Nonlinear distortions and compensations of DFB laser diode in AM-VSB lightwave CATV applications

Abstract

The nonlinear distortions of direct modulated laser diode applying to AM-VSB lightwave CATV systems are studied from the viewpoint of rate equations, A simple method for calculating composite second-order distortion (CSO) is proposed, which is denoted as the quasidynamic approach. The attribution of nonlinearity from fiber dispersion and laser chirping are also concerned. The dependences on the variations of parameters of rate equations are intensively investigated to figure out the dominant factor for CSO degradation. This approach explains quite well the experimental results and gives a clue of constructing the predistortion circuit with at least 10 dB improvement.