Radial mode dependence of optical beam shifts

Corrected theory for transmitted Goos-Hänchen and Imbert-Fedorov shifts

We analyze the role of the energy flow coefficient in beam shifts and develop the theory of the angle spectrum method to calculate the beam shifts of polarized beam reflection and transmission. By applying the self-consistency between the law of conservation of momentum and the angular Goos-Hänchen (GH) shift, we prove the necessity of the correcting energy flow coefficient of the transmitted light fields. For the air-glass interface, we find that the influence of the energy flow coefficient on the angular GH shift is very pronounced in the case of close grazing.

Depolarization of Light in Optical Fibers: Effects of Diffraction and Spin-Orbit Interaction

Polarization is measured very often to study the interaction of light and matter, so the description of the polarization of light beams is of both practical and fundamental interest. This review discusses the polarization properties of structured light in multimode graded-index optical fibers, with an emphasis on the recent advances in the area of spin-orbit interactions. The basic physical principles and properties of twisted light propagating in a graded index fiber are described: rotation of the polarization plane, Laguerre–Gauss vector beams with polarization-orbital angular momentum entanglement, splitting of degenerate modes due to spin-orbit interaction, depolarization of light beams, Berry phase and 2D and 3D degrees of polarizations, etc. Special attention is paid to analytical methods for solving the Maxwell equations of a three-component field using perturbation analysis and quantum mechanical approaches. Vector and tensor polarization degrees for the description of strongly focused light beams and their geometrical interpretation are also discussed.

Vector Laguerre-Gauss beams with polarization-orbital angular momentum entanglement in a graded-index medium

It is shown that the vector-vortex Laguerre-Gauss modes with polarization-orbital angular momentum (OAM) entanglement are the vector solutions of the Maxwell equations in a graded-index medium. Focusing of linearly and circularly polarized vortex light beams with nonzero azimuthal and radial indices in a cylindrical graded-index waveguide is investigated. The wave shape variation with distance taking into account the spin-orbit and nonparaxial effects is analyzed. The effect of long-term periodic revival of wave packets due to mode interference in a graded-index cylindrical optical waveguide is demonstrated. High efficiency transfer of a strongly focused spot through an optical waveguide over large distances takes place with a period of revival.

Subluminal group velocity and dispersion of Laguerre Gauss beams in free space

That the speed of light in free space c is constant has been a pillar of modern physics since the derivation of Maxwell and in Einstein’s postulate in special relativity. This has been a basic assumption in light’s various applications. However, a physical beam of light has a finite extent such that even in free space it is by nature dispersive. The field confinement changes its wavevector, hence, altering the light’s group velocity v_g. Here, we report the subluminal v_g and consequently the dispersion in free space of Laguerre-Gauss (LG) beam, a beam known to carry orbital angular momentum. The v_g of LG beam, calculated in the paraxial regime, is observed to be inversely proportional to the beam’s divergence θ₀, the orbital order ℓ and the radial order p. LG beams of higher orders travel relatively slower than that of lower orders. As a consequence, LG beams of different orders separate in the temporal domain along propagation. This is an added effect to the dispersion due to field confinement. Our results are useful for treating information embedded in LG beams from astronomical sources and/or data transmission in free space.

Observation of photonic spin Hall effect with phase singularity at dielectric metasurfaces

Observation of photonic spin Hall effect (SHE) near the phase singularity at dielectric metasurfaces is presented. The structured metasurface works as a space-variant Pancharatnam-Berry phase element and produces a vortex beam with phase singularity. The dynamical vortex phase is introduced to eliminate or enhance the phase singularity, thus realizing the manipulation of spin-dependent Pancharatnam-Berry phase. The spin-orbit coupling near the singularity of the Pancharatnam-Berry phase leads to the observation of the photonic SHE which manifests itself as spin-dependent splitting. The underlying mechanism is significantly different from previously reported cases. It thereby provides an alternative way to manipulate the spin states of photons.

Reflection of Laguerre-Gaussian beams carrying orbital angular momentum: a full Taylor expanded solution

Partial reflection of linearly polarized Laguerre-Gaussian beams incident at a dielectric interface are studied beyond the paraxial regime. Based on the angular spectrum method and Taylor series expansion, we derive exact analytical expressions for the reflected electric field. This result holds in both the paraxial and nonparaxial regimes. The result is then extended to beams of arbitrary polarization and used to analytically calculate the transverse and longitudinal shifts of the beams' center of gravity. Finally, several numerical examples are performed to verify the analytical formulas we derived near the Brewster angle.

Spin Hall effect of light measured by interferometry

We demonstrate a experimental method to measure the spin Hall effect of light (SHEL), which is based on the interference between two orthogonal circularly polarized beams with the help of a polarizer. Our method can measure the SHEL across the entire exit pupil, not only at the centroid as is the case with earlier methods, and hence one can scan the transverse section of the beam. We measured the SHEL of an aluminium mirror and a glass plate using a He-Ne laser at wavelength 633 nm, for incidence angles varying from 22° to 70°. The experimental results are in good agreement with theory. We also measured the shift across the transverse section of a Gaussian beam using same method.

Weak measurements of a large spin angular splitting of light beam on reflection at the Brewster angle

We reveal a large spin angular splitting of light beam on reflection at the Brewster angle both theoretically and experimentally. A simple weak measurements system manifesting itself for the built-in post-selection technique is proposed to explore this angular splitting. Remarkably, the directions of the spin accumulations can be switched by adjusting the initial handedness of polarization.