Cost-effective coherent ONU transceiver based on single directly modulated laser.

A cost-effective structure is proposed for the optical network unit (ONU) transceivers in coherent ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON), which is based on a single directly modulated laser (DML). This is the first time that a DML is used as both optical transmitter in upstream and local oscillator (LO) for coherent detection in downstream. The impact of extinction ratio (ER) of signal from DML is investigated and optimized by adapting the driving amplitude and bias of DML. Each UDWDM grid accommodates a pair of bi-directional signal, where heterodyne detection is used due to the Rayleigh backscattering (RB) from the bi-directional transmission. The impact of frequency offset (FO) between upstream and downstream signal is also investigated. Finally, 2.5-Gb/s bi-directional transmission of OOK signal over 60-km SSMF is experimentally demonstrated within the 12.5-GHz grid, achieving about -43 and -45.5 dBm receiver sensitivity in the downstream and upstream, respectively.