Optical Orbital Angular Momentum Read-Out Using a Self-Assembled Plasmonic Nanowire

Abstract

Orbital angular momentum (OAM) has emerged as an important parameter to store, control, and transport information using light. Recognizing optical beams that carry OAM at the nanoscale and their interaction with subwavelength nanostructures has turned out to be a vital task in nanophotonic signal processing and communication. The current platforms to decode information from different OAM modes are mainly based on bulk optics and requires sophisticated nanofabrication procedures. Motivated by these issues, herein we report on the utility of chemically prepared, individual plasmonic nanowire for OAM read-out. Our method is based on pattern recognition of coherent light scattering from individual nanowires that can be used as direct read-outs of two parameters of an OAM beam: magnitude of topological charge and its sign. All the experimental observations related to pattern formation are corroborated by three-dimensional numerical simulations. Given that pattern formation and recognition are exhaustively utilized in various computational domains, we envisage that our results can be interfaced with machine-learning methods, wherein direct read-out of OAM signals can be performed without human intervention. Such methods may have a direct implication on chip-scale robotics and chiral nanophotonic interfaces.

Simultaneous detection of spin and orbital angular momentum of light through scattering from a single silver nanowire

“…Here we observe 3 lobes, instead of 2 like in the case of LG 1 0 beam, indicating the magnitude of the topological charge (n + 1 lobes for LG n 0 beam). 41 The corresponding It is important to notice that the directionality values we get in the sub-critical region for σ + polarized beam is lower for LG 2 0 beam than that of LG 1 0 beam. This is because, as the topological charge magnitude of LG beam increases, the magnitude of the orbital flow increases (supplementary information S6), and dominates the total energy flow and hence it will be more difficult to distinguish the effect of the spin flow.…”

“…32,33 The uniform morphology renders them useful for low loss surface plasmon waveguiding property 34 and makes them ideal for fundamental photonic circuit applications such as plasmonic waveguide, 34,35 plasmonic antenna, 36,37 logic gates 38 as well as for optoelectrical applications. 39 Additionally, in our previous reports we have shown how an AgNW can act as a plasmonic scatterer in sensing total energy flow of an incident beam 40,41 and as well as probing the inherent spin-Hall effect. 42 In this work, a single AgNW dropcasted on a glass substrate has been used as a nanoscopic strip diffractor and the scattered pattern has been extensively analyzed to ascertain the spin and orbital angular momentum state of the incident light, as shown in Figure 1.…”

“…It must also be observed that both FP intensity distribution for x and y polarized LG 1 0 beam exhibit two lobes as well as preferential scattering pattern due to their orbital flow. 41 But, the preference for x polarized case is opposite to that of y polarized case. This can be attributed to the polarization dependent interaction of the NW with the incident beam.…”

“…The focal optical field and its orbital and spin flow constituents, upon interaction with a nano structure will lead to flow dependant scattering allowing us to determine its state. Although different nano-structures have been shown to have exhibited orbital flow dependant scattering, 29,30,40,41,46 differential sensing of spin and orbital flow is yet to be achieved by a single nano-object. To that end, we use a single crystalline silver nanowire (AgNW) to scatter the incident optical field and sense its properties.…”

Probing and Imaging Photonic Spin‐Orbit Interactions in Nanostructures

“…[ 106,107 ] It is worth mentioning that multiple effects can be combined to realize more complex functionalities, such as sorting different OAM states [ 108–110 ] and OAM readout. [ 111–113 ] More importantly, PSOI can be regarded as an optical analogy of the quantum dynamic property of electrons. Except for the QSHE of light, the optical Rashba effect [ 114–116 ] and optical skyrmions [ 117–119 ] have also been demonstrated, providing an alternative and less expensive way to study fundamental particle behaviors.…”