Detector Systems Engineering for Extremely Large Instruments

The scientific detector systems for the ESO ELT first-light instruments, HARMONI, MICADO, and METIS, together will require 27 science detectors: seventeen 2.5 $\mu$m cutoff H4RG-15 detectors, four 4K x 4K 231-84 CCDs, five 5.3 $\mu$m cutoff H2RG detectors, and one 13.5 $\mu$m cutoff GEOSNAP detector. This challenging program of scientific detector system development covers everything from designing and producing state-of-the-art detector control and readout electronics, to developing new detector characterization techniques in the lab, to performance modeling and final system verification. We report briefly on the current design of these detector systems and developments underway to meet the challenging scientific performance goals of the ELT instruments.Comment: Proceedings of the SPIE Astronomical Telescopes and Instrumentation Conference 202

Pre-correction Adaptive Optics performance of a 10 km Laser Link

For the next generation of very high throughput communication satellites, free-space optical (FSO) communication between ground stations and geostationary telecommunication satellites is likely to replace conventional RF links. To mitigate atmospheric turbulence, TNO and DLR propose Adaptive Optics (AO) to apply uplink pre-correction. In order to demonstrate the feasibility of AO pre-correction an FSO link has been tested over a 10 km range. This paper shows that AO pre-correction is most advantageous for low point ahead angles (PAAs), as expected. In addition, an optimum AO precorrection performance is found at 16 AO modes for the experimental conditions. For the specific test site, tip-tilt precorrection accounted for 4.5 dB improvement in the link budget. Higher order AO modes accounted for another 1.5 dB improvement in the link budget. From these results it is concluded that AO pre-correction can effectively improve highthroughput optical feeder links

Laboratory Demonstrator of Optical Inter-satellite Links for the Kepler System

The paper presents the laboratory demonstrator design of the bidirectional inter-satellite optical link for the Kepler system. Communication and ranging subsystem serves for data transmission at 50 Mbit/s and providing highly precise sub-millimeter ranging accuracy. The preliminary back-toback verification based on data and ranging signal transmission confirms this. For interconnection of the two systems, an optical terminal has been designed and is currently being integrated and evaluated in the laboratory. Furthermore, it will be used for emulation of channel impairments caused mainly by mechanical platform jitter

Alternative passive fiber coupling system based on multi-plane light conversion for satellite-to-ground communications

Global coverage of internet access is essential for digitalization in society, becoming a disruptive technology in industry, education or political participation for example. Satellite communications is a complementary approach to the terrestrial fiber network, which can provide world-wide coverage with few satellites in geostationary orbit or with low-earth-orbit constellations. Optical wavelengths offer multiple THz of available spectrum that can be used to connect satellites to the ground network with high-throughput links, solving the radiofrequency bandwidth bottleneck, without regulations. Cloud covereage and atmospheric turbulence are the main challenge in guaranteeing the same availability as in terrestrial fiber-based systems. While the former can be addressed by site diversity, for the latter, other mitigation strategies are required. Adaptive optics is a common approach to correct for atmospheric phase distortions and ensure stable fiber coupling. However, this approach requires a relatively complex active setup and therefore a collaboration between DLR Institute of Communications and Navigation and Cailabs has been formed to investigate alternative passive solutions for low-complexity ground stations. Coupling into multimode fibers does not require adaptive optics due to the large fiber core, however the coupled signal is distributed into multiple fiber-modes and is therefore incompatible with standard telecommunications components. Cailabs Multi-Plane Light Conversion (MPLC) technology overcomes this issue, selectively demultiplexing the fibermodes into single-mode fibers. Here, DLR's adaptive optics system and the MPLC technology in a turbulence-relevant environment for GEO communications are compared, investigating the advantages of the MPLC approach for compensating strong turbulence. This paper presents an overview of the measurement setup and analyzes the single-mode fibers outputs of the spatial demultiplexer and the measured phase-distortions from a wavefront sensor

Optical technologies for very high throughput satellite communications

Broadband internet access has become a vertex for the future development of society and industry in the digital era. Geostationary orbit (GEO) satellite can provide global broadband coverage, becoming a complementary solution to optical fiber network. Low-earth-orbit (LEO) constellations have been proposed in the last years and they may become a reality soon, but still based on radiofrequency for the ground-to-satellite links. Optical technologies offer multiple THz of available spectrum, which can be used in the feeder link. The DLRs Institute of Communications and Navigation has demonstrated Terabit-per-second throughput in relevant environment for GEO communications, in terms of the turbulent channel. In 2016 DLR set the world-record in free-space communications to 1.72 Tbit/s, and in 2017 to 13.16 Tbit/s. Two terminals, emulating the satellite and the ground station have been developed. Bi-directional communications link with single-mode-fiber coupling at both ends was demonstrated. Adaptive optics for the downlink and uplink (pre-distortion) improved the fiber-coupling in downlink and decreased signal fluctuations in uplink. A 80 Gbit/s QPSK system based on digital homodyne reception was also developed, demonstrating the use of coherent communications under strong turbulence conditions. These activities were performed in the frame of two internal DLR projects, THRUST and Global Connectivity Synergy project. Several measurement campaigns took place in the last years in a valley-to-mountain-top test-link. Turbulence has been monitored at both ends and the point-ahead-angle has been emulated by separating the downlink beacon from the receiving aperture. An overview of the system and the main results will be presented