Non-reciprocal Optical Mirrors Based on Spatio-Temporal Modulation

The recent surge of interest in temporal modulation schemes to induce magnet-free non-reciprocity has inspired several exciting opportunities for photonic technology. Here, we investigate a scheme to realize free-space isolators and highly non-reciprocal mirrors with weak modulation imparted by an acoustic wave. Conventional optical mirrors are reciprocal: in a given plane of incidence, reflection is independent of the sign of the angle of incidence, which enables two people to simultaneously look at each other through their reflection. In contrast, we propose a strategy to dramatically break this symmetry by exploiting resonant interactions between a travelling acoustic wave and highly resonant guided optical modes, inducing total reflection of an optical beam at a given angle, and no reflection at the negative angle. Different from conventional acousto-optic isolators, which are based on non-resonant frequency conversion and filtering, our proposal operates at the frequency of the optical signal by tailoring the resonant properties of the structure as well as the acoustic wave frequency and intensity, enabling 50 dB isolation with modest modulation requirements. Operation in reflection allows for close-to-zero insertion loss, enabling disruptive opportunities in our ability to control and manipulate photons

Terahertz Magnetoplasmon Energy Concentration and Splitting in Graphene PN Junctions

Terahertz plasmons and magnetoplasmons propagating along electrically and chemically doped graphene p-n junctions are investigated. It is shown that such junctions support non-reciprocal magnetoplasmonic modes which get concentrated at the middle of the junction in one direction and split away from the middle of the junction in the other direction under the application of an external static magnetic field. This phenomenon follows from the combined effects of circular birefringence and carrier density non-uniformity. It can be exploited for the realization of plasmonic isolators.Comment: 6 Pages, 10 figure

First-principles analysis of energy exchange in time-varying capacitors for energy trapping applications

Time-varying networks, consisting of lumped elements, such as resistors, capacitors, and inductors, actively modulated in time, have introduced a host of novel wave phenomena and witnessed a remarkable development during recent years. This paper investigates the scattering from a time varying capacitor and how such a load can be fully reflectionless when the capacitance is suitably modulated in time. We analytically derive the required temporal dependence of the capacitance and show how in contrast to other techniques it avoids extreme and negative values and, as a result, can be implemented in a feasible way, when the capacitor is charged with a DC voltage source. We also derive from first principles the energy balance of such a time-varying capacitor, proving that the energy of an incoming pulse is transferred to the modulation source. Our findings clarify scattering of waves from time-varying capacitors and open up a new way to matching of broadband pulses