Parity-time (PT) symmetric periodic structures, near the spontaneous PT-symmetry breaking point, can act as unidirectional invisible media. In this regime, the reflection from one end is diminished while it is enhanced from the other. Furthermore, the transmission coefficient and phase are indistinguishable from those expected in the absence of a grating. The phenomenon is robust even in the presence of Kerr nonlinearities, and it can also effectively suppress optical bistabilities.
Lin, Zin and Ramezani, H., "Unidirectional Invisibility Induced by P T -Symmetric Periodic Structures" (2011). Physics and Astronomy Faculty Publications and Presentations. 308.
Physical Review Letters