Optical vortex beam generator at nanoscale level

Denis Garoli,Francesco De Angelis,Francesco Tantussi,Pierfrancesco Zilio,Yuri Gorodetski

doi:10.1038/srep29547

Denis Garoli, Francesco De Angelis + Show 3 more

Open Access

https://doi.org/10.1038/srep29547

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Abstract

Optical beams carrying orbital angular momentum (OAM) can find tremendous applications in several fields. In order to apply these particular beams in photonic integrated devices innovative optical elements have been proposed. Here we are interested in the generation of OAM-carrying beams at the nanoscale level. We design and experimentally demonstrate a plasmonic optical vortex emitter, based on a metal-insulator-metal holey plasmonic vortex lens. Our plasmonic element is shown to convert impinging circularly polarized light to an orbital angular momentum state capable of propagating to the far-field. Moreover, the emerging OAM can be externally adjusted by switching the handedness of the incident light polarization. The device has a radius of few micrometers and the OAM beam is generated from subwavelength aperture. The fabrication of integrated arrays of PVLs and the possible simultaneous emission of multiple optical vortices provide an easy way to the large-scale integration of optical vortex emitters for wide-ranging applications.

Highlights

Optical beams carrying orbital angular momentum (OAM) can find tremendous applications in several fields
Light carrying orbital angular momentum has become the focus of a wide spectrum of research lines, with applications ranging from astronomy[1] to microscopy[2], free-space communication[3,4] and plasmonics[5,6,7,8,9,10,11,12]
We numerically demonstrated that the hole size is an important parameter to be tuned in order to successfully transmit a pure OAM state

Summary

Introduction

Optical beams carrying orbital angular momentum (OAM) can find tremendous applications in several fields. Our plasmonic element is shown to convert impinging circularly polarized light to an orbital angular momentum state capable of propagating to the far-field. PVLs transform the spin angular momentum (SAM) carried by an incident circularly polarized light beam into the OAM of the PV17–20, but can impress in principle any amount of AM, depending of the chirality (namely, the number of spiral arms) of the PVL itself. We demonstrate by numerical simulations that the hole diameter plays an important role in determining the OAM beam purity This allowed us to tune the hole radius in order to produced almost pure OAM states, which is confirmed by experimental results

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