Design considerations and analytical approximations for high continuous-wave power, broad-waveguide diode lasers

Accurate analytical approximations are derived for the equivalent transverse spot size, $d/Γ$ (<5% error), and the transverse beamwidth $θ1/2$ (<2% error), of broad-waveguide-type diode lasers, over a wide range in waveguide width: from the first-order-mode cutoff to the third-order-mode cutoff. The analytical formulas are found to be in good agreement with experimental values. For low-series-resistance and thermal-resistance devices, it is found that the junction-temperature rise $ΔTj$ in continuous wave (CW) operation is a strong function of both the characteristic temperature $T1$ for the external differential quantum efficiency $ηD$ as well as of the heatsink thermal resistance. If the device has relatively temperature-insensitive $ηD$ (i.e., $T1≳1000 K)$ the maximum CW power as well as the power density at catastrophic optical mirror damage, $P̄COMD,$ are limited, for a given active-region material, only by the heatsink heat-removal ability. For large $d/Γ,$ 0.97 μm emitting, 100 μm stripe InGaAs/InGaAs(P)/GaAs devices with $T1=1800 K,$ record-high CW and quasi-CW (100 μs wide pulses) output powers are obtained. The ratio of quasi-CW to CW $P̄COMD$ values is only 1.3, in contrast to devices of poor carrier confinement and subsequent low-$T1$ values (∼140 K), for which the ratio is 1.9, and whose maximum CW powers are ∼40% less than those obtainable from high-$T1$ devices.