Integration of optical paths and packets in a switch is a key technique to support ultra-high-speed traffic in the future Internet. However, the question of how to efficiently allocate wavelengths for optical paths and optical packets has not been solved yet due to the lack of a systematic model to evaluate the performance of the integrated switch. In this paper, we model the operation of the integrated switch as a system of two queuing models: M/M/x/x for optical paths and M/M/1/LPS for optical packets. From the model, we find an optimal policy to dynamically allocate wavelength resources in an integrated switch. Simulation results demonstrate that our mechanism achieves better performance than other methods.