Parity-time symmetric Bragg gratings and directional couplers

Parity-time symmetric Bragg gratings produce unidirectional reflection around the exceptional point. A step-in-width Ag stripe waveguide with an IR-140 dye cover solution index-matched to the substrate is utilized to implement index and gain modulated Bragg gratings operating in the long-range surface plasmon mode. We investigate directional coupling between parity-time symmetric Bragg gratings near their exceptional point (□0 ~ ((0 nm), arranged as duplicate, duplicate-shifted, duplicate-flipped gratings, or involving a bus waveguide. Unidirectional multi-wavelength reflection and coupled supermode conversion are predicted.