Ultra high efficiency 1550nm multi-junction pulsed laser diodes

The 1550nm wavelength region is critical to the development of next generation eye safe military applications such as range finding and friend or foe identification (FOE). So far the relatively low laser external efficiency was a strong limiting factor favoring shorter wavelength diode lasers. We report on the development of a new monolithic multiple junction pulsed laser diode offering an external efficiency of more than one Watt per Amp with high brightness. Peak optical output power of more than 37 Watts has been achieved from a single multi-junction diode laser. Divergence is narrow with less than 35 degrees (FWHM) in the fast axis direction. Starting from an AlGaInAs quantum well laser structure, we show the criticality of the design of InP based tunnel junctions to the growth of the three layer epitaxial monolithic laser. We then report on trenches employed to confine carriers under the contacting stripe and on growth strategies used to decouple the multiple light sources resulting from the multi-junction design. A full set of characterization data is presented concluding with a discussion on performance limitations and their potential causes.