Time-reversal and nonlocal effects in PT -symmetric nonlinear lattices with balanced gain and loss

We reveal a number of fundamentally important effects which underpin the key aspects of light propagation in photonic structures composed of coupled waveguides with loss and gain regions, which are designed as optical analogues of complex parity-time (or PT) symmetric potentials. We identify a generic nature of time-reversals in PT -symmetric optical couplers, which enables flexible control of all-optical switching and a realization of logic operations. We also show that light propagation in PT -symmetric structures can exhibit strongly nonlocal sensitivity to topology of a photonic structure. These results suggest new possibilities for shaping optical beams and pulses compared to conservative structures.