Longitudinal spatial hole burning and associated non-uniform current and carrier density profile as a power limit in high power diode lasers

Asymmetric photon density (recombination-rate) along the high-power diode laser cavity leads to longitudinal-spatialhole- burning (LSHB), which limits maximum output power. Here, we summarize recent investigations on the impact of LSHB on current (longitudinal) and carrier (lateral and longitudinal) density distribution and hence total-recombination for continuous-wave (CW) operations. Custom diode lasers with 90 μm stripe and 3000-6000 μm resonator have been fabricated with segmented p-side contact to measure local current density and backside metallization window to measure relative carrier density (via spontaneous intensity) and infer temperature (via wavelength). Also, 98% back facet reflectivity and 0.8% and 20% front facet reflectivities have been used to vary the photon density profile and hence severity of hole-burning. We present data showing that current crowds at the front facet due to the high recombinationrate, which becomes more severe as the bias and resonator length increase. The current crowding effect is reduced using higher front facet reflectivity. Longitudinal one-dimensional simulation is broadly consistent with experiments at low bias; however, the current crowding effect is substantially stronger in the experiment than simulation at high bias. Further, spatially-resolved-spontaneous-emission measurements of intensity and wavelength demonstrate that the longitudinal carrier density is also non-uniform with a higher carrier density at the back facet for 0.8% front facet reflectivity, even at low bias, while it is flat for devices with 20%. At high bias, temperature increases at the front facet, leading to lateral carrier accumulation at the stripe edges, higher current and carrier density, which is not included in the simulation.