Waveguides and proportional beam splitters in bulk poly(methyl methacrylate) produced by direct femtosecond-laser inscription

•Waveguides of diverse structures were successfully achieved in PMMA by direct femtosecond-laser inscription.•Waveguides were demonstrated to be optimized by adjusting the fabricating parameters.•Planar structures of 1 × 2 beam splitter and 3D structures of 1 × 4 beam splitter were successfully fabricated.•The 1 × 2 beam splitter of proportional splitting ratio was achieved based on Type-I waveguides.

Waveguides fabricated by direct femtosecond-laser inscription were reported in bulk poly(methyl methacrylate) (PMMA). Optimization of waveguide structures was conducted and 1 × 2 beam splitters with equal and proportional splitting ratio were fabricated. Three-dimensional structures of 1 × 4 beam splitters were also achieved based on 1 × 2 beam splitters. The largest change of the refractive index between femtosecond laser modified area and unmodified area was estimated to be 1.1 × 10−3. The minimum insertion loss of the single-mode waveguide measured with the He–Ne laser at the wavelength of 632.8 nm was 4.32 dB and propagation loss was calculated to be as low as 3.57 dB/cm.