Time-Tronics in Photonic Systems

Crystalline structures in time can be observed in systems of particles that are periodically driven. In such systems, it is also possible to realize and study phenomena known from solid-state physics that are observed in the time domain. In optical systems, it is possible to realize photonic time crystals — spatially homogeneous media that, due to the periodic modulation of the refractive index in time, exhibit a band structure in the wave number. Here, we show that periodic modulation of the refractive index in a small segment of optical waveguides allows for the creation of condensed matter phases observable in the time dimension. Unlike previously considered photonic time crystals, the required frequency and depth of refractive index modulation are experimentally achievable for systems in the optical regime. This opens a pathway for optical time-tronics, i.e., research into the practical application of crystalline structures in time in optical systems.