Integrated Testing Simplifies DCO Complexities
Pluggable coherent optics really hit mainstream in 2022 and a big part of that was the multi-vendor ZR interop at the OIF booth at OFC 2022. It was great to be involved in this public event as we have been involved in the background for many years supporting the pluggable coherent ecosystem from the earliest 100G CFP days – and we are already prepared to help simplify the considerable testing complexities for future 800G ZR.
The Maze of Complexities
Pluggable coherent optics, especially DCO where the DSP is integrated into the module, represent the highest complexity of any pluggable optical modules and offer a range of unique challenges through the R&D, design validation and integration phases. We at VIVAI have been actively supporting pluggable optics vendors since the earliest days, and many of our applications such as register peek/poke and frequency and skew variation have become the norm for client (direct detect) modules.
As 400G coherent becomes far more widespread, we see many more groups being exposed to the complexities of DCO. Even groups who are very experienced with client optics have a very steep learning curve with ZR and other coherent pluggables.
The evolution of coherent optics – from line cards to pluggables
Photonics Challenges
Of course, the obvious complexities are seen around the photonics – moving from simple intensity modulation and direct detect (IMDD) to complex modulation – with both phase and polarization diversity. Simple attenuators and spools of fiber need to be replaced by OSNR and PD scramblers and more critically, the photonics are no longer purely in the photonic domain. The DSP is a critical element and the algorithms driven by the DSP firmware are intimately related to the optical modulation and impairments – and characterization involves both optical and firmware knowledge.
Performance monitoring of the optical link is far more complex than with client optics (which typically only report a few simple parameters such as optical power). We have everything from wavelength to power to OSNR to error vector magnitude and rate of change of state of polarization to name a few. Every one of these parameters has a ‘photonic’ aspect and a DSP/firmware aspect which must be neatly orchestrated by the module firmware and later integrated with the host system to be useful.
While the majority of client interfaces are based on Ethernet, many of the pluggable coherent optics (especially CFP2 400G) can support multi-service clients for OTN, which is still the workhorse of DWDM networks used by carriers today. The multiple potential OTN, OTL and FOIC clients all need to be managed and correctly handled by the DSP. The hundreds of relevant alarms and errors need to be collated and processed by module firmware and communicated to the host – so the firmware is complex and demanding.
VIAVI ONT 800G FLEX DCO Module
ONT and MAP – a Tightly Integrated Approach
We at VIAVI realized a new approach was needed to support the latest generation of 400G and beyond coherent modules. Individual isolated applications for traffic, for module management, for photonics would no longer work, especially with the tightly integrated relationship between photonics and DSP firmware. When we developed our ONT product family we wanted to integrate our ONT applications with our photonic tools – the MAP platform.
MAP tools can dial in known OSNR or set up a precision state of polarization rate, while ONT applications manage all aspects of the module, from the very best in cooling and power through precision module management and the full range of clients across Ethernet, OTN, OTL and FOIC. The huge impact of module firmware cannot be overstated. With client optics, the firmware is relatively simple and easy to understand and debug, but the considerable complexity of the coherent DSP and performance monitoring really underpin the module functionality.
VIAVI MAP Platform
Simplify DCO Complexities with VIAVI
Contact the VIAVI team to find out more about the support we can offer with developing, validating, integrating and scaling manufacturing of pluggable coherent optics. We can help you easily navigate your product through all the complexities of these modules.
