Femtosecond laser writing of waveguide retarders in fused silica for polarization control in optical circuits.

Femtosecond laser (300 fs, 500 kHz, 522 nm) fabrication of optical waveguides in bulk silica glass is extended to waveguide retarders. We study the merits of nanograting orientation (perpendicular or parallel to the waveguide) for generating high and low birefringence waveguides. This is used together with other exposure condition to control the waveguide birefringence between 10⁻⁵ and 10⁻⁴ permitting for the simultaneous fabrication of the waveguides and the tuning of the retardance demonstrating quarter and half-wave retarders in the 1200 nm to 1700 nm spectrum. The wavelength dependence of the birefringence is also characterized over a range of exposure conditions.