The purpose of this article is to demonstrate the extension of the modulation bandwidth of single mode laser sources to reach the RF frequency range of wireless access networks such as ultra-wide band systems with low-cost solutions. In this article, we have studied optical microwave mixing using nonlinear direct modulation of a distributed feedback (DFB) laser diode. First, the nonlinear behavior of the DFB laser diode near the threshold current has been analyzed and explained based on frequency mixing measurements made with CW signals. Then, we have experimentally demonstrated frequency up-conversion of a QPSK signal. These results were compared to eye-diagram simulations based on the laser static and dynamic characteristics. Subsequently, the frequency up-conversion of a WLAN IEEE 802.11a signal was experimentally demonstrated. Best conditions in terms of DFB bias current and RF input power signals have been studied. Good conversion loss and EVM results have been obtained.