Propagation of Single-Mode and Multi-Mode Terahertz Radiation Through a Parallel-Plate Waveguide

Propagation of Single-Mode and Multi-Mode Terahertz Radiation Through a Parallel-Plate Waveguide

We investigated the propagation of single- and multi-mode terahertz (THz) radiation through a paralel-plate waveguide for various gap sizes of the plates and polarizations of the incoming THz field. Single TEM (TM0) and TE1 modes within the 4-THz frequency range propagated through a waveguide with a plate separation of 103 μm. Multi TE and TM modes were observed for a 360-μm separation. High-order modes have a very high group velocity dispersion near the cutoff frequencies, which causes extensive pulse reshaping and broadening, in addition to multimode interference in the time and frequency region. The majority dominant mode is a combination of the TE1 (97.96 %) and the TM0 (81.61 %) modes because the lowest mode has a smal absorption and an incident even field pattern. Because each mode has different transmission and coupling coefficients, absorption and propagation constant, the theoretical calculation for the total TM or TE modes requires a summation of the components. The theoretical calculation and the measured data fit wel in the frequency and time domain.

We investigated the propagation of single- and multi-mode terahertz (THz) radiation through a paralel-plate waveguide for various gap sizes of the plates and polarizations of the incoming THz field. Single TEM (TM0) and TE1 modes within the 4-THz frequency range propagated through a waveguide with a plate separation of 103 μm. Multi TE and TM modes were observed for a 360-μm separation. High-order modes have a very high group velocity dispersion near the cutoff frequencies, which causes extensive pulse reshaping and broadening, in addition to multimode interference in the time and frequency region. The majority dominant mode is a combination of the TE1 (97.96 %) and the TM0 (81.61 %) modes because the lowest mode has a smal absorption and an incident even field pattern. Because each mode has different transmission and coupling coefficients, absorption and propagation constant, the theoretical calculation for the total TM or TE modes requires a summation of the components. The theoretical calculation and the measured data fit wel in the frequency and time domain.