This Nokia Bell Labs optical researcher drives the high-speed information highway By Aron Heller | Nokia, Monday, 18 Mar 2024

Qian Hu is a cutting-edge optical transmission researcher who is constantly seeking improved data rates in the never-ending race to meet the insatiable global demand for high-speed communication.

Her challenge is to produce new and inventive ways of increasing the amount of data that can be transmitted over fiber in an energy and cost-effective manner. It’s a job she compares to that of a traffic engineer who tries to boost the flow of passengers across a busy thoroughfare.

“The optical fiber is like a highway with unlimited lanes,” she explained. “But we are limited by the number of toll gates that enter the highway and the number and speed of the cars that enter these gates.”

In this analogy, the limited number of toll gates represent the limited bandwidth of an optical system that restricts the traffic flow. The cars on the highway represent symbols, which are very short pulses of light that carry information. So, the number of cars that can pass through these gates in a defined period represent the symbol rate of the system.

Symbol rate is bound by bandwidth. For the past few years, Hu has been researching three different tracks to overcome this limitation.

The first is on devices called electronic analog multiplexers that can double the data rate of the electrical signal that drives the optical modulator. The second is an investigation into new kinds of optical modulators that can provide large bandwidth for conversion of high-speed data signals from the electrical to the optical domain. And the third relates to new signaling schemes that increase the symbol rate beyond what is conventionally possible under current bandwidth limitations, by intentionally inducing interference that can be undone.

She’ll be presenting some of these findings in a pair of talks next week in San Diego, California at the Optical Fiber Communications Conference, the most prestigious gathering of the optical research community, in which some 13,000 participants from 74 countries are expected to attend.

“The Shannon theorem tells us that the channel capacity, which is the upper limit of the amount of information you transmit in a linear channel, is determined by two factors: one is bandwidth, and the other is signal-to-noise ratio,” Hu explained, citing the famous limit established by the father of information theory, Claude Shannon. “So, any researcher who seeks to increase the channel capacity always looks for solutions to improve one or both.”

Meeting the exponential appetite for speed

The more sophisticated our technology becomes, the faster and more sophisticated the network that supports it also needs to become. In the era of ultra-high-definition video streaming, 5G (and soon 6G) mobile communications, cloud computing and gaming and the first truly practical artificial intelligence systems, there is an exponential increase in the global demand for communication channels. Therefore, there is a non-stop race for increased data volume capacity. Consumer-driven demand for capacity typically grows at a rate of 60% a year, and more recently, the increase in machine-driven demand has resulted in annual growth at a rate closer to 100%.

The fastest way we know how to communicate is through an elaborate network of high-capacity fiber optic cables. These cables contain strands of fiber, each about the diameter of a human hair, that make up the backbone of the Internet and allow us to transmit millions of text, audio and video communications at the speed of light.

These fibers already connect data centers, factories, campuses and homes. The modems, mobile phone antennas and Wi-Fi systems we use today are all ultimately connected by optical fibers as well. We will only depend more on such fiber optics in the future.

“We know that applications such as virtual reality, fully autonomous driving, machine to machine communications, the Internet of Things and so on are coming,” Hu explained. “These applications rely heavily on high-speed transmission of very large volumes of data and on availability of uninterrupted communication. The only medium that is up to the task is optical fiber.”

Still, Hu believes that there is more room for improvement, and that her work on fiber, and that of her colleagues, is laying the foundation for tomorrow’s advances.

“This is the driving power for the innovations in future technology,” she added. “I’m not worried about not meeting the demand. I think there is always room for new breakthroughs that will further push the boundaries of achievable data rates.”

Balancing speed with patience

Growing up in Wuhan, China as the daughter and granddaughter of engineers, Hu always knew she would be drawn to the sciences and imagined herself becoming an inventor. It was in high school, though, when she first heard about optical communications and knew right away that she had found her calling.

“I immediately became intrigued by the idea of transmitting information in an optical fiber using different colors. I was very curious to understand how this works in detail and how signals are coded into light and carried in the fiber,” she said. “After so many years I remain fascinated by the idea itself and the deep impact it has made on society since its invention in the 1960’s.”

So, it was an easy choice when the time came to go off to college.

Hu earned her BSc and MEng degrees from Huazhong University of Science and Technology in Wuhan before moving to Australia and earning her PhD in optical fiber communications from the University of Melbourne.

An internship in the Bell Labs optical/IP transport research lab in Stuttgart, Germany turned into a full-time position in the optical transmission systems department there, where she contributed to advanced digital signal processing techniques for high-speed optical communication systems.

In 2022, she moved to Nokia Bell Labs headquarters in Murray Hill, New Jersey where she is an optical transmission researcher in the photonic subsystems department.

Hu tends to leave the fast-paced elements of her life at the office and prefers a slower pace at home. In her spare time, she enjoys baking cakes and breads and is learning to play the electric guitar. Even there she prefers a slower tempo, and her bucket list includes studying pencil drawing.

“My life is less intense than what I do at work, in fact it’s quite the opposite,” she said. “I like to do things that test my patience, like bake cake and practice guitar, things that take time.”

But that style is not completely out of sync with her approach to research.

“I believe that practice makes perfect, and it’s also related to my work. Even though we try to increase the speed and we try to be the fastest, the work itself requires patience,” she said. “The result is that you are fast but, in reality, you actually spend a huge amount of time thinking about how to do that.”