Epsilon-Near-Zero Plasmonic Waveguides for Enhanced Coherent Optical Effects

Abstract

AbstractPlasmonic waveguides exhibit an effective epsilon-near-zero (ENZ) operation in their cut-off wavelength and Fabry-Pérot resonances at lower wavelengths. In this chapter, we demonstrate a scheme to realize nonlinear coherent perfect absorption (CPA) at the nanoscale using the ENZ plasmonic waveguide nanochannels. The strong and uniform field enhancement inside the nanochannels of the waveguides at the ENZ resonance can efficiently boost Kerr nonlinearities, resulting in a new all-optical switching intensity-dependent CPA phenomenon which can be tunable with ultrafast speed. Our findings provide a new platform to efficiently excite nonlinear phenomena at the nanoscale and design tunable coherent perfect absorbers.In addition, we demonstrate the formation of exceptional points (EP) in a nanoscale open and lossy (non-Hermitian) nanophotonic system based on gain medium embedded inside the ENZ plasmonic waveguide nanochannels. Reflectionless transmission (perfect loss compensation) at the nanoscale is realized at the EP, which coincides with the ENZ cut-off frequency of the proposed plasmonic system. This special spectral degeneracy point (EP) is a unique feature of the presented nanoscale symmetric plasmonic ENZ configuration, different from most of the previous works that were mainly focused on asymmetric bulky micron-scale active photonic configurations. When we further increase the gain coefficient of the dielectric material loaded in the waveguides, a spectral singularity occurs leading to super scattering (lasing) response at both forward and backward directions. The presented results demonstrate that ENZ plasmonic waveguides can enhance different coherent optical effects that can find a plethora of new applications.KeywordsSurface plasmonEpsilon-near-zeroPlasmonicsCoherent opticsExceptional pointNon-Hermitian