Multi-hole aperture VCSELs: single mode, high power, low resistance

Abstract

The essential performance parameters of present generations of Vertical Cavity Surface Emitting Lasers (VCSELs) like output power, f3dB cut-off frequency, are limited by extrinsic parameters. The most important among them is the shift of the gain maximum out of resonance with the DBR transmission due to increased heating of the active layer with increasing current, leading to a red shift of the emission. Another important limitation of f3dB is the unavoidable resistance by the p-type mirror and capacitance of the actual device generations. We present here a novel Multi-Hole Aperture (MuHA) VCSEL approach 1 , based on variable aperture shapes and sizes, leading to increased output power for single/multi-mode emission, reduced series resistance, and larger f3dB of the devices. Holes in symmetric or asymmetric arrangements are etched from the top to the oxidizable layer(s). The aperture shape and size is realized by controlled oxidation of the oxidizable layer(s) through the holes. The holes are subsequently filled with gold, which effectively remove heat from the active layer. In MuHA VCSELs, the temperature of the active area for any given current is thus at least 50% lower than that of a comparable VCSELs processed using a "classical" design, resulting in larger rollover current, f3dB,… Combining MuHA to Multi-Aperture devices called Multi Aperture VCSELs (MAVs) is expected to lead to pseudo single mode emission with an output power of 8-10 mW across 50 μm Multi-Mode Fiber (MMF), enabling to cover much larger transmission distances than hitherto.