Fabrication of Pancharatnam-Berry Waveguides Using Nanogratings

Waveguides based on the Pancharatnam-Berry phase (PBP) [1] exploit the geometric phase that light acquires upon a cyclic polarization transformation. In such a waveguide, the optic axis must spatially vary in the transverse plane in an even symmetric manner and be periodically modulated along the propagation direction. The longitudinal modulation enables a net accumulation of PBP [1] and results in a spin-dependent effective trapping potential proportional to the maximum rotation angle <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\theta_{0}$</tex>. If the modulation period deviates from the birefringence length, the guiding properties of the waveguide is modified [2].