An on-chip stimulated Raman scattering gas sensing system and method

Abstract

This invention discloses an on-chip stimulated Raman scattering gas sensing system and method, specifically relating to the field of gas analysis and measurement technology. The system enhances the Raman scattering process of gas molecules by interacting with the target gas in the evanescent field region of the sensing waveguide using pump light and Stokes light, and acquires the Stokes light Raman gain signal related to the gas concentration. To suppress Raman background noise caused by the waveguide material, this invention introduces different polarization modes of the Stokes light into the sensing waveguide. A micro-ring resonator and a polarization beam splitter filter out the pump light and separate the Stokes light's TE and TM fundamental modes. A balanced photodetector is used to differentially process the Raman gain signals corresponding to the two polarization modes, thereby improving the signal-to-noise ratio and sensitivity of gas detection. Simultaneously, the laser, sensing waveguide, and detection unit are integrated, resulting in a compact structure, low power consumption, and high sensitivity, enabling the detection of gases at the ppm level.

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 scattering gas sensing system and method. Background Technology

[0002] Gas sensing is of great significance for monitoring environmental climate, ensuring industrial safety, and improving energy efficiency. Traditional gas sensors, such as electrochemical and catalytic combustion sensors, suffer from problems such as slow response speed, poor selectivity, and susceptibility to environmental interference.

[0003] Waveguide-enhanced Raman spectroscopy utilizes optical waveguide structures to confine the light field within a space at the micrometer or even nanometer scale, enhancing the interaction between light and the analyte gas, increasing optical power density, and strengthening the Raman signal both laterally and longitudinally. Stimulated Raman spectroscopy, by detecting the scattering spectra generated by vibrational or rotational energy level transitions of gas molecules, possesses fingerprint-like characteristics, extremely high selectivity, and fast response speed, making it an ideal method for gas detection and measurement.

[0004] Currently, existing Raman spectroscopy gas sensing technology still faces three major bottlenecks. First, the Raman scattering cross section of gas molecules is extremely small, and within the limited interaction length on the chip, the generated Raman signal is very weak, making it difficult to detect low-concentration gases. Second, the sensing waveguide material itself generates strong Raman background noise, the intensity of which far exceeds the Raman signal of gas molecules, resulting in an extremely low signal-to-noise ratio and severely affecting the detection limit. Furthermore, achieving high-performance sensing requires integrating active and passive devices from different material systems onto the same chip; the integration process for such complex material systems is difficult and costly, and existing reports mostly present discrete solutions or solutions containing only passive waveguides, resulting in low integration density.

[0005] Therefore, there is an urgent need for an on-chip gas sensing system and method that can effectively solve problems such as weak gas Raman signals, high material background noise, and difficulty in monolithic integration. Summary of the Invention

[0006] In view of the problems mentioned in the background art, the present invention provides an on-chip stimulated Raman scattering gas sensing system and method, which solves the defects existing in the prior art.

[0007] The technical solution of the present invention to solve the above problems is as follows:

[0008] An on-chip stimulated Raman scattering gas sensing system includes:

[0009] Stimulated Raman scattering gas sensor chip, first laser driver, second laser driver, lock-in amplifier, and analysis terminal;

[0010] The stimulated Raman scattering gas sensing chip includes:

[0011] A pump laser is connected to the first laser driver;

[0012] A Stokes laser is connected to the second laser driver;

[0013] A coupler is connected to the pump laser via a pumped TE polarization input waveguide;

[0014] The sensing waveguide is connected to the output of the coupler via a coupling input waveguide, and is used to simultaneously transmit the pump light TE fundamental mode, the Stokes light TE fundamental mode, and the Stokes light TM fundamental mode, and form an evanescent field interaction region with the gas under test.

[0015] A coupling output waveguide is connected to the output terminal of the sensing waveguide;

[0016] A microring resonator is formed with the coupled output waveguide to form a lateral evanescent field coupling connection, which is used to suppress the pump light TE fundamental mode propagating along the coupled output waveguide under the resonance condition corresponding to the pump light wavelength;

[0017] The first polarization beam splitter, whose input is connected to the output of the coupled output waveguide, is used to separate the Stokes TE fundamental mode from the Stokes TM fundamental mode.

[0018] A balanced photodetector has its signal end connected to the Stokes TE fundamental mode output by the first polarization beam splitter, and its reference end connected to the Stokes TM fundamental mode output by the first polarization beam splitter. The balanced photodetector performs differential detection on the light intensity signals corresponding to the Stokes TE fundamental mode and the Stokes TM fundamental mode to eliminate the waveguide material Raman background noise that exists as common-mode noise in the Stokes TE fundamental mode and the Stokes TM fundamental mode.

[0019] The second polarization beam splitter has its input end connected to the Stokes laser via a Stokes input waveguide, and its output end connected to the coupler via a Stokes TE polarization input waveguide and a Stokes TM polarization input waveguide, respectively.

[0020] The sensing waveguide is configured such that the gain of the Stokes TE fundamental mode on the stimulated Raman scattering signal of the gas under test is higher than that of the Stokes TM fundamental mode on the gas under test.

[0021] The lock-in amplifier is connected to the first laser driver and the balanced photodetector, and is used to modulate the pump light and synchronously detect the differential detection signal;

[0022] The analysis terminal is used to receive and process the signal output by the lock-in amplifier to obtain the concentration information of the gas to be measured.

[0023] Preferably, the pump TE polarization input waveguide is configured to guide the pump light into the sensing waveguide in the TE fundamental mode; the Stokes TE polarization input waveguide and the Stokes TM polarization input waveguide are respectively configured to guide the Stokes light into the sensing waveguide in the TE fundamental mode and the TM fundamental mode.

[0024] An on-chip stimulated Raman scattering gas sensing method, applied to an on-chip stimulated Raman scattering gas sensing system, includes the following steps:

[0025] S1: Set the output wavelengths of the pump laser and the Stokes laser so that the frequency difference between them is equal to the Raman transition frequency of the gas under test, and modulate the pump light.

[0026] S2: The pump light TE fundamental mode, Stokes light TE fundamental mode and Stokes light TM fundamental mode are input into the sensing waveguide through a coupler, and the gas to be measured is introduced into the sensing area around the sensing waveguide.

[0027] S3: The pump light TE fundamental mode output from the sensing waveguide is suppressed using a micro-ring resonator, and the Stokes light TE fundamental mode and the Stokes light TM fundamental mode are separated by a first polarization beam splitter.

[0028] S4: Input the Stokes TE fundamental mode and Stokes TM fundamental mode to the signal terminal and reference terminal of the balanced photodetector respectively, and perform differential processing to eliminate the waveguide material Raman background noise that exists as common mode noise in the Stokes TE fundamental mode and Stokes TM fundamental mode.

[0029] S5: Synchronously detect the differentially processed signal and obtain the concentration information of the gas to be tested based on the detection results.

[0030] Preferably, when the pump light and Stokes light propagate in the sensing waveguide, part of their optical field extends to the sensing region in the form of an evanescent field and interacts with the gas to be measured, thereby causing stimulated Raman scattering mediated by Raman transitions of gas molecules, which converts part of the energy of the pump light into Stokes light and generates a gain on the Stokes light.

[0031] Preferably, the differential signal output by the balanced photodetector is used to characterize the stimulated Raman gain of the Stokes light, and the differential signal is related to the pump light power, the sensing waveguide length, and the Raman gain factor of the gas under test.

[0032] The beneficial effects of this invention are as follows:

[0033] (1) By integrating devices such as lasers, detectors and sensing waveguides on a single chip, and by adopting a reasonable layout of the chip structure and adjusting the corresponding connection relationship of each device, the pump laser, Stokes laser, polarization beam splitter, coupler, micro-ring resonator, balanced photodetector and various waveguides are integrated on a single chip, which significantly reduces the overall size and power consumption of the chip.

[0034] (2) By using a sensing waveguide, the pump light and Stokes light generate significant spatial overlap in the gas medium cladding on the waveguide, which improves the light-gas interaction intensity. By utilizing the stimulated Raman scattering process, part of the energy of the pump light is effectively transferred to the Stokes light, forming a Stokes signal gain, which greatly enhances the weak gas Raman signal, improves the sensing sensitivity, and can achieve a detection limit at the ppm level.

[0035] (3) The polarization gain balance detection method is adopted. By taking advantage of the difference in the degree of effect of the TE fundamental mode and the TM fundamental mode on the gas evanescent field in the sensing area, the TM fundamental mode is used as the reference channel for the material Raman background noise, thereby realizing the differential elimination of common mode noise. This improves the stability and repeatability of the system for detecting low-concentration gases and reduces the impact of device manufacturing errors and environmental disturbances on the detection results.

[0036] (4) By introducing a micro-ring resonator on the chip to selectively suppress the pump light and combining it with polarization-balanced differential detection, the interference of pump light leakage and waveguide material Raman scattering background noise on Stokes signal detection is effectively reduced, thereby significantly improving the signal-to-noise ratio of gas stimulated Raman scattering signal without increasing pump power.

[0037] (5) The stimulated Raman scattering gas sensing system of the present invention is based on on-chip optical waveguides and integrated optical devices. The functional modules are directly connected through waveguides, without the need for complex free space optical alignment structures. It has the advantages of high integration, compact structure and easy 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. Attached Figure Description

[0038] To facilitate understanding of the invention, it will be described in more detail with reference to the specific embodiments shown in the accompanying drawings. These drawings depict only typical embodiments of the invention and should not be considered as limiting the scope of protection of the invention.

[0039] Figure 1 This is a schematic diagram of the structure of the on-chip stimulated Raman scattering gas sensing system provided in an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of Stokes signal gain simulation provided in an embodiment of the present invention.

[0041] Figure label:

[0042] 1-Stimulated Raman scattering gas sensor chip, 2-Pump laser assembly, 3-Stokes laser assembly, 4-Signal analysis assembly, 5-Pump laser, 6-Stokes laser, 7-Second polarization beam splitter, 8-Coupled, 9-First polarization beam splitter, 10-Balanced photodetector, 11-Lock-in amplifier, 12-Analysis terminal, 13-First laser driver, 14-Second laser driver, 15-Pump TE polarization input waveguide, 16-Stokes input waveguide, 17-Stokes TE polarization input waveguide, 18-Stokes™ polarization input waveguide, 19-Coupled input waveguide, 20-Sensing waveguide, 21-Coupled output waveguide, 22-Micro-ring resonator, 23-Stokes TE polarization output waveguide, 24-Stokes™ polarization output waveguide. Detailed Implementation

[0043] Embodiments of the present invention are described below with reference to the accompanying drawings to enable those skilled in the art to better understand and implement the invention. However, the listed embodiments are not intended to limit the invention. Unless otherwise specified, the embodiments and technical features described below can be combined with each other, wherein identical components are denoted by the same reference numerals. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0044] Please refer to Figure 1 as well as Figure 2 , Figure 1 This is a schematic diagram of the structure of the on-chip stimulated Raman scattering gas sensing system provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of Stokes signal gain simulation provided in an embodiment of the present invention.

[0045] See Figure 1In this embodiment of the invention, the on-chip stimulated Raman scattering gas sensing system includes: a stimulated Raman scattering gas sensing chip 1, a first laser driver 13, a second laser driver 14, a lock-in amplifier 11, and an analysis terminal 12; the stimulated Raman scattering gas sensing chip 1 includes: a Stokes laser 6 connected to the second laser driver 14; a pump laser 5 connected to the first laser driver 13; a coupler 8 connected to the pump laser 5 via a pump TE polarization input waveguide 15; and a microring resonator 22 coupled to the output waveguide 2. 1. A lateral evanescent field coupling connection is formed; a first polarization beamsplitter 9 has its input end connected to a coupling output waveguide 21, its first output end connected to the signal end of a balanced photodetector 10 via a Stokes TE polarization output waveguide 23, and its second output end connected to the reference end of the balanced photodetector 10 via a Stokes TM polarization output waveguide 24; a second polarization beamsplitter 7 has its input end connected to a Stokes laser 6 via a Stokes input waveguide 16, and its first and second output ends connected to a Stokes TE polarization input waveguide 17 respectively. The Stokes™ polarization input waveguide 18 is connected to the coupler 8; and the output of the balanced photodetector 10 is connected to the input of the lock-in amplifier 11; the first and second outputs of the lock-in amplifier 11 are respectively connected to the analysis terminal 12 and the first laser driver 13; the sensing waveguide 20 is configured to simultaneously transmit the pump light TE fundamental mode, the Stokes light TE fundamental mode, and the Stokes light TM fundamental mode, with the Stokes light TE fundamental mode having a higher gain than the Stokes light TM fundamental mode for the stimulated Raman scattering signal of the gas under test; the first output of the first polarization beam splitter 9 outputs the Stokes light TE fundamental mode carrying the stimulated Raman scattering enhancement signal, and the second output of the first polarization beam splitter 9 outputs the Stokes light TM fundamental mode; the signal and reference ends of the balanced photodetector 10 receive the Stokes light TE fundamental mode and the Stokes light TM fundamental mode, respectively, and differential processing is performed on the signal and reference ends of the balanced photodetector 10 to suppress the common waveguide material Raman background noise signal in the Stokes light TE fundamental mode and the Stokes light TM fundamental mode.

[0046] Pump TE polarization input waveguide 15 is configured to guide pump light into sensing waveguide 20 in TE fundamental mode; Stokes TE polarization input waveguide 17 and Stokes TM polarization input waveguide 18 are configured to guide Stokes light into sensing waveguide 20 in TE fundamental mode and Stokes TM fundamental mode, respectively; microring resonator 22 is used to filter out the pump light TE fundamental mode output from sensing waveguide 20; second polarization beamsplitter 7 is used to separate the Stokes TE fundamental mode and Stokes TM fundamental mode output from Stokes laser 6; first polarization beamsplitter 9 is used to separate the Stokes TE fundamental mode and Stokes TM fundamental mode output from sensing waveguide 20; lock-in amplifier 11 is configured to provide a modulation signal to first laser driver 13 to achieve wavelength modulation of pump light and synchronously detect differential detection signal output from balanced photodetector 10; analysis terminal 12 is used to receive and process signals from lock-in amplifier 11 to extract and display gas concentration information.

[0047] The pump TE polarization input waveguide 15, Stokes input waveguide 16, Stokes TE polarization input waveguide 17, Stokes™ polarization input waveguide 18, coupling input waveguide 19, sensing waveguide 20, coupling output waveguide 21, Stokes TE polarization output waveguide 23, and Stokes™ polarization output waveguide 24 are any one of rectangular waveguides, ridge waveguides, slit waveguides, and photonic crystal waveguides. In another embodiment of the present invention, the pump TE polarization input waveguide 15, Stokes input waveguide 16, Stokes TE polarization input waveguide 17, Stokes™ polarization input waveguide 18, coupling input waveguide 19, coupling output waveguide 21, Stokes TE polarization output waveguide 23, and Stokes™ polarization output waveguide 24 are all selected as Si3N4 rectangular waveguides, and the sensing waveguide 20 is selected as a Si3N4 slit waveguide.

[0048] It is worth noting that in this invention, a coupling input waveguide disposed between the coupler and the sensing waveguide is used to guide the pump light and Stokes light, which have been combined by the coupler, into the sensing waveguide. The sensing waveguide is used to simultaneously transmit the pump light TE fundamental mode, the Stokes light TE fundamental mode, and the Stokes light TM fundamental mode, and forms an evanescent field interaction region with the gas under test. The balanced photodetector performs differential detection on the light intensity signals corresponding to the Stokes light TE fundamental mode and the Stokes light TM fundamental mode to eliminate the Raman background noise of the waveguide material that coexists in both signals. The sensing waveguide is configured such that the optical field overlap of the Stokes TE fundamental mode in the gas region is greater than that of the Stokes TM fundamental mode. Optical field overlap refers to the extent to which the guided mode extends outward from the waveguide in the sensing region as an evanescent field and interacts with the gas, and its magnitude is related to the field strength distribution of the guided mode in the gas region. To ensure that the gain of the Stokes TE fundamental mode on the stimulated Raman scattering signal of the gas is higher than that of the Stokes TM fundamental mode, the cross-section and cladding structure of the sensing waveguide are designed to ensure that the evanescent field proportion of the Stokes TE fundamental mode in the gas region is higher than that of the TM fundamental mode. This results in a significantly higher gain for stimulated Raman scattering of the gas by the TE fundamental mode compared to the TM fundamental mode, while the TM fundamental mode reflects the Raman background noise of the waveguide material. A microring resonator forms an evanescent field coupling with the coupled output waveguide, selectively suppressing the pump light under resonance conditions corresponding to the pump light wavelength, preventing the pump light from entering the subsequent polarization beam splitter and detector. The polarization beam splitter on the input side is used to construct two types of Stokes light incident by polarization, and the polarization beam splitter on the output side is used to extract the two polarization components after the sensing waveguide is applied for differential detection.

[0049] In another embodiment of the present invention, the on-chip stimulated Raman scattering gas sensing system includes the following functional components: a pump laser component 2, consisting of a pump laser 5 and a first laser driver 13, used to generate pump light, with its output end connected to a coupler 8 via a pump TE polarization input waveguide 15; a Stokes laser component 3, consisting of a Stokes laser 6, a second laser driver 14, and a second polarization beam splitter 7, used to generate Stokes light, with its output end connected to a coupler 8 via a Stokes TE polarization input waveguide 17 and a Stokes TM polarization input waveguide 18; and a signal analysis component 4, consisting of a balanced photodetector 10, a lock-in amplifier 11, and an analysis terminal 12, used to process the detection signal, wherein the input end of the balanced photodetector 10 is connected to the output end of the first polarization beam splitter 9, and the output end of the lock-in amplifier 11 is fed back to the first laser driver 13. The input and output terminals of pump laser 5 are connected to the output terminal of first laser driver 13 and the input terminal of coupler 8, respectively. The output terminal of pump laser 5 is the output terminal of pump laser assembly 2. The input and output terminals of Stokes laser 6 are connected to the output terminal of second laser driver 14 and the input terminal of second polarization beam splitter 7, respectively. The output terminal of second polarization beam splitter 7 is connected to the input terminal of coupler 8. The output terminal of second polarization beam splitter 7 is the output terminal of Stokes laser assembly 3. The signal and reference terminals of balanced photodetector 10 are the input terminals of signal analysis assembly 4. The signal and reference terminals of balanced photodetector 10 are connected to the two output terminals of first polarization beam splitter 9, respectively. A micro-ring resonator 22 is provided between sensing waveguide 20 and first polarization beam splitter 9. Stimulated Raman scattering gas sensing chip 1 is encapsulated in a gas chamber.

[0050] An on-chip stimulated Raman scattering (SMR) gas sensing method, applied to an on-chip SMR gas sensing system, includes: S1: setting the output wavelengths of a pump laser and a Stokes laser such that their frequency difference equals the Raman transition frequency of the gas to be measured, and modulating the pump light; S2: inputting the pump light TE fundamental mode, Stokes light TE fundamental mode, and Stokes light TM fundamental mode into a sensing waveguide via a coupler, and introducing the gas to be measured into the sensing area surrounding the sensing waveguide; S3: using a micro-ring resonator to suppress the pump light TE fundamental mode output from the sensing waveguide, and separating the Stokes light TE fundamental mode and Stokes light TM fundamental mode via a first polarization beam splitter; S4: inputting the Stokes light TE fundamental mode and TM fundamental mode to the signal and reference ends of a balanced photodetector, respectively, and performing differential processing to eliminate the waveguide material Raman background noise that exists as common-mode noise in the Stokes light TE fundamental mode and Stokes light TM fundamental mode; S5: synchronously detecting the differentially processed signal and obtaining the concentration information of the gas to be measured based on the detection results.

[0051] In an embodiment of the present invention, when the pump light and Stokes light propagate in the sensing waveguide, part of their light field extends to the sensing region in the form of an evanescent field and interacts with the gas to be measured, thereby causing a stimulated Raman scattering process mediated by Raman transitions of gas molecules, which converts part of the energy of the pump light into Stokes light and generates a gain on the Stokes light.

[0052] The signal terminal of the balanced photodetector 10 is used to receive the intensity of the Stokes light TE fundamental mode enhanced from the first polarization beam splitter 9. The reference end of the balanced photodetector 10 is used to receive the intensity of the Stokes™ fundamental mode-enhanced light output from the first polarization beam splitter 9. The signal gain of Stokes light is ;in, The enhanced Stokes intensity during stimulated Raman scattering. The initial intensity of the Stokes light. The optical power of the pump light, The length of sensing waveguide 20, Let be the refractive index of the gas to be tested. The Raman gain factor of the gas to be measured. The group refractive index is the value of the pump light propagating in the sensing waveguide 20. The group refractive index is the refractive index of Stokes light propagating in the sensing waveguide. The frequency of the pump light. The frequency of Stokes light. The integral of the overlap of the pump light and Stokes light in the gas region is given. The differential signal output by the balanced photodetector 10 is used to characterize the stimulated Raman gain of the Stokes light, and the differential signal is related to the pump light power, the sensing waveguide length, and the Raman gain factor of the gas under test.

[0053] See Figure 2 The Stokes optical signal gain increases with decreasing slit width and waveguide width. Furthermore, as the waveguide slit width increases, the range of waveguide widths that can support the transmission of both the pump light TE fundamental mode and the Stokes light TE fundamental mode in the slit waveguide decreases. Therefore, while ensuring the waveguide can effectively support the transmission of both the pump light TE fundamental mode and the Stokes light TE fundamental mode, reducing the waveguide width and slit width can significantly improve the Stokes optical signal gain.

[0054] It is worth noting that this invention integrates the laser, detector, and sensing waveguide onto a single chip by employing a rational chip structure layout and adjusting the corresponding connections of each component. This allows the pump laser, Stokes laser, polarization beam splitter, coupler, micro-ring resonator, balanced photodetector, and various waveguides to be integrated onto a single chip, significantly reducing the overall chip size and power consumption. By using a sensing waveguide, the pump light and Stokes light exhibit significant spatial overlap in the gas medium cladding on the waveguide. The cross-sectional structure and / or cladding structure of the sensing waveguide are designed so that the evanescent field proportion of the Stokes light TE fundamental mode in the sensing region is higher than that of the Stokes light TM fundamental mode. Utilizing stimulated Raman scattering, part of the pump light energy is effectively transferred to the Stokes light, forming a Stokes signal gain, which greatly enhances the weak gas Raman signal, improves sensing sensitivity, and enables a detection limit at the ppm level. A polarization gain-balanced detection method is employed, utilizing the difference in the degree of influence of the TE and TM fundamental modes on the evanescent field of the gas in the sensing region. The TM fundamental mode is used as a reference channel for material Raman background noise, achieving differential cancellation of common-mode noise. This improves the stability and repeatability of the system for detecting low-concentration gases and reduces the impact of device manufacturing errors and environmental disturbances on the detection results. By introducing a micro-ring resonator on-chip to selectively suppress the pump light, combined with polarization-balanced differential detection, the interference of pump light leakage and waveguide material Raman scattering background noise on Stokes signal detection is effectively reduced. This significantly improves the signal-to-noise ratio of the stimulated Raman scattering signal without increasing pump power. The stimulated Raman scattering gas sensing system of this invention is based on on-chip optical waveguides and integrated optical devices. The functional modules are directly connected via waveguides, eliminating the need for complex free-space optical alignment structures. It features high integration, compact structure, and ease of mass production, making it suitable for further integration with on-chip light sources, detectors, and signal processing circuits. This facilitates the realization of miniaturized, low-power, and multi-channel gas sensing systems.

[0055] 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.

[0056] 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 scattering gas sensing system, characterized in that, include: Stimulated Raman scattering gas sensor chip, first laser driver, second laser driver, lock-in amplifier, and analysis terminal; The stimulated Raman scattering gas sensing chip includes: A pump laser is connected to the first laser driver; a Stokes laser is connected to the second laser driver; A coupler is connected to the pump laser via a pumped TE polarization input waveguide; The sensing waveguide is connected to the output of the coupler via a coupling input waveguide, and is used to simultaneously transmit the pump light TE fundamental mode, the Stokes light TE fundamental mode, and the Stokes light TM fundamental mode, and form an evanescent field interaction region with the gas under test. A coupling output waveguide is connected to the output end of the sensing waveguide; A microring resonator is formed with the coupled output waveguide to form a lateral evanescent field coupling connection, which is used to suppress the pump light TE fundamental mode propagating along the coupled output waveguide under the resonance condition corresponding to the pump light wavelength; The first polarization beam splitter, whose input is connected to the output of the coupled output waveguide, is used to separate the Stokes TE fundamental mode from the Stokes TM fundamental mode. A balanced photodetector has its signal end connected to the Stokes TE fundamental mode output by the first polarization beam splitter, and its reference end connected to the Stokes TM fundamental mode output by the first polarization beam splitter. The balanced photodetector performs differential detection on the light intensity signals corresponding to the Stokes TE fundamental mode and the Stokes TM fundamental mode to eliminate the waveguide material Raman background noise that exists as common-mode noise in the Stokes TE fundamental mode and the Stokes TM fundamental mode. The second polarization beam splitter has its input end connected to the Stokes laser via a Stokes input waveguide, and its output end connected to the coupler via a Stokes TE polarization input waveguide and a Stokes TM polarization input waveguide, respectively. The sensing waveguide is configured such that the gain of the Stokes TE fundamental mode on the stimulated Raman scattering signal of the gas under test is higher than that of the Stokes TM fundamental mode on the gas under test. The lock-in amplifier is connected to the first laser driver and the balanced photodetector, and is used to modulate the pump light and synchronously detect the differential detection signal; The analysis terminal is used to receive and process the signal output by the lock-in amplifier to obtain the concentration information of the gas to be measured.

2. The on-chip stimulated Raman scattering gas sensing system according to claim 1, characterized in that, The pump TE polarization input waveguide is configured to guide pump light into the sensing waveguide in TE fundamental mode; the Stokes TE polarization input waveguide and the Stokes TM polarization input waveguide are respectively configured to guide Stokes light into the sensing waveguide in TE fundamental mode and TM fundamental mode.

3. An on-chip stimulated Raman scattering gas sensing method, applied to the on-chip stimulated Raman scattering gas sensing system according to any one of claims 1-2, characterized in that, Includes the following steps: S1: Set the output wavelengths of the pump laser and the Stokes laser so that the frequency difference between them is equal to the Raman transition frequency of the gas under test, and modulate the pump light. S2: The pump light TE fundamental mode, Stokes light TE fundamental mode and Stokes light TM fundamental mode are input into the sensing waveguide through a coupler, and the gas to be measured is introduced into the sensing area around the sensing waveguide. S3: The pump light TE fundamental mode output from the sensing waveguide is suppressed using a micro-ring resonator, and the Stokes light TE fundamental mode and the Stokes light TM fundamental mode are separated by a first polarization beam splitter. S4: Input the Stokes TE fundamental mode and Stokes TM fundamental mode to the signal terminal and reference terminal of the balanced photodetector respectively, and perform differential processing to eliminate the waveguide material Raman background noise that exists as common mode noise in the Stokes TE fundamental mode and Stokes TM fundamental mode. S5: Synchronously detect the differentially processed signal and obtain the concentration information of the gas to be tested based on the detection results.

4. The on-chip stimulated Raman scattering gas sensing method according to claim 3, characterized in that, When the pump light and Stokes light propagate in the sensing waveguide, part of their light field extends to the sensing region in the form of an evanescent field and interacts with the gas to be measured, thereby causing stimulated Raman scattering mediated by Raman transitions of gas molecules, which converts part of the energy of the pump light into Stokes light and generates a gain on the Stokes light.

5. The on-chip stimulated Raman scattering gas sensing method according to claim 4, characterized in that, The differential signal output by the balanced photodetector is used to characterize the stimulated Raman gain of the Stokes light, and the differential signal is related to the pump light power, the sensing waveguide length, and the Raman gain factor of the gas under test.

Images