State-of-the-art digital coherent optical communication MSA standard ─ OpenZR+

OpenZR+ Multi-Source Agreement (MSA) is a de-fact standard among multiple manufacturers and is established to make a competitive market for interoperable coherent small form factor pluggable module such as QSFP-DD or OSFP. The small form factor pluggable module MSA was first widely adopted for Ethernet within data centers and is currently attracting attention from the perspective of adapting to digital coherent optical communications between data centers. There is a similar 400ZR standard developed by OIF, which can transmit 400GBASE-R Ethernet (400GbE) as a client signal, whereas OpenZR+ can provide multiplex transmission of 100G/200G/400GbE. In addition, OpenZR+ MSA can provide longer transmission distances by using OFEC, which is a higher net coding gain forward error correction code than 400ZR. NTT Electronics Corp. is one of the founding members of OpenZR+ MSA as a developer and seller of digital signal processors (DSPs) and has been involved in developing the specifications. OpenZR+ MSA specification version 1.0 released in September 2020 ^[1] enables WDM transmission of 400Gbps over 1000km over 100GHz grid with a combination of erbium-doped fiber amplifier (EDFA) and Raman amplifier ^[2].

The digital coherent pluggable module with small form factor and interoperability is expected to play a big role as an enabler of state-of-the-art/highest performance pluggable modules or equipment as and when needed. Conventionally, transmission equipment used in optical networks is vertically integrated from transponders to switching functions and controlled by dedicated software, which makes it difficult to upgrade some functions of individual component units or modules. To solve this problem, a new concept called disaggregation and optical open line system (OOLS), which can freely combine and optimally control disassembled component units or modules, has been proposed. Realization of the disaggregation and OOLS is considered an important step by TIP-OOPT Group similar to the work of OpenZR+ MSA. NTT Electronics Corp. has already developed OpenZR+ compliant DSP. One of outcomes is a success of interoperability testing in a joint verification by three OpenZR+ MSA members, Fujitsu Optical Components Ltd. (FOC), Acacia Communications Inc. and NTT Electronics Corp. ^[3]. This interoperability verification test shows the effectiveness of OpenZR+ MSA, which is very important to service providers. Currently, OpenZR+ MSA is studying next specifications, for 75GHz grid and beyond 400G. NTT Electronics Corp. continues to contribute to OpenZR+ MSA as a leading member and to develop key products in a timely manner.