High Sensitivity Refractometer Based on Thermally Stable Turnaround Point Long Period Fiber Grating

This paper presents refractive index sensor based on long period fiber gratings operating near phase matching turn around point. Long period fiber gratings were fabricated in-house using frequency doubled copper vapor laser, in single mode photosensitive fiber using point-by-point method. A long period fiber grating of period 168 µm fabricated that operated near turn around point, referred as TAP-LPG. Another long period grating of period 174 µm fabricated and then annealed. The post annealed LPG provided resonance at turn around point referred as TTAP-LPG. It was experimentally observed that the SRI average sensitivity of TTAP-LPG is much higher in compared to that for TAP-LPG within the SRI range of 1.3333–1.4446. In addition, it has higher thermal stability due to thermal annealing. So this kind of TTAP-LPFG sensor is suitable for high-sensitivity sensing of SRI at high temperature environment.