An all-spheric unobstructed optical terminal for free-space quantum communication
Pernechele C., F. Tamburini, T. Jennewein, A. Zeilinger
Optical Design and Engineering IV”, L. Mazuray, R. Wartmann, A. Wood, J.-L. M. Tissot, J. M. Raynor (eds.), Proc. of SPIE 8167 (2011)