Spatially-rotatable telecom-band waveguide beam splitters fabricated by femtosecond laser in C7979 glass

We report on telecom-band depressed-cladding waveguides and Y-branch cladding-waveguide beam splitters fabricated by femtosecond laser in C7979 fused silica glass. The confocal micro-Raman (µ-Raman) spectroscopy shows that original material properties are almost unaffected in the cores of depressed-cladding waveguides. However, in femtosecond-laser-written track areas, there is a slight increase of µ-Raman intensity, corresponding to a negative change (about -0.0051) in refractive index. The effects of different splitting angles to output performances of Y-branch cladding-waveguide beam splitters have been investigated in this work. As for beam splitter with splitting angle of 1.14°, its spatial rotation (a rotation of the whole structure, including input and output parts) around propagation direction has been realized by simply designing and arranging femtosecond-laser-induced tracks, with splitting ratio of ∼1:1 almost unchanged. Our work paves a way to fabricate spatially-rotatable telecom-band waveguide beam splitters, having many potential applications in integrated photonics.