A system is disclosed for implementing WDM optical networks, without blocking, and without the need for wavelength converters. The method is based on a hypercube topology for connecting the nodes, and a novel algorithm for constructing a routing tree such that blocking cannot occur even under the stringent requirement of all-to-all broadcasting. The algorithm uses shortest paths and a small number of wavelengths to satisfy the all-to-all connectivity requirement. The number of wavelengths used may, in fact, be the minimum number needed to satisfy the all-to-all connectivity requirement, using shortest paths.