Parity-time symmetry in periodically curved optical waveguides

Forward and Backward Unidirectional Scattering by the Core-Shell Nanocube Dimer with Balanced Gain and Loss

An optical nanoantenna consisting of a Au-dielectric core-shell nanocube dimer with switchable directionality was designed and described. Our theoretical model and numerical simulation showed that switching between forward and backward directions can be achieved with balanced gain and loss, using a single element by changing the coefficient κ in the core, which can be defined by the relative phase of the polarizability. The optical response indicated a remarkable dependence on the coefficient κ in the core as well as frequency. The location of the electric field enhancement was specified by the different coefficient κ and, furthermore, the chained optical nanoantenna and coupled electric dipole emitted to the optical nanoantenna played significant roles in unidirectional scattering. This simple method to calculate the feasibility of unidirectional and switchable scattering provides an effective strategy to explore the functionalities of nanophotonic devices.

Nonreciprocal parity-time phase in magnetized waveguides

In a single magneto-optical (MO) waveguide, the dispersion of guided bulk wave is reciprocal in the Voigt configuration. Here we show that the parity-time (P T) phase in two coupled MO waveguides can be nonreciprocal if the waveguides are properly biased. The nonreciprocal P T phase is closely related to the asymmetric field profile induced by the MO effect that modifies the coupling strength between adjacent waveguides. We show that it is feasible to switch between broken and conserved P T phases by simply reversing the magnetic bias or the propagating direction of wave. Theoretical analysis and numerical calculation prove our theory. This investigation highlights a flexible method in manipulating the field dynamics of waveguide arrays by using the novel properties of P T phase especially the exceptional points.