Spectroscopic studies of rare earth doped fibers and their applications in optical amplifiers, fiber lasers, and gas sensors

Rare earth doped silica fibers were fabricated using Modified Chemical Vapor Deposition with an aerosol delivery technique. Active fiber devices were fabricated and their spectroscopic properties were characterized. In an Er{dollar}{bsol}sp{lcub}+3{rcub}{dollar} doped {dollar}{bsol}rm Ta{bsol}sb2O{bsol}sb5{dollar}-{dollar}{bsol}rm Al{bsol}sb2O{bsol}sb3{dollar}-SiO{dollar}{bsol}sb2{dollar} fiber, addition of {dollar}{bsol}rm Ta{bsol}sb2O{bsol}sb5{dollar} was found to show more spectroscopic structures of Er ions than {dollar}{bsol}rm Al{bsol}sb2O{bsol}sb3{dollar}-SiO{dollar}{bsol}sb2{dollar} glass. When pumped at 975 nm this fiber showed a gain of 26 {dollar}{bsol}pm{dollar} 1 dB over 35 nm. In a Eu doped aluminosilicate fiber a permanent index change of {dollar}2.3{bsol}times 10{bsol}sp{lcub}-5{rcub}{dollar} was observed when irradiated by 249 nm excimer laser. From UV-visible absorption spectra of the preform, it is suggested that UV photosensitivity of the fiber may be related to Eu{dollar}{bsol}sp{lcub}+2{rcub}{dollar} ions. A permanent index change of {dollar}5.1{bsol}times 10{bsol}sp{lcub}-5{rcub}{dollar} was induced in a Sm{dollar}{bsol}sp{lcub}+2{rcub}{dollar}/Sm{dollar}{bsol}sp{lcub}+3{rcub}{dollar} doped aluminosilicate fiber by irradiating 2W of multi-line output from an Ar ion laser. The origin of the photosensitivity in the Sm doped fiber may be the bleaching of Sm{dollar}{bsol}sp{lcub}2+{rcub}{dollar} ion absorption bands enhanced by multiphoton processes. Tm doped {dollar}{bsol}rm Ta{bsol}sb2O{bsol}sb5{dollar}-{dollar}{bsol}rm Al{bsol}sb2O{bsol}sb3{dollar}-SiO{dollar}{bsol}sb2{dollar} glass fiber lasers were fabricated using a Fabry-Perot type fiber laser cavity. Multi-line lasing was observed and the emission wavelength was found to depend on the cavity length and the output coupling ratio. Amplified spontaneous emission from the {dollar}{bsol}rm{bsol}sp3 H{bsol}sb4{bsol}to {bsol}sp3 H{bsol}sb6{dollar} transition of Tm{dollar}{bsol}sp{lcub}+3{rcub}{dollar} in the fiber has been observed at 1.91 {dollar}{bsol}mu{dollar}m with a FWHM of 77 nm, an output power of 1.2 mW. Continuous wave laser oscillations in a Tm{dollar}{bsol}sp{lcub}3+{rcub}{dollar} and Ho{dollar}{bsol}sp{lcub}3+{rcub}{dollar} codoped silica fiber have been observed from the {dollar}{bsol}rm{bsol}sp5 I{bsol}sb7{bsol}to{bsol}sp5 I{bsol}sb8{dollar} transition of Ho{dollar}{bsol}sp{lcub}3+{rcub}{dollar} in the 2 {dollar}{bsol}mu{dollar}m region, by pumping into a Tm{dollar}{bsol}sp{lcub}3+{rcub}{dollar} absorption between 800 and 830 nm. By changing the cavity length, the laser was tunable between 2.037 and 2.096 {dollar}{bsol}mu{dollar}m. Pumped with a Ti:Sapphire laser at 820 nm, an absorbed threshold power of 214 mW, a slope efficiency of 4.2% and maximum extracted power of 12.5 mW were measured. Using fluorescence of this fiber CO{dollar}{bsol}sb2{dollar} gas was detected down to 1% in a simple white cell spectroscopy setup.