Low cost coherent receivers for UD-WDM NRZ systems in access networks

This paper presents the first experimental achievements of the COCONUT project which aims at demonstrating ultra-dense Wavelength Division Multiplexing Passive Optical Networks (udWDM-PON) by means of low-cost coherent solutions. COCONUT should exploit low-cost optical components and simple electronics so that the cost of typical line terminals would be affordable to the end-users. Among different technical approaches considered within the project; we focus here on the solutions based on simple OOK-NRZ format. We developed an original improvement of the conventional phase-diversity coherent detection schemes providing for polarization independent operations without doubling the receiver structure. As a result we demonstrated that passive networks of high-power budget (> 45 dB i.e. up to 60 km reach and more than 64-way power splitting) are feasible over a 6.25 GHz grid by using a limited number of photodiodes a simplified analog processing and free-running DFBs.