Resonance peak shift and dual peak separation of long-period fiber gratings for sensing applications

The systematic analysis of the relationship among the transmission characteristics of long-period fiber gratings, the initial coupling strength, and the fluence of the postexposure UV beam are discussed. The UV postexposure allows for adjustment of the peak depth depending on the initial coupling strength while red-shifting the resonance wavelength. Dual peak separation can occur for high-order cladding modes, and its application to sensing of the bending curvature, transverse load, and external refractive index are described.