Photonic Floquet media with a complex time-periodic permittivity

Abstract

We study the formation of exceptional point (EP) phenomena in a photonic medium with a complex time-periodic permittivity, i.e., ( ) sin( ) or tt       . We formulate the Maxwell's equations in a form of first-order non-Hermitian Floquet Hamiltonian matrix and solve it analytically for the Floquet band structures. In the case when r  is real, to the first order in r  , the band structures show a phase transition from an exact phase with real quasienergies to a broken phase with complex quasienergies inside a region of wave vector space, the so-called kgap. We show that the two EPs at the upper and lower edges of the k-gap have opposite chiralities in the stroboscopic sense. Thus, by picking up the mode with a positive imaginary quasienergy, the wave propagation inside the k-gap can grow exponentially. In three dimensions, such pairs of EPs span two concentric spherical surfaces in the k space and repeat themselves periodically in the quasienergy space with  as the period. However, in the case when r  is purely imaginary, the k-gap disappears and gaps in the quasienergy space are opened. Our analytical results agree well with the finite-difference time-domain (FDTD) simulations. To the second order in r  , additional EP pairs are found for both the cases of real and imaginary r  .

Selective frequency conversion with coupled time-modulated cavities

“…2). This is a different effect than bandgaps that appear for propagative Floquet modes 41 . Here we study two coupled localized resonances so no true bandgap is opened.…”

Dynamically modulated perfect absorbers

“…We point out that our analysis involves scenarios for which strong non-Hermitian effects (like EPs etc) associated with the driving 44,50 are secondary as opposed to non-Hermiticity associated with material losses. Moreover, we assume that the material-related (non-radiative) losses are relatively weak and can be considered a small perturbation to the Hamiltonian of the isolated system.…”

One-Dimensional Diffraction Grating of Poly(Methacrylic Acid) Brushes For The Rapid Label-Free Detection of Yersinia Pestis With a Reflective Laser System

“…When light impinges on the periodic medium, the re ection or transmission at a speci c angle exhibits speci c spectral properties, which may not be the case for aperiodic media. Spacetime periodic (STP) media can interact remarkably with electromagnetic waves; thus, they have attracted signi cant scienti c attention for applications in numerous electromagnetic systems [10,11]. Optical properties, including electromagnetic wave propagation and scattering through time-periodic media [12,13] and STP media [14,15] are thus interesting topics of research.…”