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

Abstract

The present application relates to a kind of on-chip photo-thermal gas sensor and on-chip photo-thermal gas sensor assembly, the refractive index of the upper waveguide material layer of sensor ridge waveguide layer is greater than the refractive index of lower waveguide material layer, can support TM mode pump light and TE mode probe light simultaneously. That is, both high absorption of pump light and weak influence of probe light on the gas to be measured are considered, and the detection accuracy of the gas is improved. Moreover, a simpler waveguide structure is used, and the waveguide preparation process is simple, and the waveguide loss is relatively low. Compared with the photo-thermal interference method in optical fiber sensing, the interaction between pump light and the gas to be measured is greatly improved, the length of the detection waveguide is greatly shortened while ensuring high sensitivity, and the device size can be reduced to micrometer level. In addition, the waveguide structure of the on-chip photo-thermal gas sensor disclosed in the present application is prepared from chalcogenide glass, which has more obvious advantages for gas detection in the mid-infrared waveband.

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 photothermal gas sensor assembly. Background Technology

[0002] High-precision gas detection plays a vital role in environmental quality monitoring, industrial production, and disease diagnosis, and is an important technology concerning national livelihood, economic development, and national defense security.

[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. Among them, on-chip photothermal gas sensors have attracted widespread attention due to their low power consumption, low cost, compact structure, and ease of integration with other devices.

[0004] Currently, on-chip photothermal gas sensors are mainly divided into two types. One is the direct absorption spectrometer (DAS), which works by using the evanescent field in a waveguide to interact with the analyte gas, thereby achieving the absorption of light at a specific frequency. However, due to the weak absorption of light by molecules, it is difficult to apply to low-concentration environments. The other is a photothermal spectrometer (PTS) based on the laser photothermal effect. It uses a pump-probe method, where the absorption of pump light by the analyte gas generates thermal perturbation, thereby changing the effective refractive index during waveguide transmission and thus altering the phase of the probe light to achieve high-precision gas detection. Although the two sensing technologies have different underlying mechanisms, the core key lies in how to improve the interaction between light and the analyte gas.

[0005] Current mainstream approaches involve employing various methods to enhance the evanescent field of waveguides to improve direct absorption spectral sensors. Specifically, slit waveguides are used to concentrate the light field at the slit, significantly enhancing the interaction between light and matter. However, while on-chip fabricated slits and subwavelength gratings provide field enhancement, they also significantly increase waveguide losses, meaning sensors designed using these structures do not effectively improve sensing sensitivity.

[0006] Therefore, there is an urgent need for an optical waveguide structure that is simple in structure, has low optical loss, is easy to fabricate, and has a high confinement factor (CF) in air, in order to achieve high-precision detection of low-concentration gases. Summary of the Invention

[0007] Therefore, it is necessary to address the above problems by providing an on-chip photothermal gas sensor and an on-chip photothermal gas sensor assembly. By optimizing the waveguide structure, the distribution of the light field in the air cladding can be greatly improved without increasing the difficulty of waveguide fabrication, thereby achieving the goal of easy fabrication and high-precision detection of low-concentration gases.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] An on-chip photothermal gas sensor, comprising:

[0010] silicon substrate;

[0011] A silicon oxide cladding layer is disposed on the surfaces at both ends of the silicon substrate, and a lower air cladding layer is disposed in the middle of the silicon oxide cladding layer;

[0012] 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;

[0013] An upper air cladding layer is disposed on the surface of the ridge waveguide layer;

[0014] The pump light of the on-chip photothermal gas sensor is in TM mode, and the probe light is in TE mode.

[0015] In another embodiment, the upper waveguide material layer and the lower waveguide material layer are made of chalcogenide glass.

[0016] In another embodiment, the upper waveguide material layer is made of GeSbSe.

[0017] In another embodiment, the lower waveguide material layer is made of GeSbS.

[0018] In another embodiment, the thickness of the lower waveguide material layer is 1 / 4 to 1 / 2 of the thickness of the ridge waveguide layer.

[0019] In another embodiment, the thickness of the ridge waveguide layer is 100 nanometers to 300 nanometers.

[0020] In another embodiment, the wavelength of the pump light is the wavelength at the absorption peak of the gas to be measured, and the wavelength of the probe light is the wavelength at the non-absorption peak of the gas to be measured.

[0021] In another embodiment, the wavelength and intensity of the pump light are modulated by a periodic function.

[0022] In another embodiment, the periodic function is a trigonometric function, a periodic rectangular pulse function, or a periodic triangular function.

[0023] Another embodiment discloses an on-chip photothermal gas sensor assembly, which includes the on-chip photothermal gas sensor disclosed in any of the above embodiments.

[0024] The on-chip photothermal gas sensor disclosed in this invention has a ridge waveguide layer with a higher refractive index in the upper waveguide material layer than in the lower waveguide material layer, enabling simultaneous support for 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, improving the gas detection accuracy. Furthermore, it employs a simpler waveguide structure, simplifying the waveguide fabrication process and resulting in relatively low waveguide loss. Compared to photothermal interferometry in fiber optic sensing, this significantly enhances the interaction between the pump light and the analyte gas while greatly shortening the probe waveguide length while maintaining high sensitivity, allowing the device size to be reduced to the micrometer scale.

[0025] Furthermore, compared to traditional on-chip optical waveguide structures made of optical fibers or silicon materials, the waveguide structure of the on-chip photothermal gas sensor disclosed in this invention is made of chalcogenide glass, which has more obvious advantages for gas detection in the mid-infrared band. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of an on-chip photothermal gas sensor structure provided in an embodiment of the present invention;

[0027] Figure 2 This is a graph showing the relationship between the confinement factor and the waveguide structure, provided in an embodiment of the present invention.

[0028] Figure 3 This is a TM mode field distribution diagram provided in an embodiment of the present invention;

[0029] Figure 4 A graph showing the temperature change over time under TM mode pump light (1 kHz) according to an embodiment of the present invention;

[0030] Figure 5 The graph shows the temperature change over time under TM mode pump light (100kHz) according to an embodiment of the present invention.

[0031] Figure 6 This is a graph showing the variation of the TE probe phase difference with the pump light frequency according to an embodiment of the present invention.

[0032] Figure 7 This is a temperature distribution diagram of the pump light during initial application, provided in an embodiment of the present invention.

[0033] Figure 8 Temperature distribution diagram of pump light at 0.05 ms provided in an embodiment of the present invention;

[0034] Figure 9 This is a TE mode field distribution diagram provided in another embodiment of the present invention;

[0035] Figure 10A graph showing the temperature change over time under TE mode pump light (1 kHz) provided in another embodiment of the present invention;

[0036] Figure 11 A graph showing the temperature change over time under TE mode pump light (100kHz) provided in another embodiment of the present invention;

[0037] Figure 12 A graph showing the variation of the phase difference of the TE mode probe light with the pump light frequency, provided in another embodiment of the present invention;

[0038] Figure 13 This is a schematic diagram of an on-chip sensor assembly structure provided in another embodiment of the present invention.

[0039] In the figure, 1 is the silicon substrate; 2 is the silicon oxide cladding; 3 is the lower air cladding; 41 is the upper waveguide material layer; 42 is the lower waveguide material layer; 5 is the upper air cladding; 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 beam splitter; 16 is the first beam combiner; 17 is the on-chip photothermal gas sensor; 18 is the second beam combiner; 19 is the acousto-optic modulator; and 20 is the detector. Detailed Implementation

[0040] 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.

[0041] 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.

[0042] like Figure 1 As shown, one embodiment of the present invention discloses an on-chip photothermal gas sensor, comprising:

[0043] Silicon substrate 1;

[0044] A silicon oxide cladding layer 2 is disposed on the surfaces at both ends of the silicon substrate 1, and a lower air cladding layer 3 is disposed in the middle of the silicon oxide cladding layer 2;

[0045] A ridge waveguide layer is disposed on the surface of the silicon oxide cladding 2 and the lower air cladding 3. The ridge waveguide layer is composed of an upper waveguide material layer 41 and a lower waveguide material layer 42, and the refractive index of the upper waveguide material layer 41 is greater than the refractive index of the lower waveguide material layer 42.

[0046] Upper air cladding 5, wherein the upper air cladding 5 is disposed on the surface of the ridge waveguide layer;

[0047] The pump light of the on-chip photothermal gas sensor is in TM mode, and the probe light is in TE mode.

[0048] The on-chip photothermal gas sensor disclosed in this embodiment has a higher refractive index in the upper waveguide material layer of its 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, improving the gas detection accuracy. Furthermore, it employs a simpler waveguide structure, simplifying the waveguide fabrication process and resulting in relatively low waveguide loss. Compared to photothermal interferometry in fiber optic sensing, this significantly enhances the interaction between the pump light and the analyte gas while greatly shortening the probe waveguide length while maintaining high sensitivity, allowing the device size to be reduced to the micrometer scale.

[0049] In another embodiment, the ridge waveguide layer should have 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, hafnium oxide, and polymers.

[0050] In another embodiment, when selecting a waveguide material, the following conditions need to be met: (1) The waveguide material should be transparent in the sensing wavelength range to reduce the absorption loss of the material; (2) The refractive index difference between the core layer and the cladding should be as large as possible. Reducing the refractive index of the cladding material can reduce the light distributed in the cladding and the substrate. When the refractive index difference between the core layer and the cladding is large, reducing the size of the core layer can allow more light to be distributed in the analyte cladding to obtain a large ECF and meet the guided mode conditions; (3) The preparation process of the core layer material needs to be compatible with the properties of the cladding material. For example, it is difficult to prepare crystalline silicon (Si) or bond it to other materials except for silicon dioxide (SiO2).

[0051] Commonly used waveguide materials include silicon, silicon dioxide, silicon nitride, and silicon fluoride. Mid-infrared gas sensors perform better under the same optical path length. Silicon-on-Insulator (SOI) waveguides are unsuitable for mid-infrared sensing because SiO2 exhibits greater absorption loss in the mid-infrared band. Silicon-on-Nitride (SON) waveguides and Silicon-on-Sapphire (SOS) waveguides have very low absorption loss. Besides Si, germanium (Ge) and chalcogenide glasses (ChG) have high refractive indices in the mid-infrared band, making them suitable as waveguide core layers. ChG mainly consists of chalcogen elements sulfur (S), selenium (Se), and tellurium (Te), as well as arsenic (As), gallium (Ga), antimony (Sb), and Ge. Due to the low transition temperature of ChG (150~500℃), ChG waveguides can also be fabricated using a lift-off method in addition to etching, without damaging the photoresist mask structure. Different optical properties can be obtained by changing the ChG composition, with telluride glasses achieving a transparency wavelength of up to 20 μm. Depending on the waveguide guided mode conditions, materials with a refractive index lower than ChG can be used as the under-cladding material for ChG waveguides. Although SiO2 is not suitable for the mid-infrared band, its low refractive index makes it suitable as the under-cladding material for near-infrared waveguides. ChG (ChG-On-Oxide, COO) waveguides on SiO2 and SOI waveguides are more suitable for near-infrared gas sensing.

[0052] In this embodiment, the on-chip photothermal gas sensor is based on ChG on SiO2. Specifically, the upper and lower waveguide material layers are made of chalcogenide glass. More specifically, the upper waveguide material layer is made of GeSbSe, and the lower waveguide material layer is made of GeSbS.

[0053] Compared to traditional on-chip optical waveguide structures made of optical fiber or silicon, the waveguide structure of the on-chip photothermal gas sensor disclosed in this embodiment is made of chalcogenide glass, which has more obvious advantages for gas detection in the mid-infrared band.

[0054] 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 not so thin as 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.

[0055] like Figure 2As shown, the thickness of the lower waveguide material layer is 1 / 4 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. Therefore, in actual design, it can be adjusted according to the wavelengths of the pump light and the probe light.

[0056] In another embodiment, because the on-chip photothermal gas sensor disclosed in this invention employs a simpler waveguide structure and has a simpler waveguide fabrication process, the device size can be reduced to the micrometer scale. In this embodiment, the thickness of the silicon oxide cladding is only a few micrometers, while the thickness of the ridge waveguide layer is 100 nanometers to 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.

[0057] As can be seen, the size of the on-chip photothermal gas sensor disclosed in this embodiment can be reduced to the micrometer level. With the reduction in size, it can achieve a wider range of applications and is easier to integrate with other devices.

[0058] In another embodiment, the pump light of the on-chip photothermal gas sensor is in TM mode, and the probe light is in TE mode. That is, the waveguide design in this embodiment supports both TE and TM modes simultaneously.

[0059] The confinement factor, as a crucial parameter in waveguide transmission systems, plays a vital role in waveguide design and performance analysis. In practical applications, the magnitude and distribution of the confinement factor directly affect the transmission efficiency and performance stability of the waveguide system.

[0060] In this embodiment, the confinement factor distribution of the pump light in the upper and lower air claddings in TM mode is as follows: Figure 2 As shown. Figure 2 In this context, the thickness of the ridge waveguide layer is 200-300 nanometers, and the width is 800-100 nanometers. Furthermore, the light confinement factor Γ in air is calculated using formula (1):

[0061] ……..(1)

[0062] As can be seen from the simplified expression of the confinement factor, the confinement factor in air can be defined as the product of the waveguide group refractive index and the electric field energy density in air.

[0063] Figure 3The electric field distribution of the TM mode pump light at this structural size is shown. It can be seen that a large proportion of the light in this mode is in the air, with most of it propagating in the air and only a small portion confined within the optical waveguide. The effective refractive index of this mode is ~1.15, which is very close to the refractive index (~1) of the air cladding.

[0064] This embodiment further improves the confinement factor by optimizing the waveguide width, total waveguide height, and thickness of the planar waveguide region. More preferably, the waveguide width is 865 nm, the total waveguide height is 260 nm, and the thickness of the planar waveguide region is 65 nm. At this point, the confinement factor of the on-chip photothermal gas sensor disclosed in this embodiment reaches as high as 124%, significantly improving the interaction between the pump light and the detected gas.

[0065] In one embodiment, the wavelength and intensity of the pump light are modulated by a periodic function. The periodic function can be a trigonometric function, a periodic rectangular pulse function, or a periodic triangular function.

[0066] After periodic modulation, the pump light exhibits a periodic change in wavelength or intensity. Taking intensity modulation as an example, when the light intensity varies sinusoidally with time, the temperature of the optical waveguide caused by the pump light also changes periodically. This periodic temperature change, in turn, causes a periodic change in the refractive index of the waveguide, thereby resulting in periodic modulation of the waveguide phase. This method can eliminate the influence of background light intensity variations on the test results.

[0067] In another embodiment, the on-chip photothermal gas sensor described above is used to detect 1% concentration C2H2 gas. In this embodiment, the pump light of the on-chip photothermal gas sensor is periodically modulated by a sinusoidal function with modulation frequencies of 1 kHz and 100 kHz. During detection, the analyte (C2H2) flows within an air cladding. When the pump light irradiates the analyte (C2H2), it absorbs some of the energy from the pump light, generating heat and thus raising the temperature of the ridge waveguide. The temperature change over time under the TM mode pump light is as follows: Figure 4 (1kHz) and Figure 5 As shown in (100kHz), it can be seen that under the action of periodic pump light, the time to reach quasi-steady state and the temperature difference within the waveguide are related to the frequency of the pump light. If the pump light frequency is too high, the system cannot dissipate heat in time within one cycle, resulting in a longer time to reach quasi-steady state and a smaller temperature difference. The temperature difference within the waveguide at a frequency of 1kHz can reach 43.9mK, while at a frequency of 100kHz, the temperature difference within the waveguide is only 9.6mK.

[0068] Figure 6The graph shows the relationship between waveguide phase shift and pump light frequency. Since the refractive index of the waveguide is temperature-dependent (the thermo-optic coefficient of the waveguide material in this embodiment is 13.7 × 10⁻⁶),... -6 Therefore, changes in the pump light frequency will cause changes in the waveguide refractive index. When the probe light is coupled into the waveguide in TE mode for transmission, because TE mode light has a high confinement factor within the waveguide, even a small change in the refractive index of the waveguide material can cause a change in the effective refractive index of the waveguide, resulting in a larger phase change in the waveguide. Since the temperature difference within the waveguide decreases with increasing pump light frequency, therefore... Figure 6 As can be seen, when the pump light frequency is below 1 kHz, the phase shift of the structure remains essentially unchanged due to the balance between heat accumulation and heat conduction. As the pump light frequency increases, the phase shift of the structure decreases sharply. When the pump light frequency decreases from 1 MHz to 100 Hz, the phase shift of the device increases by 50 times.

[0069] Figure 7 and Figure 8 The temperature distribution of the structure at different times is shown when the pump light frequency is 1 kHz. Figure 7 This shows the temperature distribution during the initial application of the pump light. It can be seen that the heat source originates from the air cladding on the upper and lower surfaces of the waveguide, and after a period of heat conduction, the heat gradually transfers into the waveguide. Figure 8 The temperature distribution is shown at a time interval of 0.05 ms. Even when the highest temperature is reached, the temperature distribution within the waveguide remains relatively uniform. Experiments show that the difference between the highest temperature and the average temperature within the waveguide is less than 1 mK.

[0070] In another embodiment, the pump light is polarized in TE mode, and its electric field distribution is as follows: Figure 9 As shown. When the pump light uses TE mode, the electric field is mostly confined to the waveguide core, with a confinement factor of only 9% in the upper and lower air cladding layers. Figure 10 and Figure 11 As shown, if modulation is performed at the same frequency, the resulting maximum temperature is much lower than that obtained using TM mode. When the pump light is transmitted using TE mode, the resulting maximum temperature is only 6% of that in the previous embodiment. Consequently, the waveguide phase change due to temperature is also only about 6% of that in the previous embodiment (e.g., Figure 12 (As shown).

[0071] In some embodiments, the pump light wavelength 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 at this wavelength and thus convert more of it into heat energy. The probe light is the wavelength at the non-absorption peak of the gas to be measured, so as to reduce the influence of the gas to be measured on the intensity of the probe signal.

[0072] As can be seen, the on-chip photothermal gas sensor disclosed in this embodiment uses TM mode for the pump light and TE mode for the probe light, thus balancing the high absorption of the pump light by the gas to be measured with its weak influence on the probe light, thereby improving the detection accuracy of the gas. Compared with the photothermal interferometry in fiber optic sensing, this method greatly enhances the interaction between the pump light and the gas to be measured, significantly shortening the length of the probe waveguide while maintaining high sensitivity, allowing the device size to be reduced to the micrometer scale.

[0073] Another embodiment of the present invention discloses an on-chip photothermal gas sensor assembly, wherein the on-chip photothermal gas sensor assembly includes the on-chip photothermal gas sensor described in any of the above embodiments. Figure 13 As shown, it includes:

[0074] 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;

[0075] A first polarization controller 12 is used to convert the pump light into TM mode;

[0076] A probe light emitter 13 is used to emit probe light;

[0077] A second polarization controller 14 is used to convert the probe light into TE mode;

[0078] Beam splitter 15, which is used to split the TE mode probe light into two;

[0079] The first beam combiner 16 is used to receive TM mode pump light and TE mode probe light and transmit them to the on-chip photothermal gas sensor 17.

[0080] The second beam combiner 18 is used to receive the TE mode probe light processed by the acousto-optic modulator 19 and the light coupled by the on-chip photothermal gas sensor 17.

[0081] Detector 20 is used to receive the laser signal emitted by the second beam combiner 18 and perform a series of processing on it to obtain the corresponding parameters of the gas being measured.

[0082] The on-chip photothermal gas sensor in the described on-chip photothermal gas sensor assembly is the on-chip photothermal gas sensor described in any of the above embodiments. Its upper waveguide material layer has a higher refractive index than the lower waveguide material layer, enabling simultaneous support for 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, improving the gas detection accuracy. Furthermore, it employs a simpler waveguide structure, simplifying the waveguide fabrication process and resulting in relatively low waveguide loss. Compared to photothermal interferometry in fiber optic sensing, this method significantly enhances the interaction between the pump light and the analyte gas while greatly shortening the probe waveguide length while maintaining high sensitivity, allowing the device size to be reduced to the micrometer scale.

[0083] Furthermore, compared to traditional on-chip optical waveguide structures made of optical fibers or silicon materials, the waveguide structure of the on-chip photothermal gas sensor disclosed in this invention is made of chalcogenide glass, which has more obvious advantages for gas detection in the mid-infrared band.

[0084] 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.

[0085] 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: silicon substrate; A silicon oxide cladding layer is disposed on the surfaces at both ends of the silicon 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, 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, the upper waveguide material layer is the protruding part of the ridge waveguide layer, and 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; The pump light of the on-chip photothermal gas sensor is in TM mode, and the probe light is in TE mode.

2. The on-chip photothermal gas sensor according to claim 1, characterized in that, The upper and lower waveguide material layers are made of chalcogenide glass.

3. The on-chip photothermal gas sensor according to claim 2, characterized in that, The upper waveguide material layer is made of GeSbSe.

4. The on-chip photothermal gas sensor according to claim 2, characterized in that, The material used to fabricate the lower waveguide material layer is GeSbS.

5. The on-chip photothermal gas sensor according to claim 1, characterized in that, The thickness of the ridge waveguide layer is 100 nanometers to 300 nanometers.

6. The on-chip photothermal gas sensor according to claim 1, characterized in that, The wavelength of the pump light is the wavelength at the absorption peak of the gas to be measured, and the wavelength of the probe light is the wavelength at the non-absorption peak of the gas to be measured.

7. The on-chip photothermal gas sensor according to claim 1, characterized in that, The wavelength and intensity of the pump light are modulated by a periodic function.

8. The on-chip photothermal gas sensor according to claim 7, characterized in that, The periodic function is a trigonometric function, a periodic rectangular pulse function, or a periodic triangular function.

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

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