Broadband enhancement of on-chip single-photon extraction via tilted hyperbolic metamaterials

On-chip single-photon sources with high repetition rates are a fundamental block for quantum photonics and can enable applications such as high-speed quantum communication or quantum information processing. Ideally, such single-photon sources require a large on-chip photon extraction decay rate, especially over a broad spectral range, but this goal has remained elusive so far. Current approaches implemented to enhance the spontaneous emission rate include photonic crystals, optical cavities, metallic nanowires, and metamaterials. These approaches either have a strong reliance on the frequency resonance mechanisms, which unavoidably suffer from the issue of narrow working bandwidth, or are limited by poor outcoupling efficiency. Here, we propose a feasible scheme to enhance the on-chip photon extraction decay rate of quantum emitters through the tilting of the optical axis of hyperbolic metamaterials with respect to the end-facet of nanofibers. The revealed scheme is applicable to arbitrarily orientated quantum emitters over a broad spectral range extending up to ∼80 nm for visible light. This finding relies on the emerging unique feature of hyperbolic metamaterials if their optical axis is judiciously tilted. Hence, their supported high-k (i.e., wavevector) hyperbolic eigenmodes, which are intrinsically confined inside them if their optical axis is un-tilted, can now become momentum-matched with the guided modes of nanofibers, and more importantly, they can efficiently couple into nanofibers almost without reflection.