Effectively writing low propagation and bend loss waveguides in the silica glass by using a femtosecond laser.

We report writing low-loss waveguides (WGs) by using a femtosecond laser in silica glass. A record low propagation loss of 0.07 dB/cm is achieved, and the lowest bend loss reaches 0.001 dB/mm with the bend radius of 30 mm. The optimal effective writing speed reaches 125 µm/s, which is two orders higher than the previous reported value. Fan-out devices with well controllable low loss for three-dimensional photonic integration are also fabricated. This work provides an effective strategy to create WG devices for 3D high-density photonic integration.