Grating-Assisted Excitation of Short-Range Surface Plasmon Polariton Mode

We propose an anti-symmetric grating structure for effective excitation of the short-range surface plasmon polariton (SR-SPP) mode of a metal stripe waveguide. The structure consists of two corrugated Bragg gratings offset by half of a period formed on the two sides of the metal stripe, respectively. The SR-SPP mode is excited in the backward direction by the long-range surface plasmon polariton mode launched into the waveguide. We investigate the effects of the metal stripe thickness, the grating corrugation depth, and the number of grating periods on the transmission and reflection characteristics of the grating with the finite-difference time-domain method in detail. Our numerical results show that a peak reflection of ~57% in the SR-SPP mode can be achieved with a 50-μm long grating on a 40-nm thick gold stripe.