Design guidelines for on-chip unstable resonator cavity to suppress filamentation in GaSb-based diode lasers

Abstract

We demonstrate GaSb-based diode lasers emitting near 2.7 μm that are fabricated as on-chip unstable resonator cavities using the focused ion beam tool. A near-diffraction-limited lateral beam is observed in broad-area devices where the reflection from the cylindrical mirror at the back facet overrides direct counterpropagation in the cavity to suppress the formation of filaments. We identify a geometric parameter that can be used as a general guide to optimizing the on-chip unstable resonator cavity for maximum brightness. This parameter is the aperture within the unstable resonator cavity, a measure of the angular divergence contained within the device, and is shown to correlate with the onset of filament suppression.