Gain flattening by using dual-core fiber in erbium-doped fiber amplifier

We show that a dual-core optical fiber in which one core is doped with erbium and the other core is undoped can be used as an optical amplifier with very flat gain over the wavelength range 1520 nm to 1560 nm. The gain variation over this range is less than 0.7 db. The noise floor is less than 4 dB.