Comparison of the waveguide properties of gap surface plasmon in the terahertz region and visible spectra

The waveguide propagation properties of a channel surface plasmon polariton (SPP) guided by a terahertz (THz) wave through a subwavelength trench-like structure have been investigated and compared with the results in visible and infrared spectra. The effects of geometrical parameter and dielectric materials filling the slit on propagation properties are given and discussed. The results show that the effective index of the gap SPP mode in the THz region is smaller than that in visible and infrared spectra, while the propagation length in the THz region is larger than that in visible spectra. As the refractive index of dielectric materials filling the slit increases, the effective index increases, the propagation length decreases and the mode decreases more quickly.