Design and modeling of subpicosecond all-optical modulator using the nonlinear response of indium tin oxide

We report the design of an all-optical modulator based on the ultrafast nonlinear optical response of indium tin oxide (ITO) combined with the sharp spectral features of a high-Q resonant grating structure. Under optical excitation, a thin layer of ITO exhibits an ultrafast, reversible, and large intensity-dependent change in its refractive index. The grating structure provides rapid variation of the transmission coefficient, which is tuned to the epsilon-near-zero spectral region of ITO. The proposed design achieves all-optical modulation with a response time of 650 fs (speed >1.5  THz) using a simple design with a compact footprint.