An optical node supporting a modular deployment and upgrade of optical spectrum includes one or more C+L-Band amplifier modules; and a modular base module configured to interface one or more C-Band optical modems; wherein, in an initial deployment configuration, the modular base module provides channelized Amplified Spontaneous Emission (ASE) loading for select channels in the C-Band via a first ASE noise source coupled to a multiplexer for the C-Band, bulk ASE loading over the L-Band via a second ASE noise source coupled to an L-Band output, and an upgrade port for connection to an L-Band upgrade module. The L-Band upgrade module can selectively connect to the upgrade port to provide an L-Band upgrade configuration where the L-Band upgrade module and the modular base module coordinate transition of the bulk ASE loading to L-Band channelized ASE loading via a third ASE noise source.