Extraordinarily Large Permittivity Modulation in Zinc Oxide for Dynamic Nanophotonics

TL;DR

This paper demonstrates extraordinarily large, fast, and tunable permittivity modulation in zinc oxide thin films induced by optical excitation, enabling dynamic control of light properties for advanced nanophotonic devices.

Contribution

It reports the first large-scale, broadband, and ultrafast permittivity changes in zinc oxide, including shifting epsilon near zero points and enhancing modulation at specific wavelengths.

Findings

Up to -3.6 change in real permittivity at 1600 nm

70% broadband reflectance modulation with picosecond response

Dynamic epsilon near zero point shifting from 8.5 to 1.6 microns

Abstract

The dielectric permittivity of a material encapsulates the essential physics of light-matter interaction into the material's local response to optical excitation. Dynamic, photo-induced modulation of the permittivity can enable an unprecedented level of control over the phase, amplitude, and polarization of light. Therefore, the detailed dynamic characterization of technology-relevant materials with substantially tunable optical properties and fast response times is a crucial step in the realization of tunable optical devices. This work reports on the extraordinarily large permittivity changes in zinc oxide thin films (up to -3.6 relative change in the real part of the dielectric permittivity at 1600 nm wavelength) induced by optically generated free carriers. We demonstrate broadband reflectance modulation up to 70 percent in metal-backed oxide mirrors at the telecommunication wavelengths, with picosecond-scale relaxation times. The epsilon near zero points of the films can be dynamically shifted from 8.5 microns to 1.6 microns by controlling the pump fluence. Finally, we show that the modulation can be selectively enhanced at specific wavelengths employing metal-backed ZnO disks while maintaining picosecond-scale switching times. This work provides insights into the free-carrier assisted permittivity modulation in zinc oxide and could enable the realization of novel dynamic devices for beam-steering, polarizers, and spatial light modulators.