A new method for low noise automatic gain control of EDFAs for WDM systems in metropolitan networks

We propose a new hybrid automatic gain controlled (HAGC) EDFA which has electrical and optical feedback. The conventional optical automatic gain clamped (OAGC EDFA) has higher noise figure (NF) than the normal EDFA for its optical feedback. However the HAGC EDFA has low NF equal to the normal EDFA by the new feedback method (electrical and optical hybrid) which maintains the state just before oscillation in the optical loop. The HAGC EDFA has equal temporal response characteristics. Additionally the HAGC EDFA has lower power consumption than the OAGC EDFA by virtue of the low pump laser power, controlled by the electrical feedback.