Asymmetric and dynamic waveguide propagation based on localized parity-time symmetry

The asymmetric or unidirectional light propagation has attracted enormous research interest in optical communication system. Most of these waveguides are static and cannot be modulated. In order to achieve a dynamic and tunable asymmetric waveguide, we propose a two-dimensional photonic crystal waveguide with a localized PT-symmetry. With the band coalesce, the structure achieves a unique waveguide mode band. With an excitation of line source the light in the waveguide undergoes an asymmetric or symmetric propagation in the two opposite directions of the waveguide, dependent on the source position and frequency. For a frequency in the waveguide mode band, the contrast of the field amplitudes in the two directions change periodically with the displacement of the source; whereas for the fixed source, the contrast can be modulated by the source frequency.