Improving Limit-of-Detection in High-Sensitivity Plasmo-Photonic Mach-Zehnder Interferometer Refractive Index Sensors

This work presents a dual plasmo-photonic branch Mach-Zehnder interferometer refractive index sensor integrated on a Si₃N₄ platform, with both the sensor and reference arms hosting identical aluminum plasmonic metal stripes. Experimental evaluation of the configuration reveals a bulk sensitivity up to 8801 nm/RIU and an increased environmental noise resilience compared to state-of-the-art plasmo-photonic MZI sensors with the plasmonic section residing only on the sensor arm. The enhanced noise resilience along with the high sensitivity results in an experimentally obtained low detection limit value of 4.4 × 10⁻⁶ RIU, im-proved by an order of magnitude compared to the detection limit of 5 × 10⁻⁵ RIU that was measured in a reference MZI sensor with a plasmonic stripe only at its sensor arm.