What is ZR, ZR+, and XR optics?

400Gigabit coherent pluggables are creating a lot of excitement in the networking industry. However, these pluggables come in multiple varieties and capabilities including ZR, ZR+, and XR. It’s important to understand the differences amongst them including their relative advantages, and the applications where they have the best fit.
Lets start with 400ZR, which was the original 400G pluggable with specifications defined by the OIF. 400ZR is targeted at point-to-point metro data center interconnect applications.
Client services are limited to 400Gigabit Ethernet and distances, are limited to 80 to 120 kilometers. The transmit output power is also low, and these pluggables do not support deployment over ROADM networks.
Recognizing the need for 400G pluggables that exceed 120km, the industry created higher performance 400G pluggables, and the 400Gig ZR+ name became an umbrella term for any pluggable that offers better than 400ZR performance. 400ZR+ pluggables may comply with the Open ROADM MSA, OpenZR+ MSA, or other specifications.
400ZR+ reach is typically in the 400 to 1,000km range, though longer distances have been demonstrated including 1,800 kilometers in a live field trial with Infinera’s ICE-X ZR+ pluggable. Additional 400ZR+ enhancements include a wider range of clients including OTN, and 100Gigabit Ethernet, configurable data rates, and higher transmit power enabling transport over ROADM networks.
XR Optics provides another 400G pluggable option that delivers high performance transport over both ROADM networks, and DCI networks. In addition, XR Optics provides support for point-to-multi-point connectivity leveraging digital subcarrier technology which can revolutionize the network architecture, and deliver considerable cost savings.
Additional XR Optics benefits include high transmit output power, a single fiber working option, multi-generational interoperability, and intelligent manageability to ease deployment in routers and 3rd party devices. Standards are driven by the Open XR Forum which is also driving standards for the intelligent, and host-independent management of coherent pluggables. XR Optics also include temperature hardened variants for deployment in harsh environments.
So whatever your 400G pluggable needs I hope this explanation helps you choose the best option for your network application.