Abstract: This paper discusses the optimal allocation of wavelength converters in shared-per-link structure in WDM networks. In particular, we consider the following two cases: (1) Given the total number of converters available in the system, allocate them at outgoing links of the node, such that the total amount of traffic getting through the system is maximized. (2) Given the number of converters available at each node in the system, allocate them properly at the outgoing links of the node, such that the total amount of traffic getting through the system is maximized. An optimization algorithm is proposed to solve case (1), and a heuristic algorithm is developed to find an approximate solution for case (2). Simulation results have shown the effectiveness of our solutions.