High-spatial-resolution distributed Raman fiber temperature measurement system and method

Abstract

The invention relates to the technical field of optical fiber sensing, and provides a high-spatial-resolution distributed Raman optical fiber temperature measurement system and method. The system comprises a pulse laser, an avalanche photoelectric detector, a signal acquisition module and an upper computer, the pulse laser outputs high-repetition-frequency narrow-pulse laser which is injected into the sensing optical fiber to excite a back Raman scattering effect; the avalanche photoelectric detector converts the scattered light into an electric signal; the signal acquisition module adopts an asynchronous equivalent time sampling technology, an ADC module is controlled by an FPGA module to acquire signals point by point at a low sampling rate, a high-resolution waveform is recombined by using a small frequency difference between a sampling clock and a laser pulse repetition frequency, and a signal-to-noise ratio is improved through a plurality of times of cumulative average algorithm; and the upper computer reconstructs a complete time domain waveform and demodulates the temperature information of each position of the optical fiber. The high spatial resolution of 10cm is realized, the cost and complexity of the system are reduced, and the system is suitable for high-precision temperature measurement scenes.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a high spatial resolution distributed Raman fiber optic temperature measurement system and method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Distributed Temperature Sensing (DTS) is based on the backscattering effect in optical fibers. It measures the temperature distribution along the fiber by detecting the intensity of Stokes and anti-Stokes Raman scattered light and combining it with optical time domain reflectometry (OTDR) technology.

[0004] The typical spatial resolution of a traditional Raman spectroscopy system is about 1m, and its spatial resolution is mainly limited by three key modules: (1) Excitation source module: Traditional Raman temperature measurement systems use nanosecond (ns) level pulsed lasers. The theoretical limit of spatial resolution (Δz) is determined by the laser pulse width (τ) and the speed of light in the optical fiber. The calculation formula is Δz = c × τ / (2n), where c is the speed of light in vacuum, c ≈ 3 × 10 8 m / s, where n is the refractive index of the optical fiber, n≈1.46. For example, using a 10ns pulsed laser, the theoretical limit of its spatial resolution is approximately: Δz≈(3×10 m / s). 8 m / s×10×10 -9 The pulse width of the excitation light source is approximately 1 m (s) / (2×1.46)≈1 m, which makes it impossible to achieve higher spatial resolution.

[0005] (2) Scattered light detection module: The intensity of Raman scattered light is extremely weak (approximately 10 times the intensity of incident light). -6 ~10 -9 High-bandwidth, high-gain detectors (such as APDs) are required for effective detection. Traditional systems often use low-bandwidth APDs (bandwidth < 50MHz), which leads to signal edge distortion and makes it impossible to achieve high-precision resolution.

[0006] (3) Signal Acquisition Module: In traditional Raman thermometry systems, the ADC sampling is triggered by the synchronization signal emitted by the excitation source. That is, after each laser pulse is emitted, the ADC acquires the returned scattered signal at a fixed sampling rate. The sampling rate of the ADC directly determines the minimum time interval that the system can resolve, thus directly limiting the spatial resolution that the system can achieve. For example, to achieve a spatial resolution of 1m, the sampling time interval of the ADC is required to be 10ns (the speed of light in the optical fiber is calculated according to 2×10⁻⁶).8 (Calculated in m / s), corresponding to an ADC sampling rate of 100MHz. Pursuing higher spatial resolution requires not only narrower laser pulses but also a high sampling rate ADC, which becomes the main bottleneck in system cost and performance realization.

[0007] In the prior art, various technical improvements have emerged to enhance spatial resolution or measurement accuracy. For example, Chinese patent application number "CN2021103186784" discloses a long-distance, high spatial resolution Raman fiber multi-parameter sensing system and method. It indirectly improves resolution at the algorithmic level by employing a complex differential pulse pair algorithm and a bidirectional measurement architecture. However, this system is structurally complex and costly, and cannot fundamentally overcome the physical limitations of pulse width. Its performance improvement is essentially algorithmic compensation rather than a fundamental physical innovation. Another Chinese patent application number "CN2020106461596" discloses a multi-phase data acquisition method, system, and storage medium for DTS. It uses multi-phase synchronous sampling to increase sampling density, but still requires a laser pulse synchronous triggering framework, failing to address the cost bottleneck caused by high-speed ADCs and not optimizing for pulse width. Its core is to acquire more sampling points by inserting delays without changing the ADC hardware sampling rate. This method mainly optimizes the "density of sampling points" but does not address the fundamental parameter of "pulse width," which determines the theoretical limit of resolution. Therefore, its effect on improving spatial resolution is limited, and it is still constrained by the high requirements for ADC performance under the synchronous sampling framework, failing to fundamentally solve the cost and complexity problems brought about by high-speed acquisition. Summary of the Invention

[0008] To address the technical problems mentioned above, this invention provides a high spatial resolution distributed Raman fiber optic temperature measurement system and method. This invention achieves a high spatial resolution of 10 cm on a temperature measurement fiber less than 10 m by synergistic optimization of a pulsed laser, an avalanche photodetector, and a signal acquisition module.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of the present invention provides a high spatial resolution distributed Raman fiber optic temperature measurement system.

[0010] A high spatial resolution distributed Raman fiber optic temperature measurement system includes: a pulsed laser, an optical coupler, a wavelength division multiplexer, an avalanche photodetector, a signal acquisition module, and a host computer; The laser pulse generated by the pulsed laser is split into two paths by an optical coupler. One laser pulse is coupled into the sensing fiber through a wavelength division multiplexer to generate a Raman scattering signal. The back Raman scattering signal used for temperature detection passes through the wavelength division multiplexer and the avalanche photodetector in sequence before entering the signal acquisition module. The other laser pulse enters the repetition frequency detection module of the signal acquisition module to detect the repetition frequency signal of the laser pulse. The signal acquisition module uses the repetition frequency signal of the laser pulse as a reference clock and generates an ADC sampling clock. When the rising edge of the ADC sampling clock is detected to be aligned with the rising edge of the laser pulse repetition frequency signal, asynchronous equivalent time sampling is triggered. One data point is acquired in each laser pulse cycle. Using the frequency difference between the ADC sampling clock and the laser pulse repetition frequency, the sampling points in each subsequent laser pulse cycle are shifted backward by a set time difference relative to the Raman scattering signal waveform on the time axis. The full-time domain scan of the signal window is completed, the original signal is generated and uploaded to the host computer to demodulate the temperature information at each position of the sensing fiber. The set time difference is the difference between the ADC sampling clock period and the laser pulse repetition frequency period.

[0011] Furthermore, the signal acquisition module includes: a signal conditioning module, an ADC module, an FPGA module, a repetition rate detection module, and a communication module. The signal conditioning module is connected to the avalanche photodetector and the ADC module, respectively. The FPGA module is connected to the ADC module and the repetition rate detection module, respectively. The repetition rate detection module is connected to a pulsed laser. The Raman scattering signal detected by the avalanche photodetector is conditioned by the signal conditioning module and then enters the ADC module for signal acquisition.

[0012] Furthermore, the FPGA module has a built-in phase-locked loop circuit, which uses the repetition frequency signal input from the repetition frequency detection module as the reference clock for the built-in phase-locked loop circuit. The built-in phase-locked loop circuit is also used to generate the sampling clock for the ADC module.

[0013] Furthermore, the sampling clock frequency of the ADC module is 1% lower than the repetition frequency of the laser pulse.

[0014] Furthermore, the FPGA module communicates with the host computer via a communication module.

[0015] Furthermore, after the signal acquisition module has completed the full-time domain scan of the signal window, it performs cumulative processing on the signal to be measured within the signal window and generates the original signal through a cumulative averaging algorithm.

[0016] Furthermore, after the laser pulse enters the sensing fiber, it excites the molecules within the sensing fiber, generating a backscattering effect that includes Stokes Raman scattered light and anti-Stokes Raman scattered light.

[0017] Furthermore, the cumulative completion of the full-time domain scanning of the signal window includes: when the cumulative number of sampling points reaches the ratio of the period of the laser pulse repetition frequency to the period difference, the sampling points complete the full-time domain scanning of the signal window at a time interval of a set time difference; wherein, the period difference is calculated based on the frequency difference between the ADC sampling clock and the laser pulse repetition frequency.

[0018] Furthermore, in the asynchronous equivalent time sampling process, each laser pulse cycle is used as a signal window. All data points collected within each pulse cycle are remapped and arranged into the same signal window according to their delay relative to their respective pulse times. The mapping rule is: the first sampling point A1 corresponds to the time label t=t i The second sampling point A2 corresponds to the time label t=t i + t; ...; the nth sampling point A n The corresponding time tag t=t i +(n-1) t; where, t represents the set time difference.

[0019] A second aspect of the present invention provides a high spatial resolution distributed Raman fiber optic temperature measurement method.

[0020] A high spatial resolution distributed Raman fiber optic temperature measurement method, applied to the high spatial resolution distributed Raman fiber optic temperature measurement system described in the first aspect, includes: The laser pulse generated by the pulsed laser is split into two paths by an optical coupler. One laser pulse is coupled into the sensing fiber through a wavelength division multiplexer to generate a Raman scattering signal. The back Raman scattering signal used for temperature detection passes through the wavelength division multiplexer and the avalanche photodetector in sequence before entering the signal acquisition module. The other laser pulse enters the repetition frequency detection module of the signal acquisition module to detect the repetition frequency signal of the laser pulse. When the signal acquisition module detects that the rising edge of the sampling clock of the ADC module is phase-aligned with the rising edge of the laser pulse, it triggers the ADC module to start the first sampling. When the cumulative number of sampling points reaches the ratio of the laser pulse repetition period to the period difference, the sampling point time difference is set as the time interval to complete the full time domain scan of the signal window. When the signal under test in the signal window has completed repeated acquisition and accumulation, the accumulated original signal is uploaded to the host computer, which then completes the reconstruction of the complete time domain waveform of the Raman scattered light and demodulates the temperature information at each position of the sensing fiber.

[0021] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a high spatial resolution distributed Raman fiber optic temperature measurement system and method. The temperature measurement system includes: a pulsed laser, an avalanche photodetector, a signal acquisition module, and a host computer. The pulsed laser outputs a high repetition rate narrow pulse laser and injects it into the sensing fiber to excite the backscattering effect of Raman. The avalanche photodetector converts the scattered light into an electrical signal. The signal acquisition module uses asynchronous equivalent time sampling technology, and controls the ADC module through an FPGA module to acquire signals point by point at a low sampling rate. The high-resolution waveform is reconstructed using the small frequency difference between the sampling clock and the laser pulse repetition rate, and the signal-to-noise ratio is improved by several accumulation and averaging algorithms. The host computer reconstructs the complete time-domain waveform and demodulates the temperature information at each location in the fiber. This invention solves the technical bottlenecks of low spatial resolution and high cost of high-speed acquisition in traditional Raman fiber optic temperature measurement systems; it achieves a high spatial resolution of 10 cm, reduces system cost and complexity, and is suitable for high-precision temperature measurement scenarios.

[0022] This invention achieves high-resolution sampling at an equivalent sampling rate of 1GHz using a low sampling rate and high-precision ADC module on the order of 10MHz through asynchronous equivalent time sampling technology, without relying on high-cost, high-sampling-rate ADCs, thus significantly reducing system cost and design complexity. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0024] Figure 1 This is a structural diagram of a high spatial resolution distributed Raman fiber optic temperature measurement system shown in an embodiment of the present invention; Figure 2 This is a schematic diagram of conventional synchronous sampling as shown in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating asynchronous equivalent time sampling according to an embodiment of the present invention; Figure 4 This is a complete waveform diagram in the time domain of the backscattered Raman light (AntiStokes Raman scattering light) reconstructed by the host computer in an embodiment of the present invention. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0026] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0027] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0028] As described in the background section, existing systems suffer from significant bottlenecks in high-resolution temperature measurement scenarios (such as centimeter-level resolution). To address these issues, this invention provides a high spatial resolution distributed Raman fiber optic temperature measurement system and method to overcome the low spatial resolution of traditional Raman fiber optic temperature measurement systems. Through a designed ps pulse laser, a high-bandwidth APD detector, and an equivalent time sampling signal acquisition module, a spatial resolution of 10 cm is achieved on a temperature-measuring fiber less than 10 m long. The following describes the invention in detail through several embodiments.

[0029] Figure 1 This is a structural diagram of a high spatial resolution distributed Raman fiber optic temperature measurement system according to an embodiment of the present invention; see reference. Figure 1 The high spatial resolution distributed Raman fiber optic temperature measurement system includes: a pulsed laser (LD), an optical coupler (OC), a wavelength division multiplexer (WDM), a sensing fiber, an avalanche photodetector (APD), a signal acquisition module, a host computer, and a power supply module. The power supply module is used to power the temperature measurement system.

[0030] In this embodiment, the pulsed laser can be a pulsed laser with a pulse width on the order of picoseconds (ps), with the pulse width controlled in the range of 10ps-100ps (preferably 50ps), a center wavelength of 1550nm, and a repetition frequency of 10MHz. This laser is used to inject high-repetition-rate, narrow-width laser pulses into the sensing fiber.

[0031] The laser pulse generated by the PS pulsed laser is split into two paths by an optical coupler. One path is coupled into the sensing fiber through a wavelength division multiplexer (WDM), which simultaneously filters out and outputs the Stokes Raman scattered light generated by backscattering and the anti-Stokes Raman scattered light, respectively. The other path is output to the repetition rate detection module on the signal acquisition module to detect the repetition frequency of the laser pulse.

[0032] When the laser pulse output from the ps-level pulsed laser is injected into the sensing fiber, it excites the molecules in the sensing fiber to produce a Raman scattering effect. This effect generates two types of signals: Stokes Raman scattered light and anti-Stokes Raman scattered light. The intensity of the anti-Stokes Raman scattered light is significantly correlated with temperature and is the core signal source for temperature measurement in this system.

[0033] This invention uses a ps-level narrow pulse laser to improve the theoretical limit of spatial resolution to 5mm. Combined with asynchronous equivalent time sampling technology, it actually achieves a high spatial resolution of 10cm, meeting the requirements of high-precision temperature measurement.

[0034] Because the time width of a ps laser pulse is extremely narrow (τ≈50 ps), according to the spatial resolution formula Δz=c×τ / (2n), (where c is the speed of light in a vacuum, c≈3×10⁻⁶) 8 Given m / s, τ is the laser pulse width, and n is the fiber refractive index (n≈1.46), the theoretical limit of spatial resolution can be calculated as: Δz≈(3×10⁻⁶ m / s, τ is the laser pulse width, n is the fiber refractive index, and n≈1.46). 8 m / s×50×10 -12 The theoretical limit value of s) / (2×1.46)≈5mm is directly determined by the laser pulse width, providing a core foundation for the subsequent realization of high spatial resolution temperature measurement.

[0035] A wavelength division multiplexer filters out the Stokes Raman scattered light and the anti-Stokes Raman scattered light generated by backscattering and outputs them to an avalanche photodetector. Backscattered light (especially anti-Stokes Raman scattered light) has a weak signal intensity, and traditional photodetectors have low bandwidth and slow response speed, making it difficult to effectively acquire rapidly changing signals. This invention uses a high-bandwidth avalanche photodiode (APD) as the detection device for backscattered Raman light, which can respond to the fast scattering signal generated by ps laser pulses.

[0036] More specifically, the signal acquisition module includes: a signal conditioning module, an ADC module, an FPGA module, a repetition rate detection module, and a communication module. The signal conditioning module is connected to both the avalanche photodetector and the ADC module. The ADC module is connected to the FPGA module, which in turn is connected to the repetition rate detection module, which is further connected to the ps laser. The FPGA module communicates with the host computer via the communication module. The output of the avalanche photodetector is connected to the signal conditioning module to condition the detected Raman scattering signal before transmitting it to the ADC module for signal acquisition. Because the high-bandwidth ADC module can quickly respond to the scattering signal generated by the ps laser pulse, it can provide a high-quality raw signal for subsequent temperature calculation (signal demodulation). The FPGA module, as the control core of the signal acquisition module, is used to implement sampling control, data processing, and communication with the host computer. The repetition rate detection module is used to detect the repetition frequency of the laser pulse.

[0037] This invention employs a high-bandwidth APD detector to ensure lossless detection and conversion of ps-level fast scattering signals, avoiding signal distortion; combined with a 100,000-times cumulative averaging algorithm, it effectively suppresses noise, improves the signal-to-noise ratio, and provides high-quality data for temperature demodulation.

[0038] The sampling method of the signal acquisition module described in this invention differs from that in traditional Raman temperature measurement systems. In traditional Raman temperature measurement systems, the ADC sampling is triggered by a synchronous signal emitted from the excitation source (laser). That is, after each laser pulse is emitted, the ADC module acquires the returned scattered signal at a fixed sampling rate. This sampling method is called synchronous real-time sampling; synchronous means that the sampling of the ADC module is triggered by the synchronous signal emitted by the excitation source; real-time sampling means that within a single laser pulse cycle, the ADC module operates at a sufficiently high rate to capture the entire signal window of interest (from the near end to the end of the fiber) in a single, continuous, and complete manner. After the laser emits a laser pulse, the backscattered Raman light will return successively over a period of time (depending on the length of the sensing fiber). The ADC module must operate continuously at an extremely high sampling rate within this triggering period to completely convert the analog signal within the entire time window into a digital signal, such as... Figure 2 As shown. In a synchronous real-time sampling system, the time interval between adjacent sampling points is the sampling period of the ADC module. For example, when the sampling rate of the ADC module is 100MHz, the sampling period of the ADC module is 10ns. That is, the ADC module collects one data point every 10ns. In this case, the spatial resolution determined by the sampling rate of the ADC module is: Δz≈(3×10⁻⁶) / ( ... 8 m / s×10×10 -9 s) / (2×1.46)≈1m.

[0039] The sampling method of this invention is asynchronous equivalent-time sampling. "Asynchronous" means that the sampling of the ADC module is no longer triggered by a synchronization signal emitted by the excitation source; instead, the sampling clock of the ADC module maintains a small frequency difference with the repetition frequency of the laser pulse. "Equivalent-time" means that through multiple data acquisitions by the ADC module, only one point is acquired each time. Utilizing the small difference between the sampling clock and the repetition frequency of the laser pulse, the multiple acquired points are reconstructed into a high-resolution waveform, such as... Figure 3 As shown.

[0040] In an asynchronous equivalent time sampling system, the time interval between adjacent sampling points is the time difference between the sampling clock period of the ADC module and the repetition period of the laser pulse. For example, if the sampling clock period of the ADC module is 101ns (frequency: 9.9MHz) and the repetition period of the laser pulse is 100ns (frequency: 10MHz), then the time interval between adjacent sampling points is 1ns. When the number of sampling points accumulates to: (repetition period of the laser pulse) / (time difference between the sampling clock period of the ADC and the repetition period of the laser pulse) = 100ns / 1ns = 100, the sampling points have been "scanned" from beginning to end within a 100ns time window at 1ns intervals. This achieves high-precision sampling of the signal under test.

[0041] The asynchronous equivalent time sampling described in this invention does not have a fixed synchronization delay between sampling trigger and laser pulse emission (unlike the multi-phase synchronous sampling in the comparison document). Instead, it relies on the inherent and precisely controlled frequency difference between the two clocks to achieve the natural slippage of the sampling point. This is the key to achieving a high equivalent sampling rate with a low-speed ADC.

[0042] Equivalent time sampling (ETS) technology employs a low-speed, high-precision ADC module to piece together a complete high-resolution waveform from the signal under test through multiple sampling operations. This technique does not capture all signal information in a single triggering process; instead, it acquires only one signal point at a time through thousands or even tens of thousands of triggering operations, ultimately reassembling the discrete sampling points into a continuous waveform according to their chronological order. Based on this principle, the sampling rate of the ADC module is no longer a bottleneck in system design, enabling high-precision signal sampling using a low-sampling-rate ADC module.

[0043] In this embodiment, the FPGA module incorporates a phase-locked loop (PLL) circuit. The repetition frequency signal input from the repetition rate detection module is used as the reference clock for the PLL built into the FPGA module; that is, the 10MHz repetition frequency signal of the pulsed laser is used as the reference clock for the PLL. The PLL generates the sampling clock for the ADC module through internal frequency synthesis, and its frequency is set to (10MHz - 100kHz = 9.9MHz), meaning that the sampling clock frequency of the ADC module is 1% (one percent) lower than the repetition frequency of the laser pulse.

[0044] The ADC sampling clock frequency is set to be slightly lower than the laser repetition frequency (e.g., 1%). The selection of this frequency difference needs to balance the scanning speed of the signal window and the timing stability of the system. It is usually adjustable within the range of 0.1% to 5% to achieve the best system performance.

[0045] In this embodiment, the sampling clock frequency of the ADC module is 9.9 MHz, and it samples the Raman scattering signal excited by a 10 MHz repetition rate laser pulse. Since the frequency difference between the ADC module's sampling clock and the laser repetition rate pulse is 100 kHz, their periods differ by 1 ns. This 1 ns period difference is the core parameter of the system—the heartbeat step—specifically manifested as follows: after each laser pulse cycle, the ADC's sampling point slides backward 1 ns relative to the waveform of the backscattered light signal on the time axis.

[0046] In this invention, the FPGA module built into the signal acquisition module detects the phase relationship between the rising edge of the sampling clock of the ADC module and the rising edge of the 10MHz repetition rate laser pulse in real time. When the two phases are aligned (i.e. the ADC sampling time is completely synchronized with the laser pulse emission time), the FPGA module triggers the ADC module to start the first sampling and acquire feature point A1 on the waveform under test. For the second laser pulse, due to the slight frequency difference between the sampling clock of the ADC module and the repetition frequency of the laser pulse, the sampling time of the ADC module is delayed by 1 ns relative to the emission time of the laser pulse, which corresponds to the acquisition of feature point A2 on the waveform under test, which is 1 ns behind point A1.

[0047] Similarly, when the third laser pulse triggers sampling, the sampling point is further delayed by 1ns, and feature point A3 is obtained; the fourth laser pulse triggers sampling and obtains feature point A4.

[0048] The above process is executed cyclically. For the nth laser pulse, the total delay between the sampling time of the ADC module and the emission time of the laser pulse is (n 1) × 1 ns, corresponding to feature point A on the waveform to be measured. n .

[0049] This invention defines the period (100ns) of a single laser pulse as the sampling window of the signal under test, and remaps and arranges the discrete feature points collected within all laser pulse periods into the same sampling window according to their respective delays relative to the laser pulse emission time. The mapping rules are as follows: Feature point A1 → Time label t=t i ; Feature point A2 → Time label t=t i +1ns; Feature point A3 → Time label t=t i +2ns; Feature point A4 → Time label t=t i +3ns; ... Feature point A n Point → Time tag t=t i +(n-1)ns.

[0050] When the cumulative number of sampling points reaches the ratio of the laser pulse repetition period to the period difference, i.e., 100ns / 1ns = 100, all sampling points are used at 1ns time intervals to completely cover the 100ns sampling window, thus realizing full-time domain scanning of the signal under test.

[0051] Based on the above equivalent time sampling principle, the equivalent sampling rate of this system can reach 1 / 1 ns = 1 GHz; the corresponding spatial resolution calculation formula is Δz ≈ (3 × 108 m / s×1×10 -9 s) / (2×1.46)≈10cm.

[0052] In summary, this invention achieves high-precision signal acquisition with an equivalent sampling rate of 1 GHz within a 100 ns sampling window by using an ADC module with an actual sampling rate on the order of 10 MHz.

[0053] As mentioned above, this invention employs an asynchronous equivalent time sampling method, which performs multiple discrete sampling operations through an ADC module, acquiring only one data point of the signal under test in each sampling. By utilizing the small frequency difference between the sampling clock of the ADC module and the repetition frequency of the laser pulse, the discrete data points acquired in multiple rounds are recombined according to the time dimension to generate a high-resolution waveform of the signal under test.

[0054] Specifically, when the cumulative number of sampling points reaches: (repetition period of the laser pulse) / (time difference between the sampling clock period of the ADC and the repetition period of the laser pulse), that is, 100ns / 1ns = 100, all sampling points will perform a complete time-domain scan of the 100ns signal window at 1ns time intervals.

[0055] Given the inherently weak amplitude of Raman scattering signals, even after signal conditioning, the signal within a single 100 ns time window still suffers from a low signal-to-noise ratio, making it impossible to directly demodulate effective temperature information. To address this issue, this invention performs 100,000 repeated acquisitions of the signal under test within the 100 ns time window and employs a multiple accumulation and averaging algorithm to improve the signal-to-noise ratio. Through the aforementioned accumulation and averaging process and subsequent signal processing, the complete time-domain waveform of the backscattered Raman light can be reconstructed, thereby demodulating the temperature information corresponding to each location in the optical fiber.

[0056] In another embodiment, the present invention also provides a high spatial resolution distributed Raman fiber optic temperature measurement method, applied to the above-mentioned high spatial resolution distributed Raman fiber optic temperature measurement system, comprising the following steps: Step (1): The ps pulse laser emits laser pulses at a repetition frequency of 10 MHz; the laser pulses are coupled into the sensing fiber via a wavelength division multiplexer. At the same time, the wavelength division multiplexer separates and filters the anti-Stokes Raman scattered light and the Stokes Raman scattered light generated by backscattering, and outputs the two scattered light signals to the avalanche photodetector. Step (2): The avalanche photodetector receives the backscattered Raman light signal and converts it into an electrical signal proportional to the light intensity; Step (3): The signal acquisition module performs signal conditioning on the electrical signal output by the avalanche photodetector. After conditioning, the ADC module performs discrete sampling on the signal.

[0057] Step (4): The signal acquisition module monitors the repetition frequency signal of the laser pulse in real time through the repetition frequency detection module. When the rising edge of the sampling clock of the ADC module is detected to be aligned with the rising edge of the 10 MHz laser pulse, the ADC module is triggered to start the first sampling. When the cumulative number of sampling points reaches the ratio of the laser pulse repetition period to the period difference (i.e., 100ns / 1ns=100), the sampling points are used at 1 ns intervals to complete the full time domain scan of the 100 ns signal window.

[0058] Step (5): Repeat step (4) to perform 100,000 repeated acquisitions and accumulation operations on the signal to be measured within a 100 ns signal window; the signal acquisition module uploads the accumulated original signal to the host computer through the communication module, and the host computer reconstructs the complete time-domain waveform of the back Raman scattering light and further demodulates the temperature information at each position of the sensing fiber.

[0059] Figure 4 The complete waveform of the backscattered Raman light (AntiStokes Raman scattering light) reconstructed by the host computer in the time domain is shown. The temperature measurement area of ​​the temperature measuring fiber is about 3m long. A 10cm heating area is set in the 3m temperature measurement area. It can be seen that there is a significant change in light intensity at the corresponding position, which can demodulate the temperature information at the corresponding position.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high spatial resolution distributed Raman fiber optic temperature measurement system, characterized in that, include: Pulsed laser, optical coupler, wavelength division multiplexer, avalanche photodetector, signal acquisition module and host computer; The laser pulse generated by the pulsed laser is split into two paths by an optical coupler. One laser pulse is coupled into the sensing fiber through a wavelength division multiplexer to generate a Raman scattering signal. The back Raman scattering signal used for temperature detection passes through the wavelength division multiplexer and the avalanche photodetector in sequence before entering the signal acquisition module. The other laser pulse enters the repetition rate detection module of the signal acquisition module to detect the repetition frequency signal of the laser pulse. The signal acquisition module uses the repetition frequency signal of the laser pulse as a reference clock and generates an ADC sampling clock. When the rising edge of the ADC sampling clock is detected to be aligned with the rising edge of the laser pulse repetition frequency signal, asynchronous equivalent time sampling is triggered. One data point is acquired in each laser pulse cycle. Using the frequency difference between the ADC sampling clock and the laser pulse repetition frequency, the sampling points in each subsequent laser pulse cycle are shifted backward by a set time difference relative to the Raman scattering signal waveform on the time axis. The full-time domain scan of the signal window is completed, the original signal is generated and uploaded to the host computer to demodulate the temperature information at each position of the sensing fiber. The set time difference is the difference between the ADC sampling clock period and the laser pulse repetition frequency period.

2. The high spatial resolution distributed Raman fiber optic temperature measurement system according to claim 1, characterized in that, The signal acquisition module includes: a signal conditioning module, an ADC module, an FPGA module, a repetition rate detection module, and a communication module. The signal conditioning module is connected to the avalanche photodetector and the ADC module, respectively. The FPGA module is connected to the ADC module and the repetition rate detection module, respectively. The repetition rate detection module is connected to a pulsed laser. The Raman scattering signal detected by the avalanche photodetector is conditioned by the signal conditioning module and then enters the ADC module for signal acquisition.

3. The high spatial resolution distributed Raman fiber optic temperature measurement system according to claim 2, characterized in that, The FPGA module has a built-in phase-locked loop circuit, which uses the repetition frequency signal input from the repetition frequency detection module as the reference clock for the built-in phase-locked loop circuit. The built-in phase-locked loop circuit is also used to generate the sampling clock for the ADC module.

4. The high spatial resolution distributed Raman fiber optic temperature measurement system according to claim 3, characterized in that, The sampling clock frequency of the ADC module is 1% lower than the repetition frequency of the laser pulse.

5. The high spatial resolution distributed Raman fiber optic temperature measurement system according to claim 2, characterized in that, The FPGA module communicates with the host computer through a communication module.

6. The high spatial resolution distributed Raman fiber optic temperature measurement system according to claim 1, characterized in that, After the signal acquisition module completes the full-time domain scan of the signal window, it accumulates the signals to be measured within the signal window and generates the original signal through an accumulation averaging algorithm.

7. The high spatial resolution distributed Raman fiber optic temperature measurement system according to claim 1, characterized in that, When a laser pulse enters the sensing fiber, it excites the molecules within the fiber, generating a backscattering effect that includes both Stokes Raman scattered light and anti-Stokes Raman scattered light.

8. The high spatial resolution distributed Raman fiber optic temperature measurement system according to claim 1, characterized in that, The cumulative completion of the full-time domain scanning of the signal window includes: when the cumulative number of sampling points reaches the ratio of the period of the laser pulse repetition frequency to the period difference, the sampling points are used at time intervals of a set time difference to complete the full-time domain scanning of the signal window; wherein, the period difference is calculated based on the frequency difference between the ADC sampling clock and the laser pulse repetition frequency.

9. The high spatial resolution distributed Raman fiber optic temperature measurement system according to claim 1, characterized in that, In the asynchronous equivalent time sampling process, each laser pulse cycle is used as a signal window. All data points collected within each pulse cycle are remapped and arranged into the same signal window according to their delay relative to their respective pulse times. The mapping rule is: the first sampling point A1 corresponds to the time label t=t i The second sampling point A2 corresponds to the time label t=t i + t; ...; the nth sampling point A n The corresponding time tag t=t i +(n-1) t; where, t represents the set time difference.

10. A high spatial resolution distributed Raman fiber optic temperature measurement method, characterized in that, The high spatial resolution distributed Raman fiber optic temperature measurement system according to any one of claims 1-9 comprises: The laser pulse generated by the pulsed laser is split into two paths by an optical coupler. One laser pulse is coupled into the sensing fiber through a wavelength division multiplexer to generate a Raman scattering signal. The back Raman scattering signal used for temperature detection passes through the wavelength division multiplexer and the avalanche photodetector in sequence before entering the signal acquisition module. The other laser pulse enters the repetition frequency detection module of the signal acquisition module to detect the repetition frequency signal of the laser pulse. When the signal acquisition module detects that the rising edge of the sampling clock of the ADC module is phase-aligned with the rising edge of the laser pulse, it triggers the ADC module to start the first sampling. When the cumulative number of sampling points reaches the ratio of the laser pulse repetition period to the period difference, the sampling point time difference is set as the time interval to complete the full time domain scan of the signal window. When the signal under test in the signal window has completed repeated acquisition and accumulation, the accumulated original signal is uploaded to the host computer, which then completes the reconstruction of the complete time domain waveform of the Raman scattered light and demodulates the temperature information at each position of the sensing fiber.

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