Multi-gas sensing detection method and device based on microwave modulation FLRD

Abstract

The invention provides a multi-gas sensing detection method and device based on microwave modulation FLRD, the multi-gas sensing detection device is built based on microwave modulation FLRD, and the method comprises the following steps: determining characteristic frequency and shortest switching time; establishing a multi-wavelength absorption physical model; a gas concentration vector is solved by adopting a regularization inversion algorithm, and regularization parameters are optimized through cross validation; and temperature compensation is realized through an adaptive Kalman filtering algorithm. Compared with a traditional time domain pulse measurement mode, the method can accurately obtain the intra-cavity ring-down time without a high-speed pulse light source and an oscilloscope. According to the method, a network vector analyzer is used for extracting a system transfer function, high-sensitivity and low-noise gas absorption measurement is realized, and the system cost and complexity are remarkably reduced. Parallel recognition of multiple gas components can be realized through frequency domain analysis and a regularization inversion algorithm; and the Kalman filtering algorithm with temperature compensation is combined, so that the measurement stability and the environmental adaptability are effectively improved.

Description

Technical Field

[0001] This invention relates to the fields of electrical engineering and optical engineering, and in particular to a multi-gas sensing detection method and device based on microwave modulated FLRD. Background Technology

[0002] In traditional fiber optic ring-down time-domain (FLRD) systems, a series of optical pulses are typically used as the light source, and a photodetector (PD) directly converts the optical signal output from the fiber loop into an electrical signal. The output electrical signal is then sampled using an oscilloscope to obtain the ring-down curve. However, FLRD techniques typically suffer from high inherent losses, especially with long fiber loops. Furthermore, the low duty cycle of the light source reduces the number of pulses output, significantly limiting the system's sensitivity and response speed. To address these issues, researchers have proposed a phase-shift interferometry-based fiber optic ring-down time-domain (PS-FLRD) sensing technique. This technique injects a sinusoidally modulated continuous-wave (CW) laser beam into the fiber loop and measures the output signal by detecting the phase shift relative to the modulated signal. The system's ring-down time is determined by the phase shift value. By optimizing the duty cycle, measurement efficiency can be significantly improved. However, one of the key challenges of PS-FLRD technology is the unavoidable phase angle shift caused by time delays in the electronics and optical path, which requires additional calibration procedures before each measurement.

[0003] To achieve simultaneous detection of multiple parameters, FLRD technology relies on channel multiplexing techniques such as wavelength division multiplexing (WDM), time division multiplexing (TDM), or space division multiplexing (SDM). However, existing solutions have significant limitations: wavelength resource competition. WDM requires the absorption peaks or Bragg wavelengths corresponding to different parameters to be distributed in non-overlapping bands, but the available spectral window is limited in practical applications, resulting in a limited number of multiplexable parameters; decreased temporal resolution. TDM requires switching different sensing channels in a time-division manner, leading to a reduction in the sampling rate of a single parameter, making it difficult to meet the needs of dynamic process monitoring; uneven light intensity distribution. SDM requires distributing optical power to multiple fiber rings, and the cumulative loss of each sub-ring significantly reduces the signal-to-noise ratio, especially in long-distance distributed detection. In addition, while building a multi-ring cavity network can indeed achieve simultaneous detection of multiple physical quantities, as the number of sensors increases, the light source power attenuates severely, the output light intensity decreases, and this affects the strength of the fading signal, which is not conducive to high-sensitivity demodulation of fiber optic sensors. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the prior art by providing a multi-gas sensing and detection device based on microwave modulated FLRD, which avoids the low efficiency and high loss problems of the traditional time-domain pulse fitting method and significantly improves the system response speed and measurement accuracy.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a multi-gas sensing detection method based on microwave modulated FLRD, comprising the following steps: S1. A multi-gas sensing and detection device is built based on microwave modulation FLRD, including determining the characteristic frequency and the shortest switching time; S2. Establish a multi-wavelength absorption physical model; S3. Solve for the gas concentration vector using a regularized inversion algorithm. And optimize the regularization parameters through cross-validation. ; S4. Temperature compensation is achieved through an adaptive Kalman filter algorithm.

[0006] Furthermore, S1 specifically refers to: To achieve simultaneous detection of multiple gases, the multi-gas sensing device switches the optical signal to different fiber optic ring cavities via an optical switch. Multiple signals are separated by setting up multiple fiber optic rings of different lengths. The characteristic spectral range (FSR) of each fiber optic ring cavity is uniquely determined by its cavity length. Specifically: (101); in, The speed of light; The effective refractive index of the optical fiber; For the first The length of each fiber optic loop; By setting the switching time of the optical switch, parallel detection of multiple gases and crosstalk-free demodulation of signals can be achieved. The optimal switching period of the optical switch is: (201); in, Group velocity; This refers to the detector response time; This refers to the circuit settling time. The continuous light output from the laser is intensity modulated by an electro-optic modulator, and the modulated optical signal is represented in the time domain as follows: (301); in, The initial light intensity; For the period of decline; It is a time variable; It is the microwave modulation frequency; This is the initial phase; The network vector analyzer acquires the domain response, and the time-domain signal is Fourier transformed as follows: (401); That is, the transfer function of the multi-gas sensing device is: (501); in, This refers to the frequency response characteristics of the modulator. It is an imaginary unit and has no practical meaning; By extracting the peak-to-valley ratio at a given frequency from the amplitude spectrum, the decay time is obtained as follows: (601); in, The peak-to-valley ratio; Loss and decay time The expression is: (701); in, The initial wave decay time; This is due to gas absorption loss; This is the inherent loss of the system.

[0007] Furthermore, S2 specifically refers to: The multi-gas sensing and detection device includes multiple independent detection channels, each of which is realized through an optical fiber ring cavity; Let the first The concentration of the gas is ,in, The overall gas absorption coefficient is composed of the superposition of the corresponding absorption bands of each component. The multi-wavelength absorption physical model is as follows: (801); Among them, absorption cross section Let be a function of temperature, representing the th M The temperature-dependent absorption cross section of a gas; the multi-wavelength absorption physical model can describe the cross-absorption behavior of multiple gaseous bodies under multi-wavelength conditions; For the first M The wavelength of the gas; This refers to the actual ambient temperature. The change in oscillation time caused by gas absorption satisfies: (901); in, For the first The length of each fiber optic loop; For the first The measurement noise of each fiber optic loop, among which... ; Formula (901) can be expressed in matrix form as follows: (1001); in, It means a set of concentrations of the gas being measured; By combining all wavelength channels into a vector form, the resulting multi-gas absorption model can be expressed as: (1101); The observed change in wave decay time; This is the temperature-dependent sensitivity matrix. To measure the noise vector.

[0008] Furthermore, S3 specifically refers to: Solving the multi-gas absorption matrix equation, the gas concentration is: (1201); in, It is the set of all the concentrations of the measured gases; It is a set of optimized multi-gas concentration compositions; The observation vector is composed of the measured changes in oscillation time. This is the first regularization parameter, used to suppress the ill-conditioned nature of the inverted system and improve the numerical stability of the solution; This is the second regularization parameter, used to control sparsity, and is suitable for trace gas detection; It is a diagonal weight matrix used to weaken the coupling effect of known interfering gas components on concentration inversion; Further optimize the parameters to make The optimal parameter combination is obtained by calculating the prediction error: (1301); in, This represents the set of regularization parameters that minimizes the average verification error. For the first Measured values ​​of the gas; The first of the sensitivity matrix OK; To remove the first Regularized dissolution of the gas.

[0009] Furthermore, S4 specifically includes: To address the ring-down time measurement error caused by temperature drift, the multi-gas sensing device employs an adaptive Kalman filter algorithm for temperature compensation. First, a state vector is defined. Includes decay time, gas concentration, and temperature: (1401); in: For the first The state vector at any given time; For the first The decay of time; For the first The concentration of the gas; For the first Constantly senses the ambient temperature of the area; The multi-gas sensing device establishes a state equation that includes temperature compensation as follows: (1501); This is the state transition matrix; For the first The process noise vector at each time step; in, (1601); Let be the sensitivity coefficient of the ringing-out time to temperature, expressed as: (1701); The coefficient of thermal expansion of optical fiber. The temperature coefficient of refractive index of the optical fiber material. and For system System structure calibration coefficients, respectively reflecting the contribution weights of cavity length variation and refractive index variation to the total optical path delay; The observation equation is: (1801); in, , is the observation matrix; For observing noise; online estimation of noise covariance: (1901); Forgetting factor, =0.05; The Kalman gain calculation expression is: (2001); in, The state estimation error covariance matrix; Ultimately, the state update is achieved: (2101).

[0010] Furthermore, a multi-gas sensing and detection device based on microwave-modulated FLRD, implemented using a multi-gas sensing and detection method based on microwave-modulated FLRD, further includes: A laser is sequentially connected to an electro-optic modulator, an isolator, and an erbium-doped fiber amplifier. The side of the erbium-doped fiber amplifier away from the isolator is connected to a multiplexer. The end of the multiplexer away from the erbium-doped fiber amplifier is connected in parallel to several ring cavities. The output ends of the ring cavities are all connected to a combiner. The end of the combiner away from the ring cavities is connected to a photodetector. The end of the photodetector away from the combiner is connected to a network vector analyzer. The end of the network vector analyzer away from the photodetector is connected to the electro-optic modulator.

[0011] Furthermore, a first coupler, an optical fiber ring, a gas sensor, and a second coupler are connected in series on the annular cavity; the 10% end of the first coupler is connected to the multiplexer, and the 90% end of the second coupler is connected to the combiner.

[0012] The beneficial effects of this invention are as follows: This invention employs a fiber optic ring cavity decay detection method combining microwave modulation and frequency domain analysis. Compared to traditional time-domain pulse measurement methods, it can accurately obtain the cavity decay time without the need for a high-speed pulse light source and oscilloscope. This method utilizes a network vector analyzer to extract the system transfer function, achieving highly sensitive and low-noise gas absorption measurement, significantly reducing system cost and complexity. Through frequency domain analysis and regularized inversion algorithms, parallel identification of multiple gas components can be achieved; combined with a temperature-compensated Kalman filter algorithm, the stability and environmental adaptability of the measurement are effectively improved, thus outperforming traditional methods in terms of measurement accuracy, real-time performance, and scalability.

[0013] Compared to PS-FLRD, the main advantage of this method is that it eliminates the need for phase angle offset calibration, greatly simplifying the installation and measurement process. To achieve online monitoring of multiple physical quantities, a time-division / space-division hybrid multiplexing technique is employed for multi-parameter sensing. The time-division / space-division hybrid multiplexing sensor network can use optical switches to switch between different monitoring points; each point only needs to demodulate the signals from different gas sensors. This sensor network has a clear optical topology, and each point contains a small number of sensors, effectively avoiding the problem of light source power attenuation. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a multi-gas sensing and detection device based on microwave modulated FLRD. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0016] A multi-gas sensing detection method based on microwave modulated FLRD includes the following steps: S1. A multi-gas sensing and detection device is built based on microwave modulation FLRD, including determining the characteristic frequency and the shortest switching time; S2. Establish a multi-wavelength absorption physical model; S3. Solve for the gas concentration vector using a regularized inversion algorithm. C And optimize the regularization parameters through cross-validation. ; S4. Temperature compensation is achieved through an adaptive Kalman filter algorithm.

[0017] Specifically, S1 is: To achieve simultaneous detection of multiple gases, the multi-gas sensing device switches the optical signal to different fiber optic ring cavities via an optical switch. Multiple signals are separated by setting up multiple fiber optic rings of different lengths. The characteristic spectral range (FSR) of each fiber optic ring cavity is uniquely determined by its cavity length. Specifically: (101); in, The speed of light; The effective refractive index of the optical fiber; For the first The length of each fiber optic loop; By setting the switching time of the optical switch, parallel detection of multiple gases and crosstalk-free demodulation of signals can be achieved. The optimal switching period of the optical switch is: (201); in, Group velocity; This refers to the detector response time; This refers to the circuit settling time. After signal separation is achieved through frequency domain signal detection, the multi-gas sensing detection device can process multiple gas sensing data in parallel.

[0018] The continuous light output from the laser is intensity modulated by an electro-optic modulator. The modulation signal is provided by a network vector analyzer, and the modulated optical signal is represented in the time domain as follows: (301); in, The initial light intensity; For the period of decline; It is a time variable; It is the microwave modulation frequency; This is the initial phase; The network vector analyzer acquires the domain response, and the time-domain signal is Fourier transformed as follows: (401); That is, the transfer function of the multi-gas sensing device is: (501); in, This refers to the frequency response characteristics of the modulator. It is an imaginary unit and has no practical meaning; By extracting the peak-to-valley ratio at a given frequency from the amplitude spectrum, the decay time is obtained as follows: (601); in, The peak-to-valley ratio; Loss and decay time The expression is: (701); in, The initial wave decay time; This is due to gas absorption loss; This is the inherent loss of the system.

[0019] Specifically, S2 is: The multi-gas sensing and detection device includes multiple independent detection channels, each of which is realized through an optical fiber ring cavity; Let the first The concentration of the gas is ,in, The overall gas absorption coefficient is composed of the superposition of the corresponding absorption bands of each component. The multi-wavelength absorption physical model is as follows: (801); Among them, absorption cross section Let be a function of temperature, representing the th M The temperature-dependent absorption cross section of a gas; the multi-wavelength absorption physical model can describe the cross-absorption behavior of multiple gaseous bodies under multi-wavelength conditions; For the first M The wavelength of the gas; This refers to the actual ambient temperature. The change in oscillation time caused by gas absorption satisfies: (901); in, For the first The length of each fiber optic loop; For the first The measurement noise of each fiber optic loop, among which... ; Formula (901) can be expressed in matrix form as follows: (1001); in, It means a set of concentrations of the gas being measured; By combining all wavelength channels into a vector form, the resulting multi-gas absorption model can be expressed as: (1101); The observed change in wave decay time; This is the temperature-dependent sensitivity matrix. This is for measuring the noise vector. The sensitivity matrix changes dynamically with temperature.

[0020] Specifically, S3 is: Solving the multi-gas absorption matrix equation, the gas concentration is: (1201); in, It is the set of all the concentrations of the measured gases; It is a set of optimized multi-gas concentration compositions; The observation vector is composed of the measured changes in oscillation time. This is the first regularization parameter, used to suppress the ill-conditioned nature of the inverted system and improve the numerical stability of the solution; This is the second regularization parameter, used to control sparsity, and is suitable for trace gas detection; It is a diagonal weight matrix used to weaken the coupling effect of known interfering gas components on concentration inversion; Will The measurement data from each wavelength channel is divided into a training set and a validation set. At any given time, one channel's data is retained as the validation sample, and the rest... Each wavelength channel is used to build the training model; for each candidate optimal regularization parameter The system calculates the regularization solution on the training set and evaluates the prediction error on the validation samples; this process is repeated. This process ensures that every wavelength channel participates in the verification, and finally selects the one that minimizes the average verification error. The value is used as the optimal parameter, and the expression is: (1301); in, This represents the set of regularization parameters that minimizes the average verification error. For the first Measured values ​​of the gas; The first of the sensitivity matrix OK; To remove the first Regularized dissolution of the gas.

[0021] Specifically, S4 is: To address the ring-down time measurement error caused by temperature drift, the multi-gas sensing device employs an adaptive Kalman filter algorithm for temperature compensation. First, a state vector is defined. Includes decay time, gas concentration, and temperature: (1401); in: For the first The state vector at any given time; For the first The decay of time; For the first The concentration of the gas; For the first Constantly senses the ambient temperature of the area; The multi-gas sensing device establishes a state equation that includes temperature compensation as follows: (1501); This is the state transition matrix; For the first The process noise vector at each time step; in, (1601); Let be the sensitivity coefficient of the ring-down time to temperature, expressed as: (1701); The coefficient of thermal expansion of optical fiber. The temperature coefficient of refractive index of the optical fiber material. and For system System structure calibration coefficients, respectively reflecting the contribution weights of cavity length variation and refractive index variation to the total optical path delay; The observation equation is: (1801); in, , is the observation matrix; For observing noise; online estimation of noise covariance: (1901); Forgetting factor, =0.05; The Kalman gain calculation expression is: (2001); in, The state estimation error covariance matrix; Ultimately, the state update is achieved: (2101).

[0022] A multi-gas sensing and detection device based on microwave-modulated FLRD, implemented using a multi-gas sensing and detection method based on microwave-modulated FLRD, further includes: A laser 1 is sequentially connected to an electro-optic modulator 2, an isolator 3, and an erbium-doped fiber amplifier 4. The side of the erbium-doped fiber amplifier 4 away from the isolator 3 is connected to a multiplexer optical switch 5. Several ring cavities are connected in parallel to the end of the multiplexer optical switch 5 away from the erbium-doped fiber amplifier 4. The output ends of the multiple ring cavities are all connected to a combiner 9. The end of the combiner 9 away from the ring cavities is connected to a photodetector 10. The end of the photodetector 10 away from the combiner 9 is connected to a network vector analyzer 11. The end of the network vector analyzer 11 away from the photodetector 10 is connected to the electro-optic modulator 2.

[0023] The annular cavity is connected in series with a first coupler 601, an optical fiber ring 8, a gas sensor 7, and a second coupler 602; the 10% end of the first coupler 601 is connected to the multiplexer 5, and the 90% end of the second coupler 602 is connected to the combiner 9.

[0024] In one specific embodiment, laser 1 serves as the light source of a multi-gas sensing and detection device, emitting optical signals. The laser beam is modulated by an electro-optic modulator 2 at microwave frequency. The modulated signal is amplified by an erbium-doped fiber amplifier 4. The series of modulated optical pulse signals pass through a multiplexer 5 and enter the first ring cavity 1201 from the 10% end of the first coupler 601. After passing through the gas detection unit, the optical signal entering the first ring cavity 1201 is output through the 90% beam splitter at the other end of the second coupler 602. Every 10ms (which only needs to be longer than the complete transmission time of the light wave in a single fiber ring), the pulse signal is switched and transmitted sequentially into each ring cavity. Then, it is input into the beam combiner 9, and the photodetector 10 converts the optical signal into an electrical signal. The time-domain signal is then acquired by a network vector analyzer 11.

[0025] In the parallel structure of the multi-gas sensing and detection device, the ring cavities are relatively independent. At any given time, the input light to each ring cavity is input separately, and the signal output is unaffected by other ring cavities. The sensing measurements of each ring cavity do not exhibit crosstalk in the frequency domain. Furthermore, due to the switching time of the optical switch, a detection cycle of 10ms is defined for one ring cavity, and a detection cycle of 30ms is defined for the sensing network. Finally, the output decaying signals are clearly separated in the frequency domain according to the ring cavity sequence number.

[0026] Furthermore, the different fiber optic loop lengths connected to each cavity result in different output signal frequencies, necessitating frequency encoding for each cavity to facilitate subsequent signal processing. 10% of the output from the second coupler of each cavity is connected to the combiner 9, and after detection by the high-sensitivity photodetector 10, the spectrum is output in the network vector analyzer 11. Compared to traditional time-domain measurement methods, this avoids the problems of finding pulse points and cumbersome experimental procedures, thus improving the system's measurement accuracy.

[0027] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be defined by the appended claims.

Claims

1. A multi-gas sensing and detection method based on microwave modulated FLRD, characterized in that, Includes the following steps: S1. A multi-gas sensing and detection device is built based on microwave modulation FLRD, including determining the characteristic frequency and the shortest switching time; S2. Establish a multi-wavelength absorption physical model; S3. Solve for the gas concentration vector using a regularized inversion algorithm. And optimize the regularization parameters through cross-validation. ; S4. Temperature compensation is achieved through an adaptive Kalman filter algorithm.

2. The multi-gas sensing detection method based on microwave modulated FLRD according to claim 1, characterized in that, Specifically, S1 is: To achieve simultaneous detection of multiple gases, the multi-gas sensing device switches the optical signal to different fiber optic ring cavities via an optical switch. Multiple signals are separated by setting up multiple fiber optic rings of different lengths. The characteristic spectral range (FSR) of each fiber optic ring cavity is uniquely determined by its cavity length. Specifically: （101）； in, The speed of light; The effective refractive index of the optical fiber; For the first The length of each fiber optic loop; By setting the switching time of the optical switch, parallel detection of multiple gases and crosstalk-free demodulation of signals can be achieved. The optimal switching period of the optical switch is: （201）； in, Group velocity; This refers to the detector response time; This refers to the circuit settling time. The continuous light output from the laser is intensity modulated by an electro-optic modulator, and the modulated optical signal is represented in the time domain as follows: （301）； in, The initial light intensity; For the period of decline; It is a time variable; It is the microwave modulation frequency; This is the initial phase; The network vector analyzer acquires the domain response, and the time-domain signal is Fourier transformed as follows: （401）； That is, the transfer function of the multi-gas sensing device is: （501）； in, This refers to the frequency response characteristics of the modulator. It is an imaginary unit and has no practical meaning; By extracting the peak-to-valley ratio at a given frequency from the amplitude spectrum, the decay time is obtained as follows: （601）； in, The peak-to-valley ratio; Loss and decay time The expression is: （701）； in, The initial wave decay time; This is due to gas absorption loss; This is the inherent loss of the system.

3. The multi-gas sensing detection method based on microwave modulated FLRD according to claim 2, characterized in that, Specifically, S2 is: The multi-gas sensing and detection device includes multiple independent detection channels, each of which is realized through an optical fiber ring cavity; Let the first The concentration of the gas is ,in, The overall gas absorption coefficient is composed of the superposition of the corresponding absorption bands of each component. The multi-wavelength absorption physical model is as follows: （801）； Among them, absorption cross section Let be a function of temperature, representing the th M The temperature-dependent absorption cross section of a gas; the multi-wavelength absorption physical model can describe the cross-absorption behavior of multiple gaseous bodies under multi-wavelength conditions; For the first M The wavelength of the gas; This refers to the actual ambient temperature. The change in oscillation time caused by gas absorption satisfies: （901）； in, For the first The length of each fiber optic loop; For the first The measurement noise of each fiber optic loop, among which... ; Formula (901) can be expressed in matrix form as follows: （1001）； in, It means a set of concentrations of the gas being measured; By combining all wavelength channels into a vector form, the resulting multi-gas absorption model can be expressed as: （1101）； The observed change in wave decay time; This is the temperature-dependent sensitivity matrix. To measure the noise vector.

4. The multi-gas sensing detection method based on microwave modulated FLRD according to claim 3, characterized in that, Specifically, S3 is: Solving the multi-gas absorption matrix equation, the gas concentration is: （1201）； in, It is the set of all the concentrations of the measured gases; It is a set of optimized multi-gas concentration compositions; The observation vector is composed of the measured changes in oscillation time. This is the first regularization parameter, used to suppress the ill-conditioned nature of the inverted system and improve the numerical stability of the solution; This is the second regularization parameter, used to control sparsity, and is suitable for trace gas detection; It is a diagonal weight matrix used to weaken the coupling effect of known interfering gas components on concentration inversion; Further optimize the parameters to make The optimal parameter combination is obtained by calculating the prediction error: （1301）； in, This represents the set of regularization parameters that minimizes the average verification error. For the first Measured values ​​of the gas; The first of the sensitivity matrix OK; To remove the first Regularized dissolution of the gas.

5. A multi-gas sensing detection method based on microwave modulated FLRD according to claim 4, characterized in that, Specifically, S4 is: To address the ring-down time measurement error caused by temperature drift, the multi-gas sensing device employs an adaptive Kalman filter algorithm for temperature compensation. First, a state vector is defined. Includes decay time, gas concentration, and temperature: （1401）； in: For the first The state vector at any given time; For the first The decay of time; For the first The concentration of the gas; For the first Constantly senses the ambient temperature of the area; The multi-gas sensing device establishes a state equation that includes temperature compensation as follows: （1501）； This is the state transition matrix; For the first The process noise vector at each time step; in, (1601); Let be the sensitivity coefficient of the ringing-out time to temperature, expressed as: （1701）； The coefficient of thermal expansion of optical fiber. The temperature coefficient of refractive index of the optical fiber material. and For system System structure calibration coefficients, respectively reflecting the contribution weights of cavity length variation and refractive index variation to the total optical path delay; The observation equation is: （1801）； in, , is the observation matrix; For observing noise; online estimation of noise covariance: （1901）； Forgetting factor, =0.05; The Kalman gain calculation expression is: （2001）； in, The state estimation error covariance matrix; Ultimately, the state update is achieved: （2101）。 6. A multi-gas sensing and detection device based on microwave modulated FLRD, characterized in that: The method employs a multi-gas sensing detection method based on microwave modulated FLRD as described in any one of claims 1 to 5, and further includes: A laser (1) is connected in sequence to an electro-optic modulator (2), an isolator (3), and an erbium-doped fiber amplifier (4). The side of the erbium-doped fiber amplifier (4) that is separate from the isolator (3) is connected to a multiplexer (5). The end of the multiplexer (5) that is separate from the erbium-doped fiber amplifier (4) is connected in parallel to several ring cavities. The output ends of the multiple ring cavities are all connected to a combiner (9). The end of the combiner (9) that is separate from the ring cavity is connected to a photodetector (10). The end of the photodetector (10) that is separate from the combiner (9) is connected to a network vector analyzer (11). The end of the network vector analyzer (11) that is separate from the photodetector (10) is connected to the electro-optic modulator (2).

7. A multi-gas sensing and detection device based on microwave modulated FLRD according to claim 6, characterized in that: The annular cavity is connected in series with a first coupler (601), an optical fiber ring (8), a gas sensor (7), and a second coupler (602); the 10% end of the first coupler (601) is connected to the multiplexer (5), and the 90% end of the second coupler (602) is connected to the combiner (9).

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