Mutual coherence enhancement in coupled lasers

Experimentally, mutually coupled quantum dot lasers demonstrate a greatly reduced modal linewidth when mutually phase-locked. The authors investigate this phenomenon theoretically. Specifically, they examine a delay differential equation coupled phase model and use it to find the laser linewidth in several configurations. The numerical results are in excellent agreement with previously reported experimental findings. They show that while the model predicts a restoring force on the phase difference of the coupled lasers, this translates to an effective restoring force on the individual laser phases. The phenomenon should be robust to changes in device type and in particular for modern, integrated coupled lasers.