A quick weak light fiber grating array demodulation device and method based on reflection enhancement points

Abstract

A kind of quick weak light fiber grating array demodulation device and method based on reflection enhancement point belong to optical fiber sensing technical field, the present application is to solve the problem of wavelength grating reflection signal segmentation inaccuracy in prior art high-speed dynamic demodulation, make system demodulation error big.This application includes fast scanning laser, electric pulse signal generator, optical pulse modulator, fiber amplifier, fiber circulator, reflection enhancement point, weak grating array sensing unit, photoelectric conversion module, acquisition module, data analysis processing module and control module.Reflection enhancement point and weak grating array sensing unit are reflected to fast scanning optical pulse signal and obtain reflected signal, the reflected signal of reflection enhancement point is segmented to weak grating array reflected optical pulse signal of any wavelength, after data processing, grating position and center wavelength are obtained.The system uses reflection enhancement point to obtain the grating reflected signal of each wavelength, realizes the high-speed dynamic demodulation of weak grating array sensing unit.

Description

TECHNICAL FIELD

[0001] The application relates to a quick weak fiber grating array demodulation device and method based on reflection enhancement points and belongs to the technical field of fiber sensing. BACKGROUND

[0002] A fiber Bragg grating (FBG) sensor is a wavelength modulation type fiber sensor, which utilizes the linear correspondence between the reflection center wavelength of the FBG and the strain, temperature and other external influences on the FBG sensor to realize the sensing of external physical quantities by demodulating the center wavelength change of the FBG. The sensor has the advantages of small size, high sensitivity, anti-electromagnetic interference and corrosion resistance. By using wavelength division multiplexing (WDM), time division multiplexing (TDM) and combined multiplexing, an FBG grating array sensor can be obtained to realize multipoint sensing. However, the high reflection characteristics of the traditional FBG, the spectral shadow effect and the multiple reflection interference limit its large-scale multiplexing. In recent years, with the emergence of ultra-weak gratings, combined with optical time domain reflectometry (OTDR), sensing based on large-scale fiber grating arrays has been realized.

[0003] In actual engineering applications, such as distributed strain monitoring of an airplane wing, a large bridge and a large ship, the structures to be measured are in a vibrating state, and the traditional static monitoring technology is easy to cause the measurement data to be distorted or even failed. Therefore, it is necessary to design a quick weak grating array demodulation device and method to improve the strain sensing accuracy of the weak grating array under the vibrating working condition.

[0004] Common FBG sensor demodulation methods mainly include a spectrometer detection method, a filter detection method, an interference detection method and a scanning laser detection method. Compared with the other methods, the scanning laser detection method has the advantages of a large detection dynamic range and a fast demodulation speed, and has incomparable advantages in high-speed demodulation.

[0005] The scanning laser detection method realizes multi-wavelength scanning of the weak grating array by step tuning the wavelength of the laser. The scanning laser usually outputs two electric pulse signals: the first electric pulse signal is the same period as the whole scanning process of the laser, and the rising edge of the electric pulse is strictly synchronized with the first wavelength, which is called a period trigger signal; the second electric pulse signal is the same period as the duration of a single wavelength, and the rising edge of the electric pulse is strictly synchronized with the switching of a single wavelength, which is called a wavelength trigger signal; the wavelength scanning range of the laser needs to cover the center wavelengths of all fiber grating sensors, and when the wavelength of the laser output matches the center wavelength of the FBG, the reflection intensity is the highest, so the center wavelength of each fiber grating can be identified by scanning the wavelength of the laser. In the fast demodulation technology of the weak grating array based on the scanning laser, only the reflection signal of each wavelength can be accurately identified in the fast scanning, so that the grating position can be accurately positioned and the center wavelength of the grating can be demodulated. At present, the method for accurately obtaining the reflection signal of each wavelength in the fast scanning process mainly includes:

[0006] First, the laser electric pulse signal segmentation method: the wavelength trigger signal is used as the trigger signal of the data acquisition card, and when the rising edge of a certain wavelength trigger signal arrives, the data acquisition card starts to collect the reflection signal of the weak grating array to the current laser and stores it. This method can accurately collect the reflection signal of each wavelength, but the data acquisition card needs to have higher dynamic response capability, and the data acquisition card also needs to have double-channel acquisition capability for collecting the period trigger signal so as to identify the starting wavelength of a certain scanning period in the fast and continuous measurement. Therefore, the laser electric pulse signal segmentation method needs to use a high-performance and double-channel acquisition card, which is expensive and has high system cost.

[0007] Second, the fusion point segmentation method: this method uses the Fresnel reflection surface formed in the fusion process of the optical fiber to reflect and segment the reflection signal of each wavelength. This method does not rely on the light source electric pulse signal to segment the reflection signal of each wavelength of the weak grating array, which effectively avoids the real-time requirement of the data acquisition card, but the Fresnel reflection surface formed by fusion has certain randomness, and its reflection intensity and position in the optical fiber are uncontrollable.

[0008] Third, the sampling point segmentation method: in the system fast acquisition process, the sampling point number of the reflection signal of any wavelength pulsed light is certain, so the reflection signal of each wavelength can be segmented according to the sampling point number. However, factors such as dispersion and clock jitter inevitably cause the starting position of the reflection signal of each wavelength to change, so there is a problem of poor accuracy in segmenting the wavelength reflection signal by using this method.

[0009] Therefore, for the fast dynamic scanning process of the laser, the existing technology has the problem of inaccurate segmentation of the wavelength reflection signal when segmenting any wavelength reflection signal. SUMMARY

[0010] In order to solve the problem of inaccurate wavelength grating reflection signal segmentation in high-speed dynamic demodulation in the prior art, which causes large system demodulation error, the application provides a fast weak fiber grating array demodulation device and method based on reflection enhancement points.

[0011] In a first aspect, the application provides a fast weak fiber grating array demodulation device based on reflection enhancement points, which comprises a fast scanning laser, an electric pulse signal generator, an optical pulse modulator, a fiber amplifier, a fiber ring, a reflection enhancement point, a weak grating array sensing unit, an optical-electric conversion module, a data acquisition module, a data analysis processing module and a control module.

[0012] The fast scanning laser outputs two electric pulse signals: the first one is a wavelength trigger signal, and the second one is a periodic trigger signal. The wavelength trigger signal is used to send to the electric pulse signal generator, and the electric pulse signal generator synchronously outputs an electric pulse signal and loads it on the optical pulse modulator to modulate the continuous laser output by the laser into pulsed light. The periodic trigger signal is used to trigger the data acquisition module to acquire data.

[0013] The control module is used to make the fast scanning laser generate stepwise swept light in a preset range according to a preset rule, and transmit the stepwise swept light signal to the optical pulse modulator. The optical pulse modulator controlled by the electric pulse signal generator modulates the swept light signal into an optical pulse signal with a fixed pulse width, and transmits it to the fiber amplifier. The fiber amplifier amplifies the optical pulse signal, and transmits the amplified optical pulse signal to the reflection enhancement point and the weak grating array sensing unit via the fiber ring. The reflection enhancement point is arranged in front of the weak grating array sensing unit. The reflection enhancement point reflects the amplified optical pulse signal to obtain a reflected light signal 1, and the weak grating array sensing unit reflects the amplified optical pulse signal to obtain a reflected light signal 2. The optical-electric conversion module receives the two reflected light signals of the reflection enhancement point and the weak grating array sensing unit. The data acquisition module samples the two reflected light signals and sends them to the data analysis processing module. The data analysis processing module divides the weak grating array reflected signal 2 of any wavelength according to the reflected light signal 1 of the reflection enhancement point, and further demodulates the positions and central wavelengths of the gratings in the weak grating array sensing unit.

[0014] The control module sends instructions to the data acquisition module, the electric pulse signal generator and the fiber amplifier to control data acquisition, optical pulse output and amplification.

[0015] Preferably, the scanning range of the fast scanning laser covers the C band, the scanning step is an integer multiple of 4 pm, and the output time of each wavelength is adjustable, which can be as low as 0.1 μs.

[0016] Preferably, the optical pulse width is less than the transmission delay of the two adjacent gratings, and the output time of each wavelength of the fast scanning laser is greater than the round-trip time of light in the fiber.

[0017] Preferably, OTDR demodulation technology is used to obtain the positions of the gratings in the weak grating array sensing unit, and the positions of the gratings on the optical fiber are determined by counting the delay of the reflected light according to the spatial arrangement order of the reflection enhancement points and the weak fiber grating sensors.

[0018] Preferably, the transmission delay of the reflected light signal of the reflection enhancement point and the reflected light signal of the adjacent grating is greater than the light pulse width.

[0019] Preferably, the reflection intensity of the reflection enhancement point is significantly higher than the system noise.

[0020] In a second aspect, the present application provides a fast weak fiber grating array demodulation method based on reflection enhancement points, based on the fast weak fiber grating array demodulation device based on reflection enhancement points as described above, the method comprising the following steps:

[0021] S1: The control module sets the scanning range, scanning step, and each wavelength output time of the fast scanning laser, sets the light pulse width and the amplification factor of the optical fiber amplifier;

[0022] S2: Based on the periodic trigger signal of the fast scanning laser, the reflected light signal of one scanning period is collected, including the reflected light signal 1 of the reflection enhancement points and the reflected light signal 2 of the weak grating array sensing unit according to the spatial arrangement order;

[0023] S3: According to the reflected light signal 1 of the reflection enhancement points, the reflected light signal 2 of the weak grating array sensing unit at any scanning wavelength is divided and output; the weak grating array sensing data collected in one scanning period is composed into an i×j scanning period matrix, and each row of the scanning period matrix represents the reflected light signal of one wavelength; i is the total number of wavelength steps, and j is the number of sampling points corresponding to the length of the optical fiber;

[0024] S4: After denoising the data of each row of the scanning period matrix, i.e., the reflected light signal of each wavelength, an i×j denoising matrix is obtained;

[0025] S5: Grating positioning: the mean square deviation of each column of the above denoising matrix is calculated to obtain a row matrix of 1 row and j columns, and the sampling point corresponding to the grating position is obtained by peak searching on the data in the row matrix; one or more peak values are obtained by peak searching, and the peak value is the position with the maximum reflected light intensity; the spatial position information of m gratings is obtained after peak searching.

[0026] S6: Spectrum splicing to find the center wavelength: in the i x j denoising matrix, after determining the sampling points corresponding to the spatial positions of the m gratings, the same operation is performed on the m sampling points: extracting n columns of data with the column of data corresponding to the sampling point as the center to obtain an i x n matrix, and then obtaining a column matrix of i rows by averaging each row of the matrix, which is the spectral data of one grating, and then using the Gaussian fitting algorithm to find the peak to obtain the center wavelength of the grating.

[0027] Preferably, the positions of the reflection enhancement points and the gratings are determined by the return time of the pulsed light according to the spatial arrangement order of the reflection enhancement points and the weak grating array sensing unit; the reflection enhancement point has a reflection light signal for each incident light wavelength, and the reflection light signal 1 of the reflection enhancement point is taken as a segmentation point to segment the reflection light signal 2 of the pulsed light signal of any wavelength in the weak grating array sensing unit.

[0028] Preferably, n in S6 is determined according to the following formula:

[0029]

[0030] In the formula, τ represents the light pulse width,

[0031] f represents the sampling rate of the acquisition module

[0032] represents rounding down.

[0033] The beneficial effects of the present application: in the rapid weak fiber grating array demodulation device based on the reflection enhancement point, the reflection light signal of the reflection enhancement point for any wavelength is used to accurately segment the reflection light signal of each wavelength in the weak grating array sensing unit, the grating position and the center wavelength are demodulated, and high-speed dynamic demodulation is realized. The problem of inaccurate wavelength reflection signal segmentation is solved, and the complexity and cost of the system are reduced. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The structure schematic diagram of an embodiment of the rapid weak fiber grating array demodulation device based on the reflection enhancement point provided by the present application.

[0035] Figure 2 The schematic diagram of the rapid scanning laser electric pulse signal and the wavelength scanning output provided by the present application.

[0036] Figure 3 The reflection light pulse signal schematic diagram of the reflection enhancement point and the weak grating array sensing unit to the scanning wavelength provided by the present application.

[0037] Figure 4 The 1600-meter-long weak fiber grating array reflection light signal schematic diagram provided by the present application.

[0038] Figure 5 The 791 grating center wavelength demodulation schematic diagram provided by the present application is shown in the following table. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0040] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0041] The present application will be further described below with reference to the drawings and specific embodiments, but not as a limitation of the present application.

[0042] Specific embodiment one: the present embodiment will be described below with reference to the drawings. Figures 1 to 5 The present embodiment describes a rapid weak fiber grating array demodulation device based on reflection enhancement points, which comprises a fast scanning laser, an electric pulse signal generator, an optical pulse modulator, a fiber amplifier, a fiber ring, a reflection enhancement point, a weak grating array sensing unit, an optical-electric conversion module, a data analysis processing module and a control module. Figure 1 as shown.

[0043] The fast scanning laser outputs two electric pulse signals: the first one is a wavelength trigger signal, and the second one is a period trigger signal. The wavelength trigger signal is used to send to the electric pulse signal generator, and the electric pulse signal generator synchronously outputs the electric pulse signal and loads it to the optical pulse modulator to modulate the continuous laser output by the laser into pulsed light. The period trigger signal is used to trigger the data acquisition of the acquisition module. After receiving the period trigger signal, the acquisition module starts to acquire data. Figure 2 The schematic diagram of the electric pulse signal of the fast scanning laser and the wavelength scanning output is shown in the following table.

[0044] The fast scanning laser is controlled by the control module to generate stepped sweep light in a preset range according to a preset rule, and the stepped sweep light signal is transmitted to the optical pulse modulator; the optical pulse modulator controlled by the electric pulse signal generator modulates the sweep light signal into an optical pulse signal with a fixed pulse width, and transmits the optical pulse signal to the optical fiber amplifier; the optical fiber amplifier amplifies the optical pulse signal, and transmits the amplified optical pulse signal to the reflection enhancement point and the weak grating array sensing unit via the optical fiber circulator, and the reflection enhancement point is arranged in front of the weak grating array sensing unit; the reflection enhancement point reflects the amplified optical pulse signal to obtain reflected light signal 1, and the weak grating array sensing unit reflects the amplified optical pulse signal to obtain reflected light signal 2; the photoelectric conversion module receives the two-way reflected light signals of the reflection enhancement point and the weak grating array sensing unit, the sampling module samples the two-way reflected light signals and sends them to the data analysis processing module, and the data analysis processing module divides the weak grating array reflection signal 2 of any wavelength according to the reflected light signal 1 of the reflection enhancement point, and further demodulates the positions and center wavelengths of the gratings in the weak grating array sensing unit.

[0045] The control module sends instructions to the sampling module, the electric pulse signal generator and the optical fiber amplifier to realize control of data acquisition, optical pulse output and amplification.

[0046] The scanning range of the fast scanning laser covers the C band, the scanning step is an integer multiple of 4pm, and the minimum scanning step is 4pm; the output time of each wavelength is adjustable. The output time of each wavelength can be as low as 0.1μs. If the light source scans 100 wavelengths, the demodulation frequency can reach 100KHz.

[0047] The output time of each wavelength of the fast scanning laser is adjustable. If it is necessary to increase the demodulation distance of the weak grating array, the output time of each wavelength of the laser can be increased. For example, if a 100m long weak grating array is monitored, the output time of each wavelength of the laser can be adjusted to be greater than 1μs; if a 1000m long weak grating array is monitored, the output time of each wavelength of the laser can be adjusted to be greater than 10μs; if a 10000m long weak grating array is monitored, the output time of each wavelength of the laser can be adjusted to be greater than 100μs.

[0048] The weak grating array sensing unit comprises a plurality of fiber grating sensors connected in series on an optical fiber, and a reflection enhancement point is arranged in front of the weak grating array sensing unit. According to the spatial arrangement order of the reflection enhancement point and the weak fiber grating sensors, the position of the grating on the optical fiber can be confirmed by using the OTDR demodulation technology and by counting the delay of the reflected light. In order to avoid the overlap of the reflected light signals, the transmission delay of the adjacent two gratings should be greater than the light pulse width, and the transmission delay of the reflected light signals of the reflection enhancement point and the adjacent grating should also be greater than the light pulse width. At the same time, in order to ensure that the system only outputs one light pulse to the weak grating array within the holding time of each wavelength, the output time of each wavelength of the fast scanning laser should be greater than the round-trip time of the light in the optical fiber.

[0049] The reflected light signal contains the external environmental information and the weak grating position information. The data analysis and processing module divides the reflected light signal of each wavelength at the weak grating array sensing unit according to the position information of the reflection enhancement point in the time domain. The reflection enhancement point generates a reflected light signal at any scanning wavelength, and by using the OTDR technology, the reflected light signals of the reflection enhancement point and the weak grating array sensing unit of each scanning wavelength will appear in sequence in the time domain according to the different delays, as shown in Figure 3 The reflected light signal of the reflection enhancement point can accurately divide the weak grating reflection signal of each wavelength, solving the technical problem of inaccurate division of the reflected light signal.

[0050] In addition, the reflection enhancement point arranged behind the grating array sensing unit can also accurately divide the reflected light signal of any wavelength at the weak grating array sensing unit.

[0051] Specific implementation method two: the following will be described in combination with Figures 1 to 5 The present embodiment describes a fast weak fiber grating array demodulation method based on a reflection enhancement point, which comprises the following steps:

[0052] S1: The control module sets the scanning range, scanning step, and output time of each wavelength of the fast scanning laser, sets the light pulse width and the amplification factor of the optical fiber amplifier;

[0053] S2: Based on the periodic trigger signal of the fast scanning laser, the reflected light signal of one scanning period is collected, including the reflected light signal 1 of the reflection enhancement point and the reflected light signal 2 of the weak grating array sensing unit in the spatial arrangement order;

[0054] S3: According to the reflected light signal 1 of the reflection enhancement point, the reflected light signal 2 of the optical pulse signal of any wavelength in the weak grating array sensing unit is divided and output; the weak grating array sensing data collected in one scanning cycle is composed into an i x j scanning cycle matrix, and each row of the scanning cycle matrix represents the reflected light signal of one wavelength; i is the total number of wavelength steps, and j is the number of sampling points corresponding to the length of the optical fiber;

[0055] S4: After the noise of each row of data of the scanning cycle matrix, that is, the reflected light signal of each wavelength, is removed, an i x j denoising matrix is obtained.

[0056] S5: Grating positioning: the mean square deviation of each column of the above denoising matrix is calculated to obtain a row matrix of 1 row and j columns, and the sampling point corresponding to the grating position is obtained by peak searching on the data in the row matrix. One or more peak values are obtained by peak searching, and the peak value is the position with the maximum reflected light intensity. After peak searching, the spatial position information of m gratings is obtained.

[0057] S6: Spectrum splicing and center wavelength searching: after determining the sampling points corresponding to the spatial positions of the m gratings in the i x j denoising matrix, the same operation is performed on the m sampling points: i x n matrix is obtained by extracting n columns of data with the column of data corresponding to the sampling point as the center, the average value of each row of the matrix is calculated to obtain a column matrix of 1 column and i rows, and the column matrix is the spectral data of one grating. Then, the Gaussian fitting algorithm is used to search for the peak to obtain the center wavelength of the grating.

[0058] In order to accurately identify the reflected light signal of the reflection enhancement point, the transmission delay of the reflection enhancement point and the adjacent grating is greater than the light pulse width, and the reflected pulse light intensity of the reflection enhancement point is obviously higher than the background noise, such as one ten-thousandth of the peak power of the incident pulse light.

[0059] Since the reflection enhancement point has a reflected light signal for each incident light wavelength, the reflected light signal of the reflection enhancement point can be used as a division point to divide the reflected light signal of the optical pulse signal of each wavelength in the weak grating array sensing unit.

[0060] According to the spatial arrangement order of the reflection enhancement point and the weak grating array sensing unit, the positions of the reflection enhancement point and the grating are determined by the return time of the pulse light. The reflection enhancement point has a reflected light signal for each incident light wavelength, and the reflected light signal 1 of the reflection enhancement point is used as a division point to divide the reflected light signal 2 of the optical pulse signal of any wavelength in the weak grating array sensing unit.

[0061] In S4, due to the unstable output of the laser and other factors, the peak power of the optical pulse may fluctuate, so the reflected light signal of each wavelength is denoised respectively.

[0062] In S6, n is determined according to the following formula:

[0063] In S6, n is determined according to the following formula:

[0064] wherein τ represents the light pulse width,

[0065] f represents the sampling rate of the acquisition module

[0066] represents rounding down.

[0067] If the light pulse width is 10 ns and the sampling rate is 500M, the average number of sampling points per row can be selected as n≤9.

[0068] The method process of the present application will be described below in combination with specific embodiments.

[0069] Suppose that the noise reduction matrix i×j obtained by S4 is:

[0070]

[0071] Each row of the noise reduction matrix represents the reflected light intensity at different fiber positions after the pulse light of the corresponding wavelength reaches the weak light fiber grating array unit. Each column, i.e. the spectral data of each sampling point.

[0072] The mean square deviation of each column in the noise reduction matrix is calculated to obtain a row matrix of 1 row and j columns:

[0073] {S 1,1 S 1,2 …S 1,j-1 S 1,j}

[0074] Each data in the row matrix represents the mean square deviation value of the column. Peak searching is performed on the row matrix data to obtain the sampling points corresponding to the spatial positions of the m gratings:

[0075] {d1, d2, d3, …d m}

[0076] Taking d1 as an example, suppose that n=5, the sampling point d1 corresponding to the first grating position, the data of the d1-2, d1-1, d1, d1+1, d1+2 columns are obtained with the sampling point as the center, and the average value of each row data in the 5 columns of data is calculated: The obtained matrix of 1 column and i rows is the spectral data of the first grating:

[0077]

[0078] The above operation is performed on the m gratings respectively to obtain an i*m matrix:

[0079]

[0080] Each row of the matrix represents the reflected light intensity of different gratings after the pulsed light of corresponding wavelength reaches the weak fiber grating array unit. Each column, i.e. the spectrum data of each grating. The center wavelength of each grating can be obtained by using a Gaussian fitting algorithm to peak each column of data.

[0081] In one specific embodiment of the present application, the weak grating array sensing unit is located on a 1600m long optical fiber, and is composed of 791 gratings with a spacing of 2m, a center wavelength of 1536nm, and a reflectivity of 0.01%-0.1%.

[0082] A fast scanning laser is arranged to generate a step frequency light with a bandwidth of 3nm, a scanning range of 1534nm-1537nm, 188 steps each with a step of 16pm, and an output time of 196.05us at each wavelength. The laser emits a wavelength trigger signal corresponding to each wavelength output, and an electric pulse signal generator receives the wavelength trigger signal emitted by the laser and modulates the pulse width of a synchronous pulse to control a light pulse modulator to generate a laser with a pulse width of 18.52ns. A reflection enhancement point is arranged 3m in front of the grating array sensing unit.

[0083] According to the principle of optical time domain reflection, the incident light of the fast scanning laser is reflected by the reflection enhancement point and the weak grating array sensing unit, and reaches a photoelectric conversion module according to the spatial arrangement order of the reflection enhancement point and the gratings. The photoelectric conversion module converts the reflected light into an analog signal. The periodic trigger signal of the fast scanning laser controls the sampling of the sampling module, and the sampling module samples the analog electrical signal at a sampling rate of 500M to obtain a digital electrical signal. The sampling module collects the reflected light data of one scanning period. The data acquisition module converts the analog signal into a digital signal and performs fixed-length data sampling, and then transmits the sampled data to the data analysis processing module.

[0084] The reflected light signal at the reflection enhancement point at any scanning wavelength can be observed, as shown in FIG. 6. Figure 4 The data analysis processing module groups the sampling data of the 188 steps into a 188*8500 matrix by searching for the 188 reflected light signals of the reflection enhancement point. Each row of the matrix represents 188 wavelengths, and each column represents 8500 sampling points extracted at each wavelength. The peaks are searched in the mean square deviation matrix of each column. At the positions where the gratings exist, the difference between the reflected signal and the noise is large, so the mean square deviation value is large. At the positions where the gratings do not exist, the data corresponding to the sampling points are basically noise signals, so the mean square deviation value is small. Therefore, the positions of the gratings and the number of gratings 791 can be obtained by searching the peaks in the mean square deviation value matrix.

[0085] The sampling points corresponding to the spatial positions of the 791 gratings are determined, for any sampling point, taking the 5 column data of the sampling point as the center, the average value of each row data is calculated, and the reflection spectrum of the sampling point corresponding to the grating can be obtained. For example, the sampling point corresponding to the first grating is 43, then the average value of each row data in the 41st, 42nd, 43rd, 44th and 45th columns is calculated, and 1 column of 188 row matrix is obtained. The spectral stitching is performed on the matrix data, and the center wavelength of the first grating is obtained by using the Gaussian fitting algorithm. Similarly, the center wavelength distribution of the 791 gratings is as shown in Figure 5 .

[0086] In summary, the present application uses the reflection light signal of the reflection enhancement point at any scanning wavelength, accurately separates the reflection light signal of each wavelength of the weak grating array sensor unit under high-speed dynamic scanning, and solves the problem of inaccurate grating reflection signal separation.

[0087] Although the present application is described herein with reference to particular embodiments, it is to be understood that these examples are merely illustrative of the principles and applications of the present application. It is therefore to be understood that numerous modifications can be made to the illustrative embodiments and that other arrangements can be devised without departing from the spirit and scope of the present application as defined by the appended claims. It is to be understood that the features of the dependent claims can be combined with the features of the parent claims in different ways than explicitly set forth in the claims or occurring to the skilled artisan. It is also to be understood that features described with respect to one embodiment can be incorporated into other embodiments.

Claims

1. A fast weak fiber grating array demodulation device based on reflection enhancement points, characterized by, The application relates to a weak grating array sensing device and a sensing method thereof. The fast scanning laser outputs two paths of electric pulse signals: the first path is a wavelength trigger signal, and the second path is a period trigger signal; the wavelength trigger signal is used for sending to the electric pulse signal generator; the electric pulse signal generator synchronously outputs electric pulse signals and loads the electric pulse signals on the optical pulse modulator to modulate continuous laser output by the laser into pulsed light; the period trigger signal is used for triggering the acquisition module to acquire data. The fast scanning laser generates step scanning frequency light in a preset range according to a preset rule through the control module, and transmits the step scanning frequency light signal to the optical pulse modulator. The optical pulse modulator controlled by the electric pulse signal generator modulates the scanning frequency light signal into an optical pulse signal with a fixed pulse width, and transmits the optical pulse signal to the fiber amplifier; the fiber amplifier amplifies the optical pulse signal, and transmits the amplified optical pulse signal to the reflection enhancement point and the weak grating array sensing unit through the fiber ring; the reflection enhancement point is arranged in front of the weak grating array sensing unit; the reflection enhancement point reflects the amplified optical pulse signal to obtain reflected light signal 1, and the weak grating array sensing unit reflects the amplified optical pulse signal to obtain reflected light signal 2; the photoelectric conversion module receives the two paths of reflected light signals of the reflection enhancement point and the weak grating array sensing unit; the acquisition module samples the two paths of reflected light signals and sends the two paths of reflected light signals to the data analysis processing module; the data analysis processing module divides the weak grating array reflected light signal 2 of any wavelength according to the reflected light signal 1 of the reflection enhancement point, and further demodulates the positions and central wavelengths of the gratings in the weak grating array sensing unit; the process of demodulating the positions of the gratings in the weak grating array sensing unit is as follows: since the reflection enhancement point is arranged in front of the weak grating array sensing unit, and the reflection enhancement point has reflected light signals for each incident light wavelength; by using the OTDR demodulation technology, any wavelength of the optical pulse signal is transmitted on the optical fiber, first passes through the reflection enhancement point to generate a reflected light signal, and then passes through the weak grating array sensing unit to generate a group of reflected light signals; taking the position of the reflected light signal of the reflection enhancement point in the time domain as a benchmark, the reflected light signal of the reflection enhancement point is used to divide the reflected light signals generated by different wavelengths in the weak grating array sensing unit; the positions of the gratings on the optical fiber are confirmed by counting the time delays of different reflected lights. The control module sends instructions to the acquisition module, the electric pulse signal generator and the fiber amplifier to realize the control of data acquisition, optical pulse output and amplification.

2. The quick weak light fiber grating array demodulation device based on reflection enhancement points according to claim 1, characterized in that, The scanning range of the fast scanning laser covers the C band, the scanning step is an integer multiple of 4pm, the output time of each wavelength is adjustable, and the minimum can be as low as 0.1us.

3. The quick weak light fiber grating array demodulation device based on reflection enhancement points according to claim 2, characterized in that, The optical pulse width is less than the transmission delay of the adjacent two gratings, and the output time of each wavelength of the fast scanning laser is greater than the round-trip time of light in the optical fiber.

4. The quick weak light fiber grating array demodulation device based on reflection enhancement points according to claim 1, characterized in that, The OTDR demodulation technology is used to obtain the positions of the gratings in the weak grating array sensing unit. According to the spatial arrangement order of the reflection enhancement points and the weak fiber grating sensors, the positions of the gratings on the fiber are determined by counting the delay of the reflected light.

5. The quick weak light fiber grating array demodulation device based on reflection enhancement points according to claim 4, characterized in that, The transmission delay of the reflected light signal of the reflection enhancement point and the reflected light signal of the adjacent grating is greater than the light pulse width.

6. The quick weak light fiber grating array demodulation device based on reflection enhancement points according to claim 4, characterized in that, The reflection intensity of the reflection enhancement point is obviously higher than the system noise.

7. A method for fast weak FBG array demodulation based on reflection enhanced point, implemented by the fast weak FBG array demodulation device based on reflection enhanced point according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: S1: The control module sets the scanning range, scanning step, and each wavelength output time of the fast scanning laser, sets the light pulse width and the amplification multiple of the fiber amplifier; S2: The reflected light signal of one scanning period is collected based on the periodic trigger signal of the fast scanning laser, including the reflected light signal 1 of the reflection enhancement point and the reflected light signal 2 of the weak grating array sensing unit in the spatial arrangement order; S3: According to the reflected light signal 1 of the reflection enhancement point, the reflected light signal 2 of the weak grating array sensing unit at any scanning wavelength is divided and output; the weak grating array sensing data collected in one scanning period is composed into an i x j scanning period matrix, and each row of the scanning period matrix represents the reflected light signal of one wavelength; i is the total number of wavelength steps, and j is the number of sampling points corresponding to the fiber length; S4: After the noise of each row of data of the scanning period matrix, that is, the reflected light signal of each wavelength, is removed, an i x j denoising matrix is obtained; S5: Grating positioning: the mean square deviation of each column of the above denoising matrix is calculated to obtain a row matrix with 1 row and j columns, the data in the row matrix are searched for peaks to obtain the sampling points corresponding to the grating positions, one or more peak values are obtained after searching for peaks, and the peak value is the position with the maximum reflected light intensity; the spatial position information of m gratings is obtained after searching for peaks; S6: Spectrum splicing and center wavelength searching: in the i x j denoising matrix, after the sampling points corresponding to the spatial positions of the m gratings are determined, the same operation is performed on the m sampling points: i x n matrix is obtained by extracting n columns of data with one column of data corresponding to the sampling point as the center, the average value of each row of the matrix is calculated to obtain a column matrix with 1 column and i rows, the column matrix is the spectral data of one grating, and then a Gaussian fitting algorithm is used to search for peaks to obtain the center wavelength of the grating.

8. The method according to claim 7, wherein, According to the spatial arrangement order of the reflection enhancement points and the weak grating array sensing unit, the positions of the reflection enhancement points and the gratings are determined by the return time of the pulse light; the reflection enhancement point has a reflected light signal for each incident light wavelength, and the reflected light signal 1 of the reflection enhancement point is used as a division point to divide the reflected light signal 2 of the pulse light signal of each wavelength in the weak grating array sensing unit.

9. The method according to claim 7, wherein, In S6, n is determined according to the following formula: In the formula, τ represents the light pulse width, f represents the sampling rate of the collection module, and t represents the time interval of the trigger signal of the fast scanning laser. denotes rounding down.

Images