Time addressing frequency sweeping demodulation method of identical fiber grating array and optical time domain reflection sensing system

Abstract

The invention discloses a time addressing frequency sweep demodulation method for an identical fiber grating array, which comprises the following steps of: forming a time addressing table of each Bragg grating according to the time position of each Bragg grating in the identical fiber grating array, so as to obtain a time addressing frequency sweep of each Bragg grating under different scanning wavelengths; according to the time addressing table, effective signals corresponding to all Bragg gratings in reflected light signals output by the identical fiber grating array are collected and subjected to analog-to-digital conversion, so that effective time domain signals of the identical fiber grating array under different scanning wavelengths are obtained; and according to the effective time domain signals of the identical fiber grating array under different scanning wavelengths, the reflection spectrum corresponding to each Bragg grating is reconstructed. The time addressing frequency sweeping demodulation method has the advantages of small data acquisition amount and calculation amount, low calculation complexity, low power consumption and the like, and meanwhile, the requirement on high-performance hardware is also low. The invention further discloses an optical time domain reflection sensing system based on the method.

Description

Time-addressed sweep frequency demodulation method for identical fiber Bragg grating arrays and optical time-domain reflectometry sensing system Technical Field

[0001] This invention relates to the field of fiber optic grating sensors, and more particularly to a time-addressed sweep frequency demodulation method for identical fiber optic grating arrays and an optical time-domain reflectometry sensing system. Background Technology

[0002] In traditional fiber optic distributed sensing systems, to achieve multi-point measurements, multiple Bragg gratings with different center wavelengths are typically connected in series in the same fiber. Wavelength division multiplexing (WDM) is then used to demodulate the reflected light signal output from the fiber grating array to reconstruct the reflection spectrum corresponding to each Bragg grating. However, this method is limited by the light source bandwidth and the grating reflection spectrum width, resulting in a limited number of gratings that can be accommodated in a single channel, making it difficult to meet the requirements of long-distance, high-density distributed measurements.

[0003] To overcome the above problems, the industry has proposed an identical fiber Bragg grating array scheme in recent years. This scheme involves connecting multiple Bragg gratings with the same center wavelength in series in the same fiber and using optical time domain reflectometer (OTDR) technology to demodulate the reflected light signal output by the identical fiber Bragg grating array in order to reconstruct the reflection spectrum corresponding to each Bragg grating.

[0004] For example, Chinese patent application number CN202510213992.4 discloses a long-distance fiber optic sensor demodulation device and demodulation method. The demodulation device includes a swept-frequency laser, a signal generator, a semiconductor optical amplifier, a circulator, a photodetector, a data acquisition card, and a computer. Its demodulation method includes the following steps:

[0005] Set the scanning parameters of the sweep laser, including the start wavelength, end wavelength, step interval time, and sweep speed, to ensure coverage of the Bragg wavelength range of the grating array;

[0006] The sweeping laser generates trigger pulses, which synchronously trigger the signal generator and the data acquisition card.

[0007] The signal generator generates a drive pulse based on the trigger pulse, which drives the semiconductor optical amplifier to generate optical pulses and injects them into the grating array.

[0008] Collect the reflected light signal from the grating array and record the transmission and reception timestamps of the light pulses;

[0009] The time-domain signal is divided into multiple time windows according to the step interval time, and the wavelength and time information of the reflection peak are extracted in each window;

[0010] The center wavelength of each grating is calculated based on the wavelength demodulation formula, and its spatial position is demodulated using the position demodulation formula. The wavelength and position information are then correlated to generate sensing data.

[0011] However, when light pulses propagate within the identical fiber Bragg grating array, they are reflected not only by each Bragg grating but also by the non-grating portions. The time-domain signal acquired by the data acquisition card in the aforementioned patent at each scanning wavelength includes not only the effective signal formed by each Bragg grating but also noise signals formed by the non-grating portions. This results in problems such as large data acquisition volume and high computational complexity, which is not conducive to real-time online demodulation. Moreover, the noise signals can also interfere with measurements, requiring additional filtering and noise suppression processing. Furthermore, due to the large amount of data acquisition and computation, the aforementioned patent relies heavily on high-performance hardware such as high-speed analog-to-digital converters, large-capacity caches, and high-performance processors, leading to high hardware costs and power consumption. This limits the application of the identical fiber Bragg grating array in long-distance, high-density sensing scenarios. Summary of the Invention

[0012] To address the shortcomings of the existing technologies, this invention provides a time-addressed sweep frequency demodulation method for identical fiber grating arrays and an optical time-domain reflectometry sensing system, which has advantages such as low data acquisition and computational load, low computational complexity, and low power consumption, while also having low requirements for high-performance hardware.

[0013] The technical problem to be solved by the present invention is achieved through the following technical solution:

[0014] A time-addressed frequency sweep demodulation method for identical fiber Bragg grating arrays includes the following steps:

[0015] Step 1: Based on the time position of each Bragg grating in the identical fiber Bragg grating array, form a time addressing table for each Bragg grating;

[0016] Step 2: Within a preset wavelength range, scan the identical fiber grating array using scanning light pulses of different scanning wavelengths, wherein the wavelength range covers the center wavelength of the identical fiber grating array.

[0017] Step 3: At different scanning wavelengths, according to the time addressing table, the effective signals corresponding to each Bragg grating in the reflected light signal output by the identical fiber grating array are collected and converted from analog to digital to obtain the effective time domain signals of the identical fiber grating array at different scanning wavelengths.

[0018] Step 4: Reconstruct the reflection spectrum corresponding to each Bragg grating based on the effective time-domain signals of the identical fiber Bragg grating array at different scanning wavelengths.

[0019] Furthermore, in step 1, the step of forming a time addressing table for each Bragg grating based on the time position of each Bragg grating in the identical fiber grating array is as follows:

[0020] Step 11: Obtain the center wavelength of the identical fiber grating array;

[0021] Step 12: Scan the identical fiber Bragg grating array with an addressing optical pulse corresponding to the center wavelength, and collect and convert all reflected light signals output by the identical fiber Bragg grating array to obtain the addressing time domain signal;

[0022] Step 13: Perform peak detection on the addressed time domain signal to determine the time position corresponding to each Bragg grating;

[0023] Step 14: Number each Bragg grating according to the order of time position to establish the mapping relationship between each Bragg grating and the time position, thereby obtaining the time addressing table.

[0024] Furthermore, in step 2, the scanning of the identical fiber grating array using scanning light pulses of different scanning wavelengths within a preset wavelength range is as follows:

[0025] Step 21: Obtain the start wavelength, end wavelength, and step wavelength of the wavelength range;

[0026] Step 22: Determine multiple scanning wavelengths for scanning the identical fiber grating array based on the start wavelength, end wavelength, and step wavelength of the wavelength range;

[0027] Step 23: The identical fiber grating array is scanned sequentially using scanning light pulses corresponding to each scanning wavelength.

[0028] Furthermore, in step 3, the effective signals corresponding to each Bragg grating in the reflected light signals output by the identical fiber grating array at different scanning wavelengths are acquired and converted from analog to digital according to the time addressing table, so as to obtain the effective time-domain signals of the identical fiber grating array at different scanning wavelengths. The steps are as follows:

[0029] Step 31: Obtain the time addressing table and addressing time tolerance;

[0030] Step 32: Determine the acquisition time window corresponding to each Bragg grating based on the time addressing table and addressing time tolerance;

[0031] Step 33: Only within the acquisition time window corresponding to each Bragg grating, the reflected light signal output by the identical fiber grating array is acquired and converted from analog to digital to obtain the effective time domain signal under different scanning wavelengths.

[0032] Furthermore, if the time position of the k-th Bragg grating is tk and the addressing time tolerance is Δt, then the acquisition time window of the k-th Bragg grating is [tk-Δt, tk+Δt].

[0033] Furthermore, in step 4, the steps for reconstructing the reflection spectrum corresponding to each Bragg grating based on the effective time-domain signals of the identical fiber grating array at different scanning wavelengths are as follows:

[0034] Step 41: Compare the effective time-domain signals of each Bragg grating at each scanning wavelength individually, and take the maximum value as the effective signal peak value of each Bragg grating at each scanning wavelength;

[0035] Step 42: Using each effective signal peak value as the ordinate and the corresponding scanning wavelength as the abscissa, construct the effective peak coordinate points corresponding to each effective signal peak value:

[0036] Step 43: Group the effective peak coordinates of the same Bragg grating at different scanning wavelengths into a group, and perform curve fitting on each effective peak coordinate of the group to obtain the reflection spectrum corresponding to each Bragg grating.

[0037] An optical time-domain reflectometry sensing system includes an identical fiber grating array and an optical time-domain reflectometer.

[0038] The identical fiber grating array includes a transmission fiber and multiple Bragg gratings with the same center wavelength, and each Bragg grating is distributed sequentially along the fiber axis in the transmission fiber.

[0039] The optical time-domain reflectometer is connected to the identical fiber Bragg grating array and is used to demodulate the reflected light signal output by the identical fiber Bragg grating array using the above-mentioned time-addressed sweep frequency demodulation method, so as to reconstruct the reflection spectrum corresponding to each Bragg grating.

[0040] Furthermore, the optical time-domain reflectometer includes a tunable light source, a semiconductor optical amplifier, a fiber optic circulator, an avalanche photodetector, an ADC acquisition card, and a processor. The tunable light source is connected to a first port of the fiber optic circulator via the semiconductor optical amplifier. The transmission fiber of the identical fiber Bragg grating array is connected to a second port of the fiber optic circulator. The ADC acquisition card is connected to a third port of the fiber optic circulator via the avalanche photodetector. The processor controls the tunable light source, the semiconductor optical amplifier, and the ADC acquisition card.

[0041] The addressing beam emitted by the tunable light source is modulated by the semiconductor optical amplifier to form the scanning light pulse. The scanning light pulse enters the identical fiber Bragg grating array through the optical circulator. The reflected light signal formed by the scanning light pulse is reflected by the identical fiber Bragg grating array and output to the avalanche photodetector for photoelectric conversion through the optical circulator. The ADC acquisition card acquires and performs analog-to-digital conversion on the photoelectric converted reflected light signal. The processor saves and demodulates the analog-to-digital converted reflected light signal to reconstruct the reflection spectrum corresponding to each Bragg grating.

[0042] Furthermore, the processor employs an FPGA chip.

[0043] Furthermore, the optical time domain reflectometer also includes an erbium-doped fiber amplifier, which is connected between the semiconductor optical amplifier and the first port of the fiber optic circulator for amplifying the scanning optical pulse.

[0044] The present invention has the following beneficial effects: The time-addressed frequency sweep demodulation method of the present invention first forms a time addressing table for each Bragg grating in the identical fiber grating array according to the time position of each Bragg grating. In the scanning stage, the effective signals corresponding to each Bragg grating in the reflected light signal output by the identical fiber grating array are collected and converted from analog to digital according to the time addressing table, thereby obtaining the effective time-domain signals of the identical fiber grating array at different scanning wavelengths. However, the noise signals corresponding to the non-grating parts in the reflected light signal are not collected or converted from analog to digital, thereby reducing the acquisition frequency and data acquisition volume of the ADC acquisition card. Since the data acquisition volume is reduced, the data calculation volume and computational complexity of the processor are also reduced, and there is no noise interference from the noise signal. At the same time, the dependence on the conversion speed of the analog-to-digital converter (ADC) in the ADC acquisition card, as well as the capacity space of the data cache unit and the computational performance of the data processing unit in the processor, is also reduced, thereby further reducing the hardware cost and power consumption of the sensing system. Attached Figure Description

[0045] Figure 1 is a schematic diagram of the optical time-domain reflectometry sensing system provided by the present invention.

[0046] Figure 2 is a schematic diagram of the steps of the time-addressed frequency sweep demodulation method provided by the present invention.

[0047] Figure 3 is a step-by-step schematic diagram of step 1 in the time-addressed sweep frequency demodulation method provided by the present invention.

[0048] Figure 4 is a step-by-step schematic diagram of step 2 in the time-addressed sweep frequency demodulation method provided by the present invention.

[0049] Figure 5 is a step-by-step schematic diagram of step 3 in the time-addressed sweep frequency demodulation method provided by the present invention.

[0050] Figure 6 is a step-by-step schematic diagram of step 4 in the time-addressed sweep frequency demodulation method provided by the present invention.

[0051] Figure 7 is a spectrum of the addressing time-domain signal of the identical fiber grating array at the center wavelength in the time-addressing sweep frequency demodulation method provided by the present invention.

[0052] Figure 8 shows the spectrum of the effective time-domain signal of the identical fiber grating array at different scanning wavelengths in the time-addressed sweep frequency demodulation method provided by the present invention.

[0053] Figure 9 shows the time-domain spectral combination of the same Bragg grating before fitting at different scanning wavelengths and the reflection spectrum after fitting in the time-addressed sweep frequency demodulation method provided by the present invention. Detailed Implementation

[0054] The present invention will now be described in detail with reference to the accompanying drawings and embodiments, examples of which are shown in the drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0055] In the description of this invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0056] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature. In the description of this invention, "multiple" means two or more, unless otherwise explicitly specified.

[0057] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," and "setting," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0058] Example 1

[0059] As shown in Figure 1, an optical time-domain reflectometry sensing system includes an identical fiber grating array 1 and an optical time-domain reflectometer 2.

[0060] The identical fiber grating array 1 includes a transmission fiber and multiple Bragg gratings (FBGs) with the same center wavelength, and each Bragg grating (FBG) is distributed sequentially along the fiber axis in the transmission fiber.

[0061] The optical time-domain reflectometer 2 is connected to the identical fiber Bragg grating array 1 to input optical pulses into the identical fiber Bragg grating array 1 and to receive the reflected light signals output by the identical fiber Bragg grating array 1 for demodulation operations in order to reconstruct the reflection spectrum corresponding to each Bragg grating FBG.

[0062] Each Bragg grating FBG can be uniformly distributed along the fiber axis in the transmission fiber, that is, the spacing between any two adjacent Bragg grating FBGs is the same. Alternatively, each Bragg grating FBG can be non-uniformly distributed along the fiber axis in the transmission fiber, that is, at least two adjacent Bragg grating FBGs have a spacing that is different from the spacing between the other two adjacent Bragg grating FBGs.

[0063] The non-grating portion referred to in this invention refers to the bare fiber segment in the transmission fiber that does not have the Bragg grating (FBG) fabricated on it, mainly including the bare fiber segment before the first Bragg grating (FBG), the bare fiber segment after the last Bragg grating (FBG), and the bare fiber segment between two adjacent Bragg gratings (FBG).

[0064] The transmission optical fiber may be, but is not limited to, single-mode fiber, few-mode fiber, or multimode fiber.

[0065] The optical time-domain reflectometer 2 includes a tunable light source 21, a semiconductor optical amplifier 22, an optical fiber circulator 24, an avalanche photodetector 25, an ADC acquisition card 26, and a processor 27. The tunable light source 21 is connected to the first port of the optical fiber circulator 24 through the semiconductor optical amplifier 22, and the transmission fiber of the identical fiber grating array 1 is connected to the second port of the optical fiber circulator 24. The ADC acquisition card 26 is connected to the third port of the optical fiber circulator 24 through the avalanche photodetector 25. The processor 27 controls the tunable light source 21, the semiconductor optical amplifier 22, and the ADC acquisition card 26.

[0066] The continuous beam emitted by the tunable light source 21 is modulated by the semiconductor optical amplifier 22 to form the light pulse. The light pulse enters the identical fiber Bragg grating array 1 through the ray circulator 24. The reflected light signal formed by the reflection of the light pulse by the identical fiber Bragg grating array 1 is output to the avalanche photodetector 25 through the ray circulator 24 for photoelectric conversion. The ADC acquisition card 26 acquires and performs analog-to-digital conversion on the photoelectric converted reflected light signal and attaches the corresponding reception time to finally form the time domain signal required for demodulation. The processor 27 saves and demodulates the time domain signal to reconstruct the reflection spectrum corresponding to each Bragg grating FBG.

[0067] In this embodiment, the processor 27 uses an FPGA chip. The FPGA chip has a programmable logic unit, a data processing unit, a data buffer unit, and a data transmission unit. The data transmission unit is used to transmit data with the tunable light source 21, the semiconductor optical amplifier 22, and the ADC acquisition card 26. The programmable logic unit is used to control the tunable light source 21, the semiconductor optical amplifier 22, and the ADC acquisition card 26. The data processing unit is used to demodulate the time-domain signal. The data buffer unit is used to temporarily store the time-domain signal output by the ADC acquisition card 26 and the processing data generated by the data processing unit.

[0068] Preferably, the optical time domain reflectometer 2 further includes an erbium-doped fiber amplifier 23, which is connected between the semiconductor optical amplifier 22 and the first port of the fiber optic circulator 24 for amplifying the optical pulse.

[0069] Example 2

[0070] A time-addressed frequency sweep demodulation method for an identical fiber Bragg grating array is provided for use in the optical time-domain reflectometry sensing system described in Embodiment 1, for execution by the optical frequency-domain reflectometer. As shown in Figure 2, the time-addressed frequency sweep demodulation method includes the following steps:

[0071] Step 1: Based on the time position of each Bragg grating in the identical fiber Bragg grating array, form a time addressing table for each Bragg grating;

[0072] Step 2: Within a preset wavelength range, scan the identical fiber grating array using scanning light pulses of different scanning wavelengths, wherein the wavelength range covers the center wavelength of the identical fiber grating array.

[0073] Step 3: At different scanning wavelengths, according to the time addressing table, the effective signals corresponding to each Bragg grating in the reflected light signal output by the identical fiber grating array are collected and converted from analog to digital to obtain the effective time domain signals of the identical fiber grating array at different scanning wavelengths.

[0074] Step 4: Reconstruct the reflection spectrum corresponding to each Bragg grating based on the effective time-domain signals of the identical fiber Bragg grating array at different scanning wavelengths.

[0075] The time-addressed frequency sweep demodulation method of the present invention first forms a time addressing table for each Bragg grating in the identical fiber grating array based on the time position of each Bragg grating. During the scanning phase, the effective signals corresponding to each Bragg grating in the reflected light signal output by the identical fiber grating array are acquired and converted from analog to digital according to the time addressing table, thereby obtaining the effective time-domain signals of the identical fiber grating array at different scanning wavelengths. However, the noise signals corresponding to the non-grating parts in the reflected light signal are not acquired or converted from analog to digital, thereby reducing the acquisition frequency and data acquisition volume of the ADC acquisition card. Since the data acquisition volume is reduced, the data calculation volume and computational complexity of the processor are also reduced, and there is no noise interference from the noise signal. At the same time, the dependence on the conversion speed of the analog-to-digital converter (ADC) in the ADC acquisition card, as well as the capacity space of the data cache unit and the computational performance of the data processing unit in the processor, is also reduced, thereby further reducing the hardware cost and power consumption of the sensing system.

[0076] As shown in Figure 3, the steps in step 1 of forming the time addressing table for each Bragg grating based on its time position in the identical fiber grating array are as follows:

[0077] Step 11: Obtain the center wavelength of the identical fiber grating array;

[0078] The center wavelength of the identical fiber Bragg grating array is pre-input by the operator and stored in the processor. In step 11, the processor can directly retrieve the center wavelength of the identical fiber Bragg grating array from its internal data cache unit.

[0079] Step 12: Scan the identical fiber Bragg grating array with an addressing optical pulse corresponding to the center wavelength, and collect and convert all reflected light signals output by the identical fiber Bragg grating array to obtain the addressing time domain signal;

[0080] As shown in Figure 7, the spectrum of the addressing time-domain signal includes both the effective signals formed by each Bragg grating and the noise signals formed by the non-grating portions. In step 12, the processor controls the tunable light source to emit a continuous addressing beam and simultaneously triggers the semiconductor optical amplifier and ADC acquisition card to start working. The wavelength of the addressing beam is the same as the center wavelength of the identical fiber grating array. The semiconductor optical amplifier modulates the addressing beam into an addressing light pulse and outputs it, feeding back the emission time of the addressing light pulse to the processor. The ADC acquisition card performs analog-to-digital conversion on the real-time acquired reflected light signal, adds the corresponding reception time, forms the addressing time-domain signal, and then outputs it to the processor for storage.

[0081] Step 13: Perform peak detection on the addressed time domain signal to determine the time position corresponding to each Bragg grating;

[0082] The addressing time-domain signal is used only for addressing and positioning, and not for sensing and measurement. The noise interference caused by the noise signal has little impact on addressing and positioning. Therefore, there is no need to filter and suppress noise in the addressing time-domain signal before peak detection. Of course, filtering and suppressing noise in the addressing time-domain signal can be performed before peak detection, but this is not required here.

[0083] In step 13, the spectrum of the addressing time-domain signal is a curve with reception time on the horizontal axis and signal intensity on the vertical axis. Due to their high reflectivity, each Bragg grating will form a distinct reflection peak in the spectrum. After the processor performs peak detection on the addressing time-domain signal using a peak detection algorithm, it can determine the peak value of the reflection peak corresponding to each Bragg grating in the addressing time-domain signal. Then, by subtracting the transmission time of the addressing light pulse from the reception time of each reflection peak, the time position corresponding to each Bragg grating can be obtained.

[0084] Step 14: Number each Bragg grating according to the order of time position to establish the mapping relationship between each Bragg grating and the time position, thereby obtaining the time addressing table.

[0085] In step 14, it is assumed that there are n Bragg gratings, where n≥2. The processor numbers the Bragg grating at time position t1 as FBG1, the Bragg grating at time position t2 as FBG2, the Bragg grating at time position t3 as FBG3, and so on, until the Bragg grating at time position tn is numbered as FBGn, and finally obtains and saves the time addressing table.

[0086] As shown in Figure 4, in step 2, the scanning process of the identical fiber grating array using scanning light pulses of different scanning wavelengths within a preset wavelength range is as follows:

[0087] Step 21: Obtain the start wavelength, end wavelength, and step wavelength of the wavelength range;

[0088] The start wavelength, end wavelength, and step wavelength of the wavelength range are pre-input by the operator and stored in the processor. In step 21, the processor can directly retrieve the start wavelength, end wavelength, and step wavelength of the wavelength range from its internal data cache unit.

[0089] Step 22: Determine multiple scanning wavelengths for scanning the identical fiber grating array based on the start wavelength, end wavelength, and step wavelength of the wavelength range;

[0090] In step 22, the starting wavelength is used as the first scanning wavelength, the ending wavelength is used as the last scanning wavelength, and the values ​​are taken from the starting wavelength to the ending wavelength at intervals of the step wavelength, so as to finally determine multiple scanning wavelengths.

[0091] Step 23: The identical fiber grating array is scanned sequentially using scanning light pulses corresponding to each scanning wavelength;

[0092] In step 23, the processor controls the tunable light source to sequentially emit continuous scanning beams corresponding to each scanning wavelength, and synchronously triggers the semiconductor optical amplifier to start working. The semiconductor optical amplifier sequentially modulates the scanning beams corresponding to each scanning wavelength into scanning light pulses and outputs them, and feeds back the emission time of the scanning light pulses corresponding to each scanning wavelength to the processor.

[0093] The scanning beams are generally emitted in order of wavelength, from shortest to longest, or vice versa, from longest to shortest, or in a random and disordered manner. No specific requirements are specified here.

[0094] As shown in Figure 5, in step 3, the effective signals corresponding to each Bragg grating in the reflected light signal output by the identical fiber grating array are acquired and converted from analog to digital according to the time addressing table under different scanning wavelengths, so as to obtain the effective time-domain signals of the identical fiber grating array under different scanning wavelengths.

[0095] Step 31: Obtain the time addressing table and addressing time tolerance;

[0096] The addressing time tolerance is pre-input by the operator and stored in the processor. In step 31, the processor can directly retrieve the time addressing table and addressing time tolerance from its internal data cache unit.

[0097] Step 32: Determine the acquisition time window corresponding to each Bragg grating based on the time addressing table and addressing time tolerance;

[0098] In step 32, the time position corresponding to each Bragg grating is taken as the median value, and the addressing time tolerance is added or subtracted before and after the median value to obtain the acquisition time window corresponding to each Bragg grating. Assuming that the time position of the k-th Bragg grating is tk and the addressing time tolerance is Δt, then the acquisition time window of the k-th Bragg grating is [tk-Δt, tk+Δt].

[0099] The Bragg grating has a certain length, and each position reflects the scanning light pulse. Furthermore, each scanning light pulse has a different wavelength and a certain pulse width. Combined with environmental interference, the peak values ​​of the reflections formed by each Bragg grating at different scanning wavelengths will fluctuate within their respective reflection peaks, and will not all fall at the corresponding time positions. The purpose of setting the addressing time tolerance is to ensure that the complete and effective reflection peaks of each Bragg grating can be acquired at each scanning wavelength during the scanning phase. Therefore, the range of the addressing time tolerance Δt is... k is a safety factor greater than 1 (usually taken as 1.5 to 2), used to cover the actual broadening of the reflection peak (affected by pulse shape, fiber dispersion, etc.), τ is the pulse width of the scanning light pulse, and t unc The time delay drift is caused by clock jitter, ambient temperature, etc., n is the refractive index of the fiber, L is the grating spacing, and c is the speed of light in vacuum.

[0100] Step 33: Only within the acquisition time window corresponding to each Bragg grating, the reflected light signal output by the identical fiber grating array is acquired and converted from analog to digital to obtain the effective time domain signal under different scanning wavelengths;

[0101] As shown in Figure 8, the spectrum of the effective time-domain signal only includes the effective signals formed by each Bragg grating. In step 33, the processor starts timing after receiving the transmission time of the scanning light pulse. When the timing reaches each acquisition time window, the ADC acquisition card is triggered to start working, so that the ADC acquisition card can acquire and perform analog-to-digital conversion on the effective signals formed by each Bragg grating, and attach the corresponding reception time to form the effective time-domain signal, which is then output to the processor for storage. When the timing has not reached each acquisition time window, the ADC acquisition card is triggered to stop working, so that the ADC acquisition card does not acquire and perform analog-to-digital conversion on the noise signals formed by the non-grating parts. Specifically, the processor can send a high-level signal to the ADC acquisition card during each acquisition time window to switch the ADC acquisition card to the on state, and not send any level signal to the ADC acquisition card during other time periods outside the acquisition time windows to switch the ADC acquisition card to the off state, or send a low-level signal to the ADC acquisition card to switch the ADC acquisition card to a low-power sleep state.

[0102] As shown in Figure 6, in step 4, the steps for reconstructing the reflection spectrum corresponding to each Bragg grating based on the effective time-domain signals of the identical fiber grating array at different scanning wavelengths are as follows:

[0103] Step 41: Compare the effective time-domain signals of each Bragg grating at each scanning wavelength individually, and take the maximum value as the effective signal peak value of each Bragg grating at each scanning wavelength;

[0104] In step 41, assuming there are m scanning wavelengths and n Bragg gratings, where m and n ≥ 2, the effective time-domain signal (effective reflection peak) of FBGn acquired through the corresponding acquisition time window at the m-th scanning wavelength is compared individually, and the maximum value is taken as the effective signal peak value In(m) of FBGn at the m-th scanning wavelength, and so on.

[0105] Step 42: Using each effective signal peak value as the ordinate and the corresponding scanning wavelength as the abscissa, construct the effective peak coordinate points corresponding to each effective signal peak value:

[0106] In step 42, the scanning wavelength corresponding to the effective signal peak In(m) is λm, and the effective peak coordinate points constructed in this way are {λm, In(m)}. The construction method of other effective peak coordinate points is similar, and finally multiple effective peak coordinate points are formed as shown below.

[0107]

[0108] Step 43: Divide the effective peak coordinates of the same Bragg grating into a group at different scanning wavelengths, and perform curve fitting on each effective peak coordinate point in the same group to obtain the reflection spectrum corresponding to each Bragg grating.

[0109] In step 43, as shown in Figure 9, the effective peak coordinate points {λ1, I1(1)}, {λ2, I1(2)}, {λ3, I1(3)}, ..., {λm, I1(m)} of FBG1 under the first to m scanning wavelengths are grouped together, and curve fitting is performed on each effective peak coordinate point of this group to obtain the reflection spectrum corresponding to FBG1; the effective peak coordinate points {λ1, I2(1)}, {λ2, I2(2)}, {λ3, I2(3)}, ..., {λm, I2(m)} of FBG2 under the first to m scanning wavelengths are grouped together, and curve fitting is performed on each effective peak coordinate point of this group to obtain the reflection spectrum corresponding to FBG2. Spectrum; The effective peak coordinates of FBG3 at the first to m scanning wavelengths are grouped into a group: {λ1, I3(1)}, {λ2, I3(2)}, {λ3, I3(3)}, ..., {λm, I3(m)}. The effective peak coordinates of each group are then curve-fitted to obtain the reflection spectrum of FBG3. ... This process is repeated until the effective peak coordinates of FBGn at the first to m scanning wavelengths are grouped into a group: {λ1, In(1)}, {λ2, In(2)}, {λ3, In(3)}, ..., {λm, In(m)}. The effective peak coordinates of each group are then curve-fitted to obtain the reflection spectrum of FBGn.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention and not to limit them. Although the embodiments of the present invention have been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the embodiments of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A time-addressed sweep frequency demodulation method for an identical fiber Bragg grating array, characterized in that, The process includes the following steps: Step 1: Forming a time addressing table for each Bragg grating in the identical fiber grating array based on its time position; Step 2: Scanning the identical fiber grating array with scanning light pulses of different scanning wavelengths within a preset wavelength range, wherein the wavelength range covers the center wavelength of the identical fiber grating array; Step 3: At different scanning wavelengths, acquiring and performing analog-to-digital conversion on the effective signals corresponding to each Bragg grating in the reflected light signals output by the identical fiber grating array according to the time addressing table, to obtain the effective time-domain signals of the identical fiber grating array at different scanning wavelengths; Step 4: Reconstructing the reflection spectrum corresponding to each Bragg grating based on the effective time-domain signals of the identical fiber grating array at different scanning wavelengths.

2. The time-addressed frequency sweep demodulation method according to claim 1, characterized in that, In step 1, the steps for forming a time addressing table for each Bragg grating based on its time position in the identical fiber grating array are as follows: Step 11: Obtain the center wavelength of the identical fiber grating array; Step 12: Scan the identical fiber grating array using an addressing light pulse corresponding to the center wavelength, and collect and convert all reflected light signals output by the identical fiber grating array to digital to obtain the addressing time domain signal; Step 13: Perform peak detection on the addressing time domain signal to determine the time position corresponding to each Bragg grating; Step 14: Number each Bragg grating according to the order of time position to establish the mapping relationship between each Bragg grating and the time position, thereby obtaining the time addressing table.

3. The time-addressed frequency sweep demodulation method according to claim 1, characterized in that, In step 2, the scanning of the identical fiber Bragg grating array using scanning light pulses of different scanning wavelengths within a preset wavelength range is as follows: Step 21: Obtain the start wavelength, end wavelength, and step wavelength of the wavelength range; Step 22: Determine multiple scanning wavelengths for scanning the identical fiber Bragg grating array based on the start wavelength, end wavelength, and step wavelength of the wavelength range; Step 23: Sequentially scan the identical fiber Bragg grating array using scanning light pulses corresponding to each scanning wavelength.

4. The time-addressed frequency sweep demodulation method according to claim 1, characterized in that, In step 3, the following steps are taken to obtain the effective time-domain signals of the identical fiber Bragg grating array at different scanning wavelengths by acquiring and performing analog-to-digital conversion on the reflected light signals output by the identical fiber Bragg grating array according to the time addressing table: Step 31: Obtain the time addressing table and addressing time tolerance; Step 32: Determine the acquisition time window corresponding to each Bragg grating according to the time addressing table and addressing time tolerance; Step 33: Acquire and perform analog-to-digital conversion on the reflected light signals output by the identical fiber Bragg grating array only within the acquisition time window corresponding to each Bragg grating to obtain the effective time-domain signals at different scanning wavelengths.

5. The time-addressed frequency sweep demodulation method according to claim 4, characterized in that, If the time position of the k-th Bragg grating is tk and the addressing time tolerance is Δt, then the acquisition time window of the k-th Bragg grating is [tk-Δt, tk+Δt].

6. The time-addressed frequency sweep demodulation method according to claim 1, characterized in that, In step 4, the steps for reconstructing the reflection spectrum of each Bragg grating based on the effective time-domain signals of the identical fiber grating array at different scanning wavelengths are as follows: Step 41: Compare the effective time-domain signals of each Bragg grating at each scanning wavelength individually, and take the maximum value as the effective signal peak value of each Bragg grating at each scanning wavelength; Step 42: Construct the effective peak coordinate points corresponding to each effective signal peak value with each effective signal peak value as the vertical axis value and the corresponding scanning wavelength as the horizontal axis value; Step 43: Divide the effective peak coordinate points of the same Bragg grating at different scanning wavelengths into a group, and perform curve fitting on each effective peak coordinate point in the same group to obtain the reflection spectrum corresponding to each Bragg grating.

7. An optical time-domain reflectometry (OTDR) sensing system, comprising an identical fiber grating array and an optical time-domain reflectometer, wherein the identical fiber grating array comprises a transmission fiber and a plurality of Bragg gratings having the same center wavelength, the Bragg gratings being sequentially distributed along the fiber axis in the transmission fiber; the optical time-domain reflectometer is connected to the identical fiber grating array and is used to demodulate the reflected light signal output by the identical fiber grating array using the time-addressed frequency sweep demodulation method of claim 1, so as to reconstruct the reflection spectrum corresponding to each Bragg grating.

8. The optical time-domain reflectometry sensing system according to claim 7, characterized in that, The optical time-domain reflectometer includes a tunable light source, a semiconductor optical amplifier, a fiber optic circulator, an avalanche photodetector, an ADC acquisition card, and a processor. The tunable light source is connected to the first port of the fiber optic circulator via the semiconductor optical amplifier. The transmission fiber of the identical fiber Bragg grating array is connected to the second port of the fiber optic circulator. The ADC acquisition card is connected to the third port of the fiber optic circulator via the avalanche photodetector. The processor controls the tunable light source, the semiconductor optical amplifier, and the ADC acquisition card. The addressing beam emitted by the tunable light source is modulated by the semiconductor optical amplifier to form a scanning light pulse. The scanning light pulse enters the identical fiber Bragg grating array via the fiber optic circulator. The reflected light signal formed by the reflection of the scanning light pulse by the identical fiber Bragg grating array is output to the avalanche photodetector via the fiber optic circulator for photoelectric conversion. The ADC acquisition card acquires and performs analog-to-digital conversion on the photoelectric converted reflected light signal. The processor saves and demodulates the analog-to-digital converted reflected light signal to reconstruct the reflection spectrum corresponding to each Bragg grating.

9. The optical time-domain reflectometry sensing system according to claim 8, characterized in that, The processor uses an FPGA chip.

10. The optical time-domain reflectometry sensing system according to claim 8, characterized in that, The optical time-domain reflectometer further includes an erbium-doped fiber amplifier, which is connected between the semiconductor optical amplifier and the first port of the fiber optic circulator, and is used to amplify the scanning optical pulse.

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