Absolute wavelength stability ions

Summary form only given. Multifrequency optical communication systems are now being deployed for increased throughput of point-to-point links. It is also considered for routing identification in transparent optical networks. With high-density multifrequency channels, the precise control of optical carrier frequencies is becoming imperative to avoid cross talk or wrong identification. For wide-spread continental networks, standardized frequencies will have to be used. Moreover, with the advent of transoceanic transparent links, the frequencies assigned to each channel will be transferred between continents. These frequencies will have to be compatible between countries. Absolute frequency assignments will be a prerequisite for global deployment of multifrequency communication networks. This tutorial presents a summary of the research activities done in the field of semiconductor laser frequency control and the establishment of absolute frequency references. It reviews the criteria for the realization of an optical frequency standard and the formalism for its frequency stability characterization. Internal and external semiconductor laser frequency-control techniques are compared. Recent results on absolute optical frequency measurements and methods for the extension of absoluteness to nearby frequencies are summarized. Finally, critical issues for multifrequency optical networks like standardization and long-haul transfer are discussed