Advances in Mid‐Infrared Fiber Evanescent Wave Sensing

ABSTRACT Mid‐infrared fiber evanescent wave spectroscopy (MIR‐FEWS) offers several advantages over conventional sensing platforms, including direct access to molecular vibrational fingerprints, label‐free and non‐destructive operation, and the unique capability for remote, in situ analysis in complex media. The marriage of the molecular specificity inherent to MIR spectroscopy with the flexibility and waveguiding properties of optical fibers renders it a useful tool for environmental monitoring, biomedical diagnostics, food safety, and operando monitoring of chemical reactions. Recently, significant progress has been made in developing low‐loss infrared‐transmitting fiber materials, engineering fiber geometries to enhance evanescent field strength, and functionalizing surfaces with selective or signal‐amplifying coatings. However, the field currently lacks a comprehensive framework that systematically maps these diverse advances to targeted sensing performance. This review focuses specifically on key advances in the field of MIR‐FEWS, providing a structured analysis of its fundamental principles, materials, design principles and recent developments in fiber structure, functional coating strategies, its translation into emerging applications, and application‐oriented design trade‐off. Future challenges and directions for the field are also outlined to guide the development of next‐generation sensors.