Optical frequency offset-locking is demonstrated for application to Doppler shift compensation for a spaceborne optical communication system using a laser diode transmitter and a narrow band-pass filter with a small tuning range at the receiver. The system performs closed loop computer control of a laser diode output frequency and allows tuning of this frequency with respect to a reference. A tuning range of 21 GHz and a tuning speed of 44 THz/sec is demonstrated while maintaining a transmitting stability of <80 MHz. The theory modeling the system is shown to have agreement with the experimental results to within 5%.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.