Long-period fiber grating fabrication by high-intensity femtosecond pulses at 211 nm

Using high-intensity (110-200 GW/cm²) 250-fs 211-nm laser pulses and a point-by-point technique, the efficiency of long-period grating inscription in H₂-loaded standard telecom Corning SMF-28 and H₂-free photosensitive B-codoped Fibercore fibers was studied and compared with those at other existing recording methods (low-intensity 157-nm, 193-nm, 248-nm or high-intensity 264-nm fabrications). It was shown that at high-intensity 211-nm laser inscription, two-quantum photoreactions are responsible for long-period fiber grating (LPFG) formation, which results in a significant photosensitivity enhancement in comparison with conventional low-intensity 248-nm exposure (by 45 times for SMF-28 fiber). It was found that the grating strength in the case of SMF-28 fiber, irradiated with high-intensity 211-nm pulses, reaches 28 dB, which is the highest value among all known photochemical approaches. The thermal studies of the recorded gratings were also conducted.