In this work, the performance of a point-to-point fiber communication system that use a directly modulated (DML) VCSEL have been studied at 2.5, 10, and 40 Gb/s. We have demonstrated that a low-cost error-free transmission is possible by the appropriate choice of the shape of the driving electric pulse, the extinction ratio (ER) and the On-Off Keying (OOK) signal code (Non Return to Zero-NRZ and Return to Zero-RZ). Additionally, a theoretical model is developed to research and simulate the behavior of chirped signal transmission in dispersive media such as an optical fiber. Thus, the VCSEL-DML generated frequency chirp can be handled in order to avoid the effects of the interaction of laser chirp with fiber dispersion. The transmission performance of a 40 Gb/s optical link over Standard Single-Mode Fiber (SSMF) and over Negative Non-Zero Dispersion Shifted Fiber (NZDSF(−)) is researched by simulation.