Fischer, J. K.; Ludwig, R.; Molle, L.; Schmidt-Langhorst, C.; Schubert, C. (Fraunhofer Institut für Nachrichtentechnik, Heinrich-Hertz-Institut, Einsteinufer 37, 10587 Berlin, Germany)
Leonhardt, C. C.; Matiss, A. (u2t Photonics AG, Reuchlinstraße 10/11, 10553 Berlin, Germany)
We discuss a coherent receiver scheme exploiting optical sampling to overcome the speed limitations of electronic analog-to-digital converters. Digital coherent receivers with aggregate optical sampling rates of up to 112 GSa/s are realized experimentally. The performance of such receivers is investigated in transmission experiments. Transmission of 56 GBd quadrature phase-shift keying signals over 610 km standard single-mode fiber and coherent detection with electronic impairment mitigation is demonstrated. The employed electrical analog-to-digital converters have only 20 GHz bandwidth and a sampling rate of 50 GSa/s.