In a system for converting digital data into a modulated optical signal, an electrically controllable device having M actuating electrodes provides an optical signal that is modulated in response to binary voltages applied to the actuating electrodes. A digital-to-digital converter provides a mapping of input data words to binary actuation vectors of M bits and supplies the binary actuation vectors as M bits of binary actuation voltages to the M actuating electrodes, where M is larger than the number of bits in each input data word. The digital-to-digital converter maps each digital input data word to a binary actuation vector by selecting a binary actuation vector from a subset of binary actuation vectors available to represent each of the input data words.