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# 3D printed micro-optics for quantum technology: Optimised coupling of single quantum dot emission into a single-mode fibre

• Light: Advanced Manufacturing  2, Article number: 6 (2021)
• Future quantum technology relies crucially on building quantum networks with high fidelity. To achieve this challenging goal, it is of utmost importance to connect individual quantum systems such that their emitted single photons overlap with the highest possible degree of coherence. This requires perfect mode overlap of the emitted light from different emitters, which necessitates the use of single-mode fibres. Here, we present an advanced manufacturing approach to accomplish this task. We combined 3D printed complex micro-optics, such as hemispherical and Weierstrass solid immersion lenses, as well as total internal reflection solid immersion lenses, on top of individual indium arsenide quantum dots with 3D printed optics on single-mode fibres and compared their key features. We observed a systematic increase in the collection efficiency under variations of the lens geometry from roughly 2 for hemispheric solid immersion lenses up to a maximum of greater than 9 for the total internal reflection geometry. Furthermore, the temperature-induced stress was estimated for these particular lens dimensions and results to be approximately 5 meV. Interestingly, the use of solid immersion lenses further increased the localisation accuracy of the emitters to less than 1 nm when acquiring micro-photoluminescence maps. Furthermore, we show that the single-photon character of the source is preserved after device fabrication, reaching a $g^{(2)} (0)$ value of approximately 0.19 under pulsed optical excitation. The printed lens device can be further joined with an optical fibre and permanently fixed.This integrated system can be cooled by dipping into liquid helium using a Stirling cryocooler or by a closed-cycle helium cryostat without the necessity for optical windows, as all access is through the integrated single-mode fibre. We identify the ideal optical designs and present experiments that demonstrate excellent high-rate single-photon emission.
###### 通讯作者: 陈斌, bchen63@163.com
• 1.

沈阳化工大学材料科学与工程学院 沈阳 110142

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### Research Summary

Quantum technology: 3D printed fibre-based quantum light source

Making quantum networks a reality relies crucially on building efficient optical fibre-based quantum light sources. Here, Harald Giessen and Peter Michler from the University of Stuttgart in Germany and colleagues present an advanced manufacturing approach to accomplish this task. Complex micrometre-sized optics were 3D printed on top of individual indium arsenide quantum dots to enhance their single-photon extraction efficiency.  Different lens geometries were systematically investigated to optimise the required optical design and a significant increase in light extraction was achieved. Furthermore, a 3D printed fibre chuck was used to precisely position an optical fibre, equipped with another 3D printed in-coupling lens, onto such a quantum dot. This compact on-chip solution enables high coupling efficiency into a single-mode fibre with high-rate single-photon emission.

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## 3D printed micro-optics for quantum technology: Optimised coupling of single quantum dot emission into a single-mode fibre

• 1. Institut für Halbleiteroptik und Funktionelle Grenzflächen, Research Center SCoPE, and Integrated Quantum Science and Technology Center IQST, University of Stuttgart, 70569 Stuttgart, Germany
• 2. 4th Physics Institute, Research Center SCoPE, and Integrated Quantum Science and Technology Center IQST, University of Stuttgart, 70569 Stuttgart, Germany
• 3. Institute of Applied Optics (ITO) and Research Center SCoPE, University of Stuttgart, 70569 Stuttgart, Germany
• 4. Institute of Solid State Physics, Technical University of Berlin, 10623 Berlin, Germany
###### Harald Giessen, h.giessen@pi4.uni-stuttgart.de
• These authors contributed equally: Marc Sartison, Ksenia Weber

Abstract: Future quantum technology relies crucially on building quantum networks with high fidelity. To achieve this challenging goal, it is of utmost importance to connect individual quantum systems such that their emitted single photons overlap with the highest possible degree of coherence. This requires perfect mode overlap of the emitted light from different emitters, which necessitates the use of single-mode fibres. Here, we present an advanced manufacturing approach to accomplish this task. We combined 3D printed complex micro-optics, such as hemispherical and Weierstrass solid immersion lenses, as well as total internal reflection solid immersion lenses, on top of individual indium arsenide quantum dots with 3D printed optics on single-mode fibres and compared their key features. We observed a systematic increase in the collection efficiency under variations of the lens geometry from roughly 2 for hemispheric solid immersion lenses up to a maximum of greater than 9 for the total internal reflection geometry. Furthermore, the temperature-induced stress was estimated for these particular lens dimensions and results to be approximately 5 meV. Interestingly, the use of solid immersion lenses further increased the localisation accuracy of the emitters to less than 1 nm when acquiring micro-photoluminescence maps. Furthermore, we show that the single-photon character of the source is preserved after device fabrication, reaching a $g^{(2)} (0)$ value of approximately 0.19 under pulsed optical excitation. The printed lens device can be further joined with an optical fibre and permanently fixed.This integrated system can be cooled by dipping into liquid helium using a Stirling cryocooler or by a closed-cycle helium cryostat without the necessity for optical windows, as all access is through the integrated single-mode fibre. We identify the ideal optical designs and present experiments that demonstrate excellent high-rate single-photon emission.

### Research Summary

Quantum technology: 3D printed fibre-based quantum light source

Making quantum networks a reality relies crucially on building efficient optical fibre-based quantum light sources. Here, Harald Giessen and Peter Michler from the University of Stuttgart in Germany and colleagues present an advanced manufacturing approach to accomplish this task. Complex micrometre-sized optics were 3D printed on top of individual indium arsenide quantum dots to enhance their single-photon extraction efficiency.  Different lens geometries were systematically investigated to optimise the required optical design and a significant increase in light extraction was achieved. Furthermore, a 3D printed fibre chuck was used to precisely position an optical fibre, equipped with another 3D printed in-coupling lens, onto such a quantum dot. This compact on-chip solution enables high coupling efficiency into a single-mode fibre with high-rate single-photon emission.

show all
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