Dynamic Tuning of ENZ Region of ITO and Sensing Using a Tapered Optical Fiber

The non-trivial optical properties of indium tin oxide (ITO) near its epsilon near zero (ENZ) regime, like field confinement and enhancement, and perfect absorption makes it amenable for sensing applications. In parallel, the feasibility of control of electron density of ITO via static (doping) and dynamic (gating) means enables tuning of ITO’s ENZ regime across the near infrared region, increasing customization and scope of application. We showcase an optical device in which electrostatic gating is used to dynamically change the electron density of ITO thin films and thus spectrally tune the ENZ regime from 1280 nm to beyond 2000 nm. The change in optical properties is sensed by a tapered optical fiber placed in contact with the thin film. Evanescent fields of the tapered fiber couple to the environment, which changes the modal dispersion of the fiber and is measured using multi-modal-interference, observed in the transmitted light intensity.