Dragic's paper picked for OSA spotlight

As you read this article online, data is continuously being fetched from a server, arranged into neat packets, beamed through fiber optic cables crisscrossing the globe, and reassembled to be viewed on your computer screen.

A recent paper titled, “Brillouin Scattering Properties of Lanthano-Aluminosilicate Optical Fiber,” by Lecturer Peter D Dragic has been featured as a spotlight article by the Optical Society of America, or OSA, for a new kind of fiber optic cable he’s developed along with collaborators at Clemson University and the Institute of Photonic Technology in Jena, Germany. It has 10 times the performance of the current industry standard and dramatically improved capabilities for sensing differences in stress and temperature.

Fiber optic cables are made of long filaments of highly pure glass, and these cables form the backbone of the Internet with enormous undersea cables linking the United States to Europe and Asia. Data packets traversing the Internet are encoded at a server as pulses of light, shone in at one end of the glass filament, and guided through the cable before being reassembled at a server on the other end. There, they are again encoded and transmitted further along the massive worldwide network of networks, hopping along a chain of data hosts until they reach the user’s machine.  

Unfortunately, these fibers aren’t perfect: Tiny, random acoustic waves are constantly running along them due to small temperature differences throughout the cable. Some of these waves refract the light pulses back into themselves, causing the signal to lose strength in a process called Brillouin scattering Think of the light pulses in the fiber as arrows shot from a bow: sometimes, right after the arrow is loosed, a foul wind suddenly picks up and sweeps the arrow far from its intended target. 

Though this scattering makes it harder for signals to travel on fiber networks, it’s also possible to analyze the patterns of refracted light to measure the acoustic waves that caused them. Since the waves are caused by differences in temperature and strain all across the fiber, understanding the patterns of waves gives engineers information about temperature and stress at every point along the cable. Engineers use this data in many ways, from keeping tabs on strain levels in bridges to checking on temperature differences in oil rigs and even monitoring undersea weather, but the current technology needs improvement.

Dragic’s team, however, has found a way to control acoustic waves in the fiber by designing new cables with a mixture of lanthanum oxide, aluminum oxide, and silica. His new composite can sense any level of temperature or strain and can compensate for the acoustic waves to cancel most of them out so that the light pulses travel unimpeded. This works like an archer taking into account the wind direction before loosing his arrow. Aimed with the wind in mind, the arrow sails perfectly along its predetermined path before landing dead center on the bulls-eye. 

“Recent fibers we’ve developed eliminate enough scattering to improve industry’s state of the art more than 100 times over,” Dragic said. 

Besides better signal strength and sensing abilities, Dragic’s fibers are also cheaper to make. The process of creating ordinary fibers involves heating a cylinder of pure glass up to 4,000 degrees Fahrenheit, then drawing out and cooling trails of melted glass to make fibers. This requires huge amounts of heat and space, and is very expensive. 

Dragic’s composite fiber, on the other hand, is manufactured as part of a collaboration with Clemson University under professor John Ballato. In this process, engineers insert a crystal of carefully selected material into a tube and heat the silica tube to the point where the crystal inside melts. The melted crystal then mixes with some of the silica in the tube, and upon rapid freezing in air, it’s precisely controlled and drawn into a fiber of tailored composition that could not be fabricated using the conventional  method. This fabrication method costs a few hundred dollars to produce the same amount of fiber that $4,000 would normally buy. 

“Until recently, only specialty fibers could get even incremental improvements over the industry state of the art,” Dragic said. “With this method being even cheaper and so much more effective, the only reason it’s not in use everywhere right now is that fiber companies have to get used to the new manufacturing method.”  

Dragic’s paper was picked by the OSA because its members felt that his research was especially relevant to modern information breakthroughs and had a number of possible practical applications. 

“The investigation of the Brillouin properties of glasses is of special interest. Glasses with reduced Brillouin gain coefficients are of importance in communications, nonlinear optics, and lasers,” said OSA senior member Periklis Petropoulos in his comments on the paper on the OSA website. “The paper is important in that through a thorough study, it identifies a glass composition whose tailored characteristics may find a number of useful applications in specialized areas in fiber optics.”