Temperature Sensitivity Enhancement of the Nano-Film Coated Long-Period Fiber Gratings

We present a new method to improve the temperature sensitivity of the long-period fiber gratings (LPFGs). The atomic layer deposition technology is used to deposit Al
₂
O
₃
nano-film on the LPFG written in the conventional single-mode fiber. Then, the coated LPFG is packaged by the polymer material. The theoretical model of the hybrid modes in the four-layer cylindrical waveguide is proposed for a numerical analysis. Experimental results show that the temperature sensitivity up to 0.77 nm/°C is achieved for the HE
_1,10
mode of the LPFG coated with 200-nm nano-film and then packaged by the silicone rubber. The temperature sensitivity is almost one order magnitude larger than that of the bare LPFG. Various physical effects for the temperature sensitivity enhancement are investigated theoretically and experimentally. The experimental results are well consistent with a theoretical analysis.