Single mode operation of buried heterostructure lasers by loss stabilization

Abstract

A loss-stabilized buried heterostructure (LSBH) laser is reported that is much simpler to grow than conventional BH lasers, but has similar, near ideal, laser characteristics. Typical lasers, which incorporate an optical guide have active stripe widths <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\approx 2.5 \mu</tex> m determined by the initial mesa etching, have a laser threshold of 25 mA, and exhibit stable single transverse mode operations up to 60 mA and higher currents. The simplicity in growth results from not attempting to grow a single mode guide by carefully choosing the composition of the regrown burying layers, but instead simply forming a multiple mode guide by growing a cladding layer with a high aluminum composition. The large index discontinuity between the layer and the central mesa and the roughness of the etched mesa walls cause losses when interface scattering couples light from the initial mode into other modes. The losses rapidly increase with the mode number and, we believe, provide the selection mechanism which causes the laser to operate in the lowest mode. Calculations show that the observed variations in mesa width of 0.3 μm over distances of 10μm are adequate to explain the observed lowest mode stability.