Parity-time symmetric photonic topological coupled waveguides

Photonic topological edge states are robust against the structural disorder, paving the way of their broad applications in the field of photonics. In the meantime, the topological phase transitions of parity-time (PT) symmetric systems have been extensively investigated. This report presents another new concept, PT symmetric photonic topological waveguides, being PT symmetric as a whole, but with gain/loss waveguides supporting topological edge modes. Through the theoretical and numerical investigations, we demonstrate unidirectional propagation in valley-Hall photonic topological coupled waveguides in a PT-broken phase as an example. Such waveguides can exhibit numerous photonic functionalities observable in PT symmetric photonic systems, the performances of which are robust against the defects due to the topological nature of the constituent waveguides.