Precise control of system parameters and extensive optimization play a crucial role in enabling quantum information technologies. As a further challenge, when targeting practical manufacturable systems, the presence of manufacturing variations in components necessitates individual optimization for each system. To address this challenge, we develop a generalisable optimisation framework based on deep reinforcement learning (RL). By applying our method to real-world quantum transmitters based on optical injection locking (OIL), we demonstrate that our RL agent can autonomously identify the optimal operating regions, and generalise its knowledge for new quantum transmitters of the same type. This work presents a new avenue for efficient optimisation of complex systems using modern RL algorithm.
Real-time generation of quantum keys between satellite and ground nodes is essential for a scalable and global quantum network. We report the development of a QKD system that operate at gigahertz clock rate with multiplexed classical and quantum channels. This system is tested on a free-space link which is an emulation of the satellite to ground link with dynamic loss and random misalignments. With the assumption of a small satellite in low Earth orbit and a ground station with moderate aperture, we demonstrate the generation of >5 Mbits of quantum keys in a single emulated satellite pass.
We review our efforts in integrating optical hardware for quantum key distribution onto photonic chips and in engineering the first standalone photonic integrated QKD system. Our approach tackles various system integration challenges related to packaging, optoelectronic design and power consumption. The quantum hardware is assembled in pluggable interconnects that guarantee efficient thermal management and forward compatibility of a same host electronics with successive generations of chips. Autonomous operation and long-term stability are demonstrated in realistic operation conditions. Our work offers new pathways for practical implementations of QKD and its viable deployment at large scales.
Wavelength tunability in quantum key distribution (QKD) is desirable as noise can be introduced to the quantum channel if there is significant traffic near the same wavelength as the quantum data. Today’s QKD systems are typically of fixed wavelength due to the single-mode lasers used to encode qubits. We present a new optical transmitter design consisting of a multi-modal Fabry Perot laser optically injection locked by a tunable laser, capable of encoding qubits at GHz speeds with a tunable wavelength of < 65 nm and perform proof-of-principle BB84 QKD over a range of wavelengths with secure bit rates of order Mb/s.
Quantum key distribution (QKD) offers the highest possible levels of communication secrecy. Using the laws of quantum mechanics, QKD protocols allow two distant parties to establish symmetric encryption keys that can be proven information theoretically secure. In order to make this technology accessible to a wide range of sectors, it is essential to address the questions of cost, volume production and compatibility with standard Telecom/Datacom infrastructures. While over the last few years, a number of works were devoted to the demonstration of photonic integrated circuits for quantum communications, a practical solution to interface these chips in a complete system remained an elusive goal. We review our efforts in integrating the core optical functions of quantum key distribution onto quantum photonic chips and in demonstrating the first standalone photonic integrated QKD system. Our approach tackles various system integration challenges related to packaging, optoelectronic design and power consumption. The quantum hardware is assembled in pluggable interconnects that guarantee efficient thermal management and forward compatibility of a same host electronics with successive generations of chips. Autonomous operation and long-term stability are demonstrated in realistic operation conditions. Our work offers new pathways for practical implementations of QKD and its viable deployment at large scales.
For the adoption of QKD to grow, much effort has been devoted to making QKD systems more robust and efficient. Much of the complexity of a QKD system stems from its transmitter where quantum states encoded with bit values are prepared. Recently, optical injection locking (OIL) has emerged as a promising method to realize high-speed QKD transmitters with a compact design. This approach enables direct phase encoding without the need for external modulators, while simultaneously improving the laser characteristics. Due to these remarkable advantages, OIL has been widely applied to many QKD protocols, including BB84, MDI-QKD and TF-QKD. However, in practice, tuning the laser system to find optimal operating parameters is a very challenging task. This is because the underlying laser dynamics are rich and involve a complex interplay between multiple control parameters. It is therefore highly desirable to develop an efficient method to optimize the systems. Here, for the first time, we address this issue by demonstrating a self-tuning QKD transmitter by implementing a genetic algorithm to autonomously locate the optimum system parameters. Without any user intervention, our approach manages to optimize the quantum bit error rate down to ~2.5%, matching the state-of-the-art performance.
Twin-field (TF) quantum key distribution (QKD) fundamentally alters the rate-distance relationship of QKD, offering the scaling of a single-node quantum repeater. Although recent experiments have demonstrated the new opportunities for secure long-distance communications allowed by TF-QKD, formidable challenges remain to unlock its true potential. Here, we introduce a novel wavelength-multiplexed stabilisation scheme that overcomes past limitations and can be adapted to other phase-sensitive single-photon applications. In our work, we develop a setup that provides key rates over a record fibre distance of 605 km and increases the secure key rate at long distances by two orders of magnitude to values of practical significance.
A complete chip-based quantum communication system is demonstrated. The core functions of quantum transmitter, quantum receiver and quantum random number generator are implemented onto photonic integrated circuits (PICs) of different materials. For the first time, these PICs are all interfaced in a compact optoelectronic assembly where they operate synchronously to distribute information theoretically secure encryption keys in real-time. After reviewing the challenges of system integration for quantum photonic circuits, we present our development of plug-and-play quantum communication modules that are practical, scalable, power efficient and perform with high stability under real-life conditions.
Mid-infrared (mid-IR) fiber lasers that are based on dysprosium (Dy) as the active laser ion provide emission in the wavelength range between 2.6–3.4 μm and can thus bridge the spectral gap between holmium (Ho) and erbium (Er) based mid-IR lasers. Another distinct feature is the wide choice of pump wavelengths (1.1 μm, 1.3 μm, 1.7 μm, and 2.8 μm) that can be used. To date, pump wavelengths shorter than 1.1 μm have not been reported and all demonstrated pump wavelengths apart from in-band pumping suffer from pump excited state absorption (ESA). In this paper, we report new excitation wavelengths, 0.8 μm and 0.9 μm, for Dy-doped mid-IR fiber lasers. We have measured 18.5% and 23.7% slope efficiency (relative to launched pump power) for 0.8 μm and 0.9 μm pumping wavelengths, respectively. By comparing the residual pump power of experimental and numerical simulation data of a 0.5 m Dy-doped fiber, we have found that these new excitation wavelengths are free from pump ESA. Moreover, the high power laser diodes are commercially available at these new excitation wavelengths; therefore, the realization of a diode-pumped Dy-doped mid-infrared fiber laser might become feasible in the near future.
Mode-locked fiber lasers are currently limited to sub-3-μm wavelengths, despite application-driven demand for longer wavelength mid-IR pulse sources. Erbium- and holmium-doped fluoride fiber lasers are emerging for 2.7-2.9 μm emission, yet further extending this coverage is challenging. Here, we propose a new approach using dysprosium-doped fiber with frequency shifted feedback (FSF), achieving 33 ps pulses with up to 2.7 nJ energy, tunable from 2.97 to 3.30 μm. Notably, this is the longest wavelength mode-locked fiber laser and the most broadly tunable pulsed fiber source to date. Simulations are also performed, offering insights into the dynamics of FSF pulse generation.
The development of new, compact mid-infrared light sources is critical to enable biomedical sensing applications in resource-limited environments. Here, we review progress in fiber-based mid-IR sources, which are ideally suited for clinical environments due to their compact size and waveguide format. We first discuss recent developments in mid-IR supercontinuum sources, which exploit nonlinear optic phenomena in highly nonlinear materials (pumped by ultrashort pulse lasers) to generate broadband spectra. An emerging alternative approach is then presented, based on broadly tunable mid-IR fiber lasers, using the promising dysprosium ion to achieve orders of magnitude higher spectral power density than typical supercontinua. By employing an acousto-optic tunable filter for wavelength tuning, an electronically controlled swept-wavelength mid-IR fiber laser is developed, which is applied for absorption spectroscopy of ammonia (NH3), an important biomarker, with 0.3 nm resolution and 40 ms acquisition time.
Previously reported progress in 3 micron dysprosium doped ZBLAN fiber lasers achieved record conversion efficiency but was limited in tuneability due to the inband nature of the pumping scheme. Near infrared pumping has also been demonstrated but was limited in conversion efficiency due both to pump excited state absorption and large quantum defect. We address these limitations by employing a Raman fiber laser operating at 1700 nm as a pump source. Reduced quantum defect shows promise for efficiency gains while maintaining near infrared pumping and the increased gain bandwidth shows promise for pulsed operation.
We explore the potential of a new mid-infrared laser transition in praseodymium-doped fluoride fiber for emission around 3.4 μm, which can be conveniently pumped by 0.975 μm diodes via ytterbium sensitizer co-doping. Optimal cavity designs are determined through spectroscopic measurements and numerical modeling, suggesting that practical diode-pumped watt-level mid-infrared fiber sources beyond 3 μm could be achieved.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.