A bidirectional 1.7-Tbit/s free-space optical communications link has been set up between two buildings of the Fraunhofer Heinrich Hertz Institute HHI in Berlin. Eye-safe operation through 380-m air was successfully demonstrated at a total antenna output power of less than 10 mW. The signals in both directions consisted of 40 wavelength channels of 43 Gbit/s.
The measured bit-error rate of the channels fluctuated between 1E-8 and 0 without forward error correction. The two bidirectional terminals were placed in the same building whereas a relay mirror was placed in the other building to in-crease the link distance. Fine and coarse tracking systems stabilized the coupling into the single-mode fibers at both terminals. This result was achieved with the support of Huawei Technologies. To increase the link distance to several kilometers, additional techniques, on which the Fraunhofer HHI is currently working, will be integrated to the terminals to mitigate optical turbulence effects. Applications of interest are high-speed free-space Internet connects in converged city and access networks.
The fiber-based system that generates and demodulates the 1.7-Tbit/s signal was also successfully deployed over a free-space unidirectional 10-km link with the high-power free-space transmission system of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR).