Superimposed long period fiber grating-based refractive index sensor

A superimposed long period fiber grating design proposed for refractive index sensing is shown to be superior to conventional dual resonance and turnaround point gratings and can operate at any chosen wavelength region by appropriate design. Numerical simulations carried out on standard single mode fibers show that such sensors can operate over a wide refractive index range (1.33–1.42) exhibiting a high sensitivity of ～500–1545?nm/RIU, yielding ～10^?6–10^?7 refractive index change corresponding to the resonance relative shift of 1?pm with potential applications to chemical and biological industries. The proposed scheme can also discriminate between refractive index and temperature changes.