Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:1605.04759 · Optics Express

Near perfect mode overlap between independently seeded, gain-switched lasers

L. C. Comandar, Marco Lucamarini, B. Fröhlich, J. F. Dynes, Z. L. Yuan, A. J. Shields

Published Jul 27, 2016• 31 citations
arXivHTMLPDF

Abstract

We drastically improve the mode overlap between independently seeded, gain-switched laser diodes operating at gigahertz repetition rates by implementing a pulsed light seeding technique. Injecting pulsed light reduces the emission time jitter and enables frequency chirp synchronization while maintaining random optical phases of the emitted laser pulses. We measure interference of these pulsed sources both in the macroscopic regime, where we demonstrate near perfect mode overlap, and in the single photon regime, where we achieve a Hong-Ou-Mandel dip visibility of 0.499 ± 0.004, thus saturating the theoretical limit of 0.5. The measurement results are reproduced by Monte-Carlo simulations with no free parameters. Our light source is an ideal solution for generation of high rate, indistinguishable coherent pulses for quantum information applications.

DOI
10.1364/oe.24.017849

Related papers

Interference of short optical pulses from independent gain-switched laser diodes for quantum secure communications

Yuan, ZL, Lucamarini, M, Dynes, JF +4 more

Since the introduction of the decoy-state technique, phase-randomized weak coherent light pulses have been the key to increase the practicality of quantum-based communications. Their ultrafast generation was accomplished via compact gain-switched (GS) lasers, leading to high key rates in quantum key distribution (QKD). Recently, the question arose whether the same laser could be employed to achieve high-speed measurement-device-independent QKD, a scheme that promises long-haul quantum communications immune to all detector attacks. For that, a challenging high-visibility interference between independent picosecond optical pulses is required. Here, we answer the above question in the affirmative by demonstrating high-visibility interference from two independent GS lasers triggered at 1 GHz. The result is obtained through a careful characterization of the laser frequency chirp and time jitter. By relating these quantities to the interference visibility, we obtain a parameter-free verification of the experimental data and a numerical simulation of the achievable key rates. These findings are beneficial to other applications making use of GS lasers, including random number generation and standard QKD.

•Dec 17, 2014•34 citations

Phase-Randomized Laser Pulse Generation at 10 GHz for Quantum Photonic Applications

Yuen San Lo, Adam H. Brzosko, Peter R. Smith +7 more

Gain-switching of laser diodes is a well-established technique for generating optical pulses with random phases, where the quantum randomness arises naturally from spontaneous emission. However, the maximum switching rate is limited by the time required for phase diffusion: at high repetition rates, residual photons in the cavity seed subsequent pulses, leading to phase correlations, which degrade randomness. We present a method to overcome this limitation by employing an external source of spontaneous emission in conjunction with the laser. Our results show that this approach substantially suppresses interpulse phase correlations, restoring phase randomization at repetition rates as high as 10 GHz. This technique opens new opportunities for high-rate quantum key distribution and quantum random number generation.

quant-pharXiv:2601.04031•APL Photonics•Jan 8, 2026•1 citation

Optical Injection-Induced Timing Jitter Reduction in Gain-Switched 1550-nm Discrete Mode Semiconductor Lasers

María Duque Gijón, Ana Quirce, Jordi Tiana‐Alsina +2 more

Advanced laser modulation techniques have enabled the development of versatile and efficient light sources for quantum communications [1]. In fact, semiconductor lasers are normally used as single-photon sources in most commercial and research quantum key distribution (QKD) systems [2]. In particular, modulated single-mode semiconductor lasers, utilizing gain-switching, optical injection locking and direct phase modulations have been used to implement a great variety of QKD protocols [1]. In recently introduced protocols, like the measurement-device-independent one (MDI) based on the interference of pulses generated by two remote semiconductor laser sources, timing-jitter in gain-switched lasers affects the temporal overlap of the pulses producing a dramatic reduction in the interference visibility [1]. Very recently MDI-QKD systems using optical injection from a semiconductor laser into a gain-switched semiconductor laser have been demonstrated [1]. A reduction of timing-jitter induced by optical injection is then desirable to improve the interference visibility in this type of MDI-QKD systems.

Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•Jun 26, 2023•0 citations

Phase-correlation-free quantum key distribution source operating at gigahertz rates

Shashank Kumar, Alessandro Marcomini, Loïc Millet +8 more

Phase randomization is essential for the security of practical decoy-state quantum key distribution (QKD) systems. Commonly, implementations rely on laser sources which are either actively phase-randomized, or gain-switched. However, at high repetition rates these show correlations, which can ultimately compromise security and performance. We present a 1.25 GHz phase-randomized QKD source based on a super-luminescent light emitting diode (SLED) operating in the C-band as a compact and cost-effective alternative. The source generates $\sim100$ ps optical pulses with $400$ ps pulse-to-pulse separation, compatible with high-speed time-bin encoding. Interferometric measurements demonstrate $>99\%$ visibility between adjacent time bins, confirming strong first-order coherence within the same quantum signals, while the spontaneous-emission-driven nature of the SLED ensures intrinsic global phase randomization between adjacent signals. This work establishes a scalable SLED-based platform for high-speed prepare-and-measure QKD systems.

quant-pharXiv:2606.04947•APL Photonics•Jun 4, 2026•0 citations

Interference of Short Optical Pulses from Independent Gain-Switched Laser Diodes for Quantum Secure Communications

Z. L. Yuan, M. Lucamarini, J. F. Dynes +3 more

Gain-switched lasers are the ideal light source for quantum secure communications, as they are fast, compact, and present intrinsically randomized phase. The authors demonstrate the ability to interfere with high visibility between independent ultrashort light pulses. This result paves the way to high-bit-rate applications based on second-order interference, most notably quantum key distribution that is independent of the measurement device.

arXiv:1501.01900•Physical Review Applied•Dec 17, 2014•40 citations

Experimental demonstration of long distance quantum communication with independent heralded single photon sources

Xiao-Hai Zhan, Zhen-Qiu Zhong, Jianyu Ma +6 more

Hong-Ou-Mandel interference is essential for various quantum communication protocols, including quantum teleportation, entanglement swapping, and measurement-device-independent (MDI) quantum key distribution (QKD). A significant challenge is producing single photons that remain indistinguishable over long distances. Time jitter introduced in synchronization between remote nodes reduces temporal overlap, making photons no longer indistinguishable. To mitigate this effect, previous solutions are forced to increase the temporal overlap, typically by using narrowband filtering strategies to extend photon coherence time. However, this dramatically decreases photon rates, making them impractical for real-life applications. Here we address this dilemma by employing common laser pulses to generate intrinsically synchronized single photons, eliminating the need for extended coherence time. Without compromising photon indistinguishability, we achieved a four-fold coincidence count rate more than two orders of magnitude higher than previous methods over 50 kilometers of fiber transmission. This breakthrough enabled the implementation of MDI-QKD with passive decoy states, demonstrating the viability of our approach.

npj Quantum Information•May 8, 2025•26 citations
We drastically improve the mode overlap between independently seeded, gain-switched laser diodes operating at gigahertz repetition rates by implementing a pulsed light seeding technique. Injecting pulsed light reduces the emission time jitter and enables frequency chirp synchronization while maintaining random optical phases of the emitted laser pulses. We measure interference of these pulsed sources both in the macroscopic regime, where we demonstrate near perfect mode overlap, and in the single photon regime, where we achieve a Hong-Ou-Mandel dip visibility of 0.499 ± 0.004, thus saturating the theoretical limit of 0.5. The measurement results are reproduced by Monte-Carlo simulations with no free parameters. Our light source is an ideal solution for generation of high rate, indistinguishable coherent pulses for quantum information applications.
Since the introduction of the decoy-state technique, phase-randomized weak coherent light pulses have been the key to increase the practicality of quantum-based communications. Their ultrafast generation was accomplished via compact gain-switched (GS) lasers, leading to high key rates in quantum key distribution (QKD). Recently, the question arose whether the same laser could be employed to achieve high-speed measurement-device-independent QKD, a scheme that promises long-haul quantum communications immune to all detector attacks. For that, a challenging high-visibility interference between independent picosecond optical pulses is required. Here, we answer the above question in the affirmative by demonstrating high-visibility interference from two independent GS lasers triggered at 1 GHz. The result is obtained through a careful characterization of the laser frequency chirp and time jitter. By relating these quantities to the interference visibility, we obtain a parameter-free verification of the experimental data and a numerical simulation of the achievable key rates. These findings are beneficial to other applications making use of GS lasers, including random number generation and standard QKD.
Gain-switching of laser diodes is a well-established technique for generating optical pulses with random phases, where the quantum randomness arises naturally from spontaneous emission. However, the maximum switching rate is limited by the time required for phase diffusion: at high repetition rates, residual photons in the cavity seed subsequent pulses, leading to phase correlations, which degrade randomness. We present a method to overcome this limitation by employing an external source of spontaneous emission in conjunction with the laser. Our results show that this approach substantially suppresses interpulse phase correlations, restoring phase randomization at repetition rates as high as 10 GHz. This technique opens new opportunities for high-rate quantum key distribution and quantum random number generation.
Advanced laser modulation techniques have enabled the development of versatile and efficient light sources for quantum communications [1]. In fact, semiconductor lasers are normally used as single-photon sources in most commercial and research quantum key distribution (QKD) systems [2]. In particular, modulated single-mode semiconductor lasers, utilizing gain-switching, optical injection locking and direct phase modulations have been used to implement a great variety of QKD protocols [1]. In recently introduced protocols, like the measurement-device-independent one (MDI) based on the interference of pulses generated by two remote semiconductor laser sources, timing-jitter in gain-switched lasers affects the temporal overlap of the pulses producing a dramatic reduction in the interference visibility [1]. Very recently MDI-QKD systems using optical injection from a semiconductor laser into a gain-switched semiconductor laser have been demonstrated [1]. A reduction of timing-jitter induced by optical injection is then desirable to improve the interference visibility in this type of MDI-QKD systems.
Phase randomization is essential for the security of practical decoy-state quantum key distribution (QKD) systems. Commonly, implementations rely on laser sources which are either actively phase-randomized, or gain-switched. However, at high repetition rates these show correlations, which can ultimately compromise security and performance. We present a 1.25 GHz phase-randomized QKD source based on a super-luminescent light emitting diode (SLED) operating in the C-band as a compact and cost-effective alternative. The source generates ∼100\sim100∼100 ps optical pulses with 400400400 ps pulse-to-pulse separation, compatible with high-speed time-bin encoding. Interferometric measurements demonstrate >99%>99\%>99% visibility between adjacent time bins, confirming strong first-order coherence within the same quantum signals, while the spontaneous-emission-driven nature of the SLED ensures intrinsic global phase randomization between adjacent signals. This work establishes a scalable SLED-based platform for high-speed prepare-and-measure QKD systems.
Hong-Ou-Mandel interference is essential for various quantum communication protocols, including quantum teleportation, entanglement swapping, and measurement-device-independent (MDI) quantum key distribution (QKD). A significant challenge is producing single photons that remain indistinguishable over long distances. Time jitter introduced in synchronization between remote nodes reduces temporal overlap, making photons no longer indistinguishable. To mitigate this effect, previous solutions are forced to increase the temporal overlap, typically by using narrowband filtering strategies to extend photon coherence time. However, this dramatically decreases photon rates, making them impractical for real-life applications. Here we address this dilemma by employing common laser pulses to generate intrinsically synchronized single photons, eliminating the need for extended coherence time. Without compromising photon indistinguishability, we achieved a four-fold coincidence count rate more than two orders of magnitude higher than previous methods over 50 kilometers of fiber transmission. This breakthrough enabled the implementation of MDI-QKD with passive decoy states, demonstrating the viability of our approach.