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Optica

Single-photon dynamics of a telecom-band quantum dot emitter integrated with a double solid immersion lens

Daehyun Ahn, Ivan A. Burenkov, Lijun Ma, Young‐Ho Ko, Y. D. Jang, Ranbir Kaur, D. Lee, Mohamed Benyoucef, S. A. Polyakov

Published Sep 8, 2026• 0 citations
Publisher

Abstract

Investigating single-photon dynamics is crucial for characterization of single-photon emitters. Here, we demonstrate a telecom-band quantum dot single-photon emitter integrated with a lithographically aligned double solid immersion lens structure, achieving a collection efficiency of 18(3)% at the first lens. Using two-time correlation measurements, we observed re-excitation-induced multiphoton emission arising from a long-lived, carrier-induced capture process under non-resonant excitation. Under quasi-resonant excitation, this effect was strongly suppressed, reducing the multiphoton emission probability within a 3 ns window from 0.052(1) to 0.0163(4). We further performed second-order quantum spectroscopy based on Fourier analysis of the Hong–Ou–Mandel interference, enabling direct extraction of the exciton fine-structure splitting. This work provides a direct characterization of re-excitation dynamics and coherence properties in a telecom-band single-photon emitter.

DOI
10.1364/optica.609872

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Investigating single-photon dynamics is crucial for characterization of single-photon emitters. Here, we demonstrate a telecom-band quantum dot single-photon emitter integrated with a lithographically aligned double solid immersion lens structure, achieving a collection efficiency of 18(3)% at the first lens. Using two-time correlation measurements, we observed re-excitation-induced multiphoton emission arising from a long-lived, carrier-induced capture process under non-resonant excitation. Under quasi-resonant excitation, this effect was strongly suppressed, reducing the multiphoton emission probability within a 3 ns window from 0.052(1) to 0.0163(4). We further performed second-order quantum spectroscopy based on Fourier analysis of the Hong–Ou–Mandel interference, enabling direct extraction of the exciton fine-structure splitting. This work provides a direct characterization of re-excitation dynamics and coherence properties in a telecom-band single-photon emitter.
Semiconductor quantum dots emitting in the telecommunication O- and C-bands are promising candidates as single-photon sources for fiber-based quantum communication. In this work, we show how coherent quasi-resonant and phonon-assisted excitation help reveal the intrinsic optical properties of InAs quantum dots embedded in relaxed InGaAs matrices on top of metamorphic InGaAs layers for achieving emission in the telecom bands. By systematically comparing excitation schemes, we separate excitation-induced effects from intrinsic emitter properties. This allows us to observe linewidths as narrow as 21 μμμeV, the disappearance of slow decay channels, and single-photon purity reaching second-order autocorrelation values in the order of 10−210^{-2}10−2. Photoluminescence excitation reveals higher excited states, enabling coherent control of trion transitions and the observation of Rabi-like oscillations in both telecom bands. These results confirm the promising potential of these quantum dots for applications in quantum technologies.
Semiconductor quantum dot (QD) quantum light sources have long been established as suitable candidates for many quantum information applications, due to the on-demand emission of highly pure and highly indistinguishable single and entangled photons. A key factor in the development of this technology is the operation over the standard telecommunication optical fibre network infrastructure, where the minimum absorption wavelength window is centred on the telecom C-band (1530 – 1565 nm). Initial experiments in this work demonstrated single-photon emission of a QD light source emitting directly in the telecom C-band, under both continuous wave (CW) and 1-GHz pulsed excitation regimes. The QDs were further characterised in terms of fine-structure splitting (FSS) and coherence time, in order to determine their suitability for quantum entanglement and interference-based applications. Long coherence times were observed in the majority of the QDs considered, allowing the demonstration of Hong-Ou-Mandel-type two-photon interference of subsequently emitted photons under CW excitation. The post-selected interference visibility was found to be limited by only the detector resolution and single-photon purity. A further demonstration of high-visibility interference under the same limitations was then made using QD photons and dissimilar photons from a laser, forming the basis of a fibre-based quantum relay. Working further towards a quantum relay, polarisation-entangled photon pairs in the telecom C-band were then generated using the radiative cascade of the biexciton, where a record high fidelity to the ©+ Bell state was observed under both CW and 1-GHz pulsed excitation regimes. While an anomalous effect of the FSS was observed in a majority of the studied QDs, a further characterisation of the FSS in terms of the QD polarisation eigenstates confirmed the emission of entangled photon pairs from such an anomalous-splitting QD. Finally, the work of this thesis was combined to demonstrate a proof-of-principle quantum relay using a QD light source in the telecom C-band. The relay was operated first under CW excitation where polarisation encoded laser input qubits were used and high-fidelity quantum teleportation was observed. In an effort to demonstrate a more technologically relevant application, the quantum relay was subsequently operated at 1 GHz in order to demonstrate the teleportation of initially time-bin encoded laser input qubits. A high mean teleportation fidelity was again observed, demonstrating the potential of this telecom C-band QD quantum light source in the future of long-distance quantum information applications.
On-demand single-photon sources operating at telecom wavelengths are crucial for quantum communication and photonic quantum technologies. In this work, we demonstrate high-purity, indistinguishable single-photon generation in the telecom O-band from an InAsP/InP nanowire quantum dot. We measured a single-photon purity of g2(0)=0.006±0.003 under above-band excitation. Furthermore, we characterize two-photon interference via Hong–Ou–Mandel measurements and achieve a photon indistinguishability of 81.1%±3.7% with a temporal postselection of a 300 ps time window and 5.6%±1.5% without temporal postselection. We estimate a first-lens source efficiency of ∼28%. These results highlight the potential of nanowire quantum dots as a promising source of telecom single photons for photonic quantum applications, offering deterministic positioning, efficient photon extraction, and scalable production.
In this study, we investigate as-grown InAsP/InP quantum dots emitting in the third telecommunication window under detuned quasi-resonant excitation. A large excitation-emission detuning of 32 meV enables efficient suppression of scattered laser light while retaining several advantages of near-resonant excitation. The single-photon nature of the emission is confirmed by a Hanbury Brown and Twiss experiment, yielding a raw second-order autocorrelation value of graw(2)(0)=0.076(6)g_{\mathrm{raw}}^{(2)}(0)=0.076(6)graw(2)​(0)=0.076(6). Hong-Ou-Mandel measurement is used to determine the degree of indistinguishability of single photons and reveal as measured visibilities of V=0.094(4)V=0.094(4)V=0.094(4) and V=0.106(5)V=0.106(5)V=0.106(5) for excitation pulse separations of 13.1 ns and 5.3 ns, respectively. These results demonstrate the potential of as-grown InAsP/InP quantum dots grown via molecular beam epitaxy under not experimentally demanding detuned excitation for generating indistinguishable telecom single photons. Further improvements are to be achieved through Purcell enhancement in optical cavities.