Optimization of waveguide structures for beam splitters fabricated in fused silica by direct femtosecond-laser inscription

•Type-I waveguides were fabricated by direct femtosecond-laser inscription.•Optimization of the waveguides was demonstrated by adjustment of the parameters.•Planar structures of 1×2 beam splitter were achieved based on Type-I waveguides.•3D structures of 1×4 beam splitter were achieved based on 1×2 beam splitter.

The Type-I waveguides fabricated by femtosecond laser inscription were reported in fused silica. Optimization of waveguide structures was conducted for fabricating 1×2 and 1×4 beam splitters. The change of the refractive index between femtosecond laser modified area and unmodified area was estimated to be 9×10−4. The minimum loss of the waveguides measured with the He–Ne laser at the wavelength of 632.8 nm was determined to be as low as 1.34 dB.