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arXiv:2512.06117

High-Performance Labyrinth Circular Bragg Grating Design for Charge and Stark-Tunable Quantum Light Sources Spanning Visible to Telecom Wavelengths

Rohit Prasad, Quirin Buchinger, Fei Chi Kristy Yuen, Yorick Reum, Sven Höfling, Tobias Huber-Loyola

quant-phphysics.opticsSubmitted Dec 5, 2025• Announced Dec 9, 2025

Abstract

Semiconductor quantum dots embedded in circular Bragg gratings (CBGs) are among the most efficient integrated single-photon sources. However, the fully etched rings of conventional CBGs restrict the implementation of charge and Stark tuning via electrical contacts. To overcome this limitation, a labyrinth CBG geometry with four bridges has been proposed, yet the added bridges significantly degraded optical performance. In this work, we numerically demonstrate that a periodic labyrinth CBG design preserves both high coupling efficiency and strong Purcell enhancement while enabling electrical integration if optimized after introducing the bridges. We show three optimized designs at emission wavelengths of 780 nm, 930 nm, and 1550 nm, because these wavelengths are among the most relevant for quantum dots and show the general applicability of our approach. At all three wavelengths collection efficiencies exceeding 90% into a numerical aperture of 0.7 and Purcell factors greater than 25 are achieved. Furthermore, we propose a device layout incorporating a barrier layer that separates p- and n-doped semiconductor regions, which is incorporated to prevent tunneling of one of the charge carriers for selective charging. Also this design can be reoptimized to retain the performance of a device without tunnel barrier. These results establish labyrinth CBGs as a platform for electrically tunable quantum dot single-photon sources with high efficiency and scalability.

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Semiconductor quantum dots embedded in circular Bragg gratings (CBGs) are among the most efficient integrated single-photon sources. However, the fully etched rings of conventional CBGs restrict the implementation of charge and Stark tuning via electrical contacts. To overcome this limitation, a labyrinth CBG geometry with four bridges has been proposed, yet the added bridges significantly degraded optical performance. In this work, we numerically demonstrate that a periodic labyrinth CBG design preserves both high coupling efficiency and strong Purcell enhancement while enabling electrical integration if optimized after introducing the bridges. We show three optimized designs at emission wavelengths of 780 nm, 930 nm, and 1550 nm, because these wavelengths are among the most relevant for quantum dots and show the general applicability of our approach. At all three wavelengths collection efficiencies exceeding 90% into a numerical aperture of 0.7 and Purcell factors greater than 25 are achieved. Furthermore, we propose a device layout incorporating a barrier layer that separates p- and n-doped semiconductor regions, which is incorporated to prevent tunneling of one of the charge carriers for selective charging. Also this design can be reoptimized to retain the performance of a device without tunnel barrier. These results establish labyrinth CBGs as a platform for electrically tunable quantum dot single-photon sources with high efficiency and scalability.

We present a design study of quantum light sources based on hybrid circular Bragg gratings (CBGs) for emission wavelengths in the telecom O-band. The evaluated CBG designs show photon extraction efficiencies > 95% and Purcell factors close to 30. Using simulations based on the finite element method, and considering the influence of possible fabrication imperfections, we identify optimized high-performance CBG designs which are robust against structural aberrations. In particular, full 3D simulations reveal that the designs show robustness regarding lateral deviations of the emitter position in the device well within reported positioning accuracies of deterministic fabrication technologies. Furthermore, we investigate the coupling of the evaluated hybrid CBG designs to single-mode optical fibers, which is particularly interesting for the development of practical quantum light sources. We obtain coupling efficiencies of up to 77% for off-the-shelf fibers, and again proof robustness against fabrication imperfections. Our results show prospects for the fabrication of close-to-ideal fiber-coupled quantum light sources for long distance quantum communication.

Tunable sources of entangled and single photons are essential for implementing entanglement-based quantum information protocols, as quantum teleportation and entanglement swapping depend on photon indistinguishability. Tunable devices are fabricated from indium arsenide (InAs) quantum dots (QDs) embedded in gallium arsenide (GaAs) nanomembranes placed on monolithic piezoelectric substrates. Circular Bragg grating (CBG) resonators enhance emission brightness and exploit the Purcell effect; however, the inclusion of CBGs reduces strain-mediated tunability compared to planar nanomembranes. A simple and effective solution is introduced: filling the CBG trenches with a stiff dielectric (aluminum oxide) via atomic layer deposition (ALD) restores up to 95% of the tunability of planar structures. Finite element analysis (FEA) confirms that the tunability loss originates from bending in the device layers due to strain relief in the CBG geometry. Lowering the stiffness of intermediate layers between the QDs and the piezoelectric actuator, such as in bonding or reflector layers, further increases strain losses in uncoated CBGs. Coated devices maintain 98-99% strain-tuning efficiency across all simulated underlayer stiffnesses. The results demonstrate that advantageous optical cavity properties can be effectively combined with piezoelectric strain tuning, enabling scalable, bright, and tunable quantum light sources.

Deterministic sources of entangled photon pairs and indistinguishable photons are expected to play a key role in photonic quantum technologies. Semiconductor quantum dots are promising candidates due to their on-demand emission and compatibility with nanophotonic structures. However, current implementations face trade-offs between extraction efficiency, Purcell enhancement, as well as charge noise that causes blinking and degrades indistinguishability. Here we demonstrate a tunable nano-optoelectronic device based on a quantum dot embedded in a p-i-n diode circular-Bragg-grating-resonator and featuring extraction efficiencies up to 0.55(6) and Purcell-factor of $\sim$8. The device generates wavelength-tunable entangled photon pairs with suppressed blinking and raw (corrected) concurrence > 0.89 (0.91) over a range of 1.6 nm. The very same source also emits single, nearly Fourier-limited and highly indistinguishable photons with raw (corrected)

\mathcal{V}_{\text{HOM}}

= 0.951(4) (0.988(6)). These results demonstrate a viable platform for semiconductor quantum photonics.

In the field of quantum communication and quantum cryptography, the need for bright non-classical light sources remains a key requirement. Semiconductor quantum dots (QDs) have proven to be excellent candidates also being able to emit single-photons in the much sought after telecom bands. To overcome the high refractive index contrast between the semiconductor matrix and air, a main approach is to use cavity quantum electrodynamics (cQED). In this regard, circular Bragg gratings have achieved excellent results in the NIR regime [1] [2] . Using the existing fiber network, especially single-photons in the telecom O-band are favorable not only because of zero wave-packet dispersion but also for wavelength division multiplexing with classical communication signals in the telecom C-band.

High-performance solid-state quantum sources in the telecom band are of paramount importance for long-distance quantum communications and the quantum Internet by taking advantage of a low-loss optical fiber network. Here, we demonstrate bright telecom-wavelength single-photon sources based on In(Ga)As/GaAs quantum dots (QDs) deterministically coupled to hybrid circular Bragg resonators (h-CBRs) by using a wide-field fluorescence imaging technique. The QD emissions are redshifted toward the telecom O-band by using an ultra-low InAs growth rate and an InGaAs strain reducing layer. Single-photon emissions under both continuous wave (CW) and pulsed operations are demonstrated, showing high brightness with count rates of 1.14 MHz and 0.34 MHz under saturation powers and single-photon purities of g ( 2 ) ( 0 ) = 0.11 ± 0.02 (CW) and g ( 2 ) ( 0 ) = 0.087 ± 0.003 (pulsed) at low excitation powers. A Purcell factor of 4.2 with a collection efficiency of 11.2 % ± 1 % at the first lens is extracted, suggesting efficient coupling between the QD and h-CBR. Our work contributes to the development of highly efficient single-photon sources in the telecom band for fiber-based quantum communication and future distributed quantum networks.