A system for enabling reconfiguration of a Wavelength Division Multiplexed (WDM) optical communications network. A plurality of channel transmitters are provided for generating respective optical signals within corresponding wavelength channels of the network. A broadband light source generates a broadband continuous wave light having a bandwidth corresponding to a channel band of the network. A wavelength selective switch includes a first switch port connected to receive optical signals from the channel transmitters. A second switch port is connected to receive the broadband continuous wave light from the broadband light source. The wavelength selective switch is configured to comb the broadband continuous wave light into a plurality of narrowband lights respectively corresponding with wavelength channels of the network. A common-OUT port of the wavelength selective switch outputs a WDM signal for transmission through a downstream fiber span of the network. The wavelength selective switch is controlled to switch optical signals from the first switch port to the common-OUT port as active wavelength channels, and further to switch narrowband lights corresponding to inactive channel wavelengths to the common-OUT port. Consequently, a spectral loading of the WDM signal is independent of the number of active wavelength channels.