Researches On Applications Of Microwave Photonic Technologies In Fiber-optic Sensing

Microwave photonics is a novel interdisciplinary research field,which mainly studies the methods of microwave signal generation and processing in optical domain.As it brings together the worlds of radio frequency engineering and optoelectronics,microwave photonic technology enjoys plenty of advantages including high bandwidth,low loss,as well as immunity to the electromagnetic interference,and is widely used in modern research and business sectors,such as sensing networks,wireless access networks,satellite communications,and so on.Especially,fiber-optic sensing systems using microwave photonic technologies have attracted lots of research attention in the recent years.In this thesis,we have carried out both of the theoretical studies and experimental demonstration of the applications of microwave photonic filters and optoelectronic oscillators in fiber-optic sensing interrogation systems.Firstly,we give a brief introduction about the basic concepts and the history of microwave photonics,and listed the major research applications which show obvious advantages contrasted to traditional microwave technology,as well as the introduction for fiber-optic sensing technology.Then,we have demonstrated the theory of two microwave photonic technologies used in our thesis,which are microwave photonic filters(MPFs)and optoelectronic oscillators(OEOs),respectively.After that,the research of fiber-optic sensing interrogations using MPFs,both periodic ones and non-periodic ones has been carried out.Firstly,we have described the basic structure and theoretical analysis of MPFs based on a fiber-ring,and we have proposed and experimentally demonstrated a fiber-optic sensing interrogation system for temperature and transverse loading using a fiber-ring MPF,which shows great linearity.In order to improve the sensing performance,the single-passband MPF based on a fiber Mach-Zehnder interferometer(FMZI)and dispersive medium has been employed for fiber-optic sensing interrogation.On account of the advantage of this single-passband frequency response,a fiber-optic sensing interrogation system for simultaneous measurement of temperature and transversal loading has been proposed and experimentally demonstrated,which is simple in construction,enjoys good sensitivity and linearity,and thus shows great potential in simultaneous measurement for multi-parameters.What's more,we have introduced a fiber mirror incorporated after the FMZI to realize a switchable dual-passband microwave photonic filter,which has also been used to measure temperature and transverse loading with higher sensitivity in the experiment.In addition,a fiber-optic temperature sensor interrogation technique based on an OEO,which converts the variation of temperature into frequency shift of the harmonics,has been proposed and experimentally demonstrated.This system is simple in structure,shows good sensing linearity,and tailorable sensing responsivity,thus shows a good application potential in remote fiber-optical temperature sensing and monitoring.Finally,we summarize our work in the thesis,and make several improvements for the future work.