AbstractPhysical layer impairments (PLIs) is a matter of great concern in optical networks to achieve the optimum performance. In order to mitigate the PLI, a better routing and wavelength assignment (RWA) technique is required in optical wavelength division multiplexing (WDM) networks. In this paper, a dynamic ant colony routing algorithm with the consideration of various PLIs has been presented. This work also presents a Q-factor estimation model that includes impairments such as amplified spontaneous emission (ASE) noise, four-wave mixing (FWM), and cross phase modulation (XPM). The simulation results also prove that the proposed ant colony optimization (ACO) based algorithm significantly reduces the blocking probability as compared to dynamic load based shortest path algorithm (LB-SPA).