Direct measurement of proton-beam-written polymer optical waveguide sidewall morphorlogy using an atomic force microscope

The atomic force microscopy (AFM) technique was used to investigate the sidewall morphologies of proton-beam-written polymer waveguide structures fabricated with different stage scanning speeds. The proton-beam writing (PBW) is a direct-write micromachining technique capable of fabaricating low-loss single-mode polymer waveguides with straight and smooth sidewalls. The statistical information such as the rms roughness and the correlation length of the sidewall profile obtained from AFM scans allowed the quantification of the quality of the sidewalls and optimization of the fabrication parameters using PBW. The results show a rms roughness of 3.8±0.3 nm for a stage scanning speed of ∼10 μm/s.