Strong nonreciprocal transmission self-induced by nonlinear PT-symmetric metamaterials

Self-induced nonreciprocity based on optical nonlinear effects is a more appealing technique compared to other ways to achieve nonreciprocal response due to the absence of any kind of bias based on magnets, currents, or time modulation. We demonstrate strong self-induced nonreciprocal transmission by using a new compact nonlinear parity-time (PT) symmetric system based on epsilon-near-zero (ENZ) metamaterials photonically doped with gain and loss defects [B. Jin and C. Argyropoulos, “Nonreciprocal Transmission in Nonlinear PT-Symmetric Metamaterials Using Epsilon-near-Zero Media Doped with Defects,” Adv. Opt. Mat., p. 1901083 (2019)]. The strong self-induced nonreciprocal transmission arises from the extreme asymmetric field distribution achieved upon excitation from opposite incident directions combined with the boosted nonlinear effects at the nanoscale. The transmittance from one direction is kept exactly unity while the transmittance from the other direction is decreased to very low values, achieving very high optical isolation. The presented work can have a plethora of applications, such as nonreciprocal ultrathin coatings for the protection of sources or other sensitive equipment from external pulsed signals, circulators, and isolators without the use of bulk magnets.