Patent ID: 8301025

Claim:
A method for determining an optical signal-to-noise ratio for an optical transmission system, which comprises: adding on a receiver side an optical noise signal to a received optical data signal obtaining an optical data signal; varying a magnitude of the optical noise signal and determining a function of the signal quality of the optical data signal in dependence on the added optical noise signal as a function of an added optical signal-to-noise ratio; approximating a first straight line to a flat area of the function determined for relatively low values of the added noise and therefore high values of the added optical signal-to-noise ratio; approximating a second straight line to a rising area of the function determined for relatively high values of the added noise and therefore small values of the added optical signal-to-noise ratio; and determining the optical signal-to-noise ratio of the received optical data signal from a point of intersection between the first straight line with the second straight line.