Optical pumping of quantum dot micropillar lasers

TL;DR

This paper analyzes the efficiency limitations of quantum dot micropillar lasers under optical pumping, identifying key loss mechanisms and proposing material modifications to enhance their energy conversion efficiency for nanophotonic applications.

Contribution

It provides an in-depth experimental analysis of input-output relationships and identifies optical pumping inefficiencies, suggesting material improvements for better laser performance.

Findings

Only 3.4% of pump energy converts into excitons with non-resonant pumping.

A mere 2% of excitons contribute to lasing gain.

Proposed increase in aluminium content could significantly boost pumping efficiency.

Abstract

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.