Use of the coaxial-core profile in the erbium-doped fiber amplifier for self-regulation of gain spectrum

Coaxial-core erbium-doped fiber amplifiers (EDFA's) having a property of se lf-regulated gain spectrum are developed. The operation of a coaxial-core E DFA is based on the partial separation of the light paths for different wav elength channels in the directionally-coupled waveguides of a coaxial-core geometry. The degree of channel equalization depends on the geometrical and optical parameters of the coaxial-core EDFA and on relative channel power levels. A numerical analysis based on the coupled-mode theory and on the ra te equation shows that, under fully optimized conditions, a coaxial-core ED FA provides equalization rates in excess of -0.4 dB per dB of input-power i mbalance in the case with two WDM channels. A cascade experiment demonstrat es the effect of coaxial-core EDFA's toward channel-power equalization in f iber links with a small number of WDM channels.