Active control of transmission and helicity of nanostructured optical beams via magnetoplasmonic vortex lens

Structured optical beams have become a subject of an intense research, due to numerous potential applications in, among many others, super-resolution imaging, optical tweezing, and telecommunications. Special interest is... [ view full abstract ]

Structured optical beams have become a subject of an intense research, due to numerous potential applications in, among many others, super-resolution imaging, optical tweezing, and telecommunications. Special interest is dedicated to the interaction of structured light with metallic nanostructures, resulting in Surface Plasmon Polaritons (SPPs) carrying an orbital angular momentum (OAM). These surface confined electromagnetic distributions are generally defined by a field singularity surrounded by a helical phase front, referred here as plasmonic vortices (PVs). Besides, various practical applications in nanophotonics require fast external control of the emerging beam characteristics. In this regard magnetoplasmonic devices draw a very promising route to active nanophotonics, since an externally applied magnetic field can alter the plasmonic response leading to novel and unexpected effects [1, 2]. The main requirement of these devices is to be fabricated from a material that has both plasmonic and magnetic properties, for instance hybrid noble metal/magnetic materials. Recently we have demonstrated an efficient PV coupling to the free space via adiabatically tapered gold tip at its center [3, 4]. Here we demonstrate an architecture where a PV excited in a gold surface propagates on an adiabatically tapered magnetoplamonic tip and detaches to the far-field while carrying a well-defined OAM and helicity. We analyze the light transmission and show that, despite generally high losses of flat magnetic surface, our 3D structure exhibits high energy throughput. Moreover we show that the helicity and the OAM of the emitted beam can be tuned by applying an external and relative small (< 0.5 T) magnetic field, providing optimistic opportunities for active magnetically-driven plasmon-based structured optical beams [5].

References

[1] Armelles, G. et al., Advanced Optical Materials 1, 10-35 (2013).

[2] Maccaferri, N. et al., Nature Communications 6, 6150 (2015).

[3] Garoli, D. et al., Nano Letters 16(10), 6636–6643 (2016).

[4] Garoli, D. et al., Nanoscale 9, 6965-6969 (2017).

[5] Maccaferri, N. et al., submitted (2017).