The Study On Multi-layer Planar THz Waveguides And Their Applications

In recent years, THz waveguides have been widely studied and applied. The most famous THz waveguides include: metal wire waveguides, dielectric pipe waveguides, parallel plate waveguides, metal-clad anti-resonant reflection hollow waveguides, single metal plate waveguides. Since they were put forward for the first time, a lot of interesting experimental and theoretical results have been obtained. Many applications have also been arising, for example, the waveguides are used in transmission, sensing, filtering, and THz switches.In this paper, we research the multilayer planar THz waveguides theoretically in detail, and put forward several applications of all sorts of multilayer planar THz waveguides, such as coupling, sensing, tunable filtering, and wavelength analysis. The waveguides we put forward and study are: double-dielectric-slab waveguides, metal-film-coated single dielectric slab waveguides, plastic-coated parallel plate waveguides, single metal plate waveguides, metal-clad anti-resonant reflecting hollow waveguides, metal-film-coated double-dielectric-slab waveguides, double-metal-film waveguides.For double-dielectric-slab waveguide, we find that it can guide THz wave with low loss and small full width at half maximum(FWHM). When the mode field width is large, we propose coupling of Sommerfeld waves using odd TM mode of double-dielectric-slab waveguide. At 4.2 THz, the maximum coupling efficiency can be 43.5%.For metal-film-coated single-dielectric-slab waveguide, we analysis the transmission characteristics of TM mode theoretically.For plastic film coated parallel-plate waveguide, we find that after coating, the guiding mechanism change to anti-resonant reflecting, the losses of TM mode reduce 4 orders of magnitude after coating. And by reducing the film thickness, the maximum transmission bandwidth can be 5.12 THz.For single metal plate waveguide, we theoretically study the transmission characteristics of the bare and dielectric coated metal plate and compare the difference between them. We propose coupling the THz SPPs on a bare metal plate using single dielectric film, and the highest theory coupling efficiency we get can be 45.64%. Moreover we study the hybrid plasmonic modes of a dielectric slab above the metal plate.We study three kinds of planar waveguides with 7 layer symmetrical structure. For the metal-clad antiresonant reflecting hollow waveguides, we broaden the study in the reference on this waveguide. By changing the interval, we obtain that the maximum frequency-tuning-range is up to 2030 GHz, and the maximum sensitivity of the resonance frequency shift is up to 6950 GHz/mm at the resonance order of m = 1.For metal film coated double-dielectric-slab waveguide, detailed comparisons of transmission characteristics of the coated and uncoated double-dielectric-slab waveguide are given. We put forward using the measureable cut-off frequency of the coated waveguide for tunable filtering. We find that at n2 t = 0.06 mm, the theoretical sensitivity of cut-off frequency shift on w can be 7.65 THz/mm.For double-metal-film waveguides for THz wave guiding, in the application of wavelength analysis, we derive the formula of wavelength, and find that as long as we can detect mode field distribution in the dielectric base, we can analysis the THz wavelength. We also analyze the penetrating capability of THz wave in the waveguides.