Photonic structure with SU-8 waveguides enhanced by gold nanoarrays and indium tin oxide for Lab-on-a-Chip systems

This work presents an optical analysis of indium tin oxide (ITO) thin films as buffer layers to enhance light coupling and scattering in integrated photonic devices consisting of SU-8 polymer waveguides overlaid with gold (Au) periodic nanoarrays. The aim is to provide a low-cost, fabrication-compatible strategy for improving optical performance without altering the array geometry. Finite-Difference Time-Domain (FDTD) simulations in the visible spectrum are employed to evaluate the impact of ITO on waveguide-to-array coupling efficiency, out-of-plane scattering, and far-field beam characteristics - including intensity, focus, and deflection angle - across various grating and nanocylinder configurations. Results demonstrate that ITO significantly enhances coupling efficiency (up to 12 times for 350 nm-pitched nanocylinder arrays) and out-of-plane scattering (up to 2 times for 240 nm-pitched gratings), while preserving beam focus and angular properties. However, the performance gain is depend-ent on both the structural pitch and operational wavelength, with some configu-rations showing limited or adverse effects. The integration of ITO also offers dual functionality in biosensing applications, providing an easily functionaliza-ble surface in addition to gold, thereby enhancing chemical sensitivity. Given its compatibility with physical vapor deposition, ITO represents a simple, rapid, and cost-effective method for performance optimization in waveguide-integrated plasmonic devices, particularly where redesign or re-fabrication of nanostructures is impractical.