Design of unidirectional subwavelength slit coupler for THz surface plasmons

In this paper, we demonstrate a unidirectional subwavelength slit coupler at THz frequencies by using two-dimensional finite difference time domain (FDTD) modeling. The near-field light emitted from the narrow slit serves as a subwavelength-scaled excitation source. By placing a particular grating structure on one side of the slit, the light could be guided in only one direction. This unidirectional subwavelength slit coupler is amenable to incorporation into optical integrated circuits at THz frequencies.