On-chip stimulated raman photothermal gas sensing system and method

Abstract

The application discloses a kind of on-chip stimulated raman photo-thermal gas sensing system and method, specifically related to gas analysis measurement technical field.The application is interacted with the gas to be measured by pump light and stokes light in the evanescent field region of sensing waveguide, and the stimulated raman process of gas molecule is excited and local temperature rise is generated by thermal relaxation, so as to cause the refractive index change of gas, and make the probe light produce the phase modulation signal related to refractive index change.Difference processing is carried out by distinguishing and to the phase modulation signal related to gas photo-thermal effect and background phase disturbance, to suppress phase background noise and improve the signal-to-noise ratio and sensitivity of gas measurement.The application integrates laser, sensing waveguide and detector and other functional units on a single chip, forms a kind of compact structure, low power consumption and strong noise immunity gas measurement system, effectively solves the problem of weak signal, large background noise and low integration in traditional waveguide raman gas measurement.

Description

Technical Field

[0001] This invention relates to the field of gas analysis and measurement technology, and more specifically, to an on-chip stimulated Raman photothermal gas sensing system and method. Background Technology

[0002] Gas detection technology is widely used in environmental remediation, industrial safety, and energy utilization, with the goal of rapidly and accurately identifying and analyzing gas types and concentrations. While traditional methods such as electrochemical sensing or catalytic combustion detection are technically mature, they still have shortcomings in response speed, selectivity, and anti-interference capabilities, making it difficult to meet the demands of emerging high-precision applications.

[0003] Optical detection technologies, especially stimulated Raman scattering spectroscopy, can obtain characteristic spectral lines related to molecular structure by utilizing the scattering signals generated by the interaction of light with gas molecules, thereby achieving highly selective identification. Stimulated Raman photothermal spectroscopy, building upon this foundation, further improves detection sensitivity. However, current on-chip Raman sensors still face several key bottlenecks. First, the Raman scattering signal from gas molecules is very weak; even with enhanced coupling within waveguide structures, the detection results are still susceptible to noise. Second, the waveguide itself generates a strong background Raman signal, masking the spectral lines of the target and reducing the signal-to-noise ratio. Furthermore, integrating devices made of different materials, such as light sources and waveguides, onto a single chip is complex, costly, and suffers from poor compatibility, significantly limiting the overall system performance and large-scale application.

[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 system's dependence on complex integration processes and high-precision alignment while ensuring high device integration, thereby improving the practicality and stability of the gas sensing system. Summary of the Invention

[0005] In view of the problems mentioned in the background art, the present invention provides an on-chip stimulated Raman photothermal gas sensing system and method to overcome the defects existing in the prior art.

[0006] The technical solution of the present invention to solve the above problems is as follows:

[0007] An on-chip stimulated Raman photothermal gas sensing system includes:

[0008] Stimulated Raman photothermal gas sensor chip, first laser driver, second laser driver, lock-in amplifier, and analysis terminal;

[0009] 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.

[0010] 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;

[0011] 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 all enter the sensing waveguide. 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] Preferably, the original probe light TE fundamental mode obtains phase modulation caused by the gas photothermal effect in the sensing region 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.

[0017] An on-chip stimulated Raman photothermal gas sensing method, applied to an on-chip stimulated Raman photothermal gas sensing system, includes the following steps:

[0018] 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;

[0019] 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.

[0020] 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.

[0021] S4: Use the first microring resonator and the second microring resonator to filter out the pump light and Stokes light respectively;

[0022] 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.

[0023] 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.

[0024] Preferably, 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.

[0025] Preferably, 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 based on the amplitude of the harmonic components.

[0026] The beneficial effects of this invention are as follows:

[0027] (1) Based on the stimulated Raman photothermal effect, this invention uses the interaction between the pump light and Stokes light and the gas to be measured in the evanescent field region of the sensing waveguide to convert the Raman transition information of gas molecules into the refractive index change caused by the local thermal effect, and further convert it into the phase modulation signal of the probe light, thus realizing the effective mapping of gas information from the molecular scale to an optically detectable signal. Combined with the strong confinement capability of the sensing waveguide to the light field, the interaction intensity between light and gas is greatly enhanced, enabling the detection of trace gases at the ppm level.

[0028] (2) By simultaneously guiding the pump light, Stokes light, and probe light in the sensing waveguide, and using phase modulation of the probe light for detection, direct measurement of weak Raman scattering intensity is avoided, thus improving detection sensitivity. This method is particularly suitable for high-sensitivity detection of low-concentration gases. Using the polarization mode phase difference detection method, the photodetector acquires the Raman photothermal phase signal of the original probe light TE fundamental mode and the Raman photothermal phase signal of the probe light TE fundamental mode after conversion by the probe light TM fundamental mode. Phase difference detection suppresses phase background noise, improving the signal-to-noise ratio and detection sensitivity.

[0029] (3) By integrating the pump laser, Stokes laser, probe laser, polarization beam splitter, first coupler, microring resonator, photodetector, and various waveguides onto a single chip, the size and power consumption are effectively reduced. The system is based on on-chip optical waveguides and integrated optical devices. The functional modules are connected through waveguides, eliminating the need for complex free-space optical alignment. It has the advantages of compact structure, high integration, and ease of mass production. It is suitable for further integration with on-chip light sources, detectors, and signal processing circuits, which is conducive to realizing miniaturized, low-power, and multi-channel gas sensing systems.

[0030] (4) This invention utilizes the difference in optical field overlap of different polarization modes of probe light in the gas region, takes the polarization mode with larger optical field overlap as the signal channel, and takes the polarization mode with smaller optical field overlap as the reference channel, and suppresses the common mode background phase noise caused by waveguide material, temperature change and environmental disturbance through phase difference detection, thereby significantly improving the stability and repeatability of the detection results.

[0031] (5) By introducing a micro-ring resonator coupled to the evanescent field of the coupled output waveguide at the output end of the sensing waveguide, the pump light and Stokes light are selectively filtered out, which effectively avoids the interference of strong light signals entering the probe light channel on phase detection, improves the signal-to-noise ratio of the system and simplifies the back-end signal processing. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of an on-chip stimulated Raman photothermal gas sensing system provided in an embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of the stimulated Raman scattering energy level transition and thermal relaxation process provided in an embodiment of the present invention.

[0035] Figure label:

[0036] 1-Stimulated Raman photothermal gas sensor chip, 2-Stokes laser, 3-Pump laser, 4-Probe laser, 5-Polarization beam splitter, 6-First coupler, 7-Polarization rotation beam splitter, 8-Second coupler, 9-Photodetector, 10-Lock-in 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 input waveguide, 17-Probe TE polarization input waveguide, 18-Probe TM polarization input waveguide, 19-Coupled input waveguide, 20-Sensing waveguide, 21-First microring resonator, 22-Second microring resonator, 23-Coupled output waveguide, 24-Probe TE polarization output waveguide, 25-Probe TM-TE polarization conversion output waveguide, 26-Probe output waveguide. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0039] See Figure 1The on-chip stimulated Raman photothermal gas sensing system includes 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 includes: a pump laser 3, a Stokes laser 2, a probe 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 input waveguide 16, a probe TE polarization input waveguide 17, a probe TM polarization input waveguide 18, a coupling input waveguide 19, a sensing waveguide 20, a coupling output waveguide 23, a first microring resonator 21, a second microring resonator 22, a probe TE polarization output waveguide 24, a probe TM-TE polarization conversion output waveguide 25, and a probe output waveguide 26.

[0040] By way of example and not limitation, in this embodiment of the invention, the pump laser 3, Stokes laser 2, probe laser 4, polarization beam splitter 5, first coupler 6, polarization rotation beam splitter 7, second coupler 8, photodetector 9, pump TE polarization input waveguide 15, Stokes TE polarization input waveguide 14, probe input waveguide 16, probe TE polarization input waveguide 17, probe TM polarization input waveguide 18, coupling input waveguide 19, sensing waveguide 20, coupling output waveguide 23, first microring resonator 21, second microring resonator 22, probe TE polarization output waveguide 24, probe TM-TE polarization conversion output waveguide 25, and probe output waveguide 26 are all integrated on a SiO2 substrate.

[0041] In this embodiment of the invention, the output terminal of the pump laser 3 is connected to the input terminal of the first coupler 6; the input and output terminals of the Stokes laser 2 are connected to the output terminal of the first laser driver 12 and the input terminal of the first coupler 6, respectively; the input and output terminals of the probe laser 4 are connected to the output terminal of the second laser driver 13 and the input terminal of the polarization beam splitter 5, respectively; the output terminal of the polarization beam splitter 5 is connected to the input terminal of the first coupler 6; the output terminal of the first coupler 6 is connected to the input terminal of the sensing waveguide 20; the output terminal of the sensing waveguide 20 is connected to the input terminal of the polarization rotating beam splitter 7; the output terminal of the polarization rotating beam splitter 7 is connected to the input terminal of the second coupler 8; the output terminal of the second coupler 8 is connected to the input terminal of the photodetector 9; the output terminal of the photodetector 9 is connected to the input terminal of the lock-in amplifier 10; the modulation signal output terminal and the demodulation signal output terminal of the lock-in amplifier 10 are connected to the modulation signal input terminal of the first laser driver 12 and the input terminal of the analysis terminal 11, respectively.

[0042] Specifically, the output of pump laser 3 is connected to the input of first coupler 6 via pump TE polarization input waveguide 15; the output of Stokes laser 2 is connected to the input of first coupler 6 via Stokes TE polarization input waveguide 14; the output of probe laser 4 is connected to the input of polarization beam splitter 5 via probe input waveguide 16; the output of polarization beam splitter 5 is connected to the input of first coupler 6 via probe TE polarization input waveguide 17 and probe TM polarization input waveguide 18; the output of first coupler 6 is connected to the input of sensing waveguide 20 via coupling input waveguide 19; the output of sensing waveguide 20 is connected to the input of polarization rotating beam splitter 7 via coupling output waveguide 23; the output of polarization rotating beam splitter 7 is connected to the input of second coupler 8 via probe TE polarization output waveguide 24 and probe TM-TE polarization conversion output waveguide 25; and the output of second coupler 8 is connected to the input of photodetector 9 via probe output waveguide 26. A first microring resonator 21 and a second microring resonator 22 are provided between the sensing waveguide 20 and the polarization rotating beam splitter 7. The stimulated Raman photothermal gas sensing chip 1 is encapsulated in a gas chamber.

[0043] By way of example and not limitation, in this embodiment of the invention, 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 Si3N4 rectangular waveguides, and the sensing waveguide 20 is a Si3N4 slit waveguide.

[0044] Please see Figure 2 , Figure 2 This is a schematic diagram illustrating the stimulated Raman scattering energy level transitions and thermal relaxation processes provided in an embodiment of the present invention. Wherein, The frequency of the pump light. The frequency of Stokes light. The frequency of the Raman transition of the gas to be tested is denoted as . In this embodiment of the invention, pump light, Stokes light, and probe light are used as incident light sources. These light sources are input from the input end of the sensing waveguide 20. A portion of the light fields of the pump light and Stokes light propagate in the gas medium outside the sensing waveguide 20 as evanescent fields and overlap. The overlapping evanescent fields interact with the gas to be tested, resulting in stimulated Raman scattering mediated by Raman transitions of gas molecules. The pump light is partially converted into Stokes light, and the Stokes light signal gains gain. Gas molecules are excited from the ground state to the excited state through stimulated Raman scattering. Subsequently, the gas molecules transition back to the ground state through a thermal relaxation process. The energy of the relaxation process is released as heat, generating a heat source and causing a local temperature increase near the waveguide. Due to the thermo-optic effect, this temperature increase causes a change in the refractive index of the gas. The probe light undergoes a phase change proportional to this refractive index change. In this process, the frequency difference between the pump light and the Stokes light equals the Raman transition frequency of the gas being measured. The pump light and the Stokes light interact with the gas being measured in the evanescent field region outside the sensing waveguide. When the frequency difference between them matches the Raman transition frequency of the gas molecules, a stimulated Raman process is generated within the sensing region. This stimulated Raman process, through nonradiative relaxation, creates a local heat source, causing a change in the gas's refractive index. This results in a phase modulation of the probe light propagating within the same sensing region, which is related to the gas concentration.

[0045] This invention also provides an on-chip stimulated Raman photothermal gas sensing method, comprising the following steps:

[0046] S1: Output pump light, Stokes light, and probe light respectively, matching the frequency difference between the pump light and the Stokes light to the Raman transition frequency of the gas under test; S2: Input 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 via the first coupler, and introduce the gas under test into the gas sensing region; S3: Cause the pump light and the Stokes light to undergo a stimulated Raman process with the gas under test in the evanescent field region outside the sensing waveguide, and generate a local temperature rise through thermal relaxation, causing a change in the refractive index of the gas and causing phase modulation of the probe light; S4: Utilize the first... The micro-ring resonator and the second micro-ring resonator 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, interfere and combine the converted probe light TE fundamental mode with 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.

[0047] By exploiting the phase difference between the original probe light TE fundamental mode and the converted probe light TE fundamental mode, common mode background phase disturbances caused by environmental changes and device drift are suppressed. Harmonic components of the detection signal are extracted using a lock-in amplifier, and the concentration of the analyte gas is characterized based on the amplitude of these harmonic components.

[0048] In this invention, the probe light is split into two paths after propagating through the sensing waveguide 20. One path is the original probe light TE fundamental mode with a large evanescent field overlap in the sensing region, and the other path is the probe light TM fundamental mode with a smaller evanescent field overlap in the sensing region. The probe light TM fundamental mode is converted into a probe light TE fundamental mode with the same polarization state as the original probe light TE fundamental mode after polarization rotation. The polarization rotation beam splitter 7 is used to separate the original probe light TE fundamental mode and the probe light TM fundamental mode, and convert the probe light TM fundamental mode into a probe light TE fundamental mode obtained by converting the TM fundamental mode. The converted probe light TE fundamental mode obtained by converting the TM fundamental mode is a TE fundamental mode with the same polarization state as the original probe light TE fundamental mode. Before entering the second coupler 8, the two probe light TE fundamental modes carry phase information. The phase of the original probe light TE fundamental mode includes both phase modulation caused by the gas photothermal effect and common mode background phase perturbation, while the probe light TE fundamental mode obtained by converting the probe light TM fundamental mode carries common mode background phase perturbation. The two probe beams undergo optical interference in the second coupler 8. After photoelectric detection, the interference output converts the phase difference between the two probe beams into an electrical signal, causing the common mode background phase disturbance to cancel each other in the phase difference, thereby obtaining a phase modulation signal related to the concentration of the gas to be measured.

[0049] In this invention, the first microring resonator 21 and the second microring resonator 22 achieve selective filtering of light of a specific wavelength by forming a lateral evanescent field coupling with the coupled output waveguide 23, respectively. When the resonant wavelength of the microring resonator matches the wavelength of the corresponding light source, the light of that wavelength enters the microring through the evanescent field coupling and is suppressed, thereby preventing pump light and Stokes light from entering the subsequent probe light channel and interfering with phase detection.

[0050] In this invention, a sensing waveguide is used to guide the propagation of multiple polarization modes and interact with the gas under test through the evanescent field of the guided modes propagating in the waveguide. Due to differences in waveguide geometry and refractive index distribution, the field distribution of different polarization modes in the sensing region varies significantly. For the original probe light TE fundamental mode, its principal electric field component is parallel to the waveguide surface, exhibiting a stronger evanescent field extension in the waveguide cladding and gas region, thus forming a large optical field overlap in the gas under test region. In contrast, the principal electric field component of the probe light TM fundamental mode is mainly perpendicular to the waveguide surface, and its optical field is more concentrated inside the waveguide core, with a weaker evanescent field distribution in the gas region, resulting in a smaller optical field overlap. Optical field overlap refers to the degree of effective optical field distribution in which the guided modes propagating in the waveguide extend to the outside of the waveguide in the form of an evanescent field and interact with the gas under test within the sensing region. Its magnitude reflects the ability of the guided modes to interact with the gas medium in terms of energy and phase.

[0051] Based on the aforementioned differences, when the pump light and Stokes light undergo stimulated Raman spectroscopy with the analyte gas in the evanescent field region outside the sensing waveguide, and a local temperature rise is caused by thermal relaxation, the photothermal phase modulation caused by the change in gas refractive index mainly affects the probe light TE fundamental mode, which has a large optical field overlap, while having a weaker impact on the probe light TM fundamental mode, which has a smaller optical field overlap. Therefore, the phase information carried by the original probe light TE fundamental mode simultaneously includes the phase modulation caused by the gas photothermal effect and the common mode background phase perturbation, while the probe light TM fundamental mode reflects the common mode background phase perturbation. By utilizing the difference in optical field overlap between the original probe light TE fundamental mode and the probe light TM fundamental mode, and by performing differential processing on the phase information of the two probe lights, the phase modulation signal related to the concentration of the analyte gas can be extracted while suppressing the common mode background phase perturbation.

[0052] The various embodiments in this invention are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0053] The embodiments described above are merely preferred embodiments of the present invention. The terms "in one embodiment," "in another embodiment," "in yet another embodiment," or "in still another embodiment" used in this specification all refer to one or more of the same or different embodiments according to this disclosure. Ordinary variations and substitutions made by those skilled in the art within the scope of the present invention should be included within the protection scope of the present invention.

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.

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