OPTICAL GENERATION OF BRAGG GRATINGS IN CERIUM-DOPED FLUORIDE GLASSES

点击翻译按钮获取中文摘要

Photo-generation of Bragg grating in glass matrixes has received much attention as a key technology to assemble optical fibers and waveguides. To extend the validity of this technique, it is important to search for photo-writable system in a variety of glass materials. This is required especially in fluoride glasses because of their superiority as optical gain media. We have sensitized aluminum fluoride glasses (AFG) with cerium ions and evaluated their applicability to Bragg grating media. Samples examined were multicomponent AFG plates with the composition of 34.5A1F_3, 13.5YF_3, 52 (Mg+Ca+Sr+Ba) F_2 in mol%. The concentration of CeF_3 ranged 0.05 to 4.Omol%. The dipole-allowed 4f-5d transitions of the trivalent cerium ions (Ce^<3+>) yielded intense absorption bands at 4.5 to 6.5eV.Exposure to 5.00eV light from a KrF laser (46mJ/cm^2shot) caused a fractional bleach of the Ce^<3+> bands and growths of two new bands peaking at 3.8 and 6.2eV, The both bands increased in proportion to the Ce^3 concentration and the exposure dose, which suggests that the photo-induced valence change of the Ce^<3+> ions attributes the absorption changes. The 6.2eV band increased monotonously with the accumulation of the laser exposure up to 20000 shots, while the 3.2eV band saturated at the exposure of 200 shots, From the Kramers-Kronig relation, the maximum refractive index change was estimated to be 2.7X10^<-5>. Isochronal annealing measurements showed the 3.8eV band is almost stable up to 1000C, while the 6.2eV band up to 3000ﾟC.These results suggest that the cerium-doped AFG have a potential for Bragg grating media.