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 (LP
_0,2
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.