Generating tightly focused perfect optical vortex for ultra-secure optical encryption

TL;DR

This paper demonstrates ultra-secure optical image encryption using tightly focused perfect optical vortex beams with controllable intensity profiles and orbital angular momentum states, enabling selective nanophotonic interactions for secure data encoding.

Contribution

It introduces a simple method to generate radius-controllable perfect optical vortex beams with identical intensity profiles but different OAM states for secure encryption.

Findings

Successfully generated focused POV beams with controllable radius.

Achieved selective excitation of electromagnetic hot spots in nanorod aggregates.

Enabled ultra-secure image encryption using OAM states and polarization diversity.

Abstract

Light's orbital angular momentum (OAM) with inherent mode orthogonality has been suggested as a new way to the optical encryption. However, the dependence of annular intensity profiles on the topological charge complicates nanoscale light-matter interactions and hampers the ultra-secure encryption application. In this paper, we demonstrate ultra-secure image encryption by tightly focusing perfect optical vortex (POV) beams with controllable annular intensity profiles and OAM states. A simple scheme composed of single spatial light modulator is proposed to generate radius-controllable POV in tightly focused beams. Such focused POV beams with identical intensity profiles but varied OAM states are applied to disorder-coupled gold nanorod aggregates to selectively excite electromagnetic hot spots for encoding information through photothermal deformation. As such, ultra-secure image encryption in OAM states of POV beams in combination with different polarizations can be achieved. Our results lay the ground for diverse nanophotonic applications harnessing the OAM division of POV beams.