Weak fiber grating array ultrafast demodulation system and method based on laser array

Abstract

The invention discloses a weak fiber bragg grating array ultrafast demodulation system and method based on a laser array, and relates to the technical field of sensing, the system comprises a multi-wavelength laser array module, an optical beam splitter, an optical circulator, a weak fiber bragg grating array, a first photoelectric conversion module, a second photoelectric conversion module and a signal processing module; the output end of the multi-wavelength laser array module is connected with the input end of the light beam splitter, and the multi-wavelength laser array module integrates N wavelength channels; a first output end of the optical beam splitter is connected with the first photoelectric conversion module, and a second output end is connected with a first port of the optical circulator; a second port of the optical circulator is connected with the weak fiber grating array, and a third port is connected with the second photoelectric conversion module; the weak fiber bragg grating array comprises M weak fiber bragg gratings which are connected in series; and the output ends of the first photoelectric conversion module and the second photoelectric conversion module are connected to the signal processing module. According to the invention, ultra-high-speed demodulation can be carried out on M weak fiber gratings at the same time, and wavelength demodulation is realized.

Description

Technical Field

[0001] This invention relates to the field of sensing technology, and more specifically to an ultrafast demodulation system and method for weak fiber Bragg grating arrays based on laser arrays. Background Technology

[0002] Fiber Bragg grating (FBG) sensing technology is widely used in structural health monitoring, aerospace, energy equipment, and precision manufacturing due to its advantages such as resistance to electromagnetic interference, high sensitivity, small size, and ability to achieve quasi-distributed measurement. Traditional FBG demodulation systems often employ broadband light sources combined with spectral analysis or tunable laser scanning to achieve wavelength demodulation. However, the former suffers from limited spectral resolution and low signal-to-noise ratio, while the latter, due to the limited scanning rate of a single tunable laser, struggles to meet the real-time monitoring requirements of high-frequency dynamic signals.

[0003] With the development of on-chip integrated photonics technology, light source schemes based on multi-wavelength distributed feedback laser arrays have become an effective way to achieve high-speed fiber Bragg grating array demodulation. In traditional fiber Bragg grating demodulation systems based on wavelength division multiplexing, although the number of demodulated sensing points can be increased by expanding the scanning bandwidth of the light source, an excessively wide scanning range will significantly reduce the scanning rate of the system, thereby limiting the overall demodulation speed and real-time performance.

[0004] Therefore, how to achieve high-speed and stable signal demodulation while ensuring a large sensing capacity is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of the above problems, the present invention is proposed to provide an ultrafast demodulation system and method for weak fiber Bragg grating arrays based on laser arrays that overcomes or at least partially solves the above problems. It overcomes the shortcomings of existing fiber Bragg grating sensing systems, such as low demodulation rate and complex system structure. The system achieves complete separation of light waves in the time domain by precisely controlling the emission timing and wavelength spacing of multi-wavelength laser arrays, thereby avoiding interference of optical signals during transmission and reflection, and significantly improving the demodulation speed and signal-to-noise ratio of the system.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, embodiments of the present invention provide an ultrafast demodulation system for a weak fiber Bragg grating array based on a laser array, comprising: a multi-wavelength laser array module, an optical beam splitter, an optical circulator, a weak fiber Bragg grating array, a first photoelectric conversion module, a second photoelectric conversion module, and a signal processing module; The output of the multi-wavelength laser array module is connected to the input of the optical beam splitter. The multi-wavelength laser array module integrates N wavelength channels, where N≥2 and N is a positive integer. The first output of the optical beam splitter is connected to the first photoelectric conversion module, and the second output is connected to the first port of the optical circulator. The second port of the optical circulator is connected to the weak fiber grating array, and the third port is connected to the second photoelectric conversion module. The weak fiber grating array includes M series-connected weak fiber gratings, where M≥2 and M is a positive integer. The outputs of both the first and second photoelectric conversion modules are connected to the signal processing module.

[0007] Preferably, the wavelength spacing of each wavelength channel in the multi-wavelength laser array module is the same or similar, preferably between 0.1 and 0.8 nm; after the N wavelength channels are combined into a single output waveguide by a multi-stage Y-shaped combiner, a semiconductor optical amplifier (m-SOA) is connected as a common output end to modulate the continuous light into pulsed light, and finally output a light detection pulse; each wavelength channel includes a laser and a semiconductor optical amplifier (s-SOA) connected in series, and each wavelength channel outputs continuous light of one wavelength, wherein the s-SOA connected in series with the laser is used to control the on and off of the output continuous light.

[0008] Preferably, the 3dB bandwidth of the reflection spectrum of each weak fiber grating in the weak fiber grating array is the same or similar, preferably between 0.8 and 3 nm, and should be less than or equal to the wavelength coverage range of the output optical probe pulse of each wavelength channel in the multi-wavelength laser array module; the optical probe pulse is transmitted to each weak fiber grating sequentially through an optical beam splitter and an optical circulator, and each weak fiber grating reflects the optical probe pulse to form a reflected optical pulse. The reflectivity of each weak fiber grating is the same or similar, preferably between 1 / 10000 and 5 / 100; the spatial interval between two adjacent weak fiber gratings is greater than half the pulse width of the optical probe pulse.

[0009] Preferably, the first photoelectric conversion module uses a photodetector; the second photoelectric conversion module uses an avalanche photodetector.

[0010] Preferably, the signal processing module receives the optical detection pulse output by the first photoelectric conversion module, and the reflected light pulse that passes sequentially through the weak fiber grating array, the optical circulator, and the output of the second photoelectric conversion module. After fitting and calculation, the module outputs the center wavelength of each weak fiber grating in the weak fiber grating array.

[0011] Preferably, the s-SOA for each wavelength channel is located at the output end. The s-SOA is an on-chip integrated adjustable semiconductor optical amplifier. By precisely adjusting the drive current of the s-SOA, the continuous light output of each wavelength channel can be switched on and off.

[0012] Preferably, the signal processing module includes an FPGA and several sets of synchronous driving circuits, each set of synchronous driving circuits connected to a corresponding wavelength channel; the synchronous driving circuit includes a DAC, a current driving circuit, a modulation circuit, an ADC, and an analog switching circuit; the FPGA is connected to the DAC, modulation circuit, ADC, and analog switching circuit respectively; the FPGA controls the DAC to provide driving current to the lasers of each wavelength channel through the current driving circuit, so that N wavelength channels simultaneously output continuous light of different wavelengths; the FPGA controls the analog switching circuit, which sequentially selects N s-SOA, and at any given time, only one s-SOA is turned on; simultaneously, the FPGA sends a trigger signal to the modulation circuit, which drives the m-SOA to modulate the continuous light into pulsed light; the FPGA also synchronously triggers the ADC to perform data acquisition, the ADC is connected to the first photoelectric conversion module and the second photoelectric conversion module respectively, and is used to receive the pulses acquired by the photoelectric conversion module and perform analog-to-digital conversion; the ADC sends the digital signal back to the FPGA, which performs fitting and calculation processing. By precisely coordinating the switching timing of each s-SOA in multiple wavelength channels through a synchronous drive circuit, and using a trigger signal synchronized with the m-SOA modulation signal to control the data acquisition of a high-speed ADC, the time domain resolution of pulsed light signals with different weak fiber gratings and different wavelength reflections is achieved.

[0013] Preferably, the synchronous drive circuit also includes a temperature control circuit. The lasers of each wavelength channel achieve stable output of wavelength and power through the constant current source with micro-current precision of the current drive circuit and the high-precision temperature control unit of the temperature control circuit, thereby ensuring the wavelength consistency and repeatability of each wavelength channel under long-term operation.

[0014] Preferably, the time interval between the optical probe pulses output from two adjacent wavelength channels should be greater than the round-trip time of the light wave throughout the weak fiber grating array, to ensure that there is no cross-interference between the time-division multiplexed signals.

[0015] Secondly, embodiments of the present invention provide a method for demodulating a weak fiber grating array based on a multi-wavelength laser array, comprising the following steps: Step 1: N wavelength channels in the multi-wavelength laser array module simultaneously emit N continuous light of different wavelengths, and the s-SOA connected in series in each wavelength channel is in the off state. Step 2: Turn on the s-SOA connected in series for the i-th (i=1,2,...,N) wavelength channel, so that the channel outputs continuous light, which is then modulated by the common output terminal m-SOA after wave combining to form a photodetector pulse; Step 3: The generated optical probe pulse is input into the optical beam splitter. The optical probe pulse at the first output end of the optical beam splitter enters the first photoelectric conversion module for real-time monitoring of pulsed optical power. The optical probe pulse at the second output end of the optical beam splitter is input into the weak fiber grating array through the optical circulator. Step 4: The optical probe pulse input to the weak fiber Bragg grating array is reflected by M weak fiber Bragg gratings to form M reflected optical pulses. These M reflected optical pulses then pass through the second and third ports of the optical circulator and enter the second photoelectric conversion module. Time-division multiplexing is used to distinguish the reflected optical pulses of each weak fiber Bragg grating, thus obtaining the M reflected optical pulses corresponding to the i-th wavelength channel, denoted as I. N,M ; Step 5: Repeat steps 1 to 4 N times, sequentially activating the m-SOA in N wavelength channels, with each wavelength channel generating M reflected light pulses. Step 6: The signal processing module performs fitting calculations based on the N reflected light pulses of different wavelengths obtained in step 5 for each weak fiber grating to obtain the center wavelength of each weak fiber grating in the weak fiber grating array.

[0016] Preferably, the specific process of step 6 is as follows: Step 61: To eliminate the influence of light source power fluctuations, the reflected light pulse corresponding to each wavelength channel detected by the second photoelectric conversion module is divided by the photodetector pulse of the corresponding wavelength channel detected by the first photoelectric conversion module. This normalizes the reflected light intensity of the reflected light pulses, resulting in M ​​normalized reflected light pulses for each wavelength channel, and a total of N sets of normalized data R. N,M The normalized reflected light pulse is represented as:

[0017] in, This represents the optical probe pulse for the i-th wavelength channel; This represents the Mth reflected light pulse corresponding to the i-th wavelength channel; This represents the Mth normalized reflected light pulse corresponding to the i-th wavelength channel; the M normalized reflected light pulses corresponding to the i-th wavelength channel include... , ,..., ; Step 62: For N sets of normalized data, the normalized reflected light pulses (R) corresponding to the same weak fiber grating are... 1,M ,,R 2,M ,……,R N,M Arrange them in descending order of wavelength to obtain M. The center wavelengths of M weak fiber gratings are obtained by curve fitting of the N discrete sampled reflection spectra for each weak fiber grating.

[0018] Preferably, the multi-wavelength laser array module needs to wait for the previously emitted optical probe pulse to be completely reflected by the weak fiber grating array at the end to the second photoelectric conversion module before it can emit the next optical probe pulse.

[0019] Preferably, Gaussian curve fitting is performed on the discrete sampled reflectance spectrum, which can be expressed as: ; in, This indicates that the wavelength of the light probe pulse for the Mth weak fiber grating is... Normalized reflected light pulse at time; A M This represents the peak amplitude of the discrete sampled reflectance spectrum of the Mth weak fiber grating; This represents the center wavelength of the Mth weak fiber grating obtained by Gaussian fitting; C is the spectral width parameter. M This is the background constant.

[0020] As can be seen from the above technical solution, compared with the prior art, this invention discloses an ultrafast demodulation system and method for weak fiber Bragg grating arrays based on laser arrays. This system integrates multiple fixed-wavelength lasers on-chip to output multi-channel light sources with narrow-band spacing. By rationally designing the laser wavelength spacing, pulse width, and spatial distribution of the weak fiber Bragg gratings, it ensures that the reflected signals of each channel do not overlap in the time domain, thereby achieving high-capacity, high-speed, and low-crosstalk demodulation of the weak fiber Bragg grating array. This invention combines the advantages of both wavelength division and time division, providing a new technical path for constructing on-chip integrated intelligent fiber optic sensing systems. Specifically, it includes the following beneficial effects: (1) By adopting a structure that combines a multi-wavelength laser array module with time-division multiplexing, the sequential pulse modulation and reflection acquisition of multi-channel lasers are realized. It can demodulate multiple weak fiber gratings within a time scale of hundreds of nanoseconds and has an ultra-fast response speed.

[0021] (2) By normalizing the multi-channel laser pulse reflection signal and using Gaussian curve fitting to extract the center wavelength of the reflection spectrum of the weak fiber grating, the influence of system noise and light source power fluctuation on the measurement results is effectively suppressed, and the accuracy and stability of wavelength measurement are greatly improved.

[0022] (3) By integrating a multi-wavelength laser array and a controllable SOA module on the chip, the optical path structure of the traditional external cavity demodulation system is simplified, the system size and power consumption are significantly reduced, and the overall stability and scalability are improved.

[0023] (4) Each wavelength channel in the multi-wavelength laser array module does not require current adjustment and wavelength scanning, thus ensuring the stability of the output wavelength. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the structure of the ultrafast demodulation system based on a laser array and a weak fiber grating array provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of a multi-wavelength laser array chip provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the original reflection spectrum data of a weak fiber optic grating array provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the discrete sampling reflectance spectrum fitting results of a single weak fiber grating provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the experimental results of the system provided in this embodiment of the invention in high-frequency vibration measurement. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention discloses an ultrafast demodulation system based on a weak fiber Bragg grating array using a laser array, comprising: a multi-wavelength laser array module, an optical beam splitter, an optical circulator, a weak fiber Bragg grating array, a first photoelectric conversion module, a second photoelectric conversion module, and a signal processing module; The output of the multi-wavelength laser array module is connected to the input of the optical beam splitter. The multi-wavelength laser array module integrates N wavelength channels, where N≥2 and N is a positive integer. The first output of the optical beam splitter is connected to the first photoelectric conversion module, and the second output is connected to the first port of the optical circulator. The second port of the optical circulator is connected to the weak fiber grating array, and the third port is connected to the second photoelectric conversion module. The weak fiber grating array includes M series-connected weak fiber gratings, where M≥2 and N is a positive integer. The outputs of both the first and second photoelectric conversion modules are connected to the signal processing module.

[0028] Furthermore, the wavelength spacing of each wavelength channel in the multi-wavelength laser array module is the same or similar, preferably between 0.1 and 0.8 nm; after the N wavelength channels are combined into a single output waveguide by a multi-stage Y-shaped combiner, a semiconductor optical amplifier (m-SOA) is connected as a common output end to modulate the continuous light into pulsed light, and finally output a light detection pulse; each wavelength channel includes a laser and a semiconductor optical amplifier (s-SOA) connected in series, and each wavelength channel outputs continuous light of one wavelength, wherein the s-SOA connected in series with the laser is used to control the on and off of the output continuous light.

[0029] Furthermore, the 3dB bandwidth of the reflection spectrum of each weak fiber grating in the weak fiber grating array is the same or similar, preferably between 0.8 and 3 nm, and should be less than or equal to the coverage range of the output wavelength of each wavelength channel of the multi-wavelength laser array; the optical probe pulse is transmitted to each weak fiber grating sequentially through the optical beam splitter and optical circulator, and each weak fiber grating reflects the optical probe pulse to form a reflected optical pulse. The reflectivity of each weak fiber grating is the same or similar, preferably between 1 / 10000 and 5 / 100; the spatial interval between two adjacent weak fiber gratings is greater than half the pulse width of the optical probe pulse.

[0030] Furthermore, the first photoelectric conversion module uses a photodetector; the second photoelectric conversion module uses an avalanche photodetector.

[0031] Furthermore, the signal processing module receives the optical detection pulse output by the first photoelectric conversion module, as well as the reflected light pulse that passes through the weak fiber grating array, the optical circulator, and the second photoelectric conversion module in sequence. After fitting and calculation, it outputs the center wavelength of each weak fiber grating in the weak fiber grating array.

[0032] Furthermore, the s-SOA for each wavelength channel is located at the output end. The s-SOA is an on-chip integrated adjustable semiconductor optical amplifier. By precisely adjusting the drive current of the s-SOA, the continuous light output of each wavelength channel can be switched on and off.

[0033] Furthermore, the signal processing module includes an FPGA and several sets of synchronous driving circuits. The synchronous driving circuits include a DAC, a current driving circuit, a modulation circuit, an ADC, and an analog switching circuit. The FPGA is connected to the DAC, modulation circuit, ADC, and analog switching circuit respectively. The DAC provides driving current to the lasers of each wavelength channel through the current driving circuit, enabling N wavelength channels to simultaneously output continuous light of different wavelengths. The FPGA controls the analog switching circuit, which sequentially selects N s-SOA (s-SOA), with only one s-SOA active at any given time. Simultaneously, the FPGA sends a trigger signal to the modulation circuit, which drives the m-SOA to modulate the continuous light into pulsed light. The FPGA also synchronously triggers the ADC to acquire data. The ADC is connected to the first and second photoelectric conversion modules respectively, used to receive the pulses acquired by the photoelectric conversion modules and perform analog-to-digital conversion. The ADC sends the digital signal back to the FPGA, which performs fitting and calculation processing. By precisely coordinating the switching timing of each s-SOA in multiple wavelength channels through a synchronous drive circuit, and using a trigger signal synchronized with the m-SOA modulation signal to control the data acquisition of a high-speed ADC, the time domain resolution of pulsed light signals with different weak fiber gratings and different wavelength reflections is achieved.

[0034] Furthermore, the synchronous drive circuit also includes a temperature control circuit. The lasers of each wavelength channel achieve stable output of wavelength and power through the constant current source with micro-current precision of the current drive circuit and the high-precision temperature control unit of the temperature control circuit, thereby ensuring the wavelength consistency and repeatability of each wavelength channel under long-term operation.

[0035] Furthermore, the time interval between the optical probe pulses output from two adjacent wavelength channels must be greater than the round-trip time of the light wave throughout the weak fiber grating array to ensure that there is no cross-interference between time-division multiplexed signals.

[0036] Furthermore, in the weak fiber Bragg grating array, the spacing between two adjacent weak fiber Bragg gratings is precisely set according to the propagation time of the optical probe pulse and the system sampling rate to ensure that the reflected light pulses do not overlap in the time domain; at the same time, the 3dB bandwidth of the reflection spectrum of each weak fiber Bragg grating is kept consistent to achieve high signal distinguishability and accurate wavelength matching.

[0037] In one specific embodiment, a weak fiber grating array-based ultrafast demodulation system is as follows: Figure 1 As shown, it mainly includes the following modules: (1) Multi-wavelength laser array module: Consists of a multi-wavelength laser array chip and a driving circuit. The wavelength laser array chip is as follows: Figure 2 As shown, Figure 2 Image (a) is a schematic diagram of the structure of a multi-wavelength laser array chip. Figure 2Image (b) shows a physical diagram of the multi-wavelength laser array chip. The multi-wavelength laser array chip includes N wavelength channels, a multi-stage Y-combiner, and a semiconductor optical amplifier (m-SOA). Each wavelength channel consists of a laser LD and a semiconductor optical amplifier (s-SOA) connected in series. This chip achieves precise wavelength control based on reconfigurable equivalent chirp technology, ensuring stable and repeatable output wavelengths. In this embodiment, the chip integrates eight wavelength channels (LD1–LD8), with a wavelength spacing of approximately 0.13 nm between each channel. The center wavelengths are 1536.083 nm, 1536.208 nm, 1536.337 nm, 1536.469 nm, 1536.608 nm, 1536.746 nm, 1536.885 nm, and 1537.031 nm, respectively. Each wavelength channel integrates a semiconductor optical amplifier (s-SOA1~s-SOA8) at its end, which acts as an optical switch for time-division control of each channel's output. The light from the eight channels is combined into a single path by a three-stage Y-type multiplexer, and then intensity-modulated by the m-SOA to generate an optical pulse with a width of 10ns. Each wavelength channel is turned on sequentially for 120ns, and a complete cycle is 960ns.

[0038] (2) Optical beam splitter: The power ratio of its two output ends is 1:9, of which 10% of the optical power is connected to the first photoelectric conversion module for real-time power monitoring and normalization calibration, and the remaining 90% of the optical power enters the sensing optical path.

[0039] (3) Optical circulator: It is a three-port optical device that enables unidirectional optical transmission. The typical isolation is greater than 40 dB and the insertion loss is less than 1 dB.

[0040] (4) Weak fiber grating array: It consists of 10 weak fiber gratings connected in series. The center wavelength of each grating is about 1536.5nm, the reflectivity is about 5%, the 3dB bandwidth is 1.2nm, the spatial spacing is 1m, and the total length of the array is about 10m.

[0041] (5) First photoelectric conversion module: A photodetector (PD) with a bandwidth of 200MHz is used to monitor the 10% optical power after beam splitting in real time and provide a power normalization calibration reference for the system.

[0042] (6) Second photoelectric conversion module: an avalanche photodetector (APD) with a bandwidth of 300MHz is used to receive the reflected signal of the weak fiber grating array and convert it into an electrical signal.

[0043] (7) Signal processing module: It can complete the processing and analysis of optical signals within ≤1μs and output the center wavelength information corresponding to each weak fiber grating.

[0044] On the other hand, the demodulation method of the ultrafast demodulation system based on a laser array and a weak fiber grating array includes the following steps: S1: In the multi-wavelength laser array module, N wavelength channels simultaneously emit N continuous light of different wavelengths, and the s-SOA connected in series for each wavelength channel is in the off state. S2: Enable the s-SOA connected in series for the i-th (i=1,2,……,N) wavelength channel, so that the channel outputs continuous light, which is then modulated by the common output terminal m-SOA after wave combining to form a photodetector pulse; S3: The generated optical probe pulse is input to the optical beam splitter. The optical probe pulse passing through the first output end of the optical beam splitter enters the first photoelectric conversion module for real-time monitoring of pulsed optical power. The optical probe pulse passing through the second output end of the optical beam splitter is input to the weak fiber grating array through the optical circulator. S4: The optical probe pulse input to the weak fiber Bragg grating array is reflected by M weak fiber Bragg gratings, forming M reflected optical pulses. These M reflected optical pulses then pass through the second and third ports of the optical circulator and enter the second photoelectric conversion module. Time-division multiplexing is used to distinguish the reflected optical pulses of each weak fiber Bragg grating, thus obtaining the M reflected optical pulses corresponding to the i-th wavelength channel, denoted as I. N,M ; S5: Repeat steps 1 to 4 N times, sequentially activating the m-SOA in N wavelength channels, with each wavelength channel generating M reflected light pulses; S6: The signal processing module performs fitting calculations based on the N reflected light pulses of different wavelengths obtained in S5 for each weak fiber grating to obtain the center wavelength of each weak fiber grating in the weak fiber grating array.

[0045] Furthermore, the specific process of S6 is as follows: S61: To eliminate the influence of light source power fluctuations, the reflected light pulse corresponding to each wavelength channel detected by the second photoelectric conversion module is divided by the photodetector pulse of the corresponding wavelength channel detected by the first photoelectric conversion module. This normalizes the reflected light intensity of the reflected light pulses, resulting in M ​​normalized reflected light pulses for each wavelength channel, and a total of N sets of normalized data R. N,M The normalized reflected light pulse is represented as:

[0046] in, This represents the optical probe pulse for the i-th wavelength channel; This represents the Mth reflected light pulse corresponding to the i-th wavelength channel; This represents the Mth normalized reflected light pulse corresponding to the i-th wavelength channel; the M normalized reflected light pulses corresponding to the i-th wavelength channel include... , ,..., ;N=1,2,…,8;M=1,2,…,10; S62: For N sets of normalized data, the normalized reflected light pulses (R) corresponding to the same weak fiber grating will be... 1,M ,,R 2,M ,……,R N,M Arrange them in descending order of wavelength to obtain M. The center wavelengths of M weak fiber gratings are obtained by curve fitting of the N discrete sampled reflection spectra for each weak fiber grating. S63: By subtracting the center wavelengths of the M weak fiber gratings from their corresponding center wavelengths obtained in the first demodulation, the wavelength shift of the reflection spectrum of each weak fiber grating relative to the initial state can be obtained. Then utilize wavelength shift The relationship between strain and vibration is used to measure the vibration of a weak fiber Bragg grating array. The reflection spectrum of each weak fiber Bragg grating is a combination of the power values ​​of N discrete sampled reflection spectra corresponding to that weak fiber Bragg grating.

[0047] Furthermore, the multi-wavelength laser array module needs to wait for the previously emitted optical probe pulse to be completely reflected by the weak fiber grating array at the very end to the second photoelectric conversion module before it can emit the next optical probe pulse.

[0048] Furthermore, fitting a Gaussian curve to the discrete sampled reflectance spectrum can be expressed as:

[0049] in, This indicates that the wavelength of the light probe pulse for the Mth weak fiber grating is... Normalized reflected light pulse at time; A M This represents the peak amplitude of the discrete sampled reflectance spectrum of the Mth weak fiber grating; This represents the center wavelength of the Mth weak fiber grating obtained by Gaussian fitting; C is the spectral width parameter. M This is the background constant.

[0050] In one specific embodiment, the ultrafast demodulation method for weak fiber grating arrays based on laser arrays is as follows: S1: All 8 wavelength channels in the multi-wavelength laser array module are turned on simultaneously, and all s-SOA channels are turned off; S2: Turn on the s-SOA1 connected in series with the first wavelength channel, so that the channel outputs continuous light. After being modulated by the common output terminal m-SOA after wave combining, it forms a 10ns pulse light with a period of 960ns. S3: The generated pulsed light is input into the optical beam splitter, where the pulsed light from the first output end of the optical beam splitter enters the first photoelectric conversion module for real-time monitoring of the pulsed light power; the pulsed light from the second output end of the optical beam splitter is input into the weak fiber grating array through the second port of the optical circulator. S4: The optical pulse signal input to the weak fiber Bragg grating array is reflected successively by 10 weak fiber Bragg gratings, forming 10 reflected optical pulse signals. These 10 reflected optical pulse signals enter the second photoelectric conversion module sequentially through the third port of the optical circulator. The reflected optical pulse signals of each weak fiber Bragg grating are distinguished using time-division multiplexing, thereby obtaining the 10 reflected optical pulse signals I corresponding to that wavelength channel. N,M Where N is the wavelength channel number and M is the weak fiber grating number; for example Figure 3 The image shows the original data of the reflection spectra of 10 weak fiber gratings obtained when s-SOA1 is enabled. The reflected light pulse signals are arranged sequentially in the time domain and do not overlap with each other. The peak voltage of each reflection spectrum is: I 1,1 =0.2158V, I 1,2 =0.0629V, I 1,3 =0.1000V, I 1,4 =0.0719V, I 1,5 =0.0679V, I 1,6 =0.1039V, I 1,7 =0.0995V, I 1,8 =0.0839V, I 1,9 =0.0400V, I 1,10 =0.0160V; S5: To eliminate the influence of light source power fluctuations, the signal processing module processes the reflected light pulse signal I detected by the second photoelectric conversion module. N,M (N=1,2,…,8; M=1,2,…,10) and the pulsed light detected by the first photoelectric conversion module are used as monitoring signal I. ref,N Perform division to achieve normalization and obtain the normalized reflected signal; when N=1, we get: ; I ref,1 =0.3122V, the normalized reflection signal of the first wavelength channel corresponding to 10 weak fiber gratings is: R 1,1 =0.6911V, R 1,2 =0.2014V, R 1,3 =0.3203V, R 1,4 =0.2304V, R 1,5 =0.2176V, R 1,6 =0.3328V, R 1,7=0.3199V, R 1,8 =0.2686V, R 1,9 =0.1281V, R 1,10 =0.1208V; S6: Repeat steps S1 to S5, sequentially activating the s-SOA in each of the eight wavelength channels, obtaining normalized reflection signals from 10 weak fiber gratings each time, ultimately obtaining a total of eight sets of normalized data. ; ; That is, each weak fiber grating corresponds to a normalized reflection signal at 8 discrete wavelengths, where N represents the wavelength channel number and M represents the grating number, represented in matrix form as follows:

[0051] ; S7: Each column {R} in the matrix R obtained from S6 1,M ,R 2,M ,…,R 8,M That is, the normalized reflection signal corresponding to the Mth weak fiber grating under different wavelength channels constitutes the discrete reflection spectrum of the weak fiber grating. S8: To accurately extract the center wavelength of the reflection spectrum of each weak fiber grating The discrete reflection spectra of 10 weak fiber gratings were fitted with Gaussian curves based on the nonlinear least squares method. The fitting function expression is as follows: ; in, For the Mth weak fiber grating in matrix R, in the wavelength channel The normalized reflected signal, i.e., R N,M A M Let be the peak amplitude of the discrete reflection spectrum of the Mth weak fiber grating; The center wavelength is obtained by Gaussian fitting. C is the spectral width parameter. M The background constant is used; finally, the center wavelength vector of each weak fiber grating under this measurement is obtained as follows: ; This vector represents the center reflection wavelength of the M weak fiber gratings in the weak fiber grating array under the current state. After fitting, the center wavelengths of the 10 weak fiber gratings are obtained as follows: 1536.460nm, 1536.486nm, 1536.516nm, 1536.446nm, 1536.476nm, 1536.502nm, 1536.436nm, 1536.466nm, 1536.496nm, and 1536.506nm. The correlation coefficient R² > 0.998, indicating high fitting accuracy, which provides a basis for subsequent demodulation of wavelength drift and vibration changes. The fitting results are as follows: Figure 4 As shown; S9: Compare the measured center wavelengths of each weak fiber grating with the center wavelengths in the initial static state. Subtract the center wavelengths of the M weak fiber gratings from their corresponding center wavelengths obtained in the first demodulation to obtain the wavelength shift of the reflection spectrum of each weak fiber grating relative to the initial state. The wavelength shift is expressed as: ; in, This represents the wavelength shift of the m-th weak fiber grating; This represents the measured center wavelength of the m-th weak fiber grating; The center wavelength of the m-th weak fiber grating in its initial static state is the center wavelength obtained by the first demodulation. It is the result of the above measurement of the weak fiber grating without applying any vibrational physical quantity to it. The reflection spectrum of each weak fiber grating is a combination of the power values ​​of the N discrete sampled reflection spectra corresponding to each weak fiber grating. S10: Vibration measurement of weak fiber grating arrays is achieved by utilizing the relationship between wavelength shift and strain; the relationship between wavelength shift and strain is as follows: ; Where, p e ≈0.22 is the effective photoelasticity coefficient of the optical fiber; This represents the wavelength shift of the B-th weak fiber grating; This indicates the Bragg reflection wavelength, i.e., the center wavelength; This represents the strain generated on the optical fiber. From this, the wavelength sensitivity can be calculated to be approximately 1.2. That is, a wavelength change of 1.2 pm corresponds to a strain change of 1. Therefore, the measured wavelength change signal can be converted into a dynamic strain signal.

[0052] In this embodiment, to verify the dynamic response performance of the system, a single weak fiber Bragg grating is fixed to a vibration exciter. The vibration exciter is driven by an arbitrary waveform generator and outputs a sinusoidal excitation signal with a frequency of 1 kHz through a power amplifier. The system completes a single wavelength demodulation cycle of 960 ns, realizing high-speed dynamic strain measurement. Figure 5 (a) shows the time-domain waveform of the vibration signal obtained by demodulation after 5000 consecutive measurements. It can be seen that the interval between adjacent sampling points is 960 ns. Figure 5 In the middle (b), the corresponding power spectral density (PSD) is shown. Figure 5 As can be seen, the main frequency of the demodulated vibration signal is highly consistent with the applied excitation frequency, with a frequency deviation of less than 0.2%, which fully verifies the system's excellent frequency resolution and stability.

[0053] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0054] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A weak fiber Bragg grating array-based ultrafast demodulation system, characterized in that, include: Multi-wavelength laser array module, optical beam splitter, optical circulator, weak fiber grating array, first photoelectric conversion module, second photoelectric conversion module and signal processing module; The output of the multi-wavelength laser array module is connected to the input of the optical beam splitter. The multi-wavelength laser array module integrates N wavelength channels, where N≥2. The first output of the optical beam splitter is connected to the first photoelectric conversion module, and the second output is connected to the first port of the optical circulator. The second port of the optical circulator is connected to the weak fiber grating array, and the third port is connected to the second photoelectric conversion module. The weak fiber grating array includes M series-connected weak fiber gratings, where M≥2. The outputs of both the first and second photoelectric conversion modules are connected to the signal processing module.

2. The ultrafast demodulation system based on a laser array and a weak fiber grating array as described in claim 1, characterized in that, In a multi-wavelength laser array module, the wavelength spacing of each wavelength channel is the same or similar; N wavelength channels are combined into a single output waveguide by a multi-stage Y-shaped combiner, and then output as an optical probe pulse by a semiconductor optical amplifier; each wavelength channel includes a laser and a semiconductor optical amplifier connected in series.

3. The ultrafast demodulation system based on a laser array and a weak fiber grating array as described in claim 2, characterized in that, In a weak fiber grating array, the 3dB bandwidth of the reflection spectrum of each weak fiber grating is the same or similar, and is less than or equal to the wavelength coverage of the output optical probe pulse of each wavelength channel in the multi-wavelength laser array module; the optical probe pulse is transmitted to each weak fiber grating sequentially through an optical beam splitter and an optical circulator, and each weak fiber grating reflects the optical probe pulse to form a reflected optical pulse, and the reflectivity of each weak fiber grating is the same or similar; the spatial interval between two adjacent weak fiber gratings is greater than half the pulse width of the optical probe pulse.

4. The ultrafast demodulation system based on a laser array and a weak fiber grating array as described in claim 1, characterized in that, The first photoelectric conversion module uses a photodetector; the second photoelectric conversion module uses an avalanche photodetector.

5. The ultrafast demodulation system for weak fiber grating arrays based on laser arrays as described in claim 3, characterized in that, The signal processing module receives the optical detection pulse output by the first photoelectric conversion module, as well as the reflected light pulse that passes through the weak fiber grating array, the optical circulator, and the second photoelectric conversion module in sequence. After fitting and calculation, it outputs the center wavelength of each weak fiber grating in the weak fiber grating array.

6. The ultrafast demodulation system based on a laser array and a weak fiber grating array as described in claim 2, characterized in that, The signal processing module includes an FPGA and several sets of synchronous driving circuits, each connected to a corresponding wavelength channel. The synchronous driving circuits include a DAC, a current driving circuit, a modulation circuit, an ADC, and an analog switching circuit. The FPGA is connected to the DAC, modulation circuit, ADC, and analog switching circuit respectively. The FPGA controls the DAC to drive the laser of the wavelength channel through the current driving circuit. The FPGA controls the analog switching circuit to sequentially select the semiconductor optical amplifier of the corresponding wavelength channel. The FPGA sends a trigger signal to the modulation circuit to drive the semiconductor optical amplifier that outputs photodetector pulses. The ADC is connected to the first photoelectric conversion module and the second photoelectric conversion module respectively. The FPGA synchronously triggers the ADC to acquire data and receive the returned signal. The FPGA performs fitting calculations based on the returned signal.

7. The ultrafast demodulation system for weak fiber grating arrays based on laser arrays as described in claim 1, characterized in that, The semiconductor optical amplifiers for each wavelength channel are located at the output end. The semiconductor optical amplifiers are on-chip integrated adjustable semiconductor optical amplifiers. By adjusting their driving current, the pulse light can be switched on and off. The time interval between the optical detection pulses output by two adjacent wavelength channels is greater than the round-trip time of the light wave in the weak fiber grating array.

8. A method for ultrafast demodulation of weak fiber Bragg grating arrays based on laser arrays, characterized in that, The ultrafast demodulation system based on a laser array and a weak fiber grating array as described in any one of claims 1-7 includes the following steps: Step 1: The N wavelength channels in the multi-wavelength laser array module simultaneously emit N continuous light of different wavelengths; Step 2: Turn on the i-th wavelength channel, i=1,2,……,N, so that the continuous light output from this wavelength channel forms a photodetector pulse output; Step 3: The generated optical probe pulse is input into the optical beam splitter, wherein the optical probe pulse passing through the first output end of the optical beam splitter enters the first photoelectric conversion module; the optical probe pulse passing through the second output end of the optical beam splitter is input into the weak fiber grating array through the optical circulator; Step 4: The optical probe pulse input to the weak fiber Bragg grating array is reflected by M weak fiber Bragg gratings to form M reflected optical pulses. These M reflected optical pulses then pass through the second and third ports of the optical circulator and enter the second photoelectric conversion module. Time-division multiplexing is used to distinguish the reflected optical pulses of each weak fiber Bragg grating, thus obtaining the M reflected optical pulses corresponding to the i-th wavelength channel, denoted as I. N,M ; Step 5: Repeat steps 1 to 4 N times, sequentially activating N wavelength channels, with each wavelength channel generating M reflected light pulses; Step 6: The signal processing module performs fitting calculations based on the N reflected light pulses corresponding to each weak fiber grating to obtain the center wavelength of each weak fiber grating in the weak fiber grating array.

9. The ultrafast demodulation method for weak fiber grating arrays based on laser arrays as described in claim 8, characterized in that, The specific process of step 6 is as follows: Step 61: Divide the reflected light pulse corresponding to each wavelength channel detected by the second photoelectric conversion module by the photodetector pulse of the corresponding wavelength channel detected by the first photoelectric conversion module to obtain M normalized reflected light pulses corresponding to each wavelength channel, and obtain a total of N sets of normalized data. Step 62: Arrange the normalized reflected light pulses corresponding to the same weak fiber grating in the N sets of normalized data according to wavelength from largest to smallest, to obtain M. The center wavelengths of M weak fiber gratings are obtained by curve fitting of the N discrete sampled reflection spectra for each weak fiber grating.

10. The ultrafast demodulation method for weak fiber grating arrays based on laser arrays as described in claim 8, characterized in that, The next optical probe pulse is emitted only after the previous optical probe pulse emitted by the wavelength laser array module is completely reflected by the weak fiber grating array to the second photoelectric conversion module.

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