From vertical-cavities to hybrid metal/photonic-crystal nanocavities: Towards high-efficiency nanolasers

TL;DR

This paper demonstrates that incorporating a bottom reflector, especially a metal substrate, significantly enhances unidirectional emission and efficiency in photonic-crystal nanolasers, enabling room-temperature operation with high Q-factors.

Contribution

It introduces a hybrid metal/photonic-crystal nanocavity design with a bottom reflector that improves emission directionality and efficiency, and discusses its relation to plasmonic cavities.

Findings

Vertical emission enhanced by over six times with a dielectric or metal mirror.

Achieved cavity Q of over 1,000 at 1.3 μm with gold substrate.

Unidirectional emission with over 50% efficiency at room temperature.

Abstract

We provide a numerical study showing that a bottom reflector is indispensable to achieve unidirectional emission from a photonic-crystal (PhC) nanolaser. First, we study a PhC slab nanocavity suspended over a flat mirror formed by a dielectric or metal substrate. We find that the laser's vertical emission can be enhanced by more than a factor of six compared with the device in the absence of the mirror. Then, we study the situation where the PhC nanocavity is in contact with a flat metal surface. The underlying metal substrate may serve as both an electrical current pathway and a heat sink, which would help achieve continuous-wave lasing operation at room-temperature. The design of the laser emitting at 1.3 um reveals that relatively high cavity Q of over 1,000 is achievable assuming room-temperature gold as a substrate. Furthermore, linearly-polarized unidirectional vertical emission with the radiation efficiency over 50 % can be achieved. Finally, we discuss how this hybrid design relates to various plasmonic cavities and propose a useful quantitative measure of the degree of the `plasmonic' character in a general metallic nanocavity.