Berry phases and spin-orbit optical phenomena

Lorenzo Marrucci, Universita' di Napoli Federico II, Italy.

Spin-orbit optical phenomena involve an interaction between the light polarization and the wave spatial structure, interaction that can be best understood and described in terms of the spin eigenstates of light, or the circular polarization components [1]. Such phenomena are also inextricably linked to the Berry geometric phases arising whenever the local vectorial structure of the optical fields varies, either because of polarization manipulations in anisotropic media (Pancharatnam-Berry phases) or because of optical ray deflections in inhomogeneous media (Rytov-Vladimirskii-Berry phases) [2].

In the last decade, a number of optical phase elements that exploit in particular the Pancharatnam-Berry (PB) geometric phase for manipulating the optical wavefront has been demonstrated. All such PB-phase optical devices are very thin, with a thickness which is very small compared to the Rayleigh length of the optical beam.

A conceptual extension of the same working principle has very recently led to conceiving also the possibility of confining and guiding light across several Rayleigh lengths by using only the geometric phases arising in polarization manipulations [3]. This entirely novel waveguiding effect can be achieved with no spatial modulation of the refractive index, because the optic axis is kept everywhere orthogonal to the wavevector. This can be for example implemented in liquid crystal materials which have been patterned in 3D in a suitable way.

A first proof-of-principle experimental demonstration has been carried out by using a sequence of geometric-phase lenses arranged so as to simulate a waveguide [3].

References

          [1]      F. Cardano, L. Marrucci, Nature Photon. 9, 776-778 (2015).

          [2]      K. Y., Bliokh, F. J. Rodríguez-Fortuño, F. Nori, A. V. Zayats, Nature Photon. 9, 796-808 (2015).

          [3]      S. Slussarenko, A. Alberucci, C. P. Jisha, B. Piccirillo, E. Santamato, G. Assanto, L. Marrucci, Nature Photon. 10, 571-575 (2016).