The function described is gain clamping. In Wavelength Division Multiplexing (WDM) systems, Optical Amplifier (OA) modules, such as Erbium-Doped Fiber Amplifiers (EDFAs), are used to boost the signal. When optical channels are dynamically added or dropped, the total input power to the EDFA changes. Without a control mechanism, this would cause power fluctuations and gain variations for the remaining channels, a phenomenon known as cross-saturation. The gain clamping function stabilizes the amplifier's gain at a constant level, irrespective of input power variations, by using techniques like an all-optical feedback loop. This ensures that the performance of surviving channels remains stable, which is crucial for reconfigurable optical networks.

1. Official Vendor Documentation: Huawei WDM OTN Technology (Training Material for HCIP-Transmission). In the chapter on Optical Amplifiers

the section on "Key EDFA Technologies" describes gain locking/clamping as the mechanism to solve the problem of gain fluctuation when the number of wavelengths changes

ensuring system stability.

2. Peer-Reviewed Academic Publication: Zirngibl

M. (1991). "Gain control in erbium-doped fibre amplifiers by an all-optical feedback loop." Electronics Letters

27(7)

560-561. This foundational paper describes a method to "clamp the gain" of an EDFA

making it independent of input signal power

which is the exact function required when channels are added or dropped. (DOI: https://doi.org/10.1049/el:19910354)

3. Peer-Reviewed Academic Publication: Sun

Y.

et al. (1997). "Fast power transients in WDM optical networks with cascaded EDFAs." Electronics Letters

33(4)

313-314. This article discusses the power transients caused by channel add/drop and highlights the necessity of gain clamping in cascaded amplifier systems to maintain performance. (DOI: https://doi.org/10.1049/el:19970223)