Using frequency combs as an optical source could speed up communications by allowing coherent transmission of data streams of several terabits per second over hundreds of kilometers. A team from Karlsruhe Institute of Technology and the Swiss Federal Institute of Technology of Lusanne has achieved a data transfer rate of 1.44 Tb/s over a distance of 300 km. An optical microresonator made from silicon nitride. A single laser light is used to produce a multitude of spectral lines, forming a frequency comb. Courtesy of Karlsruhe Institute of Technology. The research demonstrates that integrated Kerr optical frequency comb sources with large line spacings can be realized on photonic chips and applied for the transmission of large data volumes. Spacing of spectral lines in conventional frequency combs is often too small for data transmission, and does not correspond to the channel spacing used in optical communications, which is typically larger than 20 GHz. To date, such frequency combs have been used mainly for high-precision optical atomic clocks and optical rulers. “The use of Kerr combs might revolutionize communication within data centers, where highly compact transmission systems of high capacity are required most urgently,” said Dr. Christian Koos, coordinator of the research. An optical microresonator made of silicon nitride was also used in the study, into which laser light is coupled through a waveguide and stored. Underlying microresonators are created with complex nanofabrication methods at the Center of Micronanotechnology at Lusanne. “Due to the high light intensity in the resonator, the Kerr effect can be exploited to produce a multitude of spectral lines from a single continuous-wave laser beam, hence forming a frequency comb,” said Jörg Pfeifle, a researcher at Karlsruhe. The team has studied 20 lines of the frequency comb in its experiments so far, but plans to expand this soon and continue its research. The work was funded by a Starting Independent Researcher Grant from the European Research Council, NCCR Nanotera, the European Space Agency and the Alfried Krupp von Bohlen and Halbach Foundation. The research is published in Nature Photonics. (doi: 10.1038/NPHOTON.2014.57) For more information, visit: www.kit.edu