Facile fabrication and optical properties of polymer waveguides with smooth surface for board-level optical interconnects

Polymer waveguides fabricated via conventional lithography or imprinting method usually have step refractive index (SI) cores. For these SI-type polymer waveguides, the surface roughness, especially sidewall roughness may induce rough-interface scattering loss, which is one of the main contributions to the signal attenuation. In this work, on the basis of imprinting method, a novel fabrication method combining thermal reflow process was developed to prepare highly desired optical polymer waveguides. The basic shapes and sizes of pre-fabricated waveguides were conveniently defined by an elastomer stamp with reverse structures of final waveguide link network. The elastomer stamp used for imprinting was fabricated by duplicating the morphology of an initial master following standard replica molding protocols. Then the pre-fabricated waveguides were treated with a low-temperature thermal reflow process to improve the surface quality via the interaction of surface tension and internal stress. The influence of processing parameters on the profiles of the resultant polymer waveguides was systematically investigated and the mode-of-action of thermal reflow process was also proposed. Finally, the optical transmittance properties, including the transmission loss and inter-channel crosstalk of the obtained polymer were investigated, and the corresponding results were carefully discussed. Owing to the decreasing scattering loss induced by surface roughness and the finely-tuned geometry, the as-fabricated waveguides exhibited better optical performance than those of polymer waveguides fabricated via photolithography. Compared with waveguides obtained by conventional photolithography, the resultant multimode optical polymer waveguides with three-dimensional smooth surface exhibited essentially lower propagation loss (0.28 dB/cm) and inter-channel crosstalk (< − 30 dB). This work presented here offers new insights for developing polymer waveguides with high surface quality and good optical performance for board-level optical interconnects by a facile and cost-effective approach.