Application of cladding modes of optical fibers for sensing: review of recent developments

This report presents a review of recent developments in the investigation of propagation, excitation, and interaction of cladding modes in optical fibers used for sensing. The use of fiber cladding modes broadens the range of possible applications of fiber optical sensors. The cladding mode resonance excited by fiber Bragg gratings, in particular tilted Bragg gratings, is discussed. The most commonly used method of excitation of cladding modes based on long-period fiber gratings is considered. We describe applications of long-period fiber gratings as sensors of strain, temperature, refractive index, chemical composition, twist, etc. Propagation of cladding modes in fiber interferometers and cascaded long-period fiber gratings is analyzed.