ArF laser induced refractive index and luminescence changes in Bi-doped aluminosilicate fibers - INVITED

Fibers doped with bismuth show broad luminescence bands around 750, 1100, and 1400 nm with spectral bandwidths of 100 to 200 nm at room temperature. The luminescence bands can be observed by pumping broad absorption bands in the visible or near infrared spectrum (around 500, 700, 800, 1000, and 1360 nm). Bismuth fiber laser action has been demonstrated using FBG in standard germanosilicate fibers as intra-core laser mirrors. In this work we report about the investigation of refractive index and luminescence changes of Bi-doped silica optical fibers under ArF irradiation. The Bi-doped fibers showed permanent photo-induced refractive index changes of ~2×10-4 and ~2×10-3 for pristine and H2-loaded fibers (Fig. 1), respectively. Such refractive index changes allow fabricating strong Bragg grating fiber laser reflectors directly in these fibers thus potentially improving the laser efficiency. Stress measurements of pristine and irradiated fibers indicate that the refractive index change is related to color centers and compaction for both pristine and H2-loaded fibers. The impact of pulsed 193-nm irradiation from an ArF excimer laser on absorption and luminescence of pristine and H2-loaded bismuth doped fibers was investigated. ArF irradiation increased the absorption strongly. At e.g. 400 nm the values changed from ~2 and ~3 dB/m to ~59 and ~174 dB/m for pristine and H2-loaded fiber, respectively. Light emission under visible Ar+ (454, 488, 514 nm), and Kr+-laser (567, 647, 676 nm) pumping was measured from 600 to1700 nm in a longitudinal arrangement. In all cases a particular strong increase in 1140 nm luminescence was measured for the H2-loaded fiber (Fig. 2). In side measurements under 1053 and 1357 nm pumping, 18 and >16 dB increase of the 1140 and 1400 nm luminescence for the H2-loaded fiber was observed. Decomposition into Gaussian bands suggests that H2-loading followed by ArF irradiation leads to the appearance of new bands in both the absorption and emission spectra.