Spin-to-orbital conversion of the angular momentum of light and its classical and quantum applications

Abstract

Few years ago the possibility of coupling and inter-converting the spin and orbital angular momentum (SAM and OAM) of paraxial light beams in inhomogeneous anisotropic media was demonstrated. An important case is provided by wave-plates having a singular transverse pattern of the birefringent optical axis, with a topological singularity of charge q at the plate center, hence named "q-plates". The introduction of q-plates has given rise in a few years to a number of new results and to a significant progress in the field of orbital angular momentum of light. Particularly promising are the quantum photonic applications, because the polarization control of OAM allows the transfer of quantum information from the SAM qubit space to an OAM subspace of a photon and vice versa. In this paper, we review the development of the q-plate idea and some of the most significant results that have originated from it, and we will briefly touch on many other related findings concerning the interaction of the SAM and OAM of light.

Manipulating the Orbital Angular Momentum of Light at the Micron Scale with Nematic Disclinations in a Liquid Crystal Film

“…A few years ago, the topological features of the local average molecular orientation of nematic liquid crystals-the director-around the defects were shown to enable the manipulation of the orbital degree of freedom of light by its polarization state via the spin-to-orbital optical angular momentum conversion phenomenon [2]. Since then, a wide range of classical or quantum applications have emerged in optics [3].…”

Optical helicity of interfering waves

“…Remarkably, the helicity flux density, s, is also the candidate for the spin density of an optical field that was put forward recently by one of us [3]. Indeed, the volume integral of s is the total spin, S, of an optical field [3][4][5]31,36], the correct form of which is due to Darwin [36,37] and to Humblet [38,39]. Although they are related, we emphasise that the optical helicity, H, and the optical spin, S, are distinct: whereas the helicity of a photon in a circularly-polarised plane wave mode is ± , its spin is ± k/|k|.…”

Subwavelength chiral surface plasmons that carry tuneable orbital angular momentum

“…7 However, interest in the angular momentum of light was reawakened in 1992 when it was demonstrated 8 that Laguerre-Gaussian beams can transport orbital angular momentum (OAM). [9][10][11][12] The OAM of EM fields has been also studied using plasmonic vortex structures, 13,14 and it has been extensively used in research areas as diverse as biophysics, micromechanics, and microfluidics. 15 At a quantum level, single photons with OAM have the potential for realizing highdimensional quantum spaces with applications in information technologies.…”