A method and apparatus for accounting for phase differences in a transmit path of an optical system is provided. A transmit control system nullifies phase errors in signals propagating from a coherent source to phase samplers and back to a transmitter sensor. A small time-dependent length modulation is applied to a feed fiber of each aperture and this modulation enables a hill-climbing servo loop to increase, or in some cases even maximize, a detected intensity. This results in a particular relationship between the phases at all the phase-sampling points. The optical system is then calibrated so that this relationship corresponds to in-phase beams when the optical system is aimed at boresight.