# The origin and influence of non-cavity modes in a micropillar Bragg microcavity

## TL;DR

This paper explores how non-cavity modes in a micropillar Bragg microcavity affect the performance of quantum light sources.

## Contribution

The study identifies and models non-cavity modes that influence photon collection and Purcell enhancement in quantum dot devices.

## Key findings

- Non-cavity modes significantly impact photon collection efficiency and Purcell enhancement.
- These modes are insensitive to Bragg reflector periodicity but depend on the cylindrical pillar geometry.
- Simulations of uniform pillars successfully reproduce non-cavity mode behavior.

## Abstract

Controlling the photonic environment of emitters is essential to the design of classical and quantum light sources. We study the case of a dipole-like emitter in a cylindrical pillar etched into a planar Bragg microcavity, which is a common design of quantum-dot single photon source. In addition to the well-known cavity modes created by the high-reflectivity of the Bragg mirrors at small in-plane wavevectors, we show the presence of broad spectral features that play a key role in controlling photon collection efficiency and Purcell enhancement. These ‘non-cavity’ modes are insensitive to the periodic index modulation of the Bragg reflectors, but arise from the cylindrical pillar geometry, as we show by comparison with simulations of uniform pillars, which reproduce the non-cavity modes. This approach provides a tool for understanding and modelling these often-disregarded decay channels as a function of source height, cavity dimensions and surface layers.