Terahertz Functional Device Based On Whispering Gallery Mode And Grating Structures

Terahertz wave has the characteristics of penetrability,low photonic energy and high coherency,which makes it to be widely applied in the field of security check,medicine and communication.In this thesis,terahertz functional devices are designed and analyzed,including terahertz filter and terahertz switch based on whisper gallery mode(WGM)cavity and terahertz absorber based on three-layer gratings.1 Theoretically analyzed the influence of structure parameters,including the radius,width and height of WGM cavity;the width and height of straight waveguide and the gap between straight waveguide and WGM cavity.A terahertz filter based on WGM cavity coupled by rectangular waveguide was designed and this structure was optimized by using MODE SOLUTIONS software.The optimized terahertz filter can achieve comb-like and narrowband filtering among the frequency range of 2.4-2.6THz with over 95% filtration efficiency,2GHz bandwidth and 30 GHz free spectral range.2 Terahertz switch based on WGM cavity is realized by changing couple efficiency between rectangular waveguide and WGM cavity,which is influenced by material(silicon)refractive index of WGM.The refractive index of silicon can be modulated by photon-generated carriers induced by 337 nm pump light.The structure of this alloptical switching is simple.Simulation results show that it can switch off 95% light energy at multi-frequency(2.41 THz,2.44 THz,2.5THz,2.56 THz,2.59 THz and 2.65THz)among the range of 2.4-2.6THz with 0.6ns switch speed.3 A terahertz absorber composed of three-layer micro-structure gratings was designed based on the effective medium theory and the theory of multi-layer antireflection coating.By using the finite-difference time-domain method,the influence of the grating period,width and depth on the reflection coefficient was analyzed.The numerical simulation results show that,in the range of 0~3THz,more than 98% terahertz absorption can be achieved with a bandwidth of 1.3THz and over 95% terahertz absorption can be obtained with a bandwidth of 2.1THz.By structural parameter optimization,the absorber can achieve more than 95% broadband terahertz absorption in the range of 0.6~6THz.