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Optical Amplifiers and Their Applications

Excited-State Absorption at 1.5 µm in Er3+-Doped Fiber Amplifiers

Peter Blixt, Johan Nilsson, Jurgis Gintautas Babonas, B. Jaskorzyńska

Published Jan 1, 1992• 2 citations

Abstract

Erbium-Doped Fiber Amplifiers (EDFAs) can very efficiently convert pump to signal energy. Quantum efficiencies higher than 80 % with 1.48 pm pump [1], and 93% when pumped at 980 nm [2] are reported. However, even higher values should be theoretically possible for an ideal EDFA. Various physical effects may lead to quantum efficiency (QE) reduction. Not all of them are quite well understood yet. At Erbium concentrations above 100 ppm by weight the pump loss is partly explained by energy transfer between two excited ions resulting in upcon- version process [3]. At low concentrations Excited-State Absorption (ESA) could be a more significant effect reducing QE. ESA of photons from 1.5 |im band have been predicted from absorption measurements [4] and also observed [5]. However, to our knowledge, no quantitative analysis has been made which would distinguish between the contributions of ESA and two-particle upconversion when measurements of short wavelength luminescence were performed.

DOI: 10.1364/oaa.1992.we2

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Laser Physics•Nov 1, 2008•7 citations

Erbium-Doped Fiber Amplifiers (EDFAs) can very efficiently convert pump to signal energy. Quantum efficiencies higher than 80 % with 1.48 pm pump [1], and 93% when pumped at 980 nm [2] are reported. However, even higher values should be theoretically possible for an ideal EDFA. Various physical effects may lead to quantum efficiency (QE) reduction. Not all of them are quite well understood yet. At Erbium concentrations above 100 ppm by weight the pump loss is partly explained by energy transfer between two excited ions resulting in upcon- version process [3]. At low concentrations Excited-State Absorption (ESA) could be a more significant effect reducing QE. ESA of photons from 1.5 |im band have been predicted from absorption measurements [4] and also observed [5]. However, to our knowledge, no quantitative analysis has been made which would distinguish between the contributions of ESA and two-particle upconversion when measurements of short wavelength luminescence were performed.

The dependence of erbium-doped fiber amplifier (EDFA) performance on the erbium ion concentration is studied experimentally and theoretically. The quantum efficiency of the amplifier is found to he strongly dependent on the erbium ion concentration, the signal wavelength, and the relative propagation direction of the pump and signal beams. This dependence is fully explained by the presence of an upconversion mechanism between ions residing in pairs or larger clusters and suggests that other sources of amplifier performance degradation (back-ground loss, excited state absorption, homogenous upconversion) are negligible. The experimental data show that in the present EDFA designs with over 80% quantum/conversion efficiency, the aluminum co-doped fibers with erbium ion concentration less than 20/spl times/10/sup 24/ m/sup -3/ (900 molar ppm Er/sup 3+/) are most suitable.

We report a study of the excited-state absorption (ESA) in erbium-doped silica fiber (EDF) pumped at 977 nm, when the fiber is simultaneously excited by signal radiation at 1531 nm. We show, both experimentally and theoretically, that ESA efficiency at 977 nm gets strongly enhanced only in the presence of signal power. Experimentally, this conclusion is supported through the detection of upconversion emission, a “fingerprint” of the ESA process, and through the measurements of the EDF nonlinear transmission coefficient for the pump wavelength, which is sensitive to the ESA value. It is shown that the experimental data are precisely modeled with an advanced five-level Er3+ model developed for the EDF.

Erbium-doped fiber amplifier(EDFA)efficiency strongly depends on erbium concentration.Highly doped erbium devices show degraded performance when compared with low concentration ones.The mechanism of upconversion is studied and the effect of it on the performance of an EDFA is analyzed numerically,by means of a set of rate equations model.Approximate analytical solutions,for the rate equations,which include the effect of the upconversion,are presented,when the amplified spontaneous emission can be neglected,compared to the pump and signal powers.Results show that the pump and signal powers all bear degradation due to upconversion.,and the effect can't be neglected when the Er3+ concentration is larger than 2.95×1025 m-3.

A gain coefficient of 3.8 dB/mW was achieved for an erbium-doped fiber amplifier pumped by a 1.48 mu m laser diode. The main reasons for the improvement are high NA (0.23) and low concentration (43 p.p.m.). Pump-to-signal energy conversion efficiency was 18% at 3 dB gain compression. A decrease in saturation power with increasing erbium concentration was also demonstrated. In high-concentration fiber, fluorescence at 0.98 mu m due to cooperative upconversion was detected. These results indicate that several kilometers of distributed fiber amplifier with high gain and high output saturation power could be possible, because the absorption coefficient at 1.48 mu m is still two orders higher than the background loss in the 43 p.p.m. fiber.>