Combining techniques used to control frequency and phase locking in microwave oscillators with those used to achieve frequency stability in gas lasers and sub-hertz linewidth in dye lasers, this reference describes the joint application of these techniques in the design of highly coherent semiconductor lasers. This book is designed to be of interest to scientists working in the areas of optical communication systems, microwave communication systems, laser radar, navigation, fabrication of semiconductor laser devices and quantum physics.