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3 October 1994 Noise considerations in twin-core channel equalizers
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Fiber optic channel equalizers 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 stabilize the channel optical powers. In multi-stage amplified optical links, channel power imbalances occur as a result of two factors. Firstly, the emission and absorption cross-section variations across the erbium-doped fiber 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. To avoid the build-up of channel power imbalances and the subsequent detrimental effects on signal-to-noise ratio in multichannel optical links, various channel equalization schemes have been proposed. They include the use of Mach-Zehnder optical filters or acousto-optic tunable filters to selectively attenuate the higher-gain channels using active servo-loops. Dynamic channel equalization can also be achieved by controlling the gain, by adjusting the pump, in a two- stage amplifier with complimentary gain spectra in each stage. Also, passive channel equalization has been demonstrated by cooling the amplifiers down to approximately 77 degree(s)K so that they become predominantly inhomogeneously broadened.
© (1994) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Michalis N. Zervas and Richard Ian Laming "Noise considerations in twin-core channel equalizers", Proc. SPIE 2289, Doped Fiber Devices and Systems, (3 October 1994);


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