Ultra-secure optical encryption based on tightly focused perfect optical vortex beams

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 to implement Fourier transform of an ideal Bessel mode with both amplitude and phase modulations is proposed to generate radius-controllable POV in tightly focused beams. Such focused POV beams with identical intensity profiles but varied local OAM density 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.

Automated summary

This paper investigates the application of light's orbital angular momentum (OAM) in optical encryption and proposes a tightly focused optical vortex beam for ultra-secure image encryption. By modulating the amplitude and phase of the beam, the annular intensity profiles and OAM states of the beam can be controlled. Information is encoded through the selective excitation of electromagnetic hot spots.