Photonic crystal cavities from hexagonal boron nitride

Sejeong Kim,James Bishop,Daniel Totonjian,Joe Christian,Igor Aharonovich,Kenji Watanabe,Marcus Straw,Milos Toth,Johannes E Fröch,Takashi Taniguchi

doi:10.1038/s41467-018-05117-4

Abstract

Development of scalable quantum photonic technologies requires on-chip integration of photonic components. Recently, hexagonal boron nitride (hBN) has emerged as a promising platform, following reports of hyperbolic phonon-polaritons and optically stable, ultra-bright quantum emitters. However, exploitation of hBN in scalable, on-chip nanophotonic circuits and cavity quantum electrodynamics (QED) experiments requires robust techniques for the fabrication of high-quality optical resonators. In this letter, we design and engineer suspended photonic crystal cavities from hBN and demonstrate quality (Q) factors in excess of 2000. Subsequently, we show deterministic, iterative tuning of individual cavities by direct-write EBIE without significant degradation of the Q-factor. The demonstration of tunable cavities made from hBN is an unprecedented advance in nanophotonics based on van der Waals materials. Our results and hBN processing methods open up promising avenues for solid-state systems with applications in integrated quantum photonics, polaritonics and cavity QED experiments.

Highlights

Development of scalable quantum photonic technologies requires on-chip integration of photonic components
As a first step toward applications, we demonstrate nanofabrication of two-dimensional (2D) and one-dimensional (1D) photonic crystal cavities (PCCs) with optical Q-factors of up to 2100
Undercutting techniques that are used to achieve suspended structures and bulk angle etch processes have not been applied successfully to these materials. This is significant because of the small refractive index of hexagonal boron nitride (hBN) of ~ 1.8 makes it hard to achieve a high refractive index contrast that is needed for efficient light confinement in the visible spectral range. We resolve these challenges by demonstrating the fabrication and iterative editing/tuning of suspended photonic cavities from the van der Waals material hBN using a combination of hBN exfoliation onto a trenched substrate, reactive ion etching (RIE) and single-step, direct-write electron beam induced chemical etching[32]

Summary

Introduction

Development of scalable quantum photonic technologies requires on-chip integration of photonic components. In recent years, layered van der Waals materials have emerged as promising hosts of ultra-bright quantum emitters[20] Integration of these light sources with dielectric and metallic waveguides has been achieved by placing flakes of the van der Waals hosts on top of the waveguides[21,22,23]. We design and fabricate optical cavities from hBN – a wide bandgap, hyperbolic van der Waals material[24] that has recently attracted considerable attention as a promising host of ultra-bright, room-temperature quantum emitters[20,25,26,27,28,29]. This, together with a high degree of inherent chemical inertness, makes hBN resilient to a broad range of environments such as liquids, and applications in sensing where the relatively low refractive index of hBN is beneficial as it leads to large evanescent fields that enhance sensing efficiency

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Results

Conclusion