Experimental investigation of long period grating working in transition mode

An experimental investigation of the transition modes of long period gratings (LPG) is reported. Coating LPGs with a material of high refractive index causes a reorganization of the cladding modes, leading to a substantial increase in sensitivity to changes in the surrounding refractive index (SRI). The thickness of polystyrene coatings on optical fibers, applied by dip-coating, was measured by scanning electron microscopy. The maximum sensitivity and corresponding SRI of each coating thickness was then determined by analyzing the attenuation bands in the transmission spectrum.