Laser-written polarizing directional coupler with reduced interaction length

Integrated optical waveguides, manufactured with femtosecond laser writing (FSLW) technology, enable precise control and manipulation of light in complicated photonic chips. However, due to the intrinsically low anisotropy of FSLW waveguides, polarizing integrated devices have had a relatively large footprint. In this Letter, we demonstrate an approach based on stress-induced anisotropy, allowing us to decrease the size of polarizing directional couplers down to 3.7 mm, almost an order of magnitude shorter than previously reported. The measured extinction ratios at the wavelength of 808 nm are 16 dB and 20 dB for the horizontal and vertical polarizations, respectively. We provide a possible theoretical model for the observed effects.