Unidirectional excitation of surface plasmon polaritons in a grating system with Parity-Time symmetry

Over the past years, there has been rapidly growing interest in non-Hermitian photonic systems. A Hamiltonian with Parity-Time (PT) symmetry can show real spectrum below a certain threshold, known as the exceptional point (EP), accompanied with novel phenomena above the EP. Here we propose a plasmonic grating system with PT symmetry to excite unidirectional surface plasmon polaritons (SPPs). We have designed realistic grating array only consisting of passive rectangular gratings (i.e., without gain materials), which can significantly reduce the challenges in fabrication and optical experiments. In addition, instead of using ideal sinusoidal permittivity modulation in simulation in former paper(2), here we demonstrate in both simulation and experiment that using discrete grating array can also achieve excellent contrast between SPPs in opposite directions
In summary, we have demonstrated a sub-wavelength scale plasmonic grating structure with PT symmetry that can realize high performance for unidirectional excitation of SPPs. These results can be employed as a new approach to designing nanoscale optical devices, such as low-loss plasmonic routers and isolators for optical computation, communication, and information processing.

1. W. Wang et al., Phys Rev Lett 119, 077401 (2017).