טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentYulevich Igor
SubjectOptical Rashba Effect in Geometric Phase Metasurfaces
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Erez Hasman
Full Thesis textFull thesis text - English Version


Abstract

Optical Rashba effect is a spin-dependent transportation phenomenon of light as an analogy to its counterpart in condensed matter physics where electrons with opposite spins undertake different trajectories in a current flow. This discovery paved a unique way to manipulate particles by spin degree of freedom and opened up the research area of spintronics. In the field of spinoptics, optical Rashba effect provides a route to control light, whereby the photon helicity - spin angular momentum - degeneracy is removed due to a geometric phase gradient onto a metasurface. Metasurfaces are metamaterials with reduced dimensionality that produce an abrupt change of the phase over a subwavelength distance, ushering in molding optical wavefronts. We report that the alliance of spinoptics and metasurfaces via the geometric phase offers to govern the light-matter interaction of a structured matter in a polarization helicity-dependent manner.

     We observed a spin degeneracy breaking in thermal radiation emitted from an inhomogeneous anisotropic lattice composed of coupled antennas supporting surface waves. The spin degeneracy removal is manifested by a spin-dependent momentum splitting of the radiative mode which analogous to the Rashba effect in electronics. The spin split dispersion arises from the inversion asymmetry of the lattice. Our experiment confirms that the spatial rate of the inhomogeneity determines the degree of the spin-dependent momentum redirection. The influence of the inversion asymmetry on the dispersion was studied by comparing the results to those produced by homogeneous lattices and characterizing the behavior of the isolated thermal antennas.

     Additionally, we report on the observation of optical spin-controlled modes from a quasicrystal metasurface as a result of an aperiodic geometric phase induced by anisotropic subwavelength structure. When geometric phase defects are introduced in the aperiodic structured surface, the modes exhibit polarization helicity dependence resulting in the optical spin-Hall effect. The radiative thermal dispersion bands from a quasicrystal structure were studied where the observed bands arise from the optical spin-orbit interaction induced by the aperiodic space-variant orientations of anisotropic antennas. The optical spin-flip behavior of the revealed modes that arise from the geometric phase pickup was experimentally observed within the visible spectrum by measuring the spin-projected diffraction patterns. Geometric phase metasurfaces constitute a wide platform for spin-controlled nanophotonic applications based on the design of the metasurface symmetry properties. We believe our findings will leverage a new era of spin-enabled optics for future optical components.