Highly Sensitive Long Period Fiber Grating Refractive Index Sensor

Long period fiber grating(LPG) is a optical device that widely used in optical communication and optical sensing field, and it has unique advantage in sensing application areas. A theoretical study on LPG is conducted firstly in this paper, and then the coupling characteristics, effective refractive index characteristics and transmission spectrum characteristics at each grating parameters of LPG are analyzed by numerical simulation. The characteristics can provide some theoretical guidance on fabricating the LPG that meet our needs.The cladding diameter of LPG has the varying degree effects on transmission spectrum of each cladding mode. In this paper, long period fiber gratings transmission spectrum of different cladding diameter and the changes of the refractive index sensitivity with the cladding diameter of each cladding mode are simulated and analyzed, explaining how the reduction of cladding diameter improve the sensitivity of refractive index theoretically. The simulation results show that we can achieve highly sensitive long period fiber gratings refractive index sensor by reducing the cladding diameter and then choosing the appropriate cladding mode.LPG with 80 ?m and 125 ?m cladding diameters respectively are used to measure the refractive index characteristics of NaCl solution in this paper, and the temperature change is compensated in the experiment. Experimental result shows that the sensitivity of LPG with a 80?m cladding diameter is 3 times higher than the ordinary long period fiber grating.