Direct generation of optical vortices

Abstract

A detailed scheme is established for the direct generation of optical vortices, signifying light endowed with orbital angular momentum. In contrast to common techniques based on the tailored conversion of the wave front in a conventional beam, this method provides for the direct spontaneous emission of photons with the requisite field structure. This form of optical emission results directly from the electronic relaxation of a delocalized exciton state that is supported by a ringlike array of three or more nanoscale chromophores. An analysis of the conditions leads to a general formulation revealing a requirement for the array structure to adhere to one of a restricted set of permissible symmetry groups. It is shown that the coupling between chromophores within each array leads to an energy level splitting of the exciton structure, thus providing for a specific linking of exciton phase and emission wavelength. For emission, arrays conforming to one of the given point-group families' doubly degenerate excitons exhibit the specific phase characteristics necessary to support vortex emission. The highest order of exciton symmetry, corresponding to the maximum magnitude of electronic orbital angular momentum supported by the ring, provides for the most favored emission. The phase properties of the emission produced by the relaxation of such excitons are exhibited on plots which reveal the azimuthal phase progression around the ring, consistent with vortex emission. It is proven that emission of this kind produces electromagnetic fields that map with complete fidelity onto the phase structure of a Laguerre-Gaussian optical mode with the corresponding topological charge. The prospect of direct generation paves the way for practicable devices that need no longer rely on the modification of a conventional laser beam by a secondary optical element. Moreover, these principles hold promise for the development of a vortex laser, also based on nanoscale exciton decay, enabling the production of coherent radiation with a tailor-made helical wave front.

Analytical investigation of optical vortices emitted from a collectively polarized dipole array

“…The compact optical vortex emitters were fabricated to convert the optical modes from whispering-gallery-modes to optical vortices [15,16]. On the other hand, the direct excitation of several emitters for producing optical vortices were recently studied in a ring molecules [17] and an antenna array [18]. This method has a potential to produce optical vortices by controlling the source conditions of the emitters without any modification of the system structure.…”

Quantum delocalization in photon-pair generation

“…Arguably the most well-known application of the theory is the formulation of the Casimir-Polder potential [47]-which takes due account of retardation effects. Contemporary examples of the spheres of application include optical trapping [48][49][50][51][52] optical binding [53][54][55][56][57][58], and optical vortices [59][60][61][62], to name but a few.…”

Nanoarrays for the generation of complex optical wave-forms

“…The theoretical basis for the direct generation of an optical vortex beam is based on a structured array composed of a number of nanoemitters; [10][11][12] for the purposes of this paper, the number chosen is five. By adopting such an array with a geometric configuration shown in Figure 1, it is possible to exploit phase relationships between the quantum amplitudes associated with emission from differing positions.…”