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Routing and Wavelength Assignment (RWA) problem in Wavelength Division Multiplexed (WDM) optical networks assumes assigning the routes and wavelengths to be used to create the lightpaths on behalf of the connection requests. The RWA problem belongs to the class of combinatorial optimization problems. The optimal solution to the RWA problem is found to be NP-hard and thus suited to heuristic approaches. We formulate an Integer Linear Programming (ILP) problem to model the RWA problem as an optimization problem and solve the formulated ILP using Genetic Algorithm (GA) heuristic to obtain a near optimal solution in polynomial time. Our primary optimization objective is the establishment of connection requests with minimum congestion among the individuals. The secondary targets are to minimize the hop count, route length, the number of fiber links utilized to honor all the lightpath requests. The GA based heuristic approach is simulated on ARPANET (Advanced Research Project Agency NETwork) and the results obtained for the multi objective GA are compared with the single objective GA. The results show that multi objective GA performs better than single objective GA while optimizing different network parameters.