modulatable semiconductor laser and a polarization controller are arranged behind a laser, a high-frequency modulation signal is given to the PZT phase modulator or the modulatable laser source, the spectrum of the modulation interference signal can be distinguished from the environmental background noise, the software distinguishes the vibration information generated by the modulation signal from other information (a band-pass or high-pass mode), the software identifies the phase difference of two paths of modulation vibration interference signals or an index (cross correlation coefficient) indirectly reflecting the phase difference of the two paths of signals, and the phase difference or the cross correlation coefficient reflects the polarization fading condition.
The invention has the following advantages:
the invention can be applied to the occasions with large environmental noise, particularly effectively solves the problems of monitoring and adjusting the system polarization state of the long-distance optical fiber sensing vibration system, overcomes the defect of large interference of environmental background noise, and ensures that the long-distance optical fiber vibration detection system is feasible in technical and engineering application because the installation position of the polarization controller is on the side of the sensing host.
Drawings
FIG. 1 is a flowchart of an embodiment 1 of a method for electronically tuning and monitoring polarization state of an optical fiber sensing system;
FIG. 2 is a schematic structural diagram of an optical fiber sensing system in accordance with embodiment 1 of a method for electronically adjusting polarization and monitoring polarization state of an optical fiber sensing system;
FIG. 3 is a flow chart of embodiment 2 of a method for electronic polarization adjustment and polarization state monitoring of an optical fiber sensing system;
fig. 4 is a schematic structural diagram of an optical fiber sensing system in embodiment 2 of a method for electronically adjusting polarization and monitoring a polarization state of the optical fiber sensing system.
Reference numerals:
1. a signal generator; 2. A laser source; 3. A polarization controller; 4. A passive sensing module; 41. A first optocoupler; 42. A second sub-optical coupler; 43. A third optical sub-coupler; 5. Receiving a detector; 51. A first photoelectric detection plate of (1); 52. A second photoelectric detection plate; 6. MCU; 7. A PZT phase modulator.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.
Example 1
As shown in fig. 1-2, a method for electronic polarization adjustment and polarization state monitoring of an optical fiber sensing system is characterized in that: the method comprises the following steps:
s1, generating a modulation signal: the signal generator 1 generates a modulation signal to modulate the laser source 2 and apply the modulated optical signal to the polarization controller 3, wherein the modulation signal is a CW dot frequency signal, the modulation signal is a high frequency signal used for distinguishing from the environmental background noise, and the modulation signal is a sine wave or square wave signal;
the laser source 2 is a modulatable laser source;
the modulation signal is a sine wave or square wave signal, and the frequency of the modulation signal is 30 kHz;
s2, interference signal transmission: the polarization controller 3 outputs the optical signal to the passive sensing module 4 and generates a two-way interference signal to be output to the receiving detector 5, the receiving detector 5 receives the two-way interference signal and converts the two-way interference signal into two-way electrical signals to be output to the signal processing device, and the laser source 2, the passive sensing module 4 and the receiving detector 5 are a double MZ interference system;
s21, outputting the optical signal to the passive sensing module 4 by the polarization controller 3;
s22, the first optical sub-coupler 41 in the passive sensing module 4 receives an optical signal and outputs the optical signal to the second optical sub-coupler 42 and the third optical sub-coupler 43, the second optical sub-coupler 42 converts the optical signal into an interference signal via the sensing arm and outputs the interference signal to the third optical sub-coupler 43 and outputs the interference signal via the conducting arm to the first photoelectric detection plate 51 of the receiving detector 5 to generate a clockwise electrical signal, and the third optical sub-coupler 43 outputs the optical signal output by the first optical sub-coupler 41 via the conducting arm to the sensing arm and converts the optical signal into an interference signal and outputs the interference signal via the second optical sub-coupler 42 to the second photoelectric detection plate 52 of the receiving detector 5 to generate a counterclockwise electrical signal;
the sensing arm is an optical fiber between the second optical sub-coupler 42 and the third optical sub-coupler 43, and the conducting arm comprises an optical fiber between the first optical sub-coupler 41 and the third optical sub-coupler 23, an optical fiber between the third optical sub-coupler 43 and the first photoelectric detection plate 51;
the first optical splitter coupler 41 is a two-to-two optical coupler, and the second optical splitter coupler 42 and the third optical splitter coupler 43 are both two-to-two optical couplers;
s3, monitoring the polarization state: the signal processing device analyzes the electric signals to obtain frequency spectrum signals corresponding to the modulation signals, phase difference or cross correlation coefficient of the frequency spectrum signals is calculated to obtain polarization state of the optical fiber sensing system, and the polarization state is used for analyzing to obtain position and mode characteristic results;
the signal processing device is a high-speed analog-to-digital converter;
the phase difference calculation method comprises the following steps: the signal processing device acquires at least more than 2 clockwise electrical signals and anticlockwise electrical signals, then performs FFT spectrum analysis to obtain clockwise spectrum signals and anticlockwise spectrum signals corresponding to the modulation signals, and calculates difference values of the clockwise spectrum signals and the anticlockwise spectrum signals to obtain phase differences;
the method for calculating the cross-correlation coefficient comprises the following steps: the signal processing device collects at least more than 2 clockwise electric signals and anticlockwise electric signals, then carries out band-pass filtering to filter out environmental background noise, and then carries out correlation operation on the clockwise electric signals and the anticlockwise electric signals to obtain cross correlation coefficients;
s4, electronic deviation adjustment: the MCU6 detects the polarization state, and adjusts the polarization controller 3 according to the phase difference or the cross correlation coefficient to make the optical fiber sensing system in a stable state;
judging whether the phase difference is zero, if so, the polarization fading of the optical fiber sensing system is small, and electronic polarization adjustment is not needed; if not, the polarization fading of the optical fiber sensing system is large, and electronic polarization adjustment is carried out by adjusting the polarization controller 3;
judging whether the cross-correlation coefficient is close to 1, if so, the polarization fading of the optical fiber sensing system is small, and electronic polarization adjustment is not needed; if not, the polarization fading of the optical fiber sensing system is large, and the electronic polarization adjustment is carried out by adjusting the polarization controller 3.
Example 2
As shown in fig. 3-4, a method for electronic polarization adjustment and polarization state monitoring of an optical fiber sensing system is characterized in that: the method comprises the following steps:
s1, generating a modulation signal: the signal generator 1 generates a modulation signal to modulate a PZT phase modulator 7 at the rear end of the laser source 2 and apply the modulated optical signal to the polarization controller 3, wherein the modulation signal is a CW dot frequency signal and is used for distinguishing from environmental background noise;
the optical fiber sensing system comprises a PZT phase modulator 7 which is electrically connected with the output end of the laser source 2 and the output end of the signal generator 1, and the output end of the PZT phase modulator 7 is electrically connected with the input end of the polarization controller 3;
the modulation signal is a sine wave or square wave signal, and the frequency of the modulation signal is 30 kHz;
s2, interference signal transmission: the polarization controller 3 outputs the optical signal to the passive sensing module 4 and generates two-way interference signals to be output to the receiving detector 5, the receiving detector 5 receives the two-way interference signals and converts the two-way interference signals into two-way electric signals to be output to the signal processing device, and the laser source 2, the passive sensing module 4 and the receiving detector 5 are a double MZ interference system;
s21, the polarization controller 3 outputs the optical signal to the passive sensing module 4;
s22, the first optical sub-coupler 41 in the passive sensing module 4 receives optical signals and outputs the optical signals to the second optical sub-coupler 42 and the third optical sub-coupler 43, the second optical sub-coupler 42 converts the optical signals into interference signals via the sensing arm and outputs the interference signals to the third optical sub-coupler 43 and outputs the interference signals to the first photoelectric detection plate 51 of the receiving detector 5 via the conducting arm to generate clockwise electrical signals, and the third optical sub-coupler 43 outputs the optical signals output by the first optical sub-coupler 41 via the conducting arm to the sensing arm to convert the optical signals into interference signals and outputs the interference signals to the second photoelectric detection plate 52 of the receiving detector 5 via the second optical sub-coupler 42 to generate counterclockwise electrical signals;
the sensing arm is an optical fiber between the second optical sub-coupler 42 and the third optical sub-coupler 43, and the conducting arm comprises an optical fiber between the first optical sub-coupler 41 and the third optical sub-coupler 23 and an optical fiber between the third optical sub-coupler 43 and the first photoelectric detection plate 51;
the first optical splitter coupler 41 is a one-to-two optical coupler, and the second optical splitter coupler 42 and the third optical splitter coupler 43 are both two-to-two optical couplers;
s3, monitoring the polarization state: the signal processing device analyzes the electric signals to obtain frequency spectrum signals corresponding to the modulation signals, phase difference or cross correlation coefficient of the frequency spectrum signals is calculated to obtain polarization state of the optical fiber sensing system, and the polarization state is used for analyzing to obtain position and mode characteristic results;
the signal processing device is a high-speed analog-to-digital converter;
the phase difference calculation method comprises the following steps: the signal processing device acquires at least more than 2 clockwise electrical signals and anticlockwise electrical signals, then performs FFT spectrum analysis to obtain clockwise spectrum signals and anticlockwise spectrum signals corresponding to the modulation signals, and calculates difference values of the clockwise spectrum signals and the anticlockwise spectrum signals to obtain phase differences;
the method for calculating the cross-correlation coefficient comprises the following steps: the signal processing device collects at least more than 2 clockwise electric signals and anticlockwise electric signals, then carries out band-pass filtering to filter out environmental background noise, and then carries out correlation operation on the clockwise electric signals and the anticlockwise electric signals to obtain cross correlation coefficients;
s4, electronic deviation adjustment: the MCU6 detects the polarization state, and adjusts the polarization controller 3 according to the phase difference or the cross correlation coefficient to make the optical fiber sensing system in a stable state;
judging whether the phase difference is zero, if so, the polarization fading of the optical fiber sensing system is small, and electronic polarization adjustment is not needed; if not, the polarization fading of the optical fiber sensing system is large, and electronic polarization adjustment is carried out by adjusting the polarization controller 3;
judging whether the cross-correlation coefficient is close to 1, if so, the polarization fading of the optical fiber sensing system is small, and electronic polarization adjustment is not needed; if not, the polarization fading of the optical fiber sensing system is large, and electronic polarization adjustment is performed by adjusting the polarization controller 3.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (6)
1. A method for electronic polarization adjustment and polarization state monitoring of an optical fiber sensing system is characterized by comprising the following steps: the method comprises the following steps:
s1, generating a modulated light signal: the signal generator (1) generates a modulation signal to modulate a laser source (2) and apply the modulated optical signal to a polarization controller (3), wherein the modulation signal is a CW high-frequency dot frequency signal, the laser source (2) generates a modulated optical signal, the modulation signal is a sine wave or a square wave signal, and the modulation signal adopts high frequency for distinguishing from environmental background noise;
the laser source (2) is a modulatable laser source, or the optical fiber sensing system further comprises a PZT phase modulator (7) electrically connected with both the output end of the laser source (2) and the output end of the signal generator (1), the output end of the PZT phase modulator (7) is electrically connected with the input end of the polarization controller (3), the signal generator (1) generates the modulation signal to modulate the PZT phase modulator (7) at the rear end of the laser source (2) and apply the modulated optical signal to the polarization controller (3), and the polarization controller (3) is installed on one side of a host of the optical fiber sensing system;
s2, interference signal transmission: the polarization controller (3) outputs the optical signal to the passive sensing module (4) and generates a two-way interference signal to be output to the receiving detector (5), the receiving detector (5) receives the two-way interference signal and converts the two-way interference signal into two-way electric signals to be output to the signal processing device, and the laser source (2), the passive sensing module (4) and the receiving detector (5) are double MZ interference systems;
s21, the polarization controller (3) outputs the optical signal to the passive sensing module (4);
s22, a first optical splitter coupler (41) in the passive sensing module (4) receives the optical signal and outputs the optical signal to a second optical splitter coupler (42) and a third optical splitter coupler (43), the second optical splitter coupler (42) converts the optical signal into an interference signal through a sensing arm and outputs the interference signal to the third optical splitter coupler (43) and outputs the interference signal to a first photoelectric detection plate (51) of the receiving detector (5) through a conducting arm to generate a clockwise electric signal, and the third optical splitter coupler (43) outputs the optical signal output by the first optical splitter coupler (41) through the conducting arm to the sensing arm and converts the interference signal and outputs the optical signal to a second photoelectric detection plate (52) of the receiving detector (5) through the second optical splitter coupler (42) to generate a counterclockwise electric signal;
s3, monitoring the polarization state: the signal processing device analyzes the electric signal to obtain the frequency domain characteristics of the electric signal, distinguishes the vibration information and other information generated by the modulation signal in a band-pass filtering or high-pass filtering mode, and calculates the phase difference or cross-correlation coefficient of the vibration interference signal of the modulation signal to obtain the polarization state of the optical fiber sensing system, wherein the polarization state is used for counteracting the phase change and signal fading caused by polarization fading;
the phase difference calculation method comprises the following steps: the signal processing device acquires at least more than 2 clockwise electric signals and more than 2 anticlockwise electric signals, then performs FFT spectrum analysis to obtain clockwise spectrum signals and anticlockwise spectrum signals corresponding to the modulation signals, and calculates the difference between the clockwise spectrum signals and the anticlockwise spectrum signals to obtain the phase difference;
s4, electronic deviation adjustment: the MCU (6) detects the polarization state, and adjusts the polarization controller (3) according to the phase difference or the cross-correlation coefficient so as to enable the optical fiber sensing system to be in a stable state;
the MCU (6) judges whether the phase difference is zero, if so, the polarization fading of the optical fiber sensing system is small, and electronic polarization adjustment is not needed; if not, the polarization fading of the optical fiber sensing system is large, and electronic polarization adjustment is carried out by adjusting the polarization controller (3).
2. The method of claim 1 for electronically tuning and monitoring polarization state of an optical fiber sensing system, wherein: the sensing arm is an optical fiber between the second optical sub-coupler (42) and the third optical sub-coupler (43), and the conducting arm comprises an optical fiber between the first optical sub-coupler (41) and the third optical sub-coupler (43) and an optical fiber between the third optical sub-coupler (43) and the first photoelectric detection plate (51).
3. The method of claim 1 for electronically tuning and monitoring polarization state of an optical fiber sensing system, wherein: the first optical splitter coupler (41) is a one-to-two optical coupler, and the second optical splitter coupler (42) and the third optical splitter coupler (43) are both two-to-two optical couplers.
4. The method of claim 1 for electronically tuning and monitoring polarization state of an optical fiber sensing system, wherein: the signal processing device is a high-speed analog-to-digital converter.
5. The method for electronically aligning and monitoring the polarization state of an optical fiber sensing system according to claim 1, wherein: in step S3, the cross-correlation coefficient is calculated by: the signal processing device collects at least more than 2 clockwise electric signals and anticlockwise electric signals, then carries out band-pass filtering to remove environmental background noise, and then carries out correlation operation on the clockwise electric signals and the anticlockwise electric signals to obtain the cross correlation coefficient;
in step S4, it is determined whether the cross-correlation coefficient is close to 1, and if so, the polarization fading of the optical fiber sensing system is small, and electronic polarization adjustment is not needed; if not, the polarization fading of the optical fiber sensing system is large, and the electronic polarization adjustment is carried out by adjusting the polarization controller (3).
6. The method of claim 1 for electronically tuning and monitoring polarization state of an optical fiber sensing system, wherein: the frequency of the modulation signal is 30 kHz.
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| US4897543A (en) * | 1989-01-25 | 1990-01-30 | The United States Of America As Represented By The Secretary Of The Navy | Apparatus and method for minimizing polarization-induced signal fading in an interferometric fiber-optic sensor using input-polarization control |
| CN100487509C (en) * | 2006-06-30 | 2009-05-13 | 中国石油天然气集团公司 | Optical fiber safety early warning polarization control system |
| CN101320502A (en) * | 2008-07-22 | 2008-12-10 | 北京航空航天大学 | Optical fiber perimeter alarm method and device for implementing anti-polarization decay |
| CN101852645B (en) * | 2010-06-25 | 2012-05-09 | 北京奥普科达科技有限公司 | Precise positioning type optical fiber distributed vibration sensor |
| CN102322880B (en) * | 2011-08-18 | 2013-06-05 | 天津大学 | Polarization sensitive distributive optical frequency domain reflection disturbance sensor and demodulation method |
| WO2015034858A1 (en) * | 2013-09-03 | 2015-03-12 | US Seismic Systems, Inc. | Interferometric sensing systems with polarization noise reduction, and methods of operating the same |
| CN106323478B (en) * | 2016-10-09 | 2019-01-18 | 中国船舶重工集团公司第七一五研究所 | The fiber optic interferometric sensor phase generated carrier modulation demodulation system of anti-polarization decay |
| CN111489514A (en) * | 2020-03-19 | 2020-08-04 | 天津大学 | Long-distance perimeter security positioning and monitoring device and method thereof |
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