On-chip stimulated Raman photo-thermal gas sensing system and method

Abstract

The invention discloses an on-chip stimulated Raman photo-thermal gas sensing system and method, and particularly relates to the technical field of gas analysis and measurement. Pump light and Stokes light interact with gas to be detected in a sensing waveguide evanescent field area to excite gas molecules to generate a stimulated Raman process and generate local temperature rise through thermal relaxation, so that the refractive index change of the gas is caused, and probe light generates a phase modulation signal related to the refractive index change. Phase modulation signals and background phase disturbance related to the gas photothermal effect are distinguished and differentiated, so that phase background noise is suppressed, and the signal-to-noise ratio and sensitivity of gas measurement are improved. Functional units such as the laser, the sensing waveguide and the detector are integrated into a single chip to form a gas measurement system which is compact in structure, low in power consumption and high in anti-noise capability, and the problems of weak signal, high background noise and low integration level in traditional waveguide Raman gas measurement are effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of gas analysis measurement technology, more particularly, to a kind of on-chip stimulated raman photothermal gas sensing system and method. BACKGROUND

[0002] Gas detection technology is widely used in environmental management, industrial safety, energy utilization and other fields, and its goal is to quickly and accurately identify and analyze gas types and concentrations. Although traditional methods such as electrochemical sensing or catalytic combustion detection are mature, they still have deficiencies in response speed, selectivity and anti-interference ability, making it difficult to meet the needs of emerging high-precision applications.

[0003] Optical detection technology, especially stimulated raman scattering spectroscopy technology, can obtain characteristic spectral lines related to molecular structure through the scattering signals generated by the interaction of light and gas molecules, thereby achieving high selectivity identification. The stimulated raman photothermal spectroscopy technology based on this further improves the detection sensitivity. However, there are still several key bottlenecks in current on-chip raman sensors. First, the raman scattering signal of gas molecules is very weak, and even with enhanced coupling in the waveguide structure, the detection result is still easily affected by noise. Second, the waveguide itself generates strong background raman signals, which mask the target spectral lines, resulting in a decrease in signal-to-noise ratio. In addition, integrating devices made of different materials such as light sources and waveguides on the same chip is complex, costly, and has poor compatibility, which greatly limits the performance and scale application of the overall system.

[0004] Therefore, there is an urgent need for a gas sensing technology that can be implemented on-chip, which can effectively enhance the gas detection signal, suppress background noise, and reduce the dependence on complex integration processes and high-precision alignment, thereby improving the practicality and stability of the gas sensing system. SUMMARY

[0005] To solve the problems mentioned in the background art, the present application provides an on-chip stimulated raman photothermal gas sensing system and method to solve the defects in the prior art.

[0006] The technical solution of the present application to solve the above problems is as follows: An on-chip stimulated raman photothermal gas sensing system, comprising: a stimulated raman photothermal gas sensing chip, a first laser driver, a second laser driver, a lock-in amplifier, and an analysis terminal; The stimulated raman photothermal gas sensing chip comprises a pump laser, a Stokes laser, a probe light laser, a polarization beam splitter, a first coupler, a coupling input waveguide, a sensing waveguide, a coupling output waveguide, a first micro-ring resonator, a second micro-ring resonator, a polarization rotation beam splitter, a second coupler, and a photodetector. The output end of the pump laser is connected to the input end of the first coupler through a pump TE polarization input waveguide, for inputting a pump light TE mode into the first coupler; the Stokes laser is connected to the first laser driver, and the output end thereof is connected to the input end of the first coupler through a Stokes TE polarization input waveguide, for inputting a Stokes light TE mode into the first coupler; the probe light laser is connected to the second laser driver, and the output end thereof is connected to the input end of the polarization beam splitter, and the two output ends of the polarization beam splitter are connected to the input end of the first coupler through a probe light TE polarization input waveguide and a probe light TM polarization input waveguide respectively, for inputting a raw probe light TE mode and a probe light TM mode into the first coupler; The output end of the first coupler is connected to the input end of the sensing waveguide through the coupling input waveguide, so that the pump light TE mode, the Stokes light TE mode, and the raw probe light TE mode and the probe light TM mode enter the sensing waveguide together, and the sensing waveguide is arranged in a gas sensing area, for enabling the evanescent field of a guided mode propagating in the sensing waveguide to interact with the gas to be measured; The output end of the sensing waveguide is connected to the input end of the polarization rotation beam splitter through the coupling output waveguide, and the first micro-ring resonator and the second micro-ring resonator are arranged on the coupling output waveguide and form a lateral evanescent field coupling with the coupling output waveguide, wherein the first micro-ring resonator is used for selectively filtering out the pump light, and the second micro-ring resonator is used for selectively filtering out the Stokes light; The polarization rotation beam splitter is used for separating the raw probe light TE mode from the probe light TM mode, and converting the probe light TM mode into a converted probe light TE mode, wherein the polarization state of the converted probe light TE mode is the same as that of the raw probe light TE mode; The second coupler is used for optically combining the raw probe light TE mode and the converted probe light TE mode to form an interference output, and the output end thereof is connected to the input end of the photodetector, and the photodetector converts the phase difference between the raw probe light TE mode and the converted probe light TE mode into an electrical signal; The output end of the photodetector is connected to the lock-in amplifier, the modulation output end of the lock-in amplifier is connected to the first laser driver, for modulating the Stokes laser and synchronously demodulating, and the analysis terminal is connected to the output end of the lock-in amplifier, for obtaining a detection signal related to the concentration of the gas to be measured.

[0007] Preferably, the original probe light TE mode obtains a phase modulation caused by a gas photo-thermal effect in the sensing region and superimposes a common mode background phase disturbance, the converted probe light TE mode carries the common mode background phase disturbance, and the common mode background phase disturbance is suppressed by a phase difference between the original probe light TE mode and the converted probe light TE mode.

[0008] An on-chip stimulated Raman photo-thermal gas sensing method applied to an on-chip stimulated Raman photo-thermal gas sensing system, comprising the following steps: S1: outputting pump light, Stokes light and probe light respectively, so that a frequency difference between the pump light and the Stokes light matches a Raman transition frequency of a gas to be measured; S2: inputting the pump light TE mode, the Stokes light TE mode, the original probe light TE mode and the probe light TM mode into a sensing waveguide through a first coupler, and inputting the gas to be measured into a gas sensing region; S3: causing the pump light and the Stokes light to undergo a stimulated Raman process with the gas to be measured in an evanescent field region outside the sensing waveguide, and causing a local temperature rise through thermal relaxation, so that the refractive index of the gas changes, and the probe light is phase-modulated; S4: filtering out the pump light and the Stokes light by using a first micro-ring resonator and a second micro-ring resonator respectively; S5: separating the original probe light TE mode from the probe light TM mode, converting the probe light TM mode to obtain converted probe light TE mode through a polarization rotation beam splitter, and interfering and combining the converted probe light TE mode with the original probe light TE mode; S6: optoelectronically detecting the combined signal, converting a phase difference between the original probe light TE mode and the converted probe light TE mode into an electrical signal, and synchronously demodulating the electrical signal to obtain a detection signal related to the concentration of the gas to be measured.

[0009] Preferably, a common mode background phase disturbance caused by environmental changes and device drift is suppressed by a phase difference between the original probe light TE mode and the converted probe light TE mode.

[0010] Preferably, a harmonic component of the detection signal is extracted by a lock-in amplifier, and the concentration of the gas to be measured is represented according to an amplitude of the harmonic component.

[0011] The present application has the following beneficial effects: (1) The present application is based on stimulated Raman photothermal effect, through the interaction of pump light and Stokes light in the evanescent field region of the sensing waveguide and the gas to be measured, the Raman transition information of gas molecules is converted into the refractive index change caused by local thermal effect, and further converted into the phase modulation signal of the probe light, realizing the effective mapping of gas information from molecular scale to optical detectable signal; combined with the strong constraint ability of the sensing waveguide to the light field, the interaction intensity of light and gas is greatly enhanced, and ppm level trace gas detection can be realized.

[0012] (2) By guiding pump light, Stokes light and probe light in the sensing waveguide at the same time, and using probe light phase modulation for detection, direct measurement of weak Raman scattering intensity is avoided, the detection sensitivity is improved, and it is especially suitable for high-sensitivity detection of low-concentration gas. Polarization mode phase difference detection method is adopted, the photoelectric detector obtains the Raman photothermal phase signal of the original probe light TE mode and the Raman photothermal phase signal of the probe light TE mode converted by the probe light TM mode, and the phase background noise is suppressed through phase difference detection, thereby improving the signal-to-noise ratio and detection sensitivity.

[0013] (3) By integrating the pump laser, Stokes laser, probe light laser, polarization beam splitter, first coupler, micro-ring resonator, photoelectric detector and various waveguides on a single chip, the volume and power consumption are effectively reduced. The system is realized based on on-chip optical waveguide and integrated optical devices, the functional modules are connected through waveguides, without complex free-space optical alignment, having the advantages of compact structure, high integration, easy batch manufacturing, suitable for further integration with on-chip light source, detector and signal processing circuit, and conducive to realizing miniaturization, low power consumption and multi-channel gas sensing system.

[0014] (4) The present application utilizes the difference of different polarization modes of probe light in the light field overlap in the gas region, uses the polarization mode with larger light field overlap as the signal channel, and uses the polarization mode with smaller light field overlap as the reference channel, and through phase difference detection, the common mode background phase noise caused by waveguide material, temperature change and environmental disturbance is suppressed, thereby significantly improving the stability and repeatability of the detection result.

[0015] (5) By introducing a micro-ring resonator which is coupled with the lateral evanescent field of the coupling output waveguide at the output end of the sensing waveguide, the pump light and the Stokes light are selectively filtered out, effectively avoiding the interference of strong light signal entering the probe light channel on the phase detection, improving the signal-to-noise ratio of the system and simplifying the back-end signal processing. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments description. Obviously, the drawings described below are only some of the embodiments of the present application, and all other drawings obtained by those of ordinary skill in the art without creative effort based on these drawings belong to the protection scope of the present application.

[0017] Figure 1 A structure schematic diagram of a chip-on-stimulated Raman optical thermal gas sensing system provided by the embodiments of the present application is shown in the figure. Figure 2 A schematic diagram of stimulated Raman scattering energy level transition and thermal relaxation process provided by the embodiments of the present application is shown in the figure.

[0018] Reference signs: 1-stimulated Raman optical thermal gas sensing chip, 2-Stokes laser, 3-pump laser, 4-probe light laser, 5-polarization beam splitter, 6-first coupler, 7-polarization rotation beam splitter, 8-second coupler, 9-photodetector, 10-phase-locked amplifier, 11-analysis terminal, 12-first laser driver, 13-second laser driver, 14-Stokes TE polarization input waveguide, 15-pump TE polarization input waveguide, 16-probe light input waveguide, 17-probe light TE polarization input waveguide, 18-probe light TM polarization input waveguide, 19-coupling input waveguide, 20-sensing waveguide, 21-first micro-ring resonator, 22-second micro-ring resonator, 23-coupling output waveguide, 24-probe light TE polarization output waveguide, 25-probe light TM-TE polarization conversion output waveguide, 26-probe light output waveguide. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the following will combine the drawings in the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the protection scope of the present application.

[0020] The embodiments of the present application will be further described in detail below with reference to the drawings.

[0021] Reference Figure 1The on-chip stimulated Raman photothermal gas sensing system comprises a stimulated Raman photothermal gas sensing chip 1, a first laser driver 12, a second laser driver 13, a lock-in amplifier 10 and an analysis terminal 11; the stimulated Raman photothermal gas sensing chip 1 comprises a pump laser 3, a Stokes laser 2, a probe light laser 4, a polarization beam splitter 5, a first coupler 6, a polarization rotation beam splitter 7, a second coupler 8, a photodetector 9, a pump TE polarization input waveguide 15, a Stokes TE polarization input waveguide 14, a probe light input waveguide 16, a probe light TE polarization input waveguide 17, a probe light TM polarization input waveguide 18, a coupling input waveguide 19, a sensing waveguide 20, a coupling output waveguide 23, a first micro-ring resonator 21, a second micro-ring resonator 22, a probe light TE polarization output waveguide 24, a probe light TM-TE polarization conversion output waveguide 25 and a probe light output waveguide 26.

[0022] By way of example and not limitation, in the embodiment of the present application, the pump laser 3, the Stokes laser 2, the probe light laser 4, the polarization beam splitter 5, the first coupler 6, the polarization rotation beam splitter 7, the second coupler 8, the photodetector 9, the pump TE polarization input waveguide 15, the Stokes TE polarization input waveguide 14, the probe light input waveguide 16, the probe light TE polarization input waveguide 17, the probe light TM polarization input waveguide 18, the coupling input waveguide 19, the sensing waveguide 20, the coupling output waveguide 23, the first micro-ring resonator 21, the second micro-ring resonator 22, the probe light TE polarization output waveguide 24, the probe light TM-TE polarization conversion output waveguide 25 and the probe light output waveguide 26 are all integrated on a SiO2 substrate.

[0023] In the embodiment of the present application, the output end of the pump laser 3 is connected with the input end of the first coupler 6; the input end and the output end of the Stokes laser 2 are connected with the output end of the first laser driver 12 and the input end of the first coupler 6 respectively; the input end and the output end of the probe light laser 4 are connected with the output end of the second laser driver 13 and the input end of the polarization beam splitter 5 respectively; the output end of the polarization beam splitter 5 is connected with the input end of the first coupler 6; the output end of the first coupler 6 is connected with the input end of the sensing waveguide 20; the output end of the sensing waveguide 20 is connected with the input end of the polarization rotation beam splitter 7; the output end of the polarization rotation beam splitter 7 is connected with the input end of the second coupler 8; the output end of the second coupler 8 is connected with the input end of the photodetector 9; the output end of the photodetector 9 is connected with the input end of the lock-in amplifier 10; the modulation signal output end and the demodulation signal output end of the lock-in amplifier 10 are connected with the modulation signal input end of the first laser driver 12 and the input end of the analysis terminal 11 respectively.

[0024] The output end of the pump laser 3 is connected with the input end of the first coupler 6 through a pump TE polarization input waveguide 15; the output end of the Stokes laser 2 is connected with the input end of the first coupler 6 through a Stokes TE polarization input waveguide 14; the output end of the probe light laser 4 is connected with the input end of the polarization beam splitter 5 through a probe light input waveguide 16, and the output end of the polarization beam splitter 5 is connected with the input end of the first coupler 6 through a probe light TE polarization input waveguide 17 and a probe light TM polarization input waveguide 18 respectively; the output end of the first coupler 6 is connected with the input end of a sensing waveguide 20 through a coupling input waveguide 19; the output end of the sensing waveguide 20 is connected with the input end of the polarization rotation beam splitter 7 through a coupling output waveguide 23; the output end of the polarization rotation beam splitter 7 is connected with the input end of the second coupler 8 through a probe light TE polarization output waveguide 24 and a probe light TM-TE polarization conversion output waveguide 25 respectively; the output end of the second coupler 8 is connected with the input end of the photodetector 9 through a probe light output waveguide 26. The first micro-ring resonator 21 and the second micro-ring resonator 22 are arranged between the sensing waveguide 20 and the polarization rotation beam splitter 7. The stimulated Raman optical thermal gas sensing chip 1 is packaged in a gas chamber.

[0025] By way of example and not limitation, in the embodiment of the present application, the pump TE polarization input waveguide 15, the Stokes TE polarization input waveguide 14, the probe light input waveguide 16, the probe light TE polarization input waveguide 17, the probe light TM polarization input waveguide 18, the coupling input waveguide 19, the coupling output waveguide 23, the probe light TE polarization output waveguide 24, the probe light TM-TE polarization conversion output waveguide 25 and the probe light output waveguide 26 are all selected to be Si3N4 rectangular waveguides, and the sensing waveguide 20 is selected to be a Si3N4 slit waveguide.

[0026] Please refer to Figure 2 , Figure 2 The present application provides a schematic diagram of the stimulated Raman scattering energy level transition and thermal relaxation process. In the diagram, is the optical frequency of the pump light, is the optical frequency of the Stokes light, The Raman transition frequency of the to-be-detected gas. In the embodiment of the present application, the pump light, the Stokes light and the probe light are taken as the incident light sources, the pump light and the Stokes light are input from the input end of the sensing waveguide 20, part of the light field of the pump light and the Stokes light propagates in the gas medium outside the sensing waveguide 20 in the form of evanescent field and overlaps with each other, the partially overlapped evanescent field interacts with the to-be-detected gas, the stimulated Raman scattering process mediated by the Raman transition of the gas molecules occurs, part of the pump light is converted into the Stokes light, the Stokes light signal obtains gain, and the gas molecules are excited from the ground state to the excited state through the stimulated Raman scattering process. Subsequently, the gas molecules transition back to the ground state through the thermal relaxation process, and the energy of the relaxation process is released in the form of heat, generating a heat source, resulting in a local temperature rise near the waveguide. Due to the thermo-optic effect, this temperature rise will cause a change in the refractive index of the gas. The probe light will experience a phase change proportional to the change in the refractive index. The frequency difference between the pump light and the Stokes light is equal to the Raman transition frequency of the to-be-detected gas. The pump light and the Stokes light interact with the to-be-detected gas in the evanescent field region outside the sensing waveguide, and when the frequency difference between the two matches the Raman transition frequency of the gas molecules, a stimulated Raman process occurs in the sensing region. The stimulated Raman process forms a local heat source through non-radiative relaxation, causing a change in the refractive index of the gas, thereby causing the probe light propagating in the same sensing region to produce a phase modulation related to the gas concentration.

[0027] The embodiment of the present application also provides an on-chip stimulated Raman optical-thermal gas sensing method, comprising the following steps: S1: outputting the pump light, the Stokes light and the probe light respectively, so that the frequency difference between the pump light and the Stokes light matches the Raman transition frequency of the to-be-detected gas; S2: inputting the pump light TE fundamental mode, the Stokes light TE fundamental mode, the original probe light TE fundamental mode and the probe light TM fundamental mode into the sensing waveguide through the first coupler, and introducing the to-be-detected gas into the gas sensing region; S3: causing the pump light and the Stokes light to undergo a stimulated Raman process with the to-be-detected gas in the evanescent field region outside the sensing waveguide, and causing a local temperature rise through thermal relaxation, so as to cause a change in the refractive index of the gas and cause the probe light to produce a phase modulation; S4: filtering out the pump light and the Stokes light by using the first micro-ring resonator and the second micro-ring resonator respectively; S5: separating the original probe light TE fundamental mode from the probe light TM fundamental mode, converting the probe light TM fundamental mode to obtain converted probe light TE fundamental mode through a polarization rotation beam splitter, and interfering and combining the converted probe light TE fundamental mode with the original probe light TE fundamental mode; S6: optoelectronically detecting the combined signal, converting the phase difference between the original probe light TE fundamental mode and the converted probe light TE fundamental mode into an electrical signal, and synchronously demodulating the electrical signal to obtain a detection signal related to the concentration of the to-be-detected gas.

[0028] The phase difference between the original probe light TE mode and the converted probe light TE mode is used to suppress the common mode background phase disturbance caused by environmental changes and device drift. The harmonic component of the detection signal is extracted by a phase-locked amplifier, and the concentration of the gas to be measured is represented by the amplitude of the harmonic component.

[0029] In the present application, the probe light is divided into two paths after propagating through the sensing waveguide 20, one of which is the original probe light TE mode with a large evanescent field overlap in the sensing region, and the other is the probe light TM mode with a small evanescent field overlap in the sensing region. The probe light TM mode is converted into the converted probe light TE mode with the same polarization state as the original probe light TE mode after polarization rotation. The polarization rotation beam splitter 7 is used to separate the original probe light TE mode from the probe light TM mode and convert the probe light TM mode into the converted probe light TE mode obtained by TM mode conversion, wherein the converted probe light TE mode obtained by TM mode conversion is in the same polarization state TE mode as the original probe light TE mode. The two paths of probe light TE mode carry phase information before entering the second coupler 8, wherein the phase of the original probe light TE mode contains both the phase modulation caused by the gas photo-thermal effect and the common mode background phase disturbance, and the probe light TE mode converted from the probe light TM mode carries the common mode background phase disturbance. The two paths of probe light undergo optical interference in the second coupler 8, and the interference output is detected by a photoelectric detector, which converts the phase difference between the two paths of probe light into an electrical signal, so that the common mode background phase disturbance is cancelled in the phase difference, thereby obtaining the phase modulation signal related to the concentration of the gas to be measured.

[0030] In the present application, the first micro-ring resonator 21 and the second micro-ring resonator 22 respectively realize selective filtering of specific wavelength light by forming a side evanescent field coupling with the coupling output waveguide 23; when the resonant wavelength of the micro-ring resonator matches the wavelength of the corresponding light source, the wavelength light enters the micro-ring through evanescent field coupling and is suppressed, thereby avoiding the pump light and Stokes light from entering the subsequent probe light channel and causing interference to the phase detection.

[0031] In the present application, the sensing waveguide is used to guide the propagation of multiple polarization modes, and the evanescent field of the guided mode propagating in the sensing waveguide interacts with the gas to be measured. Due to the difference in waveguide geometry and refractive index distribution, the field distribution of different polarization modes in the sensing region is significantly different. For the original probe light TE mode, the main electric field component is parallel to the waveguide surface, and the evanescent field extends more strongly in the waveguide cladding and gas region, thereby forming a larger optical field overlap in the gas region to be measured; in contrast, the main electric field component of the probe light TM mode is mainly perpendicular to the waveguide surface, and its optical field is more concentrated in the waveguide core layer, and the evanescent field distribution in the gas region is weaker, and the corresponding optical field overlap is smaller. The optical field overlap refers to the effective optical field distribution of the guided mode propagating in the optical waveguide in the form of evanescent field extending to the outside of the waveguide in the sensing region and interacting with the gas to be measured, which reflects the ability of the guided mode to interact with the gas medium in energy and phase.

[0032] Based on the above differences, when the pump light and the Stokes light interact with the gas to be measured in the evanescent field region outside the sensing waveguide to cause stimulated Raman process and local temperature rise through thermal relaxation, the optical-thermal phase modulation caused by the refractive index change of the gas mainly acts on the probe light TE mode with larger optical field overlap, and has weaker effect on the probe light TM mode with smaller optical field overlap. Therefore, the phase information carried by the original probe light TE mode includes both the phase modulation caused by the gas optical-thermal effect and the common-mode background phase disturbance, while the probe light TM mode reflects the common-mode background phase disturbance. By utilizing the difference in optical field overlap between the original probe light TE mode and the probe light TM mode, and differentially processing the phase information of the two probe lights, the phase modulation signal related to the concentration of the gas to be measured can be extracted while suppressing the common-mode background phase disturbance.

[0033] The embodiments in the present application are described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the related parts can be referred to the method part.

[0034] The above-described embodiments are only the preferred specific embodiments of the present application. The phrases "in one embodiment", "in another embodiment", "in yet another embodiment" or "in other embodiments" in the specification all refer to one or more of the same or different embodiments according to the present disclosure. The usual changes and replacements made by those skilled in the art within the scope of the technical solutions of the present application should be included in the protection scope of the present application.

Claims

1. An on-chip stimulated Raman photothermal gas sensing system, characterized in that, include: Stimulated Raman photothermal gas sensor chip, first laser driver, second laser driver, lock-in amplifier, and analysis terminal; The stimulated Raman photothermal gas sensing chip includes: a pump laser, a Stokes laser, a probe laser, a polarization beam splitter, a first coupler, a coupling input waveguide, a sensing waveguide, a coupling output waveguide, a first microring resonator, a second microring resonator, a polarization rotation beam splitter, a second coupler, and a photodetector. The output of the pump laser is connected to the input of the first coupler via a pump TE polarization input waveguide, for inputting the pump light TE fundamental mode to the first coupler; the Stokes laser is connected to the first laser driver, and its output is connected to the input of the first coupler via a Stokes TE polarization input waveguide, for inputting the Stokes light TE fundamental mode to the first coupler; the probe laser is connected to the second laser driver, and its output is connected to the input of the polarization beam splitter. The two outputs of the polarization beam splitter are respectively connected to the input of the first coupler via a probe light TE polarization input waveguide and a probe light TM polarization input waveguide, for inputting the original probe light TE fundamental mode and the probe light TM fundamental mode to the first coupler; The output of the first coupler is connected to the input of the sensing waveguide through the coupling input waveguide, so that the pump light TE fundamental mode, the Stokes light TE fundamental mode, the original probe light TE fundamental mode and the probe light TM fundamental mode enter the sensing waveguide together. The sensing waveguide is disposed in the gas sensing region and is used to make the evanescent field of the guided mode propagating in the sensing waveguide interact with the gas to be measured. The output end of the sensing waveguide is connected to the input end of the polarization rotating beam splitter through the coupling output waveguide. The first microring resonator and the second microring resonator are respectively disposed on the coupling output waveguide and form a lateral evanescent field coupling with the coupling output waveguide. The first microring resonator is used to selectively filter out the pump light, and the second microring resonator is used to selectively filter out the Stokes light. The polarization rotating beam splitter is used to separate the original probe light TE fundamental mode from the probe light TM fundamental mode, and to convert the probe light TM fundamental mode into the converted probe light TE fundamental mode, wherein the polarization state of the converted probe light TE fundamental mode is the same as that of the original probe light TE fundamental mode; The second coupler is used to optically combine the original probe light TE fundamental mode and the converted probe light TE fundamental mode to form an interference output. Its output end is connected to the input end of the photodetector. The photodetector converts the phase difference between the original probe light TE fundamental mode and the converted probe light TE fundamental mode into an electrical signal. The output of the photodetector is connected to the lock-in amplifier; the modulation output of the lock-in amplifier is connected to the first laser driver for modulating and synchronously demodulating the Stokes laser; the analysis terminal is connected to the output of the lock-in amplifier for acquiring a detection signal related to the concentration of the gas to be measured.

2. The on-chip stimulated Raman photothermal gas sensing system according to claim 1, characterized in that, The original probe light TE fundamental mode obtains phase modulation caused by the gas photothermal effect in the sensing area and is superimposed with a common mode background phase perturbation. The converted probe light TE fundamental mode carries the common mode background phase perturbation, and the common mode background phase perturbation is suppressed by the phase difference between the original probe light TE fundamental mode and the converted probe light TE fundamental mode.

3. An on-chip stimulated Raman photothermal gas sensing method, applied to the on-chip stimulated Raman photothermal gas sensing system according to any one of claims 1-2, characterized in that, Includes the following steps: S1: Output pump light, Stokes light and probe light respectively, so that the frequency difference between pump light and Stokes light matches the Raman transition frequency of the gas to be measured; S2: The pump light TE fundamental mode, Stokes light TE fundamental mode, original probe light TE fundamental mode and probe light TM fundamental mode are input into the sensing waveguide through the first coupler, and the gas to be measured is introduced into the gas sensing area. S3: The pump light and Stokes light undergo stimulated Raman spectroscopy with the gas under test in the evanescent field region outside the sensing waveguide, and the gas undergoes thermal relaxation to generate a local temperature rise, which changes the refractive index of the gas and causes phase modulation of the probe light. S4: Use the first microring resonator and the second microring resonator to filter out the pump light and Stokes light respectively; S5: Separate the original probe light TE fundamental mode and the probe light TM fundamental mode, and convert the probe light TM fundamental mode through a polarization rotating beam splitter to obtain the converted probe light TE fundamental mode. Then, perform interference beam combining between the converted probe light TE fundamental mode and the original probe light TE fundamental mode. S6: Perform photoelectric detection on the combined signal, convert the phase difference between the original probe light TE fundamental mode and the converted probe light TE fundamental mode into an electrical signal, and perform synchronous demodulation on the electrical signal to obtain a detection signal related to the concentration of the gas to be measured.

4. The on-chip stimulated Raman photothermal gas sensing method according to claim 3, characterized in that, The phase difference between the original probe light TE fundamental mode and the converted probe light TE fundamental mode suppresses common mode background phase disturbances caused by environmental changes and device drift.

5. The on-chip stimulated Raman photothermal gas sensing method according to claim 4, characterized in that, The harmonic components of the detection signal are extracted by a lock-in amplifier, and the concentration of the gas to be measured is characterized by the amplitude of the harmonic components.

Images