Bimodal Plasmonic Refractive Index Sensors Based on SU-8 Waveguides

Abstract: Plasmonic refractive index sensors are essential for detecting subtle variations in the ambient environment through surface plasmon interactions. Current efforts utilizing CMOS-compatible, plasmo-photonic Mach-Zehnder interferometers with active power balancing exhibit high sensitivities at the cost of fabrication and measurement complexity. Alternatively, passive bimodal plasmonic interferometers based on SU-8 waveguides present a cost-effective solution with a smaller device footprint, though they currently lack opto-mechanical isolation due to exposed photonic waveguides. In this work, we introduce innovative polymer-core and polymer-cladded bimodal plasmonic refractive index sensors with high refractive index contrast. Our sensors feature an aluminum stripe, a bilayer SU-8 photonic waveguide core, and the experimental optical cladding polymer SX AR LWL 2.0. They achieve a sensitivity of (6300 $\pm$ 460) nm/RIU (refractive index unit), surpassing both traditional and polymer-based plasmo-photonic sensors. This approach enables integrated, wafer-scale, CMOS-compatible, and low-cost sensors and facilitates plasmonic refractive index sensing platforms for various applications.