Optical Ground Station Oberpfaffenhofen Next Generation: first satellite link tests with 80 cm telescope and AO system
IQC Seminar - Johannes Prell, Institute of Communication and Navigation, OSL German Aerospace Center (DLR) Oberpfaffenhofen, Germany
Satellite-basedlaser communication technology, both classical and QKD (Quantum Key Distribution) is gaining popularity and being increasingly commercialized. Optical ground stations serve as the receiving station in satellite-to-ground scenarios. The DLR institute of Communications and Navigation hosts an experimental optical ground station for research and demonstration purpose. Supporting increasingly demanding technical requirements from current and future missions, and technology demonstrations, it was decided to replace the 40cm Cassegrain telescope an equip the new one with Nasmyth-Ports for direct experiments, a Coudé-Path to the lab and an Adaptive-Optics-System. This new 80cm (31.5inch) main aperture diameter instrument is a Nasmyth-Design Ritchey-Chretien telescope. The special feature is the Coudé-Path which is guiding the received light onto an optical table in a laboratory room below the telescope mount(see figure 1).The usage of the Coudé-Path is new implemented at DLR and offers a wide possibility for several different experiments with the same setup. The optical propagation through a custom designed lens system inside the coudé path is optimized for wave lengths used for optical communication, like 589nm, 850nm, 1064nm and 1550nm. It is possible to use the setup as a receiving station and also as a transmitting facility for beacon lasers. The transmitting system can be installed either beside the telescope as a side installation or even launched from the optical table through coudé path and telescope directly.
The optical Experiment table in the lab is equipped with an Adaptive Optics (AO)System including fiber coupling. This system uses a Shack-Hartmann Wave-front sensor, designed to match a deformable mirror in the “fried geometry”. The system couples the light into a single mode fiber, which can be connected to a coherent or Quantum encrypted communications system. 
Figure1OGSOP -System Overview
The telescope itself has four usable Nasmyth ports. The first one is reserved for the coudé path, two others are equipped with optical benches directly on the telescope, and on the last one has a fixed classical laser communication receiving setup including two cameras –one visible light and one infra-red and a signal receiving united is installed.
:Andrew Paul Reeves, Ilija R. Hristovski, Alexandru-Octavian Duliu, Stefanie Häusler, Hela Friew Kelemu, Pia Lützen, Florian Moll, Eltimir Peev, Juraj Poliak, Amita Shrestha, Joana Sul Torres; Adaptive Optics Corrected Bi-Directional Links with a Geo-Stationary Satellite from the DLR-KN Optical Ground Station