Abstract

Erbium-doped fiber amplifiers (EDFA’s) are intensively used in (D) WDM systems owing to their compatibility with the network fiber, low insertion losses, high gain and wide bandwidth. Adding or dropping channels due to the optical WDM network reconfiguration, maintenance, upgrades or technical faults leads to gain excursions of EDFA. These gain excursions result in the bit error rate (BER) increase of optical information transmission in operating WDM channels. To stabilize the EDFA behaviour and avoid BER increase, different automatic schemes have been proposed: (i) “Dummy” signal (DS) include addition of a “dummy” signal to keep the saturation level of EDFA constant;¹ (ii) Electronic feed-forward (EFF) consists of photodetector and electrical amplifier to add current to the pump laser in proportion to the input signal; (iii) Optical feedback (OFB) consists of a feedback loop with a filter and a variable attenuator to equalize losses and EDFA’s gain on the OFB lasing wavelength;^3,4 (iv) Optical feedback with a saturable absorber (OFBSA) includes OFB and a saturable absorber for suppression of the gain error arising due to spectral hole burning effect, ⁵ (vi) Dual-cavity optical feedback (DCOFB) includes dual-cavity optical feedback with different wavelengths (1532 nm and 1560 nm), cavity lengths and attenuations.⁶ (vii) Electronic feed-forward and optical feedback (EFF + OFB) uses OFB loop and EFF to stabilize gain clamping.^7,8

© 2002 Optical Society of America