Project Keraunos aims to experiment with a Low-Earth Orbit (LEO) to Ground optical communication link, including turbulence mitigation in the Optical Ground Station (OGS), enabling 10 Gbps or more data rates. Cailabs develops the pilot OGS, equipped with an 80 cm telescope, designed for robust operation under challenging conditions. This paper presents a comprehensive characterization of OGS subsystems, evaluating pointing, acquisition, tracking, beacons, and telecommunication performance with a 2.5 km horizontal link. Initial first light results with the Keraunos satellite are also showcased.
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.
Coherent combination of laser beams is crucial for high-power laser development in various applications, including defense and communication systems. A filled-aperture coherent beam combiner is introduced, which includes polarization-maintaining fiber components, Electro-Optic Modulators, EDFA, a Multi-Plane Light Converter, and a feedback loop based on the Stochastic Parallel Gradient Descent algorithm. The SPGD algorithm allows precise control of the EOMs to achieve stable optical output power. The experimental results demonstrate the proposed approach achieves coherent combination of up to 6 input channels with high efficiency, negligible power loss duration, and precise control over thermal and mechanical perturbations. This technology is directly scalable for different wavelengths.
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%.
The ability to combine incoherent sources with attractive performances enable hardware integration issues to be resolved using stable, good quality off-the-shelf components. Some new generation imaging systems can be found in the mid-infrared (MIR). The most portable laser technology at this range, our Quantum Cascade Laser source can provide light power of around 2 W, industrial grade.
With the Multi-plane Light Conversion technique and a modal approach, we present non-coherent beam combiner for QCL with optimal beam quality, demonstrating the state of the art in terms of M2.
An experimental demonstration of laser beam coherent combining with active phase control has been performed using for the first time a Multi-Plane Light Converter device (MPLC). The MPLC as a beam combiner is designed as a spatial multiplexer which output modes form a Gaussian beam when superimposed constructively, reaching theoretically 100% efficiency. Moreover, reflective free-space design allows for handling high power. The experiment combines seven 1.5 μm continuous wave fiber lasers operated at a low power level in the tens of milliwatt range using the frequencytagging LOCSET technique (Locking of Optical Coherence by Single-detector Electronic-frequency Tagging) for the phase locking. 72-% power efficiency MPLC CBC is achieved with an output combined beam close to a Gaussian beam profile. M² is lower than 1.8 depending on the transverse direction, revealing an excellent quality for the combined beam. The output beam is more than 94 % linearly polarized. Simulation of the impact of atmospheric turbulence on the propagation of the seven laser beams up to 1 km is performed. We demonstrate that it is possible to compensate for most of the atmospheric propagation detrimental effects and to perform efficient MPLC CBC through strong turbulence.
KEYWORDS: Laser countermeasures, Laser energy, Directed energy weapons, Fiber lasers, Missiles, Solid state lasers, Solid state physics, Free space optics, Chemical elements, Optical fibers
The development of the solid-state fiber laser has given a boost to the possibility of destroying a target without the need for a projectile or blind the photoreceptive element of a heat-seeker missile with laser emission. The growing presence of drones on the battlefield since 2010 and the on-board intelligence on guided missiles have given new credibility to these research programs. Solid state fiber laser, which uses optical fiber as an amplifying medium, has many advantages including efficiency, thermal and opto-mechanical stability, the elimination of free space optics using fiber components, and above all good beam quality thanks to its waveguide. In addition, these coherent sources are available at interesting wavelengths in line with military issues. However, now it is difficult to obtain a high-power fiber source (> 1 kW) while maintaining high beam quality and good spectral coherence. Power scaling whilst preserving beam quality can be achieved through coherent beam combining. The principle is to interfere constructively N mutually coherent single-mode laser beams with proper phase alignment into a single good quality beam. Conventional coherent beam combining is typically based on tiled apertures, for which theoretical maximum efficiency is 67% (due to limited lenses fill factor and secondary lobes in the far field), and for which experimental efficiency is currently below 50%. We present here a novel technique for coherent beam combining based on Multi-Plane Light Conversion. The beam combiner is designed as a spatial multiplexer which output modes form a Gaussian beam when superimposed constructively, reaching theoretically 100% efficiency. Moreover, reflective free-space design allows for high power handling up to 500W. We measure an experimental mode purity above 85% with a total efficiency of 70% (including optical losses) combining 6 beams. This system can be altered to provide error signals for easier phase-locking of the inputs.
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