Photorefractive index gratings in SnO2:SiO2 optical fibers

Permanent photorefractive gratings with considerable refractive index modulations (similar to 3x10(-4)) were written in silica optical fibers doped with very low levels of SnO2(similar to 0.15 mol %) using ultraviolet (UV) laser radiation at 248 nm. The photoinduced refractive index change does not show any sign of saturation even for long exposure times (i.e., total fluence > 20 kJ/cm(2)). A comparison with GeO2:SiO2 fibers shows that under similar UV intensities saturation takes place for shorter exposure time and comparable refractive index changes are obtainable for GeO2 concentrations similar to 10 mol %. (C) 2000 American Institute of Physics. [S0003-6951(00)03507-5].