Ultrafast all-optical modulation of wide-bandwidth pulses enabled by silicon-metasurfaces

Semiconductor metasurfaces have emerged as an effective platform for all-optical modulation thanks to their resonant light confinement and the enhancement of ultrafast optical effects like the Kerr effect and free-carrier generation. However, their narrow resonance features also restrict the available bandwidth for efficient modulation. Here, we demonstrate that a kink-like transmission spectral profile of a silicon metasurface could enable high-contrast modulation of wide-bandwidth pulses. We studied the all-optical ultrafast transmission modulation of the silicon metasurface induced by free-carrier excitation in a pump-probe configuration at different polarizations. We achieved ultrafast modulation of 28% (10%) with a speed of 25 ps and a bandwidth of up to 14 nm (49 nm) for y- and x-polarizations, respectively. Our results open up new opportunities for high-contrast, all-optical modulation of short pulses, with applications in optical communications and computing.