Coherent control of wavefronts by planar photonic metasurfaces

Abstract

The optical properties of materials can manifest differently in traveling and standing light waves. In standing waves, “coherent control” of the energy exchange between incident and scattered waves enables control of light with light without nonlinearity, at arbitrarily low intensity and on ultrashort (few optical cycle) timescales. This thesis reports on my research efforts towards application of coherent control techniques for shaping the wavefronts of light scattered by planar photonic metasurfaces: I show for the first time that the coherent control paradigm can be applied to optically thick and/or asymmetric sample/device structures, where previously only vanishingly thin (subwavelength thickness) structures were considered. I have derived the requisite illumination conditions for electric and magnetic field standing wave excitation of substrate-supported (e.g. at an air-glass substrate) meta surface structures; and numerically demonstrated applications to selective excitation spectroscopy and for thin film characterisation. I have introduced a new mechanism for active tuning of gradient index meta surfaces via coherent control of the phase gradient itself – turning what is conventionally a constant in the Generallized Snell’s law into a variable. This is demonstrated in the development of a meta surface design providing, through coherent selective excitation of Mie-type resonances in Si nano-pillars, coherently controlled beam steering (with no moving parts) over a continuous 9.1° range. I have also discussed its potential use for solid state Lidar.

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Identifiers

ORCID for Xu Fang: orcid.org/0000-0003-1735-2654

ORCID for Kevin MacDonald: orcid.org/0000-0002-3877-2976

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