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The optimization of an uncooled directly modulated laser operated at 10 Gbit/s for metropolitan area networks utilizing negative dispersion fibers is presented. The laser optimization is performed in order to accomplish two goals: maximizing the back-to-back sensitivity and the dispersion tolerance of negative dispersion single-mode fiber. Extensive numerical simulations reveal that a significant improvement of system performance can be achieved by optimizing simultaneously four laser intrinsic parameters, namely linewidth enhancement factor, photon lifetime, gain parameter, and gain compression factor. The optimal laser parameters have been obtained at a temperature of 25°C. The optimized laser shows a weak dependence of back-to-back sensitivity and dispersion tolerance on variations of laser intrinsic parameters as well as on laser temperature up to 85°C. Nevertheless, the gain compression factor is the most stringent intrinsic parameter, because it controls the right balance between the transient and adiabatic chirps. The results show also that the impact of laser parasitics on system performance is only slightly altered with the temperature increase up to 85°C. Back-to-back sensitivities of about -27.8 dBm and -29.1 dBm and 1 dB dispersion tolerances of about 1550 ps/nm and 1580 ps/nm have been achieved at 25°C and 85°C, respectively. The dispersion tolerance doubles the value of 750 ps/nm reported in a practical experiment.