Interaction of silicon sample with fundamental mode submillimeter wave in overmoded rectangular waveguide

Responses of n-Si detecting sample to TE10 mode submillimeter wave in an overmoded rectangular waveguide are numerically investigated. Relative sensitivity under fundamental mode operation for the submillimeter wave detecting structure is derived. Using a three-dimensional electromagnetic finite-difference time-domain method, the interaction of the n-Si sample with submillimeter wave within 300-400 GHz in the overmoded waveguide is calculated, and the dependences of voltage standing wave ratio (VSWR) of the structure and average electric field strength in the sample on the parameters of n-Si detecting sample are analyzed. Compared with the fundamental mode detecting structure with the same silicon sample, VSWR and average electric field strength in the sample change slightly in the overmoded detecting structure, while the fluctuations of their dependences on frequency increase. Selection of the structural parameters of the overmoded detecting structure is also studied. In working frequency range of 300-400 GHz, the optimized structure with VSWR less than 2.75 (no more than 1.8 within frequency range of 335-380 GHz) and response time of hundreds of picoseconds-level has a relative sensitivity around 0.127 kW-1 fluctuating within 20.5% and the maximum enduring power of about 0.53 kW. This detecting structure satisfies the demand of the direct detection of large power pulses at submillimeter wavelength.