Optimized designs for micropillar cavity with simultaneously high quality factor and Gaussian far field at near-wavelength diameter.

Micropillar cavities with small volumes and high quality factors (Q-factor) greatly enhance the light-matter interaction. Crucially, these cavities exhibit a near-Gaussian far-field pattern, making them highly suitable for efficiently coupling and manipulation of emitted photons. However, their miniaturization into near-wavelength scales is limited by diffraction, resulting in both Q-factor degradation and far-field emission divergence. Here, we propose a tapered micropillar cavity design that simultaneously achieves a high Q-factor (Q = 1.37 × 10) and near-Gaussian far-field emission at near-wavelength diameter (mode volume V = 0.154λ). Notably, its direct single-mode fiber coupling efficiency is 0.71, representing a remarkable 230 % improvement compared to traditional λ-micropillar cavities of the same diameter. Our results show prospects of ideal fiber-coupled platforms for cavity quantum electrodynamics experiments, particularly in the strong coupling regime.