Gas sensing method and system based on MZI-micro-ring resonant cavity enhancement

Abstract

The invention provides a gas sensing system and method based on MZI-micro-ring resonant cavity enhancement. The gas sensing system comprises a laser, a beam splitter, a first coupling module, a second coupling module, an optical switch and a coherent detection module, a light source emitted by the laser passes through the beam splitter to obtain three identical light beams, including a reference light beam, a first signal light beam and a second signal light beam; wherein the first signal light beam and the second signal light beam respectively pass through the first coupling module and the second coupling module, are subjected to channel selection of the optical switch, and then are subjected to interference measurement with the reference light beam through the coherent detection module.

Description

Technical Field

[0001] The present invention relates to the technical field of air quality detection in environmental protection, and in particular to a gas sensing method and system based on MZI-microring resonant cavity enhancement. Background Art

[0002] With the rapid development of industrialization and urbanization, environmental pollution is becoming increasingly serious, especially the emission of harmful gases, which poses a huge threat to human health and the ecological environment. In order to meet this challenge, building environmental monitoring stations to detect harmful gases has become an important solution. Although traditional gas detection technologies can provide certain information, their sensitivity and accuracy are often insufficient when facing weak harmful gases in the air.

[0003] The high quality factor of the microring resonator means that it can provide extremely high spectral resolution, allowing the sensor to detect trace gas molecules with extremely high sensitivity. In addition, the small volume of the microring resonator can interact with a variety of substances while reducing the size of the sensor, thereby achieving highly selective detection of specific gases.

[0004] However, despite the significant advantages of the microring resonator in detecting trace gases, it still faces some challenges in practical applications. First, although the amount of information obtained by the microring resonator in a strictly coupled state increases, the coupling mode of the microring resonator will change due to the absorption of the gas, which means that the microring resonator cannot always maintain the optimal working point. Second, traditional intensity detection can only collect limited data in the experiment, which limits the precise measurement of gas absorption rate and the depth of data analysis. Summary of the invention

[0005] In view of the defects in the prior art, an object of the present invention is to provide a gas sensing method and system based on MZI-microring resonant cavity enhancement.

[0006] A gas sensing system based on MZI-microring resonator enhancement provided by the present invention includes: a laser 1, a beam splitter 2, a first coupling module 3, a second coupling module 4, an optical switch 5 and a coherent detection module 6;

[0007] The light source emitted by the laser 1 passes through the beam splitter 2 to obtain three identical light beams, including: a reference light beam, a first signal light beam, and a second signal light beam;

[0008] The first signal light beam and the second signal light beam respectively pass through the first coupling module 3 and the second coupling module 4 , and then are selected by the channel of the optical switch 5 to perform interference measurement with the reference light beam through the coherent detection module 6 .

[0009] Preferably, the laser 1 is a laser with tunable output wavelength.

[0010] Preferably, the first coupling module 3 comprises a first sensing microring and a first Mach-Zehnder interferometer MZI; the first sensing microring and the first Mach-Zehnder interferometer MZI are coupled;

[0011] The first signal light beam is transmitted to the first Mach-Zehnder interferometer MZI through a straight waveguide, and then enters the first sensing microring through the first Mach-Zehnder interferometer MZI, and completes the sensing process in the first sensing microring. After the sensing process, the first signal light beam is transmitted to the first Mach-Zehnder interferometer MZI, and then transmitted to the optical switch 5 through the first Mach-Zehnder interferometer MZI;

[0012] The second coupling module 4 includes a second sensing microring and a second Mach-Zehnder interferometer MZI; the second sensing microring and the second Mach-Zehnder interferometer MZI are coupled;

[0013] The second signal light beam is transmitted to the second Mach-Zehnder interferometer MZI through a straight waveguide, and then enters the second sensing microring through the second Mach-Zehnder interferometer MZI, and completes the sensing process in the second sensing microring. After completing the sensing process, the second signal light beam is transmitted to the second Mach-Zehnder interferometer MZI, and then transmitted to the optical switch 5 through the second Mach-Zehnder interferometer MZI.

[0014] Preferably, the first signal light beam is transmitted to the first Mach-Zehnder interferometer MZI through a straight waveguide, wherein a portion of the light beam enters the first sensing microring through the first 3dB coupler 7 from the evanescent field to interact with the gas, and the other portion of the light beam continues to be transmitted forward, and the two portions of the light beam interfere with each other in the second 3dB coupler 8, and the interfered light beam is transmitted to the optical switch 5;

[0015] The second signal light beam is transmitted to the second Mach-Zehnder interferometer MZI through a straight waveguide, wherein a portion of the light beam enters the second sensing microring through the third 3dB coupler 9 from the evanescent field to interact with the gas, and the other portion of the light beam continues to be transmitted forward, and the two portions of the light beam interfere with each other in the fourth 3dB coupler 10, and the interfered light beam is transmitted to the optical switch 5.

[0016] Preferably, the radius of the first sensing microring / the second sensing microring is determined by the wavelength position of the absorption peak corresponding to the gas to be measured, including:

[0017]

[0018] Where R is the radius of the microring, λ is the wavelength of the absorption peak of the gas to be measured, m is a positive integer, and the resonance wavelength of the microring needs to be exactly equal to the absorption peak wavelength of the gas to be measured, n eff represents the effective refractive index inside the microring.

[0019] According to a gas sensing method based on MZI-microring resonant cavity enhancement provided by the present invention, the following steps are performed based on the gas sensing system based on MZI-microring resonant cavity enhancement described above:

[0020] Step S1: coating the surfaces of the first sensing microring and the second sensing microring with target polymers for detecting the first target gas and the second target gas respectively;

[0021] Step S2: adjusting the coupling coefficient between the first sensing micro-ring and the second sensing micro-ring so that the first sensing micro-ring and the second sensing micro-ring are in a strictly coupled state;

[0022] Step S3: The light source generated by laser 1 is divided into three identical light beams after passing through a beam splitter, which are marked as a first signal beam, a second signal beam and a reference beam respectively;

[0023] Step S4: the first signal light beam / the second signal light beam enters the first sensing microring resonant cavity / the second sensing microring resonant cavity coupled to the first Mach-Zehnder interferometer MZI / the second Mach-Zehnder interferometer MZI through a straight waveguide, and interacts with the target gas. After the interaction, the light beam leaves the first sensing microring resonant cavity / the second sensing microring resonant cavity through a straight waveguide, and after being selected by the optical switch 5, interferes with the reference light beam in the mixer in the coherent detection module 6, and is finally received by the detector to obtain the detector photocurrent;

[0024] Step S5: Under the condition that the photocurrent output by the detector is 0, adjust the output band of the light source and the phase modulator parameter φ on the two arms of the corresponding Mach-Zehnder interferometer MZI 1 ,φ 2 , so that the corresponding sensing microring returns to the strict coupling mode again;

[0025] Step S6: When the photocurrent data output by the detector is 0, calculate the gas absorption coefficient α A ;

[0026] Step S7: Adjust the coupling coefficient to be equal to the current loss so that the sensing microring returns to the strict coupling mode again, and estimate the gas concentration by combining the absorption coefficient and the phase shift.

[0027] Preferably, the step S2 comprises:

[0028] r=ie iΔφCM cos(Δφ d )

[0029] Where r is the equivalent coupling coefficient between microring-MZI and waveguide, φ 1 ,φ 2 are the phase shifts of the phase modulators on the MZI arms respectively.

[0030] Preferably, the detector photocurrent comprises:

[0031]

[0032] Among them, I 2 represents the detector photocurrent after bandpass filtering; S represents the photodetector gain because the detection process is a zero-difference detection process; A s Indicates the signal light amplitude, A r represents the reference light amplitude, ω s represents the signal light frequency, ω r represents the reference light frequency, Indicates the signal light phase, Indicates the reference light phase.

[0033] Preferably, step S5 comprises:

[0034]

[0035] Where Δλ represents the change in the microring resonance wavelength; Δn eff represents the change in the effective refractive index of the microring; m represents a positive integer; R represents the radius of the microring; Δφ represents the phase shift caused by gas absorption; L represents the circumference of the microring; Γ φ Represents the scale factor.

[0036] Preferably, step S6 comprises:

[0037] r = a

[0038]

[0039] α T =α I +Γ α α A

[0040] Among them, α r is the total absorption factor, α I It represents the intrinsic loss of the system, α A is the gas absorption coefficient, Γ α is the scale factor;

[0041] The gas concentrations include:

[0042] Estimate gas concentrations based on absorption coefficients, including:

[0043]

[0044] Where C is the gas concentration, K is the molar absorption coefficient, and L is the circumference of the microring α I Characterizes the intrinsic loss of the system, Γ α is the scale factor, φ 1 ,φ 2 are the phase shifts of the phase modulators on the MZI arms respectively.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. The present invention utilizes the characteristics of the micro-ring resonant cavity to achieve higher sensitivity, which enhances the ability to detect small changes, such as the absorption rate of harmful gases;

[0047] 2. The present invention uses polymers that react specifically only with the target gas, which greatly reduces the problems caused by crosstalk absorption between gases. This means that no complex algorithms are required for separation during data processing and solution, which speeds up data processing;

[0048] 3. The present invention uses a coherent detection scheme to simultaneously obtain phase and loss information, which increases the dimension of information acquisition compared to traditional intensity detection, and the detection result is more accurate;

[0049] 4. The present invention observes the output of the detector and uses the phase modulator on the MZI arm to perform feedback adjustment so that the microring resonant cavity is always maintained at the optimal working point during the measurement process, thereby improving the accuracy of parameter estimation.

[0050] 5. The present invention not only improves the measurement performance, but also simplifies the data collection and processing process, making the present invention have significant application potential and market competitiveness in the field of precision measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0052] Figure 1 Schematic diagram of the structure of the gas sensing method based on MZI-microring resonant cavity enhancement in the present invention.

[0053] Figure 2 Schematic diagram of the MZI-microring resonator coupling module in the present invention.

[0054] Among them, 1-laser; 2-beam splitter; 3-first coupling module; 4-second coupling module; 5-optical switch; 6-coherent detection module; 7-first 3dB coupler; 8-first phase modulator; 9-second 3dB coupler; 10-second phase modulator. DETAILED DESCRIPTION

[0055] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0056] Example 1

[0057] In view of the defects in the prior art, the purpose of the present invention is to provide a gas sensing system and method based on MZI-microring resonant cavity enhancement, combining Mach-Zehnder interferometer (MZI) with microring resonant cavity, and adjusting the phase parameters of Mach-Zehnder interferometer to make the resonant mode of microring resonant cavity always stable in strict coupling mode. In this mode, coherent detection is used to estimate the gas absorption rate, which can significantly improve the measurement accuracy. The present invention has two major features: one is to use a special coupling structure to keep the measurement process at the optimal working point at all times, and the other is to use coherent detection to simultaneously estimate the phase shift and loss caused by gas absorption. Compared with the traditional gas concentration detection scheme, this technology further improves the measurement accuracy, provides more reliable data support for air quality detection and environmental protection, and is suitable for systems with higher detection accuracy requirements.

[0058] The gas sensing system based on MZI-microring resonator enhancement, such as Figure 1 As shown, including:

[0059] Laser 1, beam splitter 2, first coupling module 3, second coupling module 4, optical switch 5 and coherent detection module 6;

[0060] The light source emitted by the laser 1 passes through the beam splitter 2 to obtain three identical light beams, including: a reference light beam, a first signal light beam, and a second signal light beam;

[0061] The first signal light beam and the second signal light beam respectively pass through the first coupling module 3 and the second coupling module 4 , and then are selected by the channel of the optical switch 5 to perform interference measurement with the reference light beam through the coherent detection module 6 .

[0062] Specifically, the laser 1 is a laser with tunable output wavelength.

[0063] Specifically, the first coupling module 3 includes a first sensing microring and a first Mach-Zehnder interferometer MZI; the first sensing microring and the first Mach-Zehnder interferometer MZI are coupled;

[0064] The first signal light beam is transmitted to the first Mach-Zehnder interferometer MZI through a straight waveguide, and then enters the first sensing microring through the first Mach-Zehnder interferometer MZI, and completes the sensing process in the first sensing microring. After the sensing process, the first signal light beam is transmitted to the first Mach-Zehnder interferometer MZI, and then transmitted to the optical switch 5 through the first Mach-Zehnder interferometer MZI;

[0065] The second coupling module 4 includes a second sensing microring and a second Mach-Zehnder interferometer MZI; the second sensing microring and the second Mach-Zehnder interferometer MZI are coupled;

[0066] The second signal light beam is transmitted to the second Mach-Zehnder interferometer MZI through a straight waveguide, and then enters the second sensing microring through the second Mach-Zehnder interferometer MZI, and completes the sensing process in the second sensing microring. After completing the sensing process, the second signal light beam is transmitted to the second Mach-Zehnder interferometer MZI, and then transmitted to the optical switch 5 through the second Mach-Zehnder interferometer MZI.

[0067] Specifically, the first signal light beam is transmitted to the first Mach-Zehnder interferometer MZI through a straight waveguide, wherein a portion of the light beam enters the first sensing microring through the first 3dB coupler 7 from the evanescent field to interact with the gas, and the other portion of the light beam continues to be transmitted forward, and the two portions of the light beam interfere with each other in the second 3dB coupler 8, and the interfered light beam is transmitted to the optical switch 5;

[0068] The second signal light beam is transmitted to the second Mach-Zehnder interferometer MZI through a straight waveguide, wherein a portion of the light beam enters the second sensing microring through the third 3dB coupler 9 from the evanescent field to interact with the gas, and the other portion of the light beam continues to be transmitted forward, and the two portions of the light beam interfere with each other in the fourth 3dB coupler 10, and the interfered light beam is transmitted to the optical switch 5.

[0069] Specifically, the radius of the first sensing microring / the second sensing microring is determined by the band position of the corresponding absorption peak of the gas to be measured, including:

[0070]

[0071] Where R is the radius of the microring, λ is the wavelength of the absorption peak of the gas to be measured, m is a positive integer, and the resonance wavelength of the microring needs to be exactly equal to the absorption peak wavelength of the gas to be measured, n effrepresents the effective refractive index inside the microring.

[0072] The gas sensing method based on MZI-microring resonant cavity enhancement includes:

[0073] Step 1: Divide the light emitted by the laser into three identical beams, one as the reference light path and the other two as the signal light paths for detecting the two gas components.

[0074] Step 2: In the first signal optical path, the light source first enters the first coupling module through a straight waveguide. The function of the straight waveguide is to transmit the optical signal to the input port of the first Mach-Zehnder interferometer (MZI) and finally enter the first sensing microring. Next, the gas reacts specifically with the polymer coated on the surface of the microring, changing the effective refractive index inside the microring. At the same time, the light beam interacts with the gas in the first sensing microring cavity, causing loss of the corresponding band light beam. The light beam output by the coupling module interferes with the output light of the reference optical path after being selected by the channel of the optical switch, and is then captured by the photodetector.

[0075] The second signal light path is the same as the first signal light path except for the size of the microring and the polymer coated on the microring surface. The final output interferes with the reference light path and is captured by the photodetector.

[0076] In the reference optical path, the light beam is directly output through a straight waveguide, and interferes with the output light of the first signal optical path or the second signal optical path, respectively, to perform coherent detection.

[0077] Step 3: The strict coupling condition of the microring needs to meet two conditions at the same time: the circumference of the microring is equal to an integer multiple of the input light wavelength, and the internal loss of the microring is equal to the coupling coefficient between the waveguide and the microring. Due to the specific reaction of the polymer and the gas, the effective refractive index inside the microring changes, and the circumference of the microring is no longer equal to an integer multiple of the input light wavelength. At the same time, due to the absorption of the gas, the loss inside the ring increases, and the microring resonant mode will be converted from strict coupling to other modes. It is necessary to adjust the phase modulator on the MZI arm to change the coupling coefficient between the waveguide and the microring and the frequency band of the light source input, so that the microring resonant mode remains under the strict coupling condition. According to the light measurement data captured by the photodetector in the coherent detection module, adjust the phase shift φ of the phase modulator in the signal optical path 1 and 2. 1 With φ 2 , so that the microring resonant mode returns to the strict coupling mode. In the strict coupling mode, by analyzing the outputs of the two detectors and the φ of the two arms of the MZI 1 With φ 2 , the absorption of the gas in a certain band of light source can be estimated. In addition, the change in the effective refractive index inside the microring can be inferred based on the change in the frequency of the input light source, thereby inferring the phase shift caused by the gas and estimating the concentration of the gas.

[0078] like Figure 2 As shown, the coupling module is composed of a micro-ring and an MZI, specifically:

[0079] The MZI consists of two 3dB couplers and two symmetrical arms with phase modulators. The phase shift φ 1 With φ 2 The equivalent coupling coefficient of the MZI coupler can be changed, thereby changing the coupling coefficient between the waveguide and the microring, thereby achieving control of the microring mode.

[0080] The radius of the microring is determined by the wavelength position of the corresponding absorption peak of the gas to be measured, specifically:

[0081]

[0082] Among them, R is the radius of the microring, λ is the peak wavelength of the absorption peak of the gas to be measured, m is a positive integer, and the resonance wavelength of the microring is exactly equal to the peak wavelength of the absorption peak of the gas to be measured. eff represents the effective refractive index inside the microring;

[0083] The polymer coated on the surface of the microring must be able to react specifically with the above-mentioned gas to be measured, thereby changing the effective refractive index inside the microring and further affecting the resonant wavelength of the microring, specifically:

[0084]

[0085] λ 1 =λ 0 +Δλ

[0086] Among them, λ 0 is the initial resonance wavelength of the microring, λ 1 is the changed microring resonant wavelength, n eff0 is the initial effective refractive index of the microring, Δλ is the change in the resonant wavelength of the microring, and Δn eff is the change of the effective refractive index of the microring.

[0087] Specifically, in step 2, the different micro-ring sizes in the second signal light path are:

[0088] The second signal optical path and the first signal optical path detect different gases, and the corresponding absorption peaks are also different. The micro-ring radius required for the second signal optical path can be calculated according to the gas absorption peak position.

[0089] Specifically, in step 3, the strict coupling is specifically:

[0090] Under strict coupling conditions, the microring satisfies the resonance condition and the microring-waveguide coupling coefficient r and the microring loss coefficient α are equal. At this time, the light intensity coupled into the ring waveguide is equal to the light intensity lost by the light field through the microring, and the transmittance T = 0. Preferably, the coupling coefficient r is specifically:

[0091] r=ie iΔφCM cos(Δφ d )

[0092] Where r is the equivalent coupling coefficient between microring-MZI and waveguide, φ 1 ,φ 2 are the phase shifts of the phase modulators on the MZI arms respectively.

[0093] Specifically, the changing of the input light source frequency band is specifically:

[0094] Due to the effect of the gas, the effective refractive index inside the microring changes and the resonant wavelength shifts. At this time, the original input wavelength no longer meets the resonance condition. It is necessary to change the incident wavelength through a tunable laser to meet the resonance condition again.

[0095]

[0096] Where L = 2πR is the circumference of the microring, Γ φ is the proportionality factor and Δφ is the phase shift caused by gas absorption.

[0097] From the above two equations, the phase shift of the system can be calculated according to the change in the input light source.

[0098] Specifically, the changing and adjusting coupling coefficient is specifically:

[0099] Due to the absorption of the gas, the coupling coefficient is no longer equal to the loss within the loop, the strict coupling condition changes, and the coupling coefficient needs to be adjusted.

[0100] r=α

[0101]

[0102] α T =α I +Γ α α A

[0103] Among them, α T is the total absorption factor, α I It represents the intrinsic loss of the system, α A is the absorption coefficient of the analyte, Γ α is the scale factor.

[0104] By adjusting the phase modulator φ of the two arms of the MZI 1 ,φ 2 The microring returns to the strictly coupled state again, and α can be further calculated based on the adjusted r value. A , which is the absorption loss value of the gas.

[0105] Specifically, the coherent detection light measurement data is:

[0106]

[0107] Among them, E s is the signal light field intensity, E r is the reference light field intensity, A, ω, are amplitude, frequency and phase respectively. The signal light interferes with the reference light, and the photocurrent output by the photodetector is:

[0108]

[0109] The photocurrent output by the photodetector is filtered out by a bandpass filter to remove the DC signal:

[0110]

[0111] Average photocurrent after filtering out DC signal:

[0112]

[0113] Where S is the photodetector gain. Since the detection process is a homodyne detection process, ω s =ω r .

[0114] By observing the photocurrent to adjust the coupling coefficient and the wavelength of the light source, the phase shift and light intensity loss caused by the gas can be inferred.

[0115] Specifically, the gas concentration is estimated based on the absorption coefficient, specifically:

[0116]

[0117] Where C is the gas concentration, K is the molar absorption coefficient, and L is the circumference of the microring α I Characterizes the intrinsic loss of the system, Γ α is the scale factor, φ 1 ,φ 2 are the phase shifts of the phase modulators on the MZI arms respectively. Whether the strict coupling point has been reached is determined by observing whether the reading of the photodetector is 0.

[0118] Example 2

[0119] Embodiment 2 is a preferred embodiment of Embodiment 1

[0120] The present invention proposes a gas sensing method based on MZI-microring resonant cavity enhancement. The method uses the advantages of the microring resonant cavity to adjust the coupling coefficient by coupling the MZI with the microring resonant cavity, so that the microring working mode is always kept in the strict coupling mode. Compared with other gas sensing methods based on microring resonant cavities, the present invention maintains the microring resonant cavity at the optimal working point during the measurement process, achieving more accurate parameter estimation. This improvement significantly enhances the system's ability to detect small changes in absorption rate. In addition, the detection process adopts a coherent detection method to reduce noise while obtaining the phase change and light intensity loss of gas absorption, so as to achieve high sensitivity and high accuracy measurement of the absorption rate of harmful gases.

[0121] The gas sensing method based on MZI-microring resonant cavity proposed in the present invention mainly consists of two major components: optical sensing process and detection link. In the optical sensing link, the gas interacts with the polymer-coated microring resonant cavity to capture optical information related to gas absorption. The detection link is to mix the sensing optical path with the reference optical path to obtain phase shift and loss so as to adjust the MZI coupling coefficient so that the microring is kept at the optimal working point, thereby achieving high-sensitivity detection of gas absorption rate.

[0122] The specific process of the optical sensing process is as follows:

[0123] The tunable laser is divided into three paths of light through a beam splitter, one of which is used as a reference path and the other two are sensing paths. In the sensing path, the light beam first enters the microring resonant cavity coupled to the MZI through a straight waveguide. The surface of the microring resonant cavity is coated with a corresponding polymer, and the gas reacts specifically with the polymer to change the equivalent refractive index of the microring. The light beam in the ring interacts with the gas, and there is partial absorption loss at the corresponding gas absorption peak position.

[0124] The specific process of the detection link is as follows:

[0125] The output beam of the sensing optical path is selected through an optical switch. The selected signal beam and the reference beam interfere with each other in the mixer. According to the interference output result, the phase modulator on the MZI arm and the output wavelength of the tunable laser are adjusted to make the microring return to the strict coupling state. The concentration of the gas can be estimated by the change in the laser wavelength and the adjustment of the coupling coefficient of the coupler.

[0126] Specifically, the gas sensing method based on MZI-microring resonant cavity enhancement includes the following steps:

[0127] Step A1: Polyhexamethylene biguanide hydrochloride (PHMB) and Cryptophane A are coated on the surfaces of two microrings for detecting CO2 , CH 4 gas.

[0128] Step A2: Adjust the microring coupling coefficient to make the microring in a strictly coupled state.

[0129] Step A3: generating a light source using a tunable laser;

[0130] Step A4: Split the light source into three identical light paths after passing through a beam splitter, and mark them as signal light paths and reference light paths respectively;

[0131] Step A5: The light beam in the signal optical path enters the microring resonant cavity coupled to the MZI through a straight waveguide, and interacts with the gas outside the ring through the evanescent field. The gas outside the ring reacts specifically with the polymer coated on the ring surface, changing the effective refractive index of the microring.

[0132] Step A6: After interacting with the gas, the light beam leaves the microring resonator through a straight waveguide, interferes with the reference light in the mixer in the coherent detection after being selected by the optical switch, and is finally received by the detector, specifically:

[0133]

[0134] Among them, I 2 is the detector photocurrent after bandpass filtering.

[0135] Step A7: Under the condition that the photocurrent output by the detector is 0, adjust the output band of the light source and the phase modulator parameter φ on the two arms of the MZI 1 ,φ 2 Make the microring return to strict coupling mode again, specifically:

[0136] r=ie iΔφCM cos(Δφ d )

[0137] Where r is the equivalent coupling coefficient between microring-MZI and waveguide, φ 1 ,φ 2 are the phase shifts of the phase modulators on the MZI arms respectively.

[0138] Step A8: When the photocurrent data output by the detector is 0, calculate the gas absorption coefficient α A , specifically:

[0139] r = a

[0140]

[0141] α T =α I +Γ α α A

[0142] Among them, α T is the total absorption factor, α I It represents the intrinsic loss of the system, α A is the gas absorption coefficient, Γ α is the scale factor.

[0143] Step A9: Adjust the coupling coefficient to be equal to the current loss so that the sensing microring returns to the strict coupling mode again, and estimate the gas concentration by combining the absorption coefficient and the phase shift. Change the gas concentration and repeat the above steps A1-A9.

[0144] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0145] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A gas sensing system based on MZI-microring resonator enhancement, characterized in that: include: A laser (1), a beam splitter (2), a first coupling module (3), a second coupling module (4), an optical switch (5) and a coherent detection module (6); The light source emitted by the laser (1) passes through the beam splitter (2) to obtain three completely identical light beams, including: a reference light beam, a first signal light beam, and a second signal light beam; The first signal light beam and the second signal light beam respectively pass through the first coupling module (3) and the second coupling module (4), and then are selected by the channel of the optical switch (5) to perform interference measurement with the reference light beam through the coherent detection module (6).

2. The gas sensing system based on MZI-microring resonator enhancement according to claim 1 is characterized in that: The laser (1) is a laser with tunable output wavelength.

3. The gas sensing system based on MZI-microring resonator enhancement according to claim 1 is characterized in that: The first coupling module (3) comprises a first sensing microring and a first Mach-Zehnder interferometer MZI; the first sensing microring and the first Mach-Zehnder interferometer MZI are coupled; The first signal light beam is transmitted to the first Mach-Zehnder interferometer MZI through a straight waveguide, and then enters the first sensing microring through the first Mach-Zehnder interferometer MZI, and completes a sensing process in the first sensing microring. After the sensing process, the first signal light beam is transmitted to the first Mach-Zehnder interferometer MZI, and then transmitted to the optical switch (5) through the first Mach-Zehnder interferometer MZI; The second coupling module (4) comprises a second sensing microring and a second Mach-Zehnder interferometer MZI; the second sensing microring and the second Mach-Zehnder interferometer MZI are coupled; The second signal light beam is transmitted to the second Mach-Zehnder interferometer MZI through a straight waveguide, and then enters the second sensing microring through the second Mach-Zehnder interferometer MZI, and completes a sensing process in the second sensing microring. After completing the sensing process, the second signal light beam is transmitted to the second Mach-Zehnder interferometer MZI, and then transmitted to the optical switch (5) through the second Mach-Zehnder interferometer MZI.

4. The gas sensing system based on MZI-microring resonator enhancement according to claim 3 is characterized in that: The first signal light beam is transmitted to the first Mach-Zehnder interferometer MZI through a straight waveguide, wherein a portion of the light beam enters the first sensing microring through the evanescent field through the first 3dB coupler (7) to interact with the gas, and another portion of the light beam continues to be transmitted forward, and the two portions of the light beam interfere with each other in the second 3dB coupler (8), and the interfered light beam is transmitted to the optical switch (5); The second signal light beam is transmitted to the second Mach-Zehnder interferometer MZI through a straight waveguide, wherein a portion of the light beam enters the second sensing microring through the evanescent field through a third 3dB coupler (9) to interact with the gas, and another portion of the light beam continues to be transmitted forward. The two portions of the light beam interfere with each other at a fourth 3dB coupler (10), and the interfered light beam is transmitted to the optical switch (5).

5. The gas sensing system based on MZI-microring resonator enhancement according to claim 1, characterized in that: The radius of the first sensing microring / the second sensing microring is determined by the wavelength position of the absorption peak corresponding to the gas to be measured, including: Where R is the radius of the microring, λ is the wavelength of the absorption peak of the gas to be measured, m is a positive integer, and the resonance wavelength of the microring needs to be exactly equal to the absorption peak wavelength of the gas to be measured, n eff represents the effective refractive index inside the microring.

6. A gas sensing method based on MZI-microring resonant cavity enhancement, characterized in that: The gas sensing system based on MZI-microring resonant cavity enhancement according to any one of claims 1 to 5 performs the following steps: Step S1: coating the surfaces of the first sensing microring and the second sensing microring with target polymers for detecting the first target gas and the second target gas respectively; Step S2: adjusting the coupling coefficient between the first sensing micro-ring and the second sensing micro-ring so that the first sensing micro-ring and the second sensing micro-ring are in a strictly coupled state; Step S3: the light source generated by the laser (1) is divided into three identical light beams after passing through a beam splitter, which are marked as a first signal beam, a second signal beam and a reference beam respectively; Step S4: the first signal light beam / the second signal light beam enters the first sensing micro-ring resonant cavity / the second sensing micro-ring resonant cavity coupled to the first Mach-Zehnder interferometer MZI / the second Mach-Zehnder interferometer MZI through a straight waveguide, and interacts with the target gas. After the interaction, the light beam leaves the first sensing micro-ring resonant cavity / the second sensing micro-ring resonant cavity through a straight waveguide, and after being selected by an optical switch (5), interferes with the reference light beam in a mixer in a coherent detection module (6), and is finally received by a detector to obtain a detector photocurrent. Step S5: Under the condition that the photocurrent output by the detector is 0, the output band of the light source and the phase modulator parameters φ1 and φ2 on the two arms of the corresponding Mach-Zehnder interferometer MZI are adjusted to make the corresponding sensing microring return to the strict coupling mode again; Step S6: When the photocurrent data output by the detector is 0, calculate the gas absorption coefficient α A ; Step S7: Adjust the coupling coefficient to be equal to the current loss so that the sensing microring returns to the strict coupling mode again, and estimate the gas concentration by combining the absorption coefficient and the phase shift.

7. The gas sensing method based on MZI-microring resonant cavity enhancement according to claim 6, characterized in that: The step S2 comprises: Where r is the equivalent coupling coefficient between microring-MZI and waveguide, φ1 and φ2 are the phase shifts of the phase modulators on the MZI arms, respectively.

8. The gas sensing method based on MZI-microring resonant cavity enhancement according to claim 6, characterized in that: The detector photocurrent includes: Where I2 represents the detector photocurrent after bandpass filtering; S represents the photodetector gain because the detection process is a zero-difference detection process; A s Indicates the signal light amplitude, A r represents the reference light amplitude, ω s represents the signal light frequency, ω r represents the reference light frequency, Indicates the signal light phase, Indicates the reference light phase.

9. The gas sensing method based on MZI-microring resonant cavity enhancement according to claim 6, characterized in that: The step S5 comprises: Where Δλ represents the change in the microring resonance wavelength; Δn eff represents the change in the effective refractive index of the microring; m represents a positive integer; R represents the radius of the microring; Δφ represents the phase shift caused by gas absorption; L represents the circumference of the microring; Γ φ Represents the scale factor.

10. The gas sensing method based on MZI-microring resonant cavity enhancement according to claim 6, characterized in that: The step S6 comprises: r＝a a T =a I +C α a A Among them, α T is the total absorption factor, α I It represents the intrinsic loss of the system, α A is the gas absorption coefficient, Γ α is the scale factor; The gas concentrations include: Estimate gas concentrations based on absorption coefficients, including: Where C is the gas concentration, K is the molar absorption coefficient, and L is the circumference of the microring α I Characterizes the intrinsic loss of the system, Γ α is the scale factor, φ1 and φ2 are the phase shifts of the phase modulators on the MZI arms, respectively.

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