Study On Fiber Optic Interferometer Based Microwave Photonic Filter And Its Applications

With the rapid development of wireless communication technology and information technology,an emerging technology called microwave photonic technology with the advantages of both optoelectronic technology and microwave technology has arisen,which introduces optical processing technology on the basis of microwave technology,and microwave signal can be generated,processed,controlled and distributed by using optical methods.It is widely used in military,communication network,sensor networks,satellites and so on,due to its excellent properties,such as large bandwidth,low loss,high transmission rate and immunity to electromagnetic interference.In the era of high-speed information,the traditional information technology can not meet the increasing demand for information transmission rate.Photonic generation and processing of microwave signal have attracted a lot of attention.In this paper,we study on microwave photonic filters(MPFs)based on various fiber interferometers and their applications in fiber-optic sensing.The characteristics of the MPFs and influencing factors have been studied both theoretically and experimentally.Firstly,in this paper,the basic concepts,development history and advantages of microwave photonics are summarized,and several research directions in this field are listed.Then,the working principle,classification,main performance parameters and research directions of MPFs are demonstrated.Also,the basic principle of fiber-optic interferometer using for spectrum slicer or time delay has been introduced,and the principle of fiber Mach-Zehnder interferometer(FMZI)and fiber Sagnac interferometer(SI)has been introduced,whose working principle is explained in this part.Next,the fundamental principles of the single-passband MPFs based on FMZI are analyzed theoretically in detail,and the effect of several main parameters on the passband response is analyzed through simulation,as well as demonstrated in the experiment.A dual-passband MPF based on a modified FMZI has been proposed,whose tunable and switchable characteristics of the passbands have been theoretically and experimentally analyzed.In addition,a single-passband MPF based on polarization maintaining fiber Sagnac interferometer(PMF-SI)has been presented.The relationship between the parameters of PMF and the frequency response of the filter has been also analyzed in detail in both theoretical and experimental aspects.Subsequently,the applications of two kinds of non-periodic MPFs based on fiber-optic interferometers in fiber-optic sensing interrogation are demonstrated.1)An MPF based on modified FMZI used for simultaneously measuring both the temperature and transversal loading has been studied.The spectrum changes in the optical domain caused by the variation of temperature or transversal loading are respectively converted into the changes of the passband response in the electrical domain,which shows a good linearity.2)A temperature sensing system based on PMF-SI has been presented,whose feasibility has been verified experimentally.It exhibits many advantages in the measuring range,instrument limitation and sensitivity.Then,an incoherent periodic MPF based on MZI structure and other two variant structures are studied.And the influence of the length of delay fiber and the polarization states on the frequency response is analyzed theoretically and experimentally.Finally,the studies have been summarized and sorted out,and shortcomings have been analyzed as well as solutions.