Non reciprocal writing and chirality in femtosecond laser irradiated silica.

We ascertain by measuring the surface topography of a cleaved sample in which damage lines have been written in volume by scanning with a femtosecond laser, that matter shearing occur along the laser track with alternating sign (scissor or chiral effect). We note that the shearing in the head of the laser tracks change its sign with the change in scanning direction (pen effect or non reciprocal writing). We also show that nanostructures in the head are nano-shearing, with all the same sign whatever the direction of writing may be. We suggest that symmetries revealed by the shearing mimic the laser induced electron plasma density structures and inform on their unusual symmetries induced by the laser beam structures.

Comparing the properties of various sensitization methods in H2-loaded, UV hypersensitized or OH-flooded standard germanosilicate fibers.

The properties of three sensitization processes: UV hypersensitization, OH-flooding and H2-loading have been investigated through Bragg grating (BG) inscription within standard germanosilicate fibers. More specifically, the stability of the sensitization processes and that of the UV-induced index changes have been investigated through isochronal annealing experiments. Moreover, the level of excess loss induced near 1.4 microm by both the sensitization process and the BG inscription has been estimated by means of in fiber absorption spectroscopy. The level of loss proves to be higher in the hypersensitized or OH-flooded fiber than in the H2-loaded counterpart when pulsed 248 nm light was used.

Kinetics of UV-induced blue luminescence linked with the observation of the local mean index in fiber Bragg gratings.

We exposed H2-loaded optical fibers to cw UV light and simultaneously measured the intensity of the blue luminescence from the fiber core. The UV-induced blue luminescence experiences a non monotonous evolution and thus cannot be correlated to the refractive index changes. However, a quasi-linear relationship has been found between the increase of the blue luminescence and the refractive index changes in the range 5 10-4 < Deltan mean (or Deltan mod) < 2.5 10-3. Using this property, we analyze a fiber Bragg grating by focusing a UV beam probe onto the fiber core and we record the UV-induced blue luminescence at the end of the fiber. By scanning the UV beam along the fiber, we measure thus the axial profile of the refractive index changes with a spatial resolution of 1 mum.

Self induced gratings in ternary SiO2:SnO2:Na2O bulk glasses by UV light seeding.

The diffraction efficiency of gratings written in ternary SnO2:SiO2:Na2O bulk glasses rises dramatically with time after the occultation of the cw 244nm light used to write the thick hologram. This self-induced behavior lasts for several hours and ultimately leads to refractive index changes as high as 3 10-3.

Efficient Bragg gratings in phosphosilicate and germanosilicate photonic crystal fiber.

We present ArF laser-induced dynamics of Bragg grating (BG) growths in phosphosilicate-doped or germanosilicate-doped core photonic crystal fibers (PCFs). To this end, we have adapted the technique of H2 loading, usually used in conventional fiber, to the case of microstructured fiber, allowing both the concentration of hydrogen in the PCFs to be kept nearly constant for the time of the exposure and the BG spectra to be easily recorded. We compared the characteristics of BG growths in the two types of PCF to those in conventional step-index fibers. We then conducted a study of the thermal stability of the BGs in PCFs through 30 min of isochronal annealing. At the same time we discuss the role played by the microstructuration and the doping with regard to the grating contrast and the Bragg wavelength stability.