Image: Bernd Müller for DLR
The Advanced Optical Technologies Group deals with research in the area of optical free-space transmission. Research topics comprise the study of the atmospheric turbulence and the techniques to counteract its effects: all steps from theoretical and simulation analysis up to channel measurements and demonstrations.
Optical technologies will play a central role in future navigation systems. DLR’s Institute of Communications and Navigation is proposing a new concept, which uses satellites in the same orbital slots as Galileo, in Medium Earth Orbits, and complements them by a constellation of 6 satellites in Low Earth Orbits. This concept is called Kepler System. It uses inter-satellite links between neighboring satellites in each MEO orbital plane as well as between selected MEO satellites and LEO satellites. The links are two-way optical links. They are used to synchronize the reference oscillators on the satellites in time and frequency, to measure ranges and velocities and to transport information in the constellation at a data rate of 50 Mbps.
In inter-satellite ranging a coherent link based on optical phase-locked-loop (OPLL) can provide submillimeter accuracies. In communications, coherent reception has advantages in terms of sensitivity and spectral efficiency and, especially, a digital homodyne scheme is robust against signal fluctuations because it avoids the locking time required by the OPLL. The group developed two optical communication systems for turbulence characterization and research of the atmospheric channel under strong turbulence conditions:
 DLR, World record in free-space optical communications, press-release
 Poliak, J.; Mata Calvo, R.; & Rein, F., Demonstration of 1.72 Tbit/s optical data transmission under worst-case turbulence conditions for ground-to-geostationary satellite communications, IEEE COMMUNICATIONS LETTERS, VOL. 22, NO. 9, 1818-1821, 2018
 DLR, DLR and ADVA set a new world record in optical free-space data transmission, press-release
 Mata Calvo, R.; Becker, P.; Giggenbach, D.; Moll, F.; Schwarzer, M.; Hinz, M. & Sodnik, Z., Transmitter diversity verification on ARTEMIS geostationary satellite, Proc. SPIE, 2014, 8971, 897104-897104-14
 Conroy, P.; Surof, J.; Poliak, J. & Mata Calvo, R., Demonstration of 40GBaud intradyne transmission through worst-case atmospheric turbulence conditions for geostationary satellite uplink, Appl. Opt., OSA, 2018, 57, 5095-5101
 Carrizo, C. E.; Mata Calvo, R. & Belmonte, A., Intensity-based adaptive optics with sequential optimization for laser communications, Opt. Express, OSA, 2018, 26, 16044-16053
 Mata Calvo, R.; Bonaccini Calia, D.; Barrios, R.; Centrone, M.; Giggenbach, D.; Lombardi, G.; Becker, P. & Zayer, I., Laser guide stars for optical free-space communications, Proc.SPIE, 2017, 10096, 10096 - 10096 – 12
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