Optical transmission system

It is claimed a optical transmission system (1), comprising an entangled photon source (2), a free-space receiver module (3), a fiber receiving module (4), a free-space channel (5) and a fiber channel (6), whereas the entangled photon source (2) generates entangled photon pairs comprising a signal photon and an idler photon, and whereas the entangled photon source (2) and the free-space receiving module (3) are connected via the free-space channel (5), and whereas the entangled photon source (2) and the fiber receiving module (4) are connected via the fiber channel (6), and whereas the signal photon is sent via the free-space channel (5) to the free-space receiving module (3) and the idler photon is sent via the fiber channel (6) to the fiber receiving module (4). The signal and idler photon of the entangled photon pair have non-degenerate wavelengths, a signal photon wavelength fs and an idler photon wavelength fi, with fi ≠ fs.