Large Scale Indium Tin Oxide (ITO) One Dimensional Gratings for Ultrafast Signal Modulation in the Visible

Abstract

Indium Tin Oxide (ITO) is a heavily doped semiconductor with a plasmonic response in the near infrared. When exposed to light, the distribution of conduction band electron induces a change in the real and imaginary parts of the dielectric permittivity. The coupling of the electromagnetic waves with the electrons in the conduction band of metallic nanostructures with ultrashort light pulses results in nonlinear plasmonic response Such optical modulation occurring on ultrafast time scales, e.g. picosecond response times can be exploited and used to create integrated optical components with terahertz modulation speed. Here, we present a photophysical study on an ITO one dimensional grating, realized using femtosecond micromachining technology, a technology very industrially accessible. The geometries, dimensions and pitch of the various gratings analyzed are obtained by means of direct ablation in a controlled atmosphere of a homogeneous thin layer of ITO deposited on a glass substrate. The pitch has been selected in order to obtain a higher order of the photonic band gap in the visible. Femtosecond micromachining technology guarantees precision, repeatability and extreme manufacturing flexibility. By means of ultrafast pump-probe spectroscopy we characterize both the plasmon and inter-band temporal dynamics. We observe a large optical non-linearity of ITO grating in the visible range, where the photonic band gap occurs, when pumped at the surface plasmon resonance in the near infrared (1500 nm). All together we show the possibility of all-optical signal modulation with heavily doped semiconductors in their transparency window with a picosecond response time through the formation of ITO grating structures.