Glasses for Er 3+ -Doped Fiber Lasers and Optical Amplifiers
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GLASSES FOR Er 3 +-DOPED FIBER LASERS AND OPTICAL AMPLIFIERS
W.J. MINISCALCO, L.J. ANDREWS, S. ZEMON, B.T. HALL, T. WEI, AND RIC. FOLWEILER GTE Laboratories Incorporated, 40 Sylvan Road, Waltham, MA 02254
ABSTRACT Er 3 +-doped silica fibers have demonstrated excellent performance as active optical devices at 1.5 jim. In an effort to identify promising new hosts, we have measureed absorption and emission cross sections for a variety of Er 3 +-doped glass. Compositions have been identified which have advantages over silica, particularly for pumping with AIGaAs diode lasers at 800 nm.
INTRODUCTION Although active fiber devices have a long history [1], there has recently been a surge of interest in lasers, optical amplifiers, and superluminescent sources made from rare-earthdoped3 singlemode fibers. Much of this attention has focused on the 4113/2 - 4145/2 transition of Er + since this falls within the third optical communications window at 1.5 gim, and excellent performance has been achieved for these devices. Practically all the work reported on doped fiber devices has used silica or, to a lesser extent, fluorozirconate glass. From the extensive body of research on Nd 3 +-doped glasses it is known that silica is a relatively poor host and that other glasses, particularly phosphates and fluorophosphates, provide higher cross sections and bulk-device efficiencies. Since there remain some concerns regarding the restricted gain bandwidth, limitations on optical pump wavelengths, and pump power requirements for devices operating on the 4113/2 --4 4115/2 transition, we have undertaken a survey of alternative Er 3 + hosts to determine if better glasses can be found for fiber devices at 1.5 prm. The investigation has included the synthesis of silica fibers as well as bulk samples of promising glasses, the determination of absorption and stimulated emission cross sections at 1.5 jim, and the measurement of absorption cross sections at the important 800 and 980 nm pump bands. The impact these host-dependent parameters have on the performance of Er 3 + fiber amplifiers has been discussed elsewhere [2]. In addition, the degree of inhomogeneity in the optical spectrum affects the saturation characteristics and has been reported on previously for these glasses [31. Excited state absorption (ESA) in the 800 nm pump band is a seriously debilitating process and an investigation of it is reported in another paper in this volume 141. The choice of glasses was guided by Judd-Ofelt analysis which was used to calculate the effect of glass composition on the integrated strength of the ESA transition that coincides with the ground state absorption band near 800 nm [5]. Phosphate, fluorophosphate, and heavy metal fluoride glasses were investigated, with standard Ge/P- and Al/P-doped silica fibers included for comparison. The compositions of the glasses have been included in Reference 4. The ground state absorption and stimulated emission cross sections for the bulk samples were obtained from measured absorption spectra. The integrated cro
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