Novel mechanical fiber-optic sensors based on long-period fiber gratings written by high-frequency CO_2 laser pulses

摘要

In this paper, we report novel long-period fiber gratings (LPFGs) fabricated by using a new writing method, which is mainly based on the thermal shock effect of focused high-frequency CO_2 laser pulses at several kHz. A number of unique characteristics of such a LPFG, such as bend, torsion and transverse-load, et al, are observed by experiment, for the first time, to our knowledge. Based on these unique characteristics, a novel bend-insensitive LPFG sensor that could solve the problem of cross-sensitivity between bend and other measurands, a novel torsion sensor that can realize absolute measurement of twist rate and a load sensor that can achieve simultaneous measurement of transverse load and temperature using a single LPFG element are demonstrated. These unique features are mainly due to the asymmetrical distribution of the refractive index on the cross-section of the LPFG induced by high-frequency CO_2 laser pulses.