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Building Open Optical Right – Enabling the Network for the Next Decade, or More…

Christain Uremovic

February 29, 2024
By Christian Uremovic
Senior Director, Solution Marketing

Optical networks are evolving ever faster, and making the right decisions about network architecture has never been more important. We are on the cusp of a world where coherent pluggable optics move from simple point-to-point data center interconnect (DCI) networks to wide-scale use in all optical networking scenarios. We are rapidly moving to more open networks where operators mix both embedded optical engines and pluggable optics from multiple vendors over the same open optical line system. And the whole telecom/datacom industry is rapidly adopting machine learning and advanced automation to optimize network operations. How does a network operator embrace this rapidly evolving environment and build the best optical network today that will scale to the capacity requirements of the next decade, and perhaps even longer?

First, let’s quickly take a look at recent optical engine evolution. Continuous optical networking innovation has enabled us to transport ever more data over longer distances with ever lower power consumption. For example, around eight years ago the leading DWDM technology could transport 200 Gb/s of data over a single wavelength over a distance of about 600 km without signal regeneration at 0.75 W/G. Today we can transport 800 Gb/s wavelengths over 1,000 km at 0.2 W/G, and the next evolution step to 5-nm technology in the digital signal processor (DSP) will enable 800 Gb/s wavelengths to be transported over 3,000 km only using 0.15 W/G.

A similar DSP evolution path has also enabled pluggable optics to embrace coherent DWDM technology, and the latest generation of these devices can transport a single 400G wavelength around 1,000 km. 800G coherent pluggable interfaces are just around the corner and promise to transport 800 Gb/s wavelengths approximately 2,000 km and 400 Gb/s wavelengths approximately 3,500 km, astonishing distances for such small devices!

Continuous evolution of these devices drives enormous capacity growth into optical networks. So how do we optimize the underlying optical line system to support these devices today and into the future?

Expanding Optical Spectrum with Super C-band and Super L-band

In the late 1990s, we expanded the utilization of the C-band fiber spectrum from 3.2 THz to 4.8 THz for extended C-band to support network traffic growth and transport more data over fiber. In the initial coherent era with 100 Gb/s transmission technology, this enabled a total of 9.6 Tb/s on a fiber pair. Coherent technology rapidly evolved to 200G, 400G, 600G, and then 800G, which enabled networks to absorb high-capacity growth without the need for additional optical spectrum. Today we can support 42 Tb/s per fiber pair using the extended C-band, more than four times the capacity in the same optical spectrum. For those who want to dive deeper into this topic, see these recent blogs addressing this topic in subsea networks and data center networks.

However, today we are approaching the Shannon limit, and spectral efficiency improvements with new generations of optical engine have significantly slowed. To continue to support network traffic growth, we need to expand fiber utilization into the broader Super C-band with a 6.1 THz spectrum. This provides 27% more fiber spectrum, and we can now support over 50T on a fiber in the Super C-band with today’s optical engines. Utilizing the Super L-band as well gives us an additional 6.1 THz of spectrum, enabling the 100 Tb/s era on a fiber pair.

 

Optical spectrum evolution

Figure 1: Optical spectrum evolution

This technological evolution has a positive impact on how we build optical networks today as we can leverage the improved wavelength capacity-reach to optimize network economics and efficiency.

Embracing Automation with Improved Optical Link Control

As much as everyone would love a nice greenfield network for each new generation of optical technology, that rarely happens. New generations of highly programmable coherent engines are often deployed side by side with older generations of coherent optical engines, including older 100G/200G transceivers that lack the same level of programmability. Further, open optical networking adoption is enabling wider deployment of third-party or “alien” wavelengths in the same networks. Again, interested parties can take a quick detour to a joint blog we did with Arelion discussing this topic.

This evolution creates challenges for open optical line systems, particularly in the areas of network planning, validation, and power balancing. We need new automation methodologies to balance wavelengths more efficiently and utilize real-time data from the network. One approach is to use generalized OSNR, or G-OSNR. G-OSNR takes multiple real-time measurements from the network, such as span length and pre-and post-amplifier gain, together with the provisioned passband for the specific channel. It then calculates and provisions the most optimal transmit power per wavelength fully automatically. For every given wavelength, baud rate, amplifier setting, and span length combination, the transmit power is unique and will be set to the most optimal level to realize maximum performance with the best OSNR.

G-OSNR operation

Figure 1: G-OSNR operation

This capability enables network operators to get the best efficiency out of the network even when multiple diverse generations of coherent technology are used on the same route, and regardless of whether it is a metro, core, or long-haul network.

Where and Which Part of the Network Matters

As open networking principles migrate from the data center environment to the wider service provider domain, compact modular platforms need to evolve to ensure that carrier-grade service provider requirements are included. This includes redundant field-replaceable controllers, redundant AC or DC power supplies, redundant fans, and 300-mm and 600-mm chassis deployment options.

Chassis deployment options are critical outside of the data center environment, as many service providers operate in locations requiring 300-mm chassis. The capability to support both 300-mm and 600-mm locations/chassis in the same network is key as networks shouldn’t need to be segmented into 300-mm and 600-mm domains simply to fit the constraints of the underlying optical networking platform. Another factor to consider is the “size” of the node, regardless of the chassis depth requirements. Compact modular platforms that support chassis stacking and a mix of both optical sleds, such as ROADM units or optical amplifiers, and traffic units, such as transponders, muxponders, or switchponders, can enable operators to build the node size they need to match the location’s requirements. Operators can build small, medium, or large OLS nodes from the same set of optical networking and traffic unit building blocks to support deployment requirements regardless of the location.

Additionally optical networks supporting 5G xHaul traffic need to support a high-performance optical timing channel to resiliently distribute high-accuracy timing to cell towers and other end applications needing synchronization, as discussed in this blog.

The Result: A Scalable Multi-haul Open Optical Line System

Maximum capacity per fiber, optimal performance regardless of the location in the network or the coherent technology used, the flexibility to deploy in 300-mm and 600-mm locations, FOADM and ROADM building blocks for different parts of the network – pulling all these capabilities together creates a single and highly automated multi-haul optical line system that can be deployed in multiple network domains and address multiple applications from the metro through to long-haul and subsea domains. The resulting single “flat” multi-haul domain removes the historic demarcation boundaries between networking domains to support those long-optical-reach performance figures we discussed earlier.

Operators now have the option of a single open multi-haul OLS for multiple networking applications concurrently supporting multiple network domains. These capabilities can help network designers implement an optical line system for the future that provides significantly better economics, more fiber capacity, improved and automated optical performance, and the scalability benefits of a flexible compact modular platform supporting legacy coherent optics, today’s high-performance embedded and pluggable optical engines, and future optical engines as technology continues to evolve.

The Infinera GX OLS supports the capabilities we’ve discussed in this blog and is currently being deployed by network operators around the globe to support a wide range of open optical networking scenarios. The Infinera GX solution has also been honored with a prestigious Lightwave Innovation Review in 2024. This industry-leading optical networking solution received outstanding scores from experts, highlighting its technical features and substantial benefits to network operators.  Check out our video about the solution.

And keep in mind, your choice for an optical transport network today will be your choice for an underlying telecom infrastructure for the next decade, or more.