Abstract

Most work on erbium-doped fiber amplifiers (EDFA) over the past few years has focussed on amplifiers pumped at 980 nm and at 1480 nm.^1-3 Recently, however, there has been renewed interest for file 800-nm pump band.⁴ In this paper we present a comparative study of an EDFA pumped by a Ti:sapphire laser tuned to both 800 and 980 nm in order to illustrate the effects of excited-state absorption.⁵ The erbium-doped fiber used in the experiment has a 4-μm-diameter SiO₂-Al₂O₃-GeO₂ core with a relative index difference of 0.035 and a cutoff wavelength of ~815 nm. The erbium concentration is 200 ppm. Gain and saturation measurements were per formed on different lengths of fiber, pumped at 980 nm and at some arbitrary wavelength in the 810-nm region, the optimum wavelength having been found to increase with length. Figure 1 is a plot of normalized gain for λ_s = 1533 nm as a function of pump wavelength. The 3-dB bandwidth is 14 nm. The peak gain for this 12-m piece is obtained for λ_p = 811 nm and was 25 dB for λ_s = 1533 nm and 20 dB for λ_s = 1553 nm. The maximum absorption, however, was found to be at 797 nm.

© 1991 Optical Society of America