Highly sensitive fabry-perot vernier hydrogen sensor by femtosecond laser etching

Abstract

The application provides a femtosecond laser etching high-sensitivity Fabry-Perot vernier hydrogen sensor, and belongs to the technical field of optical fiber sensing, and comprises a hollow optical fiber, an open microcavity and a test system; the open microcavity is prepared on the hollow optical fiber by a femtosecond laser etching technology and is connected in series to form a double-cavity structure, the open microcavity is a temperature sensing unit FPI-1 and a hydrogen sensing unit FPI-2 respectively, the temperature sensing unit FPI-1 is coated with a temperature sensitive material PDMS inside, and the hydrogen sensing unit FPI-2 is coated with a hydrogen sensitive material PDMS / Pd-WO3 composite coating inside. The application adopts the above-mentioned femtosecond laser etching high-sensitivity Fabry-Perot vernier hydrogen sensor, and overcomes the defects of the prior art, such as insufficient sensitivity of a hydrogen sensor, easy temperature interference, complex preparation process and the like.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a high-sensitivity Fabry-Perot vernier hydrogen sensor etched by femtosecond laser etching. Background Technology

[0002] Hydrogen, as a clean, efficient, and renewable energy source, has shown broad application prospects in many fields such as fuel cells, chemical production, and aerospace. However, hydrogen is flammable and explosive, with an explosive limit range of 4% to 75% (volume fraction). This means that even in extremely low concentration environments, hydrogen leaks can cause serious safety accidents. Therefore, highly sensitive, rapid, and accurate detection of hydrogen is of paramount practical importance in ensuring production safety and environmental monitoring.

[0003] In the field of gas sensing technology, fiber optic sensors have received widespread attention and application due to their unique advantages, such as strong resistance to electromagnetic interference, small size, light weight, and ability to withstand harsh environments. Among them, the Fabry-Pérot interferometer (FPI) type fiber optic sensor, with its compact structure, fast response speed, and ease of integration with other systems, has become an important research direction in the field of hydrogen detection.

[0004] Despite the numerous advantages of FPI-type fiber optic hydrogen sensors, several key technological bottlenecks limit their performance and reliability in practical applications. The current method of combining sensitive materials with fiber optic structures in many FPI-type hydrogen sensors is prone to instability during long-term use, leading to poor repeatability and long-term reliability. This is mainly manifested in the possibility of sensitive materials detaching due to environmental changes or prolonged use, affecting the sensor's detection accuracy and lifespan. During hydrogen detection, environmental factors such as temperature and humidity often cause significant cross-interference in the detection results, especially in low-concentration hydrogen detection scenarios. Existing sensor technologies often struggle to effectively distinguish hydrogen signals from environmental interference signals, resulting in decreased detection accuracy. Traditional FPI detection schemes have limitations in sensitivity, failing to meet the high-precision detection requirements for hydrogen concentrations below 0.5%. This has become a pressing issue in applications with extremely stringent hydrogen concentration requirements, such as fuel cell systems and aerospace. Furthermore, the fabrication process of existing FPI-type hydrogen sensors is often complex, involving multiple precision machining steps, resulting in poor dimensional controllability of the microcavity structure. This not only increases manufacturing costs, but also affects product consistency and the feasibility of mass production.

[0005] To address the aforementioned issues, femtosecond laser micromachining technology, with its advantages of high processing precision, small heat-affected zone, and strong material compatibility, offers a new technical approach to overcoming the existing technical bottlenecks of FPI-type hydrogen sensors. Femtosecond lasers can achieve high-precision microstructure fabrication within or on the surface of optical fibers, thus potentially overcoming the limitations of traditional fabrication processes and improving the overall performance of the sensor.

[0006] Currently, although some related patents and technologies have attempted to solve the problems of hydrogen sensors, such as the Chinese patent "CN121049208A" which proposes a fiber optic hydrogen sensor based on a silver film-nanowire aperture array structure, this technology lacks an effective temperature and humidity compensation unit, resulting in weak resistance to temperature and humidity interference. Another Chinese patent "CN120992703A" proposes a hydrogen sensor with an ultrafast hydrogen response speed, but its hydrogen measurement sensitivity still cannot meet the high-precision detection requirements for low-concentration hydrogen.

[0007] Therefore, developing a novel FPI-type fiber optic hydrogen sensor with high sensitivity, strong anti-interference capability, stable structure, and efficient fabrication process is of great significance for promoting the development and application of hydrogen detection technology. Summary of the Invention

[0008] The purpose of this invention is to provide a high-sensitivity Fabry-Perot vernier hydrogen sensor etched by femtosecond laser, overcoming the shortcomings of existing hydrogen sensors such as insufficient sensitivity, susceptibility to temperature interference, and complex fabrication process.

[0009] To achieve the above objectives, the present invention provides a high-sensitivity Fabry-Perot vernier hydrogen sensor etched by femtosecond laser, comprising a hollow optical fiber, an open microcavity, and a testing system; The open microcavities are fabricated on hollow optical fibers using femtosecond laser etching technology and connected in series to form a dual-cavity structure. The open microcavities are a temperature sensing unit FPI-1 and a hydrogen sensing unit FPI-2. The temperature sensing unit FPI-1 is coated with a temperature-sensitive material PDMS, and the hydrogen sensing unit FPI-2 is coated with a hydrogen-sensitive material PDMS / Pd-WO3 composite coating. The testing system includes an ASE light source, a circulator, a hydrogen test chamber, a constant temperature and humidity chamber, a humidity generator, and a spectrometer. The hydrogen sensor testing process involves the probe light emitted by the ASE light source being incident on the hydrogen sensor through the circulator. The interference spectral signal of the hydrogen sensor is transmitted to the spectrometer through the circulator. Through Fourier transform filtering of the spectral signal and Fabry-Perot vernier superposition analysis, high-precision detection of hydrogen concentration is achieved.

[0010] Preferably, the open microcavities of the temperature sensing unit FPI-1 and the hydrogen sensing unit FPI-2 are both C-type open microcavities.

[0011] Preferably, in the PDMS / Pd-WO3 composite coating inside the hydrogen sensing unit FPI-2, Pd-WO3 is the core component for hydrogen response, and PDMS is the substrate.

[0012] Preferably, the etching path of the femtosecond laser etching technology is to first outline and then inner cavity, with the microcavity size deviation ≤ ±2μm in microcavity length and ≤ ±1μm in microcavity width and depth.

[0013] Preferably, the testing range of the supporting testing system is: hydrogen concentration 0%~0.5%, temperature 24℃~59℃, humidity 19.21%RH~79.85%RH, temperature control accuracy ±0.1℃, humidity control accuracy ±1%RH, and hydrogen concentration adjustment accuracy ±0.01%.

[0014] Preferably, the preparation of the PDMS / Pd-WO3 composite coating includes: S1. Take micron-sized tungsten powder with a purity ≥99.9%, dry it at 105℃ for 2 hours, stir it with 30% H2O2 solution at 800 r / min at room temperature for 70 minutes, centrifuge the reaction solution at 8000 r / min for 20 minutes, take the upper sol, add anhydrous ethanol to replace the solvent, concentrate it at 80℃, add PdCl2, stir at 80℃ for 40 minutes to obtain Pd-WO3 composite sol; S2. Mix the PDMS prepolymer with the curing agent for 20 minutes, vacuum degas for 15 minutes, coat it onto the hollow optical fiber, semi-cur it at 60°C for 30 minutes, spin-coat Pd-WO3 powder at 40°C, and fully cure it at 80°C for 3 hours to form a composite coating.

[0015] Preferably, in the PDMS / Pd-WO3 composite coating, the mass ratio of Pd to WO3 is 1:10, and the volume ratio of PDMS prepolymer to curing agent is 10:1.

[0016] Preferably, the spectral signal processing in the testing system involves separating the interference signals of the temperature sensing unit and the hydrogen sensing unit through Fourier transform, and then using twin spectra superposition to form a vernier effect, thereby improving the detection sensitivity.

[0017] Therefore, the present invention employs the aforementioned femtosecond laser-etched high-sensitivity Fabry-Perot vernier hydrogen sensor, with the following technical advantages: 1. Significantly improved detection sensitivity: Leveraging the high-response characteristics of the PDMS / Pd-WO3 composite sensitive material, and working synergistically with the Fabry-Perot vernier detection scheme, the vernier detection mode significantly improves sensitivity compared to the conventional mode, enabling accurate identification of changes in ultra-low concentration hydrogen gas and successfully breaking through the sensitivity bottleneck of existing technologies for detecting low concentration hydrogen gas.

[0018] 2. Significantly enhanced anti-interference capability: To address temperature interference, the sensor adopts a dual open microcavity temperature compensation design, and the temperature sensing unit can offset the influence of temperature changes on hydrogen detection in real time, effectively solving the problem of temperature cross-interference; In terms of humidity interference, humidity has minimal interference with the detection signal, and the sensor can work stably in a wide humidity range without the need for an additional humidity compensation module, ensuring detection accuracy in complex environments.

[0019] 3. Significantly optimized structural stability and consistency: Femtosecond laser etching technology enables high-precision fabrication of microcavity structures with precise and controllable dimensions and a small heat-affected zone, ensuring structural consistency and repeatability in mass production of sensors. Simultaneously, PDMS serves as the substrate for the sensitive coating, allowing both temperature-sensitive and hydrogen-sensitive coatings to bond tightly to the microcavity structure, effectively preventing sensitive material detachment, extending sensor lifespan, and improving long-term reliability.

[0020] 4. Superior Adaptability to Fabrication and Applications: In terms of fabrication, no complex molds are required. Femtosecond lasers can directly etch microcavities onto hollow optical fibers, resulting in short processing cycles, controllable costs, and suitability for mass production. This solves the problems of complex fabrication processes and poor microcavity size control in traditional sensors. Regarding application adaptability, the sensor, based on an optical fiber structure, offers advantages such as electromagnetic interference resistance, small size, and light weight. It is adaptable to certain temperature and hydrogen concentration ranges, meeting the low-concentration hydrogen leak detection needs in various scenarios such as chemical plants, fuel cell systems, and aerospace. It is particularly suitable for long-term online monitoring in harsh environments. Attached Figure Description

[0021] Figure 1 The following is a schematic diagram of the high-sensitivity Fabry-Perot vernier hydrogen sensor etched by femtosecond laser of the present invention: (a) is a fiber hydrogen sensing structure formed by femtosecond laser etching of hollow fiber to form an open microcavity; (b) is a microscopic image of the temperature sensing unit; and (c) is a microscopic image of the hydrogen sensing unit. Figure 2 This is a diagram of the experimental testing system for the high-sensitivity Fabry-Perot vernier hydrogen sensor etched by femtosecond laser etching according to the present invention; Figure 3 The following are examples of hydrogen response characteristic tests for the sensing system in this embodiment of the invention: (a) the original interference spectrum; (b) the frequency domain spectrum of the original spectrum after Fourier transform; (c) the interference spectrum of the hydrogen sensing unit after Fourier transform filtering; (d) the interference spectrum of the temperature sensing unit after Fourier transform filtering; (e) the interference spectrum of the hydrogen sensing unit with different hydrogen concentrations; (f) the linear fitting of the sensitivity of the hydrogen sensing unit for hydrogen testing; (g) the interference spectrum of the temperature sensing unit with different hydrogen concentrations; and (h) the linear fitting of the sensitivity of the temperature sensing unit for hydrogen testing. Figure 4The following are temperature response characteristic tests of the sensing system in the embodiments of the present invention: (a) Interference spectra of hydrogen sensing units at different temperature gradients; (b) Linear fitting of temperature test sensitivity of hydrogen sensing units; (c) Interference spectra of temperature sensing units at different temperature gradients; (d) Linear fitting of temperature test sensitivity of temperature sensing units. Figure 5 The humidity response characteristics of the sensing system in this embodiment of the invention are tested; (a) is the interference spectrum of the hydrogen-sensitive unit with different humidity gradients; (b) is the interference spectrum of the temperature-sensitive unit with different humidity gradients. Figure 6 The fiber twin controllable vernier detection scheme in this embodiment of the invention is shown below: (a) is the original interference spectrum and its trigonometric function mathematical expression for a hydrogen concentration of 0%; (b) is the twin interference spectrum and its trigonometric function mathematical expression for a hydrogen concentration of 0%; (c) is the superimposed vernier spectrum of the original spectrum and the twin spectrum in the near-infrared band; (d) is the vernier envelope spectrum of hydrogen at different concentrations; and (e) is the linear fitting of the hydrogen sensitivity of the vernier envelope. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0024] Example 1 like Figure 1 As shown, this invention provides a high-sensitivity Fabry-Perot vernier hydrogen sensor etched by femtosecond laser. Through a precisely designed dual-open microcavity structure, a special sensitive material coating, and a vernier detection scheme, it achieves high-sensitivity and interference-resistant stable detection of low-concentration hydrogen gas of 0~0.5%.

[0025] This sensor comprises a hollow optical fiber, two open microcavities (temperature sensing unit FPI-1 and hydrogen sensing unit FPI-2), a temperature-sensitive coating, a hydrogen-sensitive coating, and a supporting testing system. The hollow optical fiber serves as the sensor's basic structure, providing the optical transmission channel. The open microcavities are fabricated on the hollow optical fiber using femtosecond laser etching technology and connected in series to form a dual-cavity structure. The open microcavities are respectively the temperature sensing unit FPI-1 and the hydrogen sensing unit FPI-2. The temperature sensing unit FPI-1 is internally coated with the temperature-sensitive material PDMS for real-time acquisition of ambient temperature signals, enabling temperature compensation. The hydrogen sensing unit FPI-2 is internally coated with a PDMS / Pd-WO3 composite coating, where Pd-WO3 is the core component for hydrogen response, and PDMS serves as the substrate to ensure the stability of the bonding between the coating and the microcavity structure.

[0026] The temperature sensing unit FPI-1 has an open microcavity length of 85μm, an opening width of 62.5μm, and a depth of 62.5μm; the hydrogen sensing unit FPI-2 has a C-shaped open microcavity with a length of 122μm, an opening width of 62.5μm, and a depth of 62.5μm. The coaxiality deviation between the optical axes of the two units is ≤0.1μm.

[0027] like Figure 2 As shown, the testing system includes an ASE light source (1540nm~1600nm), a circulator, a hydrogen testing chamber, a constant temperature and humidity chamber, a humidity generator, and a spectrometer. The hydrogen sensor testing process involves the probe light emitted from the ASE light source passing through the circulator to the hydrogen sensor. The interference spectral signal from the hydrogen sensor is transmitted to the spectrometer via the circulator. High-precision detection of hydrogen concentration is achieved through Fourier transform filtering and Fabry-Perot vernier superposition analysis of the spectral signal. The spectral signal processing in the testing system involves separating the interference signals of the temperature sensing unit and the hydrogen sensing unit through Fourier transform, and then utilizing twin spectral superposition to form a vernier effect, thereby improving detection sensitivity. The testing range of this system is: hydrogen concentration 0%~0.5%, temperature 24℃~59℃, humidity 19.21%RH~79.85%RH, temperature control accuracy ±0.1℃, humidity control accuracy ±1%RH, and hydrogen concentration adjustment accuracy ±0.01%.

[0028] This invention verifies the practicality and superiority of the sensor through material preparation and structural processing, system construction and performance testing, specifically including the following steps: I. Sensor Fabrication Fabrication of temperature sensing unit FPI-1: A high-quality hollow-core quartz fiber with an outer diameter of 125 μm and an inner diameter of 50 μm was selected, and a 122 μm length fiber segment was cut using precision instruments. Subsequently, the fiber segment underwent rigorous pretreatment steps, including precise cutting and meticulous screening under a microscope, to remove any defective products with chipped edges or cracks, ensuring the integrity and quality of the fiber segment.

[0029] The pre-treated fiber segment was securely fixed in a specially designed elastic fixture and carefully placed in deionized water to create a clean and stable processing environment. Subsequently, microcavity etching was performed using an advanced femtosecond laser micromachining platform equipped with an integrated three-dimensional precision stage. This platform is fitted with a 20× objective lens (numerical aperture NA=0.45) to ensure high processing precision. By precisely setting laser parameters, including a repetition rate of 10kHz, an output power of 51μW, and a scanning speed of 70μm / s, a fine "contour-cavity" path was used to etch a C-shaped open microcavity. The etched length of this microcavity was 122μm, and the opening width and depth were precisely controlled to 62.5μm. During the etching process, a real-time monitoring mechanism was implemented to ensure that the dimensional deviation of the microcavity was strictly controlled within the range of ≤±2μm (length) and ≤±1μm (width / depth) to guarantee the accuracy and consistency of the microcavity.

[0030] The preparation of the hydrogen sensing unit FPI-2 involves two steps: Preparation of Pd-WO3 composite sol: 2.0 g of micron-sized tungsten powder (particle size range 5-10 μm) with a purity ≥99.9% was accurately weighed and dried at 105 °C for 2 hours to remove moisture. Subsequently, the dried tungsten powder was mixed with 8 mL of 30% H2O2 solution and stirred at 800 r / min at room temperature for 70 minutes to ensure complete reaction. After the reaction, the reaction solution was centrifuged at 8000 r / min for 20 minutes to separate the upper sol layer. 8 mL of anhydrous ethanol was added to the upper sol layer for solvent replacement, and the solution was concentrated to 8 mL at 80 °C. Then, 0.2 g of PdCl2 was added (ensuring a Pd to WO3 mass ratio of 1:10), and stirring was continued at 80 °C for 40 minutes to obtain the Pd-WO3 composite sol.

[0031] Formation of the fiber-PDMS / Pd-WO3 structure: Sylgard 184 PDMS was selected as the substrate material and mixed with curing agent at a volume ratio of 10:1. A platinum catalyst was used as the curing agent, utilizing its highly efficient hydrosilylation catalysis to achieve controllable crosslinking between the PDMS matrix and the curing agent. The mixed PDMS material was thoroughly stirred for 20 minutes and then subjected to vacuum degassing for 15 minutes to eliminate internal air bubbles. Subsequently, the PDMS material was uniformly coated onto the surface of a pretreated hollow optical fiber and semi-cured at 60°C for 30 minutes. After semi-curing, the optical fiber was placed at 40°C, and Pd-WO3 powder was uniformly coated onto the PDMS surface using spin coating. Finally, a full curing treatment was performed at 80°C for 3 hours to form a stable fiber-PDMS / Pd-WO3 structure.

[0032] After the temperature sensing unit and the hydrogen sensing unit were independently fabricated, they were connected in series and fixed using a high-precision fiber optic fusion splicer. During the splicing process, the coaxiality deviation of the optical axes of the two units was strictly controlled to ensure it did not exceed 0.1 μm, in order to maintain the overall optical performance and stability of the sensor. At the same time, sufficient space was reserved as a contact channel between the sensitive layer and the environment, so that the sensor could effectively sense changes in hydrogen concentration in the external environment.

[0033] II. Test System Setup like Figure 2 The test system is set up as shown: The ASE light source, serving as the core excitation source, precisely covers the output wavelength range of 1540nm to 1600nm, exhibiting excellent power stability with fluctuations strictly controlled within ±0.1dB. The output of this light source is seamlessly connected to port 1 of the circulator via high-performance single-mode fiber, ensuring efficient transmission of optical signals.

[0034] The circulator's port 2 also utilizes single-mode fiber, tightly connected to a meticulously crafted sensor. This sensor is securely housed within a hydrogen test chamber, which is further placed within a temperature and humidity control chamber with precise environmental control capabilities. To achieve precise temperature and humidity regulation, a humidity generator is connected to the chamber via a specialized pipeline, allowing the chamber temperature to be freely adjusted within the range of 24℃ to 59℃ with a temperature control accuracy of ±0.1℃; the humidity can be flexibly set between 19.21%RH and 79.85%RH with a humidity control accuracy of ±1%RH, providing stable and controllable environmental conditions for sensor testing.

[0035] The circulator's port 3 is connected to a spectrometer via a single-mode fiber. This spectrometer has a high spectral resolution of 0.01 nm and a fast integration time of 100 ms, enabling it to accurately acquire the interference spectral signals reflected back from the sensor, providing rich and accurate information for subsequent data analysis.

[0036] The hydrogen test chamber is connected to hydrogen and nitrogen gas sources through a gas mass flow controller, enabling precise adjustment of hydrogen concentration. The adjustment range covers 0% to 0.5%, and the adjustment accuracy is as high as ±0.01%, meeting the needs of different testing scenarios.

[0037] Before the formal test, the ASE light source was turned on and preheated for 30 minutes to ensure that its output light power reached a stable state. Then, the spectrometer was adjusted to collect the background spectrum and subtracted to effectively eliminate the interference of ambient light on the test results. Finally, the initial temperature of the constant temperature and humidity chamber was set to 24℃ and the humidity to 19.21% RH, and pure nitrogen gas (hydrogen concentration of 0%) was introduced to stabilize the system for 30 minutes. At the same time, the initial spectrum was collected as the reference signal for subsequent analysis, laying a solid foundation for the accuracy and reliability of the entire test process.

[0038] III. Sensor Performance Testing and Analysis Hydrogen response characteristics test: Under constant environmental conditions, i.e., temperature stable at 24℃ and humidity maintained at 19.21%RH, the hydrogen concentration was gradually adjusted to 0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% respectively. After the system ran stably for 30 minutes at each concentration setting, the corresponding spectral data were accurately collected.

[0039] Test results are as follows Figure 3 As shown: The original interference spectrum is as follows Figure 3 (a) It exhibits complex dual-cavity superposition signal characteristics. After fine processing using Fourier transform filtering, the independent interference spectra of the hydrogen sensing unit and the temperature sensing unit were successfully separated, as shown in the figure. Figure 3 As shown in (c) and (d), the interference fringes are clearly distinguishable at this point. Figure 3 As shown in (e), with the gradual increase of hydrogen concentration, the characteristic peaks of the interference spectrum of the hydrogen sensing unit shift significantly towards shorter wavelengths. Through linear fitting analysis, Figure 3 (f) It is found that under normal detection mode, the sensitivity of the sensor is -2.503 nm / %, and the goodness of fit R is... 2 A value as high as 0.9868 indicates a good data fit. In contrast, as... Figure 3 (g) Figure 3 The spectrum of the temperature sensing unit shown in (h) does not shift significantly throughout the hydrogen concentration change process, and its sensitivity is only 0.011 nm / %. This characteristic fully demonstrates that the temperature sensing unit is not sensitive to hydrogen and can serve as a reliable benchmark for temperature compensation, providing a strong guarantee for subsequent accurate measurement of hydrogen concentration.

[0040] Temperature response characteristics test: Under fixed conditions of 0% hydrogen concentration and 19.21% RH humidity, the temperature was gradually adjusted and set to 24℃, 30℃, 36℃, 42℃, 48℃, 54℃, and 59℃. Spectral data were collected after the system stabilized for 30 minutes at each temperature setting.

[0041] Test results are as follows Figure 4 As shown: Figure 4 (a) Figure 4 (b) The interference spectrum of the hydrogen sensing unit shifts towards shorter wavelengths as the temperature increases. Linear fitting yields a temperature sensitivity of -0.452 nm / ℃, with a goodness of fit R0. 2 The value is 0.9989, indicating a high degree of linear correlation. For example... Figure 4 (c) Figure 4 The spectrum of the temperature sensing unit shown in (d) exhibits a significant linear shift with increasing temperature, with a sensitivity of -0.825 nm / ℃ and a goodness of fit R0. 2 The accuracy reached 0.9993. Based on these precise test data, advanced data fusion algorithms can effectively counteract the interference caused by temperature changes in hydrogen detection, further improving the accuracy of hydrogen concentration measurement.

[0042] Humidity response characteristic test: Under stable conditions of 0% hydrogen concentration and 24℃, the humidity was gradually adjusted to 19.21% RH, 30% RH, 50% RH, 70% RH, and 79.85% RH. Spectral data were collected after the system stabilized for 30 minutes at each humidity setting.

[0043] Test results are as follows Figure 5 As shown, under different humidity conditions, the characteristic peak positions of the interference spectra of the hydrogen-sensitive unit and the temperature-sensitive unit did not show significant shifts. This result indicates that the developed sensor possesses excellent inherent resistance to humidity interference, and can operate stably and accurately in complex humidity environments without the need for an additional humidity compensation module, greatly simplifying the sensor's structure and operating conditions.

[0044] Vernier magnification characteristic test: such as Figure 6 As shown, firstly, trigonometric function fitting was performed on the original interference spectrum with a hydrogen concentration of 0% to obtain its precise mathematical expression. Based on this mathematical expression, a matching twin interference spectrum was carefully constructed. By superimposing the original interference spectrum with the twin interference spectrum, a vernier spectrum with a significant vernier effect was successfully formed.

[0045] Subsequently, vernier envelope spectra were collected at different hydrogen concentrations, and linear fitting analysis revealed that the sensor sensitivity after vernier amplification reached -65.857 nm / %, with a goodness of fit R0. 2 The sensitivity is 0.9901. Compared with the conventional detection mode, the sensitivity is improved by about 26 times. This significant improvement greatly enhances the sensor's ability to detect trace amounts of hydrogen, providing a more accurate and efficient solution for the field of hydrogen detection.

[0046] Therefore, the present invention employs the aforementioned femtosecond laser-etched high-sensitivity Fabry-Perot vernier hydrogen sensor, which achieves high-sensitivity detection of low-concentration hydrogen gas (0%~0.5%) through a dual-open microcavity structure and vernier detection scheme. It also possesses strong resistance to temperature interference and natural resistance to humidity interference. The structural consistency and long-term reliability can be guaranteed without complex manufacturing processes, making it suitable for monitoring low-concentration hydrogen gas leaks in harsh environments such as chemical and aerospace industries.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high-sensitivity Fabry-Perot vernier hydrogen sensor etched by femtosecond laser etching, characterized in that, This includes hollow-core optical fibers, open microcavities, and testing systems; The open microcavities are fabricated on hollow optical fibers using femtosecond laser etching technology and connected in series to form a dual-cavity structure. The open microcavities are a temperature sensing unit FPI-1 and a hydrogen sensing unit FPI-2. The temperature sensing unit FPI-1 is coated with a temperature-sensitive material PDMS, and the hydrogen sensing unit FPI-2 is coated with a hydrogen-sensitive material PDMS / Pd-WO3 composite coating. The testing system includes an ASE light source, a circulator, a hydrogen test chamber, a constant temperature and humidity chamber, a humidity generator, and a spectrometer. The hydrogen sensor testing process involves the probe light emitted by the ASE light source being incident on the hydrogen sensor through the circulator. The interference spectral signal of the hydrogen sensor is transmitted to the spectrometer through the circulator. Through Fourier transform filtering of the spectral signal and Fabry-Perot vernier superposition analysis, high-precision detection of hydrogen concentration is achieved.

2. The high-sensitivity Fabry-Perot vernier hydrogen sensor etched by femtosecond laser etching according to claim 1, characterized in that, The open microcavities of temperature sensing unit FPI-1 and hydrogen sensing unit FPI-2 are both C-type open microcavities.

3. The high-sensitivity Fabry-Perot vernier hydrogen sensor etched by femtosecond laser etching according to claim 1, characterized in that, In the PDMS / Pd-WO3 composite coating inside the FPI-2 hydrogen sensing unit, Pd-WO3 is the core component for hydrogen response, and PDMS is the substrate.

4. The high-sensitivity Fabry-Perot vernier hydrogen sensor etched by femtosecond laser etching according to claim 1, characterized in that, The etching path of femtosecond laser etching technology is to first outline and then inner cavity. The microcavity size deviation is ≤±2μm in the microcavity length and ≤±1μm in the microcavity width and depth.

5. The high-sensitivity Fabry-Perot vernier hydrogen sensor etched by femtosecond laser etching according to claim 1, characterized in that, The testing range of the supporting testing system is: hydrogen concentration 0%~0.5%, temperature 24℃~59℃, humidity 19.21%RH~79.85%RH, temperature control accuracy ±0.1℃, humidity control accuracy ±1%RH, and hydrogen concentration adjustment accuracy ±0.01%.

6. The high-sensitivity Fabry-Perot vernier hydrogen sensor etched by femtosecond laser etching according to claim 1, characterized in that, The preparation of the PDMS / Pd-WO3 composite coating includes: S1. Take micron-sized tungsten powder with a purity ≥99.9%, dry it at 105℃ for 2 hours, stir it with 30% H2O2 solution at 800 r / min at room temperature for 70 minutes, centrifuge the reaction solution at 8000 r / min for 20 minutes, take the upper sol, add anhydrous ethanol to replace the solvent, concentrate it at 80℃, add PdCl2, stir at 80℃ for 40 minutes to obtain Pd-WO3 composite sol; S2. Mix the PDMS prepolymer with the curing agent for 20 minutes, vacuum degas for 15 minutes, coat it onto the hollow optical fiber, semi-cur it at 60°C for 30 minutes, spin-coat Pd-WO3 powder at 40°C, and fully cure it at 80°C for 3 hours to form a composite coating.

7. The high-sensitivity Fabry-Perot vernier hydrogen sensor etched by femtosecond laser etching according to claim 6, characterized in that, In the PDMS / Pd-WO3 composite coating, the mass ratio of Pd to WO3 is 1:10, and the volume ratio of PDMS prepolymer to curing agent is 10:

1.

8. The high-sensitivity Fabry-Perot vernier hydrogen sensor etched by femtosecond laser etching according to claim 1, characterized in that, The spectral signal processing in the testing system involves separating the interference signals of the temperature sensing unit and the hydrogen sensing unit through Fourier transform, and then using twin spectra superposition to form a vernier effect, thereby improving detection sensitivity.

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