Functional Photonic Materials for Next-Generation Waveguide Sensors: Nonlinear, Atomically Thin, and Piezoelectric Platforms: A Review

Integrated optical waveguide sensors (IOWSs) are undergoing a fundamental transformation driven by the emergence of functional photonic materials that extend sensing beyond passive evanescent-field perturbations. This review examines three major material platforms, that is, chalcogenide glasses, atomically thin 2-D materials, and ferroelectric thin films, that enable new physical transduction mechanisms through nonlinear optical response, surface-dominated light-matter interaction, and electrooptic or piezoelectric coupling. By adopting a mechanism-driven perspective, the review systematically connects material properties to sensing performance metrics, clarifying how different platforms address chemical, biological, mechanical, and electrical measurands across visible, telecom, and mid-infrared wavelengths. Chalcogenide-based waveguides provide strong χ 3 nonlinearity and broadband mid-infrared transparency for chemically selective sensing, while 2-D materials push detection toward the ultimate surface limit with electrically tunable responses. Ferroelectric thin-film waveguides enable active, low-noise sensing through fast and linear χ 2-mediated transduction. The review further highlights emerging hybrid and co-integrated architectures that decouple waveguiding, transduction, and selectivity to overcome single-material limitations. By unifying diverse platforms within a common physical framework, this work provides practical design guidance for next-generation integrated waveguide sensors and identifies key challenges and opportunities for scalable, multifunctional sensing systems.