Optical Communication Systems
RESEARCH FACULTY
Optical communications includes all methods of using light to communicate. An early demonstration was performed by Alexander Graham Bell [1847-1922], who showed that it was possible to modulate light by use of a membrane that vibrated in response to sound, thus demonstrating a free-space optical link. These free-space optical transmission links have applications today using lasers as rapidly deployable optical links with large bandwidth capacity. However, most modern optical systems rely on guiding the light in glass fibers that exhibit exceptionally low loss. The advent of the laser was followed by extensive efforts to understand and reduce the loss of glass. In the1960s to early 1970s the attenuation of glass fiber was reduced from more than 1,000 dB/km to less than 20 dB/km. The chief advantage of using light is the enormous bandwidth or signal carrying capacity that arises from the nearly 200THz carrier frequencies commonly used in fiber systems. Using only a 10GHz modulation rate, a single channel optical link can simultaneously transmit 129,000 telephone calls or can transmit more than 100 standard CDs in one minute.
(Courtesy of S. Ralph)
An optical communications system includes methods of modulating, transporting, and detecting light. Therefore, optical communications relies heavily on the advances in nearly all of the other optical and photonic research areas. Optical communications systems today routinely carry 10Gbps on each wavelength, and systems using wavelength multiplexing methods have been used to demonstrate aggregate data rates in excess of ten Terabits per second on a single fiber. In addition to the increasing data rates, the reach or distance of optical links has also increased, and undersea links are common. Advances in fiber optic optical components have allowed optics to extend closer to the end user. All of these advances in optical communications have enabled the Internet to flourish.
At Georgia Tech, researches are actively pursuing a range of studies including advanced modulation formats for >40Gbps links, impairment mitigation by both optical and electronic means, nonlinear propagation methods, and fiber to the home technologies.
