  Arrays of quantum dot micropillar lasers are an attractive technology
platform for various applications in the wider field of nanophotonics. Of
particular interest is the potential efficiency enhancement as consequence of
cavity quantum electrodynamics effects which makes them prime candidates for
next generation photonic neurons in neural network hardware. However, in
particular for optical pumping their power-conversion efficiency can be very
low. Here we perform an in-depth experimental analysis of quantum dot
microlasers and investigate their input-output relationship over a wide range
of optical pumping conditions. We find that the current energy efficiency
limitation is caused by disadvantageous optical pumping concepts and by a low
exciton conversion efficiency. Our results indicate that for non-resonant
pumping into the GaAs matrix (wetting layer), 3.4% (0.6%) of the optical pump
is converted into lasing-relevant excitons, and of those only 2% (0.75%)
provide gain to the lasing transition. Based on our findings we propose to
improve the pumping efficiency by orders of magnitude by increasing the
aluminium content of the AlGaAs/GaAs mirror pairs in the upper Bragg reflector.
