Three stage cascade diode lasers generating 500 mW near 3.2 μ m

GaSb-based type-I quantum well 3.1-3.2μm diode lasers with two- and three-cascade heterostructures were designed, fabricated, and characterized. Devices with ∼100-μm-wide aperture, 3-mm-long cavity, and anti-/high-reflection coated mirrors demonstrated continuous wave output power of 500 mW, threshold current density of ∼200A/cm², and peak power conversion efficiency of ∼7% at 17°C. This corresponds to more than twofold improvement in terms of output power and efficiency as compared to standard diode lasers operating in the same spectral region. The experiment showed that the increase in the number of cascades from two to three led to critical enhancement of the differential gain and reduction of the threshold current density. Light p-doping of the AlGaAsSb graded section did not introduce extra optical loss but aided hole transport as required for realization of the efficient multi-stage cascade pumping scheme.