High-speed Internet continues to evolve, making very quick work of downloading, streaming and communicating. But could it get faster? Researchers in California say yes. A new laser developed by a research group at the California Institute of Technology (Caltech) could eventually make possible an increase in the rate of data transmission in the optical fiber network — the backbone of the Internet. Originally, laser beams in optic fibers carried information in pulses of light; data signals were impressed on the beam by rapidly turning the laser on and off. The researchers are employing a new method of impressing the data on laser beams, which no longer requires this on-off technique. With the new method, called coherent phase communication, the data resides in small delays in the arrival time of the waves. A new laser developed by Caltech researchers includes a layer of non-light-absorbing silicon. This offers more spectral purity than the traditional S-DFB laser, and could lead to faster Internet transmissions. Courtesy of Caltech. As with the old technique — the distributed-feedback semiconductor (S-DFB) laser created in the mid-1970s as part of a collaborative effort between the Yariv group at Caltech and Hitachi Laboratories in Japan — the laser converts current to light using III-V semi-conductor material, typically gallium arsenide and indium phosphide. But the new laser stores the light in a layer of near-absorption-free silicon. Spatial patterning of this silicon layer, which is a variant of the corrugated surface of the S-DFB laser, causes the silicon to act as a light concentrator, pulling the newly generated light away from the light-absorbing III-V material and into the silicon. The S-DFB laser has long touted unparalleled spectral purity, directly translating to a larger information bandwidth of the laser beam and longer transmission distances in the optical fiber. However, this traditional spectral purity no longer satisfies today’s ever-increasing demand for bandwidth. “The present-day laser designs … have an internal architecture which is unfavorable for high spectral-purity operation. This is because they allow a large and theoretically unavoidable optical noise to comingle with the coherent laser and thus degrade its spectral purity,” said Amnon Yariv, a lead researcher and a professor of applied physics and electrical engineering at Caltech. The new laser achieves high spectral purity that is a 20 times narrower range of frequencies than is possible with the S-DFB. For decades, researchers have been trying to develop a laser that comes as close as possible to emitting just one frequency, because the purer the tone, the more information it can carry. And while limitations of physics make absolute spectral purity impossible, that which is obtained with the new laser comes as close as possible. The work was funded by the U.S. Army Research Office, the National Science Foundation, and DARPA. The research is published in Proceedings of the National Academy of Sciences. For more information, visit www.caltech.edu.