Technologies are generally described for substantially maximizing capacity in a wavelength division multiplexing (WDM) passive optical network (PON). An “achievable rate region” may be defined as a set containing admissible traffic rates of a given WDM PON system such that a volume of an achievable rate region is proportional to a capacity of the network. Deriving the achievable rate region for a particular network, decisions may be made whether incoming traffic rate can or cannot be achieved for that network. Moreover, the achievable rate region may be used to construct a WDM PON utilizing a minimum number of wavelengths, a minimum number of lasers with narrowest tuning ranges, and a minimum number of receivers, thereby reducing a capital expenditure in building the PON system.