Abstract

In conventional laser theories it is standard practice to deal with orthogonal eigenmodes. Indeed, orthogonality is a good approximation when dealing with high-Q resonators but exact orthogonality only occurs in hypothetical resonators which are fully isolated from the outside world. Even if those systems could be realized they would not be interesting for applications because no signal could get in or out. So, from the fundamental point of view there is an obvious need to include nonorthogonality in a modal description of a laser with output coupling. From the practical point of view this inclusion becomes even essential when dealing with high-gain laser systems with bad cavities. The large output coupling of these systems has a substantial influence on the electromagnetic mode structure, which in turn modifies the spontaneous and stimulated emission processes. A convincing experimental demonstration of these principles was reported in Ref. ¹. Here the measured linewidths of identical semiconductor lasers with different mirror reflectivities were compared with theoretical predictions based on Petermann's excess-noise factor.² Reasonably good agreement was obtained.

© 1991 Optical Society of America