Tailoring the birefringence of femtosecond-laser-written multi-scan waveguides in glass

TL;DR

This paper demonstrates a multi-scan femtosecond laser writing technique in glass that allows precise control over the birefringence magnitude and axis orientation of waveguides, enhancing their suitability for complex photonic applications.

Contribution

It introduces a novel multi-scan method to independently tune birefringence properties in femtosecond laser-written waveguides in fused silica.

Findings

Independent control of birefringence magnitude and axis achieved.

Low-loss waveguides with tailored birefringence demonstrated.

Efficient mode coupling with standard fibers maintained.

Abstract

Femtosecond-laser direct waveguide writing is progressively emerging as an alternative to conventional techniques to develop complex photonic devices, for applications ranging from classical and quantum information processing, to sensing and metrology. Laser written waveguides typically offer low modal birefringence, thus preserving coherence of polarization-encoded information. Integrated waveplates have been reported, as waveguides with tilted birefringence axis, but with limited flexibility in terms of achievable rotation angle, birefringence magnitude or control in the modal shape. Here we investigate the multi-scan approach to realize low-loss optical waveguides in fused silica substrate with controlled modal birefringence. We show that by tuning the horizontal and vertical shifts between subsequent scans we can independently change both the magnitude and the axis inclination of the birefringence, while keeping efficient mode coupling with standard fibers.