Optical thermal interferometry gas sensing device and detection method based on photonic crystal slow waveguide and mode phase difference

Abstract

This invention discloses a photothermal interferometric gas sensing device and detection method based on photonic crystal slow waveguides and mode phase difference, belonging to the field of optical waveguide sensor technology. The gas sensing device includes an on-chip sensor, a laser module, a mode excitation module, and a signal processing module. The laser module generates probe light and pump light. After passing through the mode excitation module, the probe light is transmitted in both odd and even modes within the on-chip sensor. The pump light alters the refractive index of the on-chip sensor device through thermal conduction. The signal processing module analyzes the concentration information of the analyte gas by detecting the phase difference between the odd and even modes of the probe light. This invention can simultaneously generate a slow light effect in multiple transmission modes of the probe light and the pump light band, increasing the effective optical path of the device, enhancing the absorption of the pump light by the analyte gas and the accumulation of the phase difference of the probe light, thereby improving the sensitivity and response speed of the sensing device.

Description

Technical Field

[0001] This invention relates to the field of optical waveguide sensor technology, and in particular to a photothermal interferometric gas sensing device and detection method based on photonic crystal slow waveguides and mode phase differences. Background Technology

[0002] Laser spectral absorption methods based on photonic crystal waveguides can detect the type and concentration of gases by measuring the position and intensity of absorption lines in different gases. However, this method has low detection sensitivity due to limitations in the evanescent field ratio factor and effective optical path of the waveguide device. Photothermal interferometry for gas detection does not directly measure changes in the transmission spectrum, but rather measures the signal generated by the photothermal effect. This avoids interference from scattering and reflection in the optical path, improving the sensitivity of the sensing device. However, most current photothermal interferometry methods detect phase modulation signals of a single laser transmission mode, are significantly affected by environmental noise, and lack the slow-light enhancement effect.

[0003] Photothermal interferometry gas sensing methods with poor detection modes are sensitive to gas absorption but insensitive to environmental disturbances, enabling higher signal-to-noise ratios. Photonic crystal waveguides can support laser transmission in multiple modes and can achieve a slow-light effect at room temperature, reducing the group velocity of light, increasing the effective optical path, and enhancing the interaction between light and the analyte. Utilizing the slow-light effect of photonic crystal waveguides, the group velocity of the probe light in both odd-mode and even-mode transmission is reduced, increasing the phase accumulation of the probe light. Simultaneously, the slow-light effect reduces the group velocity of the pump light, enhancing the absorption of the pump light and the analyte gas, and increasing the phase difference signal generated by the photothermal effect. Summary of the Invention

[0004] To address the aforementioned problems, this invention aims to provide a photothermal interferometric gas sensing device and detection method based on photonic crystal slow waveguides and mode phase differences. Simultaneously, it generates a slow light effect in multiple transmission modes of the probe light and the pump light band, increasing the effective optical path of the device, enhancing the absorption of the pump light by the gas under test and the accumulation of the phase difference of the probe light, thereby improving the sensitivity and response speed of the sensing device.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A photothermal interferometric gas sensing device based on photonic crystal slow waveguides and mode phase difference includes an on-chip sensor, a laser module, a mode excitation module, and a signal processing module. The laser module includes a first near-infrared laser for generating probe light and a second near-infrared laser for generating pump light. Both the first and second near-infrared lasers are connected to the on-chip sensor through the mode excitation module, which is connected to the signal processing module.

[0007] Furthermore, the on-chip sensor includes a photonic crystal waveguide and a gas chamber, with the photonic crystal waveguide completely covering the gas chamber.

[0008] Furthermore, the mode excitation module includes a first coupled waveguide, a second coupled waveguide, a third coupled waveguide, and a fourth coupled waveguide. The two output terminals of the first coupled waveguide are respectively connected to the input terminals of the second coupled waveguide and the third coupled waveguide. The output terminal of the third coupled waveguide is coupled to the second coupled waveguide. The output terminal of the second coupled waveguide is connected to the input terminal of the photonic crystal waveguide. The output terminal of the photonic crystal waveguide is connected to the input terminal of the fourth coupled waveguide. The output terminal of the fourth coupled waveguide is connected to the signal processing module.

[0009] Furthermore, the second coupling waveguide is a rectangular waveguide, and the third coupling waveguide is a rectangular waveguide with a gradually narrowing width.

[0010] Furthermore, the output end of the first near-infrared laser is connected to the input end of the first coupled waveguide via a first fiber coupler and a first focusing mirror; the output end of the fourth coupled waveguide is connected to the input end of the signal processing module via a second focusing mirror, a fiber circulator, and a second fiber coupler in sequence.

[0011] Furthermore, the pump light generated by the second near-infrared laser is coupled sequentially through the fiber optic circulator and the second focusing mirror into the fourth coupling waveguide, and then into the photonic crystal waveguide, where the temperature of the photonic crystal waveguide is changed through a thermal conduction process.

[0012] Furthermore, the signal processing module includes a photodetector, a high-pass filter, a lock-in amplifier, a data acquisition card, and a computer connected in sequence, and the output end of the fourth coupling waveguide is connected to the input end of the photodetector.

[0013] Furthermore, the laser module also includes a first temperature controller for controlling the temperature of the first near-infrared laser to be constant, and a first current controller for controlling the current of the first near-infrared laser to be constant.

[0014] Furthermore, the laser module also includes a second temperature controller for controlling the temperature of the second near-infrared laser to be constant, and a second current controller for controlling the current of the second near-infrared laser to be constant.

[0015] Furthermore, the present invention also includes a detection method for a photothermal interferometric gas sensing device based on a photonic crystal slow waveguide and mode phase difference, comprising the following steps:

[0016] Step 1: The probe light generated by the first near-infrared laser passes through the mode excitation module and is transmitted in the photonic crystal waveguide in odd and even modes, and then output to the signal processing module for data processing.

[0017] Step 2: Couple the pump light generated by the second near-infrared laser into the fourth coupling waveguide through the fiber optic circulator, and prevent the pump light from entering the second fiber optic coupler, while allowing the probe light to be coupled into the second fiber optic coupler.

[0018] Step 3: Adjust the current of the second near-infrared laser so that the near-infrared pump light wavelength is aligned with the absorption peak of the gas to be tested;

[0019] Step 4: The signal processing module acquires the phase difference information between the odd and even modes of the probe light output from the photonic crystal waveguide;

[0020] Step 5: Analyze the relationship between the phase difference information obtained from the detection and the concentration of the gas to be measured, and obtain the concentration information of the gas to be measured.

[0021] The beneficial effects of this invention are:

[0022] 1. The gas sensing device in this invention is based on photothermal interferometry and the principle of photonic crystal waveguide. The entire sensing device is easy to integrate on a chip. Moreover, it can generate a slow light effect in multiple transmission modes of the probe light and the pump light band at the same time, which increases the effective optical path of the device, enhances the absorption of the pump light by the gas under test and the accumulation of the phase difference of the probe light, thereby improving the sensitivity and response speed of the sensing device.

[0023] 2. The gas sensing device in this invention is based on the transmission of probe light in two modes, odd and even, in an on-chip sensor. The gas to be measured is detected by detecting the phase difference between the two modes. The method of measuring the phase difference is not sensitive to external environmental disturbances and can improve the signal-to-noise ratio of the sensor. Attached Figure Description

[0024] Figure 1 This is a system diagram of the photothermal interferometric spectroscopy gas sensing device based on photonic crystal slow waveguide and mode phase difference in this invention;

[0025] Figure 2 This is a top view of the on-chip sensor and mode excitation module in this invention;

[0026] Figure 3 This is the dispersion diagram of the sensing device in this invention;

[0027] Figure 4 This is a graph showing the group refractive index of the sensing device in the near-infrared band as a function of wavelength and the absorbance of acetylene gas in this invention.

[0028] Wherein: 001-First fiber coupler, 002-First focusing lens, 003-First coupling waveguide, 004-Photonic crystal waveguide, 005-Gas cell, 006-Fourth coupling waveguide, 007-Second focusing lens, 008-Fiber circulator, 009-Second fiber coupler, 010-Photodetector, 011-High-pass filter, 012-Lock-in-phase amplifier, 013-Data acquisition card, 014-Computer, 015-First near-infrared laser, 016-Second near-infrared laser, 017-First current controller, 018-Second current controller, 019-First temperature controller, 020-Second temperature controller, 021-Second coupling waveguide, 022-Third coupling waveguide, 100-On-chip sensor, 200-Laser module, 300-Mode excitation module, 400-Signal processing module. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0030] Example 1:

[0031] Example 1 provides a photothermal interferometric spectral gas sensing device based on a photonic crystal slow waveguide and mode phase difference, as shown in the attached figure. Figure 1 As shown, the device includes an on-chip sensor 100, a laser module 200, a mode excitation module 300, and a signal processing module 400. The laser module 200 includes a first near-infrared laser 015 for generating probe light and a second near-infrared laser 016 for generating pump light. Both the first near-infrared laser 015 and the second near-infrared laser 016 are connected to the on-chip sensor 100 through the mode excitation module 300, and the mode excitation module 300 is connected to the signal processing module 400.

[0032] Specifically, the on-chip sensor 100 includes a photonic crystal waveguide 004 and an air cell 005. The photonic crystal waveguide 004 has an input terminal and an output terminal, used to simultaneously transmit the probe light generated by the first near-infrared laser 015 and the pump light generated by the second near-infrared laser 016, and the photonic crystal waveguide 004 produces a slow light effect at both wavelengths. Preferably, the photonic crystal waveguide 004 is an etched hole array structure in a silicon substrate, with a silicon substrate, a silicon core layer, a silicon dioxide lower cladding layer, and an air upper cladding layer.

[0033] The gas chamber 005 is made of PDMS material and has an air inlet and an air outlet. The gas medium fills the gas chamber 005, and the photonic crystal waveguide 004, as the sensing area, is completely covered inside the gas chamber 005.

[0034] The first near-infrared laser 015 is used to generate probe light with a center wavelength far from any absorption peak of the gas to be tested, and the second near-infrared laser 016 is used to generate pump light with a center wavelength aligned with the absorption peak of the gas to be tested. As an auxiliary component, the laser module 200 also includes a first temperature controller 019 for controlling the temperature of the first near-infrared laser 015 to be constant, and a first current controller 017 for controlling the current of the first near-infrared laser 015 to be constant. Both the first current controller 017 and the first temperature controller 019 are connected to the first near-infrared laser 015.

[0035] Similarly, the laser module 200 also includes a second temperature controller 020 for controlling the temperature of the second near-infrared laser 016 to be constant, and a second current controller 018 for controlling the current of the second near-infrared laser 016 to be constant. Both the second current controller 018 and the second temperature controller 020 are connected to the second near-infrared laser 016. The second current controller 018 aligns the output laser wavelength of the second near-infrared laser 016 with the absorption peak of the gas to be measured.

[0036] The mode excitation module 300 includes a first coupling waveguide 003, a second coupling waveguide 021, a third coupling waveguide 022, and a fourth coupling waveguide 006.

[0037] More specifically, the first coupling waveguide 003 is a beam-splitting waveguide with a silicon substrate, a silicon core, a silicon dioxide lower cladding, and an air upper cladding. The first coupling waveguide 003 is used to split the probe light generated by the first near-infrared laser 015 into two beams of equal power. The first coupling waveguide 003 and the first near-infrared laser 015 are connected via a first fiber coupler 001 and a first focusing mirror 002. After the probe light passing through the first fiber coupler 001 is focused by the first focusing mirror 002, it is coupled into the photonic crystal waveguide 004 via the first coupling waveguide 003. After the probe light is split by the first coupling waveguide 003, the two output terminals of the first coupling waveguide 003 are connected to the input terminals of the second coupling waveguide 021 and the third coupling waveguide 022, respectively, as shown in the attached diagram. Figure 2 As shown.

[0038] The second coupling waveguide 021 is a rectangular waveguide with a silicon substrate, a silicon core, a silicon dioxide lower cladding, and an air upper cladding. It is used to transmit the probe light generated by the first near-infrared laser 015. After the probe light enters the first coupling waveguide 003 and is split, one beam propagates in its high-refractive-index TE0 mode in the second coupling waveguide 021 and is finally coupled into the photonic crystal waveguide 004. The input and output ends of the second coupling waveguide 021 are connected to the output end of the first coupling waveguide 003 and the input end of the photonic crystal waveguide 004, respectively. The TE0 mode probe light is transmitted in even-mode mode in the photonic crystal waveguide 004.

[0039] The third coupling waveguide 022 is a rectangular waveguide with a gradually narrowing width. The substrate is silicon, the core layer is silicon, the lower cladding is silicon dioxide, and the upper cladding is air. It is also used to transmit the probe light generated by the first near-infrared laser 015. After the probe light enters the first coupling waveguide 003 and is split, the other beam propagates in the third coupling waveguide 022 in TE0 mode. It is then converted from the high-refractive-index TE0 mode to the lower-refractive-index TE1 mode. The TE1 mode probe light in the third coupling waveguide 022 is finally coupled into the second coupling waveguide 021 and continues to propagate in TE1 mode. Finally, it is coupled together with the TE0 mode probe light into the photonic crystal waveguide 004. The TE1 mode probe light propagates in the photonic crystal waveguide 004 in odd-mode.

[0040] The phase difference information between the odd and even modes of the probe light is ultimately output to the signal processing module 400 for data processing via the fourth coupling waveguide 006. The input end of the fourth coupling waveguide 006 is connected to the output end of the photonic crystal waveguide 004, and a second focusing mirror 007, an optical fiber circulator 008, and a second optical fiber coupler 009 are provided between the fourth coupling waveguide 006 and the signal processing module 400. The probe light output from the fourth coupling waveguide 006 passes sequentially through the second focusing mirror 007, the optical fiber circulator 008, and the second optical fiber coupler 009 before being coupled into the signal processing module 400.

[0041] The laser module 200 in this invention can also generate pump light with its center wavelength aligned with the absorption peak of the gas to be measured. The pump light generated by the second near-infrared laser 016 is coupled sequentially through the fiber optic circulator 008 and the second focusing mirror 007 into the fourth coupling waveguide 006, and then into the photonic crystal waveguide 004. However, the pump light cannot couple into the second fiber optic coupler 009. After the pump light undergoes a photothermal effect with the gas to be measured in the gas medium, it changes the temperature of the gas medium. The gas medium changes the temperature of the photonic crystal waveguide 004 through a thermal conduction process, thereby changing the refractive index of the on-chip sensor 100. Based on this, the signal processing module detects the phase difference change of the odd-mode and even-mode modes of the probe light after transmission in the photonic crystal waveguide 004. By analyzing the relationship between the detected phase difference information and the concentration of the gas to be measured, the concentration information of the gas to be measured in the gas medium can be obtained.

[0042] Preferably, the signal processing module 400 includes a photodetector 010, a high-pass filter 011, a lock-in amplifier 012, a data acquisition card 013, and a computer 014. The photodetector 010 converts the optical signal output from the photonic crystal waveguide 004 into an electrical signal. The high-pass filter 011 is used to filter out the DC signal in the photothermal interference signal, so that the high-frequency modulation signal is input to the lock-in amplifier 012. The lock-in amplifier 012 is used to extract the photothermal interference signal, which is then acquired by the data acquisition card 013 and input to the computer 014 for data processing and analysis.

[0043] In summary, the working principle of the gas sensing device in this invention is as follows: the detection light generated by the first near-infrared laser 015 with a center wavelength far away from any absorption peak of the gas to be measured is split into two beams of equal power through the first coupling waveguide 003. One of the beams is transmitted in the second coupling waveguide 021 in TE0 mode, and then coupled to the photonic crystal waveguide 004 for transmission in even mode.

[0044] Another beam is converted from the TE0 mode to the lower refractive index TE1 mode in the third coupling waveguide 022 for transmission, then coupled to the second coupling waveguide 021 for transmission in TE1 mode, and finally coupled to the photonic crystal waveguide 004 for transmission in odd mode; the phase difference information between the odd and even modes of the probe light is finally output to the signal processing module 400 for data processing through the fourth coupling waveguide 006.

[0045] Based on this, the pump light generated by the second near-infrared laser 016, with its center wavelength aligned with the absorption peak of the gas to be measured, is coupled into the fourth coupling waveguide 006 through the fiber optic circulator 008 and the second focusing mirror 007, and then enters the photonic crystal waveguide 004. This changes the temperature of the photonic crystal waveguide 004, thereby altering the refractive index of the on-chip sensor 100. When the probe light is transmitted back to the photonic crystal waveguide 004, the signal processing module 400 detects the phase difference information between the odd-mode and even-mode modes of the probe light after transmission in the photonic crystal waveguide 004. By analyzing the relationship between the detected phase difference information and the concentration of the gas to be measured, the concentration information of the gas to be measured in the gas medium can be obtained.

[0046] Example 2:

[0047] Example 2 provides a specific detection method for the gas sensing device described in Example 1, which specifically includes the following steps:

[0048] Step 1: The first focusing mirror 002 focuses the probe light through the first fiber coupler 001, and then directly couples it into the photonic crystal waveguide 004 through the first coupling waveguide 003. Then, the probe light output through the fiber circulator 008 is coupled into the photodetector 010 through the second fiber coupler 009.

[0049] Step 2: Couple the pump light into the fourth coupling waveguide 006 through the fiber optic circulator 008, and prevent the pump light from entering the second fiber optic coupler 009, while simultaneously coupling the probe light into the second fiber optic coupler 009.

[0050] Step 3: Adjust the current of the second near-infrared laser 016 so that the near-infrared pump light wavelength is aligned with the absorption peak of the gas to be tested.

[0051] Step 4: The photodetector 010 collects the phase difference information of the odd and even modes of the probe light output by the photonic crystal waveguide 004; the signal output by the photodetector 010 is collected by the data acquisition card 013. When adjusting the pump light wavelength, the output signal of the photodetector 010 is recorded in real time to obtain the mode difference photothermal interference signal.

[0052] Step 5: Analyze the relationship between the phase difference information obtained from the detection and the concentration of the gas to be measured, and obtain the concentration information of the gas to be measured.

[0053] In step four, the phase difference between the odd and even modes of the probe light output from the photonic crystal waveguide 004 can be expressed as:

[0054]

[0055] In the formula, This refers to the phase difference generated between odd and even modes after propagation in a photonic crystal waveguide. (k = 1 or 2) represents the phase modulation generated by the odd or even mode after transmission in the photonic crystal waveguide, which can be expressed as:

[0056]

[0057] Where w is the angular frequency of the probe light; c is the speed of the probe light; n TOC It is the thermo-optic coefficient of silicon material; f silicon is the scaling factor of the probe light field in silicon; L is the distance the probe light travels in the photonic crystal waveguide; n gk n is the group refractive index for odd or even modes propagating in the photonic crystal waveguide 004. SI ΔT is the refractive index of silicon; ΔT is the temperature change caused by photothermal effects and heat conduction, which can be expressed as ΔT∝α(λ). pump )*C*P pump Where C is the concentration of the gas to be measured; P pump It is the pump light power; α(λ) pump ) is the absorption coefficient of the gas being measured. In a slow-light-enhanced photonic crystal waveguide,

[0058]

[0059] f g It is the scaling factor of the pump light field transmitted in the gaseous medium.

[0060] As attached Figure 3 The figure shows the dispersion diagram of the photonic crystal waveguide sensing device of this invention, where a is the lattice constant of the photonic crystal waveguide, λ is the wavelength, n is the refractive index of the lower cladding, and k is the wave vector; from the attached... Figure 3 As can be seen, the probe light can be transmitted in both odd and even modes in the photonic crystal waveguide 004.

[0061] As attached Figure 4 The figure shows the refractive index of the pump light band of the sensing device in this invention as a function of wavelength and the absorbance of acetylene gas. (See attached figure.) Figure 4 As can be seen, when the pump light corresponds to the acetylene gas absorption peak, a slow light effect exists during propagation in the photonic crystal waveguide 004. The probe light propagates in both odd-mode and even-mode in the photonic crystal waveguide 004, and the slow light effect exists in both modes.

[0062] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A photothermal interferometric gas sensing device based on photonic crystal slow waveguides and mode phase differences, characterized in that: The system includes an on-chip sensor (100), a laser module (200), a mode excitation module (300), and a signal processing module (400). The laser module (200) includes a first near-infrared laser (015) for generating probe light and a second near-infrared laser (016) for generating pump light. Both the first near-infrared laser (015) and the second near-infrared laser (016) are connected to the on-chip sensor (100) through the mode excitation module (300), and the mode excitation module (300) is connected to the signal processing module (400). The on-chip sensor (100) includes a photonic crystal waveguide (004) and a gas cell (005), wherein the photonic crystal waveguide (004) completely covers the gas cell (005); the photonic crystal waveguide (004) has an input end and an output end for simultaneously transmitting the probe light generated by the first near-infrared laser (015) and the pump light generated by the second near-infrared laser (016), and the photonic crystal waveguide (004) generates a slow light effect at both wavelengths; The probe light generated by the first near-infrared laser (015) is transmitted in the photonic crystal waveguide (004) in odd and even modes after passing through the mode excitation module (300), and then output to the signal processing module (400) for data processing. The signal processing module (400) acquires the phase difference information of the odd and even modes of the probe light output from the photonic crystal waveguide (004); By analyzing the relationship between the phase difference information obtained from the detection and the concentration of the gas to be measured, the concentration information of the gas to be measured can be obtained.

2. The photothermal interferometric spectral gas sensing device based on photonic crystal slow waveguide and mode phase difference according to claim 1, characterized in that: The mode excitation module (300) includes a first coupling waveguide (003), a second coupling waveguide (021), a third coupling waveguide (022), and a fourth coupling waveguide (006). The two output terminals of the first coupling waveguide (003) are connected to the input terminals of the second coupling waveguide (021) and the third coupling waveguide (022), respectively. The output terminal of the third coupling waveguide (022) is coupled to the second coupling waveguide (021). The output terminal of the second coupling waveguide (021) is connected to the input terminal of the photonic crystal waveguide (004). The output terminal of the photonic crystal waveguide (004) is connected to the input terminal of the fourth coupling waveguide (006). The output terminal of the fourth coupling waveguide (006) is connected to the signal processing module (400).

3. The photothermal interferometric gas sensing device based on photonic crystal slow waveguide and mode phase difference according to claim 2, characterized in that: The second coupling waveguide (021) is a rectangular waveguide, and the third coupling waveguide (022) is a rectangular waveguide with a gradually narrowing width.

4. The photothermal interferometric gas sensing device based on photonic crystal slow waveguide and mode phase difference according to claim 3, characterized in that: The output end of the first near-infrared laser (015) is connected to the input end of the first coupling waveguide (003) through a first fiber coupler (001) and a first focusing lens (002); the output end of the fourth coupling waveguide (006) is connected to the input end of the signal processing module (400) through a second focusing lens (007), a fiber circulator (008), and a second fiber coupler (009) in sequence.

5. The photothermal interferometric spectral gas sensing device based on photonic crystal slow waveguide and mode phase difference according to claim 4, characterized in that: The pump light generated by the second near-infrared laser (016) is coupled into the fourth coupling waveguide (006) through the fiber optic circulator (008) and the second focusing mirror (007) in sequence, and then enters the photonic crystal waveguide (004), changing the temperature of the photonic crystal waveguide (004) through the thermal conduction process.

6. The photothermal interferometric gas sensing device based on photonic crystal slow waveguide and mode phase difference according to claim 5, characterized in that: The signal processing module (400) includes a photodetector (010), a high-pass filter (011), a lock-in amplifier (012), a data acquisition card (013), and a computer (014) connected in sequence. The output end of the fourth coupling waveguide (006) is connected to the input end of the photodetector (010).

7. The photothermal interferometric gas sensing device based on photonic crystal slow waveguide and mode phase difference according to claim 1, characterized in that: The laser module (200) further includes a first temperature controller (019) for controlling the temperature of the first near-infrared laser (015) to be constant, and a first current controller (017) for controlling the current of the first near-infrared laser (015) to be constant.

8. The photothermal interferometric gas sensing device based on photonic crystal slow waveguide and mode phase difference according to claim 1, characterized in that: The laser module (200) further includes a second temperature controller (020) for controlling the temperature of the second near-infrared laser (016) to be constant, and a second current controller (018) for controlling the current of the second near-infrared laser (016) to be constant.

9. The detection method of the photothermal interferometric gas sensing device based on photonic crystal slow waveguide and mode phase difference as described in any one of claims 5-8, characterized in that, Includes the following steps, Step 1: The probe light generated by the first near-infrared laser (015) passes through the mode excitation module (300) and is transmitted in the photonic crystal waveguide (004) in odd and even modes, and then output to the signal processing module (400) for data processing; Step 2: The pump light generated by the second near-infrared laser (016) is coupled into the fourth coupling waveguide (006) through the fiber optic circulator (008), and the pump light is prevented from entering the second fiber optic coupler (009). At the same time, the probe light is coupled into the second fiber optic coupler (009). Step 3: Adjust the current of the second near-infrared laser (016) so that the near-infrared pump light wavelength is aligned with the absorption peak of the gas to be tested; Step 4: The signal processing module (400) acquires the phase difference information of the odd and even modes of the probe light output from the photonic crystal waveguide (004); Step 5: Analyze the relationship between the phase difference information obtained from the detection and the concentration of the gas to be measured, and obtain the concentration information of the gas to be measured.

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