Sodium chloride concentration sensor based on long period fiber grating with dual resonant peak

The long period fiber grating (LPFG) with dual resonant peak was fabricated by exposing the core of a photosensitive optical fiber to an ultraviolet beam. The responses of this LPFG to sodium chloride aqueous solutions were investigated. Experimental results showed that, when the concentration of sodium chloride increased gradually from 0% to 26%, the left resonant peak gradually shifted from 1369.35 nm to 1345.17 nm, and the right resonant peak gradually shifted from 1599.68 nm to 1633.45 nm. The right resonant peak is much more sensitive to sodium chloride solution than the left resonant peak. Moreover, there was a good linear relationship between the resonant wavelength and the concentration of sodium chloride. For the left peak and the right peak, the linear equations are Y = −0.91X + 1369.32 and Y = 1.29X + 1598.81, respectively. Compared with the conventional LPFG, this LPFG with dual resonant peak possesses a higher sensitivity for sodium chloride concentration detection. (paper)