Highly Sensitive Optical Refractometer Based on Edge-Written Ultra-Long-Period Fiber Grating Formed by Periodic Grooves

An ultra-long-period fiber grating with periodic groove structure (G-ULPFG) fabricated by using an edge-written method with high-frequency CO2 laser pulses is proposed in this paper. The experimental results show that the different resonant peaks of the G-ULPFG have different temperature and refractive index sensitivities and, in particular, the refractive index sensitivity is much larger than that of conventional ULPFG due to the edge-groove structure. Such a kind of G-ULPFGs could be used as a highly sensitive optical refractometer with temperature self-compensation.