Proton-beam writing of poly-methylmethacrylate buried channel waveguides

In this paper, the authors report on the fabrication and characterization of poly-methylmethacrylate (PMMA) buried channel waveguides. The waveguides were fabricated using an emerging lithographic technique known as proton-beam writing. Depending on the proton fluence used, two different waveguide-formation mechanisms are possible. Single-mode waveguides with the light confinement occurring at the end of range were fabricated using fluences < 75 nC/mm². The refractive-index profiles of these single-mode waveguides were recovered using the propagation mode near-field method. For fluences > 100 nC/mm², multimode waveguides may also be fabricated with the light confinement occurring beneath the end of range. The compaction of the PMMA surface after proton irradiation was investigated using an atomic force microscope. The propagation losses of these PMMA waveguides were also determined.