Noise considerations in twin-core channel equalisers

Fibre optic channel equalisers are devices of prime importance in multi-channel telecommunication links and networks. They are used to compensate for the channel power imbalances accumulated along amplified long links and stabilise the channel optical powers. In multi-stage amplified optical links, channel power imbalances occur as a result two factors. Firstly, the emission and absorption cross-section variations across the erbium-doped fibre amplifier (EDFA) bandwidth result in channels experiencing different gains and acquiring unequal output power. Secondly, the output power imbalances are further deteriorated by the fact that the Er3+ transition is predominantly homogeneously broadened at room temperature. Therefore, the strongest signal (channel) saturates the gain medium and compresses the gain uniformly at the expense of the power of the weaker signals