The rapidly growing field of space-to-ground laser communication offers high throughput and secure data transfer without frequency allocation. Cailabs' TILBA-ATMO, leveraging Multi-Plane Light Conversion (MPLC) technology, provides turbulence mitigation for atmospheric communication. The 8-mode version showed promise at 100 Gbps, but for Optical Ground Stations (OGS) with large telescopes, a 45-mode system is required. Our latest research demonstrates the 45-mode TILBA-ATMO effectively achieves 10 Gbps data rates, meeting OGS requirements for Low-Earth Orbit (LEO) satellite signals at high Greenwood frequency and large D/r0.

Cailabs' TILBA-ATMO, leveraging Multi-Plane Light Conversion (MPLC) technology, provides turbulence mitigation for atmospheric communication. We demonstrate turbulence mitigation over 45 modes, meeting requirements for low-Earth orbit satellite signals at high Greenwood frequency and large D/r0. Full-text article not available; see video presentation

We theoretically analyze and experimentally demonstrate the possibility of amplifying optical signals in an unrepeatered mode -division multiplexed transmission system, through inter -modal stimulated Raman scattering process between signal and pump beams coupled onto distinct modes of a few -mode graded -index optical fiber.

Space-to-ground laser communication is booming thanks to high throughput, stealth communication without frequency allocation. However, lasercom becomes really competitive beyond 10 Gbps. At this rate, fiber components, requiring SMF coupling, and thus turbulence mitigation become necessary. Based on Cailabs' core technology, Multi-Plane Light Conversion (MPLC) followed by photonic integrated chip, Cailabs develops a turbulence mitigation product entirely dedicated to lasercom. Previous work showed proof of concept for the 8-mode version. In this article we investigate last results obtained with the system including 100 Gbps communication and present the new 45-modes turbulence mitigation version.

The achievement of coherent beam combination is of paramount importance in the advancement of high-power laser systems across various fields, such as defense and communication. In this context, we present a novel filled-aperture coherent beam combiner that integrates essential components including polarization-maintaining fiber elements, Electro-Optic Modulators (EOMs), Erbium-Doped Fiber Amplifiers (EDFA), a Multi-Plane Light Converter, and a feedback loop employing the Stochastic Parallel Gradient Descent (SPGD) algorithm. By leveraging the SPGD algorithm, we attain precise control over the EOMs, enabling stable optical output power. Our experimental results demonstrate the effectiveness of this approach, as it achieves coherent combination of up to six input channels with high efficiency. Additionally, we observe negligible power loss throughout the duration of the process, while maintaining precise control over thermal and mechanical perturbations. One advantage of this MPLC technology is its direct scalability across different wavelengths. This feature enhances its applicability in a wide range of laser systems.

Incoherent beam combination consists of superposing several laser beams on a target. This technique is relatively simple to implement and uses "off-the-shelf" optical components, without active control of the phase or polarization of the input sources. With the Multi-plane Light Conversion (MPLC) technique, tailored and multi-reflective phase element, enabling to obtain an optimal beam quality in terms of divergence for a given number of input beams, we present non-coherent beam combiner of 4 Fibered high power input beams at 1µm with a total M² close to 2,5 and a combining efficiency around 92%.

Recent progress in the development of superconducting nanowire single-photon detectors (SNSPD) has delivered ex-cellent performance, and their increased adoption has had a great impact on a range of applications. One of the key characteristic of SNSPDs is their detection rate, which is typically higher than other types of free-running single-photondetectors. The maximum achievable rate is limited by the detector recovery time after a detection, which itself is linked to the superconducting material properties and to the geometry of the meandered SNSPD. Arrays of detectors biased individually can be used to solve this issue, but this approach significantly increases both the thermal load in the cryo-stat and the need for time processing of the many signals, and this scales unfavorably with a large number of detectors. One potential scalable approach to increase the detection rate of individual detectors further is based on parallelizing smaller meander sections. In this way, a single detection temporarily disables only one subsection of the whole active area, thereby leaving the overall detection efficiency mostly unaffected. In practice however, cross-talk between parallel nanowires typically leads to latching, which prevents high detection rates. Here we show how this problem can be avoided through a careful design of the whole SNSPD structure. Using the same electronic readout as with conventional SNSPDs and a single coaxial line, we demonstrate detection rates over 200 MHz without any latching, and a fibre-coupled SDE as high as 77%, and more than 50% average SDE per photon at 50 MHz detection rate under continuous wave illumination.

We use a 2.5 GHz clocked quantum key distribution system to perform long-distance and high-speed quantum key distribution. Taking benefit from superconducting detectors optimized for each operation regime and low-loss fiber, we achieve state-of-the-art performance.

One of the key properties of single-photon detectors is their recovery time, i.e., the time required for the detector to recover its nominal efficiency. In the case of superconducting nanowire single-photon detectors (SNSPDs), which can feature extremely short recovery times in free-running mode, a precise characterization of this recovery time and its time dynamics is essential for many quantum optics or quantum communication experiments. We introduce a fast and simple method to characterize precisely the recovery time of SNSPDs. It provides full information about the recovery of the efficiency in time for a single or several consecutive detections. We also show how the method can be used to gain insight into the behavior of the bias current inside the nanowire after a detection, which allows predicting the behavior of the detector and its efficiency in any practical experiment using these detectors.

In this paper we demonstrate a simple and highly sensitive method to characterize the recovery time of efficiency for different kind of superconducting nanowire single- photon detectors. We also describe several applications of these detectors.

Integrated photonics is increasing in importance for compact, robust, and scalable enabling quantum technologies. This is particularly interesting for developing quantum communication networks, where resources need to be deployed in the field. We exploit photonic chip-based Si3N4 microring resonators to realise a photon pair source with low-loss, high-noise suppression and coincidence rates of 80×103 s-1. A simple photonic noise characterisation technique is presented that distinguishes linear and nonlinear contributions useful for system design and optimisation. We then demonstrate an all-fiber 750 MHz clock-rate sequential Time-Bin entanglement scheme with raw interference visibilities > 98 %.

Recent progress in the development of superconducting nanowire single-photon detectors (SNSPDs) made of amorphous materials has delivered excellent performances and has had a great impact on a range of research fields. Despite showing the highest system detection efficiency (SDE) ever reported with SNSPDs, amorphous materials typically lead to lower critical currents, which have impacts on their jitter performance. Combining a very low jitter and a high SDE remains a challenge. Here, we report on highly efficient superconducting nanowire single-photon detectors based on amorphous MoSi, combining system jitters as low as 26 ps and a SDE of 80% at 1550 nm. We also report detailed observations on the jitter behaviour, which hints at intrinsic limitations and leads to practical implications for SNSPD performance.

We present a quantum key distribution system with a 2.5 GHz repetition rate using a three-state time-bin protocol combined with a one-decoy approach. Taking advantage of superconducting single-photon detectors optimized for quantum key distribution and ultra low-loss fiber, we can distribute secret keys at a maximum distance of 421 km and obtain secret key rates of 6.5 bps over 405 km.

In view of real world applications of quantum information technologies, the combination of miniature quantum resources with existing fibre networks is a crucial issue. Among such resources, on-chip entangled photon sources play a central role for applications spanning quantum communications, computing and metrology. Here, we use a semiconductor source of entangled photons operating at room temperature in conjunction with standard telecom components to demonstrate multi-user quantum key distribution, a core protocol for securing communications in quantum networks. The source consists of an AlGaAs chip emitting polarization entangled photon pairs over a large bandwidth in the main telecom band around 1550 nm without the use of any off-chip compensation or interferometric scheme; the photon pairs are directly launched into a dense wavelength division multiplexer (DWDM) and secret keys are distributed between several pairs of users communicating through different channels. We achieve a visibility measured after the DWDM of 87% and show long-distance key distribution using a 50-km standard telecom fibre link between two network users. These results illustrate a promising route to practical, resource-efficient implementations adapted to quantum network infrastructures.

We demonstrate monolithic AlGaAs sources generating high dimensional frequency-entangled states in the telecom band at room temperature. The reflectivity and dispersion properties of our devices allow producing qudits with d of several tens.

Superconducting nanowire single-photon detectors (SNSPDs) are a key technology for optical quantum information processing [1]. Their low dark count rate, fast response time, small jitter, and high system detection efficiency (SDE) favours their use in various demanding quantum optics applications such as high-speed or long-distance quantum key distribution, quantum networking, device-independent quantum information processing and deep-space optical communication. One recent advance in the SNSPD field has been the introduction of amorphous superconductors such as tungsten silicide (WSi), molybdenum silicide (MoSi) and molybdenum germanium (MoGe). SNSPDs based on these materials currently have the highest reported detection efficiencies (93% with WSi [3]), as well as a high fabrication yield, favouring their use in complex structures such as detectors arrays. One limitation is that they typically operate at lower bias currents, in particular with nanowire geometries that lead to a saturated detection efficiency (a plateau). As a result, high-efficiency amorphous SNSPDs reported so far have a higher detection jitter, because the latter is essentially limited by the electronic noise of the amplification chain. Some previously reported values are 150 ps with 93% detection efficiency with WSi [3], and 76 ps with 87% detection efficiency for MoSi [4]. Obtaining a low jitter and a high detection efficiency requires finding an appropriate nanowire geometry in order to maximise the critical current while keeping a plateau, as well as the use of an optical stack to maximise absorption. In this talk we will report on highefficiency SNSPDs based on amorphous MoSi exhibiting time jitters lower than 30 ps. For this we fabricated and characterised a series of devices with varying nanowire widths and fill factors. Fig. 1-a shows a jitter histogram for one device having a full-with at half maximum value of 28 ps at a temperature of 0.8 K. The corresponding detection efficiency curve is shown on Fig. 1-b; this device reaches a 75% detection efficiency with a clear detection plateau. Another device with a larger fill factor resulted in a detection efficiency of 85% with a jitter of 40 ps. The influence of the nanowire and meander geometries on the jitter and efficiency will be discussed.

We investigate the performances of AlGaAs sources of entangled photons based on spontaneous parametric down-conversion. We demonstrate a signal-to-noise ratio of 1730, opening the way to the utilization of these devices for long distance quantum communications.

The generation of nonclassical states of light in miniature chips is a crucial step towards practical implementations of future quantum technologies. Semiconductor materials are ideal to achieve extremely compact and massively parallel systems and several platforms are currently under development. In this context, spontaneous parametric down conversion in AlGaAs devices combines the advantages of room temperature operation, possibility of electrical injection and emission in the telecom band. Here we report on a chip-based AlGaAs source, producing indistinguishable and energy-time entangled photons with a brightness of $7.2\times10^6$ pairs/s and a signal-to-noise ratio of $141\pm12$. Indistinguishability between the photons is demonstrated via a Hong-Ou-Mandel experiment with a visibility of $89\pm3\%$, while energy-time entanglement is tested via a Franson interferometer leading to a value for the Bell parameter $ S=2.70\pm0.10$.

Quantum cryptography with entangled photon pairs can be more powerful than protocols based on single photons or weak coherent pulses: they can tolerate higher losses and thus allow the distribution of quantum secret keys (QKD) over longer distances [1], they also provide a way towards device-independent quantum cryptography [2]. However, in order to enable a wide use of entangled photon pairs in future quantum telecommunication systems, further developments are needed to demonstrate performant sources that can be easily fabricated and integrated into Telecom fiber networks. Here we present a source consisting of an aluminium gallium arsenide waveguide generating photon pairs in the Telecom band by type II spontaneous parametric down-conversion [3]. Such a device has already been proven to work under electrical pumping [4]. Thanks to the very small birefringence of the guided modes, the pairs are directly generated in a polarization-entangled Bell state, without the need for any post-compensation. Moreover, as the photons are emitted over a large bandwidth (about 100 nm) with a joint spectrum that exhibits frequency anticorrelation, the same source can be used to simultaneously distribute keys among multiple pairs of users by using standard Telecom wavelength demultiplexers [5]. Here, we experimentally show the distribution of quantum secret keys with the BBM92 QKD protocol [6] between four different pairs of users with a commercial 100 GHz demultiplexer (0.8 nm channel width and spacing). Under CW pumping conditions, using free-running InGaAs single-photon detectors, we achieve a secret key rate of 0.21 bits/s and a qubit error rate (QBER) of 6.9% over 50 km of standard optical fiber. Our results, obtained with a robust and simple experimental set-up, open the way towards the implementation of practical device-independent quantum communication protocols.

In view of real-world applications of quantum information technologies, the combination of miniature quantum resources with existing fibre networks is a crucial issue. Among such resources, on-chip entangled photon sources play a central role for applications spanning quantum communications, computing and metrology. Here, we use a semiconductor source of entangled photons operating at room temperature in conjunction with standard telecom components to demonstrate multi-user quantum key distribution, a core protocol for securing communications in quantum networks. The source consists of an AlGaAs chip-emitting polarisation entangled photon pairs over a large bandwidth in the main telecom band around 1550 nm without the use of any off-chip compensation or interferometric scheme; the photon pairs are directly launched into a dense wavelength division multiplexer (DWDM) and secret keys are distributed between several pairs of users communicating through different channels. We achieve a visibility measured after the DWDM of 87% and show long-distance key distribution using a 50-km standard telecom fibre link between two network users. These results illustrate a promising route to practical, resource-efficient implementations adapted to quantum network infrastructures.