Patent ID: 8879921

Claim:
An apparatus for modulation of an optical signal with a data signal, said apparatus comprising: (a) a configurable digital encoding unit adapted to encode data of said data signal to provide an encoded modulation control signal; and (b) a signal modulation unit adapted to modulate said optical signal with respect to its signal phase and/or signal amplitude in orthogonal polarization directions in response to said encoded modulation control signal, the signal modulation unit adapted to generate a four-dimensional optical signal vector, wherein said digital encoding unit comprises: an encoding data storage for storing at least two encoding lookup tables; wherein said encoded modulation control signal comprises four binary control bits, and wherein said four binary control bits form a constellation point for a four-dimensional optical signal vector generated by said signal modulation unit; wherein the generated four-dimensional optical signal vector is transported by an optical transport medium to an optical receiver comprising a demodulator; and wherein a feedback modulation control signal is feedback from said optical receiver to said modulation apparatus for selecting an encoding scheme by switching the digital encoding unit to another encoding lookup table depending on a signal quality of the four-dimensional optical signal vector received by said optical receiver via said optical transport medium.