CN116907556B - Distributed optical fiber sensing multi-feature hybrid demodulation system and method - Google Patents
Distributed optical fiber sensing multi-feature hybrid demodulation system and method Download PDFInfo
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Abstract
The invention provides a distributed optical fiber sensing multi-feature hybrid demodulation system and a method, wherein the system comprises the following steps: the optical path module is in optical path connection with the optical fiber sensors and is used for generating an excitation optical signal, outputting the excitation optical signal to the optical fiber sensors in a unidirectional manner, receiving reflected optical signals of the optical fiber sensors in a unidirectional manner and outputting the reflected optical signals in a unidirectional manner; the circuit module is connected with the optical path module, so that the optical path module is driven to work on one hand, reflected light signals of a plurality of optical fiber sensors which are output in one direction by the optical path module are received on the other hand, and photoelectric conversion and signal preprocessing are carried out on the reflected light signals; the signal processing module is electrically connected with the output end of the circuit module, and the signal processing module demodulates and processes the output signal of the circuit module sequentially through a variable threshold light intensity extraction step, a centroid method wavelength extraction step and an FFT phase information extraction step.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing and demodulation, in particular to a distributed optical fiber sensing multi-feature hybrid demodulation system and method.
Background
The FBG sensor and the optical fiber FP sensor are used as wavelength and phase modulation type optical fiber sensors, and the FBG sensor and the optical fiber FP sensor have the advantages of electromagnetic interference resistance, high temperature resistance, corrosion resistance, strong multiplexing capability, high sensitivity, portability, flexibility and the like, and are widely applied to monitoring of various physical quantities such as temperature, strain, displacement and the like in the fields of aerospace, civil engineering, petrochemical industry and the like. With the development and application of optical fiber sensing and demodulation technologies, problems are gradually derived, and the problems are specifically expressed: 1. lack of ability to demodulate multi-feature spectral information; 2. the requirements for a distributed monitoring scenario are not applicable.
The above drawbacks limit the application of fiber grating demodulation hardware, so it is necessary to provide a distributed optical fiber sensing multi-feature hybrid demodulation system and method.
Disclosure of Invention
In view of this, the present invention provides a distributed optical fiber sensing multi-feature hybrid demodulation system and method that can be applied to different optical fiber sensors and can demodulate multiple optical characteristics.
The technical scheme of the invention is realized as follows:
in one aspect, the present invention provides a distributed optical fiber sensing multi-feature hybrid demodulation system, comprising:
the optical path module is in optical path connection with the optical fiber sensors; the optical path module is used for generating an excitation light signal and outputting the excitation light signal to the optical fiber sensors in a unidirectional manner, and also receives reflected light signals of the optical fiber sensors in a unidirectional manner and further outputs the reflected light signals in a unidirectional manner outwards;
The circuit module is connected with the optical path module, and is used for driving the optical path module to work on one hand and receiving reflected light signals of a plurality of optical fiber sensors which are output in one direction by the optical path module on the other hand, and carrying out photoelectric conversion and signal preprocessing on the reflected light signals;
The signal processing module is electrically connected with the output end of the circuit module, and the signal processing module demodulates the output signal of the circuit module sequentially through a variable threshold light intensity extraction step, a centroid method wavelength extraction step and an FFT phase information extraction step.
On the basis of the technical scheme, preferably, the optical path module comprises a tunable ring cavity laser unit and a passive optical path unit; the output end of the tunable ring cavity laser unit is respectively connected with the input end of the tunable ring cavity laser unit and the input end of the passive optical path unit in an optical path way, the passive optical path unit is also connected with a plurality of optical fiber sensors in an optical path way, excitation light signals are output to the plurality of optical fiber sensors through the passive optical path unit, and the passive optical path unit also receives reflected light signals of the plurality of optical fiber sensors; the plurality of optical fiber sensors includes an optical fiber FBG sensor and an optical fiber FP sensor.
Preferably, the tunable ring cavity laser unit comprises an SOA, a first optical isolator, a tunable FP filter, a second optical isolator and an optical fiber coupler which are sequentially arranged; the output end of the SOA is in optical path connection with the input end of the first optical isolator, the output end of the first optical isolator is in optical path connection with the input end of the tunable FP filter, the output end of the tunable FP filter is in optical path connection with the input end of the second optical isolator, the output end of the second optical isolator is in optical path connection with the input end of the optical fiber coupler, the first output end of the optical fiber coupler is in optical path connection with the input end of the SOA, and the second output end of the optical fiber coupler is in optical path connection with the passive optical path unit; the ratio of output light of the first output end and the second output end of the optical fiber coupler is 10%:90%;
The passive optical path unit comprises an optical splitter and a plurality of circulators, wherein the circulators comprise a first port, a second port and a third port, the first port is in unidirectional communication with the second port, and the second port is in unidirectional communication with the third port; the input end of the optical splitter is in optical path connection with the second output end of the optical fiber coupler, the output end of the optical splitter is in optical path connection with the first ports of the plurality of circulators respectively, the second ports of the plurality of circulators are in optical path connection with an optical fiber sensor respectively, and the third ports of the plurality of circulators are all in optical path connection with the circuit module; the second port of each circulator not only transmits an excitation light signal to the optical fiber sensor, but also receives a reflected light signal of the optical fiber sensor, and the reflected light signal is unidirectionally output to the circuit module through the third port.
Preferably, the circuit module comprises a temperature control circuit, a constant current driving circuit, a plurality of photoelectric conversion signal conditioning circuits and a signal acquisition circuit; the temperature control circuit and the constant current driving circuit are both arranged at the tunable annular cavity laser unit and are electrically connected with the tunable annular cavity laser unit, the temperature control circuit is used for maintaining the temperature stability of the tunable annular cavity laser unit, and the constant current driving circuit is used for driving the tunable annular cavity laser unit to stably work; the input ends of the photoelectric conversion signal conditioning circuits are connected with the output ends of the passive optical path units, the photoelectric conversion is correspondingly carried out on the reflected light signals of the optical fiber sensors, and the signals after the photoelectric conversion are amplified and filtered; the input end of the signal acquisition circuit is electrically connected with the output ends of the photoelectric conversion signal conditioning circuits in a one-to-one correspondence manner, and is used for carrying out analog-to-digital conversion processing on the output signals of the photoelectric conversion signal conditioning circuits.
Preferably, the signal acquisition circuit comprises an analog-to-digital conversion chip and an FPGA chip; each input channel of the analog-to-digital conversion chip is electrically connected with the output ends of the photoelectric conversion signal conditioning circuits in a one-to-one correspondence manner; at least two paths of input channels of the analog-to-digital conversion chip are alternately opened, the output signals of the photoelectric conversion signal conditioning circuits are subjected to analog-to-digital conversion, and the converted digital quantity is sent to a FIFO buffer module in the FPGA chip for storage.
On the other hand, the invention provides a distributed optical fiber sensing multi-feature hybrid demodulation method, which is characterized in that the distributed optical fiber sensing multi-feature hybrid demodulation system is constructed, after a signal processing module acquires the photoelectric conversion and signal preprocessing results output by a circuit module, the signal processing module sequentially executes a variable threshold light intensity extraction step, a centroid method wavelength extraction step and an FFT phase information extraction step, and packages and sends the demodulated results to an upper computer.
Preferably, the step of extracting the variable threshold light intensity of the signal processing module includes the following steps:
S301: determining the maximum variable and a threshold Th: the method comprises the steps of comparing thresholds of digital quantities of analog-to-digital conversion processing corresponding to a path of photoelectric conversion signal conditioning circuit output by a signal acquisition circuit one by one, and taking the maximum value of the output digital quantities as the maximum variable output by the path; determining the size of a threshold Th according to a certain proportion of the maximum variable;
s302: judging the initial state: judging the size relation between the data points N i+1、Ni and Th, if N i+1 > Th and N i < Th are satisfied, entering the next step S303; n i and N i+1 are digital quantities corresponding to sampling moments i and i+1 respectively, and sampling periods of intervals between adjacent sampling moments are fixed; judging whether N i+1 > Th and N i < Th are met or not, if not, i automatically increases by 1, and comparing the conditions again, if N i+1 > Th is met and N i < Th or the current value of i reaches the upper limit, stopping the comparison process, and writing the value of N i+1 as the value of the maximum variable into the maximum variable register until all the digital quantities of the current analog-digital conversion process are compared;
s303: and (3) rising state judgment: if N i+1>Ni > Th is met, caching the data points meeting the condition into a buffer module of the FPGA; marking each data point and sequence value and proceeding to the next step S303;
S304: judging the falling state: if N i>Ni+1 > Th is met, caching the data points meeting the condition into a buffer module of the FPGA; marking each data point and sequence value to enter the next step S305;
S305: judging a termination state: if N i+1 < Th and N i > Th are met, the process jumps back to step S302 to continue searching until searching ends to stop the thresholding intensity extraction.
Preferably, the threshold Th is determined according to a certain proportion of the maximum variable, and 75% of the maximum variable is used as the threshold Th.
Preferably, the centroid method wavelength extraction step of the signal processing module extracts wavelength information from the spectrum corresponding to each data point exceeding the threshold Th through a centroid peak finding algorithm, takes the abscissa as the bit vector of the particle system and the ordinate as the mass of the particle system, assigns a weighting coefficient to each data, takes the weighted average of all the data as the wavelength lambda B： of the obtained optical fiber FBG sensor, wherein x j represents the sequence value, y j represents the light intensity value, and i+1 and k are the sequence numbers of the sequence value.
Preferably, the FFT phase information extracting step of the signal processing module is to perform fast fourier transform on a time domain signal, and then complete the calculation of the frequency domain signal extremum of the optical fiber FP sensor by using a point-by-point comparison method: Wherein X (k) represents a frequency domain value; x 1(s) represents a time-domain sampling point; s represents a sequence index of time sequence sampling points; w N/2 is N/2 times unit root; k is an index of frequency domain values, k=0, 1,2,..n-1; n is the number of sample points for which the FFT transformation is performed.
Compared with the prior art, the distributed optical fiber sensing multi-feature hybrid demodulation system and method provided by the invention have the following beneficial effects:
(1) According to the scheme, the circuit module, the light path module and the signal processing module are integrated, so that the problem that the wired connection of the system is inconvenient under a complex working condition can be solved, and the scheme is not applicable to a scene of wired data transmission in a narrow space; demodulation of a plurality of distributed optical fiber sensors can be completed by adapting to a multi-channel wide spectrum tuning range, so that scene requirements of distributed monitoring are met;
(2) For the spectrum of the fiber FBP/FP sensor, wavelength, light intensity or phase multi-feature is adopted for demodulation.
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In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a block diagram of a system architecture of a distributed optical fiber sensing multi-feature hybrid demodulation system and method of the present invention;
FIG. 2 is a signal processing flow diagram of a signal processing module of the distributed optical fiber sensing multi-feature hybrid demodulation system and method of the present invention;
FIG. 3 is a schematic diagram of a signal acquisition process of a signal acquisition circuit of the distributed optical fiber sensing multi-feature hybrid demodulation system and method of the present invention;
FIG. 4 is a flow chart of variable threshold light intensity extraction for the distributed fiber sensing multi-feature hybrid demodulation system and method of the present invention;
fig. 5 is a flow chart of parallel signal processing for the distributed optical fiber sensing multi-feature hybrid demodulation system and method of the present invention.
Reference numerals: 1. an optical path module; 2. a circuit module; 3. a signal processing module; 11. a tunable ring cavity laser unit; 12. a passive optical path unit; 111. SOA; 113. a first optical isolator; 112. a tunable FP filter; 114. a second optical isolator; 115. an optical fiber coupler; 121. an optical branching device; 122. a first circulator; 123. a second circulator; 124. a third circulator; 125. a fourth circulator; 21. a temperature control circuit; 22. a constant current driving circuit; 23. a photoelectric conversion signal conditioning circuit; 24. a signal acquisition circuit; 25. and a power supply.
Detailed Description
The following description of the embodiments of the present invention will clearly and fully describe the technical aspects of the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, are intended to fall within the scope of the present invention.
As shown in fig. 1, in one aspect, the present invention provides a distributed optical fiber sensing multi-feature hybrid demodulation system, including:
The optical path module 1 is in optical path connection with a plurality of optical fiber sensors; the optical path module 1 is used for generating an excitation light signal, outputting most of the excitation light signal to the optical fiber sensors in a unidirectional manner, returning a small part of the excitation light signal to the optical path module 1 as a seed light signal, and unidirectional receiving reflected light signals of the optical fiber sensors by the optical path module 1 and unidirectional outputting the reflected light signals outwards;
The circuit module 2 is connected with the optical path module 1, the circuit module 2 drives the optical path module 1 to work on one hand, and receives reflected light signals of a plurality of optical fiber sensors which are output by the optical path module 1 in a unidirectional way, and performs photoelectric conversion and signal preprocessing on the reflected light signals;
The signal processing module 3 is electrically connected with the output end of the circuit module 2, and the signal processing module 3 demodulates the output signal of the circuit module 2 sequentially through a variable threshold light intensity extraction step, a centroid method wavelength extraction step and an FFT phase information extraction step. As shown in fig. 1, the disadvantage that the conventional demodulator is inconvenient to move is improved by integrating the circuit module, the optical path module and the signal processing module.
Specifically, as further shown in fig. 1, the optical path module 1 includes a tunable ring cavity laser unit 11 and a passive optical path unit 12; the output end of the tunable ring cavity laser unit 11 is respectively connected with the input end of the tunable ring cavity laser unit and the input end of the passive optical path unit 12 in an optical path manner, the passive optical path unit 12 is also connected with a plurality of optical fiber sensors in an optical path manner, excitation light signals are output to the plurality of optical fiber sensors through the passive optical path unit 12, and the passive optical path unit 12 also receives reflected light signals of the plurality of optical fiber sensors; the plurality of optical fiber sensors includes an optical fiber FBG sensor and an optical fiber FP sensor. Each optical fiber sensor can adopt distributed arrangement to realize remote, multi-parameter and multi-node distributed measurement.
The tunable ring cavity laser unit 11 includes an SOA111, a first optical isolator 113, a tunable FP filter 112, a second optical isolator 114, and an optical fiber coupler 115, which are sequentially arranged; the output end of the SOA111 is in optical path connection with the input end of the first optical isolator 113, the output end of the first optical isolator 113 is in optical path connection with the input end of the tunable FP filter 112, the output end of the tunable FP filter 112 is in optical path connection with the input end of the second optical isolator 114, the output end of the second optical isolator 114 is in optical path connection with the input end of the optical fiber coupler 115, the first output end of the optical fiber coupler 115 is in optical path connection with the input end of the SOA111, and the second output end of the optical fiber coupler 115 is in optical path connection with the passive optical path unit 12; the ratio of output light of the first output end and the second output end of the optical fiber coupler 115 is 10%:90%.
The SOA111 is a semiconductor optical amplifier, and its amplification effect is determined together with the input optical power, the injection current and its gain characteristics; the tunable FP filter 112 filters the output light of the SOA to form a narrowband output light, the filtering effect of which is determined by the frequency, amplitude and frequency selective characteristics of the drive signal; the first optical isolator 113 and the second optical isolator 114 have higher coupling efficiency and can ensure unidirectional circulation of light in the resonant cavity, and prevent back scattering and reflection of an optical path in the annular cavity; the optical fiber coupler 115 functions as an optical wave splitting device, and has an input end and an output end connected to other devices in the ring cavity to form a ring resonator, and the other output end as an output end of the tunable ring cavity laser device is connected to the optical path of the passive optical path unit 12. The function of an SOA can be expressed by the interaction between light and a substance, carriers in an active region are provided by an external bias current, an optical signal is injected into the SOA at the same time, an electron in a valence band is stimulated to transit to a conduction band by a driving current, energy is released by recombination of the electron and a hole to generate photons, the photons generated in the process are stimulated to radiate under the excitation of an input signal, the photons are identical to amplified input light, and therefore the input light signal is amplified, and the amplification degree g m (v, n) is mainly related to the carrier concentration n and the recombination center angular frequency v of the stimulated radiation:
Wherein c is the speed of light; n 1 is the active region refractive index; τ is the radiative recombination carrier lifetime; h is a Planck constant; m e is electron mass; m hh is the hole mass.
The tunable FP filter 112 is constructed mainly of a single-mode fiber with both end faces coated with a high reflection film, and a piezoelectric ceramic. The single-mode fiber is fixed in the capillary glass tube and plated with the high-reflection film, and is fixed on the piezoelectric ceramics through epoxy resin. The coated end faces of the two single-mode fibers are strictly parallel, an air medium is used as a middle gap, and the distance between the end faces of the two single-mode fibers is tuned by changing the driving voltage of the piezoelectric ceramics. The parallel mirrors of the tunable FP filter are followed by optical fibers that enable a good connection to the fiber device. The high-reflection film plated on the end face of the optical fiber is a dielectric film with alternating high and low refractive indexes, and the optical thickness of each layer of film is lambda 0/4,λ0 which is the central wavelength of incident light; at the output of the tunable FP filter 112, the phase difference δ satisfies or the optical path difference satisfies 2d=mλ, λ being the wavelength of the incident light; d is the tuning cavity length; m is the number of interference orders, m=0, ±1, ±2, …; thus, if the phase difference is changed, the tuning of the filter can be realized, and if the d is differentiated on the two sides, the tunable FFP filter selects the output wavelength lambda through the tuning cavity length d, the FP cavity length is controlled through the driving voltage applied to the piezoelectric ceramics, and different driving voltages correspond to different wavelengths of the emergent light of the tunable FP filter.
The frequency selective characteristic of the tunable FP filter is determined by a free spectral range, a full width at half maximum, and a finesse, where the free spectral range is a difference between parameters corresponding to adjacent peaks in the transmission spectrum, and if the transmission spectrum uses wavelengths as arguments, the FSR is a wavelength difference corresponding to adjacent transmission peaks. The maximum condition of FP filter interference is that the optical path difference of adjacent beams is equal to an integer multiple of the wavelength of the incident light: 2d=mλ. If the light source is non-monochromatic, different orders of spectral overlap may occur. Assuming that the optical path difference Δ is 2d or an integer multiple of 2d at the center of the F-P filter, Δ=2d=mλ 2＝(m+1)λ1, that is, the m+1st-order interference of the incident light of the wavelength λ 1 and the m-th-order interference fringe of the incident light of the wavelength λ 2 overlap, the difference between λ 1 and λ 2 is Δλ, and λ0 is the average wavelength of λ 1 and λ 2. If the difference in wavelengths in the light source is less than Δλ, then this overlap will not occur. The larger the cavity length d is, the thinner and narrower the transmission spectrum of the tunable FP filter is; the larger the specular reflectivity R m, the narrower the transmission spectrum of the tunable F-P filter. Finesse F is defined as the ratio of the wavelength difference FSR corresponding to adjacent transmission peaks to the full width half maximum FWHM: /(I)
The tunable FP filter 112 is driven with a "DDS signal generator + amplification circuit" scheme, where DDS is a direct digital frequency synthesizer (DIRECT DIGITAL Systhesizer) that has the advantages of low cost, low power consumption, high resolution, and fast switching time compared to conventional frequency synthesizers. The basic structure of the device comprises four parts, namely a phase accumulator, a phase modulator, a waveform data table ROM, a D/A converter and the like: two main parameters are provided, one is a frequency word, generally an integer, and the size of the number is inversely related to the size of the output frequency; one is a phase word and the magnitude of the number controls the phase offset of the output signal. The phase accumulator is the core of the whole DDS, where phase accumulation is done, generating a phase code. Assuming that the input of the phase accumulator is a frequency word input K ', representing the phase increment, let its bit width be p, satisfy the equation K' =2p×f OUT/fCLK,fOUT be the frequency of the output signal, and f CLK be the clock frequency. If the number of the sampling data points is 4096, 4096 voltage values are output corresponding to each driving process, and a DAC chip with high enough resolution is required to achieve a good driving effect, and the proposed resolution is larger than 12 bits. The saw-tooth wave driving scheme is adopted, and the peak voltage and the bias voltage of the amplifying circuit are designed to reach the required sweep frequency wavelength range. The minimum value V min of the adjacent two driving voltages during each driving process is expressed as: A is the amplification factor of an amplifying circuit; deltaV is the range of DAC output voltages; LSB represents the resolution of the DAC. Amplified spontaneous emission ASE of the SOA111 is amplified after passing through the tunable FP filter 112 and goes round in the tunable ring cavity laser unit 11, the spectral line width is narrowed, so that the feedback is continuously filtered, the light in the passband of the filter is continuously amplified, and finally the saturated output power of the SOA is trended, so that stable laser is formed.
The passive optical path unit 12 includes an optical splitter 121 and a plurality of circulators, in one embodiment, four circulators are used, and each of the circulators is numbered in order as a first circulator 122, a second circulator 123, a third circulator 124, and a fourth circulator 125, and it should be noted that the number of circulators is given here for convenience of description, and is not considered as a specific limitation of the scheme. The circulators comprise a first port, a second port and a third port, the first port is communicated with the second port in one way, and the second port is communicated with the third port in one way; the input end of the optical splitter 121 is in optical path connection with the second output end of the optical fiber coupler 115, the output end of the optical splitter 121 is in optical path connection with the first ports of a plurality of circulators respectively, the second ports of the circulators are in optical path connection with an optical fiber sensor respectively, and the third ports of the circulators are all in optical path connection with the circuit module 2; the second port of each circulator receives the excitation light signal sent by the optical fiber sensor and the reflected light signal of the optical fiber sensor, and outputs the reflected light signal to the circuit module 2 in one direction through the third port.
The laser output by the tunable ring cavity laser unit 11 is incident into the optical fiber sensor, and when the scanning wavelength of the tunable FP filter 112 is equal to the central wavelength of the reflection spectrum of the optical fiber FBG sensor, the optical energy detected by the photodiode of the photoelectric conversion signal conditioning circuit 23 of the circuit module 2 is the largest; at this time, the electric signal output by the photodiode is collected, when the electric signal is maximum, the corresponding sawtooth wave voltage is recorded, and then the reflection wavelength and the related optical parameters are obtained according to the relation between the sawtooth wave voltage and the wavelength. The fastest time t min of tuning between two adjacent fine spectral lines is vop, which is the propagation speed of light in the fiber; n op represents the minimum number of annular turns to achieve stable laser output; l loop denotes the length of the ring cavity of the tunable ring cavity laser unit 11.
The circuit module 2 comprises a temperature control circuit 21, a constant current driving circuit 22, a plurality of photoelectric conversion signal conditioning circuits 23 and a signal acquisition circuit 24; the temperature control circuit 21 and the constant current driving circuit 22 are both arranged at the tunable annular cavity laser unit 11 and are electrically connected with the tunable annular cavity laser unit 11, the temperature control circuit 21 is used for maintaining the temperature stability of the tunable annular cavity laser unit 11, and the constant current driving circuit 22 is used for driving the tunable annular cavity laser unit 11 to stably work; the input ends of the photoelectric conversion signal conditioning circuits 23 are connected with the output ends of the passive optical path units 12, and are used for carrying out photoelectric conversion on the reflected light signals of the optical fiber sensors correspondingly and amplifying and filtering the signals after photoelectric conversion; the input end of the signal acquisition circuit 24 is electrically connected with the output ends of the photoelectric conversion signal conditioning circuits 23 in a one-to-one correspondence manner, and is used for performing analog-to-digital conversion processing on the output signals of the photoelectric conversion signal conditioning circuits 23. In addition, as shown in fig. 1, in order to provide stable operation conditions, a portion of a power supply 25 is also provided for supplying power to the temperature control circuit 21, the constant current drive circuit 22, the plurality of photoelectric conversion signal conditioning circuits 23, and the signal acquisition circuit 24.
The SOA111 is a heat-generating optical power device, a semiconductor refrigeration piece TEC, a thermistor and a laser body are integrally packaged, the temperature control circuit 21 controls the TEC of the SOA111, acquires the surface temperature of the SOA111 through a temperature sensing signal of a thermistor acquisition port and the SOA111, and feeds back and adjusts the refrigerating capacity of the semiconductor refrigeration piece TEC, so that the temperature of the cold end of the semiconductor refrigeration piece TEC attached to the SOA111 is kept stable, and the SOA111 is kept in a stable working state. The thermistor can indicate the current temperature of the surface of the SOA111 by the magnitude of the total resistance of the series of precision resistors of low temperature drift and constitute a closed loop feedback. The resistance temperature curve of the thermistor is nonlinear, and the resistance at a specific temperature can be obtained through table lookup, so that the corresponding surface temperature of the SOA111 is indirectly obtained, and details are omitted here.
The constant current driving circuit 22 is used for driving the main excitation component of the tunable ring cavity laser unit 11, namely, the SOA111, the output end of the constant current driving circuit 22 is directly welded with the driving pins of the SOA111, the constant current driving circuit 22 is composed of a constant current driving chip and surrounding circuits thereof, the chip comprises multiple paths of precise current output ports, each channel is programmable and comprises a single power pin, the full-scale output is 300mA, and the SOA can be driven by adopting a single path or multiple paths. The chip is connected to the circuit module in an SPI communication mode, and the fastest communication clock supports 50MHz. The constant current driving chip can be a MAX16807 chip, the number of output pins connected in parallel is different, and the output current is correspondingly changed.
The signal acquisition circuit 24 comprises an analog-to-digital conversion chip and an FPGA chip; each input channel of the analog-to-digital conversion chip ADC is electrically connected with the output ends of the photoelectric conversion signal conditioning circuits 23 in a one-to-one correspondence manner; at least two paths of input channels of an analog-to-digital conversion chip ADC are alternately opened, the output signals of a plurality of photoelectric conversion signal conditioning circuits 23 are subjected to analog-to-digital conversion, and the converted digital quantity is sent to a FIFO buffer module in an FPGA chip for storage. The analog-to-digital conversion chip ADC is used for four-channel electric signal acquisition based on a double-CMOS pipeline multi-step converter, has the lowest sampling rate of 1MHz and 14-bit resolution, adopts SPI protocol to realize communication with the FPGA, and internally comprises two independent ADC modules. Taking a structure corresponding to four circulators as an example, two groups of four input channels are used by the analog-digital conversion chip ADC, wherein one group of input channels are A0 and B0, and the other group of input channels are A1 and B1, so that four-channel signal acquisition is completed once in two acquisition clock cycles, t0 is the acquisition time of the channels A0 and B0, and t1 is the acquisition time of the channels A1 and B1. The FPGA chip and the peripheral interface circuit mainly have the functions of receiving, temporarily storing, processing, calculating and subsequent interface communication of signals, and the FPGA chip is used for carrying out parallel data and acquisition processing calculation and matching with a high-speed DDR memory chip due to higher frequency of acquired signals and larger data volume, so that the processing capability is high, the operation speed is high, and the data is finished and processed at high speed.
Fig. 3 shows a signal acquisition circuit 24 for acquiring and converting an ADC into a digital signal, and dividing the whole acquisition process into seven states by using a state machine transfer method:
1. Initial state: setting a chip selection signal and a clock signal to be high level, and writing serial port communication to be high-resistance state;
2. a writing state, setting serial port communication writing as a specified command, including a communication address, two-stage register setting and the like, and simultaneously pulling down a chip selection signal and outputting a clock signal;
3. a waiting state, setting waiting time according to manual time sequence diagram requirements, and pulling down a chip selection signal in the waiting state;
4. the conversion state 1 is used for receiving and converting input signals of the two ADC input channels A0 and B0 and writing a transmitting empty instruction into serial communication;
5. Response state 1: outputting data converted by the two ADC input channels A0 and B0 to an output end;
6. a conversion state 2, receiving input signals of the two ADC of A1 and B1, converting, and writing a transmission empty instruction into serial port communication;
7. response state 2: and outputting the data converted by the two ADC input channels A1 and B1 to an output end.
In addition, the invention provides a distributed optical fiber sensing multi-feature hybrid demodulation method, which is characterized in that the distributed optical fiber sensing multi-feature hybrid demodulation system is constructed, after a signal processing module 3 acquires the photoelectric conversion and signal preprocessing result output by a circuit module 2, the signal processing module 3 sequentially executes a variable threshold light intensity extraction step, a centroid method wavelength extraction step and an FFT phase information extraction step, and packages and sends the demodulated result to an upper computer.
As shown in fig. 2, the working process of the signal processing module 3 mainly includes a variable threshold light intensity extraction step, a centroid method wavelength extraction step, an FFT phase information extraction step, and a demodulation information transmission step. The following description will be given separately.
S31, a variable threshold light intensity extraction step of the signal processing module 3, referring to FIG. 5, specifically comprises the following steps:
S301: determining the maximum variable and a threshold Th: the method comprises the steps of comparing the thresholds of the digital quantity of the analog-to-digital conversion processing corresponding to one path of photoelectric conversion signal conditioning circuit 23 output by a signal acquisition circuit 24 one by one, and taking the maximum value of the output digital quantity as the maximum variable output by the path; determining the size of a threshold Th according to a certain proportion of the maximum variable; the FPGA is internally provided with a variable register of the most value, which is used for temporarily storing the value N max of the variable of the most value; and in the temporary storage process, the variable of the maximum value in the variable register is written to be unchanged, and the variable register of the maximum value is set to be zero in the beginning stage of the next spectrum acquisition, so that the variable threshold processing work is realized. In a preferred embodiment, the threshold value Th is determined in proportion to the maximum variable, and 75% of the maximum variable is used as the threshold value Th. It should be noted that, the threshold value of the digital quantity of each path of analog-to-digital conversion process needs to be determined by a corresponding maximum variable, and the maximum variables of different inputs are not necessarily equal.
S302: judging the initial state: judging the size relation between the data points N i+1、Ni and Th, if N i+1 > Th and N i < Th are satisfied, entering the next step S303; n i and N i+1 are digital quantities corresponding to sampling moments i and i+1 respectively, and sampling periods of intervals between adjacent sampling moments are fixed; referring to the flow of fig. 4, it is determined whether N i+1 > Th and N i < Th are satisfied, if not, i increases 1, and the condition comparison is performed again, if N i+1 > Th is satisfied and N i < Th condition or the current i has reached an upper limit, for example 2048 in fig. 4, the comparison process is stopped, the value of N i+1 is written into the variable register of the maximum value as the value of the maximum value variable, until the number of the current analog-digital conversion process is completely compared.
S303: and (3) rising state judgment: if N i+1>Ni > Th is met, caching the data points meeting the condition into a buffer module of the FPGA; each data point and sequence value are marked and proceed to the next step S303.
S304: judging the falling state: if N i>Ni+1 > Th is met, caching the data points meeting the condition into a buffer module of the FPGA; the data points and the sequence values are marked to proceed to the next step S305.
S305: judging a termination state: if N i+1 < Th and N i > Th are met, the process jumps back to step S302 to continue searching until searching ends to stop the thresholding intensity extraction.
S32, a centroid method wavelength extraction step of the signal processing module 3 is to extract wavelength information from a spectrum corresponding to each data point exceeding a threshold Th through a centroid peak finding algorithm, take an abscissa as a bit vector of a particle system, take an ordinate as the mass of the particle system, allocate a weighting coefficient to each data, take a weighted average of all data as a wavelength lambda B： of the obtained optical fiber FBG sensor, wherein x j represents a sequence value, y j represents a light intensity value, and i+1 and k are sequence numbers of the sequence value.
S33, the FFT phase information extraction step of the signal processing module 3 is to extract a time domain signal through fast Fourier transformation, and then complete the calculation of a frequency domain signal extremum of the optical fiber FP sensor by adopting a point-by-point comparison method: Wherein x (K) represents a frequency domain value; x 1(s) represents a time-domain sampling point; s represents a sequence index of time sequence sampling points; w N/2 is N/2 times unit root; k is an index of frequency domain values, k=0, 1,2,..n-1; n is the number of sample points for which the FFT transformation is performed.
And S34, after the demodulation information extraction is completed, a serial port communication mode is adopted to complete the multi-channel demodulation result information splicing and sending functions. Because the serial communication process involves the transmission of the cross-clock domain signals, after receiving the demodulation results of the multiple channels, the serial communication process prolongs the reading time of the information of each channel, packages the information and sends the information to the upper computer for display. The process may be transmitted in a wired or wireless manner.
As shown in fig. 5, in order to accelerate the signal processing process, a multithread parallel processing mode is adopted to divide the overall time sequence of the signal processing module, and the first stage is a signal acquisition process and performs the maximum value judgment at the same time; and extracting spectral light intensity, wavelength and phase information at the beginning of the second spectrum acquisition, and finishing demodulation result transmission in the third stage.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.
Claims (2)
1. The distributed optical fiber sensing multi-feature hybrid demodulation system is characterized by comprising:
The optical path module (1) is in optical path connection with a plurality of optical fiber sensors; the optical path module (1) is used for generating an excitation light signal and outputting the excitation light signal to the optical fiber sensors in a unidirectional manner, and the optical path module (1) also receives reflected light signals of the optical fiber sensors in a unidirectional manner and further outputs the reflected light signals in a unidirectional manner outwards;
The circuit module (2) is connected with the optical path module (1), and the circuit module (2) drives the optical path module (1) to work on one hand and receives reflected light signals of a plurality of optical fiber sensors which are output in one direction by the optical path module (1) on the other hand, and performs photoelectric conversion and signal preprocessing on the reflected light signals;
the signal processing module (3) is electrically connected with the output end of the circuit module (2), and the signal processing module (3) demodulates the output signal of the circuit module (2) sequentially through a variable threshold light intensity extraction step, a centroid method wavelength extraction step and an FFT phase information extraction step;
The optical path module (1) comprises a tunable ring cavity laser unit (11) and a passive optical path unit (12); the output end of the tunable ring cavity laser unit (11) is respectively connected with the input end of the tunable ring cavity laser unit and the input end of the passive optical path unit (12) in an optical path way, the passive optical path unit (12) is also connected with a plurality of optical fiber sensors in an optical path way, excitation light signals are output to the plurality of optical fiber sensors through the passive optical path unit (12), and the passive optical path unit (12) also receives reflected light signals of the plurality of optical fiber sensors; the plurality of optical fiber sensors comprise optical fiber FBG sensors and optical fiber FP sensors;
The tunable ring cavity laser unit (11) comprises an SOA (111), a first optical isolator (113), a tunable FP filter (112), a second optical isolator (114) and an optical fiber coupler (115) which are sequentially arranged; the output end of the SOA (111) is in optical path connection with the input end of a first optical isolator (113), the output end of the first optical isolator (113) is in optical path connection with the input end of a tunable FP filter (112), the output end of the tunable FP filter (112) is in optical path connection with the input end of a second optical isolator (114), the output end of the second optical isolator (114) is in optical path connection with the input end of an optical fiber coupler (115), the first output end of the optical fiber coupler (115) is in optical path connection with the input end of the SOA (111), and the second output end of the optical fiber coupler (115) is in optical path connection with a passive optical path unit (12); the ratio of output light of the first output end and the second output end of the optical fiber coupler (115) is 10%:90%;
The passive optical path unit (12) comprises an optical splitter (121) and a plurality of circulators, wherein the circulators comprise a first port, a second port and a third port, the first port is in unidirectional communication with the second port, and the second port is in unidirectional communication with the third port; the input end of the optical splitter (121) is in optical path connection with the second output end of the optical fiber coupler (115), the output end of the optical splitter (121) is in optical path connection with the first ports of a plurality of circulators respectively, the second ports of the circulators are in optical path connection with an optical fiber sensor respectively, and the third ports of the circulators are all in optical path connection with the circuit module (2); the second port of each circulator not only transmits an excitation light signal to the optical fiber sensor, but also receives a reflected light signal of the optical fiber sensor, and the reflected light signal is unidirectionally output to the circuit module (2) through the third port;
The circuit module (2) comprises a temperature control circuit (21), a constant current driving circuit (22), a plurality of photoelectric conversion signal conditioning circuits (23) and a signal acquisition circuit (24); the temperature control circuit (21) and the constant current driving circuit (22) are both arranged at the tunable annular cavity laser unit (11) and are electrically connected with the tunable annular cavity laser unit (11), the temperature control circuit (21) is used for maintaining the temperature stability of the tunable annular cavity laser unit (11), and the constant current driving circuit (22) is used for driving the tunable annular cavity laser unit (11) to stably work; the input ends of the photoelectric conversion signal conditioning circuits (23) are connected with the output ends of the passive optical path units (12), the reflected light signals of the optical fiber sensors are correspondingly subjected to photoelectric conversion, and the signals after photoelectric conversion are amplified and filtered; the input end of the signal acquisition circuit (24) is electrically connected with the output ends of the photoelectric conversion signal conditioning circuits (23) in a one-to-one correspondence manner, and is used for carrying out analog-to-digital conversion processing on the output signals of the photoelectric conversion signal conditioning circuits (23);
The signal acquisition circuit (24) comprises an analog-to-digital conversion chip and an FPGA chip; each input channel of the analog-to-digital conversion chip is electrically connected with the output ends of the photoelectric conversion signal conditioning circuits (23) in a one-to-one correspondence manner; at least two paths of input channels of the analog-to-digital conversion chip are alternately opened, the output signals of a plurality of photoelectric conversion signal conditioning circuits (23) are subjected to analog-to-digital conversion, and the converted digital quantity is sent to a FIFO buffer module in the FPGA chip for storage;
The demodulation method of the distributed optical fiber sensing multi-feature hybrid demodulation system specifically comprises the following steps: after the signal processing module (3) acquires the photoelectric conversion and signal preprocessing results output by the circuit module (2), the signal processing module (3) sequentially executes a variable threshold light intensity extraction step, a centroid method wavelength extraction step and an FFT phase information extraction step, and packages and sends the demodulated results to an upper computer;
the variable threshold light intensity extraction step of the signal processing module (3) comprises the following steps:
S301: determining the maximum variable and a threshold Th: the method comprises the steps of comparing thresholds of digital quantities of analog-to-digital conversion processing corresponding to a path of photoelectric conversion signal conditioning circuit (23) output by a signal acquisition circuit (24) one by one, and taking the maximum value of the output digital quantities as the maximum variable of the output path; determining the size of a threshold Th according to a certain proportion of the maximum variable;
s302: judging the initial state: judging the size relation between the data points N i+1、Ni and Th, if N i+1 > Th and N i < Th are satisfied, entering the next step S303; n i and N i+1 are digital quantities corresponding to sampling moments i and i+1 respectively, and sampling periods of intervals between adjacent sampling moments are fixed; judging whether N i+1 > Th and N i < Th are met or not, if not, i automatically increases by 1, and comparing the conditions again, if N i+1 > Th is met and N i < Th or the current value of i reaches the upper limit, stopping the comparison process, and writing the value of N i+1 as the value of the maximum variable into the maximum variable register until all the digital quantities of the current analog-digital conversion process are compared;
s303: and (3) rising state judgment: if N i+1>Ni > Th is met, caching the data points meeting the condition into a buffer module of the FPGA; marking each data point and sequence value and proceeding to the next step S303;
S304: judging the falling state: if N i>Ni+1 > Th is met, caching the data points meeting the condition into a buffer module of the FPGA; marking each data point and sequence value to enter the next step S305;
S305: judging a termination state: if N i+1 < Th and N i > Th are satisfied, the process jumps back to step S302 to continue searching until searching is finished and the variable threshold light intensity extraction is stopped;
The centroid method wavelength extraction step of the signal processing module (3) is to extract wavelength information from the spectrum corresponding to each data point exceeding a threshold Th through a centroid peak finding algorithm, take the abscissa as the bit vector of a particle system and the ordinate as the mass of the particle system, allocate a weighting coefficient to each data, take the weighted average of all data as the wavelength lambda B： of the optical fiber FBG sensor, wherein x j represents a sequence value, y j represents a light intensity value, and i+1 and k are the sequence numbers of the sequence value;
The FFT phase information extraction step of the signal processing module (3) is to extract a time domain signal through fast Fourier transformation, and then complete the calculation of the frequency domain signal extremum of the optical fiber FP sensor by adopting a point-by-point comparison method: Wherein x (K) represents a frequency domain value; x 1(s) represents a time-domain sampling point; s represents a sequence index of time sequence sampling points; w N/2 is N/2 times unit root; k is an index of frequency domain values, k=0, 1,2,..n-1; n is the number of sample points for which the FFT transformation is performed.
2. The distributed optical fiber sensing multi-feature hybrid demodulation system of claim 1 wherein the threshold Th is sized in proportion to the maximum variable and assigned to the threshold Th in 75% of the maximum variable.
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