Pseudo-parity-time symmetry in optical systems.

We introduce a novel concept of the pseudo-parity-time (pseudo-PT) symmetry in periodically modulated optical systems with balanced gain and loss. We demonstrate that whether or not the original system is PT symmetric, we can manipulate the property of the PT symmetry by applying a periodic modulation in such a way that the effective system derived by the high-frequency Floquet method is PT symmetric. If the original system is non-PT symmetric, the PT symmetry in the effective system will lead to quasistationary propagation that can be associated with the pseudo-PT symmetry. Our results provide a promising approach for manipulating the PT symmetry of realistic systems.