Gain tilt control of L-band erbium-doped fiber amplifier by using a 1550-nm band light injection

In this letter, we demonstrate a new method to control gain tilt in long wavelength erbium-doped fiber amplifiers by using an external light source in 1550-nm range (called control source). The wavelength or its input power is adjusted to reduce gain tilt. The tilted gain is diminished from 7.18 to 0.07 dB by adjusting control source wavelength, and from 9.95 to 0.62 dB by adjusting control source input power in a 1570-1590-nm signal wavelength range.