Fundamental nonlinear distortions in analog links with fiber amplifiers

The author analyzes the second-order distortion in a modulated laser-based AM subcarrier multiplexed (AM-SCM) video transport system using fiber amplifiers for power boosting. All three of the involved system elements: the laser, the fiber amplifier, and the transmission fiber, contribute to the system distortion. The laser distortion originates from the internal photon-electron interaction, whereas the fiber amplifier and dispersive distortion are directly related to the intrinsic frequency chirping of the modulated laser. From the distortion magnitude and phase analysis, the author finds that under most situations the distortions have an electronic counterpart and can be electronically compensated. In addition, the system distortion can be minimized with a combination of critically chosen elements that have minimum or counteracting distortion mechanisms. Optically amplified AM-SCM systems can thus be engineered to perform well within the stringent distortion requirements for both 1.3- and 1.55-μm wavelength ranges