We present the investigation of several methods to increase the active diameter of single transverse mode oxide confined VCSELs in both the 850 and 980nm wavelength regimes. Among the concepts considered are mode intensity specific shallow surface etched reliefs, monolithically increased cavity lengths, current confinement matching the fundamental mode intensity distribution and saturable absorbers. All approaches are introduced in theoretical considerations and corresponding measurement results are presented. Additionally, numerical simulations are performed to gain an increased understanding of some of the mode selection mechanisms. The considered concepts are evaluated in terms of decrease of the series resistance (for impedance matching/driving reasons) and device lifetime ( as derived from maximum current densities) . The results obtained are also compared to other approaches found in literature (e. g. metal apertures, photocurrent feedback, Fabry-Perot étalon, half-symmetric cavity) . Conventional devices with optimized thin oxide aperture location have shown single-mode output powers above 4 mW with an active diameter of 3.5 pm. A record high single-transverse mode output power of 5 mW at a series resistance of 98 is obtained for a 7 pm aperture device by increasing the cavity length monolithically by 4 ,am.

We compare various approaches aiming at large-area high-power single-mode oxidized VCSELs. Stable and reproducible single-mode emission with SMSR (side-mode suppression ratio) greater than 30 dB and output powers well above 5 mW are reported for the long monolithic cavity and self-aligned shallow surface etching approaches, both of which are suitable for commercial production. Additionally, Photonic Crystal SurfaceEmitting Lasers (PCSELs) are introduced, which enable advanced mode control by novel transverse optical guiding techniques.

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