Smarter Pulse Shaping for Fiber Optics
To boost the capacity of optical fibers—the glass cables that carry digital information to more than two billion internet users—engineers encode information on many wavelengths. But this technology, known as wavelength division multiplexing, is limited in how fast it can send information because of interference between signals. Writing in Physical Review Letters, researchers propose a way to eliminate this cross talk and potentially raise the rate at which future fibers transmit data.
The new approach tackles the problem of optical nonlinearity in fibers, in which an intense light pulse alters the fiber’s index of refraction. Nonlinearity causes interactions between pulses carried at different wavelengths, producing distortions that lead to errors. Since the effects are mathematically complex, they are difficult to correct when the pulses arrive at their destination. And although optical fibers are only weakly nonlinear, the effect can be significant when pulses are transmitted at distances of several-hundred-kilometers or at rates in excess of 10 gigabits/second.
Jaroslaw Prilepsky at Aston University, UK, and his colleagues modeled the passage of light through an optical fiber using the nonlinear Schrödinger equation and found a set of signal waveforms that, according to this equation, behave like sinusoidal waves in a fiber with no nonlinearities. In principle, any light signal can be generated as sums of these specially shaped pulses. As a proof of concept, the authors simulated the transmission and sending of a sequence of signals along a 2000-kilometer fiber using their new strategy and showed that the signals arrived without distortion. – Jessica Thomas