Design of unidirectional and tunable channels in two-dimensional photonic crystal composed of local PT symmetric structure

We designed a nonreciprocal and tunable waveguide with a local PT-symmetric MO structure. The on-off switch of the channels in the waveguide can be manipulated by the odd symmetry imaginary part of the eigenvalue due to the breaking of system symmetries. The odd symmetry imaginary part of the eigenvalue can be controlled by the directions of the external magnetic fields or local PT-symmetric medium rods simultaneously or individually. Furthermore, the adjacent dispersion curves tend to degenerate with a gain/loss factor increase in the local PT structure. The guided modes can be formed from a wave with frequencies in the bandgap to realize unidirectional and tunable transmission. These properties have a wide range of potential applications in several photonic devices, such as optical switches, multichannel filters, and storage of optical waves.