A distributed optical fiber high temperature sensing system based on single photon detection

Abstract

This invention provides a distributed fiber optic high-temperature sensing system based on single-photon detection, comprising a laser pumping unit, a single-crystal fiber sensing unit, a Raman signal collection unit, and a single-photon detection demodulation unit. The laser pumping unit includes a pulsed laser, a long-pass dichroic mirror, and a short-pass dichroic mirror. The single-crystal fiber sensing unit includes a fiber collimator and a single-crystal fiber. The Raman signal collection unit includes a Stokes module and an anti-Stokes module, used to collect the Stokes signal and anti-Stokes backscattered signal from the laser-excited single-crystal fiber, respectively. The single-photon detection demodulation unit includes two single-photon detectors, a time-to-digital converter, and a computer. This invention's distributed fiber optic high-temperature sensing system based on single-photon detection features high spatial resolution and is free from temperature strain vibration multi-parameter crosstalk.

Description

Technical Field

[0001] This invention relates to the field of sensors, and more particularly to a distributed fiber optic high-temperature sensing system based on single-photon detection. Background Technology

[0002] Ultra-high temperature (above 1000℃) monitoring under complex and extreme environments, with resistance to electromagnetic interference and crosstalk from vibration and strain, has significant application value in major national strategic fields such as aerospace and energy. Traditional ultra-high temperature monitoring generally uses thermocouples, temperature-indicating paint, temperature-sensing crystals, and infrared spectroscopy, but these methods have significant shortcomings in terms of electromagnetic interference resistance, temperature measurement accuracy, and resistance to crosstalk from vibration and strain in practical applications, making it difficult to meet the requirements of in-situ ultra-high temperature monitoring under complex and extreme environments. Fiber optic sensors have unique advantages such as lightweight, resistance to electromagnetic interference, and corrosion resistance, and have been rapidly developed in the field of temperature sensing. Existing fiber optic high-temperature sensors are mainly Fabry-Pérot cavity (FP) high-temperature sensors built on single-crystal fibers with ultra-high melting points, fiber gratings etched on single-crystal fibers, and distributed high-temperature sensors built on a single single-crystal fiber without any modification or processing. The former two are single-point / multi-point fiber optic high-temperature sensors, which suffer from multi-parameter crosstalk between vibration, strain, and temperature. Distributed high-temperature sensing technology based on single-crystal optical fibers can avoid the above problems, but it still suffers from insufficient spatial resolution and cannot yet meet the requirements of the aerospace and energy sectors for centimeter and sub-centimeter scale spatial resolution measurements. Summary of the Invention

[0003] To address the shortcomings of the above technologies, the present invention aims to provide a distributed optical fiber high-temperature sensing system based on single-photon detection, which has high spatial resolution and no crosstalk between temperature, strain, vibration and other parameters.

[0004] To achieve the above objectives, the present invention provides a distributed fiber optic high-temperature sensing system based on single-photon detection, comprising: Laser pumping unit, used to generate probe light pulses; A single-crystal fiber sensing unit, the input end of which is connected to the output optical path of the laser pumping unit, is used to transmit the probe light pulse and generate back-Raman scattered light. A Raman signal collection unit, whose input end is connected to the output end optical path of the laser pumping unit, is used to receive the back Raman scattered light transmitted by the laser pumping unit and to filter and collimate the back Raman scattered light. The single-photon detection and demodulation unit has its input end connected to the output end of the Raman signal collection unit via an optical path. It is used to receive the processed Raman optical signal, convert it into an electrical signal, and then demodulate it to output temperature information.

[0005] The laser pumping unit includes a pulsed laser, a long-pass dichroic mirror, and a short-pass dichroic mirror connected sequentially through an optical path.

[0006] Preferably, the pulsed laser is a picosecond pulsed laser or a femtosecond pulsed laser, with a pulse half-width of less than 100 ps.

[0007] Optionally, the laser pumping unit also includes a first mirror and a second mirror, located after the pulsed laser and before the long-pass dichroic mirror and the short-pass dichroic mirror, for use in probing the probe pulse light emitted by the collimating laser.

[0008] The single-crystal fiber sensing unit includes a first fiber collimator and a single-crystal fiber connected sequentially via an optical path.

[0009] Preferably, the single-crystal optical fiber is sapphire optical fiber with a melting point of 2054℃; or yttrium aluminum garnet (YAG) optical fiber with a melting point of 1950℃.

[0010] The Raman signal collection unit includes a Stokes module and an anti-Stokes module arranged in parallel, which are used to collect Stokes signals and anti-Stokes backscattered signals, respectively.

[0011] The Stokes module includes a first notch filter, a first bandpass filter, and a second fiber collimator arranged sequentially along the optical path.

[0012] Optionally, the Stokes module also includes a third mirror, located in the optical path of the Stokes backscattered signal, after the short-pass dichroic mirror.

[0013] Optionally, the Stokes module also includes a first transmission fiber located in the optical path of the Stokes backscattered signal, after the second fiber collimator.

[0014] The anti-Stokes module includes a second notch filter, a second bandpass filter, and a third fiber collimator arranged sequentially along the optical path.

[0015] Optionally, the anti-Stokes module also includes a fourth mirror, located in the optical path of the anti-Stokes backscattered signal, after the long-pass dichroic mirror.

[0016] Optionally, the anti-Stokes module also includes a second transmission fiber located in the optical path of the anti-Stokes backscattered signal, after the third fiber collimator.

[0017] Optionally, the first and second transmission optical fibers are ordinary single-mode optical fibers or ordinary multimode optical fibers.

[0018] The single-photon detection and demodulation unit includes: The first single-photon detector is located at the Stokes light output terminal of the Raman signal collection unit; The second single-photon detector is located at the anti-Stokes light output end of the Raman signal collection unit; The time-to-digital converter has its input terminal electrically connected to the output terminals of the first single-photon detector and the second single-photon detector, respectively, and also electrically connected to the synchronization electrical signal output terminal of the pulsed laser in the laser pumping unit. A computer, whose input is electrically connected to the output of the time-to-digital converter, is used to demodulate temperature distribution information based on photon counting time information.

[0019] Preferably, the first and second single-photon detectors are superconducting nanowire single-photon detectors (SNSPD) with time jitter <100 ps; or single-photon detectors based on semiconductor materials (SPAD) with time jitter <150 ps.

[0020] Preferably, the minimum time channel width of the time-to-digital converter is <100 ps.

[0021] The beneficial effects of this invention are: This invention uses ultra-high melting point single-crystal optical fiber as the sensing fiber and utilizes single-photon detection and time-correlated photon counting technology to construct a distributed optical fiber high-temperature sensing system. The beneficial effect is that it can realize distributed temperature measurement with ultra-high spatial resolution and no temperature vibration strain multi-parameter crosstalk. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A schematic diagram of a distributed optical fiber high-temperature sensing system based on single-photon detection is provided in an embodiment of the present invention. Figure 2 This is a histogram of photon count-distance (single-crystal fiber length) distribution of the backscattered signal of the anti-Stokes component of a distributed optical fiber high-temperature sensing system based on single-photon detection, provided as an embodiment of the present invention.

[0024] Figure 3This is a histogram of the photon count-distance (single-crystal fiber length) distribution of the Stokes component backscattered signal of a distributed optical fiber high-temperature sensing system based on single-photon detection, provided as an embodiment of the present invention.

[0025] Figure 4 This image shows the spatial resolution measurement results of a distributed optical fiber high-temperature sensing system based on single-photon detection, provided as an embodiment of the present invention.

[0026] In the diagram, 1. Pulsed laser; 2. First reflector; 3. Second reflector; 4. Long-pass dichroic mirror; 5. Short-pass dichroic mirror; 6. First fiber collimator coupler; 7. Single-crystal fiber; 8. Third reflector; 9. First notch filter; 10. First bandpass filter; 11. Second fiber collimator coupler; 12. First transmission fiber; 13. Fourth reflector; 14. Second notch filter; 15. Second bandpass filter; 16. Third fiber collimator coupler; 17. Second transmission fiber; 18. First single-photon detector; 19. Second single-photon detector; 20. Time-to-digital converter; 21. Computer; 22. Laser pump unit; 23. Single-crystal fiber sensing unit; 24. Raman signal collection unit; 25. Stokes module; 26. Anti-Stokes module; 27. Single-photon detection and demodulation unit. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Figure 1 This is a schematic diagram of a distributed optical fiber high-temperature sensing system based on single-photon detection, provided as an embodiment of the present invention. Figure 1As shown, the distributed fiber optic high-temperature sensing system based on single-photon detection provided by the present invention includes: a laser pumping unit 22, a single-crystal fiber sensing unit 23, a Raman signal collection unit 24, and a single-photon detection demodulation unit 27. The output end of the laser pumping unit 22 is connected to the input optical paths of the single-crystal fiber sensing unit 23 and the Raman signal collection unit 24, respectively, so that the probe light generated by the laser pumping unit 22 can be injected into the single-crystal fiber sensing unit 23, and the backscattered Raman light returned by the single-crystal fiber sensing unit 23 can enter the Raman signal collection unit 24 through the laser pumping unit 22. The output end of the Raman signal collection unit 24 is connected to the input optical path of the single-photon detection demodulation unit 27, which is used to convert the filtered and collimated Raman light signal into an electrical signal and demodulate it to output temperature information.

[0029] For details, please refer to Figure 1 The laser pumping unit 22 is used to generate probe light pulses. This unit includes a pulsed laser 1, a first reflector 2, a second reflector 3, a long-pass dichroic mirror 4, and a short-pass dichroic mirror 5. The optical components are connected in sequence via optical paths. The probe pulse light emitted by the pulsed laser 1 is reflected in sequence by the first reflector 2 and the second reflector 3, and then incident on the long-pass dichroic mirror 4 and the short-pass dichroic mirror 5.

[0030] The single-crystal fiber sensing unit 23 is used to transmit probe light pulses and generate backscattered Raman light. It includes a first fiber collimator coupler 6 and a single-crystal fiber 7. Laser light transmitted through a short-pass dichroic mirror 5 is coupled into the single-crystal fiber 7 via the first fiber collimator coupler 6. As the laser light propagates in the single-crystal fiber 7, it excites backscattered Raman light.

[0031] The Raman signal collection unit 24 includes a Stokes module 25 and an anti-Stokes module 26 arranged in parallel, used to collect Stokes signals and anti-Stokes backscattered signals, respectively. The Stokes module 25 is connected to the optical path of the short-pass dichroic mirror 5 and includes a third reflecting mirror 8, a first notch filter 9, a first bandpass filter 10, a second fiber collimator 11, and a first transmission fiber 12, all connected in sequence. The Stokes signal is reflected by the third reflecting mirror 8, filtered by the first notch filter 9 and the first bandpass filter 10, and then coupled into the first transmission fiber 12 by the second fiber collimator 11. The anti-Stokes module 26 is connected to the optical path of the long-pass dichroic mirror 4 and includes a fourth reflecting mirror 13, a second notch filter 14, a second bandpass filter 15, a third fiber collimator 16, and a second transmission fiber 17, all connected in sequence. The anti-Stokes backscattered signal is reflected sequentially by the fourth mirror 13, filtered by the second notch filter 14 and the second bandpass filter 15, and then coupled into the second transmission fiber 17 by the third fiber collimator 16.

[0032] The single-photon detection demodulation unit 27 is optically connected to the output of the Raman signal collection unit 24, and includes a first single-photon detector 18 and a second single-photon detector 19 arranged in parallel, a time-to-digital converter 20, and a computer 21. The Stokes light output from the first transmission fiber 12 is incident on the first single-photon detector 18; the anti-Stokes light output from the second transmission fiber 17 is incident on the second single-photon detector 19; the outputs of both the first and second single-photon detectors 18 and 19 are electrically connected to the input of the time-to-digital converter 20; the output of the time-to-digital converter 20 is electrically connected to the input of the computer 21, used to demodulate the temperature distribution information along the single-crystal fiber 7 based on the photon counting time information. Additionally, the time-to-digital converter (20) is also electrically connected to the synchronization signal output of the pulsed laser (1).

[0033] The pulsed laser 1 is a picosecond pulsed laser or a femtosecond pulsed laser. In this embodiment, the pulsed laser 1 is a picosecond pulsed laser with a center wavelength of 532 nm, a full width at half maximum (FWHM) of 15 ps, and a repetition frequency of 1 MHz.

[0034] The single-crystal optical fiber 7 is yttrium aluminum garnet (YAG) optical fiber with a melting point of 1950℃ and a length of 1 m, or sapphire optical fiber with a melting point of 2054℃. In this embodiment, the single-crystal optical fiber 7 is yttrium aluminum garnet optical fiber.

[0035] The center wavelength of the first notch filter 9 and the second notch filter 14 is 532 nm, and the optical density OD > 6.

[0036] The first transmission fiber 12 and the second transmission fiber 17 are ordinary single-mode fibers or ordinary multimode fibers. In this embodiment, both the first transmission fiber 12 and the second transmission fiber 17 are ordinary single-mode fibers. The first single-photon detector 18 and the second single-photon detector 19 are superconducting nanowire single-photon detectors (SNSPD) with time jitter <100 ps; or semiconductor-based single-photon detectors (SPAD) with time jitter <150 ps. In this embodiment, the first single-photon detector 18 and the second single-photon detector 19 are superconducting nanowire single-photon detectors with time jitter of ~80 ps.

[0037] The time-to-digital converter 20 has a minimum time channel width of 1 ps.

[0038] The workflow of the distributed fiber optic high-temperature sensing system based on single-photon detection described in this invention is as follows: The probe pulse light emitted by the pulsed laser 1 passes sequentially through the long-pass dichroic mirror 4 and the short-pass dichroic mirror 5, and after being collimated by the first fiber collimating coupler 6 in the single-crystal fiber sensing unit 23, it enters the single-crystal fiber 7, exciting Raman scattering in the single-crystal fiber. The backscattering generated as the pulse light propagates returns along the original path.

[0039] The backscattered Raman light first passes through the short-pass dichroic mirror 5 in the laser pump unit, where the Stokes component Raman signal is reflected to the Stokes module 25. The remaining light, after transmission, passes through the long-pass dichroic mirror 4, where the anti-Stokes component Raman signal is reflected to the anti-Stokes module 26.

[0040] The two separated Raman signals are filtered by a first notch filter 9 and a second notch filter 14 to remove light with the same wavelength as the pulsed laser center. Then, the desired Raman signal band is further obtained by the corresponding first bandpass filter 10 and second bandpass filter 15 before entering the single-photon detection demodulation unit 27. The first single-photon detector 18 and the second single-photon detector 19 detect Stokes and anti-Stokes backscattered signals, respectively. After passing through the first single-photon detector 18 and the second single-photon detector 19, each photon signal outputs an electrical signal. The two electrical signals are connected to the time-to-digital converter 20 via a coaxial cable.

[0041] The pulsed laser 1 emits a detection pulse light signal and simultaneously emits a corresponding electrical signal. This signal is also recorded by the time-to-digital converter 20. Based on this synchronous electrical signal, the arrival timestamp information of the electrical signals corresponding to the Stokes and anti-Stokes backscattering photon events, i.e., the time interval between them and the synchronous electrical signal, is obtained. Then, the computer 21 connected to the time-to-digital converter 20 is used for recording and data processing.

[0042] The time-to-digital converter achieves a time sampling accuracy on the picosecond level. This accuracy can be understood as the time channel width. Using this width as the unit, the propagation time along the length of the sensing fiber is divided into sequential time channels. Each time channel acts as a storage unit, incremented by 1 based on the timestamp information of the detected record. By repeatedly measuring the time interval between the backscattered photon events and the synchronization signal within multiple pulse cycles, the total count in each time channel corresponds to the signal intensity within that channel. This establishes a photon count-time (propagation time along the length of the sensing fiber) distribution histogram, yielding the original backscattered Raman signal data. Through coordinate transformation, a photon count-distance (single-crystal fiber length) distribution histogram is obtained. Based on the rising edge of the histogram (10%-90%), the spatial resolution of the distributed fiber optic high-temperature sensing system can be determined.

[0043] Figure 2 and Figure 3 The figures shown are histograms of photon count-distance (single-crystal fiber length) distribution of backscattered signals of anti-Stokes and Stokes components, respectively, where the horizontal axis represents the distance along the single-crystal fiber 7 and the vertical axis represents the photon count. Figure 4 This image shows the spatial resolution result of the distributed fiber optic high-temperature sensing system, calculated based on 10%-90% of the rising edge of the photon count-distance histogram of the anti-Stokes component backscattered signal. Based on the obtained backscattered Raman signal data, the AS / S ratio of the anti-Stokes backscattered signal data to the Stokes backscattered signal data can be calculated. At multiple different temperatures (at least five temperature values ​​from room temperature to ≥1000℃), the AS / S ratio of the anti-Stokes backscattered signal data to the Stokes backscattered signal data is calculated, resulting in a temperature-AS / S ratio relationship curve. For any location in the single-crystal fiber, the calculated AS / S ratio is substituted into the temperature-AS / S ratio relationship curve, and the temperature information at that location is demodulated.

[0044] The beneficial effects of this invention are: This invention uses ultra-high melting point single-crystal optical fiber as the sensing fiber and utilizes single-photon detection and time-correlated photon counting technology to construct a distributed optical fiber high-temperature sensing system. The beneficial effect is that it can realize distributed temperature measurement with ultra-high spatial resolution and no temperature vibration strain multi-parameter crosstalk.

[0045] The above description is merely an 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 principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A distributed fiber optic high-temperature sensing system based on single-photon detection, characterized in that, include: The laser pumping unit (22) is used to generate probe light pulses and output a trigger electrical signal synchronized with the probe light pulses; The single-crystal fiber sensing unit (23) has its input end connected to the output end of the laser pumping unit (22) via an optical path, and is used to transmit the probe light pulse and generate back-Raman scattered light. The Raman signal collection unit (24) has its input end connected to the output end of the laser pumping unit (22) via an optical path. It is used to receive the back Raman scattered light transmitted by the laser pumping unit (22) and to filter and collimate the back Raman scattered light. The single-photon detection demodulation unit (27) has its input end connected to the output end of the Raman signal collection unit (24) via an optical path. It is used to receive the processed Raman optical signal, convert it into an electrical signal, and then demodulate it to output temperature information.

2. The distributed optical fiber high-temperature sensing system according to claim 1, characterized in that, The laser pumping unit (22) includes a pulsed laser (1), a first reflector (2), a second reflector (3), a long-pass dichroic mirror (4), and a short-pass dichroic mirror (5) connected in sequence through an optical path.

3. The distributed optical fiber high-temperature sensing system according to claim 2, characterized in that, The pulsed laser (1) is a picosecond pulsed laser or a femtosecond pulsed laser with a pulse half-width of less than 100 ps.

4. The distributed optical fiber high-temperature sensing system according to claim 1, characterized in that, The single-crystal fiber sensing unit (23) includes a first fiber collimator (6) and a single-crystal fiber (7) connected in sequence through an optical path.

5. The distributed optical fiber high-temperature sensing system according to claim 2, characterized in that, The single-crystal optical fiber (7) is a sapphire optical fiber or a yttrium aluminum garnet optical fiber.

6. The distributed optical fiber high-temperature sensing system according to claim 1, characterized in that, The Raman signal collection unit (24) includes a Stokes module (25) and an anti-Stokes module (26) arranged in parallel. The Stokes module (25) is connected to the optical path of the short-pass dichroic mirror (5) and is used to collect Stokes light. The anti-Stokes module (26) is connected to the optical path of the long-pass dichroic mirror (4) and is used to collect anti-Stokes light.

7. The distributed optical fiber high-temperature sensing system according to claim 6, characterized in that, The Stokes module (25) includes a third reflector (8), a first notch filter (9), a first bandpass filter (10), a second fiber collimator (11), and a first transmission fiber (12) arranged sequentially along the optical path; the anti-Stokes module (26) includes a fourth reflector (13), a second notch filter (14), a second bandpass filter (15), a third fiber collimator (16), and a second transmission fiber (17) arranged sequentially along the optical path.

8. The distributed optical fiber high-temperature sensing system according to claim 7, characterized in that, The center wavelengths of the first notch filter (9) and the second notch filter (14) correspond to the emission wavelength of the pulsed laser (1), and the optical density OD > 6; the first transmission fiber (12) and the second transmission fiber (17) are ordinary single-mode fiber or ordinary multimode fiber.

9. The distributed optical fiber high-temperature sensing system according to claim 1, characterized in that, The single-photon detection and demodulation unit (27) includes: The first single-photon detector (18) is located at the Stokes light output end of the Raman signal collection unit (24); The second single-photon detector (19) is located at the anti-Stokes light output end of the Raman signal collection unit (24); The input terminal of the time-to-digital converter (20) is electrically connected to the output terminals of the first single-photon detector (18) and the second single-photon detector (19), respectively, and is also electrically connected to the synchronous electrical signal output terminal of the pulsed laser (1) in the laser pumping unit (22). The computer (21) has its input terminal electrically connected to the output terminal of the time-to-digital converter (20) and is used to demodulate the temperature distribution information based on the photon counting time information.

10. The distributed optical fiber high-temperature sensing system according to claim 9, characterized in that, The first single-photon detector (18) and the second single-photon detector (19) are superconducting nanowire single-photon detectors with time jitter <100 ps; or single-photon detectors based on semiconductor materials with time jitter <150 ps; the time-to-digital converter (20) has a minimum time channel width <100 ps.

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