Interrogation-Based Fiber Optic Sensors: A Comprehensive Review of Techniques, Trends, and Applications

Fiber Bragg grating (FBG) sensors have emerged as powerful tools for a wide range of sensing applications owing to their high sensitivity, immunity to electromagnetic interference, and multiplexing capability. However, the performance and practical deployment of FBG-based systems are fundamentally governed by the interrogation techniques employed. This review provides a comprehensive overview of both active and passive interrogation methods used for FBG sensor demodulation, detailing their operating principles, advantages, and limitations. Active techniques, including Fourier Domain Mode-Locked (FDML) lasers, optical frequency combs (OFCs), and tunable filters such as Fabry–Perot (FP) and acousto-optic tunable filters (AOTFs), offer high-speed and highresolution interrogation suitable for dynamic sensing scenarios. In contrast, passive methods based on edge filters, Mach–Zehnder interferometers, and wavelength division multiplexing (WDM) architectures provide compact, cost-effective, and field-deployable solutions ideal for static or quasi-static applications. Each method is critically analyzed with respect to spectral resolution, speed, system complexity, and environmental stability. The review also highlights recent technological advancements and novel architecture aimed at enhancing interrogation performance. Finally, future perspectives are discussed, emphasizing the need for photonic integration, artificial intelligence (AI)-assisted signal processing, and hybrid designs to meet the demands of next-generation smart sensing systems.