Many of us may be familiar with the adage “less is more”, first coined by the architect Ludwig Mies van der Rohe, implying that a minimalist approach to aesthetic matters is more effective.

In the case of coherent optics, one can turn that expression on its head, and instead state that “more is less”. This is especially apparent in the case of the latest sixth-generation super-coherent optics, which are optimized to maximize capacity and reach across a wide range of network types.

In this case, “more” means more scale and more performance, thereby enabling network operators to use “less” optics and lower network power consumption for a given network capacity. The benefits of sixth-generation super-coherent optics allow network operators to more efficiently transport new high-speed services such as 400 and 800 Gigabit Ethernet (400/800GE), while simultaneously benefiting from CapEx and OpEx reductions to lower network total cost of operations (TCO).

In this blog, I will look in more detail at how sixth-generation super-coherent optics enable “more is less”, in terms of both technology and its application to different network applications.

One example of sixth-generation coherent optics is the Nokia PSE-6s, which delivers “more” across all the typical parameters that define the scale and performance of coherent optics. The digital signal processor (DSP) engine that powers the PSE-6s gets an increase in operating speed to 130Gbaud or more. It is closely integrated with high-speed silicon photonics into a multi-chip module (MCM) to reduce implementation penalties and maximize performance. The PSE-6s also implements the latest advances in coherent modem algorithms such as probabilistic constellation shaping (PCS) and co-optimizes its operation with high-gain forward error correction (FEC) bringing performance to just shy of the Shannon Limit.

Together, these advances enable super-coherent optics to push the capacity per wavelength to speeds of 1.2Tb/s, or when operating at speeds of 800Gb/s, to increase the maximum reach to three times or more than current solutions, up 2000km over a single wavelength (see figure 1).

Figure 1. Sixth-generation super-coherent optics can operate at 800Gb/s speeds with three times or more the reach of existing solutions, helping eliminate regeneration sites and reduce space and power in long-haul networks.

Beyond simply pushing the envelope on capacity-reach performance, the latest generation of coherent optics also includes features such as continuous baud rate adjustment, which enables them to transmit the greatest number of bits in the least amount of spectrum across any link, no matter the distance. This is especially valuable in subsea or long-haul cables operated in a “gridless” configuration and allows the greatest total capacity to be transmitted over scarce fiber resources.

At the same time, sixth-generation super-coherent optics consume less power per bit and enable reductions of 15–40 percent compared to the prior generation of coherent optics operating at 90–100GBaud.

But there’s more “less” to be had. By increasing scale and performance, network operators can get more services and more bandwidth onto their network and use less optics for a given network capacity. Combined with lower power per bit for each optic, this has a multiplicative effect in reducing total network power consumption. 

Let’s look at how sixth-generation super-coherent optics such as PSE-6s enable these savings across a range of networks, including metro, regional and long-haul applications.

Starting big first, in long-haul networks the defining characteristic of sixth-generation optics is the ability to transport the next generation of 800GE services over practically any distance, thereby enabling IP networks to upgrade to the latest routers having more scale and better power efficiency. With solutions like PSE-6s, 800GE transport becomes possible over long spans without the need for regeneration or splitting services across two wavelengths operating at lower speeds, both of which increase CapEx, space and power.

Figure 2 shows how less optics can be used when 800GE services are transported over 800G wavelengths in three representative long-haul networks, including an Indian national long-distance network and continental scale networks spanning the United States and Europe. As can be seen, the latest performance-optimized coherent optics can reduce the number of coherent optics needed by 50 percent or more when normalized to equivalent network capacity, enabling important CapEx reductions. Also shown is the impact on total network power consumption normalized to Watts per Gb/s, where savings of over 60 percent help further reduce network TCO.

Figure 2.  Sixth-generation super-coherent optics significantly reduce the number of optics needed in regional, national continental long-haul networks, helping lower total cost of operations (TCO)

Sixth-generation super-coherent optics continue to deliver network savings as one reduces network scope from large national or continental networks to “regional” networks. These latter may span a portion of a larger continental footprint, encompass nation-wide networks across smaller countries, or may even include the greater metropolitan area of large cities.

In these cases, the ability to operate at higher wavelength speeds such as 1.2Tb/s or 1.0Tb/s allows more 400GE and 800GE services to be transported over less wavelengths, compared to prior generations of coherent optics having a maximum wavelength speed of 800Gb/s or 600Gb/s. In Nokia’s case, this greater scale is compounded by the ability to interconnect two PSE-6s optics into a single 2.4Tb/s super-channel. This provides even greater flexibility for mapping high-speed services into a larger pool of capacity, for example, supporting three 800GE services over 2.4Tb/s for metro distances, or five 400GE services over 2Tb/s across regional distances of hundreds of kilometers. In regional applications, PSE-6s can reduce the number of optics needed for a given network capacity by 20 percent or more.

A final application to explore is metro data center interconnect (DCI), especially when connections between data centers may be fiber-constrained and approaching capacity exhaustion. In this case, one could say that “more is more”, as the scale of sixth-generation super-coherent optics enables significant increases in network capacity, thus extending the ability to leverage existing fiber assets.

In metro DCI applications, a key challenge faced by data center operators is maximizing the capacity of their DCI connections in the face of surging demand, which is expected to increase further due to data center virtualization, the shift from on-premises to cloud-delivered services, and the growth of AI and ML workloads that drastically increase compute and connectivity requirements.

One option for optical DCI is to use pluggable coherent optics such as 400ZR directly equipped in 400GE router ports. While 400ZR enables lower power consumption for connections up to 80–100km, this comes at the expense of much lower performance, which limits spectral efficiency and total fiber capacity. Another solution for metro DCI is to use super-coherent optics such as PSE-6s, which can double fiber capacity compared to 400ZR. For DC operators who either lease fibers or have limited fiber deployed, high-performance coherent optics can help extend their DCI capacity, thus avoiding additional CapEx costs for more fiber.

Figure 3.  Performance-optimized 6^th-generation super-coherent optics double metro DCI capacity compared to 400ZR pluggable optics, deferring capacity exhaust for fiber-constrained operators

In such a case, PSE-6s can transmit up to 1.2Tb/s of data over 100km using only 150GHz of fiber spectrum, while 400ZR optics transmit only 400Gb/s over the same distance using up to 100GHz of spectrum (see figure 3). Super-coherent optics also support operation over the C+L bands, enabling a further doubling of fiber capacity, up to 77Tb/s! 

Pairing two 1.2Tb/s super-coherent optics into a single virtual 2.4Tb/s channel can also enable efficient transport of three 800GE services over only 300GHz of spectrum. It also allows the seamless upgrade of routers from 400GE to 800GE ports without changes to the transport solution, helping operators reduce router power per bit by 75 percent by moving to 800GE.

So, while the adage “less is more” can often be a good approach to teasing out something’s fundamental essence, one can also value that “more is less” when the result are important reductions in network TCO and carbon footprint. In the case of the latest generation of super-coherent optics, more scale and performance bring significant benefits in enabling less cost and power, and from that more value from the network.