Spontaneous emission rates of dipoles in photonic crystal membranes

TL;DR

This paper theoretically demonstrates that 2D photonic crystal membranes can significantly modify spontaneous emission rates of embedded dipoles, with potential for strong inhibition or enhancement depending on dipole orientation and position.

Contribution

The study provides a detailed theoretical analysis of emission rate modifications in 2D photonic crystal membranes, highlighting the effects of membrane confinement and crystal size.

Findings

Over 7 times inhibition of emission rate

Up to 15 times enhancement of emission rate

Emission modifications observable even outside the membrane

Abstract

We show theoretically that finite two-dimensional (2D) photonic crystals in thin semiconductor membranes strongly modify the spontaneous emission rate of embedded dipole emitters. Three-dimensional Finite-Difference Time-Domain calculations show over 7 times inhibition and 15 times enhancement of the emission rate compared to the vacuum emission rate for judiciously oriented and positioned dipoles. The vertical index confinement in membranes strongly enhances modifications of the emission rate as compared to vertically unconfined 2D photonic crystals. The emission rate modifications inside the membrane mimic the local electric field mode density in a simple 2D model. The inhibition of emission saturates exponentially as the crystal size around the source is increased, with a $1/e$ length that is inversely proportional to the bandwidth of the emission gap. We obtain inhibition of emission only close to the slab center. However, enhancement of emission persists even outside the membrane, with a distance dependence which dependence can be understood by analyzing the contributions to the spontaneous emission rate of the different vertically guided modes of the membrane. Finally we show that the emission changes can even be observed in experiments with ensembles of randomly oriented dipoles, despite the contribution of dipoles for which no gap exists.