Ostermann, J: Diffractive Optics for Polarization Control

Vertical-Cavity Surface-Emitting Lasers (VCSELs) have replaced edge-emitting laser diodes in several applications during the last years, e.g., in short distance optical data communication. Additionally, their invention has enabled new products such as optical computer mice using semiconductor lasers. However, VCSELs have intrinsically an unstable and not well-defined polarization, which has prohibited their usage in a considerable number of application areas up to now. Therefore, this thesis deals with polarization control of VCSELs. The highly sought-after polarization stabilization of VCSELs is achieved by using monolithically integrated surface gratings. The polarization control induced by these surface gratings has proven to be very reliable in thousands of grating VCSELs, under temperature variation, feedback, strain, and high-frequency modulation. Combining a surface grating with a surface relief, VCSELs having simultaneously a stable polarization and a high single-mode output power have been realized for the first time. Thus, surface grating VCSELs combine a well-defined polarization with low production costs and an excellent overall laser performance. With these properties, surface gratings outperform all other methods for polarization control of VCSELs tested before. Consequently, surface gratings have proven to be the method of choice for polarization control of VCSELs in commercial applications.