Abstract

We report on recent advances made with an optical self-locking technique that is used to stabilize the frequency of semiconductor lasers. The self-locking of the lasers to separate stable Fabry-Perot cavities is achieved by arranging to have optical feedback only at the resonance of the reference cavity. Using this method laser center frequencies are stabilized and linewidths are reduced significantly, from 20 MHz to <20 kHz. Experiments have been performed with standard single-frequency commercial lasers operating near 850 nm. The spectral characteristics of the frequency noise of the optically locked lasers are determined by heterodyne as well as interferometric techniques. These measurements provide information about the changes in the frequency spectral noise density when the laser optically self-locks. Both the long-term and short-term frequency stabilities of the lasers are measured. In addition, we describe techniques for scanning the frequency of the optically locked narrow linewidth lasers. Limitations of the method and contributions of systematic effects which can pull the frequency of the laser away from the stable cavity resonance are considered.

© 1987 Optical Society of America