Since the demand for high-capacity in optical WDM networks keeps increasing, the realization of cheap and simple Optical Cross-Connects (OXCs) becomes more and more important. In this paper we propose new solutions for the construction of WDM optical switches employing only arrayed waveguide gratings and wavelength converters. Our approach defines single-stage OXC architectures and derives their nonblocking conditions, by considering two different connection request models for the lightpaths to be set through the switch. Depending on the degree of lightpath addressability, the OXC blocking is referred to either the wavelength-to-wavelength model or the fiber-to-fiber model. Further architectural considerations are added to identify different non-blocking solutions employing multiple switching/conversion stages.