On-chip unstable resonator cavity GaSb-based quantum well lasers

The focused ion beam milling tool was used to convert a GaSb-based broad area gain-guided quantum well laser device with a standard Fabry-Perot cavity into one with an unstable resonator cavity. A cylindrical mirror was formed at the back facet of the broad area device emitting near 2 mu m. Compared to the Fabry-Perot cavity device, where the coherency of the beam is severely disrupted by filamentation, the unstable resonator cavity device exhibits an similar to 2 x diffraction limited beam. The relatively small penalty in slope efficiency demonstrates that a much higher brightness can be reached in this class of broad area devices.