Raana Sabri Khiavi’s PhD Proposal Review

“Theory and design of spatiotemporally-modulated metasurfaces for comprehensive control of light”

Abstract:

Photonic metasurfaces are key platforms for manipulating almost all properties of light such as amplitude, phase, polarization, wave vector, pulse shape, and orbital angular momentum in a sub-wavelength dimension. They are capable of providing unprecedented modulation of wavefront through imparting spatial or temporal variation on the incoming wave. Recently, considerable efforts have been devoted to design active metasurfaces that enable real-time tuning and post-fabrication control of the optical response. Toward achieving this goal, electro-optically tunable materials such as doped semiconductors, multiple-quantum-wells (MQWs), and atomically thin sheets are incorporated into the building blocks of the geometrically-fixed metasurfaces. Despite the significant progress in this field, there has been several limitations imparted to the optical response of such so-called quasi-static metasurfaces. Remarkably, the strong resonant dispersion in such metasurfaces leads to narrow spectral and angular bandwidths. In addition, the co-varying amplitude and phase response as well as the limited phase modulation give rise to undesired artefacts manifested on their output profiles. The slow response time to the external stimuli is another drawback that restricts the performance of the metasurfaces. Introducing time into the external stimulus of the metasurfaces, as an additional degree of freedom, offers a way out to surmount the obstacles facing the quasi-static metasurfaces. Modulation in time enables myriad of exotic space-time scattering phenomena, where possibility to break the reciprocity and generation/manipulation of the sideband scattered signals offer the most appealing functionalities. The objective of this work is to investigate the less explored mechanisms for yielding reconfigurable plasmonic metasurfaces in both space and time. Several realizations of quasi-static and time-modulated devices integrated with the electro-optical materials such as indium-tin-oxide (ITO) with the potential wide phase modulation is presented. It has been shown that time-modulated metasurfaces are superior to their quasi-static counterparts in terms of providing access to the dispersionless modulation-induced phase shift spanning over 2π as well as the constant amplitude at the sidebands. Novel and unique applications of space-time photonic metasurfaces by spatiotemporal manipulation of light for all-angle, broadband beam steering, suppressing the undesired sidelobes, high speed continuous beam scanning, and dispersionless dynamic wavefront engineering are studied.

Committee:

Prof. Hossein Mosallaei (Advisor)

Prof. Charles DiMarzio

Prof. Siddhartha Ghosh