Hydrogen concentration detection sensor and hydrogen concentration detection method

Abstract

The application discloses a hydrogen concentration detection sensor and a hydrogen concentration detection method, wherein the sensor comprises a substrate, a waveguide core layer arranged on the substrate, and a cladding layer covering the waveguide core layer; a subwavelength grating structure is formed in the waveguide core layer, the subwavelength grating structure supports modes and modes and can generate bimode interference, the material of the waveguide core layer has a positive thermal-optical coefficient, single-mode waveguides are coupled to two ends of the subwavelength grating structure, an asymmetric coupling structure is formed between the single-mode waveguides and the subwavelength grating structure, and the asymmetric coupling structure is used for exciting two modes of modes and modes; the material of the cladding layer has a negative thermal-optical coefficient, the surface of the cladding layer is decorated with a hydrogen-sensitive material layer, and the hydrogen-sensitive material layer can catalyze an exothermic oxidation reaction with hydrogen. The application converts the hydrogen concentration change into the shift of an interference peak wavelength, compared with a traditional sensor which only depends on a single physical effect, the sensitivity is greatly improved, the sensor is easy to be integrated on a chip, does not need external electric driving, and is intrinsically safe and reliable.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, specifically to a hydrogen concentration detection sensor and a method for detecting hydrogen concentration. Background Technology

[0002] Driven by the global carbon neutrality strategy, hydrogen, with its zero-carbon emissions and high energy density, has become a core carrier for energy transformation, widely used in hydrogen fuel cell vehicles, distributed energy storage, and chemical synthesis. However, the lower explosive limit of hydrogen is as low as 4%, and its minimum ignition energy is only 0.018 mJ. The safety risks posed by leaks severely restrict the large-scale development of the hydrogen energy industry. Therefore, developing hydrogen sensors capable of rapid and highly sensitive detection within the lower explosive limit concentration range is of great significance for ensuring the safe application of hydrogen energy.

[0003] Existing hydrogen sensors mainly include electrochemical sensors, semiconductor sensors, and optical sensors. Electrochemical sensors are susceptible to environmental interference and have a short lifespan; semiconductor sensors have weak response signals and poor selectivity; among optical sensors, fiber optic sensors are relatively large, and planar waveguide devices still need optimization in balancing sensitivity and detection range. In recent years, subwavelength gratings (SWGs) have attracted attention because their period is smaller than the operating wavelength, allowing them to be equivalent to a homogeneous medium for efficient optical field manipulation. Their two-mode interference characteristics are highly sensitive to external perturbations and can be used to construct compact, high-precision interferometric sensors. However, existing SWG sensing research focuses primarily on temperature and refractive index detection, with very few applications combining hydrogen-sensitive functional materials to achieve specific hydrogen detection. Furthermore, commonly used hydrogen-sensitive materials (such as palladium-based materials and tungsten trioxide) suffer from low sensitivity and low integration.

[0004] Therefore, further consideration is needed on how to develop a novel optical hydrogen sensor with high sensitivity, rapid response, miniaturization, and good stability. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to provide a hydrogen concentration detection sensor with high sensitivity, fast response, miniaturization and good stability.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A hydrogen concentration detection sensor includes a substrate, a waveguide core layer disposed on the substrate, and a cladding layer covering the waveguide core layer. A subwavelength grating structure is formed in the waveguide core layer, and the subwavelength grating structure supports... Model and The waveguide core material is capable of generating two-mode interference, and the subwavelength grating structure is coupled to single-mode waveguides at both ends. An asymmetric coupling structure is formed between the single-mode waveguides and the subwavelength grating structure to simultaneously excite the subwavelength grating structure. Model and There are two modes: the cladding material has a negative thermo-optic coefficient, and the surface of the cladding is modified with a hydrogen-sensitive material layer, which can undergo a catalytic oxidation exothermic reaction with hydrogen.

[0008] When the hydrogen-sensitive material layer adsorbs hydrogen and releases heat, it simultaneously increases the refractive index difference between the waveguide core and cladding, and causes a change in the periodicity of the subwavelength grating structure due to the thermal expansion of the cladding, thus amplifying the effect. Model and The hydrogen concentration is detected by measuring the phase difference between the interference modes and the shift in the wavelength of the interference peak.

[0009] As an optimization, the waveguide core layer is made of Si, the cladding layer is made of SU-8 polymer, the hydrogen-sensitive material layer is made of Pt-WO3, and the substrate is made of SiO2.

[0010] As an optimization, the period of the subwavelength grating structure is 270 nm to 300 nm, the width is 1100 nm to 1400 nm, and the duty cycle is 40% to 55%.

[0011] As an optimization, the subwavelength grating structure has a period of 280 nm, a width of 1300 nm, and a duty cycle of 50%.

[0012] As an optimization, the asymmetric coupling structure between the single-mode waveguide and the subwavelength grating structure is such that the center of the single-mode waveguide is laterally offset relative to the center of the subwavelength grating structure.

[0013] This invention also discloses a method for detecting hydrogen concentration. The method involves acquiring the aforementioned hydrogen concentration detection sensor, placing the sensor in the target environment, causing the hydrogen-sensitive material layer to adsorb hydrogen and undergo a catalytic oxidation exothermic reaction. The heat generated by the catalytic oxidation exothermic reaction simultaneously drives an increase in the refractive index difference between the waveguide core layer and the cladding, and the thermal expansion of the cladding causes a periodic change in the subwavelength grating structure, thus amplifying the subwavelength grating structure. Model and The phase difference between the interference modes causes a shift in the wavelength of the interference peak in the transmission spectrum; by detecting the shift in the wavelength of the interference peak, the hydrogen concentration in the environment under test can be calculated based on the relationship between the wavelength shift and the hydrogen concentration.

[0014] As an optimization, the calibration method for the relationship between the wavelength shift and the hydrogen concentration is as follows: place the sensor in multiple standard gases of known hydrogen concentrations, measure the corresponding interference peak wavelength shifts respectively, and establish a fitting curve between the hydrogen concentration and the wavelength shift.

[0015] Compared with existing technologies, this invention converts changes in hydrogen concentration into a shift in the wavelength of the interference peak. Compared with traditional sensors that rely on only a single physical effect (only thermo-optical or only thermal expansion), the sensitivity is greatly improved, with a wide concentration detection range and a low detection limit. It can also provide early warning before the lower explosive limit (4%). At the same time, the sensor adopts a planar waveguide structure, which is easy to integrate on the chip, requires no external electric drive, and is inherently safe and reliable. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the sensor structure of the present invention;

[0017] Figure 2 This is a schematic diagram of the SWG structure in the sensor of the present invention;

[0018] Figure 3 This is an SWG dispersion curve of the sensor of the present invention with a period of 280 nm, a duty cycle of 50%, a width of 1300 nm, and a height of 220 nm.

[0019] Figure 4 For the SWG in the sensor of this invention and Coexistence region width versus center wavelength diagram;

[0020] Figure 5 This is a SWG dispersion diagram for different widths in the sensor of this invention;

[0021] Figure 6 This is a graph showing the relationship between the numerical wavelength shift and the cladding refractive index at 1640 nm for different widths in the sensor of the present invention.

[0022] Figure 7 The mode phase shift diagrams of the SWG dual-mode structures with different widths in the sensor of the present invention are shown for 100 cycles.

[0023] Figure 8 This is a diagram showing the SWG dispersion relationship of the sensor of the present invention under different duty cycles;

[0024] Figure 9 This is a graph showing the relationship between the numerical wavelength shift and the cladding refractive index at 1640 nm under different duty cycles in the sensor of the present invention.

[0025] Figure 10 The present invention provides mode phase shift diagrams for SWG dual-mode structures with different duty cycles at 100 cycles in the sensor.

[0026] Figure 11 The transmission spectrum of the SWG bimodal sensor with a period of 280 nm, a width of 1300 nm, a duty cycle of 50%, and a period number of 200 under different offsets d in the sensor of the present invention.

[0027] Figure 12 The electric field distribution in the sensor of this invention and and Schematic diagram;

[0028] Figure 13 This is a phase shift relationship diagram of the sensor with 200 cycles in this invention under different conditions;

[0029] Figure 14 The transmission spectra of the sensor with 200 periods in this invention under different conditions are shown.

[0030] Figure 15 This is a graph showing the relationship between the absorption of hydrogen and the exothermic reaction of Pt-WO3 in the sensor of this invention.

[0031] Figure 16 This is a graph showing the relationship between the heat released by Pt-WO3 absorbing hydrogen and the refractive index of Si and SU-8 in the sensor of this invention.

[0032] Figure 17 This is a graph showing the effect of the heat released by Pt-WO3 absorbing hydrogen on the thermal expansion of Si and SU-8 in a single cycle in the sensor of this invention.

[0033] Figure 18 This is the transmission spectrum of the sensor of the present invention with a period number of 200;

[0034] Figure 19 This is a graph showing the relationship between hydrogen concentration and wavelength shift when the sensor cycle number of this invention is 200.

[0035] Figure 20 This is the transmission spectrum of the sensor of the present invention with a period number of 300;

[0036] Figure 21 This is a graph showing the relationship between hydrogen concentration and wavelength shift when the sensor cycle number of this invention is 300. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0038] The hydrogen concentration detection sensor in this specific embodiment includes a substrate, a waveguide core layer disposed on the substrate, and a cladding layer covering the waveguide core layer. A subwavelength grating structure is formed in the waveguide core layer, and the subwavelength grating structure supports... Model and The waveguide core material is capable of generating two-mode interference, and the subwavelength grating structure is coupled to single-mode waveguides at both ends. An asymmetric coupling structure is formed between the single-mode waveguides and the subwavelength grating structure to simultaneously excite the subwavelength grating structure. Model and There are two modes: the cladding material has a negative thermo-optic coefficient, and the surface of the cladding is modified with a hydrogen-sensitive material layer, which can undergo a catalytic oxidation exothermic reaction with hydrogen.

[0039] When the hydrogen-sensitive material layer adsorbs hydrogen and releases heat, it simultaneously increases the refractive index difference between the waveguide core and cladding, and causes a change in the periodicity of the subwavelength grating structure due to the thermal expansion of the cladding, thus amplifying the effect. Model and The hydrogen concentration is detected by measuring the phase difference between the interference modes and the shift in the wavelength of the interference peak.

[0040] The waveguide core layer is made of Si, the cladding layer is made of SU-8 polymer, the hydrogen-sensitive material layer is made of Pt-WO3, and the substrate is made of SiO2.

[0041] The subwavelength grating structure has a period of 270 nm to 300 nm, a width of 1100 nm to 1400 nm, and a duty cycle of 40% to 55%.

[0042] The asymmetric coupling structure between the single-mode waveguide and the subwavelength grating structure is such that the center of the single-mode waveguide is laterally offset relative to the center of the subwavelength grating structure.

[0043] A method for detecting hydrogen concentration involves acquiring the aforementioned hydrogen concentration detection sensor, placing the sensor in a test environment, causing the hydrogen-sensitive material layer to adsorb hydrogen and undergo a catalytic oxidation exothermic reaction; utilizing the heat generated by the catalytic oxidation exothermic reaction to simultaneously increase the refractive index difference between the waveguide core layer and the cladding, and the periodic change of the subwavelength grating structure caused by the thermal expansion of the cladding, thus amplifying the subwavelength grating structure. Model and The phase difference between the interference modes causes a shift in the wavelength of the interference peak in the transmission spectrum; by detecting the shift in the wavelength of the interference peak, the hydrogen concentration in the environment under test can be calculated based on the relationship between the wavelength shift and the hydrogen concentration.

[0044] The calibration method for the relationship between the wavelength shift and the hydrogen concentration is as follows: the sensor is placed in multiple standard gases of known hydrogen concentration, the wavelength shift of the corresponding interference peak is measured respectively, and a fitting curve corresponding to the hydrogen concentration and the wavelength shift is established.

[0045] WO3, a commonly used hydrogen-sensitive material, operates on the principle of an exothermic redox reaction between WO3 and H2 catalyzed by Pt. Under the catalysis of Pt, H2 molecules are decomposed into active hydrogen atoms or hydrogen ions, triggering a hydrogen-induced color change in the WO3 film, from a transparent state to a deep blue state. This reaction exhibits good reversibility: in the absence of H2 and the presence of O2, Pt again acts as a catalyst, causing the reduced tungsten bronze (… It is re-oxidized to WO3, thus ensuring the sensor's recyclability. The chemical reaction equation is as follows:

[0046]

[0047]

[0048] The above reaction continues in the presence of both H2 and O2, while the total amount of WO3, acting as a catalyst, remains constant, effectively preventing material desensitization. Notably, this oxidation reaction is strongly exothermic; the released heat causes a significant increase in the local temperature of the sensor, which in turn modulates the refractive index difference between the grating cladding and the core layer, triggering thermal expansion of the SU-8 cladding. The released heat is positively correlated with the hydrogen concentration; therefore, after calibrating the sensor, the hydrogen concentration can be quantitatively detected by monitoring the shift in the peak wavelength.

[0049] Subwavelength gratings are periodic ( ) much smaller than the working light wavelength ( The periodic dielectric structure of [the material] is characterized by significantly suppressed diffraction effects, and its light wave propagation behavior is equivalent to that in a homogeneous medium. Its subwavelength operating criterion is [the following]. ( The equivalent refractive index of the SWG structure can be flexibly designed by adjusting parameters such as the period and duty cycle, thereby enhancing the light-matter interaction. This characteristic makes SWGs of significant value in integrated photonics fields such as photonic sensing, waveguide devices, and optical beam splitters. Utilizing the two-mode dispersion characteristics of the SWG sensing structure, when the material refractive index or the SWG period changes slightly, the wave vector difference between the two SWG modes will produce a phase shift. For a given material refractive index, the wave vector difference in the propagation direction of the two SWG modes can be expressed as... ,in The wave vectors for the two modes are respectively. The wave vector differential component considering dispersion characteristics. The phase shift between the two modes ( ) is defined as:

[0050]

[0051] In the formula, L represents the length of the SWG dual-mode interference region. The wavelength-dependent nonlinear phase shift can be obtained by calculating the dispersion curve of the periodic structure and the relationship between this curve and the cladding refractive index. Subsequent sections will explore the dispersion effect in the bimodal SWG interference structure to investigate how to further improve spectral sensitivity.

[0052] Changes in the cladding refractive index will cause a wavelength shift in the sensor's spectral response. The sensitivity of this type of refractive index sensor is measured by this shift, and its bulk sensitivity (…) ) is defined as:

[0053]

[0054] In the formula, This indicates the offset of spectral features at wavelength (unit: nm). This represents the change in refractive index (unit: RIU).

[0055] Sensor sensitivity ( This is used to quantify the sensor's response to changes in hydrogen concentration, defined as the wavelength shift rate relative to changes in H2 concentration:

[0056]

[0057] In the formula, This indicates the wavelength shift caused by hydrogen sensing. This indicates the change in hydrogen concentration.

[0058] Detection limit ( The ratio of wavelength resolution to sensor sensitivity is a core indicator for evaluating the sensor's ability to detect low concentrations.

[0059]

[0060] In the formula, This indicates the smallest wavelength offset that an OSA (Optical Spectrum Analysis) instrument can resolve.

[0061] Sensor fabrication: First, using a silicon-on-insulator (SOI) wafer as the initial substrate, the silicon grating structure is patterned using electron beam lithography (EBL) and inductively coupled plasma (ICP) dry etching. Then, SU-8 photoresist is spin-coated onto the SOI substrate with the silicon grating structure, and cured by heat treatment to form a composite interface layer covering the silicon structure and the buried SiO2 layer. Simultaneously, SU-8 is pre-spray-coated onto the SiO2 receiving substrate as a receiving layer for pattern transfer. Next, the SOI structure with the SU-8 composite layer is inverted and precisely bonded to the receiving substrate. The silicon waveguide was brought into direct contact with the SU-8 receiving layer, and interlayer bubbles were removed by heating to above 60°C to improve interface adhesion and uniformity. Then, deep reactive ion etching (DRIE) was used to selectively remove the SOI bulk silicon substrate, and then buffered oxide wet etching (BOE) was used to remove the buried SiO2 layer, so that the silicon grating structure was completely transferred to the SU-8 receiving substrate. Finally, SU-8 was spin-coated again on the transferred silicon grating surface and cured to form an encapsulation layer. Then, Pt-WO3 hydrogen-sensitive material was modified to complete the fabrication of the subwavelength grating hydrogen sensor.

[0062] like Figure 1 and Figure 2 As shown, the sensor substrate is SiO2 (refractive index 1.44), with an internal Si (refractive index 3.47) grating structure, encased in SU-8 (refractive index 1.57) cladding, and a Pt-WO3 (real part 2, imaginary part 0.1) thin film modified on the surface for hydrogen detection. The single-mode input waveguide supports transverse electric (…). The polarization fundamental mode can be simultaneously excited in the SWG double-peak region by shifting the center position. Model and Two modes. These two modes propagate and interfere within the grating, exciting the output at the abrupt interface with the output single-mode waveguide. Basic model.

[0063] In mode modulation of subwavelength gratings, periodic variations not only affect the center wavelength and bandwidth, but also directly alter... The coexistence region of modes (i.e., the wavelength range in which multiple modes exist simultaneously as stable guided modes). As the lattice period continues to decrease, the wavelength originally used for two-mode interference... and The coexistence region of modes will gradually expand. While this trend can broaden the operating wavelength range of devices, it will also bring the risk of interference from additional higher-order modes.

[0064] When the period is reduced to around 280 nm, such as Figure 3 and Figure 4 As shown, the dispersion curve can be observed The guided mode region of higher-order modes is located in , Below the coexistence region; if the lattice period is further reduced, The dispersion curve of the mode will approach and fall into and The dual-mode coexistence region. Dual-mode interferometers are dependent on... and The phase difference between two specific modes achieves the signal response. The introduction of this mode will disrupt the existing dual-mode interferometry system, introducing additional phase components during transmission. This introduces extra phase components, causing the interference pattern at the output end to change from "two-mode superposition" to "multi-mode aliasing". This not only blurs the interference peak shape and increases signal noise, but may also generate additional interference peaks, ultimately destroying the stability and accuracy of the two-mode interference, resulting in distortion of the sensor's refractive index response signal and a decrease in sensitivity.

[0065] exist Figure 5 In the dispersion relation at different widths (W), as the waveguide width increases, the dispersion relation that was originally in the range of different widths (W) changes. and Outside the coexistence area In higher-order modes, the dispersion curve gradually shifts towards , The stable guided mode range is approximated because the increased waveguide width expands the mode constraint space, making it easier to satisfy the guided mode conditions of higher-order modes. When W increases to 1400 nm, The dispersion curve of the mode falls completely into and Interference occurs within the coexistence area. Figure 6 and Figure 7In the case of a cladding refractive index change of 0.01, another dimension of the influence of waveguide width on the device's response characteristics is revealed. As W increases, the bulk sensitivity of the device to changes in cladding refractive index gradually improves. This is because a wider waveguide enhances the interaction between the mode and the cladding medium, making small changes in refractive index more likely to induce significant mode phase shifts. Under the same refractive index change conditions, the phase shift amplitude increases with increasing W, and the phase difference accumulated during transmission also expands accordingly.

[0066] exist Figure 8 In the dispersion relation at different duty cycles (DC), as the duty cycle increases, the dispersion originally in the range of 100° and 100° decreases. and Outside the coexistence area In higher-order modes, the dispersion curve gradually approaches this coexistence region; when the duty cycle rises to 55%, The guide curve has clearly approached and Within the coexistence range, if the duty cycle continues to increase... The mode is highly likely to fall entirely into this region, becoming a stable guided mode and causing interference. Simultaneously, increasing the duty cycle improves the device response performance. Figure 9 and Figure 10 In the case of a cladding refractive index change of 0.01, as the duty cycle increases, and The increased phase shift between modes leads to a corresponding increase in bulk sensitivity. This is because the increased duty cycle alters the effective refractive index distribution of the SWG, making the modes more sensitive to changes in the medium environment during transmission.

[0067] To effectively stimulate the SWG structure and Two transmission modes, bandwidth (S) W The 450 nm single-mode waveguide needs to be laterally offset relative to the center position of the SWG structure. Figure 11 (The dashed line represents the simulated transmittance curve, and the solid line represents the fitted curve.) In the transmission spectra corresponding to different offsets d with a period number of 200, when the waveguide is centered (d=0 nm), only... When excited, there is no intermodal interference, and the spectral fitting curve is nearly flat; as the offset d increases, and When excited simultaneously, the phase difference accumulated during transmission coherently superimposes at the output, resulting in clear interference fringes in the spectrum. The greater the offset, the more pronounced the contrast between the bright and dark areas of the interference fringes. The most significant fluctuations in the brightness of the interference fringes are observed when d = 425 nm. Figure 12As shown in the figure, (1) the electric field at the incident end with offsets of 0 and 425 nm; (2) the electric field at the center end with offsets of 0 and 425 nm; and (3) the electric field at the output end with offsets of 0 and 425 nm. The electric field distribution further verifies this rule. When the waveguide is not offset, the electric field distribution is regular, and only the fundamental mode propagates in the SWG structure, with a nearly flat response. However, when the waveguide is offset, higher-order modes are effectively excited, and the mode coupling effect is prominent, and a clear interference pattern can be observed. Figure 12 (4) in the SWG structure contains and The two transmission modes overlap and cause intermodal interference.

[0068] System simulation optimization considering the mode characteristics, sensing performance, and coupling efficiency of the SWG bimodal sensor, with a period of 280 nm and a height (H) of 220 nm, ensures both... and The stable coexistence range, and also inhibits High-order mode interference; a waveguide width of 1300 nm and a duty cycle of 50% balance sensing sensitivity and mode constraint stability; a single-mode access waveguide offset of 425 nm achieves efficient dual-mode excitation by breaking symmetry, ensuring high contrast of the interference signal. An SU-8-wrapped SWG structure is used to achieve synergistic control of material refractive index and thermal expansion effects. To achieve uniform changes in thermal expansion and refractive index, and to reduce interference from the substrate and hydrogen-sensitive material on dual-mode interference, the structure needs to be... , The height is set at 2 µm. This height can ensure the stability of the interface between SU-8 and SWG, and can also make thermal expansion deformation and refractive index modulation take effect simultaneously through size matching, thereby avoiding interference signal distortion caused by non-uniform structural parameters.

[0069] This sensor utilizes the exothermic effect of the reaction between Pt-WO3 hydrogen-sensitive material and H2, combined with the high negative thermo-optic coefficient and thermal expansion coefficient of SU-8, to achieve synergistic regulation of the material's refractive index and thermal expansion, thereby improving the sensitivity of hydrogen detection. Figure 13 The phase shift relationship under different conditions was presented. When the SWG period increased by 1 nm and the refractive index difference between the core and cladding increased by 0.01, the phase shift curves deviated from the reference curve. When both factors worked together, the change in phase shift was more significant, resulting in an enhanced phase change. Figure 14 The corresponding transmittance relationship further indicates that increasing the period and the refractive index difference alone will cause a wavelength shift in the destructive interference valley. When both factors act together, the shift in the interference valley is significantly greater. The change in the refractive index difference and the thermal expansion of SU-8 jointly affect the interference peak shift of the double-peak SWG interference structure. The shift can be approximated as:

[0070]

[0071] In the formula, This is the offset caused by the change in refractive index. This is the offset caused by the thermal expansion of the SU-8. The overall offset is shown in Table 1, which represents the peak offset under different conditions. This result confirms that the response amplitude of the sensing signal is amplified after the phase change is enhanced, and also intuitively demonstrates the role of the synergistic regulation of refractive index and thermal expansion in improving sensing performance.

[0072]

[0073] Table 1

[0074] Based on experimental data from existing literature, the theoretically calculated relationship between temperature and H2 concentration caused by the exothermic reaction of WO3 is as follows, with an initial temperature of 25 ℃:

[0075]

[0076] The thermo-optical coefficient and thermal expansion coefficient of Si and SU-8 materials are respectively taken as 1.8 × 10⁻⁶. -4 / ℃, -3.5×10 -4 / ℃, 3.1ppm / ℃, 52 ppm / ℃. Using the thermo-optical coefficient and thermal expansion coefficient of the material, the corresponding changes in refractive index and expansion amount under different hydrogen concentrations can be approximately calculated. Figure 15 The results show the exothermic relationship between Pt-WO3 absorption of hydrogen and the heat release; the higher the concentration, the more significant the temperature rise caused by the exothermic absorption of hydrogen. Figure 16 The refractive index of Si (positive thermo-optic coefficient) increases with increasing concentration, while the refractive index of SU-8 (negative thermo-optic coefficient) decreases simultaneously, resulting in a significant difference in refractive index between the two. Figure 17 The thermal expansion of SU-8 on both sides of the SWG causes deformation of the periodic structure. The thermal expansion of a single SU-8 increases significantly with concentration, while the thermal expansion of Si is negligible. This difference causes the SWG waveguide period to change. Ultimately, the superposition effect of refractive index difference and thermal expansion amplifies the mode phase difference, greatly improving the hydrogen detection sensitivity of the sensor.

[0077] To quantitatively analyze the optical sensing response of the sensor under different hydrogen concentrations, the refractive index parameters of the Si waveguide and SU-8 cladding, as well as the SWG period size, were adjusted to intuitively reflect the modulating effect and influence of the hydrogen absorption and exothermic effect of the Pt-WO3 hydrogen-sensitive material on the sensor's optical properties. Figures 18 to 21As shown, within the H2 concentration range of 0–2%, both period numbers exhibit a good linear response relationship between H2 concentration and interference peak wavelength shift. Furthermore, increasing the grating period number only increases the number of interference peaks in the sensing spectrum, without significantly affecting the wavelength shift amplitude of the interference peaks, indicating that changing the period number does not improve sensing performance. To clarify the actual detection capability of this sensor, the H2 concentration threshold was quantitatively calculated based on the minimum spectral resolution of 20 pm of a commercial spectrometer. Using the hydrogen concentration versus wavelength shift fitting curve, the theoretical detection limit for hydrogen is approximately 13.2 ppm, and the sensitivity is approximately 15.1 nm / %, confirming that the sensor possesses accurate identification capabilities for low-concentration hydrogen, meeting the application requirements for early trace detection of hydrogen leaks. As shown in Table 2, this sensitivity is at a relatively high level among currently disclosed on-chip optical hydrogen sensors.

[0078]

[0079] Table 2

[0080] In addition to the sensors fabricated above, this embodiment also fabricated several sensors with different parameters (specifications) to study the relationship between hydrogen concentration and other gases:

[0081] A first sensor was fabricated, differing in that it had a period of 270 nm, a width of 1400 nm, and a duty cycle of 40%. Within the H2 concentration range of 0–2%, the sensor exhibited a good linear response relationship between H2 concentration and the wavelength shift of the interference peak. The fitting curve formula for the relationship between hydrogen concentration and wavelength shift is as follows: The sensor has a theoretical detection limit of approximately 14.53 ppm for hydrogen and a sensitivity of approximately 13.77 nm / .

[0082] A second sensor was fabricated, differing in that it had a period of 280 nm, a width of 1300 nm, and a duty cycle of 45%. Within the H2 concentration range of 0–2%, the sensor exhibited a good linear response relationship between H2 concentration and the wavelength shift of the interference peak. The fitting curve formula for the relationship between hydrogen concentration and wavelength shift is as follows: The sensor has a theoretical detection limit of approximately 16.86 ppm for hydrogen and a sensitivity of approximately 11.86 nm / .

[0083] A third sensor was fabricated, differing in that it had a period of 290 nm, a width of 1200 nm, and a duty cycle of 50%. Within the H2 concentration range of 0–2%, the sensor exhibited a good linear response relationship between H2 concentration and the wavelength shift of the interference peak. The fitting curve formula for the relationship between hydrogen concentration and wavelength shift is as follows: The sensor has a theoretical detection limit of approximately 19.03 ppm for hydrogen and a sensitivity of approximately 10.51 nm / .

[0084] A fourth sensor was fabricated, differing in that it had a period of 300 nm, a width of 1100 nm, and a duty cycle of 55%. Within the H2 concentration range of 0–2%, the sensor exhibited a good linear response relationship between H2 concentration and the wavelength shift of the interference peak. The fitting curve formula for the relationship between hydrogen concentration and wavelength shift is as follows: The sensor has a theoretical detection limit of approximately 25.29 ppm for hydrogen and a sensitivity of approximately 7.91 nm / .

[0085] Sensor No. 5 was fabricated, differing in that it has a period of 280 nm, a width of 1200 nm, and a duty cycle of 50%. Within the H2 concentration range of 0–2%, the sensor exhibits a good linear response relationship between H2 concentration and the wavelength shift of the interference peak. The fitting curve formula for the relationship between hydrogen concentration and wavelength shift is as follows: The sensor has a theoretical detection limit of approximately 17.59 ppm for hydrogen and a sensitivity of approximately 11.37 nm / .

[0086] 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 the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A hydrogen concentration detection sensor, characterized in that: The waveguide includes a substrate, a waveguide core layer disposed on the substrate, and a cladding layer covering the waveguide core layer. A subwavelength grating structure is formed in the waveguide core layer, and the subwavelength grating structure supports... Model and The waveguide core material is capable of generating two-mode interference, and the subwavelength grating structure is coupled to single-mode waveguides at both ends. An asymmetric coupling structure is formed between the single-mode waveguides and the subwavelength grating structure to simultaneously excite the subwavelength grating structure. Model and There are two modes: the cladding material has a negative thermo-optic coefficient, and the surface of the cladding is modified with a hydrogen-sensitive material layer, which can undergo a catalytic oxidation exothermic reaction with hydrogen. When the hydrogen-sensitive material layer adsorbs hydrogen and releases heat, it simultaneously increases the refractive index difference between the waveguide core and cladding, and causes a change in the periodicity of the subwavelength grating structure due to the thermal expansion of the cladding, thus amplifying the effect. Model and The hydrogen concentration is detected by measuring the phase difference between the interference modes and the shift in the wavelength of the interference peak.

2. The hydrogen concentration detection sensor according to claim 1, characterized in that: The waveguide core layer is made of Si, the cladding layer is made of SU-8 polymer, the hydrogen-sensitive material layer is made of Pt-WO3, and the substrate is made of SiO2.

3. The hydrogen concentration detection sensor according to claim 1, characterized in that: The subwavelength grating structure has a period of 270 nm to 300 nm, a width of 1100 nm to 1400 nm, and a duty cycle of 40% to 55%.

4. The hydrogen concentration detection sensor according to claim 3, characterized in that: The subwavelength grating structure has a period of 280 nm, a width of 1300 nm, and a duty cycle of 50%.

5. The hydrogen concentration detection sensor according to claim 1, characterized in that: The asymmetric coupling structure between the single-mode waveguide and the subwavelength grating structure is such that the center of the single-mode waveguide is laterally offset relative to the center of the subwavelength grating structure.

6. A method for detecting hydrogen concentration, characterized in that: Obtain the hydrogen concentration detection sensor according to any one of claims 1 to 5, place the sensor in the environment to be measured, and cause the hydrogen-sensitive material layer to adsorb hydrogen and undergo a catalytic oxidation exothermic reaction; utilize the heat generated by the catalytic oxidation exothermic reaction to simultaneously drive an increase in the refractive index difference between the waveguide core layer and the cladding, and the periodic change of the subwavelength grating structure caused by the thermal expansion of the cladding, thereby amplifying the subwavelength grating structure. Model and The phase difference between the interference modes causes a shift in the wavelength of the interference peak in the transmission spectrum; by detecting the shift in the wavelength of the interference peak, the hydrogen concentration in the environment under test can be calculated based on the relationship between the wavelength shift and the hydrogen concentration.

7. The method for detecting hydrogen concentration according to claim 6, characterized in that: The calibration method for the relationship between the wavelength shift and the hydrogen concentration is as follows: the sensor is placed in multiple standard gases of known hydrogen concentration, the wavelength shift of the corresponding interference peak is measured respectively, and a fitting curve corresponding to the hydrogen concentration and the wavelength shift is established.

Images