An on-chip light-thermal gas sensor and an on-chip gas sensor assembly

Abstract

The present application relates to a kind of on-chip photo-thermal gas sensor and on-chip gas sensor assembly.The on-chip photo-thermal gas sensor integrates photo-thermal gas sensor with Mach-Zehnder interference structure to on-chip, compared with traditional free space and optical fiber sensing in photo-thermal interference method, because probe arm and reference arm are on the same substrate, the influence of external vibration on interference structure is far less than optical fiber sensing system.Moreover, without additional phase control unit, such as PZT, AOM etc., simplify detection system, create possibility for the miniaturization of entire sensing detection system.At the same time, the refractive index of the upper waveguide material layer of the ridge waveguide layer of probe arm is greater than the refractive index of the lower waveguide material layer, can support TM mode pump light and TE mode probe light simultaneously.Greatly improve the interaction of pump light and the gas to be measured, and reduce the spot size of pump light, while ensuring high sensitivity, greatly shorten the length of probe waveguide.

Description

Technical Field

[0001] This invention relates to the field of integrated photonic biosensor technology, and more particularly to an on-chip photothermal gas sensor and an on-chip gas sensor assembly. Background Technology

[0002] High-precision gas detection plays a very important role in environmental quality monitoring, industrial production, and disease diagnosis.

[0003] With the advent of the 5G era, the miniaturization, intelligence, and chip-based nature of sensors have gradually become a new generation of innovative technologies that countries are vying for. In trace gas detection, photothermal spectroscopy (PTS) is a commonly used method in fiber optic sensing. PTS technology is based on the absorption of light by the analyte molecules, which excites internal energy levels. This leads to energy transfer due to collisional relaxation, resulting in a local temperature increase, and the temperature change causes a change in the material's refractive index. Unlike traditional direct absorption spectroscopy (DAS), this method is an indirect light absorption analysis method. It measures the effect caused by light absorption by the gas in the sample. PTS devices typically use a pump light source to heat the sample and a probe laser source to detect the change in refractive index caused by temperature changes. The change in refractive index causes a phase shift in the probe light passing through the heated sample. High-sensitivity measurements are achieved through interferometer structures, such as Mach-Zehnder and Fabry-Pérot resonators.

[0004] The Mach-Zehnder interferometer is a single-pass interferometer where the probe light is split into two beams. One beam penetrates the heated sample region to form the sensing beam, while the other beam remains unaffected by the heated region to form the reference beam. These beams then pass through a combiner to form interference beams. The optical power received by the detector depends on the phase difference between the two beams. Currently, in fiber optic sensing systems, PTS technology can detect trace gases at the ~ppb level. However, detection devices constructed using fiber optic systems are susceptible to interference from the external environment, making them difficult to apply outside of laboratory settings. Summary of the Invention

[0005] Therefore, it is necessary to provide an on-chip photothermal gas sensor and an on-chip gas sensor assembly to address the above problems, so as to eliminate the influence of the external environment on the interference structure through integrated on-chip waveguide design.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] An on-chip photothermal gas sensor, comprising:

[0008] Substrate;

[0009] An incident waveguide, disposed at one end on the surface of the substrate, is used to receive a probe laser.

[0010] A beam splitter is disposed on the surface of the substrate and is used to split the probe laser emitted from the incident waveguide into two beams.

[0011] A probe arm is disposed at the middle position on the substrate surface, used to fill the gas to be measured and receive the probe laser split by the beam splitter;

[0012] A reference arm is arranged side by side with the probe arm at the middle position on the substrate surface and receives the probe laser split by the beam splitter, and the length of the reference arm is not equal to the length of the probe arm;

[0013] A beam combiner, disposed on the substrate surface, is used to combine the probe lasers emitted by the probe arm and the reference arm into a single beam;

[0014] An outgoing waveguide is disposed at the other end of the substrate surface to receive the probe laser emitted by the beam combiner and to emit the probe laser from the on-chip photothermal gas sensor.

[0015] The on-chip photothermal gas sensor disclosed in this invention integrates a photothermal gas sensor with a Mach-Zehnder interferometer structure onto a single chip. Compared to traditional photothermal interferometry in free-space and fiber optic sensing, the influence of external vibrations on the interference structure is far less than in fiber optic sensing systems because both the probe arm and reference arm are on the same substrate. Furthermore, it eliminates the need for additional phase control units such as PZTs or AOMs, simplifying the detection system and creating possibilities for miniaturization of the entire sensing system.

[0016] In another embodiment, the probe laser includes a pump light in TM mode and a probe light in TE mode.

[0017] In another embodiment, the probe arm includes:

[0018] A silicon oxide cladding layer is disposed on the surface of the substrate, and a lower air cladding layer is disposed in the middle of the silicon oxide cladding layer;

[0019] A ridge waveguide layer is disposed on the surface of the silicon oxide cladding and the lower air cladding, wherein the refractive index of the upper waveguide material layer of the ridge waveguide layer is greater than the refractive index of the lower waveguide material layer;

[0020] An upper air cladding layer is disposed on the surface of the ridge waveguide layer.

[0021] In this embodiment, the refractive index of the upper waveguide material layer of the probe arm ridge waveguide is greater than that of the lower waveguide material layer, enabling simultaneous support for both TM mode pump light and TE mode probe light. That is, it simultaneously addresses the high absorption of the pump light by the analyte gas and its weak influence on the probe light, thus improving the gas detection accuracy. Therefore, the on-chip photothermal gas sensor disclosed in this invention significantly improves the interaction between the pump light and the analyte gas, reduces the pump light spot size, and greatly shortens the length of the probe waveguide while maintaining high sensitivity, achieving a highly compact photothermal gas sensor structure.

[0022] In another embodiment, the wavelength and intensity of the pump light are modulated by a periodic function.

[0023] In another embodiment, the wavelength of the pump light is the wavelength at the absorption peak of the gas being measured.

[0024] In another embodiment, the wavelength of the probe light corresponds to the wavelength at the orthogonal point of the Mach-Zehnder interference structure and is the wavelength at the non-absorption peak of the gas to be measured.

[0025] In another embodiment, the length difference between the reference arm and the probe arm is 1 micrometer to 1 centimeter.

[0026] This embodiment employs a Mach-Zehnder interferometer structure, which allows adjustment of the free spectral region (FSR) of the interference fringes by varying the lengths of the reference and probe arms. This provides greater controllability, and the interference spectrum is less susceptible to the influence of reflected light from various junctions during device fabrication. In another embodiment, a first wavelength division multiplexer is also provided within the incident waveguide.

[0027] In another embodiment, a second wavelength division multiplexer is also provided in the outgoing waveguide.

[0028] Another embodiment of the present invention discloses an on-chip gas sensor assembly, which is the on-chip photothermal gas sensor described in any of the above embodiments.

[0029] The on-chip photothermal gas sensor assembly disclosed in this invention integrates a photothermal gas sensor with a Mach-Zehnder interferometer structure onto a single chip. Compared to traditional photothermal interferometry in free-space and fiber optic sensing, the influence of external vibrations on the interference structure is far less than in fiber optic sensing systems because both the probe arm and reference arm are on the same substrate. Furthermore, it eliminates the need for additional phase control units such as PZTs or AOMs, simplifying the detection system and creating possibilities for miniaturization of the entire sensing system.

[0030] Furthermore, the refractive index of the upper waveguide material layer of the probe arm ridge waveguide layer is greater than that of the lower waveguide material layer, enabling simultaneous support for both TM mode pump light and TE mode probe light. That is, when the pump light is switched to TM mode by the first polarization controller and the probe light is switched to TE mode by the second polarization controller, the on-chip photothermal gas sensor assembly can simultaneously accommodate the high absorption of the pump light by the gas under test and its weak influence on the probe light, thus improving the gas detection accuracy. Simultaneously, the on-chip photothermal gas sensor assembly disclosed in this invention employs a Mach-Zehnder interferometer structure, allowing adjustment of the free spectral region (FSR) of the interference fringes by adjusting the lengths of the reference arm and probe arm. This provides higher controllability, and the interference spectrum is less susceptible to the influence of reflected light at various junctions during device fabrication. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of an on-chip photothermal gas sensor disclosed in an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the probe arm structure in an on-chip photothermal gas sensor according to an embodiment of the present invention;

[0033] Figure 3 This is a graph showing the relationship between the normalized power of the pump light after amplitude modulation and time, as disclosed in an embodiment of the present invention.

[0034] Figure 4 This is a graph showing the relationship between the transmittance of light after passing through the Mach-Zehnder interference structure and the wavelength, as disclosed in an embodiment of the present invention.

[0035] Figure 5 This is a graph showing the relationship between transmittance and wavelength under different refractive indices after passing through a Mach-Zehnder interference structure, as disclosed in an embodiment of the present invention.

[0036] Figure 6 This is a graph showing the relationship between the normalized detection signal and time after passing through the Mach-Zehnder interferometer structure, as disclosed in an embodiment of the present invention.

[0037] Figure 7 This is a schematic diagram of another on-chip photothermal gas sensor disclosed in another embodiment of the present invention;

[0038] Figure 8 This is a schematic diagram of another on-chip photothermal gas sensor disclosed in another embodiment of the present invention;

[0039] Figure 9 This is a schematic diagram of an on-chip sensor assembly structure disclosed in another embodiment of the present invention;

[0040] Figure 10 This is a schematic diagram of another on-chip sensor component structure disclosed in another embodiment of the present invention.

[0041] In the figure, 1 is the substrate; 2 is the incident waveguide; 3 is the beam splitter; 4 is the probe arm; 5 is the reference arm; 6 is the beam combiner; 7 is the outgoing waveguide; 21 is the first wavelength division multiplexer; 71 is the second wavelength division multiplexer; 11 is the pump light emitter; 12 is the first polarization controller; 13 is the probe light emitter; 14 is the second polarization controller; 15 is the off-chip beam combiner; 16 is the on-chip photothermal gas sensor; 17 is the detector; 41 is the silicon oxide cladding; 42 is the lower air cladding; 43 is the upper waveguide material layer; 44 is the lower waveguide material layer; and 45 is the upper air cladding. Detailed Implementation

[0042] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments or examples only and is not intended to limit the invention. The optional scope of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0044] This invention discloses an on-chip photothermal gas sensor, such as... Figure 1 As shown, the on-chip photothermal gas sensor includes:

[0045] Substrate 1, wherein substrate 1 may be a silicon-based substrate;

[0046] An incident waveguide 2 is disposed at one end of the surface of the substrate 1 and is used to receive the probe laser.

[0047] Beam splitter 3, which is disposed on the surface of the substrate 1, is used to split the detection laser emitted by the incident waveguide 2 into two beams;

[0048] The probe arm 4 is disposed at the middle position on the surface of the substrate 1, and is used to fill the gas to be measured and receive the probe laser split by the beam splitter 3.

[0049] Reference arm 5 is arranged side by side with the probe arm 4 at the middle position on the surface of the substrate 1 and receives the probe laser split by the beam splitter 3. The length of the reference arm 5 is not equal to the length of the probe arm 4.

[0050] A beam combiner 6 is disposed on the surface of the substrate 1 and is used to combine the detection lasers emitted by the detection arm 4 and the reference arm 5 into a single beam.

[0051] The outgoing waveguide 7 is disposed at the other end of the surface of the substrate 1, and is used to receive the probe laser emitted by the beam combiner 6 and emit the probe laser from the on-chip photothermal gas sensor.

[0052] in, Figure 1 middle" "This refers to the path of light transmission, i.e. Figure 1 This shows the structure of the on-chip photothermal gas sensor and the transmission of light.

[0053] In this embodiment, the probe laser consists of a probe beam and a pump beam. During gas detection, the probe laser enters through the incident waveguide 2, and is then split into two beams by the beam splitter 3. One beam enters the probe arm 4, and the other enters the reference arm 5. The pump beam entering the probe arm 4 excites the gas being measured, causing its temperature to rise. This temperature change causes a change in the refractive index of the probe arm 4, which in turn causes a phase shift in the probe beam passing through it. The probe laser beams from the probe arm 4 and reference arm 5 are then combined by the beam combiner 6 and led out through the exit waveguide 7 to the outside of the on-chip photothermal gas sensor for further processing.

[0054] The on-chip photothermal gas sensor disclosed in this embodiment integrates a photothermal gas sensor with a Mach-Zehnder interferometer structure onto a single chip. Compared to traditional photothermal interferometry in free-space and fiber optic sensing, the influence of external vibrations on the interference structure is far less than in fiber optic sensing systems because both the probe arm and reference arm are on the same substrate. Furthermore, it eliminates the need for additional phase control units such as PZTs or AOMs, simplifying the detection system and creating possibilities for miniaturization of the entire sensing system.

[0055] In another embodiment, the probe laser includes a pump light in TM mode and a probe light in TE mode.

[0056] In this embodiment, the incident waveguide, beam splitter, probe arm, reference arm, beam combiner, and exit waveguide should all simultaneously support both quasi-transverse electric (quasi-TE) and quasi-transverse magnetic (quasi-TM) modes of transmission. Specifically, the waveguide structures of the beam splitter and beam combiner include, but are not limited to, multimode interference (MMI) structures, directional coupler structures, and other devices with similar beam splitting / combining functions.

[0057] Comparatively, TM mode pump light has a better excitation effect on the measured gas. In this regard, another embodiment of the present invention discloses a detector arm structure for an on-chip photothermal gas sensor, such as... Figure 2 As shown, the probe arm includes:

[0058] A silicon oxide cladding layer 41 is disposed on the surface of the substrate 1, and a lower air cladding layer 42 is disposed in the middle of the silicon oxide cladding layer 41.

[0059] A ridge waveguide layer is disposed on the surface of the silicon oxide cladding 41 and the lower air cladding 42. The ridge waveguide layer is composed of an upper waveguide material layer 43 and a lower waveguide material layer 44, and the refractive index of the upper waveguide material layer 43 is greater than the refractive index of the lower waveguide material layer 44.

[0060] An upper air cladding layer 45 is disposed on the surface of the ridge waveguide layer.

[0061] The on-chip photothermal gas sensor disclosed in this embodiment has a higher refractive index in the upper waveguide material layer of the probe arm ridge waveguide layer than in the lower waveguide material layer, enabling it to simultaneously support TM mode pump light and TE mode probe light. That is, it simultaneously addresses the high absorption of the pump light by the analyte gas and its weak influence on the probe light, thus improving the gas detection accuracy. Therefore, the on-chip photothermal gas sensor disclosed in this invention significantly improves the interaction between the pump light and the analyte gas, reduces the pump light spot size, and greatly shortens the length of the probe waveguide while maintaining high sensitivity, achieving a highly compact photothermal gas sensor structure.

[0062] In terms of specific material selection, the ridge waveguide layer should meet the requirement of having low optical loss at both the pump light wavelength and the probe light wavelength. Therefore, its materials include, but are not limited to, silicon nitride, chalcogenide glass, niobium lithium oxide, and polymers.

[0063] In this embodiment, the upper and lower waveguide material layers of the probe arm are made of chalcogenide glass, which has a significant advantage for gas detection in the mid-infrared band. More specifically, the upper waveguide material layer is made of GeSbSe, and the lower waveguide material layer is made of GeSbS. In another embodiment, to achieve TM mode transmission, the thickness of the lower waveguide material layer of the ridge waveguide layer should be sufficiently thin, but too thin to support the cantilever beam structure. Therefore, considering the above conditions, the minimum thickness of the lower waveguide material layer should not be less than 1 / 4 of the thickness of the ridge waveguide layer, and the maximum thickness should not exceed 1 / 2 of the thickness of the ridge waveguide layer, that is, the thickness of the lower waveguide material layer is 1 / 4 to 1 / 2 of the thickness of the ridge waveguide layer. However, the thickness of the upper and lower waveguide material layers in the ridge waveguide layer must also be adapted to the wavelengths of the pump light and the probe light, so it can be adjusted according to the wavelengths of the pump light and the probe light in actual design.

[0064] In another embodiment, the thickness of the silicon oxide cladding in the probe arm is only a few micrometers, while the thickness of the ridge waveguide layer is 100-300 nanometers. Specifically, the thickness of the silicon oxide cladding can be 5 micrometers, or 2 micrometers, 3 micrometers, or 7 micrometers, etc. The thickness of the ridge waveguide layer can be 100 nanometers, 150 nanometers, 200 nanometers, 250 nanometers, and 300 nanometers, etc. In this embodiment, the thickness of the ridge waveguide layer is selected as 260 nanometers. At this time, the thickness of the lower waveguide material layer is 65 nanometers, and the thickness of the upper waveguide material layer is 195 nanometers.

[0065] In another embodiment, the confinement factor can be further improved by optimizing the width of the ridge waveguide, the total waveguide height, and the thickness of the planar waveguide region. More preferably, the ridge waveguide has a width of 865 nm, a total waveguide height of 260 nm, and a planar waveguide region thickness of 65 nm. In this case, the confinement factor of the on-chip photothermal gas sensor disclosed in this embodiment is as high as 124%, which greatly improves the interaction between the pump light and the detected gas.

[0066] In another embodiment, the length difference between the reference arm and the detector arm is 1 micrometer to 1 centimeter. Under the action of periodic function modulated pump light, the length difference between the reference arm and the detector arm actually reflects the phase difference of the detected laser signal after passing through the reference arm and the detector arm. This embodiment can adjust the free spectral region (FSR) of the interference fringes by adjusting the lengths of the reference arm and the detector arm, which has higher controllability, and the interference spectrum is not easily affected by reflected light at various junctions during device fabrication.

[0067] In another embodiment, the wavelength of the pump light is selected to be the wavelength at the absorption peak of the gas to be measured, so as to enhance the absorption of the gas to be measured at that wavelength, thereby converting more of it into heat energy.

[0068] In another embodiment, the wavelength and intensity of the pump light are modulated by a periodic function. Specifically, the periodic function is a trigonometric function, a periodic rectangular pulse function, or a periodic triangular function.

[0069] The relationship between the normalized power of the pump light after amplitude modulation and time is as follows: Figure 3 As shown. It can be seen that the amplitude of the pump light changes periodically under the modulation of the sine function, and the modulation of the pump light power can be expressed by the following formula (1):

[0070] P(t)=P avg +P m sinωt(1)

[0071] Where Pavg and Pm are the average power and power modulation amplitude of the pump light, and ω is the modulation frequency of the pump light.

[0072] During the detection process, photons of the pump light are absorbed by the analyte molecules filling the detector arm, generating a localized heat source. Through heat transfer and diffusion, the waveguide temperature changes, thus affecting its refractive index. In the reference arm, since no analyte molecules absorb the pump light, the waveguide temperature and refractive index remain unchanged. Therefore, the two probe laser beams propagating in the detector and reference arms will have a phase difference before reaching the combiner. This phase difference causes a change in the intensity of the combined light detected by the detector. This method eliminates the influence of background light intensity variations on the test results.

[0073] In another embodiment, the wavelength of the probe light corresponds to the wavelength at the orthogonal point of the Mach-Zehnder interference structure and is the wavelength at the non-absorption peak of the gas to be measured.

[0074] The specific principles for selecting the wavelength of the probe light are as follows:

[0075] The relationship between the transmittance of light after passing through the Mach-Zehnder interferometer structure and wavelength is as follows: Figure 4 As shown. The transmittance of this interference structure varies sinusoidally with wavelength. Therefore, the probe wavelength is selected at the orthogonal point of the Mach-Zehnder interference structure and should also meet the requirements that both the waveguide material and the analyte molecule have low optical absorption. Specifically, the wavelength of the probe light corresponds to the orthogonal point of the Mach-Zehnder interference structure and is the wavelength at the non-absorption peak of the analyte gas. The probe wavelength at the orthogonal point of the Mach-Zehnder interference structure is as follows. Figure 4 The point indicated by the middle arrow theoretically has half the total transmittance.

[0076] The relationship between transmittance and wavelength at different refractive indices after passing through the Mach-Zehnder interferometer structure is as follows: Figure 5As shown, when the effective refractive index of the probe arm of the Mach-Zehnder interferometer changes under the action of pump light, the transmittance of the structure changes, resulting in a spectral shift. The black dashed line represents the spectral response when the effective refractive index of the probe arm is neff1, and the black solid line represents the spectral response when the effective refractive index increases to neff2 under the influence of temperature. ΔT represents the change in the intensity of the probe light at that probe wavelength.

[0077] The relationship between the normalized detection signal and time after passing through the Mach-Zehnder interferometer structure is as follows: Figure 6 As shown. The dashed line represents the detector output signal when the phase difference between the two arms (detector arm and reference arm) in the Mach-Zehnder interference structure is 0, at which time the constructive interference light is strongest and the signal is maximum. The solid line represents the detector output signal when the phase difference between the two arms in the Mach-Zehnder interference structure is π, at which time the destructive interference light is strongest and the signal is minimum. In this embodiment, the wavelength of the probe light corresponds to the wavelength at the orthogonal point of the Mach-Zehnder interference structure and is the wavelength at the non-absorption peak of the gas to be measured. At this time, the detected signal is half of the difference between the maximum and minimum signals. Under the modulation of the periodic pump light, the modulation component of the signal power measured at the output end of the Mach-Zehnder interference structure can be expressed by formula (2):

[0078]

[0079] Therefore, as can be seen from the above analysis, under the drive of the periodic pump light modulation signal, the signal detected by the detector is a periodic signal with the same modulation frequency. The 1f and 2f signals of this signal can be obtained by Fourier transform technology. The signal is proportional to the concentration of the gas being detected, and the strength of the signal does not change with the intensity of the probe light.

[0080] Another embodiment discloses another on-chip photothermal gas sensor, wherein the incident waveguide of the on-chip photothermal gas sensor can be an on-chip end-face coupler plus a strip waveguide structure or a grating coupler plus a strip waveguide structure. For example... Figure 7 As shown, a first wavelength division multiplexer 21 is also disposed within the incident waveguide. Alternatively, as... Figure 8 As shown, a first wavelength division multiplexer 21 is also provided in the incident waveguide, and a second wavelength division multiplexer 71 is also provided in the output waveguide.

[0081] The above embodiments integrate off-chip beam combiners or off-chip beam splitters onto the chip, specifically through an on-chip wavelength division multiplexing (WDM) structure. For example, 2×2 MMIs or 2×2 directional couplers can be integrated onto the chip. By designing a dedicated on-chip WDM structure, the pump light can be transmitted only in the detector arm, while the probe light is transmitted between the detector arm and the reference arm, further improving the optical power of the pump light in the detector arm.

[0082] Furthermore, depending on the different detection schemes, the end-face coupler or grating coupler can be designed in corresponding TE or (and) TM transmission modes. For example... Figure 1 The on-chip photothermal gas sensor structure shown requires that both the incident and exit waveguides support both TM and TE modes simultaneously; that is, the end-face coupler or grating coupler used must also support both TM and TE modes. Figure 8 The on-chip photothermal gas sensor structure shown has the following characteristics: since the probe light and pump light are separately incident into and out of the on-chip photothermal gas sensor, the end-face couplers or grating couplers of the incident waveguide port and the output waveguide port corresponding to the probe light can only support TE mode, while the end-face couplers or grating couplers of the incident waveguide port and the output waveguide port corresponding to the pump light can only support TM mode.

[0083] Another embodiment of the present invention discloses an on-chip gas sensor assembly, the on-chip gas sensor assembly including the on-chip photothermal gas sensor described in any of the above embodiments.

[0084] Among them, such as Figure 9 As shown, the on-chip gas sensor assembly includes:

[0085] Pump light emitter 11, the pump light emitter being used to emit pump light, the wavelength and intensity of the pump light being modulated by a periodic function;

[0086] A first polarization controller 12 is used to convert the pump light into a preset mode, such as TM mode.

[0087] A probe light emitter 13 is used to emit probe light;

[0088] The second polarization controller 14 is used to convert the probe light into a preset mode, such as the TE mode.

[0089] Off-chip combiner 15, which is used to combine the probe light and the pump light into a probe laser beam;

[0090] An on-chip photothermal gas sensor 16, wherein the incident waveguide and the output waveguide of the on-chip photothermal gas sensor 16 simultaneously support TE mode and TM mode detection lasers, and are used to receive the detection lasers emitted by the off-chip combiner 15.

[0091] Detector 17 is used to receive the laser signal emitted by the outgoing waveguide of the on-chip photothermal gas sensor 16, and to process it in a series of ways to obtain the corresponding parameters of the gas being measured.

[0092] Or, such as Figure 10As shown, the on-chip gas sensor assembly includes:

[0093] Pump light emitter 11, the pump light emitter being used to emit pump light, the wavelength and intensity of the pump light being modulated by a periodic function;

[0094] A first polarization controller 12 is used to convert the pump light into a preset mode, such as TM mode.

[0095] A probe light emitter 13 is used to emit probe light;

[0096] The second polarization controller 14 is used to convert the probe light into a preset mode, such as the TE mode.

[0097] An on-chip photothermal gas sensor 16 is provided, wherein the incident waveguide and the exit waveguide of the on-chip photothermal gas sensor 16 simultaneously support the detection laser in TE mode and TM mode. A first wavelength division multiplexer is provided in the incident waveguide, and a second wavelength division multiplexer is provided in the exit waveguide. The on-chip photothermal gas sensor 16 is used to receive the pump light emitted by the first polarization controller 12 and the detection light emitted by the second polarization controller 14.

[0098] Detector 17 is used to receive the laser signal emitted by the outgoing waveguide of the on-chip photothermal gas sensor 16, and to process it in a series of ways to obtain the corresponding parameters of the gas being measured.

[0099] The on-chip photothermal gas sensor assembly disclosed in this invention integrates a photothermal gas sensor with a Mach-Zehnder interferometer structure onto a single chip. Compared to traditional photothermal interferometry in free-space and fiber optic sensing, the influence of external vibrations on the interference structure is far less than in fiber optic sensing systems because both the probe arm and reference arm are on the same substrate. Furthermore, it eliminates the need for additional phase control units such as PZTs or AOMs, simplifying the detection system and creating possibilities for miniaturization of the entire sensing and detection system.

[0100] Furthermore, the refractive index of the upper waveguide material layer of the probe arm ridge waveguide layer is greater than that of the lower waveguide material layer, enabling simultaneous support for both TM mode pump light and TE mode probe light. That is, when the pump light is switched to TM mode by the first polarization controller and the probe light is switched to TE mode by the second polarization controller, the on-chip photothermal gas sensor assembly can simultaneously accommodate the high absorption of the pump light by the gas under test and its weak influence on the probe light, thus improving the gas detection accuracy. Simultaneously, the on-chip photothermal gas sensor assembly disclosed in this invention employs a Mach-Zehnder interferometer structure, allowing adjustment of the free spectral region (FSR) of the interference fringes by adjusting the lengths of the reference arm and probe arm. This provides higher controllability, and the interference spectrum is less susceptible to the influence of reflected light at various junctions during device fabrication.

[0101] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The terms "first" and "second" used in this document are for distinction only and are not intended to limit the content of this invention.

[0102] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An on-chip photothermal gas sensor, characterized in that, include: Substrate; An incident waveguide, disposed at one end on the surface of the substrate, is used to receive a probe laser. A beam splitter is disposed on the surface of the substrate and is used to split the probe laser emitted from the incident waveguide into two beams. A probe arm is disposed at the middle position on the substrate surface, used to fill the gas to be measured and receive the probe laser split by the beam splitter; A reference arm is arranged side by side with the probe arm at the middle position on the substrate surface and receives the probe laser split by the beam splitter. The length of the reference arm is not equal to the length of the probe arm. A beam combiner, disposed on the substrate surface, is used to combine the probe lasers emitted by the probe arm and the reference arm into a single beam; An outgoing waveguide is disposed at the other end of the substrate surface to receive the probe laser emitted by the beam combiner and to emit the probe laser from the on-chip photothermal gas sensor. The probe arm includes: A silicon oxide cladding layer is disposed on the surface of the substrate, and a lower air cladding layer is disposed in the middle of the silicon oxide cladding layer; A ridge waveguide layer is disposed on the surface of the silicon oxide cladding and the lower air cladding. The refractive index of the upper waveguide material layer of the ridge waveguide layer is greater than that of the lower waveguide material layer. The upper waveguide material layer is the upper protruding part of the ridge waveguide layer, and the lower waveguide material layer is the flat part of the ridge waveguide layer. The thickness of the lower waveguide material layer is 1 / 4 to 1 / 2 of the thickness of the ridge waveguide layer. An upper air cladding layer is disposed on the surface of the ridge waveguide layer.

2. The on-chip photothermal gas sensor according to claim 1, characterized in that, The probe laser includes a pump light in TM mode and a probe light in TE mode.

3. The on-chip photothermal gas sensor according to claim 2, characterized in that, The wavelength and intensity of the pump light are modulated by a periodic function.

4. The on-chip photothermal gas sensor according to claim 2, characterized in that, The wavelength of the pump light is the wavelength at the absorption peak of the gas being measured.

5. The on-chip photothermal gas sensor according to claim 1, characterized in that, The wavelength of the probe light corresponds to the wavelength at the orthogonal point of the Mach-Zehnder interference structure and is also the wavelength at the non-absorption peak of the gas to be measured.

6. The on-chip photothermal gas sensor according to claim 1, characterized in that, The length difference between the reference arm and the probe arm is 1 micrometer to 1 centimeter.

7. The on-chip photothermal gas sensor according to claim 1, characterized in that, The incident waveguide also contains a first wavelength division multiplexer.

8. The on-chip photothermal gas sensor according to claim 1, characterized in that, A second wavelength division multiplexer is also provided inside the outgoing waveguide.

9. An on-chip gas sensor assembly, characterized in that, The on-chip gas sensor assembly includes the on-chip photothermal gas sensor according to any one of claims 1-8.

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