Research On Micro Optical Fiber Interferometer And Distributed Optical Fiber Sensing Technology

Recently,the state has vigorously promoted the construction of information technology.Due to the rise of information industries represented by mobile Internet and 5G,the industry of Internet of Things has developed rapidly and attracted heavy investment.This market development trend also promotes the promotion and innovation of optical fiber applications.In addition to being a signal transmission medium,due to its corrosion resistance,electrical insulation,low cost and other characteristics,optical fiber has also been developed in many new applications,such as optical fiber devices,optical fiber sensing,etc.,which are widely used in signal transmission,medical treatment,military and other fields.In order to meet the development needs of optical fiber sensing and optical fiber devices,it is truely important to do deep research on some related problems.The micro-fiber Mach-Zehnder interferometer and Brillouin optical time domain reflectometry(BOTDR)based are studied in this paper.The main research achievements are as follows:1.A micro fiber Mach-Zehnder interferometer(MZI)based on ring-core fiber(RCF)is proposed.Analyzing its working principle through simulation and experimental measurement,it is found that compared with the traditional micro-interferometer that uses inter-mode interference,the indicators in the interference process,such as the light field distribution,extinction ratio and free spectral range can be controlled by changing the length of RCF and the thickness of the ring core.Meanwhile,to explorethe practical application of the MZI,the temperature and refractive index sensing performance of the interferometer was analyzed through experimental measurement.It was found that when the RCF whose length is 5000 ?m and the ratio of the inner and outer diameter of the ring core is about 0.61,the micro-fiber MZI base on RCF is less sensitive to some external environmental disturbances,and the interference spectrum extinction ratio can reach 15.0 dB,so it has the possibility of preparing high-stability devices.In future work,the structure can be developed and applied to more fields with more improvements.2.A STFT-Brillouin optical time-domain reflectometer(BOTDR)with acousto-optic modulator(AOM)modulation frequency method of system was proposed.Compared with the traditional frequency-sweepingBOTDR system modulated by the electro-optic modulator(EOM),the pulse signal modulated by the AOM has higher extinction ratio,and the modulator has stable performance,which can be used for long-term measurement.Meanwhile,STFT-BOTDR only needs to collect one set of data in the data acquisition process to obtain the Brillouin gain spectrum along the fiber.Compared with the sweep-frequency-BOTDR that needs to collect multiple sets of data,STFT-BOTDR can save measurement time,which is beneficial to gather the change information of the surrounding environment along the fiber in time.It can be seen from the measurement results that the STFT-BOTDR system can reach the requirements of real applications,which afford an experimental platform for further optimization of the BOTDR system in the future.3.A joint algorithm of smooth pseudo Wigner-Ville distribution(SPWVD)and four-parameter particle swarm optimization(four-parameter PSO)algorithm is proposed to improve spatial resolution and frequency resolution simultaneously and increase the frequency shift extraction accuracy of Brillouin scattering spectrum.Through theoretical analysis and experimental verification,it is known that the BOTDR system based on the joint algorithm of SPWVD and four-parameter PSO,compared with the traditional STFT-BOTDR system,can save measurement time,while reducing the number of measuring period to cumulative denoising and overcoming the contradiction between spatial resolution and frequencyresolution.Meanwhile,when using the four-parameter PSO algorithm,the Brillouin frequency shift can be extracted without setting the initial value,which can reduce the time for preparation in advance.Therefore,the BOTDR system based on the joint algorithm of SPWVD and fourparameter PSO can overcome the contradiction between time resolution and spatial resolution,save the time of collecting and processing data,and improve measurement accuracy.