400G ZRx: Explore the Possibilities

400G ZRx optics are a family of pluggable coherent DWDM transceivers where the ZRx term refers to design variations including different types of Tx power, Forward Error Correction (FEC), data rates, and applications.  400G ZRx transceivers in QSFP-DD, OSFP or CFP2 form factors enable deployment directly in IP routers/switches, facilitating long haul connectivity over a DWDM network (IPoDWDM) without the need of going through specific transport equipment.    The most recent advances of packaging full coherent technologies into QSFP-DD or OSFP form factors allow these optics to consume less power per optic as well as increase the amount of transceivers per rack unit deployed in a host, all of which helps lower the total cost per 100G.  

400G ZRx Standards Variations:   How We Got Here 

There have been several efforts over the last 10-15 years to integrate the capabilities of 400G transport equipment into a pluggable form factor.  Back in 2016, the Open ROADM initiative was created by a consortium of telecom industry leaders to promote open, interoperable, and programmable optical networks. Its development was driven by Internet Service Providers (ISPs) and the need to overcome vendor lock-in, reduce costs, and enhance network efficiency through standardization and collaboration.  The main goal of Open ROADM was in support of transport backbone networks and metro applications, with multi-rate 100G-400G (both Ethernet and OTN protocols) + oFEC (Open FEC) and reach in the 100s of kilometers with amplification.  The earlier implementations of Open ROADM transceivers were mainly in a CFP2 form factor but it now has also been implemented in QSFP-DD/OSFP form factors. 

Concurrently, the OIF (Optical Internetworking Forum) 400ZR led an initiative driven by the need of Hyperscalers to achieve 400GbE DCIs (Data Center Interconnects) on DWDM amplified links up to 120km using smaller form factors such as QSFP-DD and OSFP.   Characterized by a simplified network design and a new error correcting code C-FEC (Concatenated FEC), 400ZR achieved much success in terms of establishing a widely adopted, interoperable standard for 400 Gbps coherent optical transport and meeting the growing demands of modern data centers.   These two efforts paved the way for OpenZR+, the latest standard for 400G coherent pluggables.  OpenZR+, an MSA (Multi-Source Agreement), merges some of the multi-rate capabilities from Open ROADM with higher performance oFEC and new form factors such as QSFP-DD and OSFP to build on the success and learnings of the widely adopted 400ZR standard.   For additional information about 400ZR and OpenZR+, see some of our blogs and whitepapers. 

400G ZRx Transceiver Solutions: A Practical Guide 

Precision OT offers several 400G coherent product options that adhere to both the OIF 400ZR and OpenZR+ standards.  Table 1 is a summary of our 400G ZRx product offerings: 

Table 1.  Summary of Precision OT’s 400G ZRx Products 

All these transceivers come in the QSFP-DD form factor and below are some of the key differences and practical considerations for these coherent pluggable transceivers: 

PRE-QSFP56DD-ZR => is the baseline standard OIF 400ZR product.  It’s a tunable DWDM optic which we refer to as the low Tx power option.   

PRE-QSFP56DD-ZRHT => similar to the ZR product and using the OIF 400ZR standard as a baseline but with higher TX output power to fit the needs of legacy/brownfield applications that require TX output power around ~0dBm. Also useful for longer reach unamplified links compared to the standard ZR. 

PRE-QSFP56DD-ZRXT => This product is a unique 400G transceiver for long reach point-to-point solutions.  Not DWDM tunable but fixed at DWDM ITU ch. 37, also provides a fixed TX output power (+4dBm) higher than our other solutions. This optic offers a link budget accommodating long distances up to 120km on unamplified links.  Considered the closest of the modules to being “plug-and-play” it does not require anything special regarding tunability or optical design or host compatibility. The -ZRXT is basically a big pipe of 400G up to 120km, perfect for grey links/dark fiber applications.  As a fixed DWDM optic there’s always the option of using this transceiver in a MUX/DEMUX design if you happen to have the ITU channel 37 free. 

PRE-QSFP56DD-ZRP => The baseline Open ZR+ product which can do 400G as well as all the breakout applications at N x 100G speeds and different modulation types as advertised by the MSA. It’s a full C-band DWDM tunable with Low Tx output powers and different reach depending on each application and network design. 

PRE-QSFP56DD-ZRPHT =>  This product is very similar to the 400G ZRP, but has a  High Tx  output power (up to +1 dBm), to fit the needs of implementation in legacy/brownfield Transport line systems. Also a good fit for longer reach multi-rate 100G-400G applications with unamplified links compared to the standard ZRP. 

What Precision OT Brings to 400G ZRx 

Precision OT is a systems engineering and integration company focused on end-to-end optical networking solutions.  We excel in network design, development and implementations customized to the needs of our customers.  As most everyone involved in network implementation is likely aware, coherent is much more complicated than direct detect.  Although there are standards available for the whole family of 400G ZRx products, there are intricacies and details around its implementation into routers and switches which require specialized expertise.  Precision OT has a deep technical understanding of all network layers and takes the time to fully understand our customers’ platform right down to knowing the latest SW versions needed.  We provide comprehensive network partnership including the following: 

• INTEROPERABILITY – Ensure fully interoperable and compatible modules and avoid vendor-locked/proprietary DSP based modules 

• COMPLIANCE – Follow industry standards in terms of 400ZR, OpenZR+, SFF and CMIS approved documents and agreements 

• MULTI-PLATFORM COMPATIBILITY – Perform multi-platform host system integration 

• FUNCTIONALITY – Test minimum host SW version releases for each NEM HW/SW 

• SUPPLY CHAIN – Provide supply chain diversity of 400G ZRx modules 

• DEVELOPMENTS – Participation in Industry wide standardization groups, plugfests and demos to keep up to date 

Keep an eye out for Part II of our 400G ZRx series where we’ll discuss 400G ZRx applications including grey links, amplified vs unamplified, power link budget calculations, break-out configurations and more !