Rapid weak fiber grating array demodulation device and method based on reflection enhancement points

Abstract

The invention discloses a fast weak fiber grating array demodulation device and method based on reflection enhancement points, belongs to the technical field of optical fiber sensing, and aims to solve the problem of large system demodulation error caused by inaccurate segmentation of wavelength grating reflection signals during high-speed dynamic demodulation in the prior art. The system comprises a fast scanning laser, an electric pulse signal generator, an optical pulse modulator, an optical fiber amplifier, an optical fiber circulator, a reflection enhancement point, a weak grating array sensing unit, a photoelectric conversion module, an acquisition module, a data analysis processing module and a control module. The reflection enhancement point and the weak grating array sensing unit reflect the fast scanning light pulse signal to obtain a reflection signal, the reflection signal of the reflection enhancement point divides the weak grating array reflection light pulse signal of any wavelength, and after data processing, the grating position and the center wavelength are obtained. According to the system, a grating reflection signal of each wavelength is obtained by using a reflection enhancement point, and high-speed dynamic demodulation of a weak grating array sensing unit is realized.

Description

Technical Field

[0001] The invention relates to a fast weak fiber grating array demodulation device and method based on reflection enhancement points, belonging to the technical field of optical fiber sensing. Background Art

[0002] Fiber Bragg grating (FBG) sensor is a wavelength modulated optical fiber sensor. It uses the linear correspondence between the center wavelength of the reflected light of FBG and the external influences such as strain and temperature on the FBG sensor, and realizes the sensing of external physical quantities by demodulating the change of the center wavelength of FBG. This type of sensor has the advantages of small size, high sensitivity, anti-electromagnetic interference and corrosion resistance. FBG grating array sensors are obtained by wavelength division multiplexing (WDM), time division multiplexing (TDM) and combined multiplexing methods to achieve multi-point sensing. However, the high reflection characteristics of traditional FBG, spectral shadow effects and 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) technology, sensing based on large-scale fiber grating arrays has been realized.

[0003] In actual engineering applications, such as distributed strain monitoring of aircraft wings, distributed strain monitoring of large bridges, and distributed strain monitoring of large ships, the structures being measured are all in a vibrating state, and traditional static monitoring technology is prone to distortion or even failure of measurement data. Therefore, it is necessary to design a fast weak grating array demodulation device and method to improve the strain sensing accuracy of the weak grating array under vibration conditions.

[0004] Commonly used demodulation methods for FBG sensors include spectrometer detection, filter detection, interference detection, scanning laser detection, etc. In comparison, the scanning laser detection method has the advantages of large detection dynamic range and fast demodulation speed, especially in high-speed demodulation, the scanning laser detection method has incomparable advantages.

[0005] The scanning laser detection method realizes multi-wavelength scanning of a weak grating array by step-tuning the laser wavelength. The scanning laser usually outputs two electrical pulse signals: the first electrical pulse signal has the same period as the entire scanning process of the laser, and the rising edge of the electrical pulse is strictly synchronized with the first wavelength, which is called the period trigger signal; the second electrical pulse signal has the same period as the duration of a single wavelength, and the rising edge of the electrical pulse is strictly synchronized with the switching of a single wavelength, which is called the wavelength trigger signal; the laser wavelength scanning range needs to cover the central wavelengths of all fiber grating sensors. When the optical wavelength output by the laser matches the central wavelength of the FBG, the reflection intensity is the highest. Therefore, the central wavelengths of each fiber grating can be identified by scanning the laser wavelength. In the fast demodulation technology of a weak grating array based on a scanning laser, only by accurately identifying the reflection signal of each wavelength during fast scanning can the grating position be accurately located and the central wavelength of the grating be demodulated. Currently, the main methods for accurately obtaining the reflection signal of each wavelength during fast scanning are as follows:

[0006] First, the laser electrical pulse signal segmentation method: Using the wavelength trigger signal as the trigger signal of the acquisition card, when the rising edge of a certain wavelength trigger signal arrives, the data acquisition card starts to acquire the reflection signal of the weak grating array to the current laser and stores it. This method can accurately acquire the reflection signal of each wavelength, but it requires the acquisition card to have higher dynamic response capabilities and also requires the acquisition card to have dual-channel acquisition capabilities to acquire the period trigger signal to identify the starting wavelength of a certain scanning cycle during fast continuous measurement. Therefore, the laser electrical pulse signal segmentation method requires the use of a high-performance, dual-channel acquisition card, which is expensive and the system cost is high.

[0007] Second, the fusion joint segmentation method: This method uses the Fresnel reflection surface formed during the fiber fusion process to reflect and segment the reflected optical signal of each wavelength. This method does not rely on the electrical pulse signal of the light source to segment the reflected signal of the weak grating array of each wavelength, effectively avoiding the requirement for the real-time performance of the acquisition card. However, the Fresnel reflection surface formed by fusion has a certain contingency, and its reflection intensity and position in the fiber are uncontrollable.

[0008] Third, the sampling point segmentation method: During the fast acquisition process of the system, the number of sampling points of the reflected optical signal of any wavelength pulse light is certain. Therefore, the reflected optical signal of each wavelength can be segmented according to the number of sampling points. However, factors such as dispersion and clock jitter will inevitably cause the starting positions of the reflected signals of each wavelength to change. Therefore, there is a problem of poor accuracy when using this method to segment the wavelength reflected optical signal.

[0009] Therefore, for the fast dynamic scanning process of the laser, there is a problem of inaccurate segmentation of the wavelength reflected signal in the prior art when performing the segmentation of the reflected signal of any wavelength. Summary of the Invention

[0010] To solve the problem that in the prior art, during high-speed dynamic demodulation, the wavelength grating reflection signal is not accurately segmented, resulting in a large demodulation error in the system, the present invention provides a fast weak fiber grating array demodulation device and method based on reflection enhancement points.

[0011] In a first aspect, the present invention provides a fast weak fiber grating array demodulation device based on reflection enhancement points, including a fast scanning laser, an electrical pulse signal generator, an optical pulse modulator, an optical fiber amplifier, an optical fiber circulator, a reflection enhancement point, a weak grating array sensing unit, a photoelectric conversion module, an acquisition module, a data analysis and processing module, and a control module;

[0012] The fast scanning laser outputs two electrical pulse signals: the first is a wavelength trigger signal, and the second is a period trigger signal. The wavelength trigger signal is sent to the electrical pulse signal generator, which synchronously outputs an electrical pulse signal and loads it onto 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 acquisition module to collect data;

[0013] The control module enables the fast scanning laser to generate a stepped frequency-swept light within a set range according to a preset rule, and transmits the stepped frequency-swept light signal to the optical pulse modulator; the optical pulse modulator controlled by the electrical pulse signal generator modulates the frequency-swept light signal into an optical pulse signal with a fixed pulse width and transmits it 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. The reflection enhancement point is placed in front of the weak grating array sensing unit; the reflection enhancement point reflects the amplified optical pulse signal to obtain a reflected optical signal 1, and the weak grating array sensing unit reflects the amplified optical pulse signal to obtain a reflected optical signal 2; the photoelectric conversion module receives the two reflected optical signals from the reflection enhancement point and the weak grating array sensing unit, the acquisition module samples the two reflected optical signals and sends them to the data analysis and processing module, and the data analysis and processing module divides the weak grating array reflected signal 2 of any wavelength according to the reflected optical signal 1 of the reflection enhancement point, and then demodulates the positions and central wavelengths of the gratings in the weak grating array sensing unit;

[0014] The control module sends instructions to the acquisition module, the electrical pulse signal generator, and the optical 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, the output time of each wavelength is adjustable, and the minimum can be as low as 0.1 μs.

[0016] Preferably, the optical pulse width is less than the transmission delay between 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 optical fiber.

[0017] Preferably, 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 optical fiber are confirmed by statistically analyzing the delay of the reflected light.

[0018] Preferably, the transmission delay between the reflected light signal of the reflection enhancement point and the reflected light signal of the adjacent grating is greater than the optical 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 invention provides a fast demodulation method for a weak fiber grating array based on reflection enhancement points. Based on the fast demodulation device for a weak fiber grating array based on reflection enhancement points as described above, the method includes the following steps:

[0021] S1: The control module sets the scanning range, scanning step, and output time per wavelength of the fast scanning laser, and sets the optical 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 signals in a scanning period are 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 arranged in spatial order;

[0023] 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 segmented and output; the weak grating array sensing data collected in a scanning period is formed into an i×j scanning period matrix, and each row of the scanning period matrix represents the reflected light signal at one wavelength; i is the total number of wavelength steps, and j is the number of sampling points corresponding to the optical fiber length;

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

[0025] S5: Grating positioning: The mean square deviation is calculated for each column of the above denoising matrix to obtain a 1×j row matrix. The data in the row matrix is searched for peaks to obtain the sampling points corresponding to the grating positions. One or more peaks are obtained by peak searching. The peak is the position where the reflected light intensity is the largest. After peak searching, the spatial position information of m gratings is obtained;

[0026] S6: Spectral stitching to find the central wavelength: After determining the sampling points corresponding to the spatial positions of m gratings in the i×j noise reduction matrix, the same operation is performed on all m sampling points: n columns of data are extracted with the data column corresponding to this sampling point as the center to obtain an i×n matrix, and the average value of each row of this matrix is calculated to obtain a column matrix with 1 column and i rows. This column matrix is the spectral data of one grating, and then the Gaussian fitting algorithm is used to find the peak to obtain the central wavelength of this grating.

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

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

[0029]

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

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

[0032] represents rounding down for *.

[0033] Advantages of the present invention: In the fast weak fiber grating array demodulation device based on reflection enhancement points, the reflected light signals of any wavelength at the reflection enhancement points are used to accurately segment the reflected light signals of each wavelength in the weak grating array sensing unit, demodulate the grating positions and central wavelengths, and achieve high-speed dynamic demodulation. The problem of inaccurate segmentation of wavelength reflection signals is solved, and the complexity and cost of the system are reduced. Description of the Drawings

[0034] Figure 1 It is a schematic structural diagram of an embodiment of the fast weak fiber grating array demodulation device based on reflection enhancement points provided by the present invention.

[0035] Figure 2 It is a schematic diagram of the electrical pulse signal and wavelength scanning output of the fast scanning laser provided by the present invention.

[0036] Figure 3 It is a schematic diagram of the reflected light pulse signals of the reflection enhancement points and the weak grating array sensing units for the scanned wavelengths provided by the present invention.

[0037] Figure 4 It is a schematic diagram of the reflected light signals of the 1600-meter-long weak fiber grating array provided by the present invention.

[0038] Figure 5 Schematic diagram for demodulating the central wavelengths of 791 gratings provided by the present invention. Specific embodiments

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

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

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but it is not limited to the present invention.

[0042] Specific embodiment 1: The following will be combined with Figures 1 to 5 to illustrate this embodiment. The fast weak fiber grating array demodulation device based on reflection enhancement points described in this embodiment includes a fast scanning laser, an electrical pulse signal generator, an optical pulse modulator, an optical fiber amplifier, an optical fiber circulator, reflection enhancement points, a weak grating array sensing unit, a photoelectric conversion module, an acquisition module, a data analysis and processing module, and a control module; see Figure 1 as shown.

[0043] The fast scanning laser outputs two electrical pulse signals: the first is a wavelength trigger signal, and the second is a period trigger signal. The wavelength trigger signal is sent to the electrical pulse signal generator, and the electrical pulse signal generator synchronously outputs an electrical pulse signal and loads it onto 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 acquisition module to acquire data; after receiving the period trigger signal, the acquisition module starts to acquire data. Figure 2 Schematic diagram of the electrical pulse signal of the fast scanning laser and the wavelength scanning output.

[0044] The control module causes the fast-scanning laser to generate stepped swept-frequency light within a set range according to a preset rule, and transmits the optical signal of the stepped swept-frequency light to the optical pulse modulator; the optical pulse modulator controlled by the electrical pulse signal generator modulates the optical signal of the swept-frequency light 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 optic circulator. The reflection enhancement point is placed in front of the weak grating array sensing unit; the reflection enhancement point reflects the amplified optical pulse signal to obtain the reflected optical signal 1, and the weak grating array sensing unit reflects the amplified optical pulse signal to obtain the reflected optical signal 2; the photoelectric conversion module receives the two-way reflected optical signals of the reflection enhancement point and the weak grating array sensing unit, the acquisition module samples the two-way reflected optical signals and sends them to the data analysis and processing module, and the data analysis and processing module divides the reflected optical signal 2 of the weak grating array with any wavelength according to the reflected optical signal 1 of the reflection enhancement point, and then demodulates the positions and central wavelengths of the gratings in the weak grating array sensing unit;

[0045] The control module sends instructions to the acquisition module, the electrical pulse signal generator and the fiber amplifier to control 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 4 pm, and the minimum scanning step is 4 pm; the output time of each wavelength is adjustable. The output time of each wavelength can be as low as 0.1 μs. If the light source scans 100 wavelengths, the demodulation frequency can reach 100 KHz.

[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 100 m long weak grating array is monitored, the output time of each wavelength of the laser can be adjusted to be greater than 1 μs; if a 1000 m long weak grating array is monitored, the output time of each wavelength of the laser can be adjusted to be greater than 10 μs; if a 10000 m long weak grating array is monitored, the output time of each wavelength of the laser can be adjusted to be greater than 100 μs.

[0048] The weak grating array sensing unit includes a plurality of fiber Bragg grating sensors connected in series on a single optical fiber, and a reflection enhancement point is placed in front of the weak grating array sensing unit. Using the OTDR demodulation technique, according to the spatial arrangement order of the reflection enhancement point and the weak fiber Bragg grating sensors, the grating positions on the optical fiber can be confirmed by statistically analyzing the reflection light delay. To avoid the overlap of reflection light signals, the transmission delay between two adjacent gratings should be greater than the optical pulse width, and the transmission delay between the reflection light signal of the reflection enhancement point and the reflection light signal of the adjacent grating should also be greater than the optical pulse width. At the same time, to ensure that only one optical pulse is output to the weak grating array within the holding time of each wavelength of the system, the output time of each wavelength of the fast scanning laser should be greater than the round-trip time of light in the optical fiber.

[0049] The reflection light signal contains external environment information and weak grating position information. The data analysis and processing module divides the reflection light signal of each wavelength in the weak grating array sensing unit according to the position information of the reflection enhancement point in the time domain. At any scanned wavelength, a reflection light signal is generated at the reflection enhancement point. Using the OTDR technique, according to the different delays, the reflection enhancement points of each scanned wavelength and the reflection light signals of the weak grating array sensing unit will appear sequentially in the time domain, as Figure 3 Figure for dividing the reflection light pulse signal of the weak grating array sensing unit for the scanned wavelength according to the reflection enhancement point. The data of the optical fiber sampling points corresponding to each grating can be confirmed according to the transmission delay. Using the reflection light signal of the reflection enhancement point, the weak grating reflection signals of each wavelength can be accurately divided, solving the technical problem of inaccurate division of reflection light signals.

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

[0051] Specific Embodiment 2: The following is combined with Figures 1 to 5 to illustrate this embodiment. The fast weak fiber Bragg grating array demodulation method based on a reflection enhancement point described in this embodiment includes 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, and sets the optical pulse width and the amplification factor of the optical fiber amplifier;

[0053] S2: Collect the reflection light signals of one scanning cycle based on the periodic trigger signal of the fast scanning laser, including the reflection light signal 1 of the reflection enhancement point and the reflection light signal 2 of the weak grating array sensing unit arranged in the spatial order;

[0054] S3: According to the reflected optical signal 1 of the reflection enhancement point, split and output the reflected optical signal 2 of any scanning wavelength in the weak grating array sensing unit; form an i×j scanning period matrix with the weak grating array sensing data collected within one scanning period, where each row of this scanning period matrix represents the reflected optical 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.

[0055] S4: Denoise each row of data in the scanning period matrix, that is, the reflected optical signal of each wavelength, to obtain an i×j denoising matrix.

[0056] S5: Grating positioning: Calculate the mean square error for each column of the above denoising matrix respectively to obtain a 1×j row matrix, and find the sampling points corresponding to the grating positions by peak searching for the data in the row matrix. One or more peaks are obtained by peak searching, and the peak positions are where the reflected optical intensity is the maximum. After peak searching, the spatial position information of m gratings is obtained.

[0057] S6: Spectral splicing to find the central wavelength: In the i×j denoising matrix, after determining the sampling points corresponding to the spatial positions of m gratings, perform the same operation on these m sampling points: Extract n columns of data centered on the column of data corresponding to this sampling point to obtain an i×n matrix, calculate the average value of each row of this matrix to obtain a 1×i column matrix, and this column matrix is the spectral data of one grating. Then, use the Gaussian fitting algorithm to search for the peak to obtain the central wavelength of this grating.

[0058] Among them, in order to accurately identify the reflected optical signal of the reflection enhancement point, the transmission delay between the reflection enhancement point and the adjacent grating is greater than the optical pulse width, and the reflected pulsed light intensity of the reflection enhancement point is significantly higher than the substrate noise, such as one ten-thousandth of the peak power of the incident pulsed light.

[0059] Since the reflection enhancement point has a reflected optical signal for each incident optical wavelength, using the reflected optical signal of the reflection enhancement point as the splitting point can split the reflected optical 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, determine the positions of the reflection enhancement point and the grating by the return time of the pulsed light; the reflection enhancement point has a reflected optical signal for each incident optical wavelength, and use the reflected optical signal 1 of the reflection enhancement point as the splitting point to split the reflected optical signal 2 of the optical pulse signal of any wavelength in the weak grating array sensing unit.

[0061] In S4, due to factors such as unstable output of the laser, the peak power of the optical pulse will jitter, so the reflected optical signal of each wavelength is denoised separately.

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

[0063]

[0064] In the formula, τ represents the optical pulse width,

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

[0066] represents rounding down.

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

[0068] The process of the method of the present invention will be described below in conjunction with specific embodiments:

[0069] Assume that the noise reduction matrix i×j obtained in S4 is:

[0070]

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

[0072] Calculate the mean square error for each column in the noise reduction matrix 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] Among them, each data in the row matrix represents the mean square error value of the column. Peak searching is performed on the data of this row matrix to obtain the sampling points corresponding to the spatial positions of m gratings:

[0075] {d 1 、d 2 、d 3 、…d m}

[0076] Taking d 1 as an example, assume n = 5. The sampling point d 1 corresponding to the first grating position. Taking this sampling point as the center, obtain the data of columns d 1 -2, d 1 -1, d 1 、d 1 +1、d 1 +2, and calculate the average value of each row of data in these 5 columns The obtained matrix of 1 column and i rows is the spectral data of the first grating:

[0077]

[0078] Perform the above operations on m gratings respectively to obtain an i*m matrix:

[0079]

[0080] Each row of the matrix represents the reflected light intensities of different gratings after the pulsed light of the corresponding wavelength reaches the weak fiber grating array unit. Each column is the spectral data of each grating. The central wavelength of each grating can be obtained by finding the peak of each column of data using the Gaussian fitting algorithm.

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

[0082] Set a fast-scanning laser to generate a stepped swept-frequency light with a bandwidth of 3nm, a scanning range of 1534nm to 1537nm, 188 steps with a step of 16pm each, and an output time of 196.05us for each wavelength. When the laser outputs each wavelength, a wavelength trigger signal will be emitted accordingly. The electrical pulse signal generator receives the wavelength trigger signal emitted by the laser and modulates the pulse width of the synchronous pulse to control the optical pulse modulator to generate a laser with a pulse width of 18.52ns. Set a reflection enhancement point 3 meters in front of the grating array sensing unit.

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

[0084] Reflected light signals are generated at the reflection enhancement point for any scanned wavelength, such as Figure 4As shown, the reflected light signals at the reflection enhancement points can be observed at any wavelength. By searching for 188 reflected light signals at the reflection enhancement points, the data analysis and processing module forms a 188 * 8500 matrix from the 188-step sampling data. The rows of the matrix represent 188 wavelengths, and the columns represent 8500 sampling points extracted for each wavelength. After calculating the mean square error for each column of the matrix and then finding the peaks, at the positions where the grating exists, since the difference between the reflected signal and the noise is large, the mean square error value is large. At the positions where there is no grating, the data corresponding to the sampling points are basically noise signals, and the mean square error value is small. Therefore, by finding the peaks in the mean square error value matrix, the position information of the grating and the number of gratings, which is 791, can be obtained.

[0085] Determine the sampling points corresponding to the spatial positions of the 791 gratings. For any sampling point, taking the column data of 5 sampling points centered on this sampling point and calculating the average value for each row of data, the reflected spectrum of the grating corresponding to this sampling point can be obtained. For example, if the sampling point corresponding to the position of the first grating is 43, then calculate the average value for each row of data in columns 41, 42, 43, 44, and 45 respectively to obtain a 1-column and 188-row matrix. After splicing the spectrum of the matrix data and using the Gaussian fitting algorithm, the central wavelength of the first grating can be obtained. And so on, the central wavelength distribution of the 791 gratings is as Figure 5 shown.

[0086] In summary, the present invention utilizes the reflected light signals at the reflection enhancement points at any scanning wavelength, and accurately divides the reflected light signals of the weak grating array sensing units at each wavelength under high-speed dynamic scanning, solving the problem of inaccurate division of the grating reflection signals.

[0087] Although the present invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed, as long as they do not deviate from the spirit and scope of the present invention defined by the appended claims. It should be understood that different dependent claims and the features described herein can be combined in a manner different from that described in the original claims. It should also be understood that the features described in connection with a single embodiment can be used in other described embodiments.

Claims

1. A fast weak fiber grating array demodulation device based on reflection enhancement point, characterized in that: It includes a fast scanning laser, an electric pulse signal generator, an optical pulse modulator, an optical fiber amplifier, an optical fiber circulator, a reflection enhancement point, a weak grating array sensor unit, a photoelectric conversion module, a collection module, a data analysis and processing module, and a control module; The fast scanning laser outputs two electrical pulse signals: the first is a wavelength trigger signal, and the second is a periodic trigger signal. The wavelength trigger signal is used to send to the electrical pulse signal generator, and the electrical pulse signal generator synchronously outputs the electrical pulse signal and loads it to the optical pulse modulator to modulate the continuous laser output by the laser into pulse light; the periodic trigger signal is used to trigger the acquisition module to collect data; The control module enables the fast scanning laser to generate a step-sweep frequency light within a set range according to a preset rule, and transmits the step-sweep frequency light signal to the optical pulse modulator; An optical pulse modulator controlled by an electric pulse signal generator modulates a frequency-sweeping optical signal into an optical pulse signal with a fixed pulse width, and transmits it to an optical fiber amplifier; the optical fiber amplifier amplifies the optical pulse signal, and transmits the amplified optical pulse signal to a reflection enhancement point and a weak grating array sensing unit via an optical fiber circulator, wherein the reflection enhancement point is placed in front of the weak grating array sensing unit; the reflection enhancement point reflects the amplified optical pulse signal to obtain a reflected optical signal 1, and the weak grating array sensing unit reflects the amplified optical pulse signal to obtain a reflected optical signal 2; the photoelectric conversion module receives two reflected optical signals from the reflection enhancement point and the weak grating array sensing unit, the acquisition module samples the two reflected optical signals and sends them to the data analysis and processing module, the data analysis and processing module divides the weak grating array reflected optical signal 2 of any wavelength according to the reflected optical signal 1 of the reflection enhancement point, and then demodulates the position and central wavelength of each grating in the weak grating array sensing unit; The control module sends instructions to the acquisition module, the electrical pulse signal generator and the optical fiber amplifier to control data acquisition, optical pulse output and amplification.

2. A fast weak fiber grating array demodulation device based on reflection enhancement point 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, and the output time of each wavelength is adjustable, with the minimum being as low as 0.1μs.

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

4. A fast weak 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 position of each grating in the weak grating array sensor unit. According to the spatial arrangement order of the reflection enhancement point and the weak fiber Bragg grating sensor, the grating position on the optical fiber is confirmed by counting the reflected light delay.

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

6. A fast weak fiber grating array demodulation device based on reflection enhancement points according to claim 4, characterized in that: The reflection intensity at the reflection enhancement point is significantly higher than the system noise.

7. A fast weak fiber Bragg grating array demodulation method based on reflection enhancement point, implemented based on the fast weak fiber Bragg grating array demodulation device based on reflection enhancement 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, output time of each wavelength of the fast scanning laser, sets the optical pulse width and the amplification factor of the optical fiber amplifier; S2: based on the periodic trigger signal of the fast scanning laser, the reflected light signal of one scanning cycle is collected, including the reflected light signal 1 of the reflection enhancement point arranged in a spatial order and the reflected light signal 2 of the weak grating array sensor unit; S3: According to the reflected light signal 1 of the reflection enhancement point, split and output the reflected light signal 2 of any scanning wavelength in the weak grating array sensor unit; the weak grating array sensor data collected in one scanning cycle are formed into an i×j scanning cycle matrix, and each row of the scanning cycle matrix represents a 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 optical fiber length; S4: De-noising each row of the scan period matrix, i.e., the reflected light signal of each wavelength, to obtain an i×j de-noising matrix; S5: grating positioning: calculate the mean square error of each column of the above noise reduction matrix to obtain a row matrix of 1 row and j columns, perform peak search on the data in the row matrix to obtain the sampling point corresponding to the grating position, and obtain one or more peak values ​​by peak search. The peak value is the position where the reflected light intensity is the largest. After peak search, the spatial position information of m gratings is obtained; S6: Spectral stitching to find the central wavelength: In the i×j denoising matrix, after determining the sampling points corresponding to the spatial positions of the m gratings, perform the same operation on the m sampling points: extract n columns of data with a column of data corresponding to the sampling point as the center to obtain an i×n matrix, and calculate the average value of each row of the matrix to obtain a column matrix with 1 column and i rows. The column matrix is ​​the spectral data of a grating, and then use the Gaussian fitting algorithm to find the peak and obtain the central wavelength of this grating.

8. A fast weak fiber grating array demodulation method based on reflection enhancement points according to claim 7, characterized in that: According to the spatial arrangement order of the reflection enhancement point and the weak grating array sensor unit, the position of the reflection enhancement point and the grating is determined by the pulse light return time; the reflection enhancement point has a reflected light signal for each wavelength of incident light, and the reflected light signal 1 of the reflection enhancement point is used as the dividing point to divide the light pulse signal of each wavelength into the reflected light signal 2 of the weak grating array sensor unit.

9. A fast weak fiber grating array demodulation method based on reflection enhancement points according to claim 7, characterized in that: In S6, n is determined by the following formula: In the formula, τ represents the optical pulse width, and f represents the sampling rate of the acquisition module. Indicates rounding down *.

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