Spin-orbit interactions in optically active materials

Abstract

We investigate the inherent influence of light polarization on the intensity distribution in anisotropic media undergoing a local inhomogeneous rotation of the principal axes. Whereas in general such configuration implies a complicated interaction between geometric and dynamic phase, we show that, in a medium showing an inhomogeneous circular birefringence, the geometric phase vanishes. Due to the spin-orbit interaction, the two circular polarizations perceive reversed spatial distribution of the dynamic phase. Based upon this effect, polarization-selective lens, waveguides and beam deflectors are proposed.The simplest approaches in wave optics model light as a scalar wave, an approximation valid only for paraxial beams propagating in isotropic homogeneous media [1]. The electromagnetic nature of light implies that photons have spin, appearing in the Maxwell's equations as the field polarization. Nonetheless, in case of paraxial waves propagating in isotropic materials, the spatial degree of freedom (i.e., the field distribution) is independent of the polarization. This is not rigorously true due to the vectorial nature of the Maxwell's equation, leading to a socalled classical entanglement [2,3]. The discrepancies between the two approaches are significant, for example, in case of non-paraxial beams leading to polarizationdependent focusing [4], or for polarization-dependent trajectory of light in inhomogeneous materials, the so called optical Magnus effect, aka spin Hall effect (SHE) of light [5][6][7][8].In this context, the investigation of spin-orbit interaction is rapidly becoming a central topic in optics [9]. Photons have been demonstrated to be a unique tool for the investigation of basic quantum field theory [10,11]. On the other hand, spin-orbit interaction paves the way to a new family of ultra-thin photonic devices, including gratings [12] In anisotropic media another type of geometric phase arises, the Pancharatnam-Berry phase (PBP). PBP appears in the presence of a rotation of the beam polarization for a fixed wave-vector. Noteworthy, in anisotropic materials spin-orbit effects, such as birefringence or spatial walk-off, are observed even for plane waves due to the * alessandro.alberucci@gmail.com dependency on polarization of the light-matter interaction [21]. Nonetheless, the presence of PBP in anisotropic media widens the spectrum of the observable spin-orbit effects [12,13,16], including the nonlinear case [22,23]. The PBP affects the wavefront, and thus light propagation, when the anisotropic medium is inhomogeneous and showing a point-wise rotation of the principal axes across the intensity profile. In this Letter we first analyze light propagation in inhomogeneously rotated materials considering the trade-off between the PBP and diffraction. We show that PBP vanishes if the material is optically active, the field propagation then being affected by dynamic phase alone. Unlike Refs. [5,6,8] where geometric optics is used, here the wave behavior of the electromagnetic radiation is accounted fo...

Observation of asymmetric electromagnetic field profiles in chiral metamaterials

“…6 is analogous to circulating electric current around a scatter with spin-orbit interaction, which is similar to the side-jump mechanism in electronic systems. In the past decade spin-orbit interaction of light in an analogy between light and electrons has been intensively studied in connection with the spin-Hall effect [42,43,[47][48][49][50]. The present result provides an insight to the understanding of spin-orbit interaction of light.…”

“…A superposition between the radiation and scattering may break a balance between left-handed and right-handed circularly polarized microwaves, resulting in the optical activity by the chiral meta-atom. Based on an analogy between light and electrons, the optical activity in photonic systems corresponds to the spin-orbit interaction in electronic systems [42,43]. Additionally, an electromagnetic Poynting vector represents the velocity of the center of gravity, corresponding to electric currents.…”

Interplay between Spin and Orbital Angular Momenta in Tightly Focused Higher‐Order Poincaré Sphere Beams

“…[ 3 ] By contrast, they can strongly couple with each other in nonparaxial fields. [ 4 ] Actually, spin‐orbit interactions (SOIs) are universal phenomena in optics and photonics especially at the subwavelength scales, such as the spin‐Hall effects in inhomogeneous media and at optical interfaces, [ 5–8 ] spin‐dependent effects in focused or scattered fields, [ 9–12 ] spin‐controlled shaping of light using metasurfaces, and robust spin‐directional coupling via evanescent near fields. [ 13–15 ] Recently, SOI effects have been widely applied in classical and quantum optics.…”

Spin and orbital angular momentum dynamics in counterpropagating vectorially structured light

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