Characteristics of novel long-period fibre gratings written by focused high-frequency CO2 laser pulses

In this paper, we report novel long-period fiber gratings (LPFGs) fabricated by using an improved CO2 exposure method, which is based on the thermal shock effect of high-frequency CO2 laser pulses at several kHz. Compared with the method using low-frequency laser pulses at several Hz reported previously, this new technique is more effective due to the significant increase in the transient laser energy density focused on the fibre, which is likely to cause larger densification and residual stress relief and hence larger refractive index change in the fibre. The optical and mechanical characteristics of such a type of LPFGs have been studied by experiment.