Saturable absorber reduces gain error in EDFA

Saturable absorber reduces gain error in EDFA Optical gain control (OGC) in erbium-doped fiber amplifiers (EDFAs), in which a self-oscillating laser is introduced into the system, is one method for maintaining optical gain in the surviving channels of a wavelength add/drop multiplexing system as channel loading changes. However, EDFAs can exhibit spectral hole burning at the OGC laser wavelength, causing gain error in surviving channels. Researchers at Corning Inc. (Corning, NY) have introduced a saturable absorber into the OGC laser cavity to reduce such errors.

The EDFA itself is 14 m long. A pair of wavelength-selective couplers forms a ring OGC cavity with a 1527-nm laser wavelength, while an isolator selects a path. A variable optical attenuator sets the cavity loss and thus the amplifier inversion. The saturable absorber dynamically adjusts cavity loss as a function of power. The gain spectrum was measured with eight saturable channels spaced in the 1530-1560-nm range, both with and without the saturable absorber. With seven channels dropped, the gain error was 1.3 dB for a fixed loss and 0.4 dB with the saturable absorber included. The saturable absorber has been used with a remote-control laser in the cavity for all-optical switching. Contact Chia-Chi Wang at [email protected].