Monolithic stacking of injection lasers is of interest for high power aperture-limited use. By placing two or three graded index separate confinement (GRINSCH) single quantum wells (SQWs) within a common space-charge region of a single pn junction,1 we demonstrated laser operations with a substantially higher catastrophic optical damage power level, while the differential quantum efficiency, threshold carrier density per quantum well, characteristic temperature, and operation voltage are comparable with those of the typical single quantum well lasers. The stacked lasers can operate either independently with a beam divergence equal to that of a single quantum well laser or coherently in one of the phase-locked modes, depending on the spacing between the wells. In the latter case, the fundamental mode operation with a beam divergence of <20° has been achieved in lasers with properly designed waveguide parameters. We present experimental results of two types of device structure: devices with multiple gain elements and devices with a single gain element integrated with two passive graded index waveguides.

© 1990 Optical Society of America

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