),1Fiber Optics Research Center, General Physics Institute, Russian Academy of Sciences, 38 Vavilov Street, 119991 Moscow, Russia. 2National University of Ireland, University College Cork, Cork, Ireland.
),We report investigation results of possibilities of long-period fiber gratings (LPFGs) fabrication in optical fibres by femtosecond pulses at different wavelengths. Several types of fibres were used and it was found that LPFGs with strong attenuation peaks (more than 20dB) can be induced in hydrogen-loaded germanosilicate fibres with the help of second-harmonic of a femtosecond Ti:sapphire laser without the use of an amplifier (400nm, 70 fs and 2,5nJ) and amplified, frequency-quadrupled pulses from a Nd:glass laser (264nm, 220fs and 0,4mJ).
The results of isochronal annealing for the fabricated gratings indicate that the induced refractive index has two components with different thermostability. The more thermostable component could be used for the creation of long-term stable LPFGs. The thermal properties of the recorded gratings suggest that the mechanism of the refractive index change is likely due to photochemical reactions.
