Practical design of a coherent ultra-dense WDM-PON with paired DFB lasers

Abstract

A coherent WDM-PON achieving ultra-dense spectral allocation is reported. The ONU at user premises is built of coherent transceivers with two paired low-cost DFB lasers, one as local oscillator and the other as transmitter, offering simplicity and economy hardware. The ONU DFB lasers are paired to realize a simple blind activation process, having wavelengths with limited thermal tunability controlled by thermo-electric coolers (TECs). A MAC at the OLT at central office manages the spectrum channel assignment: the OLT furnishes an optical carrier wavelength for the new active ONU to obtain reception in a Dynamic Wavelength Allocation (DWA) by a smart control algorithm, thus assigning a down-channel; subsequently, another paired up-channel is also allocated to the ONU laser transmitter. The MAC can reassign the channels because of interference, collision or any network needs. The channelization of the optical bandwidth is flexible, thus adapting to different user bandwidths, serving all sorts of bit rates and suited for 5G technologies. Measures in an activation process and in channel reassignment have been performed in environment conditions, demonstrating the system feasibility.