Study On Terahertz Microstructured Polymer Fiber And Fiber Device

Terahertz(THz)radiation lies between microwaves and far-infrared in the electromagnetic spectrum,THz technology has important applications in the fields of spectroscopy,imaging,space science and information transmission.However,as most dielectric materials have high absorption loss in the THz frequency,the development of low-loss THz waveguides remained a great challenge.In addition,new requirements for miniaturization and integration are proposed for THz systems in in-depth development of THz technology,which requires more compact functional devices.Microtructured polymer fiber has the advantages of flexible structural designation and easy to fabrication,and the polymer is also the dielectric material with relatively lowest absorption loss in THz frequency.In this dissertation,for the problems above that exist in THz technology,we focus on the research mainly about hollow-core polymer fiber for low-loss single-mode THz transmission and THz polarization splitter based on microstructured polymer fiber.The main contents of this dissertation are as follows:We briefly introduce the generation and detection of terahertz radiation,the application and research field of terahertz technology and the development status of terahertz waveguide.Then we introduce the history and research progress of terahertz polymer fiber and related functional devices.After that,the four parts of my research are addressed.Firstly,a THz polarization splitter based on a dual-elliptical-core polymer fiber is proposed.High birefringence and low-loss single-mode transmission characteristics of single-elliptical-core subwavelength polymer fiber are analyzed.Then the single-core structure is expanded to dual-core structure,the splitting process of the two orthogonal polarization states is analyzed by beam propagation method based on mode coupling thoery.Finally,the splitting length,transmission loss,extinction ratio and operation bandwidth of the polarization splitter are theoretically analyzed and optimized.Secondly,for comparing the two types of polarization splitting mechanism based on total and partial coupling,two terahertz polarization splitters based on dual slotted core polymer fiber are proposed and numerically investigated.The transmission characteristics of single slotted-core polymer fiber is analyzed,and then the single-core structure is expanded to symmetric and asymmetric dual-core structure,whose polarization splitting mechanism are based on total and partial coupling,respectively.Comparisons of the two splitters with similar structural parameters are also carried out.which shows a comparably short splitting length of?1 cm and an ultra-low transmission loss of<0.4 dB with the asymmetric structure having a broader bandwidth and better extinction ratios.Thirdly,a hollow-core polymer fiber with Bragg-structured cladding is proposed.The transmission characteristics and its relationship with the structural parameters of this fiber are analyzed by the finite element method(FEM),and the transmission loss is also optimized by combining three-demensional printing fabrication technology.The guiding mechanism of this fiber is based on anti-resonant reflecting(ARR).most of the THz radiation can be tightly confined in the hollow-core of this fiber,in which the high absorption loss of polymer material is greatly compressed.Thus,the bandwidth low-loss terahertz transmission can be achieved.Finally,a tube lattice hollow-core polymer fiber is proposed.The guiding mode,dispersion and loss property of this fiber are analyzed by FEM method,most of the guided mode can be tightly confined in the hollow-core based on ARR mechanism.so low-loss terahertz transmission can be achieved.Then the tube lattice structure is designed based on the simulation,the refractive index mathching condition is satisfied between the high order core mode and cladding mode,and resonant coupling of two modes can effective suppress the guidance of high order core mode.As a consequence,it leads to effective single-mode low-loss terahertz transmission of this fiber.