800G Generation Coherent and the New Normal

As the saying goes, “It’s hard to predict, especially the future.” Few people foresaw the huge impact COVID-19 would have on our health or the global economy, let alone our networks – though in many respects, COVID just accelerated trends like the shift to online shopping, streaming entertainment, virtual education, and remote work. Traffic patterns shifted, in terms of both geography and peak time of day, as large numbers of people were required to work or learn from home. Overall internet traffic growth increased from around 25% in a typical year to around 35%.

On the other hand, some 5G projects were delayed and incremental capacity additions on existing platforms were prioritized over network refreshes with new platforms and technologies. Chip shortages became widespread, affecting multiple sectors, from automotive to consumer electronics to networking equipment. Meanwhile, customers and governments became even less tolerant of any network downtime. Now that vaccine rollouts are gathering speed in many, though not all, parts of the world, there is light at the end of the tunnel. But what will the new normal look like?

Things just won’t be the same

The shifts to online shopping and entertainment are likely to remain. The shift to working from home is unlikely to completely reverse. However, many new home workers will be reluctant to begin commuting to the office full time again, and for many, hybrid models that mix in-person office work and remote work will become the new normal. Business travel will eventually resume, though the cost and time efficiency of online meetings and conferences means they will likely continue. Education is the most likely to return to the old normal (i.e., the classroom or lecture hall), though many of the online tools used during the pandemic will continue to be used to complement in-person learning. Internet traffic growth is forecasted to drop back to a still-healthy pre-pandemic mid-20s percentage. The pandemic-induced chip shortages won’t ease for a couple of years, until new fabrication capacity comes online. Post-pandemic, we are likely to see the resumption of delayed 5G projects, together with stimulus-backed broadband infrastructure buildouts to address the digital divide and to better connect rural and underserved communities.

In terms of optical networks, operators continue to face a number of preexisting challenges as they seek to address traffic growth in both a cost-effective and timely manner. They need to reduce the cost per bit per kilometer. They need to scale bandwidth without also scaling power consumption or the number of required rack units. Many also want to grow revenues with new services such as 400 Gigabit Ethernet (GbE) leased lines. And they need to maximize fiber capacity due to the high cost of acquiring and lighting new fiber, especially given the reduced availability of wholesale dark fiber in several markets.

Advances in coherent technology

So how can coherent optical technology help address these challenges? Well, the evolution of the silicon technology used to build ASICs that provide digital signal processing (DSP) and other digital functions to a 7-nm CMOS process node, together with additional improvements in photonic technology that support greater than 90 Gbaud symbol rates, have enabled the evolution to 800-Gbps coherent optical engines. Unlike coherent engines that are constrained by power consumption limits and the size of pluggable form factors like QSFP-DD and CFP2, embedded optical engines prioritize optical performance and the most advanced optical features with larger and more powerful ASICs/DSPs. For example, one such ASIC/DSP has more than 5 billion transistors, compared to around 1.5 billion in the ASIC/DSP of a 400G coherent pluggable.

To address the cost-per-bit-per-km challenge, 800G generation optical engines dramatically increase the outcome of the wavelength capacity-reach dynamic compared to previous generations, as shown in Figure 1. For example, a 600G generation based on 16-nm CMOS and before that a 400G generation based on 28-nm CMOS could deliver their headline data rates to distances of a few hundred kilometers. The new 800G generation can deliver 600 Gbps to more than 2,500 km and 400 Gbps to 7,500 km in terrestrial networks, with even longer distances possible in submarine networks. That 400-Gbps reach of up to 7,500 km makes this new generation ideal for cost-effectively delivering 400GbE services anywhere. With dual-wavelength optical engines, network operators can also deliver three 400GbE client services over two 600G line-side wavelengths, reducing the cost per 400GbE by a third compared to single-wavelength engines that would not be able to utilize the excess 200 Gbps of capacity in each 600-Gbps wavelength. Even the headline data rate of 800 Gbps can extend beyond 800 km with production levels of margin.

Wavelength capacity-reach matters because if an optical engine can deliver 50% more wavelength capacity, it will reduce the cost per bit by 33%, while doubling the wavelength capacity will halve the cost per bit. Wavelength capacity-reach is also closely correlated to power consumption in terms of watts per bit per km as well as footprint in terms of transponder rack units per bit per km.

Three main performance factors