Optical feeder links (OFL) are expected to become part of future Very High Throughput Satellite (VHTS) systems in response to the growing demand for higher capacity and lower costs. H2020 VERTIGO (Very High Throughput Satellite Ground Optical Link) project was set to prove key optical communication technologies and to address: 1) Throughput increase with high spectral and power efficiencies. 2) Higher optical power generation and delivery. 3) Atmospheric turbulence mitigation by optical and digital processing. Transmit and receive optical communication models were developed in rack units for assessing, in laboratory and outdoor trials, their intrinsic performance, robustness against atmospheric turbulence and compatibility with other technologies. The models for 25 Gbps OOK/DPSK and RF analog modulation with optically pre-amplified direct or differential detection are reported with the achieved performance. An atmospheric channel emulator fed with time series established by simulations was used to mimic the propagation losses and fading of the optical signal coupled into the receiver. Both the downlink and uplink under weak or strong turbulence were emulated. For digital transmission experiments, the performance metrics include BER curves, detection sensitivity and power penalty. State-of-the-art sensitivities were achieved especially under 25 Gbps DPSK. For RF analog transmission, the performance metrics were constellation diagrams and Error Vector Magnitude (EVM) measured for various modulations from QPSK to 64-QAM. Are reported the results of optical transmission experiments first performed in the laboratory under static and dynamic propagation channels, then in the outdoor trial successfully carried out in July between Jungfraujoch and Zimmerwald in Switzerland.
RF frequency conversion is a key function of telecom satellite payloads. Hereafter are presented new photonic RF sub-system concepts supporting multi-channel, wideband frequency-conversion, thus drastically reducing the amount of equipment, for frequency down- and up-conversions respectively at the inputs and outputs of a digital processor. Proof-of-concept demos are presented and the measured RF performance reviewed vs. predictions and system requirements. The so-called dual-band, multi-LO frequency-converter (DB-MLFC) concept is an extension of the multi-LO frequency-conversion scheme already proven by Thales Alenia Space. It makes use of a dual-drive modulator with wavelength-multiplexed LO input and RF signal inputs in separate frequency bands. It can be applied to digital processor-based payloads and perform down-conversion of Ka or V-band sub-bands to the C-band of the processor input. The DB-MLFC concept was proven to support down-conversion of 2 and 3 sub-bands from the Ka (~30 GHz) and V (~50 GHz) bands to the C (~6 GHz) band of the processor input. The second concept called multi-RF frequency-converter (MRFC) consists in mixing multiple RF signals on separate optical carriers with an electrical LO signal into one electro-optical mixer. RF signals to undergo the same frequency conversion are combined via a WDM and fed into the optical input port of an electro-optical modulator, the RF port being driven by the LO. The RF performance of the MRFC concept, were measured with up-conversion of up to 8 C-band RF signals from the processor output to Ka-band payload output frequencies (~20 GHz).
KEYWORDS: Free space optics, Transmitters, RF photonics, Analog electronics, Modulation, Optical transmission, Digital modulation, Analog modulation, Satellites, Laser applications
Optical technologies play an increasing role in telecom satellite payloads for analog or digital applications. When large SWaP (size, weight, and power) is prohibitive or for applications where low cost is a major design goal, an electro-absorption modulated laser (EML) can provide a good balance between integration and performance optimization through separated control of emission and modulation. 1550 nm EML for ground applications were evaluated for optical local oscillator (LO) distribution, photonic RF frequency conversion, digital and analog free-space optical (FSO) communications. An EML-based LO distribution was assessed in terms of RF output power, spectral purity and phase noise. Using optical amplification, large-scale distribution of a 13 GHz LO was achieved with similar or greater RF power and a limited noise floor penalty compared to what is possible with a CW laser and Mach-Zehnder modulator (MZM). Photonic RF frequency-conversion was assessed as well and EML was found to perform better than direct modulation laser. For optical inter-satellite links in constellations, SWAP and cost really matter and EML is therefore an interesting candidate. An EML-based transmitter was evaluated for digital modulation at 10 and 20 Gbps as well as for RF analog modulation in transmit Ka band (20 GHz). For digital modulation, an EML module exhibited a similar dynamic extinction ratio as a MZM, and a limited penalty in detection sensitivity. For RF modulation, the carrier-to-noise ratio was measured as a function of the received optical power for various EML operating conditions: equivalent RF performance were achieved as well.
This paper reports the main achievements in the development of photonic RF payload solutions for telecommunication satellites based on a multiple-frequency conversion scheme. Representative models of photonic payload equipment, including photonic frequency generation assembly and frequency-converters, have been integrated and proven in a system environment. The end-to-end RF performance for various configurations and frequency plans were tested at ambient temperature. The test plan includes forward and return repeater configurations, with photonic frequency down-conversion from 30 to 20 GHz with up to 6-local oscillators in the case of a Ka-band multi-beam broadband mission. In addition, thermal tests were run over the [−5°C, +65°C] temperature range.
The end-to-end RF performances of the photonic repeater demonstrator were assessed in detail experimentally and compared to theoretical predictions. These results are a major step towards new payload solution with enhanced capacity and in-orbit re-configurability.
KEYWORDS: Laser applications, RF photonics, Free space optics, Laser development, Free space optical communications, Frequency conversion, High power lasers, Telecommunications, Satellites, Laser damage threshold
This article reports the development of 200-mW 1.55-μm DFB laser module with RIN below -162 dB/Hz which are well suited for microwave photonics or free space optical communication applications. Specific design has allowed reaching high power (>300 mW), low noise and high spectral purity laser chip. The chip has been packaged in Butterfly module optimized for reducing the module power consumption. DFB laser module system validations have been done on three laboratory test-beds representative of target applications, namely high-frequency optical LO distribution, photonic RF frequency conversion, and free space optical communication links.
This paper describes the activities and results of an ESA-funded project concerned with the assessment of optical amplifier technologies and products for applications in fiber optic subsystems of future satellite payloads.
On-board applications are briefly introduced, together with associated system-level requirements. Optical amplifier technologies, research achievements and products are reviewed. They are compared in terms of current performance, perspectives and suitability for the target space applications. Optical fibre amplifiers, not limited to Erbium-doped amplifiers, Erbium-doped waveguide amplifiers and Semiconductor Optical Amplifiers are covered. The review includes analysis and trade-off of all performance parameters including saturation output power, noise figure, polarisation maintaining capability, wall-plug efficiency, and mass and size.
A selection of optical amplifier products for further evaluation and testing is presented. Results of extensive testing covering both functional performance and environmental behaviour (mechanical, thermal vacuum, radiations) aspects are reported. Most of the work has been completed, but an extension has been proposed for checking and comparing the behaviour of doped fibers under gamma radiation.
The distribution of high spectral purity reference signals over optical fibre in future telecommunication satellite payloads is presented. Several types of applications are considered, including the distribution of a reference frequency at 10 MHz (Ultra-Stable Reference Oscillator) as well as the distribution of a radiofrequency oscillator around 800 MHz (Master Local Oscillator). The results of both experimental and theoretical studies are reported. In order to meet phase noise requirements for the USRO distribution, the use of an optimised receiver circuit based on an optically synchronised oscillator is investigated. Finally, the optical distribution of microwave local oscillators at frequencies exceeding 20 GHz is described. Such a scheme paves the way to more advanced sub-systems involving optical frequency-mixing and optical transmission of microwave signals, with applications to multiple-beam active antennas.
Future telecom satellite based on geo-stationary Earth orbit (GEO) will require advanced payloads in Kaband so as to receive, route and re-transmit hundreds of microwave channels over multiple antenna beams.
We report on the proof-of-concept demonstration of a analogue repeater making use of microwave photonic technologies for supporting broadband, transparent, and flexible cross-connectivity. It has microwave input and output sections, and features a photonic core for LO distribution, frequency down-conversion, and cross-connection of RF channels.
With benefits such as transparency to RF frequency, infinite RF isolation, mass and volume savings, such a microwave photonic cross-connect would compare favourably with microwave implementations, and based on optical MEMS switches could grow up to large port counts.
Since several years, perspectives and assets offered by photonic technologies compared with their traditional RF counterparts (mass and volume reduction, transparency to RF frequency, RF isolation), make them particularly attractive for space applications [1] and, in particular, telecommunication satellites [2]. However, the development of photonic payload concepts have concurrently risen and made the problem of the ability of optoelectronic components to withstand space environment more and more pressing. Indeed, photonic components used in such photonic payloads architectures come from terrestrial networks applications in order to benefit from research and development in this field.
This paper presents some results obtained in the frame of an ESA-funded project, carried out by Thales Alenia Space France, as prime contractor, and Alter Technology Group Spain (ATG) and Universidad Politecnica de Madrid (UPM), as subcontractors, one objective of which was to assess commercial high frequency optical intensity modulators for space use through a functional and environmental test campaign. Their potential applications in microwave photonic sub-systems of telecom satellite payloads are identified and related requirements are presented. Optical modulator technologies are reviewed and compared through, but not limited to, a specific figure of merit, taking into account two key features of these components : optical insertion loss and RF half-wave voltage. Some conclusions on these different technologies are given, on the basis of the test results, and their suitability for the targeted applications and environment is highlighted.
Thales Alenia Space has elaborated innovative telecom payload concepts taking benefit from the capabilities of photonics and so-called microwave photonics. The latter consists in transferring RF/microwave signals on optical carriers and performing processing in the optical domain so as to benefit from specific attributes such as wavelength-division multiplexing or switching capabilities.
In the last decade, Thales Alenia Space has put significant research effort in photonic technologies for satellite applications, with the objective to provide telecom payload systems with enhanced functionality, higher performance and lower costs.
The proof-of-concept demonstration of an microwave photonics cross-connect for telecom satellite repeaters is reported. The system includes optical distribution of a high-purity local oscillator at 26 GHz, frequency down-conversion from 30 to 4 GHz, and optical cross-connection of microwave signals.
Various circuits dedicated to high spectral purity signal transmission using fiber optics are presented. Three application types are investigated: signal transmission of ultra stable oscillators at 10 MHz, IF distribution at 874 MHz and microwave synthesized signals at 3.5 GHz. The receiver circuit is an optically synchronized oscillator, which provides a good signal conditioning far from the carrier while maintaining the high input signal quality close to the carrier
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