Optimization of Broadband Y-Junction Splitters in Fused Silica by Femtosecond Laser Writing

Optical Y-junction power splitters owe their inherent broadband spectral behavior to their design. However, depending on the fabrication technique employed, asymmetries in the junction might arise, perturbing its performance; this is the case in femtosecond laser written Y-junctions where one arm is typically written over the top of the other. In this letter, the spectral behavior of Y-junctions fabricated in fused silica by the femtosecond laser direct writing technique was analyzed and optimized for the first time, to the best of our knowledge. The junction arms output power balance as well as the corresponding spectral flatness between 1300 and 1600 nm is substantially increased by the implementation of an initial separation between the arms at the junction diverging point, enabling the manufacturing of balanced broadband Y-junctions.