Hybrid silicon all-optical switching devices integrated with two-dimensional material

We propose and demonstrate hybrid all-optical switching devices that combine silicon nanocavities and two-dimensional semiconductor material. By exploiting the refractive index modulation caused by photo-induced carriers in the two-dimensional material instead of the silicon substrate, we overcome the switching performance limitation imposed by the substrate material. Air-mode photonic crystal nanobeam cavities capable of efficient interaction with two-dimensional materials are fabricated, and molybdenum ditelluride, a two-dimensional material with rapid carrier recombination, is transferred onto the cavities. The molybdenum ditelluride flake is excited by an optical pump pulse to shift the resonant wavelength of the cavity for switching operation. We have successfully achieved all-optical switching operations on the time scale of tens of picoseconds while requiring low switching energies of a few hundred femtojoules.