Plasmonic-nanowire near-field beam analyzer

Experimental near-field analysis of the output beams from the end faces of micro/nano-waveguide is very necessary, because important information such as spatial intensity distributions, mode orders, and divergence angles can be obtained, and are very important for investigating and designing nanophotonic devices. However, as far as we know, it has not been demonstrated yet. In this work, we experimentally demonstrate a plasmonic-nanowire near-field beam analyzer, utilizing a single Au nanowire (AuNW) as the probe to scan the spatial near-field distributions of emitted beams from micro/nano-waveguide end-faces. Our analyzer can resolve the trade-off between high measurement resolution and light collection efficiency in conventional beam analyzers by a reverse nanofocusing process, achieving a probe resolution of 190 nm (<λ/8) and a simulated collection efficiency of ∼47.4 % at λ = 1596 nm. These attractive advantages allow us to obtain three-dimensional (3D) scanning in a large range from the plasmonic hotspot region to the far-field region, characterizing the 3D spatial distribution evolution from a metal nanowire output beam for the first time, with an M ² factor lower than that of the ideal Gaussian beam (M ² = 1). In addition, the analyzer also demonstrates simultaneous characterization of multimodes in irregular and large-sized nanoribbons, further verifying its ability to selectively explore complex multimodes that are difficult to be predicted by numerical simulations. Our results suggest that this plasmonic-nanowire beam analyzer may hold promise for diverse near-field applications for micro/nano-waveguides such as nanolasers and biosensing, and offer a new method for understanding nanophotonic structures.