Effects of Modulation Current Shape on a Directly Modulated DFB-Laser Chirp at 2.5 Gbit/s

Semiconductor Distributed Feed-Back Direct Modulated Lasers schemes appear attractive for applications in the Metro network market due to its low cost and good performance. In this paper, a Coarse Wavelength Division Multiplexing system is studied by means of an Optical Communication System Design Software with a detailed analysis of the modulation current shape (exponential, sine and Gaussian) of lasers for operation on 2.5-Gb/s Metropolitan Area Networks to evaluate their tolerance to linear impairments such as signal-to-noise-ratio degradation and dispersion. Point-to-point links are investigated and optimum design parameters are obtained. Through extensive sets of simulation results, it is shown that some of these pulse shapes are more tolerant to dispersion when compared with conventional Gaussian pulses. In order to achieve a low Bit Error Rate, different types of optical transmitters are considered, including strongly adiabatic and transient chirp dominated lasers. Fibers with different dispersion characteristics are used, showing that the system performance depends, strongly, on the chosen laser-fiber couple.