We will discuss opportunities for light trapping and manipulation offered by creation of topological defects (e.g., vortices) in optical fields. Topological nature of an optical vortex is revealed through its quantized topological charge – the winding number of an optical wavefront around the vortex core, where the electromagnetic field is zero and the phase is undetermined. The topological charge of a vortex remains constant under continuous system deformations and in the presence of noise, although it can be altered abruptly, e.g. in the process of mutual annihilation with another vortex of the opposite charge. We exploited these intriguing properties by developing plasmonic nanostructures with ‘pinned’ topological defects in their optical near-fields. These nano-structures exhibit superior light trapping and tuning/switching properties over those of conventional single-, dimer-, or array-based plasmonic elements (1–4).
We will also report on engineering topologically-protected optical states on material interfaces by using boundary-bulk correspondence principle adopted from the solid state physics of topological materials. Instead of engineering nano-patterned surfaces, we engineer the meta-material ‘bulk’ to guarantee formation of topologically-protected states on planar interfaces, which are amenable to large-scale fabrication, are less prone to post-fabrication contamination and deformations, and provide strong uniform field enhancement across the surface accessible by target molecules and optical probes. Light coupling to topologically-protected interfacial states can result in its complete absorption, which in turn can be used to realize sensitive singular-phase optical sensors (5). We have developed planar singular-phase sensors and tested them as temperature detectors with a remote optical readout, confirming high sensitivity of the new sensing approach. We will also discuss applications of plasmonic nanostructures with interfacial states for engineering thermal emitters with spectral- and angular selectivity.
1. W. Ahn et al, Electromagnetic field enhancement and spectrum shaping through plasmonically integrated optical vortices. Nano Lett. 12, 219–27 (2012).
2. S. V. Boriskina, Plasmonics with a twist: Taming optical tornadoes on the nanoscale, Plasmonics: Theory and Applications, T. Shahbazyan, M.Stockman (Eds) Ch. 12 (2013).
3. S.V. Boriskina and N.I. Zheludev, Singular and Chiral Nanoplasmonics, Pan Stanford, 2014.
4. S. V. Boriskina et al., Losses in plasmonics: from mitigating energy dissipation to embracing loss-enabled functionalities. Adv. Opt. Photonics. 9, 775 (2017).
5. Y. Tsurimaki et al, Topological darkness of interfacial optical Tamm states for highly-sensitive singular-phase optical detection, submitted (2017).