A waveguide array gas sensing system with high sensitivity for multi-gas detection

Abstract

The application discloses a waveguide array gas sensing system for high-sensitivity multi-gas detection, comprising a waveguide substrate, a waveguide Bragg grating arranged on the waveguide substrate, a phase-shifted Bragg grating, a micro-ring resonator, a Mach-Zehnder interferometer, a waveguide array, an electric field regulation module and a signal processing unit. The application effectively improves the sensitivity and selectivity of gases such as methane and carbon dioxide through waveguide array structure, topological optical protection adsorption and other technologies, and can realize accurate detection in a complex environment. The application adopts the principle of topological optics, reduces signal loss caused by environmental noise or surface defects, and improves the stability of the sensor. The application realizes automatic calibration and temperature and humidity compensation of the system, and enhances the autonomy and operation convenience of the system. The application has strong environmental adaptability and can work stably under different temperature and humidity conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the fields of photonic integration technology, optical sensing technology, topological optics and smart materials, and particularly relates to a waveguide array gas sensing system for high-sensitivity multi-gas detection, which combines smart responsive materials and artificial intelligence algorithms to achieve efficient and accurate detection of multiple gases (such as methane, carbon dioxide, etc.). BACKGROUND

[0002] With the aggravation of environmental pollution and the increasing demand for gas detection accuracy in industrial safety and environmental monitoring, traditional gas detection technology has certain limitations in terms of accuracy, selectivity and stability. Optical waveguide gas sensors have high sensitivity and low power consumption, but it is still difficult to achieve accurate and stable detection of multiple gases in complex environments. Especially in the case of large changes in gas concentration, how to improve the sensitivity and response speed of the sensor and ensure its long-term stability is still a bottleneck for technology development.

[0003] By combining the principles of topological optics and smart responsive materials, optimizing the waveguide structure, and enhancing gas molecule adsorption, the performance of the gas sensor can be significantly improved. Therefore, there is an urgent need for an optical waveguide gas sensor system that can effectively improve the detection accuracy and stability. SUMMARY

[0004] The purpose of the present application is to provide a waveguide array gas sensing system for high-sensitivity multi-gas detection, which improves the detection sensitivity and selectivity of gases such as methane and carbon dioxide by introducing smart responsive material adsorption and other technologies. At the same time, combined with artificial intelligence algorithms, the intelligent level of the system is improved.

[0005] In order to achieve the above-mentioned task, the present application adopts the following technical solutions:

[0006] A waveguide array gas sensing system for high-sensitivity multi-gas detection, comprising a waveguide substrate, a waveguide Bragg grating arranged on the waveguide substrate, a phase-shifted Bragg grating, a micro-ring resonator, a Mach-Zehnder interferometer, a waveguide array, an electric field regulation module, and a signal processing unit; wherein:

[0007] The waveguide substrate serves as the foundation support for the entire sensor system and is located at the bottom layer of the sensor system. The waveguide substrate is made of silicon, and a waveguide array channel is constructed on the waveguide substrate;

[0008] The waveguide array channel etching is formed on the waveguide substrate, and the waveguide array channel includes the incident waveguide, the first waveguide channel to the sixth waveguide channel arranged in parallel, and the surface of each waveguide channel is coated with a smart response material; wherein: the tunable laser light grating coupler and the three-ring polarizer are connected to the incident waveguide; the optical signal in the incident waveguide is divided into two paths and enters the first waveguide channel and the second waveguide channel respectively; the optical signal entering the first waveguide channel is divided into two paths and enters the third waveguide channel and the fourth waveguide channel respectively; the optical signal entering the second waveguide channel is divided into two paths and enters the fifth waveguide channel and the sixth waveguide channel respectively;

[0009] The waveguide Bragg grating is arranged on the waveguide substrate in a pair, and the pair of waveguide Bragg gratings are respectively used for receiving the optical signals in the third waveguide channel and the sixth waveguide channel and modulating the optical signals by using the internal periodic grating structure to output the modulated optical signals S2 and S5.

[0010] The phase shift Bragg grating is arranged on the waveguide substrate in a pair and located on the side of the pair of waveguide Bragg gratings; the pair of phase shift Bragg gratings are respectively used for receiving the optical signals in the third waveguide channel and the sixth waveguide channel and phase adjusting the optical signals to output the adjusted optical signals S1 and S6.

[0011] The micro-ring resonator is used for receiving the optical signal of the fifth waveguide channel and enhancing the intensity of the optical signal by using the resonance effect to output the enhanced optical signal S4.

[0012] The Mach-Zehnder interferometer is used for receiving the optical signal of the fourth waveguide channel, the optical signal is divided into two paths in it and is subjected to different optical paths before being combined and interfered, and finally the interfered optical signal S3 is output.

[0013] The electric field regulation module includes electrodes distributed on the waveguide substrate; an external electric field is applied through the electrodes to regulate the propagation characteristics of the optical signals transmitted in the waveguide array channel.

[0014] The optical signals S1 to S6 are optoelectronically converted by the optical power meter and then input into the signal processing unit, the signal processing unit performs data integration processing to accurately detect the gas concentration; the signal processing unit is also used to control the frequency scanning range of the tunable laser and the read-write speed of the optical power meter.

[0015] When the waveguide array channel surface adsorbs to the gas molecules, because the adsorption of each gas molecule causes different changes in the refractive index, the output optical signals S1 to S6 are converted into electrical signals, which will cause changes in signal power density, voltage amplitude and signal frequency, and the signal processing unit realizes real-time detection of multiple gases according to the changes.

[0016] Further, a silicon dioxide layer and a silicon nitride layer are sequentially deposited on the silicon substrate.

[0017] Further, the waveguide thickness of the waveguide Bragg grating is 300 nm, the Bragg grating period is 498 nm, and the design wavelength is 1550 nm.

[0018] Further, the phase shift length of the phase shift Bragg grating is 498 nm, and the phase adjustment accuracy is 0.01 degrees.

[0019] Further, the micro-ring resonator has a micro-ring radius of 50 μm and a coupling gap of 100 nm.

[0020] A detection method of a waveguide array gas sensing system for high-sensitivity multi-gas detection, comprising:

[0021] Step 1, place the gas sensor system in the gas environment to be detected, and connect the incident waveguide in the system to the tunable laser through the grating coupler, single-mode optical fiber, three-ring polarization controller; the six light signals S1 to S6 at the output end of the system are connected to the optical power meter, the optical power meter is connected to the signal processing unit, and the signal processing unit controls the frequency scanning range of the tunable laser and the read-write speed of the optical power meter;

[0022] Step 2, the light signal in the incident waveguide is divided into two paths by the multimode interference beam splitter and enters the first waveguide channel and the second waveguide channel; the light signal in the first waveguide channel is again divided into two beams by the multimode interference beam splitter, one of which enters the phase shift Bragg grating and the waveguide Bragg grating in parallel through the third waveguide channel, and the other of which enters the Mach-Zehnder interferometer module through the fourth waveguide channel, and the light wave is divided and superimposed in the Mach-Zehnder interferometer module to form destructive interference or constructive interference, thereby outputting the light signal S3;

[0023] The light signal in the second waveguide channel is divided into two beams by the multimode interference beam splitter, one of which enters the micro-ring resonator, and the other of which enters the phase shift Bragg grating and the waveguide Bragg grating in parallel, and the light wave is subjected to periodic effective refractive index modulation in the phase shift Bragg grating and the waveguide Bragg grating, thereby outputting the light signals S5 and S6;

[0024] Step 3, during the gas detection process, the quality of the output light signal is adjusted by changing the voltage amplitude applied to the electrode.

[0025] Step 4, the signal processing unit receives the optical signals S1 to S6 through the optical power meter and obtains six electric signals after photoelectric conversion, and determines the type of the detected gas through the following detection method:

[0026] Firstly, when detecting a single gas, the light signals outputted through the six channels of the sensor system during the working process are the same as the template data obtained by detecting the gas in advance, so that the type of the detected gas can be determined by comparing the changes of the six light signals of the sensor system with the output light signals without the adsorbed gas.

[0027] Secondly, when multiple gases are adsorbed on the waveguide array channels, the intensity, phase and amplitude of the optical signals S1 to S6 need to be regulated, and the changes of the transmission coefficient and the transmission spectrum of the waveguide array channel during the detection of each single gas and mixed gas are determined, and then the transmission spectrum of each single gas in the mixed gas detection is obtained; by testing the single gas and the different proportions of the mixed gas, the center wavelength shift of each waveguide array channel is compared, and when the detection spectrum of the single gas is the same as the center wavelength corresponding to the proportion of the single gas in the mixed gas, it is considered that the detected is the light signal of the single gas.

[0028] Further, the intensity, phase and amplitude of the optical signals S1 to S6 are regulated, specifically the changes of the stop band width, the drift of the center wavelength and the change of the waveguide coupling coefficient of the waveguide Bragg grating and the phase shift Bragg grating are adjusted.

[0029] Compared with the prior art, the present application has the following technical features:

[0030] 1. The present application effectively improves the sensitivity and selectivity of methane, carbon dioxide and other gases by using waveguide array structure and topological optical protection adsorption technology, and can realize accurate detection in complex environment.

[0031] 2. The present application uses the principle of topological optics to reduce the signal loss caused by environmental noise or surface defects, and improves the stability of the sensor.

[0032] 3. The present application realizes automatic calibration and temperature and humidity compensation of the system, and enhances the autonomy and operation convenience of the system.

[0033] 4. The present application has strong environmental adaptability and can work stably under different temperature and humidity conditions. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 Different structures of optical waveguide sensor array are introduced;

[0035] Figure 2Structure diagram of the optical waveguide sensor array;

[0036] Figure 3 (a) is a schematic diagram of coating MOF material on the surface of the waveguide, and (b) is a schematic diagram of the intelligent response type (MOF) material adsorbing gas molecules in the cross section of the waveguide sensor;

[0037] Figure 4 Greenhouse gas (CH4 and CO2) test spectrum diagram effect of the optical waveguide sensor array DETAILED DESCRIPTION

[0038] The present application provides a high-sensitivity multi-gas detection waveguide array gas sensing system, which adopts comprehensive integration of multiple optical and sensing technologies; the core structure includes a waveguide substrate, a waveguide Bragg grating module, a phase-shifted Bragg grating module, a micro-ring resonator module, a Mach-Zehnder interferometer module, a waveguide array module, and an electric field regulation module, etc. Each module works cooperatively to form an efficient multi-gas detection system, as shown in Figure 1 and Figure 2 The structure principle, working process, and preparation process of the present application will be described in detail below with reference to the accompanying drawings.

[0039] I. Structure design

[0040] Referring to the accompanying Figure 2 , the present application provides a high-sensitivity multi-gas detection waveguide array gas sensing system, which includes a waveguide substrate, a waveguide Bragg grating, a phase-shifted Bragg grating, a micro-ring resonator, a Mach-Zehnder interferometer, a waveguide array, an electric field regulation module, and a signal processing unit arranged on the waveguide substrate; wherein:

[0041] 1. Waveguide substrate

[0042] The waveguide substrate serves as the basic support of the entire sensor system and is located at the bottom layer of the sensor system; as shown in Figure 3 (b), the waveguide substrate adopts a silicon substrate, on which a 3 μm silicon dioxide layer and a 300 nm silicon nitride layer are sequentially deposited; the waveguide array channel is constructed on the waveguide substrate.

[0043] The waveguide substrate provides a stable propagation channel for the optical signal of the sensor, and different optical waveguide paths are constructed on the waveguide substrate to ensure that the optical signal can be effectively transmitted to the subsequent optics. In addition, the design of the waveguide substrate ensures that it is closely combined with the optical elements (such as Bragg grating, phase-shifted grating, etc.) on the upper layer to form a unified optical transmission system.

[0044] 2. Waveguide array channel

[0045] The waveguide array channel etching is formed on the waveguide substrate, and the waveguide array channel includes the incident waveguide, the first waveguide channel to the sixth waveguide channel arranged in parallel, and the surface of each waveguide channel is coated with a smart response material.

[0046] The tunable laser light grating coupler and the three-ring polarizer are connected to the incident waveguide; the optical signal in the incident waveguide is divided into two paths, which enter the first waveguide channel and the second waveguide channel respectively; the optical signal entering the first waveguide channel is divided into two paths, which enter the third waveguide channel and the fourth waveguide channel respectively; the optical signal entering the second waveguide channel is divided into two paths, which enter the fifth waveguide channel and the sixth waveguide channel respectively. The third waveguide channel to the sixth waveguide channel will be connected to different optical devices, which will be described one by one below.

[0047] In this scheme, the surface of the waveguide channel is coated with a smart response material MOF, and the smart response material selectively adsorbs specific gases to improve the sensitivity and selectivity of gas detection.

[0048] 3. Waveguide Bragg grating

[0049] The waveguide Bragg grating is arranged on the waveguide substrate in a pair, and the pair of waveguide Bragg gratings are respectively used to receive the optical signals in the third waveguide channel and the sixth waveguide channel and modulate the optical signals by using the internal periodic grating structure to output the modulated optical signals S2 and S5. The periodic grating structure is provided in the waveguide Bragg grating to ensure the reflection and transmission efficiency of the signal in the waveguide; in this scheme, the waveguide thickness of the waveguide Bragg grating is 300 nm, the Bragg grating period is 498 nm, and the design wavelength is 1550 nm.

[0050] The waveguide Bragg grating detects the changes in absorption and refraction characteristics when different gases interact with the optical signal based on the principle of optical interference, thereby providing a basis for judging the type and concentration of the gas. In the attached Figure 2 In this scheme, the waveguide Bragg grating is clearly presented as a specific grating part in the waveguide structure, which is located in the key area of the optical signal transmission path and directly interacts with the optical signal to modulate the optical signal.

[0051] 4. Phase-shifted Bragg grating

[0052] The phase-shifted Bragg grating is arranged on the waveguide substrate in a pair, and the pair of phase-shifted Bragg gratings are respectively located on the side of the pair of waveguide Bragg gratings; the pair of phase-shifted Bragg gratings are respectively used to receive the optical signals in the third waveguide channel and the sixth waveguide channel and adjust the phase of the optical signals to output the adjusted optical signals S1 and S6.

[0053] The phase shift length of the phase shift Bragg grating is 498nm, and the phase adjustment accuracy is 0.01 degrees in the scheme; the phase shift Bragg grating can optimize the optical interference effect and improve the accuracy of gas detection.

[0054] 5. Micro ring resonator

[0055] The micro ring resonator is used for receiving the optical signal of the fifth waveguide channel, and outputting the enhanced optical signal S4 after enhancing the intensity of the optical signal by using the resonance effect; in the scheme, the micro ring radius of the micro ring resonator is 50pm, and the coupling gap is 100nm.

[0056] The optical signal is enhanced in intensity by using the resonance effect when passing through the micro ring resonator, so that the optical signal can be effectively amplified when passing through this area, thereby improving the sensitivity of the whole system to gas detection.

[0057] 6. Mach-Zehnder interferometer

[0058] The Mach-Zehnder interferometer is used for receiving the optical signal of the fourth waveguide channel, and outputting the interfered optical signal S3 after splitting the optical signal into two paths and performing different optical paths and then combining and interfering.

[0059] The Mach-Zehnder interferometer in the scheme is an interferometer with equal arms, so the corresponding interference fringes are the light intensity corresponding to constructive interference, which is the most stable interference intensity, because when the phase difference is zero, the interference pattern does not change with time and the output light intensity does not fluctuate, and information related to the gas is obtained according to the interference result.

[0060] 7. Electric field regulation module

[0061] The electric field regulation module includes electrodes distributed on the waveguide substrate; an external electric field is applied by the electrodes to regulate the propagation characteristics of the optical signal transmitted in the waveguide array channel; this regulation can change the way the optical signal interacts with gas molecules, further optimizing the gas detection performance. In the embodiment, the electrodes are arranged at three corners of the waveguide substrate.

[0062] 8. Signal processing unit

[0063] The optical signals S1 to S6 are converted into electrical signals by the optical power meter and then connected to the signal processing unit, which processes the data and accurately detects the gas concentration; the signal processing unit is also used to control the frequency scanning range of the tunable laser and the read-write speed of the optical power meter.

[0064] When the waveguide array channel surface is adsorbed to gas molecules, due to the different changes in refractive index caused by the adsorption of each gas molecule, the optical signals S1 to S6 at the output end are converted into electrical signals, which will cause changes in signal power density, voltage amplitude, and signal frequency. The signal processing unit realizes real-time detection of multiple gases according to the changes.

[0065] II. Working principle

[0066] The high-sensitivity multi-gas sensor system of the present application combines multiple optical principles and realizes accurate detection through multiple independently operating optical modules. The waveguide substrate includes a silicon dioxide layer (3 μm) and a silicon nitride layer (300 nm). The waveguide array channel module is etched on the silicon nitride, and a metal organic framework (MOF) material is coated on the waveguide array channel module. When the optical signal is transmitted in the waveguide, the MOF material is adsorbed with gas molecules, causing changes in its physical or chemical properties, thereby changing the transmission characteristics of the optical signal, such as light absorption and refraction. In addition, the optical signal is transmitted along the topologically protected edge state, reducing environmental noise interference and enhancing signal stability.

[0067] Specifically, the waveguide Bragg grating induces the diffraction effect of light through a periodic structure, and senses the refractive index changes caused by gas; the phase-shifted Bragg grating precisely captures the optical property changes of gas by adjusting the phase of light; the micro-ring resonator enhances the interaction between gas and light through resonance phenomenon, improving sensitivity; the Mach-Zehnder interferometer amplifies the small signal changes caused by gas concentration changes through interference effect. Each module works independently and cooperatively processes optical signals. Finally, the signal processing unit integrates the data, and accurately detects the gas concentration through intelligent algorithms.

[0068] The sensor system is placed in the environment to be detected. Since the optical waveguide sensor is often used to detect the refractive index change of the measured substance or environment, when the evanescent wave on the surface of the waveguide sensor waveguide contacts the measured substance, the change in the refractive index of the measured substance will cause the field strength of the evanescent wave to change, which in turn causes the intensity and phase of the propagating light in the waveguide sensor to change. When light propagates through the waveguide array channel, if the environment near the waveguide array channel changes (such as temperature, pressure, or chemical composition), it may cause changes in the intensity or phase of the propagating light. Therefore, it can be sensed by monitoring the output light intensity, wavelength, or propagation phase. When the waveguide sensor surface is modified with porous metal organic compound material, the sensing and detection mechanism is as follows:

[0069] ①When gas molecules enter the pore structure of the MOF material, they will interact with the metal centers or organic ligands in the MOF. These interactions cause changes in the electron density, local refractive index, and other properties of the MOF material. Because the propagation characteristics of light in the optical waveguide (such as propagation speed, phase, and reflectivity) are closely related to the refractive index of the waveguide medium, when the refractive index of the MOF material changes, the optical signal in the optical waveguide will also change accordingly. In particular, the adsorption or reaction of gas molecules (such as oxygen, nitrogen, carbon dioxide, etc.) on the surface of the MOF will cause changes in the local refractive index, thereby affecting the propagation path or reflection characteristics of light, which can be detected by the sensor.

[0070] ②The gas adsorption of the MOF material not only changes its refractive index, but also can cause changes in the microstructure of the MOF material. When gas molecules are adsorbed by the MOF material, the framework structure of the MOF expands, contracts, or changes in coordination. These small changes in structure will affect the conditions for the propagation of light on the waveguide surface, which will be reflected in the output signal of the sensor. For example, when gas molecules form coordination bonds with the metal centers or organic ligands of the MOF, the rigidity of the MOF framework may be destroyed, leading to changes in the propagation characteristics of light.

[0071] This independent and collaborative working mode significantly improves the sensitivity, accuracy, and selectivity of gas detection, breaking through the limitations of traditional sensing technology and providing strong technical support for multi-gas detection.

[0072] III. Working process

[0073] Referring to the accompanying drawings Figure 2 , the working process of the present application is as follows:

[0074] Step 1, place the gas sensor system of the present application in a carbon dioxide, methane, etc. gas environment, and connect the incident waveguide in the system through the grating coupler, single-mode optical fiber (SMF-28e), three-ring polarization controller, and tunable laser; the six-way optical signal S1 to S6 at the output end of the system is connected to the optical power meter, and the optical power meter is connected to the signal processing unit (computer end) through the LabView control program, and the signal processing unit controls the frequency scanning range of the tunable laser and the read-write speed of the optical power meter.

[0075] Step 2, the optical signal in the incident waveguide is split into two paths by a multimode interference beam splitter into a first waveguide channel and a second waveguide channel; the optical signal in the first waveguide channel is also split into two beams by a multimode interference beam splitter, one of which passes through a third waveguide channel and enters a phase-shifted Bragg grating and a waveguide Bragg grating in parallel, where periodic effective refractive index modulation processing of optical waves is performed, and after the signal stabilizes, optical signals S1 and S2 are output; the other passes through a fourth waveguide channel into a Mach-Zehnder interferometer module, and performs beam splitting and superposition of optical waves in it to form destructive interference or constructive interference processing, thereby outputting optical signal S3;

[0076] The optical signal in the second waveguide channel is split into two beams by a multimode interference beam splitter, one of which enters a micro-ring resonator, and when the optical path (i.e. the propagation distance of the optical wave in the micro-ring) in the micro-ring matches the wavelength of the light, the light will form a standing wave in the micro-ring and resonate, outputting optical signal S4; the other beam enters a phase-shifted Bragg grating and a waveguide Bragg grating in parallel, where periodic effective refractive index modulation processing of optical waves is performed, and after the signal stabilizes, optical signals S5 and S6 are output.

[0077] Step 3, during gas detection, the quality of the output optical signal is adjusted by changing the voltage amplitude applied to the electrode.

[0078] Specifically, by applying a voltage to the electrode and adjusting the voltage amplitude, the carrier dispersion effect in the optical waveguide is affected, causing changes in hole and electron pairs, thereby generating carrier diffusion between holes and electrons, and the carrier dispersion effect will affect the photoelectric conversion efficiency, modulation response, and signal quality.

[0079] Step 4, the signal processing unit receives the optical signals S1 to S6 through an optical power meter and performs photoelectric conversion to obtain six electrical signals, and determines the type of gas detected by the following detection method:

[0080] First, when detecting a single gas, the six optical signals that pass through different waveguide channels and are finally output by the sensor system during the operation of the sensor system are the same as the template data obtained by detecting the gas in advance, i.e. the gas adsorption on the sensor has not changed; therefore, by comparing the changes in the six optical signals of the sensor system with the output optical signals without adsorbing gas, the type of gas detected can be determined.

[0081] Secondly, when multiple gases are adsorbed on the waveguide array channel, the intensity, phase and amplitude of the optical signals S1 to S6 need to be regulated; specifically, the stop band width variation, center wavelength drift and waveguide coupling coefficient variation of the waveguide Bragg grating and phase shift Bragg grating are adjusted, and the transmission coefficient and transmission spectrum variation of each single gas and mixed gas detection waveguide array channel are determined, and then the transmission spectrum of each single gas in the mixed gas detection is obtained; by testing the different proportions of single gas and mixed gas, the center wavelength shift of each waveguide array channel is compared, and when the detection spectrum of the single gas is the same as the center wavelength corresponding to the proportion of the single gas in the mixed gas, it is considered that the detected is the optical signal of the single gas.

[0082] The working of the sensor starts from signal collection, and the reception of the signal is completed by the waveguide array channel module. The design of the waveguide array channel structure optimizes the transmission efficiency of the optical signal, ensuring that the signal can be efficiently transmitted from the external environment to the subsequent modules. The sensor system is placed in the environment to be detected, and the optical waveguide sensor is often used to detect the refractive index change of the measured substance or environment. When the evanescent wave on the surface of the optical waveguide sensor waveguide contacts the gas molecules, the change of the refractive index of the substance will cause the change of the field strength of the evanescent wave, which in turn causes the change of the intensity and phase of the propagating light in the waveguide sensor. When the light propagates through the waveguide, if the environment near the waveguide changes (such as temperature, pressure or chemical composition), it may cause the intensity or phase of the light propagation to change. Therefore, it can be perceived by monitoring the output light intensity, wavelength or propagation phase.

[0083] Four, preparation process

[0084] 1. Waveguide structure preparation

[0085] 1.1 Preparation of substrate

[0086] Firstly, a high-quality silicon wafer is selected as the substrate material for waveguide structure preparation. The quality of the silicon wafer directly affects the quality and performance of the subsequent waveguide growth, so it is necessary to ensure that the surface flatness is high, the crystal structure is complete and there are no obvious defects. Before use, the silicon wafer is strictly tested for quality, and atomic force microscope (AFM) can be used to measure the surface roughness to ensure that it is less than a certain value (such as 1 nm), and X-ray diffraction (XRD) is used to analyze the crystal structure to ensure that it meets the standard.

[0087] The qualified silicon wafer is subjected to a standard cleaning process. This process is crucial for removing various contaminants on the surface of the silicon wafer, as even a trace amount of impurities can affect the quality of subsequent thin film deposition and waveguide fabrication. The cleaning process starts with a rinse with a large amount of deionized water, with the purpose of initially removing large particles of dust and water-soluble impurities on the surface of the silicon wafer. Then, the silicon wafer is sequentially placed in organic solvents such as acetone and ethanol for ultrasonic cleaning. Ultrasonic cleaning utilizes the strong impact force generated by the cavitation effect of ultrasonic waves in the liquid, which can effectively remove oil, organic contaminants, and some small particles adsorbed on the surface of the silicon wafer. The ultrasonic cleaning time in acetone can be set to 10-15 minutes, and the ultrasonic cleaning time in ethanol is also 10-15 minutes, with an ultrasonic frequency of 20-40 kHz to achieve the best cleaning effect. After cleaning, the silicon wafer is blown dry with high-purity nitrogen to avoid re-adsorbing impurities during the natural drying process in the air.

[0088] 1.2 Thin film deposition

[0089] Chemical vapor deposition (CVD) is used to grow different thin film layers on the cleaned silicon substrate, which is a key step in constructing the waveguide structure. CVD technology can precisely control the growth thickness, composition, and quality of the thin film on the substrate surface, providing a good foundation for subsequent photolithography and etching processes.

[0090] First, a 300 nm thick silicon layer is grown as the lower waveguide. During the deposition of the silicon layer, silane (SiH4) is used as the silicon source gas, and hydrogen (H2) is used as the carrier gas. Silane is decomposed at high temperature and reduced by hydrogen, and silicon atoms are deposited on the surface of the silicon substrate to form a silicon layer. The reaction temperature is controlled at 600-800°C, which is beneficial for the decomposition of silane and the diffusion of silicon atoms, ensuring the uniformity of silicon layer growth and the quality of the crystal. The reaction pressure is maintained at 100-500 Pa, and the growth rate of the silicon layer is controlled by precisely adjusting the flow ratio of silane and hydrogen. Generally, the silane flow can be set to 10-50 sccm, and the hydrogen flow is between 100-500 sccm, so that the growth rate remains within a stable range (such as 0.1-0.5 nm / s), thereby obtaining a silicon layer with uniform thickness and good quality.

[0091] Then a 100 nm thick silicon dioxide layer is grown on the silicon layer as an intermediate active layer. Plasma enhanced chemical vapor deposition (PECVD) technology is selected, with tetraethyl orthosilicate (TEOS) as the silicon source and oxygen (O2) as the reaction gas. The deposition is carried out at a radio frequency power of 100-300 W and a temperature of 300-400°C. The radio frequency power serves to excite the plasma, enhance the activity of the reaction gas, and promote the deposition reaction of silicon dioxide. The temperature control is crucial for the decomposition of TEOS and the formation rate of silicon dioxide, and within this temperature range, the growth quality and uniformity of the silicon dioxide layer can be ensured. The growth rate of the silicon dioxide layer is precisely controlled by adjusting the flow rates of TEOS and O2, with TEOS flow rate being 5-20 sccm and O2 flow rate being 50-200 sccm. The film thickness is monitored in real time to ensure that the design requirement of 100 nm is met.

[0092] Finally, a 200 nm thick silicon nitride layer is grown on the silicon dioxide layer as an upper waveguide. Again, the PECVD method is used, with silane (SiH4) and ammonia (NH3) as the reaction gas. The deposition is carried out at a temperature of 250-350°C, a pressure of 200-500 Pa, and a radio frequency power of 150-350 W. Silane and ammonia react in the plasma environment to form silicon nitride, which is deposited on the silicon dioxide layer. The flow ratio of the reaction gas is precisely controlled, with silane flow rate being generally 5-15 sccm and ammonia flow rate being 30-100 sccm, and the deposition time is also controlled to ensure that a silicon nitride layer with uniform thickness, good quality, and small surface roughness (e.g., less than 0.5 nm) is obtained, providing a good foundation for subsequent photolithography processes.

[0093] 1.3 Photolithography and Etching

[0094] After the deposition of the silicon nitride layer, photolithography is performed to define the geometric structure of the waveguide. Photolithography is a key step of accurately transferring the pre-designed waveguide pattern to the silicon nitride layer, and its precision and accuracy directly affect the performance of the waveguide.

[0095] First, photoresist is spin-coated on the surface of the silicon nitride. The type and thickness of the photoresist need to be selected according to the specific requirements of the photolithography process. Generally, positive photoresist is selected, and its thickness is determined according to the depth and accuracy requirements of the subsequent etching process, usually between 1-3 μm. The spin-coating process is carried out on a spin coater. After the photoresist is dropped onto the surface of the silicon nitride, it is rotated at a speed of 1000-3000 rpm for 30-60 seconds to ensure uniform coating of the photoresist on the surface of the silicon nitride. The control of the rotation speed and time is crucial for the uniformity of the photoresist thickness, and too high rotation speed or too long time may result in uneven photoresist thickness or even edge effects, affecting the photolithography accuracy.

[0096] Then the photoresist is exposed using electron beam lithography or ultraviolet lithography technology. Electron beam lithography has higher resolution and is suitable for making high-precision waveguide patterns, but its equipment cost is higher and the exposure time is longer; ultraviolet lithography is relatively low in cost and high in efficiency, and is suitable for mass production. During the exposure process, the exposure dose and time are accurately controlled according to the characteristics of the photoresist and the design requirements of the waveguide. The exposure dose is generally between 10-100 mJ / cm 2 , and the exposure time is between a few seconds and tens of seconds, ensuring that the pre-designed waveguide pattern is accurately transferred to the photoresist.

[0097] The exposed photoresist is developed to remove the unexposed part and form a photoresist mask. The selection of the developing solution and the developing time need to be optimized according to the type of the photoresist, and the developing time is generally between 30-120 seconds. The developing process needs to be carried out in a strictly controlled temperature and humidity environment, with the temperature controlled at 20-25°C and the humidity between 40%-60%, to ensure the consistency and accuracy of the developing effect.

[0098] Then the silicon nitride layer is etched using a plasma etching process, with the photoresist mask as protection. The etching gas is selected from fluorine-based gases (such as CF4, SF6, etc.), and the active fluorine ions generated in the plasma environment can chemically react with silicon nitride to remove the unnecessary silicon nitride. By accurately adjusting the flow rate of the etching gas, the radio frequency power and the etching time, the etching depth is accurately controlled to 200 nm to form the waveguide structure. The flow rate of the etching gas is generally between 20-100 sccm, the radio frequency power is between 100-500 W, and the etching time is calculated according to the etching rate and the required etching depth, generally between a few minutes and tens of minutes. During the etching process, the etching depth is monitored in real time, and measurement techniques such as optical interference method or ellipsometer can be used to ensure the accuracy of the etching depth. After etching is completed, the photoresist mask is removed, which can be done by oxygen plasma ashing or solvent immersion. Oxygen plasma ashing uses the chemical reaction between oxygen plasma and photoresist to decompose the photoresist into volatile gas for removal; solvent immersion uses a specific organic solvent (such as N-methyl-2-pyrrolidone, NMP) to dissolve and remove the photoresist. After removing the photoresist, the waveguide structure is cleaned to remove residual impurities and etching products, ensuring the cleanliness of the waveguide surface.

[0099] 1.4 Waveguide surface treatment

[0100] In order to reduce the loss of optical signals in the waveguide and improve the transmission efficiency of optical signals, the etched waveguide surface is treated for smoothing. Chemical mechanical polishing (CMP) technology is used, which is a surface treatment method combining chemical corrosion and mechanical grinding, which can effectively remove the small defects and roughness of the waveguide surface, making the surface reach nanometer level flatness.

[0101] In the CMP process, a specially formulated polishing solution is used, which contains abrasive particles (such as silica particles), chemical etchants (such as potassium hydroxide, KOH), and buffering agents. The abrasive particles polish the waveguide surface through mechanical action, removing the protruding parts of the surface; the chemical etchant reacts with the waveguide material, making it easier to remove, while the buffering agent controls the pH value of the polishing solution, maintaining the stability of the chemical etching reaction. During polishing, the polishing pressure is controlled between 1-5 psi, the polishing disc speed is controlled between 50-150 rpm, and the polishing solution flow rate is controlled between 50-200 mL / min. Excessive polishing pressure can cause excessive wear of the waveguide surface, affecting the structural integrity of the waveguide; the control of the polishing disc speed and the polishing solution flow rate is crucial for the uniformity and efficiency of polishing. By precisely controlling these parameters, the surface roughness of the waveguide can be reduced to the nanometer level (such as less than 0.5 nm), significantly improving the transmission efficiency of optical signals in the waveguide.

[0102] 2. Waveguide design (modular structure design) and waveguide array integration

[0103] 2.1 Bragg grating design and integration

[0104] Parameter determination

[0105] According to the system requirements, the design parameters of the waveguide Bragg grating are determined. The waveguide thickness is set to 200 nm, the Bragg grating period is 300 nm, and the design wavelength is 1550 nm. These parameters are selected based on theoretical analysis and simulation calculation of the transmission characteristics of optical signals in the waveguide, aiming to enable the Bragg grating to effectively modulate optical signals of a specific wavelength, so as to realize the detection of refractive index changes caused by gas.

[0106] The etching depth of the grating is calculated and optimized through strict optical theory formulas and simulation software (such as R-soft, FDTDSolutions, etc.). The etching depth will affect the optical properties of the grating such as reflectivity and transmissivity. Generally, by simulating the effect of the grating on the optical signal under different etching depths, and combining the requirements of reflectivity and transmissivity in actual application, the optimal etching depth is determined. For example, after multiple simulations, it is found that when the etching depth is between 100-150 nm, it can ensure a high reflectivity while the transmitted optical signal still has sufficient intensity for subsequent module processing.

[0107] Manufacturing process

[0108] Bragg grating structure is fabricated on the waveguide using electron beam lithography technology. Electron beam lithography has high precision characteristics, which can accurately define the line width and period of the grating. During the lithography process, the dose and scanning speed of the electron beam are accurately controlled to ensure the accuracy and clarity of the grating pattern. The electron beam dose is generally between 100-500μC / cm 2 , and the scanning speed is adjusted according to the complexity and accuracy requirements of the grating, usually between 1-10μm / s.

[0109] After lithography, plasma etching process is carried out to transfer the grating pattern to the waveguide material. The etching gas is selected as fluorine-based gas (such as CF4, CHF3, etc.), and by accurately controlling the flow, pressure and etching time of the etching gas, the waveguide material is accurately etched to form a Bragg grating with periodic structure. The etching gas flow can be between 20-100sccm, the pressure is maintained at 10-100Pa, and the etching time is determined according to the etching depth and etching rate, usually between a few minutes to tens of minutes. After etching, the waveguide is cleaned to remove residual etching gas and impurities, ensuring the cleanliness and flatness of the grating surface.

[0110] 2.2 Phase-shift grating design and integration

[0111] Parameter determination

[0112] The key parameters of the phase-shift grating are determined, with the phase-shift length set to 150nm and the phase adjustment accuracy of 0.01 degrees. These parameters are crucial for accurately adjusting the phase of the optical signal, optimizing the optical interference effect and improving the accuracy of gas detection. The determination of phase-shift length and phase adjustment accuracy is based on in-depth research on the principle of light interference and a large number of simulation calculations to ensure that the phase-shift grating can play the best role in phase adjustment in the system.

[0113] According to the overall optical layout of the system and the requirements for phase adjustment of the optical signal, the appropriate phase-shift method is selected, such as changing the refractive index or geometric structure of the grating to achieve phase shift. For example, different materials can be introduced at specific positions of the grating or the grating line width can be changed to achieve precise phase shift.

[0114] Fabrication process

[0115] The phase-shift grating is also fabricated using electron beam lithography and plasma etching process. During the electron beam lithography process, according to the design pattern of the phase-shift grating, the exposure position and dose of the electron beam are accurately controlled to form a photoresist pattern with a specific phase-shift structure. The exposure dose is generally between 50-300μC / cm 2 , and the exposure position accuracy is controlled at the nanometer level.

[0116] Then, plasma etching is performed to transfer the photoresist pattern to the waveguide, forming the phase-shifted grating structure. During etching, the etching rate and uniformity are closely monitored to ensure the accuracy and stability of the phase-shifted regions. After etching, a strict cleaning and inspection process is carried out to remove residual photoresist and impurities, ensuring the quality of the phase-shifted grating.

[0117] 2.3 Mach-Zehnder interferometer design and integration

[0118] Structural design

[0119] The structure of the Mach-Zehnder interferometer is designed, and parameters such as the length difference of the two interference arms and the waveguide width are determined. The selection of the length difference of the interference arms is based on the theoretical analysis of the relationship between the optical path difference and the interference effect, and is generally determined according to the range of optical path changes caused by the concentration changes of the gas to be detected. For example, in order to be able to detect small changes in gas concentration, the length difference of the interference arms is selected to be between a few microns and a few tens of microns. Through precise calculation and simulation, the length difference that can make the interferometer have the highest sensitivity to the concentration change of the gas is found. The design of the waveguide width takes into account the transmission mode and loss of the optical signal in the waveguide, and is generally between 1-5μm. By optimizing the waveguide width, efficient transmission and stable interference of the optical signal in the interferometer are ensured.

[0120] The input and output coupling structures of the interferometer are designed to ensure that the optical signal can enter and leave the interferometer efficiently. Directional couplers or multimode interference couplers are used, and the parameters of the coupler such as coupling length and waveguide spacing are precisely calculated and optimized to achieve high coupling efficiency and low insertion loss. The coupling length is generally between a few tens of microns and a few hundred microns, and the waveguide spacing is between a few hundred nanometers and a few microns. Through simulation and experimental optimization, the input optical signal can be uniformly distributed to the two interference arms, and the interference signal can be effectively output after interference.

[0121] Fabrication process

[0122] The Mach-Zehnder interferometer structure is fabricated on the waveguide chip using photolithography and etching processes. During photolithography, precise alignment and exposure are performed to form the patterns of the two interference arms and the coupling structure of the interferometer. The exposure accuracy is controlled at the sub-micron level to ensure the accuracy of the length difference of the interference arms and the coupling structure.

[0123] The etching process uses the same plasma etching technology as the previous waveguide fabrication to transfer the lithography pattern to the waveguide material, forming a Mach-Zehnder interferometer with precise structure. During etching, the etching depth and sidewall perpendicularity are strictly controlled to ensure the performance of the interferometer. After etching, cleaning and surface treatment are performed to remove residual impurities and optimize the waveguide surface quality to reduce the loss of the optical signal in the interferometer.

[0124] 2.4 Micro-ring resonator design and integration

[0125] Parameter determination

[0126] The key parameters of the micro-ring resonator are determined, with the micro-ring radius set to 10 μm and the coupling gap set to 100 nm. These parameters are selected based on theoretical research and simulation analysis of the resonant characteristics of the micro-ring resonator and the coupling efficiency with the waveguide. The micro-ring radius affects the resonant wavelength and the quality factor (Q value). A smaller radius can make the resonator more compact, but may reduce the Q value; a larger radius can improve the Q value, but will increase the chip size. By weighing the pros and cons, a micro-ring radius of 10 μm is chosen, which can ensure a certain Q value and keep the chip size within a reasonable range. The size of the coupling gap directly affects the coupling efficiency between the micro-ring and the waveguide. After multiple simulations and experiments, a coupling gap of 100 nm is determined, which can ensure high coupling efficiency while avoiding excessive coupling that leads to signal loss and mode hybridization.

[0127] The resonant wavelength of the micro-ring resonator is calculated based on the geometric parameters of the micro-ring and the refractive index of the waveguide material using the optical resonance theory formula. The accuracy of the resonant wavelength is crucial for the application of the micro-ring resonator in gas detection, because gas adsorption will cause changes in the refractive index of the waveguide, leading to a shift in the resonant wavelength. By accurately calculating the resonant wavelength, the gas concentration can be detected based on the amount of shift.

[0128] Fabrication process

[0129] The micro-ring resonator is fabricated using electron beam lithography and plasma etching processes. During the lithography process, the exposure path of the electron beam is precisely controlled to form a circular micro-ring pattern and the waveguide coupling part connected to it. The control of exposure dose and speed ensures the roundness and size accuracy of the micro-ring, with a roundness error controlled within nanometers and a size accuracy within ±0.1 μm.

[0130] During the plasma etching process, the etching parameters are optimized for the characteristics of the micro-ring structure to ensure smooth and flat sidewalls of the micro-ring and accurate etching depth. The etching gas flow, pressure, and time are adjusted according to the waveguide material and micro-ring structure, for example, the etching gas flow is between 30-80 sccm, the pressure is between 20-80 Pa, and the etching time is determined based on the etching depth and rate, generally between a few minutes and tens of minutes. After etching, cleaning and inspection are performed to remove residual impurities and ensure the optical performance of the micro-ring resonator.

[0131] 3. Coating of intelligent responsive materials

[0132] 3.1 Material selection and preparation

[0133] According to the type of gas to be detected, a metal-organic framework (MOF) material with high selective adsorption and good optical response characteristics is selected. MOF materials have unique porous structures and adjustable chemical compositions, enabling them to strongly interact with specific gas molecules, thus achieving high sensitivity detection of gases. For example, for methane detection, a MOF material with appropriate pore size and chemical active sites can be selected, such as a copper-based MOF material (Cu-BTC), which has good adsorption performance for methane; for carbon dioxide detection, a MOF material with high affinity for carbon dioxide can be selected, such as a zinc-based MOF material (Zn-MOF-74).

[0134] The selected MOF material is prepared into a solution form to facilitate coating on the waveguide surface. The choice of solvent is based on the properties of the MOF material, and common solvents include methanol, ethanol, dimethylformamide (DMF), etc. The solution concentration is adjusted according to the coating process and performance requirements of the MOF material, generally between 0.1-10 mg / mL. Too high a concentration may result in excessive solution viscosity, leading to uneven coating; too low a concentration may affect the adsorption amount of the MOF material on the waveguide surface and the optical response effect. When preparing the solution, a magnetic stirrer or ultrasonic oscillator is used to ensure that the MOF material is fully dissolved, ensuring the uniformity of the solution.

[0135] 3.2 Coating process

[0136] The MOF solution is uniformly coated on the waveguide surface using the spin coating method. Spin coating is a simple and effective thin film coating technique that can form a uniform, thickness-controllable MOF film on the waveguide surface. The waveguide sample is fixed on the sample stage of the spin coater, and an appropriate amount of MOF solution is added to the waveguide surface using a microsyringe. The amount of solution added is calculated based on the area of the waveguide and the concentration of the solution, generally 10-100 μL of solution per square centimeter of waveguide surface. When adding the solution, ensure that the solution is evenly distributed on the waveguide surface to avoid local accumulation or flow.

[0137] The rotation speed and time of the spin coater are set, generally between 500-5000 rpm and 30-120 seconds, respectively. During the spin coating process, as the spin coater rotates, the solution spreads to the edge of the waveguide under the action of centrifugal force and gradually thins out, while the solvent begins to evaporate, eventually forming a uniform MOF film on the waveguide surface. The rotation speed directly affects the thickness and uniformity of the film, with higher rotation speeds resulting in thinner and more uniform films, but excessively high rotation speeds may cause the solution to splash and the film to be defective; the time control ensures that the solvent has enough time to evaporate, allowing the MOF film to stably adhere to the waveguide surface.

[0138] 3.3 Thermal treatment

[0139] The coated waveguide sample is subjected to heat treatment, which is crucial for improving the adhesion and stability of the MOF material on the waveguide surface. Heat treatment can promote physical or chemical interactions between the MOF material and the waveguide surface, making the MOF film more firmly bonded to the waveguide surface, while removing residual solvents in the film and improving the crystallinity and optical properties of the film.

[0140] The waveguide sample coated with the MOF film is placed in an oven for heat treatment at an appropriate temperature. The heating temperature is determined according to the properties of the MOF material, generally between 50-200℃. For some MOF materials with good thermal stability, a higher heat treatment temperature (such as 150-200℃) can be chosen to enhance their bonding force with the waveguide surface; while for MOF materials with poor thermal stability, a lower temperature (such as 50-100℃) is used to avoid material decomposition or structural damage. The heating time is generally 1-5 hours, and too short time may not achieve the desired effect, while too long time may adversely affect the MOF material or waveguide structure. During heat treatment, the atmosphere in the oven can be selected according to the requirements of the MOF material, generally air or inert gas (such as nitrogen) atmosphere. After heat treatment, the waveguide sample is naturally cooled to room temperature in the oven to avoid film cracking or peeling due to sudden temperature drop.

[0141] 4. Topological protection edge state design

[0142] 4.1 Selection and introduction of topological insulator material

[0143] Select appropriate topological insulator materials such as mercury telluride (HgTe), bismuth antimony alloy (BiSb), etc. These materials have special electronic band structures that can support the transmission of topologically protected edge states. According to the waveguide structure and performance requirements, determine the introduction method of the topological insulator material. Epitaxial growth technology can be used to grow a topological insulator film layer in a specific area of the waveguide structure.

[0144] During epitaxial growth, accurately control growth temperature, pressure, reaction gas flow, etc. to obtain high-quality, uniform topological insulator films. For example, for the growth of HgTe films, the growth temperature can be controlled between 180-250℃, and the pressure is between 10-100Pa. Use tellurium source (such as Te2) and mercury source (such as Hg) as reaction gas, adjust the gas flow ratio and growth time to obtain a film layer with a thickness of 50-200nm. During growth, techniques such as reflection high-energy electron diffraction (RHEED) can be used to monitor the growth quality and crystal structure of the film in real time, ensuring that it meets expectations.

[0145] 4.2 Waveguide edge design

[0146] A waveguide edge structure is designed to support the transmission of topologically protected edge states. By changing the geometry and material composition of the waveguide edge, the optical signal is guided to transmit along the edge state. For example, a sawtooth or trapezoidal waveguide edge structure can be used to make the energy distribution of the edge state more concentrated in the edge region, reducing the scattering of optical signals to the interior of the waveguide.

[0147] At the interface between the waveguide edge and the topological insulator material, optimization is performed to ensure good electrical and optical contact. Surface treatment processes such as plasma treatment, chemical modification, etc. can be used to improve the flatness and adhesion of the interface, reduce interface scattering and loss. Plasma treatment can use oxygen plasma or argon plasma to remove surface contaminants and activate surface atoms, enhancing the bonding force with the topological insulator material. Chemical modification can use self-assembled monolayer (SAM) technology to form an organic molecular layer on the surface of the waveguide edge, improving the chemical properties of the interface and promoting the formation and stable transmission of topologically protected edge states.

[0148] 4.3 Performance testing and optimization

[0149] The performance of the waveguide structure with topologically protected edge states is tested, and the main test indicators include scattering loss, transmission efficiency and tolerance to environmental noise of optical signals. The transmission loss of optical signals in the waveguide is measured by experiment, and compared with the waveguide structure without topologically protected edge states to evaluate the effect of topologically protected edge states on reducing loss.

[0150] Optical time domain reflectometer (OTDR) and other equipment are used to measure the transmission loss and reflection of optical signals in the waveguide, and analyze the influence of topologically protected edge states on the transmission characteristics of optical signals. At the same time, the performance of the waveguide is tested under different environmental noise conditions (such as electromagnetic interference, temperature fluctuation, etc.), and the stability of the optical signal is observed. According to the test results, the parameters of the topological insulator material (such as thickness, doping concentration, etc.) and the design of the waveguide edge structure are further optimized. For example, if the scattering loss is still large, the thickness of the topological insulator film or the curvature radius of the waveguide edge can be adjusted to improve the performance of the topologically protected edge state. Through multiple tests and optimization, the waveguide structure with topologically protected edge states can achieve lower loss, higher transmission efficiency and stronger environmental anti-interference ability.

[0151] 5. Optical signal acquisition and processing

[0152] 5.1 Spectrometer selection and setting

[0153] A high-resolution, wide-wavelength range, and high-sensitivity optical spectrum analyzer is selected to ensure accurate measurement of the spectral characteristics of the optical signal. The resolution needs to reach the nanometer level, such as 0.1 nm, to accurately distinguish the slight changes in the wavelength of the optical signal; the wavelength range covers the wavelength range of the optical signal involved in the system, such as 1500-1600 nm, to meet the detection needs of different wavelength optical signals; and high sensitivity ensures that weak changes in the optical signal can be detected, with a minimum detectable optical power of nanowatt level.

[0154] Before using the optical spectrum analyzer, parameters are set according to the working wavelength and measurement accuracy requirements of the system. The center wavelength is set to 1550 nm (consistent with the system design wavelength), and the scanning range is set to 1530-1570 nm to cover the wavelength shift range that may be caused by factors such as gas adsorption. The scanning step is set to 0.05 nm to ensure that detailed spectral information can be obtained within this range. At the same time, a suitable integration time, such as 1 second, is set to balance the measurement speed and signal-to-noise ratio, improving the accuracy of the measurement.

[0155] 5.2 Optical signal acquisition

[0156] The optical spectrum analyzer is connected to the output end of the waveguide array module through an optical fiber to ensure the coupling efficiency between the optical fiber and the waveguide. A high-precision optical fiber coupler is used, with an alignment accuracy of sub-microns, to reduce the loss of optical signals during coupling. During the connection process, attention should be paid to the cleanliness and integrity of the optical fiber end face to avoid factors such as dust and scratches affecting the transmission of optical signals.

[0157] When the sensor system is working, the optical signal is transmitted in the waveguide and interacts with the intelligent response material coated on the surface of the waveguide, and then output from the waveguide array. The optical spectrum analyzer collects the spectral data of the output optical signal in real time, recording the optical power values at different wavelengths. In order to improve the accuracy and reliability of the measurement, multiple measurements (such as 10 times) are performed on each waveguide structure, and the average value is taken as the optical signal spectral data of the waveguide structure.

[0158] 5.3 Data processing and analysis

[0159] Feature extraction

[0160] The collected spectral data is pre-processed to remove noise and outliers. Filtering algorithms such as median filtering or mean filtering are used to smooth the spectral curve and reduce random noise interference during measurement. Then, feature parameters related to gas detection are extracted from the spectral data. These feature parameters include spectral peak position, peak intensity, full width at half maximum (FWHM), and optical power change rate at different wavelengths, etc.

[0161] For example, for the waveguide Bragg grating module, attention is paid to the change in the peak position of its reflection spectrum, because gas adsorption will cause the refractive index of the waveguide to change, thereby causing the peak of the reflection spectrum to shift; for the micro-ring resonator module, the intensity change of its resonance peak and the shift of its resonance wavelength are analyzed, the intensity change of the resonance peak is related to the optical signal loss caused by gas molecule adsorption, and the shift of the resonance wavelength directly reflects the change of the refractive index of the waveguide.

[0162] Model establishment and training

[0163] A mathematical model can be established according to the extracted characteristic parameters for predicting the gas concentration. For example, a multiple linear regression model is used, different characteristic parameters are taken as independent variables, and the gas concentration is taken as the dependent variable. A large amount of experimental data is used for fitting to determine the coefficients of the model. Or a more complex nonlinear model such as an artificial neural network model is constructed, which has strong nonlinear mapping ability and can model the complex relationship between the gas concentration and the optical signal characteristics.

[0164] If a neural network model is used, the network structure is determined, such as the number of input layer nodes is determined according to the number of characteristic parameters (assuming that 5 characteristic parameters are extracted, then the input layer node is 5), the number of output layer nodes is the number of gas species to be detected (such as detecting methane and carbon dioxide, then the output layer node is 2), the number of hidden layers and nodes is determined by experimental optimization. The training set data is used to train the model, and appropriate optimization algorithms (such as gradient descent algorithm, Adam algorithm, etc.) and loss functions (such as mean square error function) are used to continuously adjust the model parameters and improve the prediction accuracy of the model.

[0165] 5.4 Gas concentration calculation and determination

[0166] According to the established model or directly using the empirical relationship between the characteristic parameters and the gas concentration, the concentration of the gas to be measured is calculated. If a mathematical model is used, the extracted characteristic parameters are substituted into the model formula to obtain the predicted value of the gas concentration. For different waveguide structure modules, the final gas concentration is calculated according to their contribution and characteristics to gas detection.

[0167] For example, the measurement results of the waveguide Bragg grating module and the phase shift grating module can be used to assist in determining the gas species, and the measurement data of the micro-ring resonator module and the Mach-Zehnder interferometer module are mainly used to calculate the gas concentration. By comparing the calculation results with the preset concentration threshold, it is determined whether the gas concentration is over standard or within the normal range. At the same time, error analysis is performed on the calculation results to evaluate the accuracy of the measurement. The sources of error may include the measurement error of the spectrum analyzer, the model error, the loss in the process of optical signal transmission, etc. By continuously optimizing the measurement and calculation process, the error is reduced and the detection accuracy is improved.

[0168] 6. Signal processing and multi-gas separation

[0169] 6.1 Independent waveguide channel design and optimization

[0170] Multiple independent waveguide channels are designed for different gas detection needs. Each waveguide channel is coated with a smart responsive material that selectively adsorbs specific gases, such as the previously mentioned MOF materials. The size (e.g., width, height) and length of the waveguide channel are optimized based on the size, polarity, and other characteristics of the gas molecules to increase the contact probability and adsorption efficiency of the gas molecules with the material.

[0171] For example, for small molecule gases (e.g., methane), relatively narrow waveguide channels can be designed to increase the residence time of the gas molecules within the channel; for large molecule gases (e.g., carbon dioxide), the channel width can be appropriately increased to reduce diffusion resistance. At the same time, the length of the waveguide channel is adjusted so that the gas molecules have sufficient time to interact with the material within the channel, with a general channel length of 1-10 mm. Through simulation calculations and experimental tests, the optimal waveguide channel parameters corresponding to different gases are determined. Simulation calculations can use finite element analysis software to analyze the diffusion behavior and adsorption kinetics of gas molecules in channels of different sizes, providing theoretical guidance for experimental design. Experimental testing involves actually preparing waveguide channels with different parameters to detect their adsorption performance and optical signal response for specific gases, and finding the optimal design scheme.

[0172] 6.2 Signal processing algorithm development

[0173] Signal processing algorithms are developed to achieve simultaneous detection and separation of multiple gas concentrations. The algorithms are designed based on the characteristics of the optical signal changes caused by the adsorption of different gases on the MOF material. First, a mathematical model is established between different gas concentrations and optical signal changes (e.g., light absorption, refraction, resonance frequency shift, etc.).

[0174] Through experimental measurements of various parameter changes in the optical signal before and after adsorption of different concentrations of gas, a mathematical model is established using data fitting methods. For example, for the relationship between light absorption changes and gas concentration, the Lambert-Beer law can be extended to consider the changes in the optical properties of the MOF material after adsorbing the gas, establishing a more accurate model. Then, from the collected optical signals, feature parameters related to gas concentration are extracted, such as spectral peak position, peak intensity, bandwidth, etc. Using multivariate linear regression, principal component analysis (PCA), and other algorithms, these feature parameters are fitted with the established mathematical model to calculate the concentration values of different gases. At the same time, signal separation algorithms such as independent component analysis (ICA) are used to decompose the optical signal changes caused by mixed gases into the contributions of each single gas, achieving separation and detection of multiple gases. During the algorithm development process, a large amount of experimental data is used to verify and optimize the algorithm, ensuring its accuracy and reliability.

[0175] 6.3 Machine Learning Technique Application

[0176] Machine learning techniques are introduced to further improve the accuracy and reliability of signal processing. A large amount of optical signal data of mixed gases with different concentrations is collected, including various gases at different proportions. These data are divided into training and test sets, and machine learning models such as support vector machines (SVM), neural networks, etc. are trained using the training set.

[0177] The input of the machine learning model is the feature parameters of the optical signal, and the output is the concentration value of different gases. Through training, the model can learn the complex relationship between different gas concentration combinations and optical signal features. In actual detection, the real-time collected optical signal features are input into the trained model to obtain accurate gas concentration prediction results. At the same time, machine learning techniques are used to compensate for cross-interference, improving the independence and accuracy of the detection signal. For example, by learning the mutual influence law between different gases, the detection results are corrected to reduce errors caused by gas interaction. By continuously increasing the training data and optimizing the model parameters, the performance of the machine learning model in complex gas environments is improved, making it able to adapt to different working conditions and gas composition changes in detection requirements.

[0178] 7. Reliability Test

[0179] 7.1 Environmental Adaptability Test

[0180] Test system performance under different temperature and humidity conditions to simulate various environmental situations that may be encountered in actual applications. Set the temperature range to -20℃ to 60℃, and the humidity range to 20% RH to 95% RH. Perform gas detection experiments on the sensor system under different temperature and humidity combinations.

[0181] During the test, use standard gas sources to provide gases with known concentrations (such as methane, carbon dioxide, etc.), and observe the measurement accuracy, response time, and stability of the sensor system under different environmental conditions. Record the measurement data and analyze the impact of temperature and humidity changes on system performance. For example, high temperature and high humidity environments may affect the adsorption performance of MOF materials and the optical properties of waveguides, leading to increased measurement errors or longer response times. Through experimental data, determine the performance variation law of the system under different environmental conditions and evaluate its environmental adaptability.

[0182] 7.2 Long-term Stability Test

[0183] Perform long-term stability tests to evaluate the performance changes of the system during long-term operation. Run the sensor system continuously for a certain period of time, such as 1000 hours or more, and use standard gases for calibration and detection at regular intervals (such as every 24 hours), and record the measurement data.

[0184] Analyze the trend of the measured data to observe whether the performance indicators such as sensitivity and accuracy of the system change significantly over time. If performance degradation is found, further analyze the reasons, which may include material aging, component wear, etc. For example, MOF materials may undergo structural changes or adsorption performance decay during long-term use, and the waveguide surface may be contaminated or damaged. According to the test results, take appropriate measures to improve the long-term stability of the system, such as optimizing material selection and improving packaging process, etc.

[0185] 7.3 Anti-interference test

[0186] Test the anti-interference ability of the system, including resistance to electromagnetic interference, vibration interference, etc. In the presence of electromagnetic interference sources (such as strong electromagnetic field equipment nearby), conduct gas detection experiments to observe the stability and accuracy of the system's measurement results. At the same time, apply a certain frequency and amplitude of vibration to the system to simulate the vibration environment in actual application and detect the performance of the system under vibration conditions.

[0187] Through the anti-interference test, evaluate the reliability of the system in a complex interference environment, and provide a basis for its application in harsh environments such as industrial sites. If the system's performance is found to be affected in an interference environment, take appropriate anti-interference measures such as electromagnetic shielding design and vibration reduction structure optimization to improve the system's anti-interference ability and ensure its accurate and stable operation under various interference conditions.

[0188] Example:

[0189] This scheme has been tested in greenhouse gas (such as methane CH4, carbon dioxide CO2) monitoring. Sensor arrays are deployed in agricultural greenhouse sheds and industrial emission areas to detect greenhouse gas emissions in agricultural production and possible leakage sources in industrial processes, such as Figure 4 as shown.

[0190] Agricultural scenario: Sensors are installed on the top of the greenhouse, and by monitoring CH4 and CO2 concentrations in real time, they help agricultural producers optimize ventilation strategies and greenhouse environment management. Industrial scenario: Sensors are used to monitor industrial exhaust emissions, and combined with artificial intelligence algorithms, they upload gas concentration data to the environmental monitoring platform in real time.

[0191] Actual effect

[0192] Sensitivity and accuracy: The detection error rate of CH4 and CO2 is less than ±2% in the concentration range of 5ppm to 100ppm. Under the interference of background gases (such as water vapor), the detection performance remains stable. Environmental adaptability: The system has no significant signal drift under conditions of high humidity (90% RH) and temperature fluctuations (10°C-40°C).

[0193] The above examples are only used to illustrate the technical solutions of the present application, but not limit the same; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced by equivalent ones; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A waveguide array gas sensing system for high sensitivity multi-gas detection, characterized in that, The sensor system comprises a waveguide substrate, a waveguide Bragg grating arranged on the waveguide substrate, a phase-shifted Bragg grating, a microring resonator, a Mach-Zehnder interferometer, a waveguide array channel, an electric field regulation module and a signal processing unit. The topological protection edge state design of the waveguide array channel comprises: The topological insulator material is selected, and the introduction mode of the topological insulator material is determined, including an epitaxial growth technology, so as to grow a topological insulator thin film layer on the waveguide array channel; during the growth process, a reflection high-energy electron diffraction technology is used to monitor the growth quality and crystal structure of the topological insulator thin film layer in real time; the topological insulator material comprises mercury telluride and bismuth antimony alloy; The geometric shape and material composition of the topologically protected edge state are changed to guide the transmission of the optical signal along the topologically protected edge state; the geometric shape comprises a zigzag shape or a trapezoidal shape; the interface between the edge of the waveguide array channel and the topological insulator material is subjected to optimization treatment; the optimization treatment comprises ion plasma treatment and chemical modification; the ion plasma treatment uses oxygen plasma or argon plasma to remove surface contaminants and activate surface atoms; the chemical modification adopts a self-assembled monolayer technology to form an organic molecular layer on the surface of the edge of the waveguide array channel; The waveguide substrate serves as the basic support of the entire sensor system and is located at the bottom layer of the sensor system; the waveguide substrate adopts a silicon substrate, and the waveguide array channel is constructed on the waveguide substrate; The waveguide array channel is etched on the waveguide substrate and comprises an incident waveguide, a first waveguide channel to a sixth waveguide channel arranged in parallel, and a metal-organic framework material coated on the surface of each waveguide channel; wherein: a tunable laser grating coupler and a three-loop polarizer are connected to the incident waveguide; the optical signal in the incident waveguide is divided into two paths and enters the first waveguide channel and the second waveguide channel respectively; the optical signal entering the first waveguide channel is divided into two paths and enters the third waveguide channel and the fourth waveguide channel respectively; the optical signal entering the second waveguide channel is divided into two paths and enters the fifth waveguide channel and the sixth waveguide channel respectively; The waveguide Bragg grating is arranged in a pair on the waveguide substrate, and the pair of waveguide Bragg gratings are respectively used to receive the optical signals in the third waveguide channel and the sixth waveguide channel and modulate the optical signals by using the internal periodic grating structure to output the modulated optical signals S2 and S5; The phase-shifted Bragg grating is arranged in a pair on the waveguide substrate and located on the side of the pair of waveguide Bragg gratings; the pair of phase-shifted Bragg gratings are respectively used to receive the optical signals in the third waveguide channel and the sixth waveguide channel and perform phase adjustment processing on the optical signals to output the adjusted optical signals S1 and S6; The microring resonator is used to receive the optical signal of the fifth waveguide channel and enhance the intensity of the optical signal by using the resonance effect to output the enhanced optical signal S4; The Mach-Zehnder interferometer is used to receive the optical signal of the fourth waveguide channel, the optical signal is divided into two paths and subjected to different optical paths in the Mach-Zehnder interferometer, and then the two paths are combined and interfered to finally output the interfered optical signal S3. The electric field regulation module comprises electrodes distributed on the waveguide substrate; an external electric field is applied through the electrodes to regulate the propagation characteristics of the optical signals transmitted in the waveguide array channels; The optical signals S1 to S6 are converted into electrical signals by the optical power meter and then input into the signal processing unit, which integrates and processes the data to detect the gas concentration; the signal processing unit is also used to control the frequency scanning range of the tunable laser and the read-write speed of the optical power meter; When the waveguide array channel surface is adsorbed to the gas molecules, the refractive index changes due to the different adsorption characteristics of each gas molecule, which causes the signal power density, voltage amplitude and signal frequency of the output optical signals S1 to S6 to change after the optical signals are converted into electrical signals, and the signal processing unit realizes real-time detection of multiple gases according to the changes.

2. The waveguide array gas sensing system for high sensitivity multi-gas detection of claim 1, wherein, A silicon dioxide layer and a silicon nitride layer are sequentially deposited on a silicon substrate.

3. The waveguide array gas sensing system for high sensitivity multi-gas detection of claim 1, wherein, The waveguide thickness of the waveguide Bragg grating is 300 nm, the Bragg grating period is 498 nm, and the design wavelength is 1550 nm.

4. The waveguide array gas sensing system for high sensitivity multi-gas detection of claim 1, wherein, The phase shift length of the phase shift Bragg grating is 498 nm, and the phase adjustment accuracy is 0.01 degrees.

5. The waveguide array gas sensing system for high sensitivity multi-gas detection of claim 1, wherein, The micro-ring radius of the micro-ring resonator is 50 µm, and the coupling gap is 100 nm.

6. A detection method of a waveguide array gas sensing system for high sensitivity multi-gas detection, characterized in that, Comprising: Step 1, place the gas sensor system in the environment to be detected, and connect the incident waveguide in the system to the tunable laser through the grating coupler, single-mode optical fiber and three-ring polarization controller; the six-way optical signals S1 to S6 at the output end of the system are connected to the optical power meter, the optical power meter is connected to the signal processing unit, and the signal processing unit controls the frequency scanning range of the tunable laser and the read-write speed of the optical power meter; Step 2, the optical signals in the incident waveguide are divided into two paths through the multimode interference beam splitter and enter the first waveguide channel and the second waveguide channel; the optical signals in the first waveguide channel are also divided into two beams through the multimode interference beam splitter, one of which enters the phase shift Bragg grating and the waveguide Bragg grating in parallel, and the other enters the Mach-Zehnder interferometer module and is subjected to beam splitting and superposition to form destructive interference or constructive interference, thereby outputting the optical signal S3; The optical signals in the second waveguide channel are divided into two beams through the multimode interference beam splitter, one of which enters the micro-ring resonator, and the other enters the phase shift Bragg grating and the waveguide Bragg grating in parallel, and the two beams are subjected to periodic effective refractive index modulation processing in the phase shift Bragg grating and the waveguide Bragg grating, respectively, and then output the optical signals S5 and S6; Step 3, during the gas detection process, the quality of the output optical signals is adjusted by changing the voltage amplitude applied to the electrodes; Step 4, the signal processing unit receives the optical signals S1 to S6 through the optical power meter, converts them into electrical signals, and determines the type of gas detected by the following detection method: The first kind, when detecting a single gas, the light signals outputted by the six channels of the sensor system during the operation are the same as the template data obtained by detecting the gas in advance; therefore, by comparing the six light signals of the sensor system with the outputted light signals without the adsorbed gas, the type of the detected gas can be determined; The second kind, when multiple gases are adsorbed on the waveguide array channels, the intensity, phase and amplitude of the light signals S1 to S6 need to be regulated, and the transmission coefficient and the transmission spectrum change of the waveguide array channel during the detection of each single gas and mixed gas are determined, and then the transmission spectrum of each single gas in the mixed gas detection is obtained; by testing the single gas and the different proportions of the mixed gas, the center wavelength shift of each waveguide array channel is compared, when the detection spectrum of the single gas is the same as the center wavelength corresponding to the proportion of the single gas in the mixed gas, it is considered that the detected is the light signal of the single gas.

7. The method of claim 6, wherein, The intensity, phase and amplitude of the light signals S1 to S6 are regulated, specifically adjusting the stop band width change, the center wavelength drift and the waveguide coupling coefficient change of the waveguide Bragg grating and the phase shift Bragg grating.

Images