טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentNiv Avi
SubjectSpace-Variant Polarization-state Manipulation by Use of
Subwavelength Gratings
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Erez Hasman


Abstract

A novel method for designing and realizing nonuniformly polarized beams using computer-generated space-variant subwavelength gratings is presented in this thesis. We show that by correctly determining the direction, period, and depth of the grating, one can obtain any desired continuous polarization. First, we demonstrate a Talbot effect involving a unique type of polarization-diffraction grating that comprises a periodic space-variant wave plate. We show that for any incident polarization the resultant field undergoes self-imaging and fractional Talbot effects that involve polarization, intensity and phase. We also demonstrate the formation of a class of nondiffracting beams with periodically space-varying polarization based on computer-generated subwavelength gratings. By correctly determining the local period and direction of the grating, we control the polarization and phase of the resulting field to yield propagation-invariant beams with uniform intensity and continuous space-varying polarization. The formation of linearly polarized axially symmetric beams based on computer-generated space-variant subwavelength gratings is also presented. In this case the polarization state manipulations are accompanied by phase modification of a helical structure that results from the Pancharatnam-Berry phase. We show that formation of a continuous half-integer polarization order linearly polarized axial symmetric beams must be accompanied by a Pancharatnam phase and that a beam with Pancharatnam phase of any polarization order does not maintain its polarization state during propagation. Finally, Propagation-invariant vectorial Bessel beams with linearly polarized axial symmetry based on quantized Pancharatnam-Berry phase optical elements are investigated. Using these beams we demonstrate controlled rotation of a propeller-shaped intensity pattern through simple rotation of a polarizer.