Hybrid laser written waveguides in fused silica for low loss and polarization independence

Photonic integrated circuits (PICs) written with an ultrashort pulsed laser provide advantages in a range of applications, such as photon-based quantum information processing, where low insertion loss and low polarization dependence are critical concerns. Here we demonstrate the inscription of hybrid waveguides in fused silica at a pulse repetition rate of 1MHz that fulfill both these criteria. The mechanisms for propagation and coupling losses are identified and decoupled, with separate sections of the waveguide minimizing for each and an adiabatic mode conversion between the two. Moreover, differing sources of birefringence were revealed to be non-parallel for the waveguides, such that structures can be designed where these competing sources cancel to remove any polarization dependence.