Gas concentration sensor based on resonant cavity, preparation method of gas concentration sensor and detection system

Abstract

The invention relates to the technical field of gas concentration detection, in particular to a gas concentration sensor based on a resonant cavity, a preparation method of the gas concentration sensor and a detection system. The gas concentration sensor based on the resonant cavity comprises a microcavity which comprises an input end, a first Bragg grating and a second Bragg grating which are arranged in sequence; the input end is configured to receive a laser light source; the first Bragg grating and the second Bragg grating are symmetrically arranged, and the periodicity and the etching depth of the first Bragg grating and the second Bragg grating are the same; the resonant cavity is located between the first Bragg grating and the second Bragg grating; the gas chamber covers the second Bragg grating, and gas to be detected is contained in the gas chamber; the output end is coupled with the microcavity in an evanescent field mode, and the output end is configured to output an optical signal corresponding to the gas to be detected. The resonant cavity-based gas concentration sensor provided by the embodiment of the invention is simple in structure and simple in preparation process, and the detection precision of gas concentration can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of gas concentration detection, and in particular to a resonant cavity-based gas concentration sensor, a preparation method thereof, and a detection system. Background Art

[0002] Currently, the demand for precise detection technology for trace and ultra-low concentration gases is increasingly urgent in numerous fields, including industrial production, energy conservation and environmental protection, aerospace, and explosion disaster warning. Traditional gas detection methods, such as those based on electrochemistry and semiconductor principles, often suffer from limitations such as low accuracy, slow response speed, and the inability to simultaneously detect multiple components, making them unable to meet the demands of modern industrial and technological development.

[0003] Optical microcavity gas sensors have the advantages of high quality factor and small mode volume. They can effectively increase the interaction time between the light field and the gas, thereby achieving high-sensitivity gas detection to solve the above problems.

[0004] Currently, one approach to improving the sensitivity of optical microcavity gas sensors is to enhance the interaction between the evanescent field of the resonant cavity and the gas being measured, increasing the change in the effective refractive index of the resonant cavity and thereby improving the modulation of the light field. However, such structures are complex, typically constructed from submicron-scale photonic crystals, and require very high fabrication processes, resulting in non-reproducibility.

[0005] Another method to improve the sensitivity of optical microcavity gas sensors is to enhance the response to the target gas by adding surface-modified sensitive materials. However, different gas molecules may produce similar interactions with the sensitive materials, leading to cross-sensitivity problems, making it difficult for the sensor to accurately distinguish and quantitatively detect different components in the mixed gas.

[0006] Therefore, it is urgent to propose a new gas concentration sensor to solve the above technical problems. Summary of the Invention

[0007] To solve the above problems, the present application provides a gas concentration sensor based on a resonant cavity, a preparation method thereof, and a detection system, which has a simple structure and a simple preparation process and can improve the detection accuracy of gas concentration.

[0008] In a first aspect, a resonant cavity-based gas concentration sensor is provided, comprising: a microcavity, comprising an input end, a first Bragg grating, and a second Bragg grating arranged in sequence; the input end is configured to receive a laser light source; the first Bragg grating and the second Bragg grating are symmetrically arranged, and the first Bragg grating and the second Bragg grating have the same number of periods and etching depth; the resonant cavity is located between the first Bragg grating and the second Bragg grating; a gas chamber covers the second Bragg grating, and the gas chamber contains a gas to be detected; and an output end is coupled to the microcavity via an evanescent field, and the output end is configured to output an optical signal corresponding to the gas to be detected.

[0009] Based on this solution, by constructing a resonant cavity-based gas concentration sensor with a dual Bragg grating resonant cavity, when a change in the gas concentration in the gas chamber is detected, the amplitude of the light in the resonant cavity changes relatively, so that the change in gas concentration can be measured based on the amplitude change, that is, the concentration of the gas is measured. In addition, high-sensitivity sensing can be achieved without adopting other means to enhance the interaction between the evanescent field of the resonant cavity and the gas to be detected. At the same time, the resonant cavity-based gas concentration sensor provided in the embodiment of the present application adopts a symmetrical dual Bragg grating resonant cavity. When the external environment (such as temperature, etc.) changes as a whole, since the external environment affects the first Bragg grating and the second Bragg grating at the same time, the amplitude of the light in the resonant cavity will change as a whole, without causing a change in a certain resonance peak, thereby reducing the impact of the overall change of the external environment on the detection results of the resonant cavity-based gas concentration sensor and having good stability.

[0010] In an optional implementation, the microcavity further includes: a first grating coupler and a bus waveguide; wherein the first grating coupler, the bus waveguide, the first Bragg grating, the resonant cavity and the second Bragg grating are arranged in sequence; the first grating coupler constitutes the input end; and the output end is coupled to the bus waveguide through an evanescent field.

[0011] In another optional implementation, the output end includes: an output waveguide and a second grating coupler optically connected to each other; the output waveguide and the bus waveguide are coupled via an evanescent field; and the second grating coupler is configured to output an optical signal corresponding to the gas to be detected.

[0012] In yet another optional implementation, the gas chamber includes: a porous aluminum oxide film covering the second Bragg grating, wherein the porous aluminum oxide film has a nanoporous structure.

[0013] In yet another optional implementation, the resonant cavity-based gas concentration sensor further includes: a substrate, and the microcavity, the output end, and the gas chamber are all arranged on the substrate.

[0014] In a second aspect, a method for preparing a gas concentration sensor based on a resonant cavity is provided, comprising: depositing a thin film silicon layer on a silicon dioxide layer; spin-coating photoresist on the thin film silicon layer to expose the thin film silicon layer corresponding to the microcavity and the output end; etching the exposed thin film silicon layer; removing the remaining photoresist to obtain a first device; covering the first device with a silicon dioxide protective layer; spin-coating photoresist on the silicon dioxide protective layer to expose the silicon dioxide protective layer corresponding to the gas chamber; etching the exposed silicon dioxide protective layer to expose the second Bragg grating to obtain a second device having a cavity corresponding to the second Bragg grating; constructing a gas chamber on the cavity of the second device to obtain a gas concentration sensor based on a resonant cavity as provided in the first aspect and any optional implementation thereof.

[0015] Based on this approach, a cavity-based gas concentration sensor with a dual Bragg grating resonant cavity can be fabricated. This achieves highly sensitive sensing without resorting to other methods to enhance the interaction between the cavity's evanescent field and the gas being detected. Furthermore, it reduces the impact of overall changes in the external environment (such as temperature) on the detection results.

[0016] In an optional implementation, a gas chamber is constructed on the cavity of the second device, including: introducing Al(CH3)3 and H2O precursor gases into the cavity of the second device to grow an Al2O3 film layer by layer on the second Bragg grating; calcining the Al2O3 film to generate a porous structure in the Al2O3 film; and removing remaining photoresist and the Al2O3 film outside the gas chamber.

[0017] In a third aspect, a gas concentration detection system is provided, comprising: a laser, a resonant cavity-based gas concentration sensor photodetector and a computing device; the laser, the resonant cavity-based gas concentration sensor and the photodetector are optically connected in sequence; the laser is configured to output laser light; the resonant cavity-based gas concentration sensor comprises a resonant cavity-based gas concentration sensor as provided in the first aspect and any optional implementation thereof, or a resonant cavity-based gas concentration sensor prepared by the preparation method of a resonant cavity-based gas concentration sensor as provided in the second aspect and any optional implementation thereof; the resonant cavity-based gas concentration sensor comprises an input end, a gas chamber and an output end, the input end receives the laser light output by the laser, the gas chamber contains the gas to be detected, and the output end outputs an optical signal corresponding to the gas to be detected; the photodetector is arranged at the output end of the resonant cavity-based gas concentration sensor, and the photodetector is configured to convert the optical signal output from the output end into an electrical signal; the computing device is communicatively connected to the photodetector, and the computing device is configured to receive the electrical signal and demodulate the electrical signal to obtain the concentration of the gas to be detected.

[0018] This approach enables the detection of gas concentrations based on the optical signal output by a resonant cavity-based gas concentration sensor. High-sensitivity sensing is achieved without resorting to other methods to enhance the interaction between the resonant cavity's evanescent field and the gas being detected. Furthermore, the impact of overall environmental changes (such as temperature) on detection results is minimized.

[0019] In an optional implementation, the computing device is configured to: construct a first current spectrum based on the electrical signal; determine the amplitude deviation between the first current spectrum and the first initial spectrum; the first initial spectrum corresponds to the spectrum when the concentration of the gas is 0; based on the amplitude deviation, determine the concentration of the gas corresponding to the first current spectrum according to the mapping relationship.

[0020] In another optional implementation, the computing device is configured to: construct a second current spectrum based on the electrical signal; adjust the preset parameters to change the second current spectrum to a second initial spectrum, where the preset parameters are the concentration of the gas; the second initial spectrum corresponds to the spectrum when the concentration of the gas is 0; and the preset parameters represent the change in the concentration of the gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0022] Figure 1 This is a first structural diagram of the gas concentration detection system provided in an embodiment of the present application; Figure 2 Schematic diagram of the structure of a gas concentration sensor based on a resonant cavity provided in an embodiment of the present application; Figure 3 Schematic diagram of the planar structure of a gas concentration sensor based on a resonant cavity provided in an embodiment of the present application; Figure 4 This is a schematic diagram of the first spectrum generated by the resonant cavity-based gas concentration sensor provided in an embodiment of the present application; Figure 5 This is a schematic diagram of a second spectrum generated by the resonant cavity-based gas concentration sensor provided in an embodiment of the present application; Figure 6 1 is a flow chart of a method for preparing a gas concentration sensor based on a resonant cavity provided in an embodiment of the present application; Figure 7 A schematic diagram of the preparation process of a resonant cavity-based gas concentration sensor provided in an embodiment of the present application; Figure 8 This is a second structural diagram of the gas concentration detection system provided in an embodiment of the present application; Figure 9 This is a schematic diagram of light propagation in a resonant cavity-based gas concentration sensor provided in an embodiment of the present application.

[0023] Reference numerals: 100. Gas concentration detection system; 1. Laser; 2. Cavity-based gas concentration sensor; 21. Microcavity; 211. First Bragg grating; 212. Second Bragg grating; 213. Cavity; 214. First grating coupler; 215. Bus waveguide; 22. Gas chamber; 23. Output terminal; 231. Output waveguide; 232. Second grating coupler; 24. Substrate; 3. Photodetector; 4. Computing device; 41. Cell phone; 42. Computer. 10. Silicon dioxide layer; 20. Thin film silicon layer; 30. Photoresist; 40. Silicon dioxide protective layer; 50. Porous aluminum oxide film. DETAILED DESCRIPTION

[0024] The following will clearly describe the technical solutions in the embodiments of the present application in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments of the present application, other embodiments obtained by ordinary technicians in this field without making any creative work are all within the scope of protection of this application.

[0025] Hereinafter, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified with "first," "second," etc., may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0026] In addition, in this application, directional terms such as "upper", "lower", "inner" and "outer" are defined relative to the orientation of the components in the drawings. It should be understood that these directional terms are relative concepts. They are used for relative description and clarification, and they can change accordingly according to changes in the orientation of the components in the drawings.

[0027] The following first describes the related technology.

[0028] In today's society, the demand for precise detection technology for trace and ultra-low concentration gases is increasingly urgent in numerous fields, including industrial production, energy conservation and environmental protection, aerospace, and explosion disaster warning. Traditional gas detection methods, such as those based on electrochemistry and semiconductor principles, often suffer from limitations such as low detection accuracy, slow response speed, and the inability to simultaneously detect multiple components, making them unable to meet the demands of modern industrial and technological development.

[0029] Optical microcavity gas sensors have become a research hotspot in the field of gas sensing due to their unique advantages. With wavelength-scale dimensions, optical microcavities offer advantages such as high quality factors and small mode volumes, effectively increasing the interaction time between the light field and the gas, thereby enabling highly sensitive gas detection. Furthermore, their compact size, fast response speed, inherent safety, and immunity to electromagnetic interference make it possible to develop long-range, real-time, and low-detection-limit gas sensors.

[0030] In related technologies, an optical microcavity gas sensor uses an active microring resonant cavity, which is made of As2S3 (arsenic trisulfide, also known as arsenous sulfide) or As2Se3 (arsenic selenide) material doped with praseodymium (Pr) or dysprosium (Dy), achieving high-sensitivity detection of multiple gas molecules.

[0031] In another optical microcavity gas sensor, by coupling the Mach-Zehnder interferometer (MZI) with the microring resonant cavity, the resonance peak is always in a strictly coupled state, making the sensor's sensitivity less susceptible to external environmental factors and always maintaining high sensitivity.

[0032] However, in the above two optical microcavity gas sensors, the response to the target gas is enhanced by adding surface-modified sensitive materials. However, different gas molecules may produce similar interactions with the sensitive materials, resulting in cross-sensitivity problems, making it difficult for the sensor to accurately distinguish and quantitatively detect different components in the mixed gas.

[0033] In another optical microcavity gas sensor, a subwavelength photonic crystal structure is used to prepare a ring resonator, which greatly enhances the interaction between the light field and the ambient gas to improve sensitivity.

[0034] However, in the aforementioned optical microcavity gas sensors, the use of a photonic crystal structure greatly enhances the interaction between the evanescent field and the gas being measured. However, such structures are complex, typically composed of submicron-scale photonic crystals, and have high processing requirements and are not repeatable.

[0035] Furthermore, from a sensing principle perspective, these sensors all shift the resonant wavelength by changing the effective refractive index of the resonant cavity due to changes in gas concentration. However, due to inherent material properties, the magnitude of the resonant peak frequency shift is limited. Furthermore, the microring resonant cavity itself is extremely sensitive to ambient temperature, and a single microring resonator cannot eliminate interference with gas sensing caused by changes in ambient temperature.

[0036] To address the aforementioned issues, this application provides a resonant cavity-based gas concentration sensor, its fabrication method, and a gas concentration detection system. These sensors achieve high-sensitivity sensing without requiring additional means to enhance the interaction between the resonant cavity's evanescent field and the gas being detected. Furthermore, they can reduce the impact of overall changes in the external environment (such as temperature) on detection results.

[0037] Figure 1 This is the first structural diagram of the gas concentration detection system provided in the embodiment of the present application.

[0038] Combine Figure 1 As shown, the gas concentration detection system 100 includes: a laser 1, a gas concentration sensor based on a resonant cavity 2, a photodetector 3 and a computing device 4. The laser 1 is optically connected to the gas concentration sensor based on a resonant cavity 2 and the photodetector 3 ( Figure 1 The solid arrow in the middle is schematically indicated). The photodetector 3 is connected to the computing device 4 for communication ( Figure 1 (Schematically indicated by dashed arrows in the figure). Laser 1 is configured to output laser light to resonant cavity-based gas concentration sensor 2. Resonant cavity-based gas concentration sensor 2 is configured to output an optical signal corresponding to the concentration of the gas to be detected. Photodetector 3 is configured to receive the optical signal output by resonant cavity-based gas concentration sensor 2 and convert it into an electrical signal. Computing device 4 is configured to receive the electrical signal and demodulate the electrical signal to obtain the concentration of the gas to be detected.

[0039] The gas concentration detection system 100 provided in the embodiment of the present application can output an optical signal corresponding to the concentration of the gas to be detected through the resonant cavity-based gas concentration sensor 2, and demodulate the optical signal to obtain the concentration of the gas to be detected.

[0040] It is worth noting that the computing device 4 may include a mobile phone 41, a tablet computer, a computer 42, a laptop computer, a mobile computing device or an industrial computer, etc., and this application does not impose any restrictions on this.

[0041] Exemplarily, the laser 1 is a broadband light source.

[0042] Figure 2 Schematic diagram of the structure of a gas concentration sensor based on a resonant cavity provided in an embodiment of the present application. Figure 3 Schematic diagram of the planar structure of the resonant cavity-based gas concentration sensor provided in an embodiment of the present application.

[0043] In some embodiments, combined Figure 2 and Figure 3 As shown, the resonant cavity-based gas concentration sensor 2 includes a microcavity 21 , a gas chamber 22 and an output end 23 .

[0044] The microcavity 21 includes an input end, a first Bragg grating 211 and a second Bragg grating 212 which are arranged in sequence.

[0045] The input end is configured to receive a laser light source, wherein the laser light source is the laser output by the laser 1 .

[0046] Figure 4 This is a schematic diagram of the first spectrum generated by the resonant cavity-based gas concentration sensor provided in the embodiment of the present application. Figure 4 The middle curves A and B correspond to different gas concentrations.

[0047] The first Bragg grating 211 and the second Bragg grating 212 are symmetrically arranged, and the period number and etching depth of the first Bragg grating 211 and the second Bragg grating 212 are the same. The resonant cavity 213 is located between the first Bragg grating 211 and the second Bragg grating 212. In this way, a symmetrical double Bragg grating resonant cavity 213 is formed, so that a spectrum with two split resonance peaks (such as Figure 4 shown).

[0048] The gas chamber 22 covers the second Bragg grating 212 and contains the gas to be detected. The gas to be detected affects the effective refractive index of the second Bragg grating 212, thereby affecting the energy distribution within the resonant cavity 213 between the first Bragg grating 211 and the second Bragg grating 212. This, in turn, changes the amplitudes of the two resonant peaks in the output spectrum, facilitating measurement of the concentration of the gas to be detected within the gas chamber 22.

[0049] Output port 23 is coupled to microcavity 21 via an evanescent field and is configured to output an optical signal corresponding to the gas to be detected. Thus, the optical signal affected by the gas to be detected within microcavity 21 is transmitted through output port 23 to facilitate measurement of the concentration of the gas to be detected within gas chamber 22.

[0050] The resonant cavity-based gas concentration sensor 2 provided in the embodiments of the present application is constructed with a dual Bragg grating resonant cavity 213. When a change in gas concentration within the gas chamber 22 is detected, the amplitude of light in the resonant cavity 213 changes relative to the amplitude of light. This amplitude change is used to measure the change in gas concentration, thereby determining the gas concentration. Furthermore, high-sensitivity sensing is achieved without the need for other means of enhancing the interaction between the evanescent field of the resonant cavity 213 and the gas being detected.

[0051] At the same time, the resonant cavity-based gas concentration sensor 2 provided in the embodiment of the present application adopts a symmetrical dual Bragg grating resonant cavity 213. When the external environment (such as temperature, etc.) changes as a whole, since the external environment affects the first Bragg grating 211 and the second Bragg grating 212 at the same time, the amplitude of the light in the resonant cavity 213 will change as a whole without causing a change in a certain resonance peak, thereby reducing the impact of the overall change of the external environment on the detection results of the resonant cavity-based gas concentration sensor 2 and having good stability.

[0052] Specifically, laser light is emitted from the laser 1, input through the input end of the microcavity 21 and coupled into the resonant cavity-based gas concentration sensor 2. When passing through the second Bragg grating 212, the light will be reflected and transmitted in a certain proportion, forming a resonant cavity 213 between the two Bragg gratings. The light that meets the resonance conditions is retained in the resonant cavity 213 to form a standing wave, and the other light is reflected or transmitted out of the Bragg grating. The reflected light will be coupled out of the chip by the output end 23 and detected by the photodetector 3.

[0053] In some examples, continue to refer to Figure 2 and Figure 3 The microcavity 21 further includes: a first grating coupler 214 and a bus waveguide 215 .

[0054] The first grating coupler 214, the bus waveguide 215, the first Bragg grating 211, the resonant cavity 213, and the second Bragg grating 212 are sequentially arranged. The first grating coupler 214 constitutes the input terminal. The output terminal 23 is coupled to the bus waveguide 215 via an evanescent field.

[0055] In this embodiment, a first grating coupler 214 is provided to receive the laser light output by the laser 1, and a bus waveguide 215 is provided to output the light reflected by the first Bragg grating 211, so as to detect the concentration of the gas to be detected in the gas chamber 22 according to the output spectrum of the resonant cavity 213.

[0056] In some examples, continue to refer to Figure 2 and Figure 3 The output end 23 includes an output waveguide 231 and a second grating coupler 232. The output waveguide 231 couples with the bus waveguide 215 via an evanescent field. The second grating coupler 232 is configured to output an optical signal corresponding to the gas to be detected. Thus, through the coupling between the output waveguide 231 and the bus waveguide 215, the light reflected by the first Bragg grating 211 is output.

[0057] In some examples, the gas chamber 22 includes a porous aluminum oxide membrane 50 .

[0058] The porous aluminum oxide film 50 covers the second Bragg grating 212 , and the porous aluminum oxide film 50 has a nanoporous structure.

[0059] In this way, the gas can adhere to the pore walls of the porous aluminum oxide film 50 to change the refractive index of the porous aluminum oxide film 50 , thereby affecting the refractive index of the second Bragg grating 212 .

[0060] In some examples, combined Figure 2 As shown, the resonant cavity-based gas concentration sensor 2 further includes a substrate 24 . The microcavity 21 , the output end 23 and the gas chamber 22 are all disposed on the substrate 24 .

[0061] Illustratively, the substrate 24 includes a silicon dioxide layer 10 , a thin film silicon layer 20 , and a silicon dioxide protection layer 40 .

[0062] Specifically, the porous alumina film 50 is in direct contact with the second Bragg grating 212, forming a "grating-porous medium" optical interface. The photonic devices in the non-gas chamber 22 area are completely wrapped by the silicon dioxide layer 10, isolated from the gas environment to avoid contamination or performance degradation. The internal space of the porous alumina film 50 is connected to the outside world, allowing gas molecules to enter the pores by diffusion. The environment above the film is open, forming a suspended gas chamber 22 with "open top and embedded silicon grating at the bottom". When gas molecules are adsorbed onto the inner wall of the porous alumina pores, they change the refractive index of the porous alumina film 50, thereby modulating the effective refractive index of the second Bragg grating 212, resulting in energy shift of the resonant cavity 213.

[0063] Since the two Bragg gratings have the same period number and etching depth and are both in the air, a symmetrical structure is formed and the resonance mode is split. Two split resonance peaks can be seen from the spectrum (such as Figure 4 At this time, by adjusting the gas concentration in the gas chamber 22, the effective refractive index of the porous aluminum oxide film 50 will change, and thus the effective refractive index of the second Bragg grating 212 will change. At this time, the system changes from symmetric to asymmetric, and the energy balance in the resonant cavity 213 between the two Bragg gratings is destroyed. From the spectrum, the amplitudes of the two split resonance peaks change relative to each other (as shown in FIG. Figure 4 By calculating the relative change in the amplitudes of the two split resonance peaks, the change in the gas concentration in the gas chamber 22 can be obtained.

[0064] For example, the porous alumina film 50 has a pore size of 2-20 nm and a porosity of 30%-70%.

[0065] Taking methane gas as an example, methane gas has a strong absorption line near 1650nm, so a broad spectrum light source with a wavelength of 1650nm (±5nm) can be selected to completely cover one mode of the coupled resonant cavity 213. Then, the length of the resonant cavity 213 is obtained by the standing wave condition of the double Bragg grating system. for: (1); in, is the mode number of the resonant cavity 213 (m=1,2,3…), is the wavelength of incident light, is the effective refractive index. is 2.5022, and the length of the resonant cavity 213 is calculated to be 56 μm.

[0066] Then, through the Prague conditions: The resulting Bragg grating has a period of 318nm and a duty cycle of 50%. Each Bragg grating contains 250 periods and has a total length of 80μm. Each Bragg grating is shallowly etched 70nm to form a periodic perturbation of Δn=0.1, resulting in a reflectivity of >99%.

[0067] The gas chamber 22 is then covered on the second Bragg grating 212. The gas chamber 22 uses mesoporous alumina (porous alumina film 50) as a gas-sensitive functional layer. It can selectively adsorb the target gas through the mesoporous structure (pore size 50-200nm). Gas adsorption changes the effective refractive index of the material, thereby affecting the optical response of the second Bragg grating 212.

[0068] When the gas concentration in the gas chamber 22 changes, the local effective refractive index of the second Bragg grating 212 Corresponding changes occur: (2); in, is the saturated adsorption capacity of gas, K is the adsorption equilibrium constant, and C is the gas concentration.

[0069] Subsequently, the reflection phase of the second Bragg grating 212 is caused to Offset, generating offset : (3); This destroys the uniformity of the system's energy distribution, causing energy to gather toward the first Bragg grating 211 . The energy change can be reflected by the amplitude of the resonance peak, thereby converting the change in gas concentration into a change in the resonance cavity amplitude.

[0070] Figure 5This is a schematic diagram of a second spectrum generated by the resonant cavity-based gas concentration sensor provided in an embodiment of the present application.

[0071] The transmission spectra generated by the resonant cavity-based gas concentration sensor 2 at different methane concentrations are shown in Figure 2. Figure 5 As shown, the measured sensitivity is 2.5% / 20ppm. Curve C is the transmission spectrum when the methane concentration is 0, curve D is the transmission spectrum when the methane concentration is 20ppm, and curve E is the transmission spectrum when the methane concentration is 40ppm.

[0072] Figure 6 : is a flow chart of a method for preparing a gas concentration sensor based on a resonant cavity provided in an embodiment of the present application, Figure 7 Schematic diagram of the preparation process of the resonant cavity-based gas concentration sensor provided in an embodiment of the present application.

[0073] Combine Figure 2 and Figure 3 The gas concentration sensor 2 based on the resonant cavity is shown. In some embodiments, a method for preparing the gas concentration sensor 2 based on the resonant cavity is also provided. Figure 6 As shown, the preparation method includes the following steps S1-S8: S1 , depositing a thin film silicon layer 20 on the silicon dioxide layer 10 .

[0074] The silicon dioxide layer 10 is a standard 220 nm silicon-on-insulator (SOI).

[0075] In this step, a thin film silicon layer 20 is deposited on the silicon dioxide layer 10 by chemical vapor deposition (CVD) or plasma-enhanced chemical vapor deposition (PECVD) to obtain a silicon dioxide layer 10. Figure 7 The structure shown in (a).

[0076] S2 , spin-coating a photoresist 30 on the thin film silicon layer 20 to expose the thin film silicon layer 20 corresponding to the microcavity 21 and the output end 23 .

[0077] In this way, after the photoresist 30 is spin-coated on the thin film silicon layer 20, the following is obtained: Figure 7 The structure shown in (b) is shown in FIG. The photoresist 30 is exposed to expose the first grating coupler 214, the second output grating coupler 232, the bus waveguide 215, the output waveguide 231, the first Bragg grating 211, the resonant cavity 213 and the second Bragg grating 212 to obtain the structure shown in FIG. Figure 7 The structure shown in (c).

[0078] S3, etching the exposed thin film silicon layer 20.

[0079] In this step, the thin film silicon layer 20 is etched by reactive ion etching (RIE) to obtain Figure 7 The structure shown in (d).

[0080] S4, removing the remaining photoresist 30 to obtain a first device.

[0081] In this step, we get Figure 7 The structure shown in (e).

[0082] S5, covering the first device with a silicon dioxide protection layer 40.

[0083] The silicon dioxide protection layer 40 is connected to the silicon dioxide layer 10 to protect the photonic device.

[0084] In this step, we get Figure 7 The structure shown in (f).

[0085] S6 , spin-coating the photoresist 30 on the silicon dioxide protection layer 40 to expose the silicon dioxide protection layer 40 corresponding to the gas chamber 22 .

[0086] In this step, we get Figure 7 The structure shown in (g).

[0087] S7 , etching the exposed silicon dioxide protection layer 40 to expose the second Bragg grating 212 , so as to obtain a second device having a cavity corresponding to the second Bragg grating 212 .

[0088] In this step, the photoresist 30 is used as a mask, and the silicon dioxide protective layer 40 is etched by buffered hydrofluoric acid to form an opening only in the area directly above the second Bragg grating 212. Figure 7 The structure shown in (h).

[0089] S8, constructing a gas chamber 22 on the cavity of the second device to obtain a gas concentration sensor based on a resonant cavity as provided in any of the above embodiments.

[0090] In one implementation, step S8 includes the following steps S81-S83: S81, Al(CH3)3 and H2O precursor gas are introduced into the cavity of the second device to grow the porous aluminum oxide film 50 (Al2O3 film) layer by layer on the second Bragg grating 212. In this way, the following is obtained: Figure 7 The structure shown in (i).

[0091] S82, calcining the Al2O3 film to generate a porous structure in the Al2O3 film.

[0092] S83, remove the remaining photoresist and the Al2O3 film outside the gas chamber to form a gas chamber. Figure 7 The structure shown in (j).

[0093] By using the method for fabricating a resonant cavity-based gas concentration sensor 2 provided in the embodiments of the present application, a resonant cavity-based gas concentration sensor 2 having a dual Bragg grating resonant cavity 213 can be fabricated. This sensor achieves high-sensitivity sensing without requiring additional means to enhance the interaction between the evanescent field of the resonant cavity 213 and the gas being detected. Furthermore, the impact of overall changes in the external environment (such as temperature) on the detection results can be reduced.

[0094] It is understood that the air chamber 22 may be Figure 7 The structure shown in (j) is that the aluminum oxide film is higher than the silicon dioxide protective layer 40 , and may also be a structure with a partial cavity at the upper end, which is not limited in the present application.

[0095] Figure 8 This is a second structural diagram of the gas concentration detection system provided in an embodiment of the present application.

[0096] Corresponding to the above-mentioned embodiments of the resonant cavity-based gas concentration sensor 2 or the method for preparing a resonant cavity-based gas concentration sensor, the present application also provides a gas concentration detection system 100, comprising: a laser 1, a resonant cavity-based gas concentration sensor 2, a photodetector 3, and a computing device 4. The laser 1 is configured to output laser light. The resonant cavity-based gas concentration sensor 2 comprises the resonant cavity-based gas concentration sensor 2 provided in any of the above-mentioned embodiments, or the resonant cavity-based gas concentration sensor 2 prepared by the method for preparing a concentration sensor provided in any of the above-mentioned embodiments. The resonant cavity-based gas concentration sensor 2 comprises an input end, a gas chamber 22 containing the gas to be detected, and an output end. The input end receives the laser light output by the laser 1, the gas chamber 22 contains the gas to be detected, and the output end outputs an optical signal corresponding to the gas to be detected. The photodetector 3 is disposed at the output end of the resonant cavity-based gas concentration sensor 2 and is configured to convert the optical signal output from the output end into an electrical signal. The computing device 4 is communicatively connected to the photodetector 3 and is configured to receive the electrical signal and demodulate the electrical signal to obtain the concentration of the gas to be detected.

[0097] The gas concentration detection system 100 provided in the embodiments of this application can detect the corresponding gas concentration based on the optical signal output by the resonant cavity-based gas concentration sensor 2. This system achieves high-sensitivity sensing without requiring additional means to enhance the interaction between the evanescent field of the resonant cavity 213 and the gas being detected. Furthermore, it can reduce the impact of overall changes in the external environment (such as temperature) on the detection results.

[0098] In one implementation, the computing device 4 is specifically configured to perform the following steps S10-S12: S10: constructing a first current spectrum based on the electrical signal.

[0099] S11, determining an amplitude deviation between a first current spectrum and a first initial spectrum, wherein the first initial spectrum corresponds to a spectrum when the concentration of the gas is 0.

[0100] S12: Determine the concentration of the gas corresponding to the first current spectrum based on the amplitude deviation and according to the mapping relationship.

[0101] In this embodiment, by comparing the first current spectrum with the first initial spectrum, the amplitude deviation of the optical signal output by the gas concentration sensor 2 based on the resonant cavity under the influence of the gas to be detected is calculated, so that the concentration of the gas corresponding to the amplitude deviation can be determined according to the preset mapping relationship.

[0102] Specifically, the gas concentration detection system 100 determines the gas concentration by comparing the amplitude deviation of the optical signal between the output spectrum when the gas concentration is 0 and the output spectrum at the current gas concentration.

[0103] The mapping relationship can be to actively adjust the concentration of the gas in the gas chamber 22 to obtain different spectra at different concentrations, so as to calculate the amplitude deviation between the spectrum at each concentration and the spectrum when the concentration is 0, so as to construct a comparison table of amplitude deviation and concentration.

[0104] In another implementation, the computing device 4 is specifically configured to perform the following steps S13-S14: S13, constructing a second current spectrum based on the electrical signal.

[0105] S14, adjusting a preset parameter so that the second current spectrum changes to a second initial spectrum, where the preset parameter is the concentration of the gas. The second initial spectrum corresponds to a spectrum when the concentration of the gas is 0. The preset parameter represents the amount of change in the concentration of the gas.

[0106] In this embodiment, the preset parameters are adjusted to fit the second current spectrum to the second initial spectrum, and the obtained preset parameters are the concentration of the gas.

[0107] Figure 9This is a schematic diagram of light propagation in a resonant cavity-based gas concentration sensor provided in an embodiment of the present application.

[0108] The following combination Figure 9 The derivation process of the transmission spectrum of the resonant cavity-based gas concentration sensor 2 is described.

[0109] Combine Figure 9 As shown, where E in is the incident signal, 、 are the magnitudes of the incident signal and the reflected signal at the left port of the first Bragg grating 211, 、 are the magnitudes of the incident signal and the reflected signal at the right port of the first Bragg grating 211, 、 are the magnitudes of the incident signal and the reflected signal at the left port of the second Bragg grating 212, respectively. and are the coupling coefficients of the Bragg grating to the incident signal and the reflected signal respectively. Since the two Bragg gratings have the same structure, the first Bragg grating 211 and the second Bragg grating 212 have the same and Equal in size.

[0110] The coupling matrix between the bus waveguide and the first Bragg grating 211 can be expressed as: .

[0111] Meanwhile, the coupling matrix of the first Bragg grating 211 and the second Bragg grating 212 can be expressed as: .

[0112] in, is the distance between the first Bragg grating 211 and the second Bragg grating 212, ,in , , For The effective wave propagation constant in the region, is the effective refractive index when the external gas concentration remains unchanged, When the external gas concentration changes The effective propagation constant of the region, When the external gas concentration changes The average effective refractive index change, is the transmission loss, is the coupling coefficient between the first Bragg grating 211 and the second Bragg grating 212 .

[0113] By passing the matrix, 、 、 、 、 and There are also the following relationships: ; ; in, , , , , , is the change in the effective propagation constant of the first Bragg grating 211 when the ambient gas concentration changes, is the change in the effective propagation constant of the second Bragg grating 212 when the ambient gas concentration changes, is the average effective refractive index change of the first Bragg grating 211 after the ambient gas concentration changes, is the average effective refractive index change of the second Bragg grating 212 when the ambient gas concentration changes.

[0114] Through the above formula, we can finally get the signal strength at b0: ; in, ; ; ; ; .

[0115] Finally, E. out The field transmission t can be expressed as: ; Thus, the relationship between the transmission spectrum and the change in gas concentration is established. By changing the gas concentration above the second Bragg grating 212, changes, thus affecting E out Field transmission t.

[0116] In summary, in this embodiment, the preset parameters can be adjusted by adjusting , fitting the second current image to the second initial image, and obtaining The value of is the concentration of the gas.

[0117] It should be noted that those skilled in the art will readily conceive of other embodiments of the present application after considering the specification and practicing the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered merely as exemplary, and the true scope of this application is indicated by the claims.

[0118] It should be understood that the present application is not limited to the exact structures described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A gas concentration sensor based on a resonant cavity, characterized in that: include: A microcavity (21) comprises an input end, a first Bragg grating (211), a resonant cavity (213), and a second Bragg grating (212) arranged in sequence; the input end is configured to receive a laser light source; the first Bragg grating (211) and the second Bragg grating (212) are symmetrically arranged, and the first Bragg grating (211) and the second Bragg grating (212) have the same number of periods and etching depth; the resonant cavity (213) is located between the first Bragg grating (211) and the second Bragg grating (212); a gas chamber (22) covering the second Bragg grating (212), wherein the gas chamber (22) contains a gas to be detected; The output end (23) is coupled to the microcavity (21) through an evanescent field, and the output end (23) is configured to output a light signal corresponding to the gas to be detected.

2. The resonant cavity-based gas concentration sensor according to claim 1, characterized in that: The microcavity (21) further comprises: a first grating coupler (214) and a bus waveguide (215); Wherein, the first grating coupler (214), the bus waveguide (215), the first Bragg grating (211), the resonant cavity (213), and the second Bragg grating (212) are arranged in sequence; The first grating coupler (214) constitutes the input end; The output end (23) is coupled to the bus waveguide (215) via the evanescent field.

3. The resonant cavity-based gas concentration sensor according to claim 2, characterized in that: The output end (23) comprises: An output waveguide (231) and a second grating coupler (232) optically connected to each other; The output waveguide (231) is coupled to the bus waveguide (215) via the evanescent field; The second grating coupler (232) is configured to output an optical signal corresponding to the gas to be detected.

4. The resonant cavity-based gas concentration sensor according to any one of claims 1 to 3, characterized in that: The air chamber (22) comprises: A porous aluminum oxide film (50) covers the second Bragg grating (212), and the porous aluminum oxide film has a nanoporous structure.

5. The resonant cavity-based gas concentration sensor according to any one of claims 1 to 3, characterized in that: Also includes: A substrate (24), the microcavity (21), the output end (23) and the gas chamber (22) are all arranged on the substrate (24).

6. A method for preparing a gas concentration sensor based on a resonant cavity, characterized in that: include: depositing a thin film silicon layer (20) on the silicon dioxide layer (10); Spin-coating a photoresist (30) on the thin film silicon layer (20) to expose the thin film silicon layer (20) corresponding to the microcavity (21) and the output end (23); Etching the exposed thin film silicon layer (20); removing the remaining photoresist (30) to obtain a first device; Covering the first device with a silicon dioxide protective layer (40); Spin-coating a photoresist (30) on the silicon dioxide protective layer (40) to expose the silicon dioxide protective layer (40) corresponding to the gas chamber (22); Etching the exposed silicon dioxide protective layer (40) to expose the second Bragg grating (212), thereby obtaining a second device having a cavity corresponding to the second Bragg grating (212); A gas chamber (22) is constructed on the cavity of the second device to obtain a gas concentration sensor (2) based on a resonant cavity as claimed in any one of claims 1 to 5.

7. The method for preparing a gas concentration sensor based on a resonant cavity according to claim 6, characterized in that: The step of constructing an air chamber (22) on the cavity of the second device comprises: introducing Al(CH3)3 and H2O precursor gases into the cavity of the second device to grow an Al2O3 thin film layer by layer on the second Bragg grating (212); calcining the Al2O3 film to generate a porous structure in the Al2O3 film; The remaining photoresist (30) and the Al2O3 film outside the gas chamber (22) are removed.

8. A gas concentration detection system, characterized in that: include: Laser (1), cavity-based gas concentration sensor (2), photodetector (3), and computing device (4); The laser (1), the resonant cavity-based gas concentration sensor (2), and the photodetector (3) are optically connected in sequence; The laser (1) is configured to output laser light; The resonant cavity-based gas concentration sensor (2) comprises the resonant cavity-based gas concentration sensor (2) according to any one of claims 1 to 5, or the resonant cavity-based gas concentration sensor (2) prepared by the method for preparing a resonant cavity-based gas concentration sensor according to claim 6 or 7; The resonant cavity-based gas concentration sensor (2) comprises an input end, a gas chamber (22), and an output end, wherein the input end receives the laser light output by the laser (1), the gas chamber (22) contains a gas to be detected, and the output end outputs a light signal corresponding to the gas to be detected; The photodetector (3) is arranged at the output end of the resonant cavity-based gas concentration sensor (2), and the photodetector (3) is configured to convert the optical signal output from the output end into an electrical signal; The computing device (4) is communicatively connected to the photoelectric detector (3), and the computing device (4) is configured to receive the electrical signal and demodulate the electrical signal to obtain the concentration of the gas to be detected.

9. The gas concentration detection system according to claim 8, characterized in that: The computing device (4) is configured to: constructing a first current spectrum based on the electrical signal; determining an amplitude deviation between the first current spectrum and a first initial spectrum, wherein the first initial spectrum corresponds to a spectrum when the concentration of the gas is 0; Based on the amplitude deviation and according to a mapping relationship, the concentration of the gas corresponding to the first current spectrum is determined.

10. The gas concentration detection system according to claim 8, characterized in that: The computing device (4) is configured to: constructing a second current spectrum based on the electrical signal; Adjust the preset parameters until the second current spectrum changes to a second initial spectrum, wherein the preset parameter is the concentration of the gas; the second initial spectrum corresponds to the spectrum when the concentration of the gas is 0; and the preset parameter represents the amount of change in the concentration of the gas.

Images