Dual-stage erbium-doped, erbium/ytterbium-codoped fiber amplifier with up to +26-dBm output power and a 17-nm flat spectrum

Abstract
By concatenating an aluminum-codoped erbium-doped fiber with an efficient erbium/ytterbium-codoped fiber, we produce a gain spectrum that is flat within 0.5 dB for 17 nm from 1544 to 1561 nm. By using energy transfer between erbium and ytterbium ions, we are able to pump the second stage with a high-power 1064-nm source to achieve an output power as high as +26 dBm. Using 980-nm pumping of the first stage, we produce an overall noise figure below 5 dB.