TE40-Based Multimode Interferometer for Optical Refractive Index Sensors

We experimentally demonstrate the robust and selective excitation of the higher-order mode TE40 in a Si3N4 multimode interferometer (MMI), aiming to enhance evanescent field interactions for refractive index sensing. Through output intensity monitoring and the integration of a microfluidic module, the sensor demonstrates a bulk sensitivity of 780 RIU-1 and a detection limit of 2.2 × 10-5 RIU. These results highlight the potential of high-order-mode photonic sensors for compact and highly sensitive refractive index detection.