Gain competition in optical amplifiers: A case study

Transparent optical networks based on wavelength-division multiplex (WDM) are an emerging solution for growing network traffic demands. However, compared to traditional electro-optic networks, transparency also brings new security challenges, accompanied by new vulnerabilities in the network. One such vulnerability is associated with optical amplification. The most commonly used optical amplifier is the EDFA (Erbium-doped fiber amplifier), which uses doped optical fiber as a gain medium to amplify an optical signal. Due to the limited number of the available upper-state photons necessary for amplification, EDFAs have limited gain, which is divided among all incoming signals. Each of the signals is granted photons proportionally to its power level, which can lead to a situation called gain competition. In this paper, we investigate the effects of gain competition with a case study in the laboratory, and analyze the associated risks for network operation.