Design And Transmission Characteristic Investigations Of Terahertz Hollow-Core Waveguide Based On Antiresonace Principle

Terahertz has many special properties due to its special location in the electromagnetic spectrum,and it has a wide range of applications in biomedicine,nondestructive testing,classified communications,and national defense security.So far,many terahertz systems are based on the condition that terahertz waves are transmitted in free space,which are bulky,not easily integrated and vulnerable to external influences,which is a major reason limiting the development of terahertz technology.Therefore,the development of low-loss broadband terahertz waveguides can effectively promote the integration of terahertz systems and thus promote the application of terahertz waves.This paper first introduces the properties of terahertz waves,the applications of terahertz technology,and the current status of research on terahertz waveguides.Among them,the development process of polymer terahertz waveguide is introduced in detail,and it is analyzed that the prerequisite for the current application of terahertz technology needs to solve the problem of low-loss terahertz waveguide.Therefore,this paper addresses the research on low-loss terahertz waveguides,detailing the following three aspects of work.1.A low-loss terahertz waveguide based on an anti-resonant structure is designed.The field intensity distribution of the fundamental mode and the effective mode refractive index are obtained using COMSOL finite element simulation software.The simulation results show that the fiber can be highly birefringent by making a difference between the longitudinal and horizontal half-tube thicknesses;under the asymmetric structure,the fiber has high polarization-related loss at different horizontal half-tube thicknesses,and can achieve single-polarization transmission in a certain frequency range;the designed hollow-core anti-resonant fiber can be birefringent over a wide frequency range of 0.25 THz,with birefringence greater than 1.5×10^-4,transmission loss is less than 10d B/m.2.A hollow-core terahertz fiber with Bragg structure as the basic unit of the anti-resonant fiber cladding is designed.Numerical simulations show that the four-tube hollow-core terahertz fiber composed of Bragg structure as the anti-resonant unit has both anti-resonant transmission and Bragg bandgap light conduction,which breaks the bound loss limit of the anti-resonant fiber,compared with the hollow-core anti-resonant fiber composed of a single dielectric layer,which can reduce the Compared with the hollow core anti-resonant fiber composed of single dielectric layer,the binding loss of the anti-resonant fiber can be reduced by 2～3 orders of magnitude.Finally,the analysis of fiber bending loss shows that using Bragg structure as the basic unit of the cladding of the anti-resonant fiber can reduce the bending loss of the fiber by more than one order of magnitude;secondly,the reasonable selection of the outer ring diameter of the fiber can effectively suppress the coupling between the core mode and the cladding mode and reduce the coupling loss.3.The transmission characteristics of the Bragg anti-resonant terahertz fiber with hexagonal mode field distribution are investigated,which can effectively reduce the coupling loss of the source compared with the square mode field of the quadrangular structure.Numerical simulations show that the bundle loss of the fiber can be reduced by 1～2 orders of magnitude compared with a single dielectric layer of six-tube anti-resonant fiber.Secondly,the analysis of the bending loss shows that the introduction of Bragg structure can reduce the bending loss of the fiber by more than one order of magnitude;secondly,the smaller outer ring diameter can effectively reduce the mode coupling between the core and cladding modes;finally,the analysis also shows that when the bending angle of the fiber is different,the corresponding bending loss will also be different.