Abstract

Recently there has been considerable interest in heterodyne optical communications for intersatellite links, in particular, using semiconductor lasers, because of the potential for substantial performance Improvement over direct detection systems.¹ However, phase or frequency modulated systems will require a stable Intermediate frequency (IF) signal for demodulation with low bit error rates. Stabilizing the frequency of GaAlAs lasers by locking to an external reference has been demonstrated previously.² However, such schemes by themselves will not suffice in space communications applications because links between platforms moving relative to each other can experience Doppler shifts of 10 GHz or more at 1 μm.³ Therefore, frequency locking the receiver’s local oscillator (LO) to the Incoming signal is required.

© 1983 Optical Society of America