Enhancing coupling efficiency of SPP on a metal waveguide using varied shaped grooves

In this paper, we demonstrate a novel approach to couple freely propagating THz pulses onto a metal wire waveguide utilizing grating as various shaped grooves; rectangular, triangular and circular grooves fabricated directly into the metal. Using broadband THz pulses incident on the wire, we use metal segments containing number of uniformly, symmetric spaced grooves around subwavelength aperture to launch surface propagating multi-cycle pulses along the wire. THz radiation detected at the end of the waveguide with grooves showed overall improved signal amplitude and increased bandwidth as compared to that for the non-machined waveguide. We observe a one-to-one correspondence between the groove number and the number of oscillations in the THz wave form radiated from the end of the waveguide. We further demonstrate that this coupled radiation is radially polarized. Although the alteration of cross-sectional parameters of the grooves, the shape of the individual grooves, in a controlled manner should allow for arbitrarily shaped THz pulses to be launched on the waveguide, all of which compared to rectangular grooves’ output signal and the efficient shaped groove has been chosen