CN112461353B - Encoding device and method for distributed optical fiber vibration sensing under light amplification - Google Patents
Encoding device and method for distributed optical fiber vibration sensing under light amplification Download PDFInfo
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Abstract
The application relates to the technical field of optical fiber sensing, in particular to a coding device and a coding method for distributed optical fiber temperature sensing under optical amplification, wherein the method comprises the following steps: the coding modulator prestores a 2N +1 order coding matrix S; step two: the coded modulator sequentially outputs coded modulated laser pulses of each row of the matrix S, the back scattering light returning from the sensing optical fiber enters the optical fiber polarization beam splitter through the optical fiber circulator to obtain back scattering Rayleigh O light and E light, the coded modulator sequentially outputs synchronous electric pulses when each row of the matrix S is coded, the A/D two paths of the back scattering Rayleigh O light and the E light are synchronously collected, and the matrix is used as a unit cycle and can be triggered for multiple times to be repeatedly collected. Step three: and judging whether a fiber breaking event occurs. Step four: and analyzing the vibration structure with larger vibration amplitude, and judging the vibration behaviors of the points. Compared with the traditional coding, the invention has the advantages that the coding matrix is easy to generate, the odd-numbered orders are easier to set than the exponential orders, and the span is not large. The code has no continuous code, and the sensor has good stability.
Description
Technical Field
The application relates to the technical field of optical fiber sensing, in particular to a coding device and a coding method for distributed optical fiber temperature sensing under optical amplification.
Background
The distributed optical fiber vibration sensing device is a sensor for measuring the spatial vibration field distribution in real time, and in the sensor, an optical fiber is a transmission medium and a sensing medium. The phase sensitive effect of the optical fiber is utilized, the vibration field of each point of the space where the optical fiber is positioned modulates the optical carrier transmitted in the optical fiber, and after demodulation, the information of the space vibration field is displayed in real time. The measured vibration point is positioned by the propagation speed of light in the optical fiber and the time of a back light echo by using an Optical Time Domain Reflection (OTDR) technology. The distributed optical fiber vibration sensor can forecast the on-site vibration and the orientation of vibration change on line in real time, and optical signals transmitted by the optical fiber are not electrified, so that the distributed optical fiber vibration sensor has strong anti-electromagnetic interference performance, is an intrinsically safe linear vibration detector, and has been successfully applied to the fields of security protection, geological disaster monitoring and the like.
The distributed optical fiber vibration sensing with high spatial resolution and high dynamic range plays an important role in an optical fiber measuring system, can improve the vibration measuring precision and measuring length of the optical fiber, and provides powerful guarantee for the vibration early warning and accurate positioning in the optical fiber system.
The high spatial resolution is influenced by the optical pulse time domain width, the optical receiver bandwidth and the A/D sampling rate. The dynamic range is affected by the peak power of the injected optical pulse, the pulse time domain width, the transmission loss of light in the fiber, and the optical receiver loss. It can be seen that it is not possible to obtain both a large high spatial resolution and a high dynamic range, which are not compatible.
When the injected optical pulse signal is modulated into the coded optical pulse signal as the detection signal of the distributed optical fiber vibration sensor by using the modern digital signal processing technology (i.e. a pulse coding mode), the fiber-entering optical power of the distributed optical fiber vibration sensor is increased, and the increase mode of the optical power is not obtained by the traditional increase of the pulse width, namely the pulse width is still kept unchanged. The increase in fiber-entering optical power will result in an increase in the dynamic range of the distributed fiber vibration sensor, while the pulse width, i.e., spatial resolution, remains unchanged.
The existing distributed optical fiber vibration sensing usually uses an optical fiber narrow linewidth laser as a seed light source, the optical peak power is weak, and an optical fiber amplifier is required to be directly connected to meet the excited phase sensitive effect to obtain a backscattering Rayleigh signal with higher signal-to-noise ratio. In this case, the stability of the backscattered rayleigh signal obtained with a single laser pulse of fixed pulse width is very good.
The encoding methods used in engineering practice include Simpleson code (Simplex code) and Gray codeCodes (Golay codes) and Complementary related Orthonormal Sequence codes (CCPONS). The Simpson coding matrix is formed by removing the first row and the first column of a Hadamard matrix and is converted, and the order N is 2m-1(m is a natural number), the gray code and the complementary related orthonormal sequence code matrix are converted by a tree-type addition method, and the order N is 2m(m is a natural number). Continuous codes exist in codes of the optical fiber and the optical fiber (refer to Chinese invention patent CN201210170373), under the condition of direct-coupled light amplification, the laser power of an incident optical fiber generated by a single code and the continuous codes is not in a simple linear relation, and a backscattered Rayleigh signal obtained by coding and decoding has poor stability.
Disclosure of Invention
The invention aims to provide a coding device and a coding method for distributed optical fiber vibration sensing under optical amplification, which are completed by a group of unipolar odd-order coding matrixes (unipolar pulses refer to transmitting 0 or 1 instead of-1 or 1), so that the stability, high dynamic range and high spatial resolution of the sensing device are improved, and stable and higher vibration measurement precision and measurement length are obtained.
In order to achieve the technical effects, the specific scheme of the application is as follows:
the invention adopts Rayleigh back-scattered light to demodulate distributed optical fiber vibration sensing, and the specific scheme is as follows:
a distributed optical fiber vibration sensing coding device under light amplification comprises a semiconductor laser, a driving module, a coding modulator, an optical fiber amplifier, an optical fiber circulator, an optical fiber polarization beam splitter, a sensing optical fiber, an APD detector module, an A/D module and an industrial personal computer; the industrial personal computer is connected with the code modulator, the industrial personal computer and the code modulator are respectively connected with the A/D module, the semiconductor laser and the driving module are connected with the code modulator through optical fibers, the code modulator is connected with the optical fibers of the optical fiber amplifier, the optical fiber amplifier is connected with the input end of the optical fiber circulator, the output end of the optical fiber circulator is connected with the sensing optical fibers, the return end of the optical fiber circulator is connected with the optical fiber polarization beam splitter, the optical fiber polarization beam splitter is connected with the APD detector module, and the APD detector module is connected with the A/D module.
Furthermore, the industrial personal computer and the code modulator are connected through a USB interface, the industrial personal computer and the A/D module are connected through a PCIex16 interface, and the synchronous electric signals of the code modulator are connected with an external synchronous port of the A/D module through electric wires.
Furthermore, the semiconductor laser and the driving module select an ultra-narrow linewidth DFB semiconductor laser driving module, the coding modulator uses a semiconductor optical amplifier as a coding modulator of a core device, the optical fiber amplifier selects an erbium-doped optical fiber amplifier, the optical fiber circulator selects a single-mode optical fiber 1X2 optical fiber circulator, the optical fiber polarization beam splitter selects a single-mode optical fiber 1X2 optical fiber polarization beam splitter, the APD detector module selects Xiameningling APD 1550-100M-40 dBm, the A/D module selects Beijing Kunjun Chi QT1144.X, and the industrial personal computer selects the Hua YT70 series.
A coding method for distributed optical fiber vibration sensing under optical amplification comprises the following steps:
the method comprises the following steps: the code modulator prestores 2N +1 order code matrix S ═ (a)ij) Wherein N is a natural number, when i equals j, aijWhen i is equal to 0>A when j, i-j is an even numberijWhen i is equal to 0>A when j, i-j are oddijWhen i is equal to 1<A when j, j-i is evenijWhen i is equal to 1<A when j, j-i is oddij0, such that each row has N-1 "1S," each "1" being separated by a "0," there being no consecutive code, where a is a matrix element, i and j element indices, where a is a matrix element, i denotes the ith row in matrix S, j denotes the jth column in matrix S, 0<＝i，j<2N + 1; when the industrial personal computer executes program initialization, the maximum odd-order 2N +1 is generated according to the set laser pulse width N nanosecond, the average number m and the measurement length L meter<10L/N, minimum measurement time (2N +1) mL/10 ns, which is 2N +1 times the monopulse measurement time, the reversible matrix S of S-1＝(bij) When i is equal to j or i>j, j-i-1 or i-0, j-2N, bij(1-N)/N, if the above condition is not satisfied, bij1/N; b is an inverse matrix of S;
step two: when an industrial personal computer executes a measuring program, a starting signal is sent to a code modulator, the code modulator sequentially outputs matrix S each row of code modulation laser pulses to be injected into an optical fiber amplifier, an optical fiber circulator and a sensing optical fiber, back scattering light returned from the sensing optical fiber enters an optical fiber polarization beam splitter through the optical fiber circulator to obtain back scattering Rayleigh light O and E, and then the back scattering Rayleigh light O and E enter corresponding APD detector modules, the A/D modules are connected behind APDs, and the A/D modules are connected with the industrial personal computer; the code modulator outputs synchronous electric pulses when each row of codes of the matrix S are output in sequence, starts two paths of A/D synchronous collection of backscattered Rayleigh O light and E light information and stores the information in an A/D buffer area, a pipeline mode is transmitted into an internal memory of an industrial personal computer, and the matrix is used as a unit period and can be triggered for multiple times to carry out repeated collection.
Step three: when the industrial personal computer executes a program to obtain the backscattered Rayleigh O light and E light information, when the backscattered Rayleigh light information (the square sum of the O light and the E light) is calculated, the backscattered Rayleigh light information of each point on the sensing optical fiber is solved, whether a fiber breakage event occurs is judged, if so, an alarm is given, and if not, the step four is carried out.
Step four: adjusting the parameters of a light path and a circuit to ensure that the variation of the initial phase difference of interference is small, the Rayleigh back scattering optical signal and the external vibration have a linear relation in (0,2 pi), setting a threshold, and possibly vibrating at the moment when the Rayleigh back scattering optical signal exceeds the threshold, sequencing the vibrating points, analyzing the vibrating structure with larger vibration amplitude, and judging the vibrating behaviors of the points.
Codec versus signal-to-noise ratio for digital averaging in general:
the mean square error of a curve obtained by accumulating and averaging the traditional single-pulse optical fiber vibration sensor for 2N +1 times is
The optical fiber vibration sensor using 2N +1 order S matrix coding as detection signal includes N optical pulses instead of 1 optical pulse in each emission coding, and the mean square error of the measurement curve is
Therefore, after S matrix coding with the order of 2N +1 is used as a detection signal, the signal-to-noise ratio detected by the sensor is improved from the signal-to-noise ratio detected by the traditional single pulse after 2N +1 times of common accumulation average processing, namely, the coding gain CG:
where σ represents the distribution or degree of dispersion of the mean value of any process parameter.
This coding yields good benefits when the order is odd, greater than 5.
The coding matrix of the present invention is easy to generate.
Distributed optical fiber vibration sensing principle:
when external vibration acts on the optical fiber, the fiber core in the optical fiber is deformed, so that the refractive index and the length of the fiber core are subjected to nano-variation, and the optical phase in the optical fiber is correspondingly changed; injecting narrow-linewidth light pulse into optical fiber as detection signal, when the light pulse is propagated along the optical fiber, due to the action of photon and fiber core lattice, continuously backward-transmitting Rayleigh scattering light, and detecting the size and arrival time of backward scattering light at input end by proper optical coupler and high-speed response photoelectric detector, so as to measure vibration distribution characteristic f (t) and length L of optical fiber, and incident light intensity I in the optical fiber0The back scattering Rayleigh intensity Ir：
Zeta is the scattering coefficient, Δ is the optical amplification gain, α is the loss coefficient, δλIs the polarization angle, and d θ is the initial phase difference of the interference.
Adjusting optical and electrical path parameters to minimize delta d θ, IrAnd f (t) having a linear relation in (0,2 pi), setting a threshold, possibly vibrating at the moment when the threshold is exceeded, sequencing the vibration points, analyzing the vibration structure with larger vibration amplitude, and judging the vibration behaviors of the points.
The invention has the beneficial effects that:
1. compared with the traditional three Simplex, Golay code and CCPONS codes, the code matrix is easy to generate, odd orders are easier to set than exponential orders, and the span is not large.
2. The code has no continuous code, the back scattering signal of the coded pulse and the single pulse back scattering signal have linear relation under the light amplification, and the stability of the sensor is good.
3. The coded pulses generate higher gain than the single pulses, the signal-to-noise ratio of the sensor is improved, and the dynamic range and the spatial resolution of the sensor are improved.
Drawings
Fig. 1 is a schematic diagram of a distributed fiber optic vibration sensing apparatus under optical amplification.
In the drawings: the system comprises 10-sensing optical fibers, 11-industrial personal computers, 12-coding modulators, 13-optical fiber amplifiers, 14-optical fiber circulators, 15-optical fiber polarization beam splitters, 16-APD detector modules, 17-A/D modules, 18-semiconductor lasers and driving modules.
Detailed Description
The technical solutions of the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings, and it is to be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
Referring to fig. 1, the device for encoding distributed optical fiber vibration sensing under light amplification comprises a semiconductor laser and driving module 18, an encoding modulator 12, an optical fiber amplifier 13, an optical fiber circulator 14, an optical fiber polarization beam splitter 15, a sensing optical fiber 10, an APD detector module 16, an a/D module 17 and an industrial personal computer 11. An industrial personal computer (11) is connected with a code modulator (12) through a Universal Serial Bus (USB) and an analog-to-digital (A/D) module (17 PCIex 16), a semiconductor laser and driving module (18) is in optical fiber connection with the code modulator (12), the code modulator (12) is in optical fiber connection with an optical fiber amplifier (13), the optical fiber amplifier (13) is connected with the input end of an optical fiber circulator (14), the output end of the optical fiber circulator (14) is connected with a sensing optical fiber (10), the return end of the optical fiber circulator (14) is connected with an optical fiber polarization beam splitter (15), the optical fiber polarization beam splitter (15) is connected with an Avalanche Photo Diode (APD) detector module (16), and the APD detector module (16) is connected with the A/D module (17). In the embodiment, vibration field measurement at a distance of 10km is realized, single-mode optical fiber sensing is adopted, the laser pulse width is 10ns, 16-bit 100mhz a/D is adopted, 9-order encoding is realized, the number of times of repetition is 1 thousand, and an encoding matrix S { (001010101), (100101010), (010010101), (101001010), (010100101) }.
When the industrial personal computer 11 executes a measurement program, a starting signal is sent to the code modulator 12, the code modulator 12 sequentially outputs 10 nanosecond pulse width and 5mW peak power of each row of code modulation laser pulse of the matrix S, the pulse width and the peak power are injected into the optical fiber amplifier 13 and the gain of the optical fiber amplifier 13 is 20dbm, the peak power of the injection optical fiber circulator 14 and the sensing optical fiber 10 reaches 4X500mW, back scattering light returning from the sensing optical fiber 10 enters the optical fiber polarization beam splitter 15 through the optical fiber circulator 14, back scattering Rayleigh O light and back scattering Rayleigh E light are obtained by dividing the two paths, the back scattering Rayleigh O light and the back scattering Rayleigh E light are sent to the corresponding APD detector module 16, the APD is connected with the A/D module 17, and the A/D module 17 is connected with the industrial personal computer 11. The code modulator 12 outputs synchronous electric pulses when each row of codes of the matrix S are output in sequence, starts A/D (analog/digital) synchronous collection of backscattered Rayleigh O light and E light information and stores the information in an A/D buffer area, and the information is transmitted into the internal memory of the industrial personal computer 11 in a pipeline mode and can be triggered to collect 1 thousand times by taking the matrix as a unit cycle. The 100MHz A/D sampling frequency is aligned with 10ns optical pulse, when the detector APD bandwidth is more than 100MHz, the sensing optical fiber space resolution is 1m, when the sampling and calculating double-line operation is carried out, the minimum measuring time is 0.9 s.
Example 2
A distributed optical fiber vibration sensing coding device under light amplification comprises a semiconductor laser and driving module 18, a coding modulator 12, an optical fiber amplifier 13, an optical fiber circulator 14, an optical fiber polarization beam splitter 15, a sensing optical fiber 10, an APD detector module 16, an A/D module 17 and an industrial personal computer 11; the industrial personal computer 11 is connected with the code modulator 12, the industrial personal computer 11 and the code modulator 12 are respectively connected with the A/D module 17, the semiconductor laser and driving module 18 is connected with the code modulator 12 through an optical fiber, the code modulator 12 is connected with the optical fiber amplifier 13 through an optical fiber, the optical fiber amplifier 13 is connected with the input end of the optical fiber circulator 14, the output end of the optical fiber circulator 14 is connected with the sensing optical fiber 10, the return end of the optical fiber circulator 14 is connected with the optical fiber polarization beam splitter 15, the optical fiber polarization beam splitter 15 is connected with the APD detector module 16, and the APD detector module 16 is connected with the A/D module 17.
Furthermore, the industrial personal computer 11 and the code modulator 12 are connected through a USB interface, the industrial personal computer 11 and the a/D module 17 are connected through a pci ex16 interface, and the synchronous electric signal of the code modulator 12 is connected with an external synchronous port of the a/D module 17 through an electric wire.
Furthermore, the semiconductor laser and the driving module 18 select an ultra-narrow linewidth DFB semiconductor laser driving module, the coded modulator 12 uses a semiconductor optical amplifier as a coded modulator of a core device, the optical fiber amplifier 13 selects an erbium-doped optical fiber amplifier, the optical fiber circulator 14 selects a single-mode optical fiber 1X2 optical fiber circulator, the optical fiber polarization beam splitter 15 selects a single-mode optical fiber 1X2 optical fiber polarization beam splitter, the APD detector module 16 selects Xiamen APD 1550-100M-40 dBm, the A/D module 17 selects Beijing Kun Ching QT1144.X, and the industrial personal computer 11 selects Mihua YT70 series.
A coding method for distributed optical fiber vibration sensing under optical amplification comprises the following steps:
the method comprises the following steps: the code modulator 12 prestores a 2N +1 order code matrix S ═ (a)ij) Wherein N is a natural number, when i ═ j, aijWhen i is equal to 0>A when j, i-j is an even numberijWhen i is equal to 0>A when j, i-j are oddijWhen i is equal to 1<A when j, j-i is evenijWhen i is equal to 1<A when j, j-i is oddij0, such that each row has N-1 "S, each" 1 "is separated by a" 0 ", there is no consecutive code, where a is a matrix element, i and j element subscripts, where a is a matrix element, i denotes the ith row in matrix S, j denotes the jth column in matrix S, 0<＝i，j<2N + 1; when the industrial personal computer 11 executes program initialization, the maximum odd-order 2N +1 is generated according to the set laser pulse width N nanosecond, the average number m and the measurement length L meter<10L/N, minimum measurement time (2N +1) mL/10 ns, which is 2N +1 times the monopulse measurement time, the reversible matrix S of S-1＝(bij) When i is equal to j or i>j, j-i-1 or i-0, j-2N, bij(1-N)/N, if the above condition is not satisfied, bij1/N; b is an inverse matrix of S;
step two: when the industrial personal computer 11 executes a measurement program, a starting signal is sent to the code modulator 12, the code modulator 12 sequentially outputs each row of code modulation laser pulses of the matrix S and injects the code modulation laser pulses into the optical fiber amplifier 13, the optical fiber circulator 14 and the sensing optical fiber 10, back scattering light returned from the sensing optical fiber 10 enters the optical fiber polarization beam splitter 15 through the optical fiber circulator 14 to obtain back scattering Rayleigh light O and E, and then enters the corresponding APD detector module 16, the A/D module 17 is connected behind the APD, and the A/D module 17 is connected with the industrial personal computer 11; the code modulator 12 outputs synchronous electric pulses when each row of codes of the matrix S are output in sequence, starts an A/D two-path synchronous collection of backscattered Rayleigh O light and E light information and stores the information in an A/D buffer area, and the information is transmitted into the internal memory of the industrial personal computer 11 in a pipeline mode and can be triggered for multiple times to carry out repeated collection by taking the matrix as a unit cycle.
Step three: when the industrial personal computer 11 executes a program to acquire backscattered rayleigh O light and E light information, and calculates backscattered rayleigh light information (square sum of O light and E light reopening), the backscattered rayleigh light information of each point on the sensing optical fiber is solved, and whether a fiber breakage event occurs is judged, if so, an alarm is given, and if not, the fourth step is performed.
Step four: adjusting the parameters of a light path and a circuit to ensure that the variation of the initial phase difference of interference is small, the Rayleigh back scattering optical signal and the external vibration have a linear relation in (0,2 pi), setting a threshold, and possibly vibrating at the moment when the Rayleigh back scattering optical signal exceeds the threshold, sequencing the vibrating points, analyzing the vibrating structure with larger vibration amplitude, and judging the vibrating behaviors of the points.
Codec versus signal-to-noise ratio for digital averaging in general:
the mean square error of a curve obtained by accumulating and averaging the traditional single-pulse optical fiber vibration sensor for 2N +1 times is
The optical fiber vibration sensor using 2N +1 order S matrix coding as detection signal includes N optical pulses instead of 1 optical pulse in each emission coding, and the mean square error of the measurement curve is
Therefore, after S matrix coding with the order of 2N +1 is used as a detection signal, the signal-to-noise ratio detected by the sensor is improved from the signal-to-noise ratio detected by the traditional single pulse after 2N +1 times of common accumulation average processing, namely, the coding gain CG:
where σ represents the distribution or degree of dispersion of the mean value of any process parameter.
This coding yields good benefits when the order is odd, greater than 5.
The coding matrix of the present invention is easy to generate.
Distributed optical fiber vibration sensing principle:
when external vibration acts on the optical fiber, the fiber core in the optical fiber is deformed, so that the refractive index and the length of the fiber core are subjected to nano-variation, and the optical phase in the optical fiber is correspondingly changed; injecting narrow-linewidth light pulse into optical fiber as detection signal, when the light pulse is propagated along the optical fiber, due to the action of photon and fiber core lattice, continuously backward-transmitting Rayleigh scattering light, and detecting the size and arrival time of backward scattering light at input end by proper optical coupler and high-speed response photoelectric detector, so as to measure vibration distribution characteristic f (t) and length L of optical fiber, and incident light intensity I in the optical fiber0The back scattering Rayleigh intensity Ir：
Zeta is the scattering coefficient, Δ is the optical amplification gain, α is the loss coefficient, δλIs the polarization angle, and d θ is the initial phase difference of the interference.
Adjusting optical and electrical path parameters to minimize delta d θ, IrAnd f (t) there is a linear relationship in (0,2 π), setting a threshold, beyond which there may be vibration at a time, sorting the vibration points, analyzing the vibration structure with a larger vibration amplitude,judging the vibration behavior of the points.
Compared with the traditional Simplex, Golay code and CCPONS codes, the invention has the advantages that the code matrix is easy to generate, the odd order is easier to set than the exponential order, and the span is not large. The code has no continuous code, the backscattering signal of the code pulse and the single pulse backscattering signal have linear relation under the condition of light amplification, and the stability of the sensor is good. The coded pulse generates higher gain than a single pulse, the signal-to-noise ratio of the sensor is improved, and the dynamic range and the spatial resolution of the sensor are improved.
It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.
Claims (5)
1. A distributed optical fiber vibration sensing coding method under optical amplification is characterized in that: the method comprises the following steps:
the method comprises the following steps: the code modulator (12) prestores a 2N + 1-order code matrix S ═ aij) Wherein N is a natural number, when i ═ j, aijWhen i is equal to 0>A when j, i-j is an even numberijWhen i is equal to 0>A when j, i-j are oddijWhen i is equal to 1<A when j, j-i is evenijWhen i is equal to 1<A when j, j-i is oddij0, such that each row has N-1 "S, each" 1 "is separated by a" 0 "and there is no consecutive code, where a is the matrix element, i is the index of the matrix element, i denotes the ith row in matrix S, j denotes the jth column in matrix S, 0<＝i，j<2N + 1; when the industrial personal computer (11) executes program initialization, the maximum odd-order 2N +1 is generated according to the set laser pulse width N nanosecond, the average number m and the measurement length L meter<10L/N, minimum measurement time (2N +1) mL/10 ns, which is 2N +1 times the monopulse measurement time, the reversible matrix S of S-1＝(bij) When i is equal to j or i>j, j-i-1 or i-0, j-2N, bij(1-N)/N, if the above condition is not satisfied, bij1/N; b is an inverse matrix of S;
step two: when an industrial personal computer (11) executes a measurement program, a starting signal is sent to a code modulator (12), the code modulator (12) sequentially outputs each row of code modulation laser pulses of a matrix S to be injected into an optical fiber amplifier (13), an optical fiber circulator (14) and a sensing optical fiber (10), back scattering light returning from the sensing optical fiber (10) enters an optical fiber polarization beam splitter (15) through the optical fiber circulator (14) to obtain back scattering Rayleigh light O light and E light, and then enters a corresponding APD detector module (16), an A/D module (17) is connected behind an APD, and the A/D module (17) is connected with the industrial personal computer (11); the code modulator (12) outputs synchronous electric pulses to start an A/D two-path synchronous collection of backscattered Rayleigh O light and E light information when each row of codes of the matrix S are output in sequence and stored in an A/D buffer area, the information is transmitted into the memory of the industrial personal computer (11) in a pipeline mode, and the information can be triggered for multiple times to be repeatedly collected by taking the matrix as a unit cycle;
step three: when the industrial personal computer (11) executes a program to obtain the backscattered Rayleigh O light and E light information and calculates the backscattered Rayleigh light information, the backscattered Rayleigh light information of each point on the sensing optical fiber is solved, whether a fiber breaking event occurs or not is judged, if yes, an alarm is given, and if not, the fourth step is carried out;
step four: adjusting light path and circuit parameters to ensure that the variation of the initial phase difference of interference is small, the Rayleigh back scattering light signals and external vibration have a linear relation in (0,2 pi), setting a threshold, and possibly vibrating at the moment when the Rayleigh back scattering light signals exceed the threshold, sequencing the vibrating points, analyzing the vibrating structure with larger vibration amplitude, and judging the vibrating behaviors of the points;
the coding device adopted by the method comprises a semiconductor laser, a driving module (18), a coding modulator (12), an optical fiber amplifier (13), an optical fiber circulator (14), an optical fiber polarization beam splitter (15), a sensing optical fiber (10), an APD detector module (16), an A/D module (17) and an industrial personal computer (11); the industrial personal computer (11) is connected with the code modulator (12), the industrial personal computer (11) and the code modulator (12) are respectively connected with the A/D module (17), the semiconductor laser and the driving module (18) are connected with the code modulator (12) through optical fibers, the code modulator (12) is connected with the optical fiber amplifier (13) through the optical fibers, the optical fiber amplifier (13) is connected with the input end of the optical fiber circulator (14), the output end of the optical fiber circulator (14) is connected with the sensing optical fiber (10), the return end of the optical fiber circulator (14) is connected with the optical fiber polarization beam splitter (15), the optical fiber polarization beam splitter (15) is connected with the APD detector module (16), and the APD detector module (16) is connected with the A/D module (17).
2. The encoding method for distributed optical fiber vibration sensing under optical amplification according to claim 1, wherein: the optical fiber vibration sensor uses 2N +1 order S matrix coding as detection signals, each emission coding comprises N optical pulses, the mean square error of a measurement curve is
After S matrix coding with the order of 2N +1 is used as a detection signal, the signal-to-noise ratio detected by a sensor is improved with the signal-to-noise ratio obtained after the traditional single pulse is subjected to 2N +1 times of common accumulation average processing, namely, the coding gain CG:
where σ represents the distribution or degree of dispersion of the mean value of any process parameter.
3. The encoding method for distributed optical fiber vibration sensing under optical amplification according to claim 1, wherein: in the fourth step, when external vibration acts on the optical fiber, the fiber core in the optical fiber is deformed, so that the refractive index and the length of the fiber core are changed in a nano mode, and the optical phase in the optical fiber is correspondingly changed; injecting narrow-linewidth light pulse into the optical fiber as a detection signal, continuously transmitting Rayleigh scattering light backwards due to the action of photons and fiber core lattices when the light pulse is transmitted along the optical fiber, detecting the size and the arrival time of the backward scattering light at an input end through an optical coupler and a photoelectric detector with high-speed response, and measuring the vibration distribution characteristic f (t) and the length L of the optical fiber, wherein the incident light intensity I in the optical fiber0Is of the backscatter RayleighLight intensity Ir：
Zeta is the scattering coefficient, Δ is the optical amplification gain, α is the loss coefficient, δλIs the polarization angle, d θ is the initial phase difference of the interference;
adjusting optical and electrical path parameters to minimize delta d θ, IrAnd f (t) having a linear relation in (0,2 pi), setting a threshold, possibly vibrating at the moment when the threshold is exceeded, sequencing the vibration points, analyzing the vibration structure with larger vibration amplitude, and judging the vibration behaviors of the points.
4. The encoding method for distributed optical fiber vibration sensing under optical amplification according to claim 1, wherein: the industrial personal computer (11) and the code modulator (12) are connected through a USB interface, the industrial personal computer (11) is connected with the A/D module (17) through a PCIex16 interface, and a synchronous electric signal of the code modulator (12) is connected with an external synchronous port of the A/D module (17) through an electric wire.
5. The encoding method for distributed optical fiber vibration sensing under optical amplification according to claim 1, wherein: the semiconductor laser and the driving module (18) select a DFB semiconductor laser driving module with an ultra-narrow line width, the coded modulator (12) uses a semiconductor optical amplifier as a coded modulator of a core device, the optical fiber amplifier (13) selects an erbium-doped optical fiber amplifier, the optical fiber circulator (14) selects a single-mode optical fiber 1X2 optical fiber circulator, and the optical fiber polarization beam splitter (15) selects a single-mode optical fiber 1X2 optical fiber polarization beam splitter.
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