טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentShitrit Nir
SubjectSpinoptical Metasurface Route to Spin-Controlled Photonics
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Erez Hasman
Full Thesis textFull thesis text - English Version


Abstract

Photonic metasurfaces are metamaterials with reduced dimensionality composed of engineered subwavelength-scale meta-atoms enabling a custom-tailored electromagnetic response of the medium. The peculiarity of metasurfaces is their ability to produce an abrupt phase change over a subwavelength distance, ushering in molding optical wavefronts with ultrathin planar components. Alongside, spinoptics provides an additional route to control light, whereby the photon helicity (spin angular momentum) degeneracy is removed due to a geometric gradient onto a metasurface. 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 observe the optical spin Hall effects in plasmonic chains manifested by a spin-dependent momentum redirection. The effect occurring solely as a result of the curvature of the coupled localized plasmonic chain is regarded as the locally isotropic effect, while the locally anisotropic effect arises from the interaction between the optical spin and the local anisotropy of the plasmonic mode rotating along the chain. A wavefront phase dislocation is observed, in which the dislocation strength is enhanced by the locally anisotropic effect. In the near field, we introduce spin-controlled plasmonics based on interfering topological defects. We utilize the scattering dynamics of surface plasmons from localized vortex sources to create spinoptical devices as an ensemble of nanoantennas to observe a spin-dependent plasmonic vortex and a plasmonic focusing lens.

We also show that polarization-controlled optical modes of metasurfaces arise where the spatial inversion symmetry is violated. The emerged spin-split dispersion of spontaneous emission due to the optical Rashba effect originates from the spin-orbit interaction of light, generating a selection rule based on symmetry restrictions in an inversion asymmetric spinoptical metasurface of anisotropic optical antenna patterns. Additionally, we observe a polarization helicity degeneracy removal in a surface-wave excitation via Rashba-type metasurfaces. By designing the metasurface symmetry using nanoantennas with space-variant orientations, we govern the light-matter interaction to control the propagation direction, arising in spin-based surface-wave wavelength tunable unidirectional and multidirectional excitations. We also control the photonic transport by disordered metasurfaces, supporting extraordinary information capacity, with a custom-tailored geometric phase. By manipulating the local orientations of anisotropic nanoantennas, we observe spin-dependent near- and far-field open channels providing a route for multitask wavefront shaping via a single ultrathin nanoscale photonic device. Spinoptical metasurfaces pave the way for new era of light manipulation via state-of-the-art polarization-based nanophotonic devices which can integrate with nanoelectronic circuits.