Exceptional point and its effect on wave propagating in a parity-time symmetric structure

The Parity-Time (PT) symmetric systems- first presented in the realm of quantum mechanics- have received a wide currency within the last two decades. On the whole it can be pronounced that even Non-Hermitian systems can give totally real spectra, as long as their equivalent Hamiltonians commute with the PT operator. Recently some investigations have revealed that implementation of photonic configurations based on PT symmetry is quite conceivable. Taking into account the similarities between quantum mechanical Schrödinger equations and the paraxial wave equations of optics, a required, but not enough condition for optical PT symmetry could be stated in form of n*(-r)=n(r). The most interesting point about such system is the fact that a PT- symmetric system is able to show an exceptional point where the eigenvalues coalesce. Analogously, in a photonic PT symmetric structure, by establishing an accurate balance between the gain and loss, this exceptional point could be accessible. In many recent studies like, the configuration including two identical ring resonators has employed to realize photonic PT symmetric systems, in which one ring provides gain and another loss. The most outstanding point which could be achieved from such PT symmetric structure is ability to support eigenstates with wholly real eigenvalues during unbroken PT symmetry. Under these circumstances, the modes neither grow nor decay, but as gain- loss contrast are increased, broken PT symmetry regime emerges and then, in this case there would be some modes which might experience gain or loss as in the form of conjugated sets.

کلیدواژه ها:

Exceptional point ، Eigen mode ، Parity-time symmetry.