Dispersion turning point enhanced on-chip bimodal interferometry.

A transverse-magnetic (TM) polarized strip bimodal waveguide (BiMW) sensor operating near a dispersion turning point (DTP) is proposed and experimentally demonstrated on a silicon-on-insulator platform. To enhance the sensitivity of common-path BiMW sensors, near-DTP operation is realized by driving the modal group-index difference toward zero. By exploiting the intrinsic width-dependent dispersion of the TM modes, the DTP is achieved in a standard strip waveguide configuration through waveguide-width optimization, without complex dispersion-engineering structures. With a sensing length of only 0.8 mm, the sensor achieves a refractive-index sensitivity of 7456 nm/RIU and a limit of detection (LoD) of 1.57 × 10-6 RIU. This work provides a compact, fabrication-accessible, and experimentally validated approach for high-performance on-chip refractive-index sensing, with potential applications in biochemical sensing.