Generating Optical Birefringence and Chirality in Silicon Nanowire Dimers

Abstract

Narrow high refractive index nanowires sustain weakly guided modes with significant mode volume outside of the nanowire. This modal spillover makes them interesting photonic materials for a multitude of applications. In this article we fabricate dimers of nanowires with lengths up to 1.4 μm, radii down to 55 nm, and edge-to-edge separation down to 60 nm through anisotropic etching from crystalline silicon (Si). We investigate how the properties of the weakly confined fundamental HE1,1 mode in Si nanowires are modified by their integration into dimers. In particular, we characterize through a combination of experimental spectroscopy and numerical electromagnetic simulations how the lifting of the degeneracy of HE1,1x and HE1,1y modes in dimers of Si nanowires generates linear birefringence, spin angular momentum, and superchirality. Achiral Si nanowire dimers are found to create locations of strongly enhanced near-field chirality in the gap between the nanowires, where the field can interact with the ambie...