Boundary-induced temporal interfaces: analysis of a waveguide-to-waveguide transition

Temporal metamaterials are artificial materials whose electromagnetic properties vary over time. An abrupt change of the refractive index over time realizes the socalled temporal interface, that induces the generation of a reflected and a refracted wave. In this contribution, we investigate on the possibility to emulate temporal interfaces by acting on the boundary conditions rather than on the material properties. We demonstrate that by suddenly changing the geometrical properties of a waveguide, it is possible to have an equivalent temporal interface, without acting on the material properties. Such an approach opens the door to a simplified exploitation of the properties of temporal interfaces, relaxing the requirements of material modulation.