When top-notch athletes shatter world records it is often the Olympic motto that is their driving force: “Faster, Higher, Stronger.”
But in the world of high-speed optical transmission a more apt slogan would likely be: “Faster, Farther, and more efficient.”
That’s because the father of information theory, Claude Shannon, told us there is a finite limit to the quantity of error-free information that can be transmitted over any communication channel. Further pushing against that immovable boundary is often less valuable than improving the efficiency of the overall transmission.
Still, records are meant to be broken and while The Shannon Limit is here to stay, Nokia Bell Labs’ latest record breaker says he keeps all these motivations in mind while chasing previously unthinkable levels of optical speed.
“We want to reduce as much as possible the complexity of optical transmission,” said Sylvain Almonacil, an optical research engineer in France. “We are close to the edge of what is possible and, if you want to reach the edge, it can require a huge amount of effort for a minor gain. So, it’s not only capacity but also how efficiently you carry this capacity.”
Almonacil and his colleagues at Nokia and Alcatel Submarine Networks recently scored a breakthrough on both fronts, setting a pair of world records.
The first was “the transmission of 800 Gbps Net Bit Rate per Wavelength over Transoceanic Distance Using 148-GBaud PCS-16QAM.” Extending the current distance record by a factor of four, it guarantied transatlantic transmission and further reduced the cost per bit of transcontinental communication systems.
The second was a “C-band Unrepeated Transmission System over 291-km at Net Throughput of 41.3-Tbps without remote amplification.” This addresses the global digital divide by advancing what is possible to achieve over submarine cables, offering a low-cost way to provide increased communication capacity to remote islands, coastal areas, or oil and gas rigs that are highly inaccessible.
Almonacil will be presenting the findings of both these records this week in Glasgow, Scotland at ECOC 2023, the 49th European Conference on Optical Communications, which is one of the most prestigious gatherings of the optical research community.
A race against exponential demand
It’s a never-ending race for capacity and spectral efficiency since the global demand for communication continues to increase at a historic pace. Consumer-driven demand for capacity typically grows at a rate of 60% a year, but in the age of artificial intelligence the increase in machine-driven demand is growing at a rate closer to 100% annually.
Therefore the biggest trends in optical research today are focused on multiple-spectral bands, multiple-core and multiple-mode systems, technologies that alter the infrastructure by increasing the number of transmission channels rather than increase the efficiency of an individual channel.
But there is still efficiency to be gained in the individual channel level and that’s what Almonacil and his colleagues focus on – pushing the limit by packing more bits of information into a single wavelength and transmitting it over the longest possible distance. In the world of optical networks, that speed is determined by how quickly a laser can “blink” and send light pulses down a strand of fiber.
Almonacil calls this “communicating near Shannon’s Limit,” alluding to the immutable law of physics that Nokia Bell Labs’ most famous mathematician Claude Shannon established in Information Theory 75 years ago.
While there may be no more order-of-magnitude-gains to be had in that quest, Almonacil and his colleagues continue to push for new and improved world records.
He explained that the quicker a laser can “blink” the farther it can transmit information. The recent world record, for example, achieved a transoceanic transmission with a single laser blinking 148 billion times per second.
“We believe that higher distances can be achieved by making the laser blinking even faster,” he said. “But this requires further improvements of opto-electronics devices to convert this information from the digital to the physical world.”
Almonacil said the key, though, was to find the most efficient trade off in cost per bit and that today only about half as many transceivers are required compared to previous generations. It’s what the industry demanded as a business and what sustainability required from a carbon footprint standpoint.
“The story of the new generation of optics is not just to increase capacity but to reduce the power we need to carry this capacity,” he explained. “The industry is looking for more efficient, simpler products. I can always give you more but the one who will win the game at the end is the one that can give the ultimate capacity at lower cost and lower power consumption.”
Speed, efficiency and performance
The quest for speed and efficiency translates into Almonacil’s personal journey.
He was born near Paris and raised by two teachers who instilled in him an early curiosity. What started as a love of computers and video games quickly translated into more technical expertise when, at age 17, he entered an intensive technician’s program while also working for the French national railway company, where he measured aerodynamical constraints generated by high-speed trains.
Aside from a brief internship in Italy, he has spent his entire life in France. He received his M.Sc. engineering degree in optics and photonics from the Institut d’Optique, Palaiseau and his Ph.D in physics from Paris-Saclay University.
Since 2016, he has been a Research Engineer in the Optical Systems and Devices Research Lab at Nokia Bell Labs in Massy. Since completing his Ph.D in 2019, he has specialized in high-speed optical transmissions systems in contexts such as submarine transmissions and free space optical satellite communications.
Currently living just outside Paris, the 32-year-old Almonacil is also in a hurry in his private endeavors. He spends most of his downtime cycling in the French countryside and competing in bike races. He’s also a licensed pilot who enjoys flying planes on the weekends and says these hobbies help him in his professional missions to keep pushing for greater speed, efficiency and performance.
“The human body has a limited amount of energy it can use on the bike. So, if you want the best result, if you want to win the race, if you want to be first, you must make the best use of what you have. You must optimize everything, in terms of food, sleep, everything,” he said. “This logic, this way of dealing with the race, it is the same as dealing with breaking a record in your lab. It is the same methodology.”