Magnet-less gyrotropy using time-periodic modulation of permittivity

Time-varying (TV) media in electromagnetics have unlocked new paths to important electromagnetic effects such as non-reciprocity, frequency conversion, and parametric amplification. In light of such advances over the past decade, a curious question arises as to whether chirality or/and gyrotropy, may also be achieved using TV dielectrics. In this paper, we propose a suitable time-modulation of the permittivity tensor in a static achiral and non-gyrotropic crystal and thereby emulate gyrotropy without the need of magnetic materials and external magnetic bias field. The emulated gyrotropy is owed to the temporal rotation of the principal axes of the permittivity tensor, which sustains only circularly/elliptically polarized eigenmodes. A possible realization using modulated electro-optic effects in a nonlinear crystal is proposed, showing a feasible approach to realize gyrotropy by time variation in non-magnetic achiral media.