High-sensitivity multi-gas detection waveguide array gas sensing system

Abstract

The invention discloses a waveguide array gas sensing system for high-sensitivity multi-gas detection. The waveguide array gas sensing system comprises a waveguide substrate, and a waveguide Bragg grating, a phase shift Bragg grating, a micro-ring resonator, a Mach-Zehnder interferometer, a waveguide array, an electric field regulation and control module and a signal processing unit which are arranged on the waveguide substrate. Through the waveguide array structure, topological optical protection adsorption and other technologies, the sensitivity and selectivity of methane, carbon dioxide and other gases are effectively improved, and accurate detection can be achieved in a complex environment; according to the invention, a topological optical principle is adopted, signal loss caused by environmental noise or surface defects is reduced, and the stability of the sensor is improved; according to the invention, automatic calibration and temperature and humidity compensation of the system are realized, and autonomy and operation convenience of the system are enhanced; the system has high environment adaptability and can stably work under different temperature and humidity conditions.

Description

Technical Field

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

[0002] With the aggravation of environmental pollution and the increasing requirements for gas detection accuracy in industrial safety and environmental monitoring, traditional gas detection technology has certain limitations in terms of accuracy, selectivity, stability, etc. Optical waveguide gas sensors have the advantages of 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 in the development of technology.

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

[0004] The purpose of the present invention is to provide a waveguide array gas sensor system with high sensitivity for multi-gas detection, which improves the detection sensitivity and selectivity of gases such as methane and carbon dioxide by introducing technologies such as intelligent response material adsorption; at the same time, it combines artificial intelligence algorithms to improve the intelligence of the system.

[0005] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0006] A waveguide array gas sensing system for high-sensitivity multi-gas detection includes 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, an electric field control module, and a signal processing unit; wherein:

[0007] The waveguide substrate is 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 a waveguide array channel is constructed on the waveguide substrate.

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

[0009] A pair of waveguide Bragg gratings is arranged on the waveguide substrate, and the pair of waveguide Bragg gratings are respectively used to receive optical signals in the third waveguide channel and the sixth waveguide channel and modulate the optical signals using the internal periodic grating structure, and then output modulated optical signals S2 and S5;

[0010] A pair of phase-shifted Bragg gratings are arranged on the waveguide substrate, and are respectively located on the sides of a 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, and then output the adjusted optical signals S1 and S6;

[0011] The microring resonator is used to receive the optical signal of the fifth waveguide channel, and after enhancing the intensity of the optical signal by utilizing the resonance effect, output the enhanced optical signal S4;

[0012] The Mach-Zehnder interferometer is used to receive the optical signal of the fourth waveguide channel, and the optical signal is divided into two paths inside the Mach-Zehnder interferometer and then combined and interfered after going through different optical paths, and finally outputs the interfered optical signal S3;

[0013] The electric field control module includes electrodes, which are distributed on the waveguide substrate; an external electric field is applied through the electrodes to control the propagation characteristics of the optical signal transmitted in the waveguide array channel;

[0014] The optical signals S1 to S6 are connected to the signal processing unit after photoelectric conversion by the optical power meter. After data integration processing, the signal processing unit accurately detects the gas concentration. The signal processing unit is also used to control the frequency sweep range of the tunable laser and the reading and writing speed of the optical power meter.

[0015] When gas molecules are adsorbed onto the surface of the waveguide array channel, the refractive index changes differently due to the adsorption exhibited by each gas molecule. As a result, after the optical signals S1 to S6 at the output end are converted into electrical signals, changes in signal power density, voltage amplitude, and signal frequency will occur. The signal processing unit realizes real-time detection of multiple gases based on the changes.

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

[0017] Furthermore, 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] Furthermore, the phase shift length of the phase-shift Bragg grating is 498 nm, and the phase adjustment accuracy is 0.01 degrees.

[0019] Furthermore, the microring radius of the microring resonator is 50 μm, and the coupling gap is 100 nm.

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

[0021] Step 1, placing the gas sensor system in the gas environment to be detected, and connecting the incident waveguide in the system to the tunable laser through a grating coupler, a single-mode optical fiber, and a three-ring polarization controller; six optical signals S1 to S6 at the output end of the system are connected to an optical power meter, the optical power meter is connected to a signal processing unit, and the signal processing unit is used to control the tunable laser sweep range and the optical power meter reading and writing speed;

[0022] Step 2, the optical signal in the incident waveguide is divided into two paths and enters the first waveguide channel and the second waveguide channel through a multimode interference beam splitter; the optical signal in the first waveguide channel is further divided into two beams through the multimode interference beam splitter, one of which enters the phase-shifted Bragg grating and the waveguide Bragg grating in parallel through the third waveguide channel, and performs periodic effective refractive index modulation processing of the light wave respectively therein, and outputs the optical signal S1 and the optical signal S2 after the signal is stabilized; the other beam enters the Mach-Zehnder interferometer module through the fourth waveguide channel, and performs beam splitting and superposition of the light wave therein to form destructive interference or constructive interference processing, thereby outputting the optical signal S3;

[0023] The optical signal in the second waveguide channel is divided into two beams by a multimode interference beam splitter, one of which enters the microring resonator. When the optical path through the microring matches the wavelength of the light, the light will form a standing wave in the microring and undergo resonance processing, and output an optical signal S4; the other light beam enters the phase-shifted Bragg grating and the waveguide Bragg grating in parallel, and after the periodic effective refractive index modulation processing of the light wave is performed respectively, the optical signals S5 and S6 are output;

[0024] Step 3, during the gas detection process, adjusting the quality of the output optical signal by changing the voltage amplitude applied to the electrode;

[0025] Step 4: The signal processing unit receives the optical signals S1 to S6 through an optical power meter, performs photoelectric conversion on them to obtain six electrical signals, and determines the type of gas detected by the following detection method:

[0026] First, when detecting a single gas, the six optical signals that pass through different waveguide channels and are finally output during the operation of the sensor system are the same as the template data obtained in advance for the detection of the gas; therefore, by comparing the six optical signals of the sensor system with the changes in the output optical signals when there is no adsorbed gas, the type of gas detected can be determined;

[0027] The second method is that when multiple gases are adsorbed on the waveguide array channel, it is necessary to regulate the intensity, phase and amplitude of the optical signal S1 to the optical signal S6, and determine the changes in the transmission coefficient and transmission spectrum of the waveguide array channel during the detection of each single gas and mixed gas, and then obtain the transmission spectrum of each single gas in the mixed gas detection; by testing different ratios of single gases and mixed gases, the center wavelength offset of each waveguide array channel is compared. When the detection spectrum of a single gas is the same as the center wavelength corresponding to the ratio of the single gas in the mixed gas, it is considered that the optical signal detected is the single gas.

[0028] Furthermore, the intensity, phase and amplitude of the optical signals S1 to S6 are regulated, specifically, the stopband width change of the waveguide Bragg grating and the phase-shift Bragg grating, the drift of the central wavelength, and the change of the waveguide coupling coefficient are adjusted.

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

[0030] 1. The present invention effectively improves the sensitivity and selectivity of gases such as methane and carbon dioxide through waveguide array structure and topological optical protection adsorption and other technologies, and can achieve accurate detection in complex environments.

[0031] 2. The present invention adopts the principle of topological optics, reduces signal loss caused by environmental noise or surface defects, and improves the stability of the sensor.

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

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

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

[0035] Figure 2is a schematic diagram of the structure of an optical waveguide sensor array;

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

[0037] Figure 4 Optical waveguide sensor array for greenhouse gases (CH 4 and CO 2 ) Test the spectrum effect DETAILED DESCRIPTION

[0038] The present invention provides a waveguide array gas sensing system for high-sensitivity multi-gas detection, which adopts the comprehensive integration of multiple optical and sensing technologies; its 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 control module. Each module works together to form an efficient multi-gas detection system, such as Figure 1 and Figure 2 The structural principle, working process and preparation process of the present invention are described in detail below with reference to the accompanying drawings.

[0039] 1. Structural design

[0040] See attached Figure 2 The present invention provides 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 microring resonator, a Mach-Zehnder interferometer, a waveguide array, an electric field control module, and a signal processing unit; wherein:

[0041] 1. Waveguide substrate

[0042] The waveguide substrate is the basic support of the entire sensor system and is located at the bottom layer of the sensor system; Figure 3 As shown in (b), the waveguide substrate adopts a silicon substrate, and a 3μm silicon dioxide layer and a 300nm silicon nitride layer are sequentially deposited on the silicon substrate; a 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. 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 close integration with the upper optical elements (such as Bragg gratings, phase shift gratings, etc.) to form a unified optical transmission system.

[0044] 2. Waveguide array channel

[0045] The waveguide array channel is etched and formed on the waveguide substrate. The waveguide array channel includes an incident waveguide, a first waveguide channel to a sixth waveguide channel arranged in parallel. The surface of each waveguide channel is coated with an intelligent response material; wherein:

[0046] The tunable laser is connected to the incident waveguide through a grating coupler and a three-ring polarizer; the optical signal in the incident waveguide is divided into two paths, entering the first waveguide channel and the second waveguide channel respectively; the optical signal entering the first waveguide channel is divided into two paths, entering the third waveguide channel and the fourth waveguide channel respectively; the optical signal entering the second waveguide channel is divided into two paths, entering the fifth waveguide channel and the fourth and sixth optical paths 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 the smart response material MOF, and the smart response material is used to selectively adsorb specific gases to improve the sensitivity and selectivity of gas detection.

[0048] 3. Waveguide Bragg Grating

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

[0050] Based on the principle of optical interference, the waveguide Bragg grating detects the changes in absorption and refraction characteristics caused by the interaction between different gases and light signals, thus providing a basis for determining the type and concentration of the gas. Figure 2 In the figure, 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, directly interacting with the optical signal and modulating it.

[0051] 4. Phase-Shifted Bragg Grating

[0052] A pair of phase-shifted Bragg gratings are arranged on the waveguide substrate, respectively located on the sides of a pair of waveguide Bragg gratings; the pair of phase-shifted Bragg gratings are respectively used to receive optical signals in the third waveguide channel and the sixth waveguide channel and perform phase adjustment processing on the optical signals, and then output adjusted optical signals S1 and S6.

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

[0054] 5. Microring Resonator

[0055] The microring resonator is used to receive the optical signal of the fifth waveguide channel, and after enhancing the intensity of the optical signal by utilizing the resonance effect, output the enhanced optical signal S4; in this scheme, the microring radius of the microring resonator is 50 μm, and the coupling gap is 100 nm.

[0056] When the optical signal passes through the microring resonator, the resonance effect is used to enhance the intensity of the optical signal, so that the optical signal can be effectively amplified when passing through this area, thereby improving the sensitivity of the entire system to gas detection.

[0057] 6. Mach-Zehnder Interferometer

[0058] The Mach-Zehnder interferometer is used to receive the optical signal of the fourth waveguide channel. The optical signal is divided into two paths inside the interferometer and then combined and interfered after passing through different optical paths, and finally the interfered optical signal S3 is output.

[0059] The Mach-Zehnder interferometer in this scheme is an interferometer with two equal arms, so the corresponding interference fringes are constructive interference, and the light intensity corresponding to it is the largest and most stable interference intensity. Because when the phase difference is zero, the interference pattern will not change with time, and the output light intensity will not fluctuate. Information related to the gas is obtained based on the interference results.

[0060] 7. Electric field control module

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

[0062] 8. Signal processing unit

[0063] Optical signals S1 to S6 are photoelectrically converted by an optical power meter and then connected to a 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 sweep range of the tunable laser and the reading and writing speed of the optical power meter.

[0064] When gas molecules are adsorbed onto the surface of the waveguide array channel, the refractive index changes differently due to the adsorption exhibited by each gas molecule. As a result, after the optical signals S1 to S6 at the output end are converted into electrical signals, changes in signal power density, voltage amplitude, and signal frequency will occur. The signal processing unit realizes real-time detection of multiple gases based on the changes.

[0065] 2. Working Principle

[0066] The high-sensitivity multi-gas sensor system of the present invention combines a variety of optical principles and achieves precise detection through multiple independently working optical modules. The waveguide substrate includes a silicon dioxide layer (3μm) and a silicon nitride layer (300nm), the waveguide array channel module is etched on the silicon nitride, and the waveguide array channel module is coated with a metal organic framework (MOF) material. When the optical signal is transmitted in the waveguide, the MOF material adsorbs the gas molecules, causing changes in their 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, which reduces environmental noise interference and enhances signal stability.

[0067] Specifically, the waveguide Bragg grating triggers the diffraction effect of light through the periodic structure, sensing the refractive index change caused by the gas; the phase-shifted Bragg grating uses the light phase adjustment to accurately capture the optical property changes of the gas; the microring resonator enhances the interaction between gas and light through the resonance phenomenon and improves the sensitivity; the Mach-Zehnder interferometer amplifies the tiny signal changes caused by the change of gas concentration through the interference effect. Each module works independently and processes the optical signal in coordination, and finally integrates the data through the signal processing unit, and accurately detects the gas concentration through the intelligent algorithm.

[0068] The sensor system is placed in the environment to be detected. Since optical waveguide sensors are often used to detect changes in the refractive index of the substance to be detected or the environment, when the evanescent wave on the waveguide surface of the optical waveguide sensor contacts the substance to be detected, the change in the refractive index of the substance to be detected will cause the field intensity of the evanescent wave to change. In turn, the evanescent wave causes the intensity 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 changes in temperature, pressure or chemical composition), it may cause the intensity or phase of light propagation to change. Therefore, it can be sensed by monitoring the output light intensity, wavelength or propagation phase. When the surface of the waveguide sensor is modified with porous metal organic compound materials, the sensing detection mechanism is as follows:

[0069] ① After gas molecules enter the pore structure of MOF materials, they will interact with the metal center or organic ligand in MOF. These interactions cause changes in the electron density and local refractive index of MOF materials. Because the light propagation characteristics in the optical waveguide (such as propagation speed, phase and reflectivity, etc.) are closely related to the refractive index of the waveguide medium, when the refractive index of the MOF material changes, the light 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 MOF surface will cause changes in the local refractive index, thereby affecting the light propagation path or reflection characteristics, which can then be detected by the sensor.

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

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

[0072] 3. Working Process

[0073] See attached Figure 2 , the working process of the present invention is as follows:

[0074] Step 1, placing the gas sensor system of the present invention in a gas environment such as carbon dioxide and methane, and connecting the incident waveguide in the system to a tunable laser through a grating coupler, a single-mode optical fiber (SMF-28e), and a three-ring polarization controller; six optical signals S1 to S6 at the output end of the system are connected to an optical power meter, and the optical power meter is connected to a signal processing unit (computer side) by writing a LabView control program, and the signal processing unit controls the tunable laser sweep range and the optical power meter reading and writing speed.

[0075] Step 2, the optical signal in the incident waveguide is divided into two paths and enters the first waveguide channel and the second waveguide channel through a multimode interference beam splitter; the optical signal in the first waveguide channel is further divided into two beams through the multimode interference beam splitter, one of which enters the phase-shifted Bragg grating and the waveguide Bragg grating in parallel through the third waveguide channel, and performs periodic effective refractive index modulation processing of the light wave respectively therein, and outputs the optical signal S1 and the optical signal S2 after the signal is stabilized; the other beam enters the Mach-Zehnder interferometer module through the fourth waveguide channel, and performs beam splitting and superposition of the light wave therein to form destructive interference or constructive interference processing, thereby outputting the optical signal S3;

[0076] The optical signal in the second waveguide channel is divided into two beams by a multimode interference beam splitter, one of which enters the microring resonator. When the optical path through the microring (i.e., the propagation distance of the light wave in the microring) matches the wavelength of the light, the light will form a standing wave in the microring and undergo resonance processing, and output an optical signal S4; the other light beam enters the phase-shifted Bragg grating and the waveguide Bragg grating in parallel, where the periodic effective refractive index modulation of the light wave is respectively performed, and then outputs an optical signal S5 and an optical signal S6.

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

[0078] Specifically, by applying voltage through electrodes and adjusting the voltage amplitude, the carrier dispersion effect in the optical waveguide is affected, causing the hole and electron pairs to change, thereby generating carrier diffusion between holes and electrons. 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, performs photoelectric conversion on them to obtain six electrical signals, and determines the type of gas detected by the following detection method:

[0080] The first one is that when a single gas is detected, the six optical signals that pass through different waveguide channels and are finally output during the operation of the sensor system are the same as the template data obtained in advance for the detection of the gas, that is, 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 when there is no adsorbed gas, the type of gas detected can be determined.

[0081] The second type is that when multiple gases are adsorbed on the waveguide array channel, the intensity, phase and amplitude of the optical signal S1 to the optical signal S6 need to be regulated; specifically, the stopband width change of the waveguide Bragg grating and the phase-shift Bragg grating, the drift of the central wavelength, the change of the waveguide coupling coefficient, and the change 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 different ratios of single gases and mixed gases, the central wavelength offset of each waveguide array channel is compared, and when the detection spectrum of the single gas is the same as the central wavelength corresponding to the ratio of the single gas in the mixed gas, it is considered that the detected optical signal is the single gas.

[0082] The work of the sensor starts with signal acquisition, and the signal reception 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 each subsequent module. The sensor system is placed in the environment to be detected, because optical waveguide sensors are often used to detect changes in the refractive index of the measured material or environment. When the evanescent wave on the surface of the waveguide of the optical waveguide sensor contacts the gas molecules, the change in the refractive index of the material will cause the field intensity of the evanescent wave to change, and in turn the evanescent wave causes the intensity phase of the propagating light in the waveguide sensor to change. When light propagates through the waveguide, if the environment near the waveguide changes (such as changes in temperature, pressure or chemical composition), it may cause the intensity or phase of the light propagation to change. Therefore, it can be sensed by monitoring the output light intensity, wavelength or propagation phase.

[0083] 4. Preparation process

[0084] 1. Waveguide structure preparation

[0085] 1.1 Substrate preparation

[0086] First, high-quality silicon wafers are selected as the substrate material for the preparation of waveguide structures. The quality of the silicon wafer directly affects the quality and performance of the subsequent waveguide growth, so it is necessary to ensure that its surface is flat, the crystal structure is complete and has no obvious defects. Before use, the silicon wafer is strictly inspected for quality. The surface roughness can be measured by atomic force microscopy (AFM) to ensure that it is less than a certain value (such as 1nm). At the same time, the crystal structure is analyzed by X-ray diffraction (XRD) to ensure that it meets the standards.

[0087] The qualified silicon wafers are subjected to a standard cleaning process. This process is crucial for removing various contaminants on the surface of the silicon wafer, because even trace amounts of impurities may affect the quality of subsequent thin film deposition and waveguide production. The cleaning process begins with rinsing with a large amount of deionized water, the purpose of which is to initially remove large particles of dust and water-soluble impurities on the surface of the silicon wafer. Then, the silicon wafers are placed in organic solvents such as acetone and ethanol for ultrasonic cleaning. Ultrasonic cleaning uses the powerful impact force generated by the cavitation effect of ultrasonic waves in liquids to effectively remove grease, organic pollutants and some tiny particles adsorbed on the surface of the silicon wafer. The time for ultrasonic cleaning in acetone can be set to 10-15 minutes, and the time for ultrasonic cleaning in ethanol is also 10-15 minutes. The ultrasonic frequency is selected between 20-40kHz to achieve the best cleaning effect. After cleaning, the silicon wafer is blown dry with high-purity nitrogen to avoid re-adsorption of impurities during the natural drying process in the air.

[0088] 1.2 Thin film deposition

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

[0090] First, a 300nm thick silicon layer is grown as the lower waveguide. During the deposition of the silicon layer, silane (SiH 4 ) as silicon source gas, hydrogen (H 2 ) as a carrier gas. Silane decomposes under the reducing effect of high temperature and 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. This temperature range is conducive to the decomposition of silane and the diffusion of silicon atoms, ensuring the growth uniformity and crystallization quality of the silicon layer. The reaction pressure is maintained at 100-500Pa, and the growth rate of the silicon layer is controlled by precisely adjusting the flow ratio of silane and hydrogen. Generally, the silane flow rate can be set at 10-50sccm, and the hydrogen flow rate is between 100-500sccm, so that the growth rate is kept within a stable range (such as 0.1-0.5nm / s), thereby obtaining a silicon layer with uniform thickness and good quality.

[0091] Then, a 100 nm thick silicon dioxide layer was grown on the silicon layer as the intermediate active layer. Plasma enhanced chemical vapor deposition (PECVD) technology was used, tetraethoxysilane (TEOS) was used as the silicon source, and oxygen (O 2) as the reaction gas. Deposition is carried out under the conditions of RF power of 100-300W and temperature of 300-400℃. The role of RF power is to excite plasma, enhance the activity of the reaction gas, and promote the deposition reaction of silicon dioxide. Temperature control is crucial to the decomposition of TEOS and the formation rate of silicon dioxide. Within this temperature range, the growth quality and uniformity of the silicon dioxide layer can be guaranteed. By adjusting the TEOS and O 2 The growth rate of the silicon dioxide layer can be precisely controlled by adjusting the flow rate. The TEOS flow rate can be between 5-20 sccm. 2 The flow rate is between 50-200sccm, and the film thickness is monitored in real time to ensure that the design requirement of 100nm is met.

[0092] Finally, a 200nm thick silicon nitride layer is grown on the silicon dioxide layer as the upper waveguide. The PECVD method is also used to deposit silane (SiH 4 ) and ammonia (NH 3 ) is the reaction gas. Deposition is carried out under the conditions of temperature of 250-350℃, pressure of 200-500Pa, and RF power of 150-350W. Silane and ammonia react in a plasma environment to generate silicon nitride, which is deposited on the silicon dioxide layer. The flow ratio of the reaction gases is accurately controlled. The silane flow rate is generally 5-15sccm, the ammonia flow rate is between 30-100sccm, and the deposition time is also controlled to ensure a silicon nitride layer with uniform thickness and good quality. The surface roughness also needs to be controlled within a small range (such as less than 0.5nm) to provide a good foundation for subsequent photolithography processes.

[0093] 1.3 Lithography and Etching

[0094] After the silicon nitride layer is deposited, a photolithography process is performed to define the geometric structure of the waveguide. The photolithography process is a key step in 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, spin-coat the photoresist on the silicon nitride surface. The type and thickness of the photoresist need to be selected according to the specific photolithography process requirements. Generally, positive photoresist is selected, and its thickness is determined according to the depth and precision requirements of the subsequent etching process, usually between 1-3μm. The spin coating process is carried out on a spin coater. After the photoresist is dropped on the silicon nitride surface, it is rotated at a speed of 1000-3000rpm for 30-60 seconds to evenly coat the photoresist on the silicon nitride surface. The control of rotation speed and time is crucial to the uniformity of the thickness of the photoresist. Too high a rotation speed or too long a time may cause uneven thickness of the photoresist or even edge effects, affecting the accuracy of photolithography.

[0096] Then, the photoresist is exposed using electron beam lithography or ultraviolet lithography. 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 large-scale production. During the exposure process, the exposure dose and time are precisely controlled according to the characteristics of the photoresist and the waveguide design requirements. The exposure dose is generally 10-100mJ / cm 2 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] After exposure, the photoresist is developed to remove the unexposed parts and form a photoresist mask. The choice of developer and development time need to be optimized according to the type of photoresist, and the development time is generally between 30-120 seconds. The development 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 development effect.

[0098] Then, the silicon nitride layer is etched using a plasma etching process with a photoresist mask as protection. The etching gas is a fluorine-based gas (such as CF 4 , SF 6 The active fluorine ions generated by the fluorine-based gas in the plasma environment can react chemically with silicon nitride to remove the unwanted silicon nitride. By precisely adjusting the parameters such as the flow rate of the etching gas, the RF power and the etching time, the etching depth is precisely controlled to reach 200nm to form a waveguide structure. The etching gas flow rate is generally between 20-100sccm, the RF power is between 100-500W, and the etching time is calculated and determined based on 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 interferometry or ellipsometer can be used to ensure the accuracy of the etching depth. After the etching is completed, the photoresist mask is removed, and methods such as oxygen plasma ashing or solvent immersion can be used. Oxygen plasma ashing uses the chemical reaction of oxygen plasma and photoresist to decompose the photoresist into volatile gases 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 to ensure that the waveguide surface is clean.

[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 surface of the waveguide after etching is smoothed. Chemical mechanical polishing (CMP) technology is used, which is a surface treatment method that combines chemical corrosion and mechanical grinding. It can effectively remove tiny defects and roughness on the waveguide surface and make the surface flat at the nanometer level.

[0101] During the CMP process, a specially formulated polishing liquid is used, which contains abrasive particles (such as silica particles), chemical corrosive agents (such as potassium hydroxide, KOH) and buffers. Abrasive particles grind the waveguide surface through mechanical action to remove the protruding parts of the surface; chemical corrosive agents react chemically with the waveguide material to make the surface material easier to remove. At the same time, buffers are used to control the pH value of the polishing liquid to maintain the stability of the chemical corrosion reaction. During the polishing process, the polishing pressure is controlled between 1-5psi, the polishing disc speed is between 50-150rpm, and the polishing liquid flow rate is between 50-200mL / min. Excessive polishing pressure may cause excessive wear on the waveguide surface and affect the structural integrity of the waveguide; the control of the polishing disc speed and the polishing liquid flow rate is crucial to the uniformity and efficiency of polishing. By precisely controlling these parameters, the surface roughness of the waveguide reaches the nanometer level (such as less than 0.5nm), thereby significantly improving the transmission efficiency of the optical signal 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 200nm, the Bragg grating period is 300nm, and the design wavelength is 1550nm. The selection of these parameters is based on the theoretical analysis and simulation calculation of the transmission characteristics of optical signals in the waveguide, aiming to enable the Bragg grating to effectively modulate the optical signal of a specific wavelength to detect the refractive index change caused by the gas.

[0106] Calculate the etching depth of the grating and optimize it 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 transmittance. Generally, the optimal etching depth is determined by simulating the effect of the grating on the optical signal at different etching depths and combining the requirements of reflectivity and transmittance for actual applications. For example, after many simulations, it was found that when the etching depth is between 100-150nm, it can ensure a high reflectivity while still ensuring that the transmitted light signal has sufficient intensity for processing by subsequent modules.

[0107] Production process

[0108] Electron beam lithography is used to make Bragg grating structures on waveguides. Electron beam lithography is characterized by high precision and 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 precisely controlled to ensure the accuracy and clarity of the grating pattern. The electron beam dose is generally 100-500μC / cm 2 The scanning speed is adjusted according to the complexity and accuracy requirements of the grating, usually between 1-10μm / s.

[0109] After the photolithography is completed, a plasma etching process is performed to transfer the grating pattern to the waveguide material. The etching gas is a fluorine-based gas (such as CF 4 , CHF 3 The waveguide material is precisely etched by precisely controlling the flow rate, pressure and etching time of the etching gas to form a Bragg grating with a periodic structure. The etching gas flow rate can be between 20-100 sccm, the pressure is maintained at 10-100 Pa, and the etching time is calculated and determined according to the etching depth and etching rate, generally between a few minutes and tens of minutes. After the etching is completed, the waveguide is cleaned to remove the residual etching gas and impurities to ensure 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, the phase shift length is set to 150nm, and the phase adjustment accuracy is 0.01 degrees. These parameters are crucial for accurately adjusting the phase of the optical signal, which can optimize the optical interference effect and improve the accuracy of gas detection. The determination of the phase shift length and phase adjustment accuracy is based on in-depth research on the principle of optical interference and a large number of simulation calculations to ensure that the phase shift grating can play the best phase adjustment role in the system.

[0113] According to the overall optical layout of the system and the need for phase adjustment of the optical signal, a suitable phase shift method is selected, such as changing the refractive index or geometric structure of the grating to achieve phase shift. For example, precise phase shift can be achieved by introducing different materials at specific positions of the grating or changing the width of the grating lines.

[0114] Production process

[0115] Phase shift gratings are also made by electron beam lithography and plasma etching. In the process of electron beam lithography, the exposure position and dose of the electron beam are precisely controlled according to the design pattern of the phase shift grating to form a photoresist pattern with a specific phase shift structure. The exposure dose is generally 50-300μC / cm 2 The exposure position is controlled at the nanometer level.

[0116] Then plasma etching is performed to transfer the photoresist pattern to the waveguide to form a phase-shift grating structure. During the etching process, close attention is paid to the etching rate and uniformity to ensure the accuracy and stability of the phase-shift region. After the etching is completed, a strict cleaning and inspection process is carried out to remove residual photoresist and impurities to ensure the quality of the phase-shift grating.

[0117] 2.3 Mach-Zehnder interferometer design and integration

[0118] Structural design

[0119] Design the structure of the Mach-Zehnder interferometer and determine parameters such as the length difference between its two interference arms and the waveguide width. The selection of the interference arm length difference 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 changes in gas concentration that need to be detected. For example, in order to be able to detect tiny changes in gas concentration, the interference arm length difference is selected to be between a few microns and tens of microns. Through precise calculation and simulation, find the length difference that enables the interferometer to have the highest sensitivity to changes in gas concentration. The design of the waveguide width must take into account the transmission mode and loss of the optical signal in the waveguide, which is generally between 1-5μm. By optimizing the waveguide width, the 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. Using structures such as directional couplers or multimode interference couplers, the parameters of the coupler, such as coupling length, waveguide spacing, etc., are accurately calculated and optimized to achieve high coupling efficiency and low insertion loss. The coupling length is generally between tens of microns and hundreds of microns, and the waveguide spacing is between hundreds of nanometers and a few microns. Through simulation and experimental optimization, the input optical signal can be evenly distributed to the two interferometer arms, and the interference signal can be effectively output after interference.

[0121] Production process

[0122] The Mach-Zehnder interferometer structure is fabricated on the waveguide chip using photolithography and etching processes. During the photolithography process, 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 length difference of the interference arms and the accuracy of the coupling structure.

[0123] The etching process uses the same plasma etching technology as the previous waveguide production to transfer the photolithography pattern to the waveguide material to form a Mach-Zehnder interferometer with a precise structure. During the etching process, the etching depth and sidewall verticality are strictly controlled to ensure the performance of the interferometer. After the etching is completed, cleaning and surface treatment are carried out to remove residual impurities and optimize the waveguide surface quality to reduce the loss of optical signals in the interferometer.

[0124] 2.4 Microring Resonator Design and Integration

[0125] Parameter determination

[0126] The key parameters of the microring resonator are determined, and the microring radius is set to 10μm and the coupling gap is 100nm. The selection of these parameters is based on theoretical research and simulation analysis of the resonance characteristics of the microring resonator and the coupling efficiency with the waveguide. The radius of the microring 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 increase the Q value, but will increase the chip area. Through trade-offs, a microring radius of 10μm is selected to ensure a certain Q value while keeping the chip size within a reasonable range. The size of the coupling gap directly affects the coupling efficiency between the microring and the waveguide. The coupling gap of 100nm is determined after multiple simulations and experiments. It can ensure a high coupling efficiency while avoiding signal loss and mode hybridization caused by excessive coupling.

[0127] Calculate the resonant wavelength of the microring resonator using the optical resonance theory formula based on the geometric parameters of the microring and the refractive index of the waveguide material. The accuracy of the resonant wavelength is crucial for the application of microring resonators in gas detection, because gas adsorption will cause changes in the refractive index of the waveguide, resulting in a shift in the resonant wavelength. By accurately calculating the resonant wavelength, the gas concentration can be detected based on its shift.

[0128] Production process

[0129] The microring resonator is made by electron beam lithography and plasma etching. During the lithography process, the exposure path of the electron beam is precisely controlled to form a circular microring pattern and a waveguide coupling part connected to it. The exposure dose and speed are controlled to ensure the roundness and dimensional accuracy of the microring. The roundness error is controlled at the nanometer level and the dimensional accuracy is within ±0.1μm.

[0130] During the plasma etching process, the etching parameters are optimized according to the characteristics of the microring structure to ensure that the sidewalls of the microring are smooth and flat, and the etching depth accurately meets the design requirements. The adjustment of the etching gas flow, pressure and time should be optimized according to the waveguide material and the microring structure. For example, the etching gas flow is between 30-80sccm, the pressure is between 20-80Pa, and the etching time is determined according to the etching depth and rate calculation, generally between a few minutes and more than ten minutes. After the etching is completed, it is cleaned and inspected to remove residual impurities and ensure the optical performance of the microring resonator.

[0131] 3. Coating of smart responsive materials

[0132] 3.1 Material selection and preparation

[0133] Depending on the type of gas to be detected, a metal organic framework (MOF) material with highly selective adsorption and good optical response characteristics is selected. MOF materials have a unique porous structure and adjustable chemical composition, which enables them to interact strongly with specific gas molecules, thereby achieving high-sensitivity detection of gases. For example, for methane detection, MOF materials with suitable pore sizes and chemically active sites can be selected, such as copper-based MOF materials (Cu-BTC), which have good adsorption properties for methane; for carbon dioxide detection, MOF materials with high affinity for carbon dioxide are selected, such as zinc-based MOF materials (Zn-MOF-74).

[0134] The selected MOF material is prepared in the form of a solution to facilitate coating on the waveguide surface. The choice of solvent is based on the properties of the MOF material. Commonly used solvents include methanol, ethanol, dimethylformamide (DMF), etc. The solution concentration is adjusted according to the coating process and the performance requirements of the MOF material, generally between 0.1-10 mg / mL. Too high a concentration may cause the solution to be too viscous and unevenly coated; too low a concentration may affect the adsorption amount and optical response effect of the MOF material on the waveguide surface. When preparing the solution, use a magnetic stirrer or an ultrasonic oscillator to fully dissolve the MOF material to ensure the uniformity of the solution.

[0135] 3.2 Coating process

[0136] The MOF solution is evenly coated on the waveguide surface by spin coating. Spin coating is a simple and effective thin film coating technology that can form a uniform MOF film with controllable thickness on the waveguide surface. The waveguide sample is fixed on the sample stage of the spin coater, and a micro-syringe is used to drop an appropriate amount of MOF solution on the waveguide surface. The amount of solution is calculated and determined based on the area of ​​the waveguide and the concentration of the solution. Generally, 10-100 μL of solution is added per square centimeter of the waveguide surface. When adding the solution, it is necessary to ensure that the solution is evenly distributed on the waveguide surface to avoid local accumulation or flow.

[0137] Set the speed and time of the spin coater. The speed is generally between 500-5000rpm and the time is 30-120 seconds. During the spin coating process, as the spin coater rotates, the solution diffuses to the edge of the waveguide under the action of centrifugal force and gradually becomes thinner. At the same time, the solvent begins to evaporate, and finally forms a uniform MOF film on the surface of the waveguide. The speed directly affects the thickness and uniformity of the film. The higher the speed, the thinner the film and the better the uniformity. However, too high a speed may cause solution splashing and film defects. Time control ensures that the solvent has enough time to evaporate, so that the MOF film can be stably attached to the waveguide surface.

[0138] 3.3 Heat treatment

[0139] The coated waveguide samples are heat treated, which is crucial to improving the adhesion and stability of the MOF material on the waveguide surface. Heat treatment can promote the physical or chemical interaction 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 and heated at an appropriate temperature. The heating temperature is determined according to the properties of the MOF material, generally between 50-200°C. For some MOF materials with good thermal stability, a higher heat treatment temperature (such as 150-200°C) can be selected to enhance its bonding with the waveguide surface; while for MOF materials with poor thermal stability, a lower temperature (such as 50-100°C) is used to avoid material decomposition or structural damage. The heating time is generally 1-5 hours. If the time is too short, the expected effect may not be achieved, and if it is too long, it may have an adverse effect on the MOF material or waveguide structure. During the heat treatment process, 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 the heat treatment is completed, the waveguide sample is naturally cooled to room temperature in the oven to avoid cracking or falling off of the film due to a sudden drop in temperature.

[0141] 4. Topological protection edge state design

[0142] 4.1 Selection and introduction of topological insulator materials

[0143] Select appropriate topological insulator materials, such as mercury telluride (HgTe) and bismuth antimony alloy (BiSb), which have special electronic band structures and can support the transmission of topologically protected edge states. Determine the introduction method of topological insulator materials based on the waveguide structure and performance requirements. Epitaxial growth technology can be used to grow topological insulator thin film layers in specific areas of the waveguide structure.

[0144] During the epitaxial growth process, the growth temperature, pressure, reaction gas flow rate and other parameters are precisely controlled to obtain high-quality, uniform topological insulator films. For example, for the growth of HgTe thin films, the growth temperature can be controlled at 180-250°C, the pressure is between 10-100 Pa, and tellurium source (such as Te2) and mercury source (such as Hg) are used as reaction gases. By adjusting the gas flow ratio and growth time, a film layer with a thickness of 50-200 nm is obtained. During the growth process, 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 to ensure that it meets expectations.

[0145] 4.2 Waveguide edge design

[0146] Design a waveguide edge structure that supports topologically protected edge state transmission. 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 zigzag or trapezoidal waveguide edge structure can be used to make the energy distribution of the edge state more concentrated in the edge area, reducing the scattering of the optical signal into the waveguide.

[0147] At the interface between the waveguide edge and the topological insulator material, optimization treatment is performed to ensure good electrical and optical contact. Surface treatment processes such as plasma treatment and chemical modification can be used to improve the flatness and adhesion of the interface and reduce interface scattering and loss. Plasma treatment can use oxygen plasma or argon plasma to remove surface contaminants and activate surface atoms to enhance the binding 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, improve the chemical properties of the interface, and promote the formation and stable transmission of topologically protected edge states.

[0148] 4.3 Performance Testing and Optimization

[0149] The performance of the waveguide structure designed with topologically protected edge states was tested. The main test indicators included the scattering loss of the optical signal, transmission efficiency, and tolerance to environmental noise. The transmission loss of the optical signal in the waveguide was measured experimentally and compared with the waveguide structure without topologically protected edge states to evaluate the effect of topologically protected edge states on reducing losses.

[0150] The transmission loss and reflection of the optical signal in the waveguide are measured by using equipment such as an optical time domain reflectometer (OTDR), and the influence of the topological protection edge state on the transmission characteristics of the optical signal is analyzed. At the same time, the performance of the waveguide is tested under different environmental noise conditions (such as electromagnetic interference, temperature fluctuations, etc.) to observe the stability of the optical signal. 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 it is found that the scattering loss is still large, you can try to increase the thickness of the topological insulator film or adjust the curvature radius of the waveguide edge to improve the performance of the topological protection edge state. Through multiple tests and optimizations, the waveguide structure can achieve lower loss, higher transmission efficiency and stronger environmental interference resistance in the case of topological protection edge states.

[0151] 5. Optical signal acquisition and processing

[0152] 5.1 Spectrum Analyzer Selection and Setup

[0153] Select an optical spectrum analyzer with high resolution, wide wavelength range and high sensitivity to ensure that the spectral characteristics of the optical signal can be accurately measured. The resolution needs to reach the nanometer level, such as 0.1nm, so as 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 1500-1600nm, to meet the detection requirements of optical signals of different wavelengths; high sensitivity ensures that weak changes in optical signals can be detected, and its minimum detectable optical power can reach the nanowatt level.

[0154] Before using the spectrum analyzer, set the parameters according to the system's operating wavelength and measurement accuracy requirements. Set the central wavelength to 1550nm (consistent with the system design wavelength) and the scanning range to 1530-1570nm to cover the wavelength deviation range that may be caused by factors such as gas adsorption. Set the scanning step size to 0.05nm to ensure that sufficiently detailed spectral information can be obtained within this range. At the same time, set a suitable integration time, such as 1 second, to balance the measurement speed and signal-to-noise ratio to improve the measurement accuracy.

[0155] 5.2 Optical signal acquisition

[0156] Connect the spectrum analyzer 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. Use a high-precision optical fiber coupler with an alignment accuracy of sub-micron level to reduce the loss of optical signals during the coupling process. During the connection process, pay attention to the cleanliness and integrity of the optical fiber end face to avoid dust, scratches and other factors that affect the transmission of optical signals.

[0157] When the sensor system is working, the optical signal is transmitted in the waveguide and interacts with the smart response material coated on the waveguide surface before being output from the waveguide array. The spectrum analyzer collects the spectrum data of the output optical signal in real time and records the optical power values ​​at different wavelengths. In order to improve the accuracy and reliability of the measurement, each waveguide structure is measured multiple times (e.g., 10 times) and the average value is taken as the optical signal spectrum data of the waveguide structure.

[0158] 5.3 Data processing and analysis

[0159] Feature extraction

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

[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 waveguide refractive index to change, thereby causing the peak of the reflection spectrum to shift; for the microring resonator module, the intensity change of its resonance peak and the shift of the resonance wavelength are analyzed. The change in the resonance peak intensity is related to the optical signal loss caused by the adsorption of gas molecules, and the shift of the resonance wavelength directly reflects the change in the waveguide refractive index.

[0162] Model building and training

[0163] A mathematical model can be established based on the extracted characteristic parameters to predict gas concentration. For example, a multivariate linear regression model can be used to take different characteristic parameters as independent variables and gas concentration as dependent variable, and the coefficients of the model can be determined by fitting a large amount of experimental data. Alternatively, a more complex nonlinear model can be constructed, such as an artificial neural network model, which uses its powerful nonlinear mapping capability to model the complex relationship between gas concentration and 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, the number of input layer nodes is 5), the number of output layer nodes is the number of gas types to be detected (such as detecting methane and carbon dioxide, the number of output layer nodes is 2), and the number of hidden layers and nodes is determined through experimental optimization. Use the training set data to train the model, use appropriate optimization algorithms (such as gradient descent algorithm, Adam algorithm, etc.) and loss functions (such as mean square error function), and continuously adjust the model parameters to improve the prediction accuracy of the model.

[0165] 5.4 Calculation and determination of gas concentration

[0166] The concentration of the gas to be measured is calculated based on the established model or directly using the empirical relationship between the characteristic parameters and the gas concentration. 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 comprehensively based on 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 type of gas, while the measurement data of the microring 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 exceeds the standard or is within the normal range. At the same time, the calculation results are analyzed for errors to evaluate the accuracy of the measurement. The sources of error may include measurement errors of the spectrometer, model errors, losses in the optical signal transmission process, etc. By continuously optimizing the measurement and calculation process, the error can be reduced and the detection accuracy can be improved.

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

[0169] 6.1 Independent waveguide channel design and optimization

[0170] To meet different gas detection requirements, multiple independent waveguide channels are designed. Each waveguide channel surface is coated with an intelligent responsive material that selectively adsorbs specific gases, such as the MOF material mentioned above. According to the size, polarity and other characteristics of the gas molecules, the size (such as width, height) and length of the waveguide channel are optimized to increase the contact probability and adsorption efficiency between the gas molecules and the material.

[0171] For example, for small molecule gases (such as methane), a relatively narrow waveguide channel can be designed to increase the residence time of gas molecules in the channel; for large molecule gases (such as 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 enough time to adsorb with the material in the channel. The general channel length is between 1-10mm. The optimal waveguide channel parameters corresponding to different gases are determined through simulation calculations and experimental tests. Simulation calculations can use finite element analysis software to analyze the diffusion behavior and adsorption dynamics of gas molecules in channels of different sizes, providing theoretical guidance for experimental design. Experimental tests actually prepare waveguide channels with different parameters, detect their adsorption performance and optical signal response to specific gases, and find the optimal design solution.

[0172] 6.2 Signal Processing Algorithm Development

[0173] Develop a signal processing algorithm to achieve simultaneous detection and separation of multiple gas concentrations. The algorithm is designed based on the characteristics of light signal changes caused by different gases adsorbed on MOF materials. First, a mathematical model between different gas concentrations and light signal changes (such as light absorption, refraction, resonant frequency shift, etc.) is established.

[0174] Through experimental measurement of the changes in various parameters of the optical signal before and after the adsorption of gases of different concentrations, a mathematical model is established using methods such as data fitting. For example, for the relationship between the change in light absorption and the gas concentration, the Lambert-Beer law can be used as a basis for expansion, considering the changes in the optical properties of the MOF material after the adsorption of gas, and establishing a more accurate model. Then, characteristic parameters related to the gas concentration are extracted from the collected optical signal, such as the spectral peak position, peak intensity, bandwidth, etc. These characteristic parameters are fitted with the established mathematical model using algorithms such as multivariate linear regression and principal component analysis (PCA), and the concentration values ​​of different gases are calculated. At the same time, signal separation algorithms such as independent component analysis (ICA) are used to decompose the changes in the optical signal caused by the mixed gas into the contribution of each single gas, so as to achieve the separation and detection of multiple gases. During the algorithm development process, the algorithm is verified and optimized through a large amount of experimental data to ensure its accuracy and reliability.

[0175] 6.3 Application of Machine Learning Technology

[0176] The introduction of machine learning technology further improves the accuracy and reliability of signal processing. Collect a large amount of optical signal data of mixed gases with different concentrations, including the situation of multiple gases in different proportions. Divide these data into training sets and test sets, and use the training sets to train machine learning models, such as support vector machines (SVMs), neural networks, etc.

[0177] The input of the machine learning model is the characteristic 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 characteristics. In actual detection, the optical signal characteristics collected in real time are input into the trained model to obtain accurate gas concentration prediction results. At the same time, machine learning technology is used to compensate for cross-interference and improve the independence and accuracy of the detection signal. For example, by learning the laws of mutual influence between different gases, the detection results are corrected to reduce the errors caused by gas interactions. By continuously increasing training data and optimizing model parameters, the performance of the machine learning model in complex gas environments is improved, so that it can adapt to the detection needs of different working conditions and changes in gas composition.

[0178] 7. Reliability test

[0179] 7.1 Environmental adaptability test

[0180] Test the system performance under different temperature and humidity conditions to simulate various environmental conditions 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, and perform gas detection experiments on the sensor system under different temperature and humidity combinations.

[0181] During the test, a standard gas source is used to provide gases of known concentration (such as methane, carbon dioxide, etc.) to observe the sensor system's measurement accuracy, response time, and stability of gas concentration under different environmental conditions. The measurement data is recorded to analyze the impact of temperature and humidity changes on system performance. For example, a high temperature and high humidity environment may affect the adsorption properties of MOF materials and the optical properties of waveguides, resulting in increased measurement errors or longer response times. Through experimental data, the performance change patterns of the system under different environmental conditions are determined to evaluate its environmental adaptability.

[0182] 7.2 Long-term stability test

[0183] Conduct long-term stability tests to evaluate changes in system performance during long-term operation. Run the sensor system continuously for a certain period of time, such as more than 1,000 hours, and calibrate and test it regularly (such as every 24 hours) using standard gas, and record the measurement data.

[0184] Analyze the changing trend of the measurement data and observe whether the system's performance indicators such as sensitivity and accuracy 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 experience structural changes or adsorption performance decay during long-term use, and the waveguide surface may be contaminated or damaged. Based on the test results, take corresponding measures to improve the long-term stability of the system, such as optimizing material selection and improving packaging processes.

[0185] 7.3 Anti-interference test

[0186] Test the system's anti-interference ability, including its resistance to electromagnetic interference, vibration interference, etc. In an environment with 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 vibrations of a certain frequency and amplitude to the system to simulate the vibration environment in actual applications and test the system's performance under vibration conditions.

[0187] Through anti-interference testing, the reliability of the system in complex interference environments is evaluated, providing a basis for its application in harsh environments such as industrial sites. If it is found that the system performance is affected in an interference environment, take corresponding anti-interference measures, such as electromagnetic shielding design, vibration reduction structure optimization, etc., to improve the system's anti-interference ability and ensure that it can work accurately and stably under various interference conditions.

[0188] Example:

[0189] This scheme reduces greenhouse gases (such as methane CH 4 、Carbon dioxide CO 2 ) monitoring. The sensor arrays were deployed in agricultural greenhouses and industrial emission areas to detect greenhouse gas emissions in agricultural production and possible leakage sources in industrial processes, such as Figure 4 shown.

[0190] Agricultural scenario: The sensor is installed on the top of the greenhouse to monitor CH 4 and CO 2 Concentration, helping agricultural producers optimize ventilation strategies and greenhouse environmental management. Industrial scenario: Sensors are used to monitor industrial waste gas emissions, combined with artificial intelligence algorithms, to upload gas concentration data to the environmental monitoring platform in real time.

[0191] Actual Results

[0192] Sensitivity and accuracy: CH 4 and CO 2The detection error rate is less than ±2%. The detection performance remains stable under the interference of background gas (such as water vapor). Environmental adaptability: The system has no obvious signal drift under high humidity (90% RH) and temperature fluctuation (10℃-40℃) conditions.

[0193] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all 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: It includes 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, an electric field control module and a signal processing unit; wherein: The waveguide substrate is 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 a waveguide array channel is constructed on the waveguide substrate. The waveguide array channel is etched and formed on the waveguide substrate, and the waveguide array channel includes an incident waveguide, a first waveguide channel to a sixth waveguide channel arranged in parallel, and a smart response material is coated on the surface of each waveguide channel; wherein: a tunable laser is connected to the incident waveguide through a grating coupler and a three-ring polarizer; an optical signal in the incident waveguide is divided into two paths, respectively entering the first waveguide channel and the second waveguide channel; an optical signal entering the first waveguide channel is divided into two paths, respectively entering the third waveguide channel and the fourth waveguide channel; an optical signal entering the second waveguide channel is divided into two paths, respectively entering the fifth waveguide channel and the fourth and sixth optical paths; A pair of waveguide Bragg gratings is arranged on the waveguide substrate, and the pair of waveguide Bragg gratings are respectively used to receive optical signals in the third waveguide channel and the sixth waveguide channel and modulate the optical signals using the internal periodic grating structure, and then output modulated optical signals S2 and S5; A pair of phase-shifted Bragg gratings are arranged on the waveguide substrate, and are respectively located on the sides of a 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, and then output the adjusted optical signals S1 and S6; The microring resonator is used to receive the optical signal of the fifth waveguide channel, and after enhancing the intensity of the optical signal by utilizing the resonance effect, output the enhanced optical signal S4; The Mach-Zehnder interferometer is used to receive the optical signal of the fourth waveguide channel, and the optical signal is divided into two paths inside the Mach-Zehnder interferometer and then combined and interfered after going through different optical paths, and finally outputs the interfered optical signal S3; The electric field control module includes electrodes, which are distributed on the waveguide substrate; an external electric field is applied through the electrodes to control the propagation characteristics of the optical signal transmitted in the waveguide array channel; The optical signals S1 to S6 are connected to the signal processing unit after being photoelectrically converted by the optical power meter. The signal processing unit detects the gas concentration after data integration processing. The signal processing unit is also used to control the frequency sweep range of the tunable laser and the reading and writing speed of the optical power meter. When gas molecules are adsorbed onto the surface of the waveguide array channel, the refractive index changes differently due to the adsorption exhibited by each gas molecule. As a result, after the optical signals S1 to S6 at the output end are converted into electrical signals, changes in signal power density, voltage amplitude, and signal frequency will occur. The signal processing unit realizes real-time detection of multiple gases based on the changes.

2. The waveguide array gas sensor system for high sensitivity multi-gas detection according to claim 1 is characterized in that: A silicon dioxide layer and a silicon nitride layer are sequentially deposited on a silicon substrate.

3. The waveguide array gas sensor system for high sensitivity multi-gas detection according to claim 1 is characterized in that: 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 sensor system for high sensitivity multi-gas detection according to claim 1 is characterized in that: 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 sensor system for high sensitivity multi-gas detection according to claim 1, characterized in that: The microring radius of the microring resonator is 50 μm, and the coupling gap is 100 nm.

6. A detection method of a waveguide array gas sensor system for high-sensitivity multi-gas detection, characterized in that: include: Step 1, placing the gas sensor system in the gas environment to be detected, and connecting the incident waveguide in the system to the tunable laser through a grating coupler, a single-mode optical fiber, and a three-ring polarization controller; six optical signals S1 to S6 at the output end of the system are connected to an optical power meter, the optical power meter is connected to a signal processing unit, and the signal processing unit is used to control the tunable laser sweep range and the optical power meter reading and writing speed; Step 2, the optical signal in the incident waveguide is divided into two paths and enters the first waveguide channel and the second waveguide channel through a multimode interference beam splitter; the optical signal in the first waveguide channel is further divided into two beams through the multimode interference beam splitter, one of which enters the phase-shifted Bragg grating and the waveguide Bragg grating in parallel through the third waveguide channel, and performs periodic effective refractive index modulation processing of the light wave respectively therein, and outputs the optical signal S1 and the optical signal S2 after the signal is stabilized; the other beam enters the Mach-Zehnder interferometer module through the fourth waveguide channel, and performs beam splitting and superposition of the light wave therein to form destructive interference or constructive interference processing, thereby outputting the optical signal S3; The optical signal in the second waveguide channel is divided into two beams by a multimode interference beam splitter, one of which enters the microring resonator. When the optical path through the microring matches the wavelength of the light, the light will form a standing wave in the microring and undergo resonance processing, and output an optical signal S4; the other light beam enters the phase-shifted Bragg grating and the waveguide Bragg grating in parallel, and after the periodic effective refractive index modulation processing of the light wave is performed respectively, the optical signals S5 and S6 are output; Step 3, during the gas detection process, adjusting the quality of the output optical signal by changing the voltage amplitude applied to the electrode; Step 4: The signal processing unit receives the optical signals S1 to S6 through an optical power meter, performs photoelectric conversion on them to obtain six electrical signals, and determines the type of gas detected by the following detection method: First, when detecting a single gas, the six optical signals that pass through different waveguide channels and are finally output during the operation of the sensor system are the same as the template data obtained in advance for the detection of the gas; therefore, by comparing the six optical signals of the sensor system with the changes in the output optical signals when there is no adsorbed gas, the type of gas detected can be determined; The second method is that when multiple gases are adsorbed on the waveguide array channel, it is necessary to regulate the intensity, phase and amplitude of the optical signal S1 to the optical signal S6, and determine the changes in the transmission coefficient and transmission spectrum of the waveguide array channel during the detection of each single gas and mixed gas, and then obtain the transmission spectrum of each single gas in the mixed gas detection; by testing different ratios of single gases and mixed gases, the center wavelength offset of each waveguide array channel is compared. When the detection spectrum of a single gas is the same as the center wavelength corresponding to the ratio of the single gas in the mixed gas, it is considered that the optical signal detected is the single gas.

7. The method according to claim 6, characterized in that The intensity, phase and amplitude of the optical signals S1 to S6 are regulated, specifically, the stopband width change of the waveguide Bragg grating and the phase-shift Bragg grating, the drift of the central wavelength, and the change of the waveguide coupling coefficient are adjusted.

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