Pulse compression by a refractive index front in periodically modulated silicon waveguide

In this study, we report the experimental demonstration of optical pulse compression with a gradual refractive index front comoving in a periodically modulated silicon waveguide. This spatiotemporal effect, also called optical push broom, captures and confines the input signal pulse inside a faster propagating refractive index front, driven by a pump pulse. The signal is accelerated by the approaching front until its velocity matches the front's velocity, effectively stopping the light relative to the front. In contrast with the previous experiment where we used a cw signal, we now utilized a pulsed signal and thus can vary the initial delay between the signal and the pump. We employ the slowly varying envelope approximation to model the effect and successfully reproduce the experimental frequency shift at the output corresponding to the temporal delay at the input.