Electromagnetic wave propagation in time-periodic chiral media

Within the framework of coupled-wave theory, we investigate the propagation of light in a time-periodic chiral medium whose permittivity, permeability, and chirality parameter are periodic functions of time. For non-constant impedance, we show that two first-order momentum gaps emerge in the Brillouin diagram, resulting in parametric amplification with distinct amplification factors and corresponding momenta for right- and left-handed modes. The presence of chirality plays a pivotal role in manipulating lightwave signals, controlling the center of resonance, the corresponding bandgap size, and the amplification factor in a unique manner for each handedness. For a finite “time-slab” of the considered medium, we analytically derive the scattering coefficients as functions of both time and momentum. Additionally, we discuss how extreme values of optical rotation grant access to the temporal analog of the chirality-induced negative refraction regime. Finally, we elucidate the mechanism by which the orientation of the electric field, associated with elliptical polarizations, is altered as the wave propagates within a first-order momentum gap, thereby undergoing simultaneous optical rotation and parametric amplification.