Robust dual-wavelength ring-laser based on two spectrally different erbium-doped fiber amplifiers

The authors demonstrate simultaneous lasing at two wavelengths in a fiber ring-laser containing two erbium-doped fiber amplifiers with different spectral characteristics. The lasing wavelengths were selected by a filter combination. For certain wavelength pairs, the ring co-lased even if the loss at one wavelength increased by 8 dB relative to the loss at the other one, while a 1-dB change was enough to prevent co-lasing in a ring with two similar amplifiers. The increased robustness-to-loss variations is a consequence of the overall spectral gain inhomogeneity that results from combining two amplifiers with different gain spectra. The concept is also applicable to dual-wavelength transmission.