Unique characteristics of long-period fibre gratings fabricated by high-freque ncy CO2 laser pulses

Abstract

In this paper, we report novel long-period fibre gratings (LPFGs) written by focused high-frequency CO2 laser pulses. A number of unique characteri stics of such a LPFG, such as stroin, temperature, bend, torsion and transverse-load, etc., are observed by experiment, for the first time to our knowledge. These uni que features are mainly due to the asymmetrical distribution of the refractive i ndex on the cross section of the LPFG induced by high-frequency CO2 l aser puls es. Based on these unique characteristics, we have proposed a novel bend-insensi tive LPFG sensor that could solve the problem of cross-sensitivity between bend and other measurements, a novel torsion sensor that can realize absolute measure ment of twist rate and a load sensor that can achieve simultaneous measurement o f transverse load and temperature using a single LPFG element.