Adaptive Optical Surfaces for Long Wavelength Light

Abstract

The ability to control the intensity and phase of infrared and terahertz waves plays a crucial role in emerging applications such as thermal camouflage, radiative cooling, non-invasive imaging, wireless communication, active plasmonics, multispectral displays, and tuneable light-matter interaction. However, the lack of active optical material in infrared and terahertz wavelengths has hampered the efficient and dynamic control of light and the further development of these technologies. Graphene is a promising optical platform due to its unique band structure and tuneable optical properties in a wide spectral range. Electrical tunability of the high mobility charge carriers on graphene enables dynamic control of absorption of light by tuning interband and intraband electronic transitions. In this thesis, I have investigated the gate-tuneable optical properties of graphene for long-wavelength optoelectronic applications. I have designed and fabricated graphene-based optical devices using electrolyte gating and electro-intercalation of ions into the graphene layers. These devices consist of single or multilayer graphene films, the electrolyte layer, and the counter electrode. Tuning the Fermi energy up to 1.5 eV has enabled significant intensity >80% and phase modulation ~4π in the terahertz, variable thermal emissivity between 0.7 and 0.25 in the infrared, tuneable colour change in the visible. I have also observed new topological features in the operation of these devices, which could enable new tools for controlling the long-wavelength light. I anticipate these results provide realistic approaches for programmable smart optical surfaces with a potential utility in many scientific and engineering fields.

Date of Award	21 Aug 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Coskun Kocabas (Supervisor) & Brian Derby (Supervisor)