Single-photon sources are important components in the field of quantum information science. They are good candidates for the creation of critical building blocks for quantum key distribution, quantum computing, and quantum networks. During the last two decades, semiconductor quantum dots (QDs) have emerged as efficient single-photon sources with low multiphoton contribution, being able to generate on-demand single photons with near unity indistinguishability. In combination with waveguides, they offer the possibility for generating and manipulating photonic states on-chip.
Nevertheless, despite intensive research efforts aimed at achieving the collection of every single photon into a defined optical mode, coupling or interfacing on-demand single-photon sources at cryogenic temperatures with efficiencies close to unity remains an unresolved challenge. Efficient coupling to optical fibers is particularly desirable in this regard, due to their low loss, and highbandwidth transmission capabilities over long distances. Different fiber-coupling methods for single-photon sources have been extensively researched. For instance, some groups employed an epoxy method to attach a fiber, while others utilized a nanobeam attached to a tapered fiber, a graded index lens assembly in combination with a nanowire waveguide to couple light to a single-mode fiber, a bullseye design attached to the end of a single-mode fiber, evanescent coupling to a μ-fiber or a 3D printed fiber chuck and a microlens. Nevertheless, these methods are often not optimized for resonant excitation and suffer from limited scalability as well as rather high multiphoton contributions and placement accuracies in the μm range. A recently published work (ref.) gives a more detailed overview of the variety of different fiber-coupling methods described. Herein, we explore the use of photonic wire bonds (PWBs), which are flexible interconnections with low insertion loss for laser-to-chip and fiberto-chip integration. They also have been applied in hybridintegrated compact optical transceivers. Furthermore, PWBs have been employed to address the complex packaging requirements of neuromorphic photonic accelerator architectures.