Cooperative interactions between nano-antennas in a high-Q cavity for unidirectional light sources

Kévin G Cognée,A F Koenderink,Philippe Lalanne,Hugo M Doeleman

doi:10.1038/s41377-019-0227-x

Abstract

We analyse the resonant mode structure and local density of states in high-Q hybrid plasmonic-photonic resonators composed of dielectric microdisks hybridized with pairs of plasmon antennas that are systematically swept in position through the cavity mode. On the one hand, this system is a classical realization of the cooperative resonant dipole–dipole interaction through a cavity mode, as is evident through predicted and measured resonance linewidths and shifts. At the same time, our work introduces the notion of ‘phased array’ antenna physics into plasmonic-photonic resonators. We predict that one may construct large local density of states (LDOS) enhancements exceeding those given by a single antenna, which are ‘chiral’ in the sense of correlating with the unidirectional injection of fluorescence into the cavity. We report an experiment probing the resonances of silicon nitride microdisks decorated with aluminium antenna dimers. Measurements directly confirm the predicted cooperative effects of the coupled dipole antennas as a function of the antenna spacing on the hybrid mode quality factors and resonance conditions.

Highlights

Tailoring optical resonators to have any desired quality factor Q and mode volume V is a major endeavour in nano- and micro-optics as the basic stepping stone to controlling the light-matter interaction in diverse scenarios that range from cavity QED, to nonlinear optics, to vibrational spectroscopy, to building lasers and solidstate lighting devices[1,2]
We have reported a simple model for the emission enhancement properties of multimode, multi-antenna hybrid plasmon-photonic resonators, in particular focusing on whispering gallery mode (WGM) cavities coupled to plasmon antenna dimers
The essential physics of this hybridization is confirmed by experiments in an experimental platform based on silicon nitride microdisks and aluminium nano-antennas

Summary

Introduction

Tailoring optical resonators to have any desired quality factor Q and mode volume V is a major endeavour in nano- and micro-optics as the basic stepping stone to controlling the light-matter interaction in diverse scenarios that range from cavity QED, to nonlinear optics, to vibrational spectroscopy, to building lasers and solidstate lighting devices[1,2]. It is desirable to independently control the field strength per photon (gauged by V), the resonator linewidth Q3, and the channel to which the resonator favourably couples with far-field radiation. When controlling the rate of spontaneous emission experienced by a quantum emitter placed in a resonator, it is desirable to control the Purcell factor F 1⁄4 ð3λ3=4π2ÞQ=V while at the same time tuning the cavity to the emitter frequency, making sure that the cavity linewidth is matched to the emitter spectrum[4,5] and ensuring that light extraction occurs through one highly efficient channel. Similar arguments hold for strong coupling between light and matter[3,6,7], SERS and cavity/molecular optomechanics[8] and, generally, processes that at the same time need high field enhancement yet matching of the linewidths to other experimental constraints. Reaching very large F at intermediate 5 < Q < 104 factors, has remained elusive, despite the large possible relevance for matching the linewidths of room-temperature emitters

Methods

Results

Conclusion