CN115993141B - Double-end demodulation system and method for long-distance fiber grating sensing network - Google Patents

Double-end demodulation system and method for long-distance fiber grating sensing network Download PDF

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CN115993141B
CN115993141B CN202211456583.XA CN202211456583A CN115993141B CN 115993141 B CN115993141 B CN 115993141B CN 202211456583 A CN202211456583 A CN 202211456583A CN 115993141 B CN115993141 B CN 115993141B
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CN115993141A (en
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王加琪
李政颖
肖灼华
桂鑫
王洪海
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Wuhan University of Technology WUT
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Abstract

The invention discloses a double-end demodulation system and a double-end demodulation method of a long-distance fiber grating sensing network, wherein the double-end demodulation system comprises a light source module, an optical fiber branching device, a first pulse modulation unit, a second pulse modulation unit, a first optical fiber circulator, a second optical fiber circulator, a fiber grating sensing network, a first photoelectric conversion unit, a second photoelectric conversion unit and a signal processing unit; the invention firstly proposes to utilize the double ends of the fiber bragg grating sensing network to demodulate, on the basis of the existing hardware platform, one path of pulse optical signals are added, pulse optical signals are injected from the two ends of the sensing network in a staggered mode, reflected signals of the sensing network are processed at a receiving end according to the OTDR technical principle, and the limitation of the sensing length of the OTDR technology on demodulation speed is broken through and demodulation frequency is improved while the advantages of simplicity, maturity and easiness in implementation of the prior art scheme are maintained.

Description

Double-end demodulation system and method for long-distance fiber grating sensing network
Technical Field
The invention relates to the technical field of fiber bragg grating sensing, in particular to a double-end demodulation system and a double-end demodulation method of a long-distance fiber bragg grating sensing network.
Background
The long-distance fiber Bragg grating (Fiber Bragg Grating, FBG, abbreviated as fiber bragg grating) sensing network has the advantages of large multiplexing capacity, on-line preparation, strong reflected signal and the like, integrates sensing and transmission, and can realize sensing of physical quantities such as long-distance and large-range vibration (mainly phase demodulation), temperature/strain (mainly wavelength demodulation) and the like on a single fiber. In many demodulation systems of the sensing network, the demodulation scheme based on the optical time domain reflectometry (Optical Time Domain Reflectometer, OTDR) technology is considered to be the most practical in the field of engineering application due to the advantages of long detection distance, simple demodulation algorithm, mature technical scheme and the like. In the OTDR technology, in order to ensure that the reflected signals of the sensing network do not have aliasing in the Time domain under the action of two adjacent pulse lights, the system needs to send the next pulse light after the signal reflected by the sensing network under the action of the previous pulse light is received, so the demodulation speed of the system is limited by the Round-Trip Time (RTT) of the pulse light transmitted in the sensing network, and in the theoretical case, when the sensing length is 10km, the RTT is 100 microseconds.
In the phase demodulation technology, single demodulation of the FBG sensing network is realized under the action of a single pulse. The existing system increases laser wavelength and equally-spaced emission laser pulse by adopting a wavelength division multiplexing technology, and detects sensing signals of each wavelength at a receiving end by adopting a wavelength division demultiplexing technology, thereby improving the demodulation speed of the system. However, the method is not different from the method for detecting the same sensing network by utilizing a plurality of hardware platforms in a time-sharing way, the system complexity is high, the cost of the high-coherence pulse laser source is high, and the method is difficult to popularize in practical engineering application.
In the wavelength demodulation technology, a single demodulation of the FBG sensing network needs to poll the reflected signals of the sensing network under the pulse light with different wavelengths, so as to obtain the wavelength value of each FBG in the sensing network, and the demodulation speed of the system is limited by N times of RTT assuming that the wavelength scanning frequency is N. It can be seen that the demodulation speed of the wavelength demodulation system is more seriously affected by RTT. The demodulation system cannot solve the problem.
Disclosure of Invention
The invention aims to provide a double-end demodulation system and a double-end demodulation method for a long-distance fiber grating sensing network.
The invention discloses a double-end demodulation system of a long-distance fiber grating sensing network, which is characterized by comprising a light source module, an optical fiber branching device, a first pulse modulation unit, a second pulse modulation unit, a first optical fiber circulator, a second optical fiber circulator, a fiber grating sensing network, a first photoelectric conversion unit, a second photoelectric conversion unit and a signal processing unit; the light source control signal output end of the signal processing unit is connected with the light source control signal input end of the light source module, the narrow-linewidth continuous light signal output end of the light source module is connected with the input end of the optical fiber branching device, the first-path narrow-linewidth continuous light signal output end of the optical fiber branching device is connected with the signal input end of the first pulse modulation unit, the second-path narrow-linewidth continuous light signal output end of the optical fiber branching device is connected with the signal input end of the second pulse modulation unit, the first modulation control signal output end of the signal processing unit is connected with the control signal input end of the second pulse modulation unit, the first-path pulse light signal output end of the power amplification of the first pulse modulation unit is connected with the first communication end of the first optical fiber circulator, the second communication end of the first optical fiber circulator is connected with one end of the optical fiber grating sensing network, and the third communication end of the first optical fiber circulator is connected with the signal input end of the first photoelectric conversion unit; the power amplification second path pulse optical signal output end of the second pulse modulation unit is connected with the first communication end of the second optical fiber circulator, the second communication end of the second optical fiber circulator is connected with the other end of the fiber bragg grating sensing network, and the third communication end of the second optical fiber circulator is connected with the signal input end of the second photoelectric conversion unit; the signal output end of the first photoelectric conversion unit and the signal output end of the second photoelectric conversion unit are connected with the signal input end of the signal processing unit.
The invention has the beneficial effects that:
Compared with the traditional single-end demodulation system and method of the long-distance fiber grating sensing network based on the OTDR technology, the method provided by the invention has the advantages that the detection distance of the original technology is long, the demodulation algorithm is simple, the technical scheme is mature, and meanwhile, only part of light paths and circuit modules are added to realize the improvement of demodulation frequency, so that the limitation of the sensing length of the OTDR technology on the demodulation speed is broken through, and the application scene of the fiber grating sensing network is widened.
Drawings
FIG. 1 is a schematic diagram of the structure of the present invention;
FIG. 2 is a schematic diagram of a first non-equal arm interferometer according to the present invention;
FIG. 3 is a schematic diagram of a second non-equal arm interferometer according to the present invention;
FIG. 4 is a schematic diagram of a phase demodulation method according to the present invention;
fig. 5 is a schematic diagram of a wavelength demodulation method according to the present invention.
The device comprises a 1-light source module, a 2-optical fiber splitter, a 3-first pulse modulation unit, a 4-second pulse modulation unit, a 5-first optical fiber circulator, a 6-second optical fiber circulator, a 7-optical fiber grating sensing network, an 8-first photoelectric conversion unit, a 9-second photoelectric conversion unit, a 10-signal processing unit, an 11-first 1x2 coupler, an 11.1-second 1x2 coupler, a 12-first delay optical fiber, a 12.1-second delay optical fiber, a 13-first 3x3 coupler, a 13.1-second 3x3 coupler, a 14-first photoelectric detector and a 14.1-second photoelectric detector.
Detailed Description
The invention is described in further detail below with reference to the attached drawings and specific examples:
The double-end demodulation system of the long-distance fiber grating sensing network as shown in fig. 1-5 comprises a light source module 1, a fiber splitter 2, a first pulse modulation unit 3, a second pulse modulation unit 4, a first fiber circulator 5, a second fiber circulator 6, a fiber grating sensing network 7, a first photoelectric conversion unit 8, a second photoelectric conversion unit 9 and a signal processing unit 10; the light source control signal output end of the signal processing unit 10 is connected with the light source control signal input end of the light source module 1, the narrow-linewidth continuous optical signal output end of the light source module 1 is connected with the input end of the optical fiber branching device 2, the first path of narrow-linewidth continuous optical signal output end of the optical fiber branching device 2 is connected with the signal input end of the first pulse modulation unit 3, the second path of narrow-linewidth continuous optical signal output end of the optical fiber branching device 2 is connected with the signal input end of the second pulse modulation unit 4, the first modulation control signal output end of the signal processing unit 10 is connected with the control signal input end of the second pulse modulation unit 4, the first path of pulse optical signal output end of the power amplification of the first pulse modulation unit 3 is connected with the first communication end of the first optical fiber circulator 5, the second communication end of the first optical fiber circulator 5 is connected with one end of the optical fiber grating sensing network 7, and the third communication end of the first optical fiber circulator 5 is connected with the signal input end of the first photoelectric conversion unit 8; the second path of pulse optical signal output end of the power amplification of the second pulse modulation unit 4 is connected with the first communication end of the second optical fiber circulator 6, the second communication end of the second optical fiber circulator 6 is connected with the other end of the fiber bragg grating sensing network 7, and the third communication end of the second optical fiber circulator 6 is connected with the signal input end of the second photoelectric conversion unit 9; the signal output terminal of the first photoelectric conversion unit 8 and the signal output terminal of the second photoelectric conversion unit 9 are connected to the signal input terminal of the signal processing unit 10.
In embodiment 1, when the double-end demodulation system of the long-distance fiber grating sensing network is applied to phase demodulation:
the light source module 1 adopts 1550nm narrow linewidth laser module of the company LUNA in the United states, and the linewidth is 1kHz; the optical fiber branching device 2 adopts a conventional 1-division-2 optical fiber branching device; the first pulse modulation unit 3 and the second pulse modulation unit 4 both adopt high-speed switch type semiconductor optical amplifier KY-PLM-16-M-FA modules, have a pulse optical signal amplification function and small signal gain of 15dB, respectively modulate continuous optical signals input into the pulse modulation units into optical pulse signals with pulse width of 20ns and period of 80us through an external trigger mode, and the phase delay of the two paths of pulse optical signals is 40us; the first optical fiber circulator 5 and the second optical fiber circulator 6 are conventional optical fiber circulators, and the loss is less than 1dB;
the fiber grating sensing network 7 adopts a wide-spectrum grating array, the grating spectrum is 3nm wide, the central wavelength is 1550nm, the sensing network length is 5km, the grating spacing is 5m, the number of gratings is 1000, the theoretical RTT value is 50us, 80us is taken in practical application, namely the maximum value of the theoretical detection frequency of a system adopting a single-end demodulation method is 20kHz, and the detection frequency is 12.5kHz in practical application;
in the double-end phase demodulation system of the long-distance fiber grating sensing network of embodiment 1, the signal processing unit 10 is used for controlling the light source module 1 to output 1550nm narrow linewidth continuous optical signals, the linewidth of the phase demodulated light source is 100 Hz-1 MHz, and the optical fiber splitter 2 divides the narrow linewidth continuous optical signals into two paths of narrow linewidth continuous optical signals according to the equal power ratio.
In embodiment 1, the first pulse modulation unit 3 is configured to modulate the first-path narrow-linewidth continuous optical signal into a first-path pulse optical signal with adjustable period, pulse width and phase under the control of the signal processing unit 10, and perform power amplification on the first-path pulse optical signal with adjustable period, pulse width and phase; the second pulse modulation unit 4 is configured to modulate the second path of narrow linewidth continuous optical signal into a second path of pulse optical signal with adjustable period, pulse width and phase under the control of the signal processing unit 10, and perform power amplification on the second path of pulse optical signal with adjustable period, pulse width and phase;
the first optical fiber circulator 5 is used for inputting a first path of pulse optical signals amplified by power into the optical fiber grating sensing network 7, and reflecting and transmitting the first path of pulse optical signals in the optical fiber grating sensing network 7 to form a first path of reflected pulse optical signals and a first path of transmitted pulse optical signals; the second optical fiber circulator 6 is used for inputting a second path of pulse optical signals amplified by power into the fiber grating sensing network 7, and reflecting and transmitting the second path of pulse optical signals and the second path of transmitted pulse optical signals in the fiber grating sensing network 7.
In embodiment 1, the first optical fiber circulator 5 is configured to input a first path of reflected pulse optical signal and a second path of transmitted pulse optical signal into the first photoelectric conversion unit 8; the second optical fiber circulator 6 is used for inputting the first path of transmitted pulse optical signals and the second path of reflected pulse optical signals into the second photoelectric conversion unit 9.
Assuming that the first pulse optical signal output by the first pulse modulation unit 3 is output to the head end of the fiber bragg grating sensing network 7 at the moment 0, outputting the first pulse optical signal output by the second pulse modulation unit 4 to the tail end of the fiber bragg grating sensing network 7 after 40 us;
In embodiment 1, a first photoelectric conversion unit 8 firstly divides a first path of reflected pulse optical signal into two beams of pulse optical signals a according to equal power proportion through a first 1x2 coupler 11, then delays one beam of pulse optical signal a through a first delay optical fiber 12, so that a reflected signal of a previous grating and a reflected signal of a next grating in an optical fiber grating sensing network 7 contained in the first path of reflected pulse optical signal simultaneously reach a first photoelectric detector 14 through a first 3x3 coupler 13 to interfere to obtain three paths of forward sensing signals containing phase information, then the first 1x2 coupler 11 divides a second path of transmitted pulse optical signal into two beams of pulse optical signals B with equal power proportion, then delays one beam of pulse optical signals B through a first delay optical fiber 12, and finally the two beams of pulse optical signals B reach the first photoelectric detector 14 through the first 3x3 coupler 13 to form a first passive signal without sensing information, and the first 1x2 coupler 11, the first delay optical fiber 12, the first photoelectric detector 13 and the first photoelectric detector arm 13 are connected to form a first passive signal by an interferometer, and the first passive optical interferometer is connected to the first passive interferometer;
The second photoelectric conversion unit 9 firstly divides the first path of transmitted pulse optical signals into two beams of pulse optical signals C with equal power according to equal power proportion through the second 1x2 coupler 11.1, then delays one beam of pulse optical signals C through the second delay optical fiber 12.1, finally the two beams of pulse optical signals C sequentially pass through the second 3x3 coupler 13.1 to reach the second photoelectric detector 14.1 to obtain a second useless signal without sensing information, then the second 1x2 coupler 11.1 divides the second path of reflected pulse optical signals into two beams of pulse optical signals D according to equal power proportion, delays one beam of pulse optical signals D through the second delay optical fiber 12.1, so that the reflected signals of the previous grating and the reflected signals of the next grating in the second path of reflected pulse optical signals simultaneously pass through the second 3x3 coupler 13.1 to reach the second photoelectric detector 14.1 to obtain three paths of backward sensing signals containing phase information, and the second 1x2 coupler 11.1, the second delay optical fiber 12.1 is used for the second interferometer to output the second interference signals to the second interferometer 14.1, and the like.
The input end of the 1x2 coupler is an input end of the photoelectric conversion unit, the first output end of the 1x2 coupler is connected to the first input end of the 3x3 coupler, the second output end of the 1x2 coupler is connected with the head end of the delay optical fiber, the tail end of the delay optical fiber is connected to the third input end of the 3x3 coupler, the second input end of the 3x3 coupler is knotted to avoid the reflection of the end face of an optical signal, and three paths of output optical signals of the 3x3 coupler are converted into three paths of electrical signals through the photoelectric detector and are connected to the output end of the photoelectric conversion unit;
The 1x2 coupler adopts a conventional 5:5 optical fiber coupler, the delay optical fiber is a common single-mode optical fiber, the length is twice the grating spacing, the grating spacing is 5m for example, the delay optical fiber is 10m, the 3x3 coupler adopts a delta-shaped fused tapered optical fiber coupler, the splitting ratio of three paths of output signals is 1:1:1, the phase difference of each path of output signals is 2 pi/3, the photoelectric detector consists of three sets of photodiodes, transimpedance operational amplifiers with clamping functions and the like, the photoelectric detector is used for converting three paths of output optical signals of the 3x3 coupler into electric signals, and the purpose of adopting the transimpedance operational amplifiers with the clamping functions is to reduce the influence of pulse optical signals transmitted by the fiber grating sensing network;
The core component of the signal processing unit 10 is an FPGA chip, the FPGA chip controls six paths of 14-bit analog-to-digital conversion chips to collect electric signals output by the first photoelectric conversion unit 8 and the second photoelectric conversion unit 9, processes the signals to realize phase demodulation of a sensing network, and in addition, the signal processing unit 10 realizes pulse modulation control of the first pulse modulation unit 3 and the second pulse modulation unit 4 in a TTL level triggering mode and controls the stability of signals output by the light source module 1 through controlling a constant temperature constant current circuit.
When a first pulse optical signal pulse #11 output by the first pulse modulation unit 3 is transmitted in the fiber grating sensing network 7, each FBG is reflected when encountering, as the length of the sensing network is 5km, the pulse #11 after 25us is transmitted out of the fiber grating sensing network 7 and enters the second photoelectric conversion unit 9 through the second fiber circulator 6, the reflected signals of each FBG enter the first photoelectric conversion unit 8 through the first fiber circulator 5, and the reflected signals of all FBGs all reach the first photoelectric conversion unit 8 and take 50us;
When the first pulse optical signal pulse #21 output by the second pulse modulation unit 4 is transmitted in the fiber grating sensing network 7, the pulse #21 is reflected when encountering each FBG, and the pulse #21 is transmitted out of the fiber grating sensing network 7 and enters the first photoelectric conversion unit 8 through the first fiber circulator 5, the reflected signals of each FBG enter the second photoelectric conversion unit 9 through the second fiber circulator 6, and the reflected signals of all the FBGs take 50us when reaching the second photoelectric conversion unit 9;
All signals entering the first photoelectric conversion unit 8 output three-path interfered optical signals through the first unequal-arm interferometer and are converted into electric signals S 11、S12、S13 through the first photodetector 14. Likewise, all signals entering the second photoelectric conversion unit 9 will also output three electrical signals S 21、S22、S23, as shown in fig. 4;
In embodiment 1, the signal processing unit 10 is configured to collect three forward sensing signals and filter out a first useless signal, and then extract phase information of each sensor from front to back in the fiber bragg grating sensing network 7 based on a 3x3 coupler phase demodulation algorithm from the three forward sensing signals;
The signal processing unit 10 is used for filtering the second unwanted signal and collecting three backward sensing signals, and then extracting phase information of each sensor from the back to the front in the fiber bragg grating sensing network 7 from the three backward sensing signals based on a 3x3 coupler phase demodulation algorithm;
The signal processing unit 10 is configured to correspond the phase information of each sensor from front to back and the phase information of each sensor from back to front of the fiber bragg grating sensing network 7 one by one and arrange the phase information according to a time sequence, so as to implement double-speed phase demodulation of the fiber bragg grating sensing network 7.
According to the OTDR technical principle, as can be seen from fig. 4, the time delays t ds of the pulse optical signal output photoelectric conversion units corresponding to each sensing unit are different, the relationship between the time delay t ds and the position D of the sensing unit is t ds＝2neff D/c, where n eff is the refractive index of the fiber core of the FBG sensing network, and c is the propagation speed of light in vacuum;
The phase demodulation method comprises the following steps: according to the principle of a 3x3 coupler decoupling algorithm, the output signals S x1、Sx2、Sx3 of the first photoelectric conversion unit 8 and the second photoelectric conversion unit 9 are the phase information carried by the m-th sensor in (x=1, 2) The following formula is satisfied:
Wherein A is the direct current component of the interference signal, B is the alternating current component of the interference signal, and M (S x1,m)、M(Sx2,m)、M(Sx3, M) is the interference intensity of the M-th sensor in the signal S x1、Sx2、Sx3 respectively;
the simultaneous equation S x1、Sx2、Sx3 can demodulate the phase
In the above technical scheme, the period of the pulse optical signal is 80us and the theoretical minimum value is 50us, so the theoretical maximum value of the demodulation frequency is 20kHz, the actual value is 12.5kHz, the phase delay t pd of the two paths of pulse optical signals takes 40us to combine the results of double-end demodulation to realize equidistant sampling, the demodulation frequency is increased to 25kHz at this time, and the theoretical maximum value is increased to 40kHz.
The order of the positions of the sensing units in the output signals of the first photoelectric conversion unit 8 and the second photoelectric conversion unit 9 is reversed.
In embodiment 1, in order to ensure that the reflected signals of the fiber grating sensing network 7 are not aliased in the time domain under the action of the two adjacent pulse optical signals input from the single end of the fiber grating sensing network 7, according to the OTDR technical principle, the pulse widths w of the first path of power amplified pulse optical signals output by the first pulse modulation unit 3 and the second path of power amplified pulse optical signals output by the second pulse modulation unit 4 both satisfy the formula: w <2n eff d/c, where n eff is the refractive index of the fiber core of the fiber grating sensing network 7, about 1.5, c is the propagation speed of light in vacuum, d is the spacing between adjacent gratings in the fiber grating sensing network 7, and the period T of the first path of pulse optical signal and the period T of the second path of pulse optical signal (the periods of the first path of pulse optical signal and the second path of pulse optical signal are equal and are denoted by T) should be greater than the round trip time RTT of the pulse light transmitted in the fiber grating sensing network 7. Calculating to obtain w <50ns, wherein w=20ns is adopted in practical application; the period of the generated pulse optical signal is larger than the RTT value, 50us can be obtained by calculating the RTT value by the length 5km of the fiber bragg grating sensing network 7, and the period of the pulse optical signal is 80us in practical application;
In embodiment 1, in order to ensure that the reflected signal of the fiber grating sensing network 7 under the action of a single pulse optical signal input from one end of the fiber grating sensing network 7 and the transmitted signal of the fiber grating sensing network 7 under the action of a single pulse optical signal input from the other end of the fiber grating sensing network 7 are not aliased in the time domain, according to the OTDR technical principle, a phase delay T pd,tpd exists between a first path of power amplified pulse optical signal output by the first pulse modulation unit 3 and a second path of power amplified pulse optical signal output by the second pulse modulation unit 4 to satisfy RTT/2.ltoreq.t pd.ltoreq.t-RTT/2, and T pd =40us is taken in practical application;
The signal processing unit 10 realizes pulse modulation control of the first pulse modulation unit 3 and the second pulse modulation unit 4 in a TTL level triggering mode, and modulates a first path of narrow-line-width continuous optical signal into a first path of pulse optical signal with adjustable period, pulse width and phase, and modulates a second path of narrow-line-width continuous optical signal into a second path of pulse optical signal with adjustable period, pulse width and phase. The constant temperature and constant current circuit is controlled to control the stability of the output signal of the light source module 1.
A double-end phase demodulation method of a long-distance fiber grating sensing network comprises the following steps:
Step 1: the signal processing unit 10 controls the light source module 1 to output a narrow-linewidth continuous light signal with fixed wavelength, and the optical fiber branching device 2 divides the narrow-linewidth continuous light signal with fixed wavelength into two paths of narrow-linewidth continuous light signals according to the equal power proportion;
Step 2: the first pulse modulation unit 3 modulates the first path of narrow linewidth continuous optical signals into first path of pulse optical signals under the control of the signal processing unit 10, and performs power amplification on the first path of pulse optical signals; the second pulse modulation unit 4 modulates the second path of narrow linewidth continuous optical signal into a second path of pulse optical signal under the control of the signal processing unit 10, and performs power amplification on the second path of pulse optical signal;
the first optical fiber circulator 5 inputs a first path of pulse optical signals amplified by power into the optical fiber grating sensing network 7, and reflects and transmits the first path of pulse optical signals in the optical fiber grating sensing network 7 to form a first path of reflected pulse optical signals and a first path of transmitted pulse optical signals; the second optical fiber circulator 6 inputs a second path of pulse optical signals with amplified power into the optical fiber grating sensing network 7, and reflects and transmits the second path of pulse optical signals in the optical fiber grating sensing network 7 to form a second path of reflected pulse optical signals and a second path of transmitted pulse optical signals;
step 3: the first optical fiber circulator 5 inputs the first path of reflected pulse optical signals and the second path of transmitted pulse optical signals into the first photoelectric conversion unit 8; the second optical fiber circulator 6 inputs the first path of transmitted pulse optical signals and the second path of reflected pulse optical signals into a second photoelectric conversion unit 9;
Step 4: the first photoelectric conversion unit 8 firstly divides a first path of reflected pulse optical signals into two beams of pulse optical signals A according to the power equal proportion through a first 1x2 coupler 11, delays one beam of pulse optical signals A through a first delay optical fiber 12, enables the reflected signals of a previous grating and the reflected signals of a later grating in the fiber grating sensing network 7 contained in the first path of reflected pulse optical signals to reach a first photoelectric detector 14 through a first 3x3 coupler 13 at the same time to interfere to obtain three paths of forward sensing signals containing phase information, then the first 1x2 coupler 11 divides a second path of transmitted pulse optical signals into two beams of pulse optical signals B with the same power according to the power equal proportion, delays one beam of pulse optical signals B through the first delay optical fiber 12, and finally enables the two beams of pulse optical signals B to reach the first photoelectric detector 14 through the first 3x3 coupler 13 in sequence to obtain a first useless signal without sensing information;
The second photoelectric conversion unit 9 firstly divides a first path of transmitted pulse optical signals into two beams of pulse optical signals C with equal power according to equal power proportion through a second 1x2 coupler 11.1, delays one beam of pulse optical signals C through a second delay optical fiber 12.1, and finally the two beams of pulse optical signals C sequentially pass through a second 3x3 coupler 13.1 to reach a second photoelectric detector 14.1 to obtain a second useless signal without sensing information, then the second 1x2 coupler 11.1 divides a second path of reflected pulse optical signals into two beams of pulse optical signals D according to equal power proportion, delays one beam of pulse optical signals D through a second delay optical fiber 12.1, so that the reflected signals of a front grating and the reflected signals of a rear grating in the optical fiber grating sensing network 7 contained in the second path of reflected pulse optical signals simultaneously pass through a second 3x3 coupler 13.1 to reach the second photoelectric detector 14.1 to generate interference, and three paths of backward sensing signals containing phase information are obtained;
Step 5: the signal processing unit 10 collects three paths of forward sensing signals and filters first useless signals, and then phase information of each sensor from front to back in the fiber bragg grating sensing network 7 is extracted from the three paths of forward sensing signals based on a 3x3 coupler phase demodulation algorithm;
The signal processing unit 10 filters out the second useless signal and collects three backward sensing signals, and then extracts phase information of each sensor from the back to the front in the fiber grating sensing network 7 from the three backward sensing signals based on a 3x3 coupler phase demodulation algorithm;
The signal processing unit 10 is used for realizing double-speed phase demodulation of the fiber grating sensing network 7 by arranging the phase information of each sensor from front to back and the phase information of each sensor from back to front of the fiber grating sensing network 7 in a one-to-one correspondence manner according to a time sequence.
Embodiment 2, when the double-end demodulation system of the long-distance fiber grating sensing network is applied to wavelength demodulation:
The light source module 1 adopts a wavelength tunable light source, the wavelength scanning range covers 1520nm to 1560nm, the minimum wavelength stepping value is 10pm, and TTL trigger signals are output after the wavelength is switched successfully; the optical fiber branching device 2 adopts a conventional 1-division-2 optical fiber branching device; the first pulse modulation unit 3 and the second pulse modulation unit 4 both adopt high-speed switch type semiconductor optical amplifier KY-PLM-16-M-FA modules, have a pulse optical signal amplifying function, have a small signal gain of 15dB, respectively modulate continuous optical signals input into the pulse modulation units into optical pulse signals with a pulse width of 20ns and a period of 80us through an external trigger mode, and have a phase delay of 40us; the first optical fiber circulator 5 and the second optical fiber circulator 6 are conventional optical fiber circulators, and the loss is less than 1dB;
The fiber grating sensing network 7 adopts a narrow-band grating array, the grating spectrum width is 0.1nm, the central wavelength is 1550nm, the sensing network length is 5km, the grating spacing is 5m, the number of gratings is 1000, the theoretical RTT value is 50us, 80us is taken in practical application, the light source scanning range is 2nm, the light source wavelength stepping value is 10pm, the single demodulation frequency maximum value of a system adopting a single-ended demodulation method is 100Hz, and the demodulation frequency is 62.5Hz in practical application;
the first photoelectric conversion unit 8 is composed of a photodiode, a transimpedance operational amplifier with a clamping function and the like, and is used for converting an input optical signal into an electric signal, and the purpose of adopting the transimpedance operational amplifier with the clamping function is to reduce the influence of a pulse optical signal transmitted by the fiber bragg grating sensing network 7;
the second photoelectric conversion unit 9 is the same as the first photoelectric conversion unit 8;
The core component of the signal processing unit 10 is an FPGA chip, the FPGA chip controls two paths of 14-bit analog-to-digital conversion chips to acquire electric signals output by the first photoelectric conversion unit 8 and the second photoelectric conversion unit 9 and process the signals to realize the wavelength demodulation of a sensing network, in addition, the signal processing unit 10 realizes the pulse modulation control of the first pulse modulation unit 3 and the second pulse modulation unit 4 in a TTL level triggering mode, and obtains the wavelength of the signals output by the light source module 1 in a TTL level communication mode;
In the dual-end wavelength demodulation system of the long-distance fiber grating sensing network of embodiment 2, the center wavelength of the FBG is 1550nm, the working temperature range of a conventional industrial product is-40-80 ℃, the working wavelength of the FBG sensing network is 1549.6-1550.8 nm, the wavelength scanning range of the light source module 1 is set to 1549.2-1551.19 nm, the scanning step is set to 10pm, the wavelength is stepped for 200 times, a TTL trigger signal is output for the signal processing unit 10 to obtain after each wavelength step is completed, the signal processing unit 10 controls the light source module 1 to output a continuous light signal with tunable wavelength, the linewidth of a light source with tunable wavelength is 10 kHz-100 MHz, and the optical fiber splitter 2 divides the continuous light signal with tunable wavelength into two paths according to the power and the like;
The first pulse modulation unit 3 modulates the continuous optical signal with tunable first path wavelength into a first path of pulse optical signal with adjustable period, pulse width and phase under the control of the signal processing unit 10, and performs power amplification on the first path of pulse optical signal with adjustable period, pulse width and phase; the second pulse modulation unit 4 modulates the second path of continuous optical signals with tunable wavelengths into second path of pulse optical signals with adjustable periods, pulse widths and phases under the control of the signal processing unit 10, and amplifies the power of the second path of pulse optical signals with adjustable periods, pulse widths and phases;
the first optical fiber circulator 5 inputs a first path of pulse optical signals amplified by power into the optical fiber grating sensing network 7, and reflects and transmits the first path of pulse optical signals in the optical fiber grating sensing network 7 to form a first path of reflected pulse optical signals and a first path of transmitted pulse optical signals; the second optical fiber circulator 6 inputs a second path of pulse optical signals with amplified power into the optical fiber grating sensing network 7, and reflects and transmits the second path of pulse optical signals in the optical fiber grating sensing network 7 to form a second path of reflected pulse optical signals and a second path of transmitted pulse optical signals;
In order to ensure that the reflected signals of the fiber bragg grating sensing network 7 are not aliased in the time domain under the action of the adjacent two pulse optical signals input from the single end of the fiber bragg grating sensing network 7, according to the OTDR technical principle, the pulse width w of the generated pulse optical signals should satisfy the formula: w <2n eff d/c, wherein n eff is the refractive index of the fiber core of the FBG sensing network, about 1.5, c is the propagation speed of light in vacuum, d is the interval between adjacent FBGs 5m, w <50ns is calculated, and w=20ns is taken in practical application; the period of the generated pulse optical signal is larger than the RTT value, 50us can be obtained by calculating the RTT value by the length 5km of the fiber bragg grating sensing network 7, and the period of the pulse optical signal is 80us in practical application;
In order to ensure that a reflected signal of the fiber grating sensing network 7 under the action of a single pulse light signal input from one end of the fiber grating sensing network 7 and a transmission signal of the fiber grating sensing network 7 under the action of a single pulse light signal input from the other end of the fiber grating sensing network 7 are not aliased in a time domain, a phase delay t pd exists between two paths of pulse light signals output by the first pulse modulation unit 3 and the second pulse modulation unit 4, and the phase delay t pd is 40us;
After the wavelength steps 1, 3,5, … and 199 succeed, the signal processing unit 10 controls the first pulse modulation unit 3 to complete pulse modulation operation, and after the wavelength steps 2, 4, 6, … and 200 succeed, the signal processing unit 10 controls the second pulse modulation unit 4 to complete pulse modulation operation, as shown in fig. 5, the signal processing unit 10 cooperatively processes synchronous operations of the light source module 1, the first pulse modulation unit 3 and the second pulse modulation unit 4;
In embodiment 2, the first optical fiber circulator 5 inputs the first path of reflected pulse optical signal and the second path of transmitted pulse optical signal to the first photoelectric conversion unit 8; the second optical fiber circulator 6 inputs the first path of transmitted pulse optical signals and the second path of reflected pulse optical signals into a second photoelectric conversion unit 9;
Assuming that the first pulse optical signal output by the first pulse modulation unit 3 is output to the head end of the fiber bragg grating sensing network 7 at the moment 0, outputting the first pulse optical signal output by the second pulse modulation unit 4 to the tail end of the fiber bragg grating sensing network 7 after 40 us;
in embodiment 2, the first photoelectric conversion unit 8 converts the first path of reflected pulse light signal into a forward sense signal first, and then converts the second path of transmitted pulse light signal into a first useless signal without sense information;
The second photoelectric conversion unit 9 firstly converts the first path of transmitted pulse light signals into second useless signals without sensing information, and then converts the second path of reflected pulse light signals into backward sensing signals;
When a first pulse optical signal pulse #11 output by the first pulse modulation unit 3 is transmitted in the fiber grating sensing network 7, each FBG is reflected, the intensity of the reflected signal can be used as the reflectivity of each FBG under the current wavelength, and as the length of the sensing network is 5km, the pulse #11 after 25us is transmitted out of the fiber grating sensing network 7 and enters the second photoelectric conversion unit 9 through the second fiber ring device 6, the reflected signals of each FBG enter the first photoelectric conversion unit 8 through the first fiber ring device 5, and the time for the reflected signals of all FBGs to reach the first photoelectric conversion unit 8 is 50us;
When the first pulse optical signal pulse #21 output by the second pulse modulation unit 4 is transmitted in the fiber grating sensing network 7, the reflection occurs when each FBG is encountered, the reflected signal intensity can be used as the reflectivity of each FBG under the current wavelength, the pulse #21 is transmitted out of the fiber grating sensing network 7 and enters the first photoelectric conversion unit 8 through the first fiber circulator 5 when 65us, the reflected signals of each FBG enter the second photoelectric conversion unit 9 through the second fiber circulator 6, and the reflected signals of all FBGs take 50us when reaching the second photoelectric conversion unit 9;
All signals entering the first photoelectric conversion unit 8 will be converted into electrical signals. Likewise, all signals entering the second photoelectric conversion unit 9 are also converted into electric signals;
In embodiment 2, the signal processing unit 10 collects the forward sensing signals and filters the first useless signals, and then traverses the forward sensing signals under different wavelengths to obtain the reflectivity of each sensor from front to back in the fiber bragg grating sensing network 7 under each wavelength, and further obtains the wavelength information of each sensor from front to back by using a fitting algorithm;
The signal processing unit 10 filters out the second useless signals and collects backward sensing signals, and then traverses the backward sensing signals under different wavelengths to obtain the reflectivity of each sensor from back to front in the fiber bragg grating sensing network 7 under each wavelength, and further obtains the wavelength information of each sensor from back to front by using a fitting algorithm;
The signal processing unit 10 is used for realizing double-speed wavelength demodulation of the fiber grating sensing network 7 by corresponding the wavelength information of each sensor from front to back of the fiber grating sensing network 7 and the wavelength information of each sensor from back to front in a one-to-one correspondence manner and arranging the wavelength information according to a time sequence.
According to the OTDR technical principle, the positioning of the FBGs is realized through the time sequence of pulse optical signals reflected by each FBG in the collected reflected signals of the fiber bragg grating sensing network 7, the relation between the time t for collecting the reflected signals and the position D of the FBG sensor is t=2n eff D/c, wherein n eff is the refractive index of the fiber core of the FBG sensing network, and c is the propagation speed of light in vacuum;
The wavelength demodulation method comprises the following steps: the reflectivities of the FBGs under different wavelengths are represented by the intensities of reflected signals of the FBGs under the action of pulse optical signals with corresponding wavelengths, the reflection spectrum of the FBGs is reconstructed according to the reflectivities of the FBGs under different wavelengths, and the central wavelength value of the reflection spectrum is obtained according to a Gaussian fitting algorithm or a centroid algorithm, so that the demodulation of the sensing network can be completed.
In the above technical scheme, the period of the pulse optical signal is 80us, the theoretical minimum value is 50us, and because the wavelength scanning needs 200 times, the theoretical maximum value of the demodulation frequency is 100Hz, the actual value is 62.5Hz, and the phase delay t pd of the two paths of pulse optical signals takes 40us to finally combine the results of double-end demodulation to realize equidistant sampling, and simultaneously the demodulation frequency is doubled.
The order of the positions of the sensing units in the output signals of the first photoelectric conversion unit 8 and the second photoelectric conversion unit 9 is reversed.
A double-end wavelength demodulation method of a long-distance fiber grating sensing network comprises the following steps:
step A: the signal processing unit 10 controls the light source module 1 to output a continuous optical signal with tunable wavelength, and the optical fiber splitter 2 splits the continuous optical signal with tunable wavelength into two paths according to the equal proportion of power;
and (B) step (B): the first pulse modulation unit 3 modulates a first path of continuous optical signal with tunable wavelength into a first path of pulse optical signal under the control of the signal processing unit 10, and performs power amplification on the first path of pulse optical signal; the second pulse modulation unit 4 modulates the second path of continuous optical signal with tunable wavelength into a second path of pulse optical signal under the control of the signal processing unit 10, and performs power amplification on the second path of pulse optical signal;
the first optical fiber circulator 5 inputs a first path of pulse optical signals amplified by power into the optical fiber grating sensing network 7, and reflects and transmits the first path of pulse optical signals in the optical fiber grating sensing network 7 to form a first path of reflected pulse optical signals and a first path of transmitted pulse optical signals; the second optical fiber circulator 6 inputs a second path of pulse optical signals with amplified power into the optical fiber grating sensing network 7, and reflects and transmits the second path of pulse optical signals in the optical fiber grating sensing network 7 to form a second path of reflected pulse optical signals and a second path of transmitted pulse optical signals;
step C: the first optical fiber circulator 5 inputs the first path of reflected pulse optical signals and the second path of transmitted pulse optical signals into the first photoelectric conversion unit 8; the second optical fiber circulator 6 inputs the first path of transmitted pulse optical signals and the second path of reflected pulse optical signals into a second photoelectric conversion unit 9;
step D: the first photoelectric conversion unit 8 firstly converts a first path of reflected pulse optical signals into forward sensing signals, and then converts a second path of transmitted pulse optical signals into first useless signals without sensing information;
The second photoelectric conversion unit 9 firstly converts the first path of transmitted pulse light signals into second useless signals without sensing information, and then converts the second path of reflected pulse light signals into backward sensing signals;
Step E: the signal processing unit 10 collects forward sensing signals and filters first useless signals, and then traverses the forward sensing signals under different wavelengths to obtain the reflectivity of each sensor from front to back in the fiber bragg grating sensing network 7 under each wavelength, and further obtains the wavelength information of each sensor from front to back by using a fitting algorithm;
The signal processing unit 10 filters out the second useless signals and collects backward sensing signals, and then traverses the backward sensing signals under different wavelengths to obtain the reflectivity of each sensor from back to front in the fiber bragg grating sensing network 7 under each wavelength, and further obtains the wavelength information of each sensor from back to front by using a fitting algorithm;
The signal processing unit 10 is used for realizing double-speed wavelength demodulation of the fiber grating sensing network 7 by corresponding the wavelength information of each sensor from front to back of the fiber grating sensing network 7 and the wavelength information of each sensor from back to front in a one-to-one correspondence manner and arranging the wavelength information according to a time sequence.
What is not described in detail in this specification is prior art known to those skilled in the art.

Claims (10)

1. The double-end demodulation system of the long-distance fiber grating sensing network is characterized by comprising a light source module (1), an optical fiber splitter (2), a first pulse modulation unit (3), a second pulse modulation unit (4), a first fiber circulator (5), a second fiber circulator (6), a fiber grating sensing network (7), a first photoelectric conversion unit (8), a second photoelectric conversion unit (9) and a signal processing unit (10); the light source control signal output end of the signal processing unit (10) is connected with the light source control signal input end of the light source module (1), the narrow-linewidth continuous optical signal output end of the light source module (1) is connected with the input end of the optical fiber branching device (2), the first path of narrow-linewidth continuous optical signal output end of the optical fiber branching device (2) is connected with the signal input end of the first optical fiber ring (5), the second path of narrow-linewidth continuous optical signal output end of the optical fiber branching device (2) is connected with the signal input end of the second optical fiber grating sensing network (4), the first modulation control signal output end of the signal processing unit (10) is connected with the control signal input end of the first optical fiber modulation unit (3), the second modulation control signal output end of the signal processing unit (10) is connected with the control signal input end of the second optical fiber modulation unit (4), the first path of pulse optical signal output end of the power amplification of the first optical fiber branching device (3) is connected with the first communication end of the first optical fiber ring (5), the second communication end of the first optical fiber grating sensing network (5) is connected with one end of the optical fiber grating sensing network (7), and the first communication end of the first optical fiber ring (5) is connected with the first communication end of the optical fiber communication unit (8); the power amplification second path pulse optical signal output end of the second pulse modulation unit (4) is connected with the first communication end of the second optical fiber circulator (6), the second communication end of the second optical fiber circulator (6) is connected with the other end of the fiber grating sensing network (7), and the third communication end of the second optical fiber circulator (6) is connected with the signal input end of the second photoelectric conversion unit (9); the signal output end of the first photoelectric conversion unit (8) and the signal output end of the second photoelectric conversion unit (9) are connected with the signal input end of the signal processing unit (10).
2. The dual-end demodulation system of a long-distance fiber grating sensing network according to claim 1, wherein: the signal processing unit (10) is used for controlling the light source module (1) to output a narrow-linewidth continuous optical signal, and the optical fiber branching device (2) divides the narrow-linewidth continuous optical signal into two paths of narrow-linewidth continuous optical signals according to the power equal proportion.
3. The dual-end demodulation system of a long-distance fiber grating sensing network according to claim 2, wherein: the first pulse modulation unit (3) is used for modulating a first path of narrow linewidth continuous optical signal into a first path of pulse optical signal under the control of the signal processing unit (10) and amplifying the power of the first path of pulse optical signal; the second pulse modulation unit (4) is used for modulating a second path of narrow linewidth continuous optical signal into a second path of pulse optical signal under the control of the signal processing unit (10) and carrying out power amplification on the second path of pulse optical signal;
The first optical fiber circulator (5) is used for inputting a first path of pulse optical signals amplified by power into the fiber grating sensing network (7), and reflecting and transmitting the first path of pulse optical signals and the first path of transmitted pulse optical signals in the fiber grating sensing network (7); the second optical fiber circulator (6) is used for inputting a second path of pulse optical signals amplified by power into the optical fiber grating sensing network (7), and reflecting and transmitting the second path of pulse optical signals and the second path of transmitted pulse optical signals in the optical fiber grating sensing network (7).
4. The dual-end demodulation system of a long-distance fiber grating sensing network of claim 3, wherein: the first optical fiber circulator (5) is used for inputting a first path of reflected pulse optical signals and a second path of transmitted pulse optical signals into the first photoelectric conversion unit (8); the second optical fiber circulator (6) is used for inputting the first path of transmitted pulse optical signals and the second path of reflected pulse optical signals into the second photoelectric conversion unit (9).
5. The dual-end demodulation system of a long-distance fiber grating sensing network of claim 4, wherein: the first photoelectric conversion unit (8) firstly divides a first path of reflected pulse optical signals into two beams of pulse optical signals A according to the power equal proportion through a first 1x2 coupler (11), then delays one beam of pulse optical signals A through a first delay optical fiber (12), so that the reflected signals of a previous grating and the reflected signals of a later grating in the optical fiber grating sensing network (7) contained in the first path of reflected pulse optical signals are simultaneously interfered by the first 3x3 coupler (13) to reach a first photoelectric detector (14) to obtain three paths of forward sensing signals containing phase information, then the first 1x2 coupler (11) divides a second path of transmitted pulse optical signals into two beams of pulse optical signals B with the same power according to the power equal proportion, then delays one beam of pulse optical signals B through the first delay optical fiber (12), and finally the two beams of pulse optical signals B sequentially pass through the first 3x3 coupler (13) to reach the first photoelectric detector (14) to obtain a first wireless signal without sensing information;
The second photoelectric conversion unit (9) firstly divides a first path of transmission pulse optical signals into two paths of pulse optical signals C with equal power according to equal proportion by a second 1x2 coupler (11.1), then delays one of the two paths of pulse optical signals C by a second delay optical fiber (12.1), finally the two paths of pulse optical signals C sequentially pass through a second 3x3 coupler (13.1) to reach a second photoelectric detector (14.1) to obtain a second useless signal without sensing information, then the second 1x2 coupler (11.1) divides the second path of reflection pulse optical signals into two paths of pulse optical signals D according to equal proportion of power, and delays one of the two paths of pulse optical signals D by the second delay optical fiber (12.1) so that the reflection signal of the previous grating and the reflection signal of the next grating in the second path of reflection pulse optical signals simultaneously pass through the second 3x3 coupler (13.1) to reach the second photoelectric detector (14.1) to obtain three paths of interference sensing signals containing phase sensing information.
6. The dual-end demodulation system of a long-distance fiber grating sensing network of claim 5, wherein: the signal processing unit (10) is used for collecting three paths of forward sensing signals and filtering first useless signals, and then extracting phase information of each sensor from front to back in the fiber bragg grating sensing network (7) from the three paths of forward sensing signals based on a 3x3 coupler phase demodulation algorithm;
The signal processing unit (10) is used for filtering the second useless signal and collecting three backward sensing signals, and then extracting phase information of each sensor from back to front in the fiber bragg grating sensing network (7) from the three backward sensing signals based on a 3x3 coupler phase demodulation algorithm;
the signal processing unit (10) is used for enabling the phase information of each sensor from front to back of the fiber bragg grating sensing network (7) to correspond to the phase information of each sensor from back to front one by one and arranging the phase information according to time sequence, so that double-speed phase demodulation of the fiber bragg grating sensing network (7) is realized.
7. The dual-end demodulation system of a long-distance fiber grating sensing network according to claim 1, wherein: the pulse width w of the power amplified first path pulse optical signal output by the first pulse modulation unit (3) and the pulse width w of the power amplified second path pulse optical signal output by the second pulse modulation unit (4) both meet the formula: w <2n eff d/c, wherein n eff is the refractive index of the fiber core of the fiber grating sensing network (7), c is the propagation speed of light in vacuum, d is the interval between adjacent gratings in the fiber grating sensing network (7), and the period T of the first path of pulse light signal and the second path of pulse light signal is larger than the round trip time RTT of the pulse light transmitted in the fiber grating sensing network (7).
8. The dual-end demodulation system of a long-distance fiber grating sensing network according to claim 1, wherein: the phase delay RTT/2 is not less than T pd and not more than T-RTT/2 exists between the first path of power amplified pulse optical signals output by the first pulse modulation unit (3) and the second path of power amplified pulse optical signals output by the second pulse modulation unit (4), the RTT is the round trip time of pulse light transmission in the fiber grating sensing network (7), and the T is the period of the first path of pulse optical signals and the second path of pulse optical signals; the signal processing unit (10) realizes pulse modulation control of the first pulse modulation unit (3) and the second pulse modulation unit (4) in a TTL level triggering mode, realizes that a first path of narrow-line-width continuous optical signal is modulated into a first path of pulse optical signal with adjustable period, pulse width and phase, and a second path of narrow-line-width continuous optical signal is modulated into a second path of pulse optical signal with adjustable period, pulse width and phase.
9. The double-end phase demodulation method of the long-distance fiber grating sensing network based on the system of claim 1 is characterized by comprising the following steps:
step 1: the signal processing unit (10) controls the light source module (1) to output a narrow-linewidth continuous light signal with fixed wavelength, and the optical fiber branching device (2) divides the narrow-linewidth continuous light signal with fixed wavelength into two paths of narrow-linewidth continuous light signals according to the power equal proportion;
Step 2: the first pulse modulation unit (3) modulates a first path of narrow linewidth continuous optical signal into a first path of pulse optical signal under the control of the signal processing unit (10), and performs power amplification on the first path of pulse optical signal; the second pulse modulation unit (4) modulates a second path of narrow linewidth continuous optical signal into a second path of pulse optical signal under the control of the signal processing unit (10), and performs power amplification on the second path of pulse optical signal;
The first optical fiber circulator (5) inputs a first path of pulse optical signals amplified by power into the fiber grating sensing network (7), and reflects and transmits the first path of pulse optical signals to form a first path of reflected pulse optical signals and a first path of transmitted pulse optical signals in the fiber grating sensing network (7); the second optical fiber circulator (6) inputs a second path of pulse optical signals with amplified power into the optical fiber grating sensing network (7), and reflects and transmits the second path of pulse optical signals in the optical fiber grating sensing network (7) to form a second path of reflected pulse optical signals and a second path of transmitted pulse optical signals;
step 3: the first optical fiber circulator (5) inputs a first path of reflected pulse optical signals and a second path of transmitted pulse optical signals into the first photoelectric conversion unit (8); the second optical fiber circulator (6) inputs the first path of transmitted pulse optical signals and the second path of reflected pulse optical signals into a second photoelectric conversion unit (9);
Step 4: the first photoelectric conversion unit (8) firstly divides a first path of reflected pulse optical signals into two beams of pulse optical signals A according to the power equal proportion through a first 1x2 coupler (11), then delays one beam of pulse optical signals A through a first delay optical fiber (12), so that the reflected signals of a previous grating and the reflected signals of a later grating in the optical fiber grating sensing network (7) contained in the first path of reflected pulse optical signals are simultaneously interfered by the first 3x3 coupler (13) to reach a first photoelectric detector (14) to obtain three paths of forward sensing signals containing phase information, then the first 1x2 coupler (11) divides a second path of transmitted pulse optical signals into two beams of pulse optical signals B with the same power according to the power equal proportion, then delays one beam of pulse optical signals B through the first delay optical fiber (12), and finally the two beams of pulse optical signals B sequentially pass through the first 3x3 coupler (13) to reach the first photoelectric detector (14) to obtain a first wireless signal without sensing information;
The second photoelectric conversion unit (9) firstly divides a first path of transmission pulse optical signals into two paths of pulse optical signals C with equal power according to equal power proportion through a second 1x2 coupler (11.1), then delays one of the two paths of pulse optical signals C through a second delay optical fiber (12.1), the last two paths of pulse optical signals C sequentially pass through a second 3x3 coupler (13.1) to reach a second photoelectric detector (14.1) to obtain a second useless signal without sensing information, then the second 1x2 coupler (11.1) divides the second path of reflection pulse optical signals into two paths of pulse optical signals D according to equal power proportion, and delays one of the two paths of pulse optical signals D through a second delay optical fiber (12.1), so that the reflection signal of a previous grating and the reflection signal of a next grating contained in the second path of reflection pulse optical signals simultaneously pass through the second 3x3 coupler (13.1) to reach the second photoelectric detector (14.1) to generate three paths of interference signals containing phase sensing information;
step 5: the signal processing unit (10) collects three paths of forward sensing signals and filters first useless signals, and then phase information of each sensor from front to back in the fiber bragg grating sensing network (7) is extracted from the three paths of forward sensing signals based on a 3x3 coupler phase demodulation algorithm;
The signal processing unit (10) filters out the second useless signal and collects three backward sensing signals, and then extracts phase information of each sensor from back to front in the fiber bragg grating sensing network (7) from the three backward sensing signals based on a 3x3 coupler phase demodulation algorithm;
The signal processing unit (10) is used for enabling the phase information of each sensor from front to back of the fiber bragg grating sensing network (7) to correspond to the phase information of each sensor from back to front one by one and arranging the phase information according to time sequence, so that double-speed phase demodulation of the fiber bragg grating sensing network (7) is realized.
10. The double-end wavelength demodulation method of the long-distance fiber grating sensing network based on the system of claim 1 is characterized by comprising the following steps:
Step A: the signal processing unit (10) controls the light source module (1) to output a continuous optical signal with tunable wavelength, and the optical fiber branching device (2) divides the continuous optical signal with tunable wavelength into two paths according to the power equal proportion;
And (B) step (B): the first pulse modulation unit (3) modulates a first path of continuous optical signal with tunable wavelength into a first path of pulse optical signal under the control of the signal processing unit (10), and performs power amplification on the first path of pulse optical signal; the second pulse modulation unit (4) modulates a second path of continuous optical signals with tunable wavelengths into a second path of pulse optical signals under the control of the signal processing unit (10), and performs power amplification on the second path of pulse optical signals;
The first optical fiber circulator (5) inputs a first path of pulse optical signals amplified by power into the fiber grating sensing network (7), and reflects and transmits the first path of pulse optical signals to form a first path of reflected pulse optical signals and a first path of transmitted pulse optical signals in the fiber grating sensing network (7); the second optical fiber circulator (6) inputs a second path of pulse optical signals with amplified power into the optical fiber grating sensing network (7), and reflects and transmits the second path of pulse optical signals in the optical fiber grating sensing network (7) to form a second path of reflected pulse optical signals and a second path of transmitted pulse optical signals;
Step C: the first optical fiber circulator (5) inputs a first path of reflected pulse optical signals and a second path of transmitted pulse optical signals into the first photoelectric conversion unit (8); the second optical fiber circulator (6) inputs the first path of transmitted pulse optical signals and the second path of reflected pulse optical signals into a second photoelectric conversion unit (9);
Step D: the first photoelectric conversion unit (8) firstly converts a first path of reflected pulse optical signals into forward sensing signals, and then converts a second path of transmitted pulse optical signals into first useless signals without sensing information;
The second photoelectric conversion unit (9) firstly converts the first path of transmitted pulse optical signals into second useless signals without sensing information, and then converts the second path of reflected pulse optical signals into backward sensing signals;
Step E: the signal processing unit (10) collects forward sensing signals and filters first useless signals, then traverses the forward sensing signals under different wavelengths to obtain the reflectivity of each sensor from front to back in the fiber bragg grating sensing network (7) under each wavelength, and further obtains the wavelength information of each sensor from front to back by using a fitting algorithm;
The signal processing unit (10) filters out second useless signals and collects backward sensing signals, then traverses the backward sensing signals under different wavelengths to obtain the reflectivity of each sensor from back to front in the fiber bragg grating sensing network (7) under each wavelength, and further obtains the wavelength information of each sensor from back to front by using a fitting algorithm;
The signal processing unit (10) is used for enabling the wavelength information of each sensor from front to back of the fiber bragg grating sensing network (7) to correspond to the wavelength information of each sensor from back to front one by one and arranging the wavelength information according to time sequence, so that double-speed wavelength demodulation of the fiber bragg grating sensing network (7) is realized.
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