User-friendly single-photon sources with high photon-extraction efficiency are crucial building blocks for photonic quantum applications. For many of these applications, such as long-distance quantum key distribution, the use of single-mode optical fibers is mandatory, which leads to stringent requirements regarding the device design and fabrication. We report on the on-chip integration of a quantum dot (QD) microlens with a 3D-printed micro-objective in combination with a single-mode on-chip fiber coupler. The practical quantum device is realized by the deterministic fabrication of the QD-microlens via in situ electron-beam lithography and the 3D two-photon laser writing of the on-chip micro-objective and fiber chuck. A QD with a microlens is an efficient single-photon source, whose emission is collimated by the on-chip micro-objective. A second polymer microlens is located at the end facet of the single-mode fiber and ensures that the collimated light is efficiently coupled into the fiber core. For this purpose, the fiber is placed in an on-chip fiber chuck, which is precisely aligned to the QD-microlens thanks to the sub-micrometer processing accuracy of high-resolution two-photon direct laser writing. The resulting quantum device has a broadband photon extraction efficiency, a single-mode fiber-coupling efficiency of 22%, a measured single-photon flux of 42 kHz (8.9 kHz) under cw (pulsed) optical excitation, which corresponds to 1.5 MHz (0.3 MHz) at the single-mode fiber output, and a multi-photon probability in terms of g⁽²⁾(0) = $0.00{\pm }_{0.00}^{0.04}$ (0.13 ± 0.05) under cw (pulsed) optical excitation. The stable design of the developed fiber-coupled quantum device makes it highly attractive for integration into user-friendly plug-and-play quantum applications.

中文翻译：

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具有3D打印微物镜的量子点单光子发射耦合到单模光纤中

具有高光子提取效率的用户友好型单光子源是光子量子应用的关键组成部分。对于许多此类应用（例如长距离量子密钥分发），必须使用单模光纤，这导致对设备设计和制造的严格要求。我们报告了量子点（QD）微透镜与3D打印微物镜结合单模片上光纤耦合器的片上集成。通过确定性地通过原位制造QD微透镜来实现实用的量子器件电子束光刻和片上微物镜和光纤卡盘的3D双光子激光写入。具有微透镜的量子点是一种有效的单光子源，其发射通过片上微物镜准直。第二个聚合物微透镜位于单模光纤的端面，并确保将准直的光有效地耦合到光纤纤芯中。为此，将光纤放置在芯片上的光纤卡盘中，由于高分辨率的两光子直接激光写入具有亚微米级的处理精度，因此可以将其与QD微透镜精确对准。所得的量子器件具有宽带光子提取效率，22％的单模光纤耦合效率，在cw（脉冲）光激发下测得的42 kHz（8.9 kHz）单光子通量，对应于1.5 MHz（ 0。^（2）（0）=$0.00{\pm }_{0.00}^{0.04}$（脉冲）光激发下（0.13±0.05）。所开发的光纤耦合量子设备的稳定设计使其非常适合集成到用户友好的即插即用量子应用中。