CI Advanced Features / Glass

Improving Optical Fiber Throughput

Researchers have discovered a way to increase optical fiber capacity and boost telecommunications throughput by a factor of 10.

February 1, 2014
Trans

Optical fibers carry data in the form of pulses of light over distances of thousands of miles at amazing speeds. They are one of the glories of modern telecommunications technology. However, their capacity is limited, as the pulses of light need to be lined up one after the other in the fiber with a minimum distance between them so the signals don’t interfere with each other. This leaves unused empty space in the fiber.

Jump to:

EPFL’s Camille Brès and Luc Thévenaz have developed a method for fitting pulses together within the fibers, thereby reducing the space between pulses. Their approach, published in Nature Communications,1 makes it possible to use all the capacity in an optical fiber. This opens the door to a 10-fold increase in throughput in our telecommunications systems.

 

Fiber Optics at a Crossroads

“Since it appeared in the 1970s, the data capacity of fiber optics has increased by a factor of 10 every four years, driven by a constant stream of new technologies,” says Brès, who works in the Photonics Systems Laboratory (PHOSL). “But for the last few years, we’ve hit a sort of ceiling, and scientists all over the world are trying to break through.”

“Since it appeared in the 1970s, the data capacity of fiber optics has increased by a factor of 10 every four years, driven by a constant stream of new technologies." 

There have been several different approaches to the problem of supplying more throughput to respond to growing consumer demand, but they often require changes to the fibers themselves. That would entail pulling out and replacing the existing infrastructure. Here, the EPFL team took a different approach, looking at the fundamental issue of how to process the light itself (i.e., how best to generate the pulses that carry the digital data). This approach would not entail a need to replace the entire optical fiber network. Only the transmitters would need to be changed.

 

Traffic Problems on the Information Superhighway

In modern telecommunications exchanges (e.g., when two cell phones are communicating with each other), the data are transported between the two antennae on optical fibers, by means of a series of light pulses that form codes. Simply put, an “on” pulse corresponds to the number 1, while an “off” pulse corresponds to 0. The messages are thus sets of ones and zeros. These codes are decoded by the receiver, providing the initial message. The problem with this system is that the volume of data transmitted at one time can’t be increased. If the pulses get too close together, they no longer reliably deliver the data.

“There needs to be a certain distance between each pulse, so they don’t interfere with each other,” says Luc Thévenaz of EPFL’s Fiber Optics Group (GFO). However, the EPFL team noticed that changes in the shape of the pulses could limit the interference.Their breakthrough is based on a method that can produce what are known as “Nyquist sinc pulses” almost perfectly.

“These pulses have a shape that’s more pointed, making it possible to fit them together, a little bit like the pieces of a jigsaw puzzle lock together,” says Brès. “There is of course some interference, but not at the locations where we actually read the data.”

The idea of putting pulses together like a puzzle to boost optic fibers’ throughput isn’t new; however, the “puzzle” had never been solved before. Despite attempts using sophisticated and costly infrastructures, nobody had managed to make it work accurately enough—until now. The EPFL team used a simple laser and modulator to generate a pulse that is more than 99% perfect.

 

Fine Tuning the System

Practically speaking, the shape of a pulse is determined by its spectrum. In this case, in order to be able to generate the “jigsaw puzzle,” the spectrum needs to be rectangular. This means that all the frequencies in the pulse need to be of the same intensity. Professors Brès and Thévenaz had this in mind when modulating their lasers.

Simple lasers are generally made up essentially of just one color (i.e., one optical frequency) with a very narrow spectrum. This is rather like a violin that has only one string. However, a laser can be subtly modulated (using a device called a modulator) so that it has other colors/frequencies. The result is a pulse composed of several different colors, with a larger spectrum. The problem is that the pulse’s main color generally still tends to be more intense than the others. This means the spectrum won’t have the rectangular shape needed. For that, each color in the pulse needs to be of the same intensity, rather like getting the strings of a violin to vibrate with the same force, but without making any other strings nearby vibrate.

The team thus made a series of subtle adjustments based on a concept known as a frequency comb and succeeded in generating pulses with almost perfectly rectangular spectrum. This constitutes a real breakthrough, since the team has succeeded in producing the long-sought-after “Nyquist sinc pulses.” Thévenaz recounts how it all started: “Camille and I were talking with a visiting professor at the University of Leipzig, and we realized that by teaming up we might be able to develop this new approach.”

 

A Mature Technology

The new pulses could well generate interest among many telecommunications industry market participants. The technology is already mature, as well as 100% optic and relatively inexpensive. In addition, it appears that it could fit on a simple chip. “It almost seems too good to be true,” Thévenaz says. 


For more information, visit www.epfl.ch/index.en.html.


Reference

 1.         Soto, M.A., et al. “Optical Sinc-Shaped Nyquist Pulses of Exceptional Quality,” Nat. Commun, 4:2898 doi: 10.1038/ncomms3898 (2013). 

Did you enjoy this article? Click here to subscribe to Ceramic Industry Magazine.

You must login or register in order to post a comment.

Multimedia

Videos

Image Galleries

In-Depth Features

These articles detail innovative advanced ceramic and glass materials and technologies.

Podcasts

Sapphire: An Extreme Performer

Ian Doggett of Goodfellow and CI Editor Susan Sutton discuss the benefits and opportunities provided by industrial sapphire.

More Podcasts

Ceramic Industry Magazine

CI April 2014 cover

2014 April

Our April issue features details on advanced materials such as ceramic matrix composites and piezoelectric ceramics, among many others. Be sure to check it out!

Table Of Contents Subscribe

THE CERAMIC INDUSTRY STORE

M:\General Shared\__AEC Store Katie Z\AEC Store\Images\Ceramics Industry\handbook of advanced ceramics.gif
Handbook of Advanced Ceramics Machining

Ceramics, with their unique properties and diverse applications, hold the potential to revolutionize many industries, including automotive and semiconductors.

More Products

Clear Seas Research

Clear Seas ResearchWith access to over one million professionals and more than 60 industry-specific publications,Clear Seas Research offers relevant insights from those who know your industry best. Let us customize a market research solution that exceeds your marketing goals.

Directories

CI Data Book July 2012

Ceramic Industry's Directories including Components, Equipment Digest, Services, Data Book & Buyers Guide, Materials Handbook and much more!

STAY CONNECTED

facebook_40px twitter_40px  youtube_40pxlinkedin_40