Analysis of the Lowest Order Cladding Mode of Long Period Fiber Gratings near Turn Around Point

A long period fiber grating (LPFG) sensor has been fabricated, after theoretical analysis, obtaining the maximum enhancement of the evanescent field working with the lowest order cladding mode (LP0,2 cladding mode) near turn around point. Both the wavelengths of the dual peak resonance and the coupling conditions of the mode have been analyzed in detail. A flow cell has been fabricated to characterize the sensor in term of surrounding refractive index (SRI) sensitivity. The sensitivity of the sensor resulted to be ~ 8751 nm/SRIU, with a resolution in the order of 10-5, within the SRI range of 1.333 to 1.3335.