Core Regulation of Long Period Grating Based on Ring-Core Hollow Fiber and the Application of Temperature Sensing

We propose a novel long-period grating (LPG) based on a ring-core hollow fiber (RCHF) filled with functional liquid as a tunable material. The RCHF structure is simple. The effective refractive index tuning characteristics of the liquid-filled RCHF-LPG are investigated. The RCHF-LPG functions as a tunable device filling with a functional liquid. The temperature sensitivities of three RCHF-LPG samples filled with dimethylacetamide (DMA) or DMA–glycerin mixtures are measured. The results show that the sample with high-RI liquid has higher sensitivity to temperature variation. The maximum linear sensitivity of the temperature can reach −618 pm/°C.