CO2 and CO Dual-Parameter Measuring Optical Waveguide Gas Sensor and Its Usage Method

Abstract

The present invention discloses an optical waveguide gas sensor for measuring dual parameters of CO2 and CO, which includes an input waveguide. The input waveguide is connected to a splitter. The splitter equally divides the light of the input waveguide into a first branch waveguide, a second branch waveguide, and a third branch waveguide. The light in the first branch waveguide, the second branch waveguide, and the third branch waveguide is coupled by a combiner and output to an output waveguide. The first branch waveguide and the third branch waveguide form an asymmetric Mach-Zehnder interferometer for selectively adsorbing CO2, and the second branch waveguide and the third branch waveguide form an asymmetric Mach-Zehnder interferometer for selectively adsorbing CO. The present invention also discloses a method for using the optical waveguide gas sensor for measuring dual parameters of CO2 and CO. The present invention can achieve the simultaneous measurement of CO2 gas and CO gas.

Description

Technical Field

[0001] The present invention relates to a gas sensor, in particular to a waveguide gas sensor for measuring two parameters of CO2 and CO, belonging to the technical field of waveguide sensing. Background Art

[0002] CO2 is a known gas that can affect the human body. Indoors, CO2 levels of 2000 ppm to 5000 ppm (0.2% to 0.5%) can cause negative effects such as headaches, drowsiness, increased heart rate, and decreased concentration in people. Compared with CO2 gas, CO gas will combine with hemoglobin in human blood, causing hypoxia in cells of various tissues. When the concentration is relatively low (50 ppm to 400 ppm), it will cause symptoms such as headaches and fatigue in people, and high-concentration CO gas will pose a greater threat to human life and health. In daily life and production processes, CO2 gas and CO gas often appear simultaneously. Therefore, it is particularly important to develop sensors that can detect CO2 gas and CO gas simultaneously.

[0003] Metal-organic framework materials (MOFs) have become potential sensing materials due to their high porosity and selective gas adsorption ability. Among them, ZIF-8 has excellent thermal stability and chemical stability, a large specific surface area, high selective adsorption of CO2 gas, and insensitivity to humidity. In addition, polyaniline is a polymer with high selective adsorption of CO gas, which is easy to prepare and has good stability. By using the excellent performance of copper oxide in catalysis and other aspects, the composite of copper oxide and polyaniline in an appropriate proportion can improve the selectivity of polyaniline to CO gas and eliminate the cross-sensing situation.

[0004] A sensor that realizes selective detection of CO2 gas by growing ZIF-8 on the surface of an optical waveguide has the advantages of small volume, immunity to electromagnetic interference, easy integration, high sensitivity, and low cost. However, when fabricating ZIF-8 on the surface of an optical waveguide to modulate the light in the waveguide through the evanescent field to measure the refractive index or gas concentration of the external environment of the waveguide, there are problems such as time-consuming sensor fabrication, high requirements for the uniformity of the ZIF-8 film, and low sensor sensitivity. At the same time, there is no relevant report on an optical waveguide sensor for simultaneously measuring the contents of CO2 and CO. Summary of the Invention

[0005] The present invention aims to provide a waveguide gas sensor for measuring two parameters of CO2 and CO. The sensor forms an asymmetric Mach-Zehnder interferometer for selectively adsorbing CO2 through the first branch waveguide and the third branch waveguide, and forms an asymmetric Mach-Zehnder interferometer for selectively adsorbing CO through the second branch waveguide and the third branch waveguide, so as to realize the simultaneous measurement of CO2 gas and CO gas.

[0006] The present invention is implemented as follows:

[0007] A CO2 and CO dual-parameter measurement optical waveguide gas sensor, which includes an input waveguide, a splitter, a first branch waveguide, a second branch waveguide, a third branch waveguide, a combiner, and an output waveguide;

[0008] The input waveguide is connected to the splitter; the splitter equally divides the light of the input waveguide into the first branch waveguide, the second branch waveguide, and the third branch waveguide; the light of the first branch waveguide, the second branch waveguide, and the third branch waveguide is coupled by the combiner and output to the output waveguide;

[0009] The lengths of the first branch waveguide and the third branch waveguide are different, the lengths of the second branch waveguide and the third branch waveguide are different, and the three branch waveguides form a three-beam Mach-Zehnder interferometer;

[0010] The first branch waveguide and the third branch waveguide form an asymmetric Mach-Zehnder interferometer for selective adsorption of CO2, and the second branch waveguide and the third branch waveguide form an asymmetric Mach-Zehnder interferometer for selective adsorption of CO, so as to realize the simultaneous measurement of CO2 gas and CO gas.

[0011] A further solution is:

[0012] The first branch waveguide, the second branch waveguide, and the third branch waveguide are respectively composed of a first branch waveguide core layer, a second branch waveguide core layer, and a third branch waveguide core layer provided on the waveguide lower cladding. A waveguide upper cladding is also provided above the first branch waveguide core layer and the third branch waveguide core layer, and a second branch waveguide upper cladding is provided above the second branch waveguide core layer.

[0013] A further solution is:

[0014] The first branch waveguide, the second branch waveguide, and the third branch waveguide are single-mode waveguides with a length of 1 to 2 cm.

[0015] A further solution is:

[0016] The minimum distance between the first branch waveguide core layer, the second branch waveguide core layer, and the third branch waveguide core layer is 50 to 200 μm. Here, the minimum distance refers to the distance between the independent transmission regions of each branch waveguide, and this limitation ensures that light does not couple with each other when independently transmitted in the branch waveguides.

[0017] A further solution is:

[0018] The core layer of the first branch waveguide uses a composite gas-sensitive material of polymer and metal-organic framework material, specifically a composite material of PDMS and ZIF-8, where the average particle size of ZIF-8 is 40±10nm, and ZIF-8 / PDMS is 1-5wt%.

[0019] ZIF-8 has excellent thermal and chemical stability, a large specific surface area, high selective adsorption of CO2 gas, and is insensitive to humidity. At the same time, PDMS has become an excellent carrier for ZIF-8 materials due to its relatively low price, flexibility, chemical inertness, thermal stability, good permeability to CO2 gas, and good light transmittance. ZIF-8 and PDMS form a ZIF-8 / PDMS composite gas-sensitive material as the optical transmission medium through simple stirring and mixing, which can effectively reduce optical transmission loss.

[0020] A further solution is:

[0021] The upper cladding of the second branch waveguide is a polyaniline / cupric oxide composite gas-sensitive material with strong selective adsorption ability for carbon monoxide. Among them, polyaniline is a polymer with high selectivity for CO gas, which is easy to prepare and has good stability. By using the excellent properties of cupric oxide in catalysis and other aspects, the composite of cupric oxide and polyaniline can improve the sensitivity of polyaniline to CO gas and eliminate the situation of cross-sensing.

[0022] A further solution is:

[0023] The polymer material of the core layer of the third branch waveguide is PDMS. The refractive index of the polymer material of the core layer of the second branch waveguide is lower than that of the polymer material of the core layer of the third branch waveguide, and n eff3 L3 - n eff2 L2 > 0, n eff1 L1 - n eff3 L3 > 0 holds, where n eff1 , n eff2 , n eff3 are the effective refractive indices of the core layers of the first, second, and third branch waveguides respectively, and L1, L2, and L3 are the lengths of the core layers of the first, second, and third branch waveguides respectively. For example, the polymer material of the core layer of the second branch waveguide can be polymer materials such as NOA 144, NOA 142, ZPU13, etc.

[0024] A further solution is:

[0025] The refractive index of the polymer material of the lower cladding of the waveguide is lower than that of the polymer materials of the three branch waveguide core layers, so that light is confined to the optical waveguide core layer for transmission. The upper cladding material of the waveguide is a porous material with a pore size larger than that of ZIF-8, and allows the gas to be measured to adsorb / desorb with ZIF-8 through the upper cladding.

[0026] Specifically, the lower cladding material can be polymer materials such as NOA 144, NOA142, NOA 139, ZPU 13, etc. with refractive indices lower than that of the waveguide core layer. The upper cladding material of the waveguide can be materials such as mesoporous aerogel films and mesoporous silica films with a pore size larger than that of ZIF-8 and a refractive index lower than that of the core layer material.

[0027] A further solution is:

[0028] The free spectral range (FSR) of the spectra formed by the interferometer composed of the first branch waveguide and the third branch waveguide and the interferometer composed of the second branch waveguide and the third branch waveguide is 5-20 nm, and the difference between the two FSRs is greater than 5 nm. The simultaneous measurement of CO2 gas and CO gas is achieved by monitoring the drift of the two spectra of the spectrometer.

[0029] The present invention also provides a method for using an optical waveguide gas sensor for measuring CO2 and CO dual parameters, specifically including:

[0030] When the concentrations of external CO2 gas and CO gas change, the asymmetric Mach-Zehnder CO2 gas interferometer composed of the first branch waveguide and the third branch waveguide responds quickly to the change in the concentration of external CO2 gas. The ZIF-8 / PDMS composite gas-sensitive material in the core layer of the first branch waveguide adsorbs CO2 gas molecules, and the effective refractive index of the core layer increases. Since n eff1 L1-n eff3 L3>0, the difference in the effective refractive indices between the core layer of the first branch waveguide and the core layer of the third branch waveguide increases, which is manifested as a red shift of the spectrum in the output spectrum of the interferometer, and its drift amount is expressed by the following formula

[0031]

[0032] where Δn eff1 is the change in the effective refractive index of the core layer of the first branch waveguide, and a positive value indicates a red shift of the spectrum.

[0033] At the same time, the asymmetric Mach-Zehnder CO gas interferometer composed of the second branch waveguide and the third branch waveguide responds quickly to the change in the concentration of external CO gas. The copper oxide / polyaniline composite material on the upper cladding of the second branch waveguide adsorbs CO gas molecules, and the refractive index of the cladding increases. The effective refractive index of the core layer of the second branch waveguide also increases through evanescent field sensing. Since n eff3L3-n eff2 Since L2 > 0, the effective refractive index difference between the second-branch waveguide core layer and the three-branch waveguide core layer decreases, which is manifested as a blue shift in the interference spectrum at the output of the interferometer. The drift amount Δλ CO is expressed by the following formula

[0034]

[0035] where Δn eff2 is the change in the effective refractive index of the second-branch waveguide core layer, and Δλ CO being negative indicates a blue shift in the spectrum.

[0036] By filtering, the interference spectra formed by the first-branch waveguide and the third-branch waveguide, and the interference spectra formed by the second-branch waveguide and the third-branch waveguide are obtained respectively. By monitoring the red shift and blue shift amounts of the two spectra, the changes in the CO2 gas concentration and the CO gas concentration can be measured simultaneously.

[0037] The present invention has at least the following prominent beneficial effects:

[0038] The present invention forms a three-beam Mach-Zehnder interferometer structure through three branch waveguides, that is, two parallel Mach-Zehnder interferometers. Compared with the structure of connecting two Mach-Zehnder interferometers in series for traditional dual-parameter measurement, the structure is simpler and more miniaturized. Specifically, an asymmetric Mach-Zehnder interferometer for selective adsorption of CO2 is formed by the first-branch waveguide and the third-branch waveguide, and an asymmetric Mach-Zehnder interferometer for selective adsorption of CO is formed by the second-branch waveguide and the third-branch waveguide, so as to realize the simultaneous measurement of CO2 gas and CO gas;

[0039] Furthermore, the ZIF-8 / PDMS composite gas-sensitive material is used as the optical transmission medium, which solves the problems of time-consuming production of ZIF-8 on the surface of the optical waveguide, high requirement for the uniformity of the ZIF-8 film, and low sensor sensitivity. At the same time, by using the good light transmittance of PDMS, the ZIF-8 / PDMS composite gas-sensitive material solves the problems of serious light scattering and large transmission loss of ZIF-8;

[0040] Furthermore, the polyaniline / cupric oxide composite gas-sensitive material is used as the specific sensitive upper cladding material, which can realize the simultaneous high-sensitivity reaction measurement of CO2 gas and CO gas;

[0041] Furthermore, the core layer of the first-branch waveguide adopts the PDMS / ZIF-8 composite gas-sensitive material. By using the good light transmittance of PDMS and its simple mixing production method, the problems of long production time and difficult uniform growth when integrating ZIF-8 on the waveguide surface in the past are solved; at the same time, the problems of serious light scattering and large transmission loss when ZIF-8 is directly used as the optical transmission medium are solved;

[0042] Furthermore, the first branch waveguide core layer uses a composite gas-sensitive material of PDMS / ZIF-8, and the second branch waveguide upper cladding material is a polyaniline / cupric oxide composite gas-sensitive material with high selectivity for CO gas adsorption, enabling simultaneous measurement of CO2 gas and CO gas; BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is the basic structure diagram of the optical waveguide gas sensor of the present invention;

[0044] Figure 2 is Figure 1 a schematic cross-sectional view at the position of A-A' in

[0045] In the figure: 1. Input waveguide, 2. Splitter, 3. First branch waveguide, 4. Second branch waveguide, 5. Third branch waveguide, 6. Combiner, 7. Output waveguide, 10. Waveguide lower cladding, 12. Waveguide upper cladding, 31. First branch waveguide core layer, 41. Second branch waveguide core layer, 42. Second branch waveguide upper cladding, 51. Third branch waveguide core layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0047] The present invention provides an optical waveguide gas sensor for measuring CO2 and CO dual parameters, realizing simultaneous highly sensitive reaction measurement of CO2 gas and CO gas.

[0048] As Figure 1 shown, the present invention provides an optical waveguide gas sensor for measuring CO2 and CO dual parameters, including an input waveguide 1 that inputs light from the input waveguide into a splitter 2. The splitter 2 equally divides the light into a first branch waveguide 3, a second branch waveguide 4, and a third branch waveguide 5, and then couples the light from the three branch waveguides to a combiner 6 and an output waveguide 7. The first branch waveguide 3, the second branch waveguide 4, and the third branch waveguide 5 are respectively composed of a first branch waveguide core layer 31, a second branch waveguide core layer 41, and a third branch waveguide core layer 51 provided on a waveguide lower cladding 10. A waveguide upper cladding 12 is further provided above the first branch waveguide core layer and the third branch waveguide core layer, and a second branch waveguide upper cladding 42 is provided above the second branch waveguide core layer 41.

[0049] Three branch waveguides form a three-beam Mach-Zehnder interferometer. The lengths of the first branch waveguide and the third branch waveguide are different (with a difference of 1 - 2 cm), and the lengths of the second branch waveguide and the third branch waveguide are different (with a difference of 1 - 2 cm). The minimum distance between the core layers of adjacent branch waveguides is 50 - 200 μm.

[0050] The core layer of the first branch waveguide is a composite gas-sensitive material of PDMS and ZIF-8. The average particle size of ZIF-8 is 40 ± 10 nm, and the ZIF-8 / PDMS is 1 - 5 wt%. ZIF-8 has excellent thermal stability, chemical stability, a large specific surface area, high selective adsorption of CO2 gas, and is insensitive to humidity. At the same time, due to its relatively low price, flexibility, chemical inertness, thermal stability, good permeability to CO2, and good light transmittance, the PDMS material becomes an excellent carrier for the ZIF-8 material. ZIF-8 and PDMS form a ZIF-8 / PDMS composite gas-sensitive material as the optical transmission medium through simple stirring and mixing, which can effectively reduce the optical transmission loss.

[0051] Among them, PDMS can be Sylgard 184 PDMS, which is divided into PDMS prepolymer A and curing agent B, and is a well-known and commonly used PDMS in the art. The preparation method of the ZIF-8 / PDMS composite gas-sensitive material is as follows: ZIF-8 is dissolved in a methanol solution, and the methanol solution containing ZIF-8 is mixed and stirred with PDMS prepolymer A and curing agent B. During the stirring process, methanol will volatilize, and when the methanol has completely volatilized, a uniformly mixed ZIF-8 / PDMS composite gas-sensitive material can be obtained. The methanol solution can be replaced with ethanol or acetone; the ratio of PDMS prepolymer A to curing agent B is 5:1.

[0052] Part of the upper cladding of the core layer of the second branch waveguide is a polyaniline / cupric oxide composite gas-sensitive material with a strong selective adsorption ability for carbon monoxide. Among them, polyaniline is a polymer with high selectivity for CO gas. It is easy to prepare and has good stability. By combining cupric oxide and polyaniline in an appropriate ratio, the sensitivity of polyaniline to CO gas can be improved and the cross-sensing situation can be eliminated.

[0053] The core layer of the third branch waveguide is a PDMS polymer material, and the core layer of the second branch waveguide is a polymer material with a refractive index lower than that of PDMS, and n eff3 L3 - n eff2 L2 > 0, n eff1 L1 - n eff3 L3 > 0 holds, where n eff1 、n eff2 、n eff3are the effective refractive indices of the first branch waveguide core layer, the second branch waveguide core layer, and the third branch waveguide core layer, respectively. L1, L2, and L3 are the lengths of the first branch waveguide core layer, the second branch waveguide core layer, and the third branch waveguide core layer, respectively. The refractive index of the waveguide lower cladding polymer material is lower than that of the polymer materials of the three branch waveguide core layers, so that light can be confined to transmit in the core layer. The waveguide upper cladding material is a porous material with a pore size larger than that of ZIF-8, and allows the gas to be measured to undergo adsorption / desorption with ZIF-8 through the upper cladding.

[0054] The light emitted by the light source enters the optical splitter through the input waveguide and is equally divided into three branch waveguides. The light transmitted along the first branch waveguide and the second branch waveguide interferes with the light transmitted along the third branch waveguide respectively to form two sets of interference signals. Among them, the first branch waveguide and the third branch waveguide form an asymmetric Mach-Zehnder interferometer with high selectivity for CO2 adsorption, and the second branch waveguide and the third branch waveguide form an asymmetric Mach-Zehnder interferometer with high selectivity for CO adsorption. The FSR of the spectra formed by the two interferometers is 5-20 nm, and the difference between the two FSRs is greater than 5 nm. For the interference signals formed by the two interferometers, the output intensity can be expressed by the following formula

[0055]

[0056]

[0057] where I1, I2, and I3 are the light intensities passing through the first branch waveguide core layer, the second branch waveguide core layer, and the third branch waveguide core layer, respectively. is the phase difference between the two beams of light in the first branch waveguide and the third branch waveguide. is the phase difference between the two beams of light in the second branch waveguide and the third branch waveguide, and is expressed by the formula

[0058]

[0059]

[0060] where n eff1 , n eff2 , n eff3 are the effective refractive indices of the first branch waveguide core layer, the second branch waveguide core layer, and the third branch waveguide core layer, respectively. L1, L2, and L3 are the lengths of the first branch waveguide core layer, the second branch waveguide core layer, and the third branch waveguide core layer, respectively, and λ is the wavelength of the incident light source. From formulas (1), (2), (3), and (4), it can be seen that when and , the output light intensity is destructive interference, and the output light intensity at this time is

[0061]

[0062]

[0063] At this time, it corresponds to an interference trough in the transmission spectrum

[0064]

[0065]

[0066] When the concentrations of external CO2 gas and CO gas change, the asymmetric Mach-Zehnder CO2 gas interferometer composed of the first branch waveguide and the third branch waveguide responds quickly to the change in the concentration of external CO2 gas. The ZIF-8 / PDMS composite gas-sensitive material in the core layer of the first branch waveguide adsorbs CO2 gas molecules, and the effective refractive index of the core layer increases. Since n eff1 L1 - n eff3 L3 > 0, so the difference in the effective refractive indices between the core layer of the first branch waveguide and the core layer of the third branch waveguide increases, which is manifested as a red shift in the output spectrum of the interferometer. The drift amount can be expressed by the following formula:

[0067]

[0068] where Δn eff1 is the change in the effective refractive index of the core layer of the first branch waveguide, and a positive value indicates a red shift in the spectrum.

[0069] At the same time, the asymmetric Mach-Zehnder CO gas interferometer composed of the second branch waveguide and the third branch waveguide responds quickly to the change in the concentration of external CO gas. The copper oxide / polyaniline composite material on the upper cladding of the second branch waveguide adsorbs CO gas molecules, and the refractive index of the cladding increases. Through evanescent field sensing, the effective refractive index of the core layer of the second branch waveguide also increases. Since n eff3 L3 - n eff2 L2 > 0, so the difference in the effective refractive indices between the core layer of the second branch waveguide and the core layer of the third branch waveguide decreases, which is manifested as a blue shift in the output spectrum of the interferometer. The drift amount Δλ CO can be expressed by the following formula:

[0070]

[0071] where Δn eff2 is the change in the effective refractive index of the core layer of the second branch waveguide, and Δλ CO and a negative value indicates a blue shift in the spectrum.

[0072] By filtering, the interference spectra formed by the first branch waveguide and the third branch waveguide, and the interference spectra formed by the second branch waveguide and the third branch waveguide are obtained respectively. By monitoring the redshifts and blueshifts of the two spectra, the changes in the CO2 gas concentration and the CO gas concentration can be measured simultaneously.

[0073] Although the present invention has been described herein with reference to illustrative embodiments thereof, the above embodiments are only preferred embodiments of the present invention, and the embodiments of the present invention are not limited by the above embodiments. It should be understood that those skilled in the art can design many other modifications and embodiments, which will fall within the scope and spirit of the principles disclosed in this application.

Claims

1. A dual-parameter measurement optical waveguide gas sensor for CO2 and CO, characterized in that: It includes an input waveguide, a beam splitter, a first branch waveguide, a second branch waveguide, a third branch waveguide, a light combiner, and an output waveguide; The input waveguide is connected to the beam splitter; the beam splitter equally divides the light of the input waveguide into the first branch waveguide, the second branch waveguide, and the third branch waveguide; the light of the first branch waveguide, the second branch waveguide, and the third branch waveguide is coupled by the light combiner and output to the output waveguide; The first branch waveguide and the third branch waveguide form an asymmetric Mach-Zehnder interferometer for selective adsorption of CO2, and the second branch waveguide and the third branch waveguide form an asymmetric Mach-Zehnder interferometer for selective adsorption of CO, thereby realizing the simultaneous measurement of CO2 gas and CO gas; The first branch waveguide, the second branch waveguide, and the third branch waveguide are respectively composed of a first branch waveguide core layer, a second branch waveguide core layer, and a third branch waveguide core layer provided on the waveguide lower cladding. A waveguide upper cladding is also provided above the first branch waveguide core layer and the third branch waveguide core layer, and a second branch waveguide upper cladding is provided above the second branch waveguide core layer; The first branch waveguide core layer adopts a composite material of PDMS and ZIF-8, wherein the average particle size of ZIF-8 is 40±10 nm, and ZIF-8 / PDMS is 1-5 wt%; The second branch waveguide upper cladding is a polyaniline / cupric oxide composite gas-sensitive material with strong selective adsorption ability for carbon monoxide; The polymer material of the third branch waveguide core layer is PDMS, and the refractive index of the polymer material of the second branch waveguide core layer is lower than that of the polymer material of the third branch waveguide core layer, and it is ensured that n eff3 L3 - n eff2 L2 > 0, n eff1 L1 - n eff3 L3 > 0 holds, where n eff1 , n eff2 , n eff3 are the effective refractive indices of the first branch waveguide core layer, the second branch waveguide core layer, and the third branch waveguide core layer respectively, and L1, L2, and L3 are the lengths of the first branch waveguide core layer, the second branch waveguide core layer, and the third branch waveguide core layer respectively.

2. The dual-parameter measurement optical waveguide gas sensor for CO2 and CO according to claim 1, characterized in that: The first branch waveguide, the second branch waveguide, and the third branch waveguide are single-mode waveguides with a length of 1-2 cm.

3. The dual-parameter measurement optical waveguide gas sensor for CO2 and CO according to claim 1, characterized in that: The minimum adjacent distance between the first branch waveguide core layer, the second branch waveguide core layer, and the third branch waveguide core layer is 50-200 μm.

4. The dual-parameter measurement optical waveguide gas sensor for CO2 and CO according to claim 1, characterized in that: The refractive index of the polymer material of the waveguide lower cladding is lower than that of the polymer materials of the three branch waveguide core layers, so that light is restricted to be transmitted in the optical waveguide core layer. The waveguide upper cladding material is a porous material with a pore size larger than that of ZIF-8, and allows the gas to be measured to adsorb / desorb with ZIF-8 through the upper cladding.

5. The dual-parameter measurement optical waveguide gas sensor for CO2 and CO according to claim 1, characterized in that: The free spectral range (FSR) of the spectra formed by the interferometer composed of the first branch waveguide and the third branch waveguide and the interferometer composed of the second branch waveguide and the third branch waveguide is 5-20 nm, and the difference between the two FSRs is greater than 5 nm. The simultaneous measurement of CO2 gas and CO gas is realized by monitoring the drift of the two spectra of the spectrometer.

6. The method of using the dual-parameter measurement optical waveguide gas sensor for CO2 and CO according to any one of claims 1 to 5, characterized in that It includes: When the concentrations of external CO2 gas and CO gas change, the asymmetric Mach-Zehnder CO2 gas interferometer composed of the first branch waveguide and the third branch waveguide responds quickly to the change in the concentration of external CO2 gas. The ZIF-8 / PDMS composite gas-sensitive material in the core layer of the first branch waveguide adsorbs CO2 gas molecules, and the effective refractive index of the core layer increases; due to n eff1 L1 - n eff3 L3 > 0, so the effective refractive index difference between the core layer of the first branch waveguide and the core layer of the third branch waveguide increases, which is manifested as a red shift in the output spectrum of the interferometer, and its drift amount is expressed by the following formula where Δn eff1 is the change in the effective refractive index of the core layer of the first branch waveguide, and a positive value indicates a redshift in the spectrum; Meanwhile, the asymmetric Mach-Zehnder CO gas interferometer formed by the second branch waveguide and the third branch waveguide responds quickly to changes in the external CO gas concentration. The copper oxide / polyaniline composite material on the upper cladding of the second branch waveguide adsorbs CO gas molecules, increasing the cladding refractive index. Through evanescent field sensing, the effective refractive index of the core layer of the second branch waveguide also increases; since n eff3 L3 - n eff2 L2 > 0, the effective refractive index difference between the core layer of the second branch waveguide and the core layer of the three-branch waveguide decreases, manifested as a blue shift in the interference spectrum at the output of the interferometer. Its drift amount Δλ CO is expressed by the following formula where Δn eff2 is the change in the effective refractive index of the second branch waveguide core layer, and Δλ CO being negative indicates a blue shift in the spectrum; The interference spectra formed by the first branch waveguide and the third branch waveguide and the interference spectra formed by the second branch waveguide and the third branch waveguide are respectively obtained through filtering. The changes in the CO2 gas concentration and the CO gas concentration can be simultaneously measured by monitoring the red shift and blue shift amounts of the two spectra.

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