Modeling high-speed optical transmission systems

Computer simulation of a 2.5-Gb/s intensity-modulated/direct-detected optical system with high path dispersion is described. This simulation, based on single-mode laser diode rate equations, includes transmit and receiver circuit filtering, receiver circuit noise, avalanche photodiode noise, fiber dispersion, and laser chirp. The rate equations are sufficiently general to model mode-offset distributed feedback laser diodes. The system power penalty, due to laser chirp and fiber dispersion, is calculated using Gaussian quadrature numerical integration. By simulating a population of some 12800 laser diodes and correlating the performance of each laser in a transmission system with its spectral characteristics, it is possible to deduce laser specifications that will assure satisfactory operation in long-span links. These results are used to study a laser diode specification under consideration by CCITT, and, by studying the simulated laser line shapes, some modifications to the CCITT specification are considered