Multi-Rate Multi-Format CFP/CFP2 Digital Coherent Interfaces for Data Center Interconnects, Metro, and Long-Haul Optical Communications

New customer usages, such as high-definition videos, business analytics, and cloud services, stress more and more optical transport networks. This demand for ever-increasing capacity combined with the hard competition between telcos results in requests for lower costs in wavelength division multiplexing (WDM) transport. As WDM transceivers operating at 100G and beyond represent a large part of transmission system cost, a strong pressure is applied on vendors so that they lower the price of line-side interfaces. For the past 6-7 years, some equipment suppliers have focused their efforts on the development of pluggable optics adapted to 100G and beyond WDM transport. Thanks to photonic integrated circuits, they develop multisource agreement form factors that are able to generate/detect 100G at a very efficient cost, with notably reduced power consumption and high port density. Two flavors are used for pluggable optics that integrate or not the digital signal processing circuitry into the form factor, i.e., digital coherent optics (DCO) and analog coherent optics, that are supported by two kinds of form factors, i.e., CFP and CFP2. The corresponding cost decrease involved by pluggable optics is really impressive: over the 2014-2018 period the WDM 100G port price has been divided by a factor of ~6, while the power consumption per 100G port oscillates today between 10 and 30 W (depending on vendors). In addition, CFP-DCO and CFP2-DCO are now able to generate 100G and 200G data rates with multiple modulation formats (i.e., QPSK, 8QAM, and 16QAM) resulting in a very high level of flexibility for these interfaces making them suitable for a wide range of applications. In this invited paper, we present the work performed since 2015 on both 100G CFP-DCO and 100G/200G CFP2-DCO interfaces used in various contexts: short-reach and data center interconnects, metro/regional, long-haul and ultra long-haul optical communications.