Long-wavelength-band Er/sup 3+/-doped fiber amplifier incorporating a ring-laser as a seed signal generator

A novel dual-stage architecture for long-wavelength-band (L-band) erbium-doped fiber amplifier, which incorporates a gain-clamped amplifier based on a ring-laser feedback as a seed signal generator in the first stage is described. This technique has elevated the intensity of a short-wavelength amplified spontaneous emission (ASE) by 29%, from 11.3 mW of ASE power to 14.6 mW with a feedback lasing at 1560 nm. This strong laser then improves the L-band gain enormously, as large as 17.1 dB and noise figures are lower than 4.8 dB for the entire signal range in the flat-gain operation. The seeding signal reduces pump-to-ASE losses in the second stage to 38% compared to a conventional amplifier without feedback. Noise figure penalties are negligible due to efficient low-noise characteristics in the first stage. The proposed amplifier provides 25 dB gain for 50 wavelength-division-multiplexed signals at -30 dBm/ch with gain flatness less than 1.1 dB with only 980 nm pumping.