Spectral and Sensing Performance of Long-Period Fiber Gratings at 2 μm Waveband

In this paper, we demonstrate the transmission spectral and surrounding refractive index (SRI) sensing performance of long-period fiber gratings (LPFGs) at 2 μm waveband. The cladding modes operating at 2 μm waveband show higher SRI sensitivity than 1.55 μm waveband. The influence of a little off resonance region of grating period, refractive index modulation and duty cycle of gratings are analyzed theoretically. Additionally, the LPFGs of LP₀₈ mode near dispersion turning point operating at 2 μm waveband are investigated theoretically and experimentally. Mode splitting brings out with the increasing SRI. After the resonant dip splitting into two dips (dip A and dip A′), the SRI sensitivity of dip A are measured to be as high as −8495.2 nm/RIU in the SRI region of 1.445–1.457. The proposed 2-μm-waveband LPFGs makes it a potential in biochemical and environmental monitoring.