Photonic wheels in the slow-light regime of photonic crystal waveguides

Abstract

Optical interconnects represent the most appropriate technologies, from both power consumption and speed points of view, to route data inter- as well as intra-chip. Among the maturity indicators of nano-photonic devices, their capacity to control the polarisation and (counter-intuitively) slow-down optical signals are arguably some of the most important. Photonic crystals are promising for engineering both these properties on the smallest possible footprint. However, it remains challenging to impose the slow-down effect in its conventional regime on photonic modes with dominant circular polarisation. This project aimed to design, fabricate and study both theoretically and experimentally photonic crystal waveguide modes that hold both spin and orbital angular momenta of light (circular polarisation and optical vortices respectively) even in the zero-groupvelocity regime. The main achievements of this work are 1) the experimental verification of the chosen method to implement zero-group-velocity coupled modes at anomalous position and the reliable 3D-FDTD simulations that confirm that these modes holds prominent circular polarisation, 2) the elaboration of a simple theoretical model that connects electromagnetic waves and Schr¨odinger equations to efficiently explain how the method associates spectral properties and polarisation changes in the photonic crystal waveguide, and 3) a comprehensive study on the 3D wavefields properties of the modes which uncovers that the spin and orbital angular momenta of these zero-goup-velocity modes couple and take distinct spatial organisations.

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