Injection locking in vertical cavity surface emitting lasers

Abstract

Semiconductor lasers are used in a large variety of applications and play a key role in communication technology. Spectral features and properties of semiconductor lasers are therefore of great interest to physicists. A relatively new type of semiconductor laser is the Vertical Cavity Surface Emitting Laser (VCSEL). In a VCSEL the cavity is smaller than in an ordinary edge emitting semiconductor laser. On the other hand, the ratio between the emitting surface area of the cavity and its length is much larger. As a result, the crystal birefringence for a VCSEL is far more pronounced than for edge emitting lasers (where the birefringence is perpendicular to the direction of light propagation). As a result, VCSELs under certain operation conditions produce linear or circular polarized light or becomes completely unstable. Polarization properies have been observed experimentally. San Miguel et al., developed a theoretical model to investigate the polarization properties of a quantum well VCSEL. Noting the ability of VCSELs to show different polarization properties under different operation conditions (determined by temperature and current) it is interesting to see whether these properties can also be effected externally, and if so, under what conditions. In the present study the San Miguel model has been extended to include injection locking of a VCSEL. Theoretical results are presented on the polarization properties of a quantum well VCSEL under different conditions of injection seeding.