All-Optical Silicon-Based Modulators Driven by an Ultrafast Phase-Change Material

With increasing demand for higher-speed telecommunications, there is a need for optical modulators (OMs) designed to operate at the telecommunications wavelength. Although switching speeds of OMs compatible with current Si-based CMOS technology have increased recently, most devices are limited by the weak electro-optic effect in Si. We incorporated a phase-change material, vanadium dioxide (VO$_{2}$), into the model Si-based OM geometry, the silicon ring resonator (SRR). VO$_{2}$ thin films irradiated with ultrafast pulses can switch from their insulating ground state to an excited metallic state exhibiting different optical constants in a fraction of a picosecond. Capitalizing on this large, reversible refractive index change, VO$_{2}$ films with footprints $<$1 $\mu$m$^{2}$ have induced record phase modulations as high as $\pi$/5 rad/$\mu$m in these VO$_{2}$-enhanced SRRs. The resulting resonance shifts of almost 3 nm are $\sim$60 times larger than their silicon-only analogues. Using these devices, we have demonstrated both thermal switching induced with a cw laser and switching with $\sim$20 ns laser pulses. Since the VO$_{2}$ phase transition occurs in $<$100 fs, harnessing this light-induced ultrafast transition could be the key to designing ultrafast OMs.