| The rapid development of the Internet has accelerated the industrial transformation of the entire society.With the wide application of 5G communication,big data and artificial intelligence technology,the realization of the interconnection of everything has become the primary goal of the development of the information age.Sensors are an indispensable part of the Internet of Things,and optical sensors have attracted much attention for their excellent performance.With the increasing demand for intelligent detection accuracy,the integration of optical sensing technology and traditional industries has become an important direction for future development.Obtaining accurate wavelength drift and improving the demodulation sensitivity of the sensing system have become the focus of research to ensure the reliability of on-line monitoring of physical quantities.Based on the principle of edge filtering in wavelength demodulation of grating sensors,this thesis researches the transmission characteristics of all-fiber composite devices,focusing on the analysis of the performance of all-fiber dual-channel edge demodulation based on micro-resonant rings.At the same time,the temperature monitoring software of grating sensor is developed based on Lab VIEW.Based on the optical propagation theory of human tissue,a dual-wavelength multi-detector omni-directional blood oxygen saturation detection scheme is proposed.On this basis,it is proposed to combine the grating temperature sensing with the optical detection of blood oxygen saturation to realize the dual monitoring of temperature and blood oxygen,which provides an effective basis for the blood flow status detection of skin flaps.The main research contents and innovations of this thesis are as follows:(1)The characteristic analysis of the all-fiber combined device applied to edge linear demodulation is proposed.The working principles of the all-fiber single-stage M-Z device structure,the all-fiber multi-stage M-Z device structure and the all-fiber micro-ring resonator are studied.The simulation results show that when the two couplers are 3dB couplers,the single-stage Mach-Zehnder interference structure obtains the maximum linear range of the output spectrum;When the second coupling angle is 0.25π,and the sum of the first coupling angle and the third coupling angle is 0.25π,the multi-stage Mach-Zehnder interference structure has the best demodulation characteristics;The transmission characteristics of the all-fiber micro-ring resonator are related to the normalized transmission coefficient and the optical fiber loss coefficient,and the linear range of the output spectrum increases with the increase of these two parameters.(2)An all-fiber dual-path edge demodulation scheme of micro-resonant ring used in grating wavelength demodulation system is proposed.The transfer matrix method is used to derive the analytical expressions of the upper and lower output spectral responses,and the transfer function and output results are simulated and analyzed.The simulation results show that the prerequisite for dual-channel wavelength demodulation is the ratio of the cumulative phase of the micro-ring to the phase delay between the interferometer arm is 1/2.When the micro-ring is lossless,the demodulation accuracy increases as the coupling coefficient K of the micro-ring decreases,but the wavelength range becomes narrower.The output characteristic satisfies the mathematical expression Tout1(k1,k2)=Tout1(π/2-k1,π/2-k2).In addition,different transmission loss factor α have different effects on the transmission spectrum.By adjusting various parameters,the difference between the wavelength demodulation range and accuracy of the two ports was discussed in detail.Finally,based on Lab VIEW,the upper computer software of temperature monitoring of grating sensor is developed,which realizes the functions of temperature alarm,real-time temperature monitoring,spectrogram,parameter setting and historical data reproduction.(3)An omni-directional blood oxygen saturation sensing scheme based on dual-wavelength multi-detectors is proposed.Firstly,the optical model of biological tissue was established,and the local migration path of photons was obtained by Monte Carlo simulation.Therefore,the dual wavelength and multi-directional structure of blood oxygen saturation was proposed,and the theoretical derivation was carried out.Then the curves of molar absorption coefficient in human tissues were analyzed,and the best light sources were selected at 650nm and 850nm.On this basis,the grating sensor was combined with the blood oxygen detection to realize the dual monitoring of temperature and blood oxygen,and an optical sensing system suitable for blood flow detection of skin flaps was designed.Finally,a photoelectric test system was used to detect blood oxygen and temperature values of 20 volunteers.The experimental results show that the measured value of the oxygen and the reference value relative error is-3.03%～2.11%,the temperature of the measured values and the reference temperature is-0.3℃～0.4℃.The two data are relatively close,indicating that the blood flow photoelectric test system proposed in this program can basically achieve the expected function,which further verifies the feasibility and accuracy of the program. |
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