Patent ID: 8744277

Claim:
A method of calibrating an optical downconverter configured to receive an optical input signal at a signal input and an optical reference signal at a reference input, and to provide a plurality of characterizing signals at a plurality of output nodes for characterizing the optical input signal, wherein the downconverter comprises a plurality of receivers, having optical inputs and electrical outputs corresponding to the plurality of output nodes, respectively providing the plurality of characterizing signals, and a plurality of optical signal paths, each optical signal path being connected between one of the signal and reference inputs and one of the optical inputs of the plurality of receivers, the method comprising: determining signals at the plurality of output nodes; deriving from the determined signals a first set of correction values for correcting the plurality of characterizing signals, wherein the first set of correction values relate to insertion loss on the plurality of optical signal paths as a time-independent property of the characterizing signals; and correcting the plurality of characterizing signals with one or more of the derived first set of correction values.