Femtosecond Laser Writing Of Polarization Devices For Optical Circuits In Glass

Abstract

Waveguides fabricated in fused silica by femtosecond laser exposure have birefringent properties due to the inherent anisotropies of this nonlinear absorption mechanisms. This birefringence can be controlled by tuning the laser fabrication parameters and lead to the fabrication of polarization dependent devices with a wide range of photonic applications. A femtosecond fiber laser was used to fabricate optical waveguides and directional couplers with either low or high birefringence associated with strong form birefringence and the orientation of nanogratings that align perpendicular to the writing laser polarization. Birefringence measurements were demonstrated by the polarization splitting of Bragg grating stopbands, together with cross-polarization transmission of uniform waveguides, enabling the control of retardance and polarization dependent coupling. Zero-order quarter-wave and half-wave retarders together with polarization beam splitters were demonstrated with this technique.