Optical fiber expansion demodulation method, device and system of parallel measurement optical frequency domain reflection technology

Abstract

The invention discloses an optical fiber expansion demodulation method for a parallel measurement optical frequency domain reflection technology. The method comprises the following steps: obtaining mixed reference signals of all sensing optical fibers; acquiring a reference spectrum of each fiber bragg grating in the mixed reference signal according to the wavelength bandwidth of each fiber bragg grating; obtaining mixed measurement signals of all sensing optical fibers; according to the wavelength bandwidth of each fiber bragg grating, obtaining the measurement spectrum of each fiber bragg grating in the mixed measurement signal; performing drift demodulation on the reference spectrum and the measurement spectrum of each fiber bragg grating to obtain a central wavelength drift distance of each fiber bragg grating; and according to the central wavelength drift distance of each fiber grating, the central wavelength drift spectrum of each sensing fiber is obtained through combination. According to the optical fiber expansion demodulation method, the number of sensing optical fibers in a parallel channel can be increased without sacrificing the spatial resolution and precision of system sensing. The invention discloses an optical fiber expansion demodulation device based on the optical fiber expansion demodulation method and a parallel measurement optical frequency domain reflection system.

Description

Technical Field

[0001] The present invention relates to optical frequency domain reflection technology, and in particular to an optical fiber capacity expansion demodulation method, device and system for parallel measurement of optical frequency domain reflection technology. Background Art

[0002] With the rapid development of optical fiber communication technology, optical fiber sensing technology has quickly become an important component of sensing technology. Compared with traditional sensing technology, optical fiber sensing technology has many advantages, such as high sensitivity, electrical insulation, ability to be used in high and low temperature environments, corrosion resistance, and electromagnetic interference resistance, which has attracted extensive attention from researchers.

[0003] Optical Frequency Domain Reflectometry (OFDR) is a fiber optic sensing and measurement technology. Its working principle is to use the Rayleigh backscattering phenomenon when light propagates in the optical fiber, and to detect the changes in physical parameters along the optical fiber, such as temperature and strain, by analyzing the frequency changes of the optical signal emitted by the light source in the optical fiber. It plays an important role in national and civil perimeter security monitoring, oil and gas pipeline monitoring, wind turbine health monitoring, deep sea and submarine earthquake monitoring, etc.

[0004] In order to realize the signal collection of multiple sensing fibers, the Chinese patent application number CN202210554559.3 discloses that in the optical frequency domain reflectometer, the signals of different sensing fibers can be distinguished according to the unique Rayleigh scattered light between each sensing fiber, and a coupler is used instead of an optical switch to realize the parallel collection of multi-channel data, and then the wavelength drift spectrum of each sensing fiber is demodulated by a cross-correlation algorithm to realize multi-channel sensing. In addition, the principle of this technical solution is analyzed in the literature (Lv T, WeiR M, Zhou DP, Peng W, Chen L, Bao X Y. Multiple optical fiber sensing with asingle data channel of optical frequency-domain reflectometry [J]. OpticsLetters, 2022, 47(16): 4068-4071.).

[0005] However, there is a mutually restrictive relationship between the number of sensing optical fibers in the parallel channel and the sensing performance of the system. That is, as the number of sensing optical fibers in the parallel channel increases, the spatial resolution and accuracy of the system sensing will gradually decrease. Summary of the invention

[0006] In order to solve the above-mentioned deficiencies of the prior art, the present invention provides an optical fiber capacity expansion demodulation method for parallel measurement of optical frequency domain reflection technology, which can increase the number of sensing optical fibers in parallel channels without sacrificing the spatial resolution and accuracy of system sensing.

[0007] The present invention provides an optical fiber capacity expansion demodulation device and a parallel measurement optical frequency domain reflection system based on the optical fiber capacity expansion demodulation method.

[0008] The technical problem to be solved by the present invention is achieved through the following technical solutions: A fiber capacity expansion demodulation method for parallel measurement of optical frequency domain reflection technology is used to demodulate a multi-channel fiber optic sensing module, wherein the multi-channel fiber optic sensing module includes a plurality of sensing optical fibers arranged in parallel, each sensing optical fiber is provided with a grating array, each grating array is composed of a plurality of fiber gratings, and the fiber gratings in the same sensing optical fiber have the same wavelength bandwidth, and the fiber gratings in different sensing optical fibers have different wavelength bandwidths; the fiber capacity expansion demodulation method comprises the following steps: Step 100: obtaining mixed reference signals of all sensing optical fibers; Step 200: acquiring a reference spectrum of each fiber Bragg grating in the mixed reference signal according to the wavelength bandwidth of each fiber Bragg grating; Step 300: obtaining mixed measurement signals of all sensing optical fibers; Step 400: acquiring a measurement spectrum of each fiber Bragg grating in the mixed measurement signal according to the wavelength bandwidth of each fiber Bragg grating; Step 500: performing drift demodulation on the reference spectrum and the measurement spectrum of each fiber Bragg grating to obtain the center wavelength drift of each fiber Bragg grating; Step 600: According to the central wavelength drift of each fiber grating, the central wavelength drift spectrum of each sensing optical fiber is obtained by combining.

[0009] Furthermore, in step 200, according to the wavelength bandwidth of each fiber Bragg grating, the step of obtaining the reference spectrum of each fiber Bragg grating in the mixed reference signal is as follows: Step 210: Performing a fast Fourier transform on the mixed reference signal to convert the mixed reference signal from the time domain to the range domain; Step 220: According to the position range of each fiber grating, the mixed reference signal is windowed and valued to obtain multiple groups of first window data; Step 230: performing an inverse fast Fourier transform on each group of first window data to convert the mixed reference signal in each group of first window data from the range domain to the frequency domain; Step 240: According to the wavelength bandwidth of each fiber grating, a reference spectrum corresponding to each fiber grating is intercepted in each group of first window data.

[0010] Furthermore, in step 400, according to the wavelength bandwidth of each fiber Bragg grating, the steps of obtaining the measurement spectrum of each fiber Bragg grating in the mixed measurement signal are as follows: Step 410: Performing a fast Fourier transform on the mixed measurement signal to convert the mixed measurement signal from the time domain to the distance domain; Step 420: windowing the mixed measurement signal according to the position range of each fiber grating to obtain multiple groups of second window data; Step 430: performing an inverse fast Fourier transform on each set of second window data to convert the mixed measurement signal in each set of first window data from the distance domain to the frequency domain; Step 440: According to the wavelength bandwidth of each fiber grating, intercept the measurement spectrum corresponding to each fiber grating in each group of first window data.

[0011] Furthermore, the central wavelengths of the fiber gratings in the same sensing optical fiber are the same or similar.

[0012] Furthermore, the optical fiber lengths of the sensing optical fibers are the same or different.

[0013] Furthermore, all the sensing optical fibers are provided with optical fiber gratings at the same distance, or only some of the sensing optical fibers are provided with optical fiber gratings at the same distance.

[0014] Furthermore, the lengths of the fiber gratings in the same sensing optical fiber are the same or different.

[0015] Furthermore, the spacings of the fiber gratings in the same sensing optical fiber are the same or different.

[0016] A fiber capacity expansion demodulation device for parallel measurement of optical frequency domain reflection technology includes a processor and a memory. The memory stores a computer program for execution by the processor. When the processor executes the computer program, the processor performs the above-mentioned fiber capacity expansion demodulation method.

[0017] A parallel measurement optical frequency domain reflection system comprises a data acquisition device, an optical frequency domain reflectometer, an optical fiber coupler, a multi-channel optical fiber sensing module and the above-mentioned optical fiber expansion demodulation device, wherein the multi-channel optical fiber sensing module comprises a plurality of sensing optical fibers arranged in parallel, each sensing optical fiber is provided with a grating array, each grating array is composed of a plurality of optical fiber gratings, and the optical fiber gratings in the same sensing optical fiber have the same wavelength bandwidth, and the optical fiber gratings in different sensing optical fibers have different wavelength bandwidths; the optical frequency domain reflectometer is respectively connected to each sensing optical fiber through the optical fiber coupler, and the optical fiber expansion demodulation device is connected to the optical frequency domain reflectometer.

[0018] The present invention has the following beneficial effects: the fiber capacity expansion demodulation method of the present invention forms the fiber grating array by respectively manufacturing the fiber grating array in each parallel-arranged sensing optical fiber, and the fiber gratings in the same sensing optical fiber have the same wavelength bandwidth, and the fiber gratings in different sensing optical fibers have different wavelength bandwidths. During the fast Fourier inverse operation, the reference signals and test signals of different sensing optical fibers are separated into different wavelength ranges of the spectrum by utilizing the difference in wavelength bandwidths, thereby realizing signal separation of different sensing optical fibers during parallel measurement in the optical frequency domain, so that different sensing optical fibers will not affect each other during signal demodulation, and the number of sensing optical fibers in the parallel channel can be increased without sacrificing the spatial resolution and accuracy of system sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the structure of the parallel measurement optical frequency domain reflection system provided by the present invention.

[0020] Figure 2 A schematic diagram of the structure of an optical frequency domain reflectometer in the parallel measurement optical frequency domain reflectometer system provided by the present invention.

[0021] Figure 3 A flowchart of the optical fiber capacity expansion and demodulation method provided by the present invention.

[0022] Figure 4 This is a block diagram of the steps of step 200 in the optical fiber capacity expansion demodulation method provided by the present invention.

[0023] Figure 5 This is a block diagram of the steps of step 400 in the optical fiber capacity expansion demodulation method provided by the present invention.

[0024] Figure 6 It is a spectrum diagram of a mixed reference signal or a mixed measurement signal in the distance domain in the optical fiber capacity expansion demodulation method provided by the present invention.

[0025] Figure 7 It is a spectrum diagram of a mixed reference signal or a mixed measurement signal in the frequency domain in the optical fiber capacity expansion demodulation method provided by the present invention.

[0026] Figure 8The central wavelength drift spectrum of each sensing optical fiber at different measurement values ​​in the optical fiber capacity expansion demodulation method provided by the present invention. DETAILED DESCRIPTION

[0027] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments, examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0028] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0029] In addition, the terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second", and "third" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0030] In the present invention, unless otherwise clearly specified and limited, the terms "install", "connect", "connect", "fix", "set" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0031] Embodiment 1 like Figure 1As shown, a parallel measurement optical frequency domain reflection system includes a data acquisition device 2, an optical frequency domain reflectometer 3, a first optical fiber coupler 4, a multi-channel optical fiber sensing module 5 and an optical fiber expansion demodulation device 1, wherein the multi-channel optical fiber sensing module 5 includes a plurality of sensing optical fibers 51 arranged in parallel, each sensing optical fiber 51 is provided with a grating array, each grating array is composed of a plurality of optical fiber gratings 52, and each optical fiber grating 52 in the same sensing optical fiber 51 has the same wavelength bandwidth, and each optical fiber grating 52 in different sensing optical fibers 51 has different wavelength bandwidths; the optical frequency domain reflectometer 3 is respectively connected to each sensing optical fiber 51 through the first optical fiber coupler 4, the data acquisition device 2 is connected to the optical frequency domain reflectometer 3, and the data acquisition device 2 is connected to the optical fiber expansion demodulation device 1.

[0032] During operation, the measuring optical signal emitted by the optical frequency domain reflectometer 3 is divided into multiple paths by the first optical fiber coupler 4, and each path of the measuring optical signal enters each sensing optical fiber 51 respectively. The Rayleigh scattered light generated by each sensing optical fiber 51 is aggregated by the first optical fiber coupler 4 and input into the optical frequency domain reflectometer 3. The optical frequency domain reflectometer 3 converts the Rayleigh scattered light into a beat frequency signal and outputs it to the data acquisition device 2. The data acquisition device 2 collects the beat frequency signal, obtains a reference signal and a measurement signal, and then outputs them to the optical fiber expansion demodulation device 1. The optical fiber expansion demodulation device 1 demodulates the reference signal and the measurement signal, and finally obtains the wavelength drift spectrum of each sensing optical fiber 51.

[0033] In this embodiment, the first optical fiber coupler 4 is a 1*N coupler, which can be connected to at most N sensing optical fibers 51 at the same time, where N≥2.

[0034] like Figure 2 As shown, the optical frequency domain reflectometer 3 includes a tunable laser 31, a second fiber coupler 32, an auxiliary interferometer arm, a main interferometer arm, a first photoelectric balance detector 314, a second photoelectric balance detector 315 and a third photoelectric balance detector 316. The tunable laser 31 is connected to the auxiliary interferometer arm and the main interferometer arm respectively through the second fiber coupler 32, the auxiliary interferometer arm is connected to the first photoelectric balance detector 314, the main interferometer arm is connected to the second photoelectric balance detector 315 and the third photoelectric balance detector 316 respectively, and the first photoelectric balance detector 314, the second photoelectric balance detector 315 and the third photoelectric balance detector 316 are all connected to the data acquisition device 2.

[0035] The auxiliary interference arm includes a first fiber circulator 33, a third fiber coupler 34, a delay fiber 35, a first Faraday rotator reflector 36 and a second Faraday rotator reflector 37. The first port of the first fiber circulator 33 is connected to the second fiber coupler 32, the second port of the first fiber circulator 33 is connected to the first port of the third fiber coupler 34, and the third port of the first fiber circulator 33 is connected to the first photoelectric balanced detector 314; the second port of the third fiber coupler 34 is connected to the first photoelectric balanced detector 314, the third port of the third fiber coupler 34 is connected to the first Faraday rotator reflector 36 via the delay fiber 35, and the fourth port of the third fiber coupler 34 is connected to the second Faraday rotator reflector 37.

[0036] The main interferometer arm includes a fourth fiber coupler 38, a polarization controller 39, a second fiber circulator 310, a fifth fiber coupler 311, a first polarization beam splitter 312 and a second polarization beam splitter 313. The first port of the fourth fiber coupler 38 is connected to the second fiber coupler 32, the second port of the fourth fiber coupler 38 is connected to the first port of the fifth fiber coupler 311 via the polarization controller 39, and the third port of the fourth fiber coupler 38 is connected to the first port of the second fiber circulator 310; the second port of the second fiber circulator 310 is connected to the first fiber coupler 4, and the third port of the second fiber circulator 310 is connected to the second port of the fifth fiber coupler 311; the third port of the fifth fiber coupler 311 is connected to the second photoelectric balanced detector 315 and the third photoelectric balanced detector 316 respectively via the first polarization beam splitter 312, and the fourth port of the fifth fiber coupler 311 is connected to the second photoelectric balanced detector 315 and the third photoelectric balanced detector 316 respectively via the second polarization beam splitter 313.

[0037] When in use, the swept-frequency light emitted by the tunable laser 31 passes through the second fiber coupler 32 and is split at a ratio of 1:99, wherein 1% of the swept-frequency light enters the auxiliary interference arm, and the other 99% of the swept-frequency light enters the main interference arm; the swept-frequency light in the auxiliary interference arm is divided into two beams after passing through the first fiber circulator 33 and the third fiber coupler 34, wherein one of the swept-frequency light beams passes through the delay fiber 35 and reaches the first Faraday rotator reflector 36, and the other swept-frequency light beam directly reaches the second Faraday rotator reflector 37; the two swept-frequency light beams are respectively reflected by the first Faraday rotator reflector 36 and the second Faraday rotator reflector 37, and then return to the third fiber coupler 34 along the original path to generate a first beat-frequency interference light, which is finally input into the first photoelectric balance detector 314 for photoelectric signal conversion to form a first beat-frequency interference light. frequency signal; the swept-frequency light in the main interference arm is split by the fourth optical fiber coupler 38, and one beam of swept-frequency light passes through the polarization controller 39 to enter the fifth optical fiber coupler 311, and the other beam of swept-frequency light passes through the second optical fiber circulator 310 and enters the first optical fiber coupler 4, and after forming Rayleigh scattered light in each sensing optical fiber 51, it passes through the second optical fiber circulator 310 and enters the fifth optical fiber coupler 311, and the Rayleigh scattered light and the swept-frequency light generate a second beat frequency interference light in the fifth optical fiber coupler 311, and the second beat frequency interference light is split by the fifth optical fiber coupler 311, and then polarized by the first polarization beam splitter 312 and the second polarization beam splitter 313 respectively, and finally input into the second photoelectric balance detector 315 and the third photoelectric balance detector 316 for photoelectric signal conversion to form a second beat frequency signal.

[0038] The data acquisition device 2 uses the first beat frequency signal as a sampling clock signal to acquire the second beat frequency signal to obtain time domain data of the reference signal and the measurement signal. When the measurement parameters such as temperature and strain in the target environment do not change, the time domain data acquired by the data acquisition device 2 is the reference signal. When the measurement parameters such as temperature and strain in the target environment change, the time domain data acquired by the data acquisition device 2 is the measurement signal.

[0039] Embodiment 2 like Figure 3 As shown, a fiber capacity expansion demodulation method for parallel measurement of optical frequency domain reflection technology is used in the parallel measurement of optical frequency domain reflection system described in Example 1 to demodulate the multi-channel optical fiber sensor module; the fiber capacity expansion demodulation method comprises the following steps: Step 100: Obtain mixed reference signals of all sensing optical fibers.

[0040] In step 100, all the sensing optical fibers are first connected to the first optical fiber coupler, the first optical fiber coupler has a plurality of connection ports, and each sensing optical fiber is connected to the first optical fiber coupler through a corresponding connection port. When the measurement parameters such as temperature and strain in the target environment do not change, the optical frequency domain reflectometer simultaneously receives the Rayleigh scattered light of all the sensing optical fibers through the first optical fiber coupler, and outputs a second beat frequency signal to the data acquisition device, so that the data acquisition device can acquire the mixed reference signal and transmit it to the optical fiber expansion demodulation device.

[0041] It can be seen that when the data acquisition device collects the reference signal, the optical frequency domain reflectometer connects all the sensing optical fibers to the first optical fiber coupler at the same time to simultaneously receive the Rayleigh scattered light of all the sensing optical fibers through the first optical fiber coupler. Therefore, the data acquisition device collects only one group of reference signals, and this group of reference signals simultaneously contains the time domain data of all the sensing optical fibers, so it is called a mixed reference signal.

[0042] Step 200: According to the wavelength bandwidth of each fiber Bragg grating, obtain the reference spectrum of each fiber Bragg grating in the mixed reference signal.

[0043] In step 200, the fiber Bragg grating has a central wavelength. When the measurement parameters such as temperature and strain in the target environment change, the central wavelength of the fiber Bragg grating will drift within a certain range. This drift range is the wavelength bandwidth of the fiber Bragg grating. For example, the central wavelength of a fiber Bragg grating is 1550nm. When the measurement parameters such as temperature and strain in the target environment change, the central wavelength of the fiber Bragg grating will drift to 1540nm at the minimum and 1560nm at the maximum. Then the wavelength range of 1540nm-1560nm is the wavelength bandwidth of the fiber Bragg grating.

[0044] Since the wavelength bandwidths of the fiber Bragg gratings in different sensing fibers are different, the central wavelengths of the fiber Bragg gratings in different sensing fibers must also be different, while the central wavelengths of the fiber Bragg gratings in the same sensing fiber can be the same or similar, as long as the central wavelength of the fiber Bragg gratings in the same sensing fiber can drift within the same wavelength bandwidth when the measurement parameters such as temperature and strain in the target environment change.

[0045] Specifically, Figure 4 As shown, in step 200, according to the wavelength bandwidth of each fiber Bragg grating, the steps of obtaining the reference spectrum of each fiber Bragg grating in the mixed reference signal are as follows: Step 210: Perform fast Fourier transform on the mixed reference signal to convert the mixed reference signal from the time domain to the range domain.

[0046] In step 210, after being transformed to the distance domain by fast Fourier transform, the hybrid reference signal has a data length, and the data length corresponds to the fiber length of each sensing fiber. It can be understood that one data point of the hybrid reference signal in the distance domain corresponds to the Rayleigh scattering point of each sensing fiber at the same distance position, and the data volume of each data point is consistent with the number of the sensing fibers. For example, taking four sensing fibers as an example, the data point of the hybrid reference signal at 5m in the distance domain corresponds to the Rayleigh scattering point of the four sensing fibers at the 5m position, and the data point has four values, one value corresponding to one sensing fiber.

[0047] Of course, the fiber lengths of the various sensing fibers may not be the same, in which case the data length of the hybrid reference signal in the distance domain should correspond to the fiber length of the sensing fiber with the longest length, and the amount of data at each data point should not exceed the number of the sensing fibers. For example, continuing to take four sensing fibers as an example, the first sensing fiber, the second sensing fiber, and the third sensing fiber are only 4 meters long, while the fourth sensing fiber is 5 meters long, then the data length of the hybrid reference signal in the distance domain should correspond to the fiber length of the fourth sensing fiber, and the data point of the hybrid reference signal at 4 meters in the distance domain has four values, corresponding to the Rayleigh scattering points of the four sensing fibers at the 4-meter position, but the data point at 5 meters has only one value, corresponding to the Rayleigh scattering point of the fourth sensing fiber at the 5-meter position.

[0048] Step 220: According to the position range of each fiber grating, the mixed reference signal is windowed and valued to obtain multiple groups of first window data.

[0049] In step 220, since the mixed reference signal has been converted from the time domain to the distance domain by fast Fourier transform in advance, each fiber grating can find the corresponding data point range in the mixed reference signal according to its position range in the sensing fiber, thereby distinguishing the distance domain data of each fiber grating from the distance domain data of each ordinary Rayleigh scattering point.

[0050] When taking values ​​with windows, the length of each value window should be adapted to the length of each fiber grating, and the spacing of each value window should be adapted to the spacing of each fiber grating, so that each value window can correspond to the position range of each fiber grating after being placed in the mixed reference signal.

[0051] Among them, a value window or a group of first window data corresponds to the fiber gratings of each sensing optical fiber in the same position range, that is, if fiber gratings are formed in all sensing optical fibers in the same position range, then the corresponding first window data includes the distance domain data of the fiber gratings of all sensing optical fibers in the position range; if fiber gratings are not formed in some sensing optical fibers and fiber gratings are formed in some sensing optical fibers in the same position range, then the corresponding first window data only includes the distance domain data of the fiber gratings of some sensing optical fibers in the position range.

[0052] The lengths of the various value windows are not necessarily the same, that is, the lengths of the fiber gratings in the same sensing fiber can be the same or different. The central wavelength of the fiber grating depends on its refractive index and grating period. Since the central wavelengths of the fiber gratings in the same sensing fiber can be the same or similar, different grating periods can be designed for the fiber gratings in the same sensing fiber, and then the refractive index of each fiber grating is adjusted to make the central wavelengths the same or similar. When the grating periods of each fiber grating are different, the lengths of the fiber gratings in the same sensing fiber will naturally be different.

[0053] The spacing between the value windows is not necessarily the same, that is, the spacing between the fiber gratings in the same sensing fiber can be the same or different, and different sensing fibers can all be formed with fiber gratings in the same position range, or only partially formed with fiber gratings. The position distribution of each fiber grating can be determined according to the position distribution of the measurement points in the target environment.

[0054] Step 230: Perform inverse fast Fourier transform on each group of first window data to convert the mixed reference signal in each group of first window data from the range domain to the frequency domain.

[0055] In step 230, after inverse fast Fourier transform to the frequency domain, since the fiber gratings in different sensing fibers have different wavelength bandwidths, the reference signals of different sensing fibers in the same group of first window data will be separated into different wavelength ranges. Since the fiber gratings in the same sensing fiber have the same wavelength bandwidth, the reference signals of the same sensing fiber in different groups of first window data will be separated into the same wavelength range.

[0056] For example, continuing to take four sensing optical fibers as an example, the wavelength bandwidth of the fiber Bragg grating in the first sensing optical fiber is 1500-1520nm, the wavelength bandwidth of the fiber Bragg grating in the second sensing optical fiber is 1520-1550nm, the wavelength bandwidth of the fiber Bragg grating in the third sensing optical fiber is 1550-1570nm, and the wavelength bandwidth of the fiber Bragg grating in the fourth sensing optical fiber is 1570-1590nm. Figure 6As shown in FIG. 1 , the first window data obtained by windowing contains the distance domain data of the fiber gratings of the four sensing fibers at the same distance position. At this time, the data domain data of the four sensing fibers are mixed together. After being inversely transformed to frequency domain data by fast Fourier transform, as shown in FIG. Figure 7 As shown, there are four peaks in the mixed reference spectrum of the first window data, and these four peaks correspond to the central wavelengths of the fiber gratings of the four sensing optical fibers at the same distance position, and these four peaks are respectively located in the four wavelength ranges of 1500-1520nm, 1520-1550nm, 1550-1570nm and 1570-1590nm.

[0057] Step 240: According to the wavelength bandwidth of each fiber grating, a reference spectrum corresponding to each fiber grating is intercepted in each group of first window data.

[0058] In step 240, since each group of first window data has been converted from the distance domain to the frequency domain through inverse fast Fourier transform, in the mixed reference spectrum converted from each group of first window data, the peaks of the fiber gratings with different wavelength bandwidths are separated into different wavelength ranges. Therefore, the reference spectrum of each fiber grating can be obtained by directly intercepting the spectrum in different wavelength ranges in the converted mixed reference spectrum according to the wavelength bandwidth of each fiber grating.

[0059] Step 300: Acquire mixed measurement signals of all sensing optical fibers.

[0060] In step 300, all the sensing optical fibers are first connected to the first optical fiber coupler. The connection port of each sensing optical fiber on the first optical fiber coupler is the same as the connection port when the mixed reference signal is collected in step 100. When the measurement parameters such as temperature and strain in the target environment change, the optical frequency domain reflectometer simultaneously receives the Rayleigh scattered light of all the sensing optical fibers through the first optical fiber coupler, and outputs a second beat frequency signal to the data acquisition device, so that the data acquisition device can collect the mixed measurement signal and transmit it to the optical fiber expansion demodulation device.

[0061] It can be seen from this that when the data acquisition device collects the measurement signals of each sensing optical fiber, the optical frequency domain reflectometer connects all the sensing optical fibers to the first optical fiber coupler at the same time to simultaneously receive the Rayleigh scattered light of all the sensing optical fibers through the first optical fiber coupler. Therefore, the data acquisition device collects only one group of measurement signals, and this group of measurement signals simultaneously includes the measurement signals of all the sensing optical fibers.

[0062] Step 400: According to the wavelength bandwidth of each fiber Bragg grating, obtain the measurement spectrum of each fiber Bragg grating in the mixed measurement signal.

[0063] In step 400, the measurement spectrum of each fiber Bragg grating in the mixed measurement signal can be obtained by using, but not limited to, the same method as in step 200.

[0064] Specifically, Figure 5 As shown, in step 400, according to the wavelength bandwidth of each fiber Bragg grating, the steps of obtaining the measurement spectrum of each fiber Bragg grating in the mixed measurement signal are as follows: Step 410: Performing a fast Fourier transform on the mixed measurement signal to convert the mixed measurement signal from the time domain to the distance domain; Step 420: windowing the mixed measurement signal according to the position range of each fiber grating to obtain multiple groups of second window data; Step 430: performing an inverse fast Fourier transform on each set of second window data to convert the mixed measurement signal in each set of first window data from the distance domain to the frequency domain; Step 440: According to the wavelength bandwidth of each fiber grating, intercept the measurement spectrum corresponding to each fiber grating in each group of first window data.

[0065] Since the method for obtaining the measurement spectrum of each fiber grating in step 400 of this embodiment is exactly the same as the method for obtaining the reference spectrum of the fiber grating in step 200, the specific contents of each sub-step in step 400 can refer to the sub-steps in step 200 and will not be explained in detail here.

[0066] Step 500: performing drift demodulation on the reference spectrum and the measurement spectrum of each fiber Bragg grating to obtain the central wavelength drift of each fiber Bragg grating.

[0067] In step 500, the reference spectrum and the measurement spectrum of the same fiber Bragg grating are drift demodulated to obtain the center wavelength drift of the fiber Bragg grating before and after the measurement parameters such as temperature, strain, etc. in the target environment change.

[0068] Specifically, a cross-correlation function can be used to perform cross-correlation calculation on the reference spectrum and the measured spectrum of the same fiber grating to obtain the center wavelength drift of the fiber grating, or the center wavelengths of the reference spectrum and the measured spectrum can be respectively obtained by a fitting method, and then the center wavelengths of the reference spectrum and the measured spectrum are subtracted to obtain the center wavelength drift of the fiber grating.

[0069] Step 600: According to the central wavelength drift of each fiber grating, the central wavelength drift spectrum of each sensing optical fiber is obtained by combining.

[0070] In step 600, if Figure 8As shown, by combining the center wavelength drift amounts of each fiber grating in the same sensing fiber, the center wavelength drift spectrum of each sensing fiber can be obtained; when the measurement parameters such as temperature and strain in the target environment change to different degrees, each sensing fiber has a center wavelength drift spectrum with different drift degrees.

[0071] Embodiment 3 A fiber capacity expansion demodulation device for parallel measurement of optical frequency domain reflection technology is used in the parallel measurement of optical frequency domain reflection system described in Example 1 to demodulate the multi-channel optical fiber sensing module; the fiber capacity expansion demodulation device includes a processor and a memory, the memory stores a computer program for execution by the processor, and when the processor executes the computer program, the fiber capacity expansion demodulation method described in Example 2 is performed.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention rather than to limit them. Although the embodiments of the present invention have been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the embodiments of the present invention can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fiber capacity expansion demodulation method for parallel measurement of optical frequency domain reflection technology, characterized in that: The method is used for demodulating a multi-channel optical fiber sensing module, wherein the multi-channel optical fiber sensing module includes a plurality of sensing optical fibers arranged in parallel, each sensing optical fiber is provided with a grating array, each grating array is composed of a plurality of optical fiber gratings, and the optical fiber gratings in the same sensing optical fiber have the same wavelength bandwidth, and the optical fiber gratings in different sensing optical fibers have different wavelength bandwidths; the optical fiber expansion demodulation method comprises the following steps: Step 100: obtaining mixed reference signals of all sensing optical fibers; Step 200: acquiring a reference spectrum of each fiber Bragg grating in the mixed reference signal according to the wavelength bandwidth of each fiber Bragg grating; Step 300: obtaining mixed measurement signals of all sensing optical fibers; Step 400: acquiring a measurement spectrum of each fiber Bragg grating in the mixed measurement signal according to the wavelength bandwidth of each fiber Bragg grating; Step 500: performing drift demodulation on the reference spectrum and the measurement spectrum of each fiber Bragg grating to obtain the center wavelength drift of each fiber Bragg grating; Step 600: According to the central wavelength drift of each fiber grating, the central wavelength drift spectrum of each sensing optical fiber is obtained by combining.

2. The optical fiber capacity expansion demodulation method according to claim 1, characterized in that: In step 200, according to the wavelength bandwidth of each fiber Bragg grating, the steps of obtaining the reference spectrum of each fiber Bragg grating in the mixed reference signal are as follows: Step 210: Performing a fast Fourier transform on the mixed reference signal to convert the mixed reference signal from the time domain to the range domain; Step 220: According to the position range of each fiber grating, the mixed reference signal is windowed and valued to obtain multiple groups of first window data; Step 230: performing an inverse fast Fourier transform on each group of first window data to convert the mixed reference signal in each group of first window data from the range domain to the frequency domain; Step 240: According to the wavelength bandwidth of each fiber grating, a reference spectrum corresponding to each fiber grating is intercepted in each group of first window data.

3. The optical fiber capacity expansion demodulation method according to claim 1, characterized in that: In step 400, according to the wavelength bandwidth of each fiber Bragg grating, the steps of obtaining the measurement spectrum of each fiber Bragg grating in the mixed measurement signal are as follows: Step 410: Performing a fast Fourier transform on the mixed measurement signal to convert the mixed measurement signal from the time domain to the distance domain; Step 420: windowing the mixed measurement signal according to the position range of each fiber grating to obtain multiple groups of second window data; Step 430: performing an inverse fast Fourier transform on each set of second window data to convert the mixed measurement signal in each set of first window data from the distance domain to the frequency domain; Step 440: According to the wavelength bandwidth of each fiber grating, intercept the measurement spectrum corresponding to each fiber grating in each group of first window data.

4. The optical fiber capacity expansion demodulation method according to claim 1, characterized in that: The central wavelengths of the fiber gratings in the same sensing fiber are the same or similar.

5. The optical fiber capacity expansion demodulation method according to claim 1, characterized in that: The optical fiber lengths of the various sensing optical fibers are the same or different.

6. The optical fiber capacity expansion demodulation method according to claim 1, characterized in that: All the sensing optical fibers are formed with optical fiber gratings at the same distance, or only some of the sensing optical fibers are formed with optical fiber gratings at the same distance.

7. The optical fiber capacity expansion demodulation method according to claim 1, characterized in that: The lengths of the fiber Bragg gratings in the same sensing fiber are the same or different.

8. The optical fiber capacity expansion demodulation method according to claim 1, characterized in that: The spacings of the fiber gratings in the same sensing fiber are the same or different.

9. An optical fiber capacity expansion demodulation device for parallel measurement of optical frequency domain reflection technology, comprising a processor and a memory, wherein the memory stores a computer program for execution by the processor, characterized in that: When executing the computer program, the processor performs the optical fiber capacity expansion demodulation method according to claim 1.

10. A parallel measurement optical frequency domain reflection system, further characterized in that it includes a data acquisition device, an optical frequency domain reflectometer, an optical fiber coupler, a multi-channel optical fiber sensing module and the optical fiber expansion demodulation device according to claim 9, wherein the multi-channel optical fiber sensing module includes a plurality of sensing optical fibers arranged in parallel, each sensing optical fiber is provided with a grating array, each grating array is composed of a plurality of optical fiber gratings, and the optical fiber gratings in the same sensing optical fiber have the same wavelength bandwidth, and the optical fiber gratings in different sensing optical fibers have different wavelength bandwidths; the optical frequency domain reflectometer is respectively connected to each sensing optical fiber through the optical fiber coupler, and the optical fiber expansion demodulation device is connected to the optical frequency domain reflectometer.

Images