Fabrication of twisted long period fiber gratings with high frequency CO₂laser pulses and its bend sensing

Abstract

We experimentally demonstrated a simple and effective method to write long period fiber gratings (LPFGs) with low fiber grating birefringence using high frequency CO2 laser pulses. Such LPFGs were fabricated by introducing twist strains to the fiber and then exposing the fiber to the laser. We theoretically analyzed the influence of the twist strains on the spectra of the LPFGs, and examined bend characteristics of twisted long period fiber gratings (T-LPFGs). Experimental results showed that T-LPFGs exhibited clear spectra, low insertion loss, and low polarization-dependent loss (PDL) compared with conventional LPFGs exposed to a single-side CO2 laser beam. The slope of the linear equation of the distance between the two split resonance peaks in the bending experiment is 20.55 nm/m−1, which makes T-LPFGs sensitive bending sensors.