A 
transmitter comprising a programmable optical vector modulator and method for coherent optical 
signal communication. The 
transmitter includes a 
transmitter laser whose output is coupled by way of an 
optical fiber to an amplitude modulator. The output of the amplitude modulator is coupled by way of a length of 
optical fiber to a phase modulator. The phase modulator generates a modulated light output from the transmitter. 
Amplitude modulation is achieved by inputting data and a data 
clock signal to amplitude 
symbol mapping logic whose outputs are selectively weighted, summed, amplified and input to the amplitude modulator to amplitude modulate the output of the transmitter 
laser. 
Phase modulation is achieved by inputting the modulating data and the data 
clock signal to 
phase angle symbol mapping logic whose outputs are selectively weighted, summed, amplified, delayed to synchronize with the arrival of the light from the amplitude modulator, and input to the phase modulator to phase modulate the amplitude modulated output of the transmitter 
laser. The programmability of the vector modulator allows the transmission of an M-ary modulation format that maximizes the 
data transmission for a given optical 
dynamic range and 
bit error rate target. Also, the programmability allows for rapid change in modulation format to maximize 
data transmission for changes in optical 
dynamic range and 
bit error rate target. The M-ary 
constellation may be predistorted to compensate for equipment piece part variation and 
fiber nonlinear effects; in particular the effect commonly known as “self-
phase modulation”.