Optimized diamond inverted nanocones for enhanced color center to fiber coupling

TL;DR

This paper designs and optimizes diamond inverted nanocones to significantly improve fiber coupling efficiency of color centers, demonstrating high performance and robustness through finite element simulations and proposing hybrid structures for further enhancement.

Contribution

It introduces optimized inverted nanocone designs for enhanced fiber coupling of diamond color centers, including broadband performance and hybrid structures, with detailed simulation analysis.

Findings

Achieved 66% fiber coupling efficiency at 619 nm wavelength.

Demonstrated broadband efficiencies of 55% (fiber) and 76% (free-space).

Identified a hybrid nanocone design increasing fiber coupling to 71%.

Abstract

Nanostructures can be used for boosting the light outcoupling of color centers in diamond; however, the fiber coupling performance of these nanostructures is rarely investigated. Here, we use a finite element method for computing the emission from color centers in inverted nanocones and the overlap of this emission with the propagation mode in a single-mode fiber. Using different figures of merit, the inverted nanocone parameters are optimized to obtain maximal fiber coupling efficiency, free-space collection efficiency, or rate enhancement. The optimized inverted nanocone designs show promising results with 66% fiber coupling or 83% free-space coupling efficiency at the tin-vacancy center zero-phonon line wavelength of 619 nm. Moreover, when evaluated for broadband performance, the optimized designs show 55% and 76% for fiber coupling and free-space efficiencies respectively, for collecting the full tin-vacancy emission spectrum at room temperature. An analysis of fabrication insensitivity indicates that these nanostructures are robust against imperfections. For maximum emission rate into a fiber mode, a design with a Purcell factor of 2.34 is identified. Finally, possible improvements offered by a hybrid inverted nanocone, formed by patterning into two different materials, are investigated, and increases the achievable fiber coupling efficiency to 71%.