Weak reflection FBG demodulation system and method adopting Fourier domain mode locking frequency sweeping chaotic laser

Abstract

The invention provides a weak reflection FBG demodulation system and method adopting a Fourier domain mode-locking frequency-sweeping chaotic laser. According to the invention, the kHz-level demodulation speed and the femtometer-level wavelength demodulation precision are realized at the same time through the wide-spectrum frequency sweeping and rapid tuning capability of the FDML-SCL; through a real-time wavelength self-calibration algorithm, wavelength drift introduced by high-speed frequency sweeping is effectively compensated, and demodulation stability is ensured; through a chaos related demodulation technology, overlapped signals are accurately separated by utilizing the time-frequency chaos characteristic of the signals, and 367 wavelength division multiplexing channels in a 43nm range and the time division multiplexing capability of a 70ps interval are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing and spectrum analysis, and particularly relates to a weak reflection FBG demodulation system and method using a Fourier domain mode-locked frequency-sweeping chaotic laser. Background Art

[0002] Fiber Bragg Gratings (FBGs), with their high sensitivity, immunity to electromagnetic interference, and miniaturization, enable precise measurement of stress, strain, and temperature through reflection wavelength shifting. Weakly reflecting FBGs significantly reduce reflectivity, effectively minimizing crosstalk between channels and significantly enhancing system multiplexing capabilities. Combined with high-speed demodulation technology, they excel in applications requiring high-speed, real-time monitoring and enabling rapid response to environmental changes. Consequently, they are widely used in critical areas such as pipeline monitoring, power grid security, bridge health diagnostics, aerospace, and border security.

[0003] The development of high-speed, weak-reflection FBG demodulation technology is driving the evolution of fiber-optic sensing systems towards higher speeds and higher precision. Traditional spectrometer demodulation schemes, limited by the inherent characteristics of optical splitters, are no longer able to meet the demands of high-speed dynamic measurements. In recent years, demodulation schemes based on swept-frequency light sources, combined with photodetectors or A / D systems, have shown significant promise in high-speed measurements in the kHz-to-GHz range. Two representative types of swept-frequency light sources are time-stretched and Fourier-domain mode-locked (FDML) swept-frequency light sources. Time-stretched light sources employ dispersive Fourier transform technology to temporally stretch optical pulses through long single-mode fibers, chirped fiber gratings, and other dispersive devices, enabling high-speed measurements in the MHz-to-GHz range. While this method offers unique speed advantages for high-speed, weak-reflection FBG demodulation, it is challenging to precisely manage dispersion. The broadband spectrum comes at the cost of signal attenuation, compromising both measurement capacity and measurement distance, making it challenging to implement in scenarios requiring high stability, multi-channel, or long-distance monitoring. FDML swept-frequency light sources achieve high-speed kHz-MHz frequency sweeps through Fourier mode locking. Compared to time-stretched light sources, they are easier to control and offer the advantage of simultaneously performing wavelength and time division multiplexing with a single detector. However, their wavelength stability is affected by filter nonlinearities and intracavity dispersion, necessitating external calibration systems such as grating arrays. This external calibration is susceptible to environmental interference and increases system complexity. Furthermore, while improving multiplexing capabilities, FDML swept-frequency light sources face challenges in identifying the central wavelength due to time-domain overlap of target signals. This issue has not yet been fundamentally resolved, limiting the system's practical multiplexing performance.

[0004] In summary, current high-speed, weak-reflection FBG demodulation technology faces technical gaps, including wavelength instability, environmental interference, limited accuracy, and complex wavelength identification when multiplexing increases. Therefore, developing a demodulation method that can achieve stability, high speed, high resolution, and wavelength identification without relying on complex calibration systems is a key technological breakthrough to meet the future needs of high-speed dynamic measurement. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems of unstable wavelength of swept-frequency light source, environmental interference, limited accuracy, limited multiplexing capability and complex wavelength recognition algorithm of the demodulation system in the existing high-speed weak-reflection FBG demodulation technology. A weak-reflection FBG demodulation system and method using Fourier domain mode-locked swept-frequency chaotic laser are proposed.

[0006] The present invention is achieved through the following technical solutions. The present invention proposes a weak reflection FBG demodulation system using a Fourier domain mode-locked swept chaotic laser. The system includes a Fourier domain mode-locked swept chaotic laser FDML-SCL, a one-to-three optical coupler, and a data acquisition device. The FDML-SCL outputs the periodic frequency-sweep chaotic laser into three paths through a one-to-three optical coupler. The first path is the laser path, the second path is the calibration path, and the third path is the detection path. The three paths are respectively input into a data acquisition device, and the collected data is input into Matlab for target recognition processing. The detection path includes several groups of weak-reflection FBG arrays, which are connected to the FDML-SCL and the data acquisition device through an optical circulator. The weak-reflection FBG array uses weak-reflection FBGs with different central wavelengths in series to form a wavelength division multiplexing unit. By connecting multiple identical wavelength division multiplexing units in series using single-mode optical fiber, time division multiplexing is further achieved on the basis of wavelength division multiplexing.

[0007] Furthermore, the data acquisition device consists of three high-bandwidth optoelectronic converters connected to three channels of a high-speed, high-bandwidth oscilloscope; channel one of the oscilloscope is the FDML-SCL signal, channel two is the initial wavelength calibration signal, and channel three is the weak-reflection FBG array reflection signal.

[0008] Furthermore, the laser path is specifically as follows: the laser path connects the optical coupler signal to the first photoelectric converter, and the output signal thereof is input into the oscilloscope channel 1 Ch1 for detection.

[0009] Furthermore, the calibration path is specifically as follows: the calibration path connects the optical coupler signal to the single-wavelength FBG, the single-wavelength FBG is calibrated as a normal reflectivity grating, its output is connected to the comb filter, the comb filter output is connected to the second photoelectric converter, and the output of the second photoelectric converter is connected to the oscilloscope channel 2 Ch2 for detection.

[0010] Furthermore, the detection path is specifically as follows: the detection path connects the optical coupler signal to the optical circulator, thereby entering several groups of weak-reflection FBG arrays. The target signals returned by the several groups of weak-reflection FBG arrays enter the third photoelectric converter through the optical circulator and are finally detected in channel three Ch3 of the oscilloscope.

[0011] Furthermore, the several groups of weak-reflection FBG arrays include three groups of weak-reflection FBG arrays, each of which contains several weak-reflection FBG1-FBGn with different wavelengths, wherein the transmitted light of the first group of weak-reflection FBG array enters the first single-mode optical fiber, generates a delay and then enters the second group of weak-reflection FBG array, and the transmitted light enters the second single-mode optical fiber, also generates a delay and then enters the third group of weak-reflection FBG array, and the three groups of weak-reflection FBG arrays have the same wavelength.

[0012] Furthermore, the first single-mode optical fiber and the second single-mode optical fiber are used to realize time division multiplexing, separating different groups of FBG arrays in the time domain, which facilitates the positioning and identification of the target. The first single-mode optical fiber and the second single-mode optical fiber are only used to ensure that the weak-reflection FBGs of the same wavelength have a time delay, allowing the weak-reflection FBGs of different wavelengths to overlap in the time domain.

[0013] The present invention also proposes a weak reflection FBG demodulation method using a Fourier domain mode-locked swept chaotic laser. The demodulation method is implemented using the demodulation system described above. The demodulation method specifically includes: First, the three channels of data are delayed and compensated. The delay depends on the fixed optical path difference of the three optical paths to ensure that the light of the laser path, calibration path, and detection path remain synchronized. The synchronized data are first subjected to initial wavelength calculation; the second step is to perform modal analysis on the channel 2 data to extract the low-frequency signal; the third step is to search for the peak of the low-frequency curve; the fourth step is to correspond the peak time interval to the preset wavelength interval of the interferometer, and fit the sine function to the time-wavelength curve; the fifth step is to perform wavelength self-calibration, and split the initial cycle laser signal calculated in the fourth step. The segmentation range is required to ensure that it can produce cross-correlation with the second cycle, and the segmented parts are sequentially Perform a cross-correlation operation with the next cycle to locate the delay corresponding to the same wavelength. After completing the positioning of all segmented parts, the time-wavelength curve can be fitted. The whole process is an iterative process, and finally the time-wavelength curve of all cycles is output to achieve self-calibration; the sixth step is to extract each FBG peak in the data of channel three and perform a cross-correlation operation with the laser signal of channel one; the seventh step is to determine the position of the cross-correlation peak within a cycle. When the number of cross-correlation peaks is 1, it means that there is no time domain overlap of FBG. When the number of cross-correlation peaks is multiple, it means that the time domain is overlapped by multiple groups of FBGs; finally, the cross-correlation peak delay is used to locate the wavelength value of the weak reflection FBG.

[0014] The present invention also proposes an electronic device, comprising a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the weak reflection FBG demodulation method using a Fourier domain mode-locked swept chaotic laser are implemented.

[0015] The present invention also provides a computer-readable storage medium for storing computer instructions, which, when executed by a processor, implement the steps of the weak reflection FBG demodulation method using a Fourier domain mode-locked swept chaotic laser.

[0016] Beneficial effects of the present invention: This invention proposes three innovative breakthroughs for weak-reflection FBG demodulation systems. 1. A demodulation system based on FDML-SCL was developed. By leveraging the wide spectrum characteristics, fast frequency sweeping capability, and anti-interference capabilities of FDML-SCL, it simultaneously achieves kHz-level speed and femtometer-level high-precision wavelength demodulation. 2. An innovative self-calibration scheme for FDML-SCL was proposed. Through a real-time calibration algorithm, the wavelength drift problem during high-speed frequency sweeping was effectively solved. 3. To address the problem of signal overlap in wavelength division and time division hybrid multiplexing systems, a chaotic feature demodulation method was proposed. The unique time-frequency characteristics of chaotic signals were utilized to accurately separate overlapping signals. This method theoretically achieves 367 channels of wavelength division multiplexing within a 43nm range, while also enabling time division multiplexing with a channel spacing of only 70ps, providing a high-density, high-dynamic solution for large-scale structural health monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0018] Figure 1 This is a diagram of the weak reflection FBG demodulation system using a Fourier domain mode-locked swept chaotic laser as described in the present invention.

[0019] Figure 2 This is a flow chart of the weak reflection FBG demodulation method using a Fourier domain mode-locked swept chaotic laser according to the present invention.

[0020] Explanation of symbols in the figure: 1. Fourier-domain mode-locked swept chaotic laser FDML-SCL; 2. One-to-three optical coupler; 3. Optical circulator; 4. First weak-reflection FBG array; 5. First single-mode fiber; 6. Second weak-reflection FBG array; 7. Second single-mode fiber; 8. Third weak-reflection FBG array; 9. Third photoelectric converter; 10. First photoelectric converter; 11. Single-wavelength FBG; 12. Comb filter; 13. Second photoelectric converter; 14. Oscilloscope. DETAILED DESCRIPTION

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0022] Specifically, combined Figure 1 and Figure 2 The present invention proposes a weak reflection FBG demodulation system using a Fourier domain mode-locked swept chaotic laser, the system comprising a Fourier domain mode-locked swept chaotic laser FDML-SCL, a one-to-three optical coupler and a data acquisition device; The FDML-SCL outputs the periodic frequency-sweep chaotic laser into three paths through a one-to-three optical coupler. The first path is the laser path, the second path is the calibration path, and the third path is the detection path. The three paths are respectively input into a data acquisition device, and the collected data is input into Matlab for target recognition processing. The detection path includes several groups of weak-reflection FBG arrays, which are connected to the FDML-SCL and data acquisition device through an optical circulator. The weak-reflection FBG array uses weak-reflection FBGs with different central wavelengths connected in series to form a wavelength division multiplexing unit. Each group of FBGs has a unique Bragg wavelength and the reflectivity is controlled below 1%. By connecting multiple identical wavelength division multiplexing units in series using single-mode optical fiber, time division multiplexing is further achieved on the basis of wavelength division multiplexing.

[0023] The FDML-SCL utilizes the FDML mechanism to achieve kHz-level high-speed frequency sweeping capabilities. The combined gain of a semiconductor optical amplifier (SOA) and an erbium-doped fiber amplifier (EDFA) enables wide-range wavelength tuning. A narrowband fiber Fabry-Perot tunable filter (FFP-TF) ensures stable, high-bandwidth chaotic characteristics exceeding GHz. The chaotic randomness is enhanced through nonlinear feedback from high-power laser light in long optical fibers. The FDML-SCL exhibits correlation between adjacent cycles of chaotic lasers with the same wavelength, while lacking correlation between different wavelengths, enabling wavelength self-calibration.

[0024] The data acquisition device consists of three high-bandwidth optoelectronic converters connected to three channels of a high-speed, high-bandwidth oscilloscope. The overall bandwidth of the device should be no less than 8 GHz to accommodate high-bandwidth chaotic signal acquisition. The oscilloscope's sampling rate should be sufficiently fast to ensure a high number of valid data points in the FBG signal. The three channels should have the same bandwidth and sampling rate to ensure accurate demodulation results. Channel 1 of the oscilloscope is the FDML-SCL signal, channel 2 is the initial wavelength calibration signal, and channel 3 is the reflection signal from the weakly reflective FBG array.

[0025] The laser circuit is specifically as follows: the laser circuit connects the optical coupler signal to the first photoelectric converter, and the output signal thereof is input to the oscilloscope channel 1 Ch1 for detection.

[0026] Specifically, the calibration path connects the optical coupler signal to a single-wavelength FBG, which serves as a calibration grating with normal reflectivity. Its output is connected to a comb filter, which is then connected to a second photoelectric converter. The output of the second photoelectric converter is then detected in oscilloscope channel 2 (Ch2). The calibration path consists of a grating connected to the comb filter. The grating wavelength should be within the FDML-SCL frequency sweep range, and the grating must have high reflectivity and a narrow bandwidth to ensure accurate wavelength calibration. The comb filter's wavelength response range should be wider than the frequency sweep range to enable full-range wavelength calibration. Furthermore, the comb filter should exhibit high finesse and dense comb teeth to simplify subsequent algorithms and ensure calibration accuracy.

[0027] Specifically, the detection path connects the optical coupler signal to an optical circulator, thereby entering several groups of weak-reflection FBG arrays. The target signals returned by the several groups of weak-reflection FBG arrays enter the third photoelectric converter through the optical circulator and are finally detected in channel three Ch3 of the oscilloscope.

[0028] The several groups of weak-reflection FBG arrays include three groups of weak-reflection FBG arrays, each of which contains several weak-reflection FBG1-FBGn with different wavelengths. The transmitted light of the first group of weak-reflection FBG arrays enters the first single-mode optical fiber, generates a delay, and then enters the second group of weak-reflection FBG arrays. The transmitted light enters the second single-mode optical fiber and also generates a delay and then enters the third group of weak-reflection FBG arrays. The three groups of weak-reflection FBG arrays have the same wavelength.

[0029] The first single-mode optical fiber and the second single-mode optical fiber are used to realize time division multiplexing, separating different groups of FBG arrays in the time domain, which is convenient for positioning and identifying the target. The first single-mode optical fiber and the second single-mode optical fiber are only used to ensure that the weak-reflection FBGs of the same wavelength have a time delay, allowing the weak-reflection FBGs of different wavelengths to overlap in the time domain.

[0030] The present invention also proposes a weak-reflection FBG demodulation method using a Fourier domain mode-locked swept chaotic laser. The demodulation method is implemented using the demodulation system described above. The time information of a single FBG in channel three and the comb filter comb teeth are extracted for comparison, and the time-wavelength function curve of the initial cycle is fitted. The initial cycle of the FDML-SCL laser in channel one is divided into several parts, and cross-correlated with the second cycle laser in sequence to obtain the time delay of the same wavelength, thereby obtaining the time-wavelength curve of the second cycle laser. The above process is repeated in adjacent cycles, and wavelength self-calibration is achieved through an iterative process. The reflection signal of each weak-reflection FBG in channel three is extracted and cross-correlated with the FDML-SCL laser signal in channel one. The position of the highest cross-correlation peak is the accurate wavelength of the weak-reflection FBG. Specifically, the demodulation method includes: First, the three channels of data are delayed and compensated. The delay depends on the fixed optical path difference of the three optical paths to ensure that the light of the laser path, calibration path, and detection path remain synchronized. The synchronized data are first subjected to initial wavelength calculation; the second step is to perform modal analysis on the channel 2 data to extract the low-frequency signal; the third step is to search for the peak of the low-frequency curve; the fourth step is to correspond the peak time interval to the preset wavelength interval of the interferometer, and fit the sine function to the time-wavelength curve; the fifth step is to perform wavelength self-calibration, and split the initial cycle laser signal calculated in the fourth step. The segmentation range is required to ensure that it can produce cross-correlation with the second cycle, and the segmented parts are sequentially Perform a cross-correlation operation with the next cycle to locate the delay corresponding to the same wavelength. After completing the positioning of all segmented parts, the time-wavelength curve can be fitted. The whole process is an iterative process, and finally the time-wavelength curve of all cycles is output to achieve self-calibration; the sixth step is to extract each FBG peak in the data of channel three and perform a cross-correlation operation with the laser signal of channel one; the seventh step is to determine the position of the cross-correlation peak within a cycle. When the number of cross-correlation peaks is 1, it means that there is no time domain overlap of FBG. When the number of cross-correlation peaks is multiple, it means that the time domain is overlapped by multiple groups of FBGs; finally, the cross-correlation peak delay is used to locate the wavelength value of the weak reflection FBG.

[0031] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

[0032] Combined with attachment Figure 1 The FDML-SCL-based weak-reflection FBG demodulation system uses an FDML-SCL with a sweep rate of 39.458 kHz, a sweep range of 43 nm, and a chaotic bandwidth of 14.6 GHz. A 1×3 coupler is used to split the signal into three paths. One path is connected to an optoelectronic converter 10 and detected in Ch1 of oscilloscope 14. The other path is connected to a single-wavelength FBG 11. FBG 11 serves as a calibration, using a normal reflectivity grating with a reflectivity of 95% and a bandwidth of 0.1 nm. The transmitted light is connected to a comb filter 12, which serves as a calibration with a free spectral range of 50 GHz and a finesse of 13. The transmitted light is then connected to a second optoelectronic converter 13 and detected in Ch2 of oscilloscope 14. One path connects to an optical circulator 3 and enters a weak-reflection FBG array. This weak-reflection FBG array comprises three groups of weak-reflection FBG arrays. The first weak-reflection FBG array 4 includes several weak-reflection FBGs 1-FBGn with different wavelengths. Transmitted light enters a first single-mode fiber 5, experiencing a time delay before entering a second weak-reflection FBG array 6. The transmitted light enters a second single-mode fiber 7, also experiencing a time delay before entering a third weak-reflection FBG array 8. These weak-reflection FBG arrays 4, 6, and 8 have the same wavelength. The first and second single-mode fibers 5 and 7 are used to implement time division multiplexing, separating the different groups of FBG arrays in the time domain to facilitate target location and identification. In the present invention, the lengths of the first and second single-mode fibers 5 and 7 are sufficient only to ensure a time delay between weak-reflection FBGs of the same wavelength, allowing for overlap in the time domain between weak-reflection FBGs of different wavelengths. The target signal returned from the weak-reflection FBG array passes through the optical circulator 3 and enters the third optoelectronic converter 9, ultimately detected on channel 3, Ch3, of an oscilloscope 14. The third, first, and second photoelectric converters 9, 10, and 13 maintain the same 10 GHz bandwidth, the sampling rate of the three channels Ch1, Ch2, and Ch3 is 40 GS / s, the reflectivity of all weak-reflection FBGs is less than 1%, and the bandwidth is 0.1 nm.

[0033] Attachment Figure 2The entire data processing process is demonstrated in the figure: First, delay compensation is performed on the three-channel data. The delay is determined by the fixed optical path difference between the three optical paths, ensuring synchronization of the laser, calibration, and detection paths. The synchronized data is then used to calculate the initial wavelength. Second, modal analysis is performed on the channel 2 data to extract the low-frequency signal. Third, peak detection is performed on the low-frequency curve. Fourth, the peak time intervals are mapped to the 50 GHz wavelength interval of the interferometer, and a sine function is fitted to the time-wavelength curve. Fifth, wavelength self-calibration is performed. The initial cycle laser signal calculated in step 4 is segmented within a range that ensures cross-correlation with the second cycle. This range is determined by the instantaneous 3dB bandwidth of the FDML-SCL, which is 0.117 nm. The segmented segments are then cross-correlated with the next cycle to locate the delay corresponding to the same wavelength. Once all segments are located, the time-wavelength curve can be fitted. The entire process is iterative, ultimately outputting time-wavelength curves for all cycles, achieving self-calibration. The sixth step extracts each FBG peak from channel three's data and performs a cross-correlation operation with the laser signal from channel one. The seventh step determines the location of the cross-correlation peak within a cycle. A single cross-correlation peak indicates no FBG overlap in the time domain. Multiple cross-correlation peaks indicate time domain overlap between multiple groups of FBGs. Finally, the cross-correlation peak delay is used to locate the wavelength of the weakly reflecting FBG.

[0034] In summary, the present invention proposes a weak-reflection FBG demodulation method and system using a Fourier-domain mode-locked swept chaotic laser. This invention can achieve a demodulation speed of 39.458 kHz within a 43 nm wavelength range, with a wavelength accuracy of approximately 60 fm. Theoretically, the wavelength division multiplexing capability of this method depends on the instantaneous linewidth of the FDML-SCL, which is approximately 0.117 nm. Approximately 367 wavelength division multiplexing capacities can be achieved within the 43 nm range. In practical applications, time division multiplexing capacity is limited by the bandwidth and sampling rate of the data acquisition device. In this system, a time channel separation of approximately 70 ps can be achieved.

[0035] The present invention also proposes an electronic device, comprising a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the weak reflection FBG demodulation method using a Fourier domain mode-locked swept chaotic laser are implemented.

[0036] The present invention also provides a computer-readable storage medium for storing computer instructions, which, when executed by a processor, implement the steps of the weak reflection FBG demodulation method using a Fourier domain mode-locked swept chaotic laser.

[0037] The memory in the embodiments of the present application may be a volatile memory or a non-volatile memory, or may include both volatile and non-volatile memories. The non-volatile memory may be a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), or a flash memory. The volatile memory may be a random access memory (RAM), which is used as an external cache. By way of example and not limitation, many forms of RAM are available, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), and direct RAM bus RAM (DR RAM). It should be noted that the memory used in the methods described herein is intended to include, but is not limited to, these and any other suitable types of memory.

[0038] In the above embodiments, all or part of the embodiments can be implemented using software, hardware, firmware, or any combination thereof. When implemented using software, all or part of the embodiments can be implemented in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that can be accessed by a computer, or a data storage device such as a server or data center that integrates one or more available media. The available medium may be a magnetic medium (eg, a floppy disk, a hard disk, a magnetic tape), an optical medium (eg, a high-density digital video disc (DVD)), or a semiconductor medium (eg, a solid state disc (SSD)).

[0039] During implementation, each step of the above method can be completed by an integrated logic circuit of the hardware in the processor or by instructions in the form of software. The steps of the method disclosed in conjunction with the embodiments of the present application can be directly embodied as being executed by a hardware processor, or can be executed by a combination of hardware and software modules in the processor. The software module can be located in a storage medium mature in the art such as a random access memory, a flash memory, a read-only memory, a programmable read-only memory or an electrically erasable programmable memory, a register, etc. The storage medium is located in the memory, and the processor reads the information in the memory and completes the steps of the above method in conjunction with its hardware. To avoid repetition, it will not be described in detail here.

[0040] It should be noted that the processor in the embodiments of the present application can be an integrated circuit chip with signal processing capabilities. During implementation, each step of the above-described method embodiments can be completed by hardware integrated logic circuits in the processor or by software instructions. The above-described processor can be a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic device, or discrete hardware components. The methods, steps, and logic block diagrams disclosed in the embodiments of the present application can be implemented or executed. The general-purpose processor can be a microprocessor or any conventional processor. The steps of the methods disclosed in the embodiments of the present application can be directly implemented and executed by a hardware decoding processor, or by a combination of hardware and software modules in the decoding processor. The software modules can be located in a storage medium well-known in the art, such as random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, registers, etc. The storage medium is located in the memory, and the processor reads the information in the memory and, in conjunction with its hardware, completes the steps of the above-described method.

[0041] The weak reflection FBG demodulation system and method using a Fourier domain mode-locked swept chaotic laser proposed in the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A weak reflection FBG demodulation system using a Fourier domain mode-locked swept chaotic laser is characterized by: The system includes a Fourier domain mode-locked swept frequency chaotic laser FDML-SCL, a one-to-three optical coupler and a data acquisition device; The FDML-SCL outputs the periodic frequency-sweep chaotic laser into three paths through a one-to-three optical coupler. The first path is the laser path, the second path is the calibration path, and the third path is the detection path. The three paths are respectively input into a data acquisition device, and the collected data is input into Matlab for target recognition processing. The detection path includes several groups of weak-reflection FBG arrays, which are connected to the FDML-SCL and the data acquisition device through an optical circulator. The weak-reflection FBG array uses weak-reflection FBGs with different central wavelengths in series to form a wavelength division multiplexing unit. By connecting multiple identical wavelength division multiplexing units in series using single-mode optical fiber, time division multiplexing is further achieved on the basis of wavelength division multiplexing.

2. The system according to claim 1, wherein: The data acquisition device consists of three high-bandwidth photoelectric converters connected to three channels of a high-speed, high-bandwidth oscilloscope; channel one of the oscilloscope is the FDML-SCL signal, channel two is the initial wavelength calibration signal, and channel three is the weak-reflection FBG array reflection signal.

3. The system according to claim 2, characterized in that The laser circuit is specifically as follows: the laser circuit connects the optical coupler signal to the first photoelectric converter, and the output signal thereof is input to the oscilloscope channel 1 Ch1 for detection.

4. The system according to claim 2, wherein: The calibration path is specifically as follows: the calibration path connects the optical coupler signal to the single-wavelength FBG, the single-wavelength FBG is used as a calibration normal reflectivity grating, its output is connected to the comb filter, the comb filter output is connected to the second photoelectric converter, and the output of the second photoelectric converter is connected to the oscilloscope channel 2 Ch2 for detection.

5. The system according to claim 2, wherein: Specifically, the detection path connects the optical coupler signal to an optical circulator, thereby entering a plurality of weak-reflection FBG arrays. The target signals returned by the plurality of weak-reflection FBG arrays enter the third photoelectric converter through the optical circulator and are finally detected in channel 3 Ch3 of the oscilloscope.

6. The system according to claim 5, characterized in that The several groups of weak-reflection FBG arrays include three groups of weak-reflection FBG arrays, each of which contains several weak-reflection FBG1-FBGn with different wavelengths. The transmitted light of the first group of weak-reflection FBG arrays enters the first single-mode optical fiber, generates a delay, and then enters the second group of weak-reflection FBG arrays. The transmitted light enters the second single-mode optical fiber and also generates a delay and then enters the third group of weak-reflection FBG arrays. The three groups of weak-reflection FBG arrays have the same wavelength.

7. The system according to claim 6, characterized in that The first single-mode optical fiber and the second single-mode optical fiber are used to realize time division multiplexing, separating different groups of FBG arrays in the time domain, which is convenient for positioning and identifying the target. The first single-mode optical fiber and the second single-mode optical fiber are only used to ensure that the weak-reflection FBGs of the same wavelength have a time delay, allowing the weak-reflection FBGs of different wavelengths to overlap in the time domain.

8. A weak reflection FBG demodulation method using a Fourier domain mode-locked swept chaotic laser is characterized in that: The demodulation method is implemented by the demodulation system according to any one of claims 1 to 7, and the demodulation method specifically includes: First, the three channels of data are delayed and compensated. The delay depends on the fixed optical path difference of the three optical paths to ensure that the light of the laser path, calibration path, and detection path remain synchronized. The synchronized data are first subjected to initial wavelength calculation; the second step is to perform modal analysis on the channel 2 data to extract the low-frequency signal; the third step is to search for the peak of the low-frequency curve; the fourth step is to correspond the peak time interval to the preset wavelength interval of the interferometer, and fit the sine function to the time-wavelength curve; the fifth step is to perform wavelength self-calibration, and split the initial cycle laser signal calculated in the fourth step. The segmentation range is required to ensure that it can produce cross-correlation with the second cycle, and the segmented parts are sequentially Perform a cross-correlation operation with the next cycle to locate the delay corresponding to the same wavelength. After completing the positioning of all segmented parts, the time-wavelength curve can be fitted. The whole process is an iterative process, and finally the time-wavelength curve of all cycles is output to achieve self-calibration; the sixth step is to extract each FBG peak in the data of channel three and perform a cross-correlation operation with the laser signal of channel one; the seventh step is to determine the position of the cross-correlation peak within a cycle. When the number of cross-correlation peaks is 1, it means that there is no time domain overlap of FBG. When the number of cross-correlation peaks is multiple, it means that the time domain is overlapped by multiple groups of FBGs; finally, the cross-correlation peak delay is used to locate the wavelength value of the weak reflection FBG.

9. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to claim 8 are implemented.

10. A computer-readable storage medium for storing computer instructions, characterized in that: When the computer instructions are executed by a processor, the steps of the method according to claim 8 are implemented.

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