400G Optical Transceivers

Two main standards dominate the market today. One is published by the Optical Internetworking Forum (OIF), 400ZR, and the second is published by the Open ROADM multisource agreement (MSA). The 400ZR Implementation Agreement recently published by the OIF is designed to reduce the cost and challenges associated with high-bit-rate data center interconnect (DCI) and network flexibility. It creates a simple, footprint-optimized, and economical method for transmitting 400 Gigabit Ethernet over DCI links for short distances (typically up to 80 km). The 400ZR specification uses DWDM and higher-order modulation such as 16QAM.

The 400ZR specification also has an industry-derived variant called ZR+. The ZR+ module consumes about 15 W (more than the 400ZR specs), which allows more powerful signal processing techniques to span 200 km. The ZR+ compromises between the unique needs of the data center market and the telecom market. It offers the smallest form factor to push 400G speeds but relieves the reach limitations of 400ZR.

400G pluggable coherent modules solve some of the challenges faced by different industries and segments in the data transport market. Short distance 400G pluggable transceivers using PAM4 demand multiple lasers that cannot operate at long distances. For this reason, 400G pluggable coherent modules use coherent optics that combine phase and amplitude modulation as well as orthogonal polarization in transmission with approximately 64 Gbaud rate. This enables the 400G pluggable coherent modules to offer up to 1,000-km reach with a single laser, and as a result, far lower investment and opex. The 400ZR standard also calls for unprecedented interoperability at high speeds, which enables operators to mix equipment from multiple vendors in the same network for the first time.