Correction of Wavefront Tilt Caused by Atmospheric Turbulence Using Quadrant Detectors for Enabling Fast Free-Space Quantum Communications in Daylight

Fernández, Verónica; Gómez-García, Jorge; Ocampos-Guillen, Alejandro; Carrasco‐Casado, Alberto

doi:10.1109/access.2018.2791099

Cited by 12 publications

(12 citation statements)

References 21 publications

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“…Since beam wander and angle-of-arrival fluctuations are dominant in turbulence, a simple tip/tilt mirror can be used as a rudimentary adaptive optics system, ensuring that the received beam is always aligned onto the detector or detection hologram [235]. In addition, the receiver and / or transmitter can also be tilted to compensate for beam wander and pointing jitter [236].…”

Section: Impact On Optical Signal Processingmentioning

confidence: 99%

Structured Light in Turbulence

Cox

Mphuthi

Nape

et al. 2021

IEEE J. Select. Topics Quantum Electron.

105

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Optical communication is an integral part of the modern economy, having all but replaced electronic communication systems. Future growth in bandwidth appears to be on the horizon using structured light, encoding information into the spatial modes of light, and transmitting them down fibre and free-space, the latter crucial for addressing last mile and digitally disconnected communities. Unfortunately, patterns of light are easily distorted, and in the case of free-space optical communication, turbulence is a significant barrier. Here we review recent progress in structured light in turbulence, first with a tutorial style summary of the core concepts, before highlighting the present state-of-the-art in the field. We support our review with new experimental studies that reveal which types of structured light are best in turbulence, the behaviour of vector versus scalar light in turbulence, the trade-off of diversity and multiplexing, and how turbulence models can be exploited for enhanced optical signal processing protocols. This comprehensive treatise will be invaluable to the large communities interested in free-space optical communication with spatial modes of light.

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Section: Impact On Optical Signal Processingmentioning

confidence: 99%

Structured Light in Turbulence

Cox

Mphuthi

Nape

et al. 2021

IEEE J. Select. Topics Quantum Electron.

105

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“…However, working in the focal plane is sometimes tricky for PSDs. On one hand, spot displacements in this plane are usually very small for lateral-effect PSDs to detect with sufficient SNR [28]. As for quadrant detectors (QDs), if the beam is too small it can fall into the gap or insensitive area where it cannot be detected, and in general, they are preferably used with lager beams to increase their linear region [28].…”

Section: Methodsmentioning

confidence: 99%

“…On one hand, spot displacements in this plane are usually very small for lateral-effect PSDs to detect with sufficient SNR [28]. As for quadrant detectors (QDs), if the beam is too small it can fall into the gap or insensitive area where it cannot be detected, and in general, they are preferably used with lager beams to increase their linear region [28]. Furthermore, if the correction must be achieved in several planes of the quantum receiver where the detectors are placed, as it is the case in many QKD protocols, the QKD receiver must be carefully aligned to place all its detectors at exactly equivalent planes to that of the PSD.…”

Section: Methodsmentioning

confidence: 99%

“…The SKR was calculated with and without the maximum improvement factor in the coupling efficiency (a factor −2) for both the SMF and MMF fibers in strong turbulence regime (C 2 n = 1 × 10 −13 m −2/3 ) and daylight conditions (solar QBER contribution of 4%). The remaining parameters were chosen similar to those in [28]:…”

Section: B Improvement In Optical Flber Coupling Efficiencyafter Cormentioning

confidence: 99%

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Double-Loop Wavefront Tilt Correction for Free-Space Quantum Key Distribution

et al. 2019

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Both free-space and optical fiber quantum key distribution (QKD) links will coexist in future quantum networks, requiring efficient coupling between both types of channels. However, wavefront distortions introduced by the atmospheric channel can severely affect this efficiency. Active mechanisms such as precise beam tracking or steering can correct for some of these wavefront distortions, considerably improving the signal-to-noise ratio of the received quantum signal in many scenarios. A tracking system that uses two, instead oftypically one, controlling loops for tilt correction, stabilizes the beam in the whole optical axis of the receiver relaxing the restrictions of the receiver's optical design, and reduces the area of beam fluctuations in the receiver's focal plane a 24% more than a single-loop configuration. The tracking system was characterized in a QKD system at a 300 meter-link in moderate to strong turbulent conditions (C 2 n − 10 −14 − 10 −13 m −2/3) and an improved coupling efficiency of a factor of 2.1 and 1.6 was obtained for a 9.5 µm-core diameter standard telecommunications Single Mode Fiber (SMF) and a 25 µm-core diameter multimode fiber (MMF), respectively. This reduces the quantum bit error rate (QBER) caused by solar background photons in a 52 % for the former and 39% for the latter, enabling an increase in the secret key rate ofmore than one order ofmagnitude for SMF and a factor of five for MMF. These results are promising for enabling QKD free-space links and their interconnection to fiber optic infrastructure in realistic scenarios of communication networks of high turbulence regimes and daylight conditions. INDEX TERMS Quantum key distribution, beam steering, beam tracking, free-space quantum communication, quantum cryptography, wavefront tilt correction. I. INTRODUCTION Recent research in free-space Quantum Key Distribution (QKD) has focused on increasing the feasibility of practical systems in real scenarios, which implies fulfilling several challenges like increasing the key rate, the propagating distance and making practical systems compact, robust, and low cost [1]-[7]. Many advances on stationary links have been reported in the last few years [8]-[11], whereas other potential scenarios for mobile systems, such as aircrafts [12], hotair balloons [13] and Unmanned Aerial Vehicles (UAVs) [14] have also been explored. In addition, after several tests and proofs to analyze their possibilities, links involving satellites have also been recently demonstrated [15]-[18]. The associate editor coordinating the review of this article and approving it for publication was Wei Huang.

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“…A 50/50 beamsplitter then divides the beam in two paths: one for tracking purposes with two QDs, each in a feedback loop to a FSM, and another path composed of a lateral effect PSD and an optical fibre for observing the correction. Both correcting systems are in closed-loop, which have been proven to perform better than the open-loop strategy [14].…”

Section: Experimental Set Upmentioning

confidence: 99%

Optimising the interconnection of free-space to fibre quantum networks

2019

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Optimising the interconnection between free-space and fibre links will be necessary for future quantum communication networks. In daylight free-space quantum communication based on direct detection, the required Field Of View (FoV) of the receiver system needs to be minimised to reduce solar background noise coupling into the detectors. Reducing the FoV requires minimising beam wander effects caused by atmospheric turbulence through active optics. We implement a fine tracking system designed to correct tip and tilt wavefront aberrations, using two feedback loops; each of them consisting of a quadrant detector and a fast steering mirror for stabilising the beam in the whole optical axis of the receiver. We test the performance of the tracking system with different optical fibres in order to evaluate the reduction in the quantum bit error rate (QBER) caused by solar background noise. A reduction of 75% for single mode fibre was obtained, and 45% reduction for a 25 µm core diameter fibre, both cases for strong turbulence (Cn2~10-12 – 10-13 m-2/3) and 100 m propagating channel. These results look promising for enabling free-space Quantum Key Distribution (QKD) in wireless networks for realistic/adverse conditions such as daylight and strong turbulent regimes.

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Correction of Wavefront Tilt Caused by Atmospheric Turbulence Using Quadrant Detectors for Enabling Fast Free-Space Quantum Communications in Daylight

Cited by 12 publications

References 21 publications

Structured Light in Turbulence

Structured Light in Turbulence

Double-Loop Wavefront Tilt Correction for Free-Space Quantum Key Distribution

Optimising the interconnection of free-space to fibre quantum networks

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