Design optimization for manufacturing polymer microring lasers: Focus on surface scattering losses

Surface roughness scattering significantly affects the performance of microcavity lasers by influencing various design parameters. This study focuses on the design and fabrication of polymer-based microcavity lasers to achieve optimal specifications. We employed femtosecond direct laser writing on SU-8 films doped with Rhodamine B dye. Key parameters, including size, quality factor, mode volume, filling factor, and losses (bending and surface scattering), were theoretically analyzed. We specifically investigated the impact of sidewall roughness-induced scattering loss on polymer microring lasers, validating our findings through simulations and experimental characterization. Assuming a surface roughness of less than 10 nm, we designed and fabricated a single-mode double microring laser with radii of 30 µm and 32 µm, featuring a waveguide cross-sectional area of 1 × 2 µm². These high-performance single-mode lasers have potential applications in optical sensing, nonlinear optics, and quantum photonics.