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In this paper, we propose a novel lightpath rerouting algorithm to optimize network resources allocation in WDM all-optical networks in order to set up an incoming lightpath demand to be blocked for lack of resources or due to the absence of a suitable path and a suitable wavelength that meet the minimum Quality of Transmission (QoT) requirements. Indeed, in such networks, transmitted optical signal has to traverse crossconnect switches, fiber segments and optical amplifiers. Thus, while propagating through the network, the signal may degrade in quality as it encounters crosstalk at the cross-connect switches and collects amplified spontaneous emission noise at the optical amplifiers. Since these impairments continue to degrade the signal quality as it progresses toward its destination, the received Bit Error Rate (BER) at the destination node might become unacceptably high. Rerouting aims at reassigning the wavelength and/or the path of one or several established connections in order to free enough wavelengths to satisfy the incoming demand. Rerouting refers implicitly to dynamic traffic. Simulation results show that our algorithm improves the rejection ratio and is less CPU time consuming than rerouting algorithms previously presented in the literature.