Measurements of polarization properties (polarization dependent loss and differential group delay) of a long-period
grating inscribed by means of high-intensity femtosecond 264 nm pulses in an endlessly single mode photonic crystal
fibre are reported. Strong modulation in the spectra of polarization dependent loss and differential group delay with
periods of 2.6 nm and 1.3 nm, respectively, were found. As such an effect has not been observed in standard optical
fibres, it is believed that this is due to the specific mode structure of the holey fibre used for grating fabrication.
We inscribed long-period gratings in a hydrogenated SMF-28 fiber by high-intensity femtosecond near-UV pulses via a three-photon absorption mechanism. Due to energy deposition in the fiber cladding, such gratings are similar to those fabricated by C0<sub>2</sub> laser induced heating, mechanical pressure or electric arc. We found that these gratings exhibit significant polarization properties.
Using high-intensity (around 200 GW/cm<sup>2</sup>) femtosecond 264 nm laser light and phase mask technique, Bragg grating inscription in a range of different photosensitive and standard telecom fibres (both H2-free and H2-loaded) was studied. The dependencies of the induced refractive index modulation versus the incident fluence were compared with similar dependencies for gratings fabricated by other existing methods. It was shown that at high-intensity UV laser irradiation, two-quantum photoreactions occur in the irradiated fibre core, which results in a significant photosensitivity enhancement of the investigated fibres in comparison with conventional low-intensity 248 nm exposure (by 6-128 times, depending on fibre type and irradiation intensity).
Using high-intensity (100-500 GW/cm<sup>2</sup>) 264 nm laser radiation, we fabricated long-period fiber gratings in telecom and photosensitive fibers, studied their temperature sensing properties and demonstrated the effect of thermal recovery of a LPFG resonance peak.