High-precision high-spatial-resolution grating array optical fiber demodulation system and method

Abstract

The invention provides a high-precision and high-spatial-resolution grating array optical fiber demodulation system and method, and relates to the technical field of fiber grating sensing, and the system comprises a pulse signal modulation module, a signal detection demodulation module and a grating array sensing module, the pulse signal modulation module is respectively connected with the signal detection demodulation module and the grating array sensing module; the signal detection demodulation module is connected with the grating array sensing module and comprises a photoelectric detector, a plurality of analog-to-digital conversion units, a signal accumulation unit and a signal demodulation unit, and the photoelectric detector is electrically connected with the signal accumulation unit through the analog-to-digital conversion units; the phase difference between any two analog-to-digital conversion units is 2pi / N, N represents the number of the analog-to-digital conversion units, the signal accumulation unit is electrically connected with the signal demodulation unit, and the demodulation precision and the spatial resolution of optical signals can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber grating sensing, and in particular to a high-precision and high-spatial-resolution grating array fiber demodulation system and method. Background Art

[0002] In a grating array fiber wavelength demodulation system based on optical time domain reflectometry (OTDR), the duration and modulation depth of the optical pulse respectively affect the spatial resolution and demodulation accuracy of the system. On the one hand, the shorter the duration, the higher the spatial resolution of the system, but it poses higher requirements on the bandwidth and sampling rate of the hardware, thereby increasing the overall cost of the system hardware. On the other hand, the modulation depth is closely related to the turn-off performance of the pulse modulation unit. The better the turn-off performance, the greater the modulation depth, the smaller the leakage light power, thereby reducing the introduction of optical noise and improving the demodulation accuracy of the system.

[0003] Chinese Patent with publication number CN116839758A discloses a fiber optic sensing demodulation system with high signal-to-noise ratio and high precision and its implementation method, including an optical path demodulation unit, a photoelectric conversion circuit unit and a signal processing unit; the optical path demodulation unit includes a fiber grating FBGA as a reference fiber grating, a fiber grating FBGB as a sensing fiber grating, an acousto-optic modulator AOM for modulating the light source into pulsed light, a first 3-port circulator for splitting the transmitted light and incident light of the fiber grating FBGA, and a second 3-port circulator for connecting the reflected light of the fiber grating FBGB to the photoelectric receiving sub-module ROSA; the photoelectric conversion circuit unit includes a photoelectric receiving sub-module ROSA for converting the reflected light of the fiber grating FBGB into a current signal and converting it into a voltage signal by connecting a resistor in series; the signal processing unit includes a phase-locked loop PLL for collecting the voltage signal and an MCU with integrated display. However, it is difficult to modulate an optical signal with a narrow duration in the above solution, and as the duration of the optical pulse shortens, the requirement of the system for the sampling rate increases, which easily leads to a decrease in the demodulation accuracy of the demodulation system. Therefore, it is very necessary to provide a high-precision and high-spatial-resolution grating array fiber demodulation system and method, which helps to improve the demodulation accuracy and spatial resolution of optical signals. Summary of the Invention

[0004] In view of this, the present invention proposes a high-precision and high-spatial-resolution grating array fiber demodulation system and method. By modulating the light source twice by a pulse signal modulation module and adopting a multi-channel alternating sampling and signal accumulation method, the digital conversion accuracy of the fiber reflection signal can be greatly improved, and the demodulation accuracy and spatial resolution of the optical signal can be enhanced.

[0005] The present invention provides a high-precision and high-spatial-resolution grating array optical fiber demodulation system, which includes a pulse signal modulation module, a signal detection and demodulation module, and a grating array sensing module. Among them,

[0006] The pulse signal modulation module is respectively connected to the signal detection and demodulation module and the grating array sensing module. The pulse signal modulation module is used to perform two signal modulations on the light beam emitted by the light source;

[0007] The signal detection and demodulation module is connected to the grating array sensing module. The signal detection and demodulation module includes a photodetector, a plurality of analog-to-digital conversion units, a signal accumulation unit, and a signal demodulation unit. The photodetector is electrically connected to the signal accumulation unit through a plurality of analog-to-digital conversion units, and the phase difference between any two analog-to-digital conversion units is 2π / N, where N represents the number of analog-to-digital conversion units. The signal accumulation unit is electrically connected to the signal demodulation unit. The signal detection and demodulation module is used to convert the reflected light signal output by the grating array sensing module into a digital signal and perform precise demodulation on the digital signal in the form of multi-channel alternating sampling and signal accumulation.

[0008] Based on the above technical solutions, preferably, the pulse signal modulation module includes a light source, a first optical circulator, an optical pulse modulation unit, a delay optical fiber, and a Faraday rotator. The light source is respectively connected to the signal detection and demodulation module and the first port of the first optical circulator. The second port of the first optical circulator is connected to the optical pulse modulation unit. The third port of the first optical circulator is connected to the grating array sensing module. The optical pulse modulation unit is respectively connected to the signal detection and demodulation module and the delay optical fiber. The delay optical fiber is connected to the Faraday rotator.

[0009] Based on the above technical solutions, preferably, the grating array sensing module includes a second optical circulator and an optical fiber grating sensing array. The first port of the second optical circulator is connected to the third port of the first optical circulator. The second port of the second optical circulator is connected to the optical fiber grating sensing array. The third port of the second optical circulator is connected to the photodetector.

[0010] More preferably, when the optical pulse modulation unit receives a high-level pulse signal, the optical pulse modulation unit amplifies the optical signal input to the first optical circulator. When the optical pulse modulation unit receives a low-level pulse signal, the optical pulse modulation unit attenuates the optical signal input to the first optical circulator.

[0011] More preferably, the modulated optical signal output by the optical pulse modulation unit is incident on the Faraday rotator mirror through the delay optical fiber, and the modulated optical signal returns to the optical pulse modulation unit through the Faraday rotator mirror. The expression for the total delay time introduced by the delay optical fiber is as follows:

[0012] t2 = 2L×n1 / c

[0013] Where, t2 represents the total delay time introduced by the delay optical fiber, L represents the length of the delay optical fiber, n1 represents the refractive index of the delay optical fiber, and c represents the propagation speed of light in vacuum.

[0014] More preferably, the expression for the grating position in the fiber Bragg grating sensing array is as follows:

[0015] D x = x / F×c / 2n2

[0016] Where, D x represents the grating position with the peak point horizontal axis coordinate value of x, x represents the peak point horizontal axis coordinate value of the reflected optical signal, F represents the sampling rate of the fiber Bragg grating sensing array, n2 represents the refractive index of the fiber Bragg grating sensing array, and c represents the propagation speed of light in vacuum.

[0017] More preferably, the pulse duration of the optical pulse modulation unit is 50ns - 1μs, the gain of the optical pulse modulation unit is 10dB, and the original modulation depth of the optical pulse modulation unit is 30dB.

[0018] More preferably, the fiber Bragg grating sensing array is an all-identical weak reflectivity grating array, the spacing between any two gratings in the fiber Bragg grating sensing array is 5m, and the central wavelength of the fiber Bragg grating sensing array is 1550.96nm.

[0019] More preferably, the light source is a wavelength tunable light source, the output wavelength range of the wavelength tunable light source is 1520nm - 1560nm, and the step scanning value of the wavelength tunable light source is 10pm.

[0020] In the second aspect of the present application, a high-precision and high-spatial-resolution grating array fiber demodulation method is provided. The method includes:

[0021] Performing two signal modulations on the continuous light beam generated by the light source in the pulse signal modulation module to enable the pulse signal modulation module to output a modulated optical pulse;

[0022] Sending the modulated optical pulse into the grating array sensing module, enabling the modulated optical pulse to form a reflected optical signal in the grating array sensing module, and inputting the reflected optical signal into the signal detection and demodulation module;

[0023] The reflected optical signal is converted into a digital signal by the photodetector in the signal detection and demodulation module, and high-sampling-rate data is obtained in the multi-analog-to-digital conversion unit in an alternating sampling manner. After being processed by the signal accumulation unit and the signal demodulation unit, the change in the reflected pulse area at each grating in the grating array sensing module is extracted for precise demodulation.

[0024] The high-precision and high-spatial-resolution grating array fiber demodulation system and method provided by the present invention have the following beneficial effects compared with the prior art:

[0025] (1) The light source is modulated twice by the pulse signal modulation module to improve the modulation depth and compress the duration of the optical signal, thereby improving the spatial resolution and avoiding the dependence on high-performance optoelectronic devices and complex drive circuits. By using the multi-channel alternating sampling and signal accumulation method, the digital conversion accuracy of the fiber optic reflection signal can be greatly improved, thus enhancing the demodulation accuracy of the optical signal. The use of multiple analog-to-digital conversion units makes the sampling of each channel staggered in phase, and the signal acquisition effect is optimized through signal accumulation to significantly improve the spatial resolution of the system for the output signal of the grating array sensing module. At the same time, the signal accumulation unit and the signal demodulation unit realize the wavelength adjustment of the light source, the synchronous control of the pulse signal and the multi-channel acquisition unit, complete the acquisition and demodulation of the grating array reflection signal, and realize the low-speed acquisition and parallel processing of the high-speed return signal, thus significantly reducing the requirements for high sampling rate and hardware resources.

[0026] (2) The first optical circulator and the second optical circulator are used to separate and direct the transmission of multiple optical signals in the transmission path, ensuring that the signals between modules do not interfere with each other, improving the utilization efficiency of the optical path and the overall stability of the system. An optical pulse modulation unit, a delay fiber, and a Faraday rotator mirror are introduced into the pulse signal modulation module. By precisely regulating the optical signal modulated twice, not only the high precision in the modulation process is ensured, but also the polarization effect in the optical signal transmission process can be effectively compensated, further improving the demodulation accuracy. At the same time, the second optical circulator is used to process the reflected optical signal output by the sensing module through the fiber grating sensing array and then transmit it to the photodetector, ensuring efficient and low-loss acquisition in the process of optical sensing to electrical signal conversion, realizing precise signal routing, high-precision modulation, and effective polarization compensation, and significantly enhancing the demodulation accuracy, spatial resolution, and system stability of the grating array fiber sensing system. Description of the Drawings

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0028] Figure 1 It is a schematic framework diagram of the high-precision and high-spatial-resolution grating array optical fiber demodulation system provided by the present invention;

[0029] Figure 2 It is a schematic framework diagram of the signal detection and demodulation module provided by the present invention;

[0030] Figure 3 It is a schematic principle diagram of pulse width compression provided by the present invention;

[0031] Figure 4 It is a schematic principle diagram of pulse width narrowing of a pulse optical signal provided by the present invention;

[0032] Figure 5 It is a demodulation schematic diagram of the multi-channel signal acquisition and processing process provided by the present invention.

[0033] Explanation of reference numerals: 1. Pulse signal modulation module; 11. Light source; 12. First optical circulator; 13. Optical pulse modulation unit; 14. Delay optical fiber; 15. Faraday rotator mirror; 2. Signal detection and demodulation module; 21. Photoelectric detector; 22. Analog-to-digital conversion unit; 23. Signal accumulation unit; 24. Signal demodulation unit; 3. Grating array sensing module; 31. Second optical circulator; 32. Grating array sensing grating. Detailed implementation manners

[0034] Next, in combination with the implementation manners of the present invention, the technical solutions in the implementation manners of the present invention will be clearly and completely described. Obviously, the described implementation manners are only some implementation manners of the present invention, rather than all implementation manners. Based on the implementation manners in the present invention, all other implementation manners obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0035] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings as understood by those of ordinary skill in the art to which the present invention pertains. The "first", "second" and similar terms used in the present invention do not denote any order, quantity or importance, but are only used to distinguish different components. Similarly, terms such as "a" or "an" do not denote a quantity limitation, but mean that there is at least one. The terms such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms such as "upper", "lower", "left" and "right" are only used to indicate relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationship also changes accordingly.

[0036] Reference Figure 1 and Figure 2 , the present invention provides a high-precision and high-spatial-resolution grating array optical fiber demodulation system, including a pulse signal modulation module 1, a signal detection and demodulation module 2, and a grating array sensing module 3. Among them,

[0037] The pulse signal modulation module 1 is respectively connected to the signal detection and demodulation module 2 and the grating array sensing module 3. The pulse signal modulation module 1 is used to perform two signal modulations on the light beam emitted by the light source 11.

[0038] In this embodiment, the pulse signal modulation module 1 includes a light source 11, a first optical circulator 12, an optical pulse modulation unit 13, a delay optical fiber 14, and a Faraday rotator 15. The light source 11 is respectively connected to the signal detection and demodulation module 2 and the first port of the first optical circulator 12. The second port of the first optical circulator 12 is connected to the optical pulse modulation unit 13. The third port of the first optical circulator 12 is connected to the grating array sensing module 3. The optical pulse modulation unit 13 is respectively connected to the signal detection and demodulation module 2 and the delay optical fiber 14. The delay optical fiber 14 is connected to the Faraday rotator 15.

[0039] Further, the light source 11 is a wavelength-tunable light source 11. The output wavelength range of the wavelength-tunable light source 11 is 1520 nm to 1560 nm, and the step-scan value of the wavelength-tunable light source 11 is 10 pm. The wavelength control of the light source 11 can adopt an external modulation method, that is, the wavelength value is changed by an external signal trigger. The first optical circulator 12 is used to input the optical signal output by the light source 11 into the optical pulse modulation unit 13, and input the optical signal returned by the optical pulse modulation unit 13 into the second optical circulator 31. The optical pulse modulation unit 13 is a semiconductor optical amplifier. The optical pulse modulation unit 13 is built-in with a drive circuit, and the input optical signal is pulse-modulated by an external signal control. The pulse duration of the optical pulse modulation unit 13 is 50 ns to 1 μs. The specific pulse duration is determined by the duration of the external drive signal. The gain of the optical pulse modulation unit 13 is 10 dB, and the original modulation depth of the optical pulse modulation unit 13 is 30 dB. The delay optical fiber 14 is a common single-mode optical fiber with a loss of 0.2 dB / km, and the length of the common single-mode optical fiber is 4 m.

[0040] When the optical pulse modulation unit 13 receives a high-level pulse signal, the optical pulse modulation unit 13 amplifies the optical signal input by the first optical circulator 12. When the optical pulse modulation unit 13 receives a low-level pulse signal, the optical pulse modulation unit 13 attenuates the optical signal input by the first optical circulator 12.

[0041] The modulated optical signal output by the optical pulse modulation unit 13 is incident on the Faraday rotator mirror 15 through the delay optical fiber 14. The modulated optical signal returns to the optical pulse modulation unit 13 via the Faraday rotator mirror 15. The expression for the total delay time introduced by the delay optical fiber 14 is:

[0042] t2 = 2L×n1 / c

[0043] Wherein, t2 represents the total delay time introduced by the delay optical fiber 14, L represents the length of the delay optical fiber 14, n1 represents the refractive index of the delay optical fiber 14, and c represents the propagation speed of light in a vacuum.

[0044] The signal detection and demodulation module 2 is connected to the grating array sensing module 3. The signal detection and demodulation module 2 includes a photodetector 21, a plurality of analog-to-digital conversion units, a signal accumulation unit 23, and a signal demodulation unit 24. The photodetector 21 is electrically connected to the signal accumulation unit 23 through a plurality of analog-to-digital conversion units, and the phase difference between any two analog-to-digital conversion units is 2π / N, where N represents the number of analog-to-digital conversion units. The signal accumulation unit 23 is electrically connected to the signal demodulation unit 24. The signal detection and demodulation module 2 is used to convert the reflected optical signal output by the grating array sensing module 3 into a digital signal, and accurately demodulate the digital signal in the form of multi-channel alternating sampling and signal accumulation.

[0045] In this embodiment, the grating array sensing module 3 includes a second optical circulator 31 and an optical fiber grating sensing array. The first port of the second optical circulator 31 is connected to the third port of the first optical circulator 12, the second port of the second optical circulator 31 is connected to the optical fiber grating sensing array, and the third port of the second optical circulator 31 is connected to the photodetector 21.

[0046] Further, the second optical circulator 31 is used to guide the optical signal output by the first optical circulator 12 to the optical fiber grating sensing array and send the returned signal to the photodetector 21 for optoelectronic signal conversion. The optical fiber grating sensing array is prepared by the in-line grating inscription technology of a drawing tower. A 5-km all-identical weak reflectivity grating array is adopted, where the grating pitch is 5 m, a total of 1000 gratings are included, and the central wavelength is 1550.96 nm. Since a grating with a 5-m pitch requires an optical signal with a pulse width of less than 25 ns, the target pulse width here is 10 ns. The photodetector 21 is composed of components such as a photodiode and a low-noise high-precision operational amplifier, and is used to convert the reflected optical signal of the sensing optical fiber into an electrical signal and divide the electrical signal into multiple paths for output. In this embodiment, the photodetector 21 is selected to have 4 channels to correspond to the 4-channel analog-to-digital conversion unit 22. The analog-to-digital conversion unit 22 is mainly composed of a multi-channel analog-to-digital conversion chip and an operational amplifier, and is used to synchronously collect the multiple electrical signals output by the photodetector 21. The analog-to-digital conversion unit 22 selects an analog-to-digital conversion chip with a 12-bit sampling accuracy and a sampling rate of 125 Msps. The core of the signal accumulation unit 23 and the signal demodulation unit 24 is a high-performance FPGA chip with a 28-nm process, which is responsible for driving the multi-channel analog-to-digital conversion chip, converting the output analog signal of the photodetection module into a digital signal, and completing the signal demodulation process to achieve precise demodulation of the optical fiber grating sensing array.

[0047] In this embodiment, the first optical circulator 12 and the second optical circulator 31 are adopted to realize the separation and directional transmission of multiple optical signals in the transmission path, ensure that the signals between modules are not confused, improve the utilization efficiency of the optical path and the overall stability of the system. The optical pulse modulation unit 13, the delay optical fiber 14, and the Faraday rotator 15 are introduced into the pulse signal modulation module 1. By precisely regulating the optical signal modulated twice, not only the high precision in the modulation process is ensured, but also the polarization effect in the optical signal transmission process can be effectively compensated, further improving the demodulation accuracy. At the same time, the second optical circulator 31 is used to process the reflected optical signal output by the sensing module through the optical fiber grating sensing array and then transmit it to the photodetector 21, ensuring efficient and low-loss acquisition in the process from optical sensing to electrical signal conversion, realizing precise signal routing, high-precision modulation, and effective polarization compensation, and significantly improving the demodulation accuracy, spatial resolution, and system stability of the grating array fiber sensing system.

[0048] Please refer to Figure 3 and4 , setting the output pulse width of the optical pulse modulation unit 13 to 50ns, the first optical signal entering the optical pulse modulation unit 13 from the first optical circulator 12 is modulated to 50ns and transmitted to the Faraday rotator. The length of the delay optical fiber 14 is 4m, and a total delay of 40ns is introduced to the optical signal. When the reflected signal returns to the optical pulse modulation unit 13, the optical pulse modulation unit 13 is still in the output state, and only 10ns of output time is left. Therefore, after secondary modulation, the pulse width of the reflected signal of the first pulse optical signal is compressed to 10ns. Driven by the pulse driving signal, the peak power of the first optical pulse signal is 10dBm, and the noise floor is -20dBm. The signal characteristics reflected by the Faraday rotator are the same as those of the first optical pulse signal, with a delay of 40ns. After entering the optical pulse modulation unit 13 again, the power of the 10ns pulse signal is 20dBm, the power of the 40ns pulse signal is -10dBm, the noise floor is 40dBm, and the maximum extinction ratio is 60dB, which is 30dB higher than the original extinction ratio of 30dB.

[0049] See also Figure 5 , the signal accumulation unit 23 and the signal demodulation unit 24 generate 4 clock signals with a frequency of 125MHz and phases of 0°, 90°, 180° and 270° respectively, and transmit them to the 4 analog-to-digital conversion chips respectively, and collect their digital signal outputs at the same time. Based on the principle of alternating sampling, the output signals of the 4 analog-to-digital conversion chips are reorganized and spliced ​​to be equivalent to a 500Msps high sampling rate signal. This splicing method expands the number of data points to 4 times that of a single 125Msps sampling, while the logic resource occupancy is proportional to the number of data points, resulting in a significant increase in hardware complexity and resource requirements. By calculating the area of ​​a single grating reflecting a pulse signal under a specific wavelength optical pulse signal, it is directly used as the reflectivity of the grating at this wavelength. Using this method, the 4 acquisition signals are directly added to generate a signal carrying the position and wavelength information of the grating array optical fiber. The equivalent sampling rate of the signal is 12Msps, and the number of data points remains unchanged. This method significantly reduces the occupancy of logic resources and the complexity of data processing, while ensuring the demodulation accuracy.

[0050] In this embodiment, the expression of the grating position in the fiber Bragg grating sensor array is:

[0051] D x =x / F×c / 2n2

[0052] Among them, D x represents the grating position with the horizontal axis coordinate value of the peak point being x, x represents the horizontal axis coordinate value of the peak point of the reflected light signal, F represents the sampling rate of the fiber grating sensor array, n2 represents the refractive index of the fiber grating sensor array 32, and c represents the propagation speed of light in a vacuum.

[0053] Furthermore, by analyzing the accumulation of the reflected pulse signals, the positions and wavelengths of the gratings are determined. The reflectivity of each grating at different wavelengths is represented by the intensity of the accumulated signal under the action of the optical pulses at the corresponding wavelengths. Combining the reflectivities of the gratings at different wavelengths, the reflected spectral curve is reconstructed. Subsequently, the Gaussian fitting or centroid algorithm is used to extract the spectral center wavelength as the working wavelength of the grating.

[0054] The fiber Bragg grating sensing array is an array of identical weakly reflective gratings. The distance between any two gratings in the fiber Bragg grating sensing array is 5 m, and the center wavelength of the fiber Bragg grating sensing array is 1550.96 nm.

[0055] In one example, the wavelength range of the light source 11 is set as [λ s , λ e , and the wavelength scanning interval is Δλ. The signal accumulation unit 23 and the signal demodulation unit 24 control the light source 11 to sequentially output optical signals with different wavelengths through TTL signals. The intensity of the optical signal is I0, and the optical signal is introduced into the optical pulse modulation unit 13 through the first optical circulator 12.

[0056] The optical pulse modulation unit 13 is built-in with a drive circuit. After receiving the pulse drive signals sent by the signal accumulation unit 23 and the signal demodulation unit 24, it modulates the input optical signal. The duration of the modulation is τ. When the pulse drive signal is at a high level, the optical pulse modulation unit 13 amplifies the optical signal with a gain of a; when it is at a low level, it attenuates the optical signal with an attenuation factor of b, thereby realizing the modulation of the pulse signal, and the modulation depth is a / b.

[0057] While controlling the light source 11 to output an optical signal with a specific wavelength, the signal accumulation unit 23 and the signal demodulation unit 24 output pulse drive signals to the optical pulse modulation unit 13 to modulate the optical signal. Within the linear working region of the optical pulse modulation unit 13, the duration of the modulated first optical pulse is τ, the intensity is a×I0, the background noise is b×I0, and the modulation depth is a / b. The modulated optical signal enters the Faraday rotator mirror 15 through the delay optical fiber from the output port of the optical pulse modulation unit 13, and after reflection, returns to the optical pulse modulation unit 13 through the delay optical fiber again and is output from its input port. The total delay time introduced by the delay optical fiber is t2 = 2L×n / c, where L is the length of the delay optical fiber, c is the propagation speed of light in vacuum, and n is the refractive index of the delay optical fiber. By selecting an appropriate length L of the delay optical fiber such that t2 < τ, the duration of the second optical pulse output from the optical pulse modulation unit 13 is shortened to τ - t2, the signal intensity is a 2 ×I0, the background noise is b 2 ×I0, and the modulation depth is a 2 / b 2 .

[0058] The optical pulse output from the first optical interface of the optical pulse modulation unit 13 enters the grating array sensing grating 32 through the second optical circulator 31. The reflected signal of the grating array sensing grating 32 is then transmitted through the second optical circulator 31 to the photoelectric converter for photoelectric conversion, and the converted electrical signal is connected to the multi-channel acquisition unit through N output ports.

[0059] The signal accumulation unit 23 and the signal demodulation unit 24 internally generate N clock signals with a frequency of x, and the phase shift values between each signal differ by 360 / N degrees in sequence. By using the method of alternating sampling, the N acquired signals are spliced into a signal with an equivalent sampling rate of N*x. Using the area of the reflected pulse signal of a single grating under a specific wavelength optical pulse as the reflectivity of the grating at the corresponding wavelength, by directly adding the N signals, a signal containing the fiber position and wavelength information of the grating array is obtained. Finally, the precise demodulation of the grating array optical fiber is completed through the signal demodulation module.

[0060] In this embodiment, the light source 11 is modulated twice by the pulse signal modulation module 1, thereby improving the modulation depth and compressing the duration of the optical signal, and avoiding the dependence on high-performance optoelectronic devices and complex drive circuits. By adopting the multi-channel alternating sampling and signal accumulation method, the digital conversion accuracy of the fiber reflected signal can be greatly improved, ensuring the high-precision demodulation of the finally acquired data. The use of multiple analog-to-digital conversion units 22 makes the sampling of each channel staggered in phase, and the signal acquisition effect is optimized through signal accumulation, thereby greatly improving the spatial resolution of the system for the output signal of the grating array sensing module 3. At the same time, the signal accumulation unit 23 and the signal demodulation unit 24 realize the wavelength adjustment of the light source 11 and the synchronous control of the pulse signal and the multi-channel acquisition unit, complete the acquisition and demodulation of the grating array reflected signal, and realize the low-speed acquisition and parallel processing of the high-speed return signal, thereby significantly reducing the requirements for high sampling rate and hardware resources.

[0061] Based on the above system, an embodiment of the present application discloses a high-precision and high-spatial-resolution grating array optical fiber demodulation method, and the method includes:

[0062] By performing two signal modulations on the continuous light beam generated by the light source 11 in the pulse signal modulation module 1, so that the pulse signal modulation module 1 outputs a modulated optical pulse;

[0063] The modulated optical pulse is sent into the grating array sensing module 3, so that the modulated optical pulse forms a reflected optical signal in the grating array sensing module 3, and the reflected optical signal is input to the signal detection and demodulation module 2;

[0064] The reflected optical signal is converted into a digital signal by the photodetector 21 in the signal detection and demodulation module 2, and high-sampling-rate data is acquired in an alternating sampling manner in the multi-analog-to-digital conversion unit 22. After being processed by the signal accumulation unit 23 and the signal demodulation unit 24, the change in the reflected pulse area at each grating in the grating array sensing module 3 is extracted for precise demodulation.

[0065] In one example, the use of the above system in conjunction with the high-precision and high-spatial-resolution grating array optical fiber demodulation method is as follows:

[0066] Step S1: According to the central wavelength of the grating, 1550.96 nm, assuming its operating wavelength range is ±1 nm, the wavelength scanning range of the light source 11 is set to 1550 - 1552 nm, and the scanning step is set to 10 pm. The signal accumulation unit 23 and the signal demodulation unit 24 control the light source 11 to sequentially output optical signals of different wavelengths (intensity 0 dBm) through TTL level, and guide them to the optical pulse modulation unit 13 through the first optical circulator 12.

[0067] Step S2: The optical pulse modulation unit 13 has a built-in drive circuit. After receiving the pulse drive signal given by the signal accumulation unit 23 and the signal demodulation unit 24, it modulates the input optical signal into a pulsed optical signal. When the pulse drive signal is at a high level, the optical pulse modulation unit 13 amplifies the optical signal with a gain of 10 dB. When it is at a low level, the optical signal is attenuated to -20 dB, achieving a pulse modulation with an extinction ratio of 30 dB. The initial pulse width is 50 ns, the signal intensity is 10 dBm, and the background noise is -20 dBm.

[0068] The signal accumulation unit 23 and the signal demodulation unit 24 control the light source 11 to output an optical signal of a specific wavelength and then output a pulse drive signal to the optical pulse modulation unit 13 to perform pulse modulation on the light output of the light source 11. In the linear working region of the optical pulse modulation unit 13, the pulse width of the modulated first optical pulse signal is 50 ns, the intensity is 10 dBm, the background noise is -20 dBm, and the extinction ratio is 30 dB. The modulated optical pulse signal is output from the second optical interface of the optical pulse modulation unit 13 and input into the Faraday rotator mirror 15 through a 4-m long delay optical fiber 14. The optical signal entering the Faraday rotator mirror 15 is reflected, passes through the delay optical fiber 14 again, is input from the second optical interface of the optical pulse modulation unit 13, and is output from the first optical interface. The total time delay introduced by the delay optical fiber 14 is t2 = 2Ln / c = 40 ns, where L is the length of the delay optical fiber 14, which is 4 m, c is the propagation speed of light in vacuum, which is 3×10^8 m / s, and n is the refractive index of the core of the delay optical fiber 14, which is approximately 1.5. Then, the pulse width of the second optical pulse signal output from the first optical interface of the optical pulse modulation unit 13 is 10 ns, the intensity of the optical pulse signal is 20 dBm, the background noise is -40 dBm, and the extinction ratio is 60 dB. In actual engineering, compared with the 50-ns pulse signal, the spatial resolution of the 10-ns pulse signal is increased by 5 times, but the sampling rate of the system is also increased by 5 times, and it is usually selected as 500 Msps.

[0069] The optical pulse signal output from the first optical interface of the optical pulse modulation unit 13 enters the grating array sensing optical fiber through the second optical circulator 31. The reflected signal of the grating array sensing optical fiber passes through the second optical circulator 31 and enters the photoelectric converter for photoelectric signal conversion. The converted electrical signal is connected to 4 output ports.

[0070] Step S3: The signal accumulation unit 23 and the signal demodulation unit 24 internally generate 4 clock signals with a frequency of 125 MHz and phases of 0°, 90°, 180°, and 270° respectively. According to the signal interleaved sampling method, the 4 collected signals are spliced to be equivalent to 1 signal with a sampling rate of 500 Msps. Using the method that the area of the reflected pulse signal of a single grating under an optical pulse signal of a specific wavelength is used as the reflectivity of the grating at that wavelength, by accumulating the 4 signals, the composite signal carrying the grating position and wavelength information is directly extracted, and the final demodulation is completed using the traditional grating demodulation algorithm.

[0071] Compared with the existing FBG demodulation scheme based on the OTDR technology and wavelength scanning method, the present invention effectively improves the extinction ratio and spatial resolution of the optical signal by constructing a round-trip optical transmission path and adding a delay structure, while avoiding the dependence on high-performance optoelectronic devices and complex drive circuits. The combination of the improvement of the signal-to-noise ratio and the pulse width compression technology realizes the low-speed acquisition and parallel processing of the high-speed return signal, thereby significantly reducing the requirements for high sampling rate and hardware resources, and providing a new technical path for the wide application of low-cost, high-precision, and high-spatial-resolution fiber optic sensing systems.

[0072] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-precision and high-spatial-resolution grating array fiber demodulation system, characterized in that: It comprises a pulse signal modulation module (1), a signal detection demodulation module (2) and a grating array sensing module (3), wherein: The pulse signal modulation module (1) is connected to the signal detection and demodulation module (2) and the grating array sensor module (3) respectively, and the pulse signal modulation module (1) is used to perform signal modulation twice on the light beam emitted by the light source (11); The signal detection and demodulation module (2) is connected to the grating array sensor module (3), and comprises a photodetector (21), a plurality of analog-to-digital conversion units, a signal accumulation unit (23), and a signal demodulation unit (24). The photodetector (21) is electrically connected to the signal accumulation unit (23) via the plurality of analog-to-digital conversion units, and the phase difference between any two analog-to-digital conversion units is 2π / N, where N represents the number of analog-to-digital conversion units. The signal accumulation unit (23) is electrically connected to the signal demodulation unit (24). The signal detection and demodulation module (2) is used to convert the reflected light signal output by the grating array sensor module (3) into a digital signal, and to accurately demodulate the digital signal in the form of multi-channel alternating sampling and signal accumulation.

2. The high-precision and high-spatial-resolution grating array fiber demodulation system according to claim 1, characterized in that: The pulse signal modulation module (1) comprises a light source (11), a first optical circulator (12), an optical pulse modulation unit (13), a time-delay optical fiber (14) and a Faraday rotator (15); the light source (11) is respectively connected to the signal detection and demodulation module (2) and the first port of the first optical circulator (12); the second port of the first optical circulator (12) is connected to the optical pulse modulation unit (13); the third port of the first optical circulator (12) is connected to the grating array sensor module (3); the optical pulse modulation unit (13) is respectively connected to the signal detection and demodulation module (2) and the time-delay optical fiber (14); and the time-delay optical fiber (14) is connected to the Faraday rotator (15).

3. The high-precision and high-spatial-resolution grating array fiber demodulation system according to claim 2, characterized in that: The grating array sensor module (3) comprises a second optical circulator (31) and a fiber grating sensor array, wherein a first port of the second optical circulator (31) is connected to a third port of the first optical circulator (12), a second port of the second optical circulator (31) is connected to the fiber grating sensor array, and a third port of the second optical circulator (31) is connected to the photodetector (21).

4. The high-precision and high-spatial-resolution grating array fiber demodulation system according to claim 2, characterized in that: When the optical pulse modulation unit (13) receives a high-level pulse signal, the optical pulse modulation unit (13) performs gain on the optical signal input by the first optical circulator (12); when the optical pulse modulation unit (13) receives a low-level pulse signal, the optical pulse modulation unit (13) performs attenuation on the optical signal input by the first optical circulator (12).

5. The high-precision and high-spatial-resolution grating array fiber demodulation system according to claim 2, characterized in that: The modulated optical signal output by the optical pulse modulation unit (13) is incident on the Faraday rotator (15) via the delay optical fiber (14), and the modulated optical signal is returned to the optical pulse modulation unit (13) via the Faraday rotator (15). The total delay time introduced by the delay optical fiber (14) is expressed as: t2=2L×n1 / c Wherein, t2 represents the total delay time introduced by the delay optical fiber (14), L represents the length of the delay optical fiber (14), n1 represents the refractive index of the delay optical fiber (14), and c represents the propagation speed of light in a vacuum.

6. The high-precision and high-spatial-resolution grating array fiber demodulation system according to claim 2, characterized in that: The expression of the grating position in the fiber grating sensor array is: D x =x / F×c / 2n2 Among them, D x The grating position whose horizontal axis coordinate value of the peak point is x, x represents the horizontal axis coordinate value of the peak point of the reflected light signal, F represents the sampling rate of the fiber grating sensor array, n2 represents the refractive index of the fiber grating sensor array (32), and c represents the propagation speed of light in a vacuum.

7. The high-precision and high-spatial-resolution grating array fiber demodulation system according to claim 2, characterized in that: The pulse duration of the optical pulse modulation unit (13) is 50ns-1μs, the gain of the optical pulse modulation unit (13) is 10dB, and the original modulation depth of the optical pulse modulation unit (13) is 30dB.

8. The high-precision and high-spatial-resolution grating array fiber demodulation system according to claim 1, characterized in that: The fiber grating sensor array is an identical weak reflectivity grating array, the distance between any two gratings in the fiber grating sensor array is 5m, and the central wavelength of the fiber grating sensor array is 1550.96nm.

9. The high-precision and high-spatial-resolution grating array fiber demodulation system according to claim 1, characterized in that: The light source (11) is a wavelength tunable light source (11), the output wavelength range of the wavelength tunable light source (11) is 1520nm-1560nm, and the step scanning value of the wavelength tunable light source (11) is 10pm.

10. A high-precision and high-spatial-resolution grating array fiber demodulation method, characterized in that: The method comprises: Performing signal modulation twice on a continuous light beam generated by a light source (11) in a pulse signal modulation module (1), so that the pulse signal modulation module (1) outputs a modulated light pulse; The modulated light pulse is sent into a grating array sensor module (3), so that the modulated light pulse forms a reflected light signal in the grating array sensor module (3), and the reflected light signal is input into a signal detection and demodulation module (2); The reflected light signal is converted into a digital signal by a photoelectric detector (21) in the signal detection and demodulation module (2), and high sampling rate data is acquired in an alternating sampling manner in a multi-analog-to-digital conversion unit (22). After being processed by a signal accumulation unit (23) and a signal demodulation unit (24), the change in the reflected pulse area at each grating in the grating array sensor module (3) is extracted to perform accurate demodulation.

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