Widely Tunable, Monochromatic THz Generation via Cherenkov-Type Difference Frequency Generation in an Asymmetric Waveguide

Cherenkov-type monochromatic terahertz (THz) generation via difference frequency generation in a general asymmetric sandwich-like waveguide is investigated theoretically. An efficient geometry-conversion from a transverse electric (TE) pump mode to a TE THz mode is mainly considered. The general expression for a Cherenkov THz field is obtained by solving the nonlinear wave equation analytically. Numerical simulation is performed on specific devices with three typical substrate materials: 1) nondoped LiNbO
₃
; 2) BK7 glass; and 3) quartz. Characteristics of this type of THz source and parametric dependence of conversion efficiency are discussed. It is predicted that the conversion efficiency would be increased by one order by optimizing the waveguide structure.