Patent ID: 8059970

Claim:
A method of controlling a polar optical transmitter comprising a signal path comprising a multi-bit digital stage cascaded with an analog stage having a pair of branches for supplying a respective analog drive signal to each branch of a dual branch Mach-Zehnder (MZ) modulator, the analog drive signals being derived from corresponding digital drive signals computed by the multi-bit digital stage in accordance with a target optical E-field computed by the multi-bit digital stage, the method comprising steps of: providing a set of one of more cost functions, each cost function being dependent on a parameter of the signal path and indirectly indicative of a feature of an output optical E-field output by the MZ modulator, and for each cost function, a respective predetermined target value representative of a desired feature of the output optical E-field; independently dithering a set of two or more selected components of the drive signals traversing the signal path using a respective digital dither signal for each selected component, a respective frequency of a first dither signal being selected to avoid overlap with a second dither signal or harmonics of the second dither signal; detecting at least one artefact of the dither signals in the optical signal at the output of the MZ modulator; calculating a cost function value based on the detected artefacts and a selected one of the set of cost functions; and a controller progressively adjusting at least one parameter of the signal path to drive the calculated cost function value to the respective predetermined target value.