ABSTRACT
Coherent detection for access networks enables superior receiver sensitivity that allows extended power budget and high-frequency selectivity for closely spaced DWDM/ultra-DWDM channels without the need of narrow-band optical filters. An access network is a totally different environment as compared with long haul and metro. In access applications, a shorter transmission reach induces less distance-dependent signal degradation, less required link equalization, and less DSP processing for impairment compensation, such as CD compensation, PMD compensation, and polarization tracking. Moreover, the cost of transceivers close to the user side should be in particular reduced in an access network. The standardization of coherent optics in access networks has mainly been led by CableLabs®. A closer look at the United States cable network is illuminating to assess the potential growth of coherent optics links and economies of scale for components used in the access. The access network is the largest component of the network in terms of physical/geographic scale and investment.
