Negatively charged nitrogen vacancy (${{\rm{NV}}^ -}$) centers in diamond are required to be coupled to optical systems for various applications. A slowly varied tapered waveguide displays a near-unity power transfer from an optical fiber to on-chip photonic devices. This physical situation refers to an adiabatic transition of photons from a highly effective confinement mode to a lower effective confinement mode or vice versa. Here, we report tunable bidirectional coupling with enhanced efficiency in a hybrid structure of elliptically faceted (ELFA) diamond nanowire with ${{\rm{NV}}^ -}$ centers integrated to optical nanowire. Initiating from diabatic transition to adiabatic transition, corresponding to smaller length to longer wire length, respectively, the coupling efficiency oscillates and asymptotically saturates to a maximum value. Our calculations indicate coupling efficiencies of 85% and 84% for azimuthal and radial dipole configurations for the hybrid structure, respectively. The structure with optimum geometry provides similar coupling efficiency of ${\sim}{{81}}\%$ for radial and azimuthal dipole configurations. By excitation of one of few dipoles placed strategically at various locations in the cylindrical region of the diamond nanowire will allow one to tune coupling efficiency in the two directions. Tailored size and tunable bidirectional coupling of ELFA diamond nanowire with enhanced efficiency will enable its wide-field applications including multi-scale quantum photonics devices.

中文翻译：

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金刚石发射器与光学纳米线的双向耦合：可调且高效

金刚石中带负电荷的氮空位 ( ${{\rm{NV}}^ -}$ ) 中心需要与光学系统耦合以用于各种应用。缓慢变化的锥形波导显示出从光纤到片上光子器件的近乎统一的功率传输。这种物理情况是指光子从高效约束模式到较低有效约束模式的绝热跃迁，反之亦然。在这里，我们报告了具有${{\rm{NV}}^ -}$的椭圆刻面 (ELFA) 金刚石纳米线混合结构中效率更高的可调双向耦合中心集成到光学纳米线。从非绝热过渡到绝热过渡，分别对应于较小的长度到较长的导线长度，耦合效率振荡并渐近饱和到最大值。我们的计算表明，混合结构的方位角和径向偶极子配置的耦合效率分别为 85% 和 84%。具有最佳几何形状的结构提供了类似的耦合效率${\sim}{{81}}\%$用于径向和方位偶极子配置。通过激发在金刚石纳米线的圆柱形区域中战略性地放置在不同位置的少数偶极子之一将允许在两个方向上调整耦合效率。具有增强效率的 ELFA 金刚石纳米线的定制尺寸和可调双向耦合将使其包括多尺度量子光子学器件在内的广泛领域应用成为可能。