We present experimental results for intradyne detection as an alternative for current homodyne systems in optical inter-satellite links. Our approach is based on digital frequency offset and phase noise compensation for more flexible coherent systems.

We present an alternative approach for current homodyne detection systems in optical intersatellite links. Our approach is based on digital frequency offset compensation instead of optical phase-locked loop techniques, in order to achieve a more flexible coherent detection scheme.

We present a numerical investigation of current high-speed optical intersatellite communication. The considered laser communication terminal (LCT) uses an optical phase-locked loop (OPLL) which ensures stable homodyne detection. The corresponding phase and frequency acquisition will be investigated in detail together with the main impairments like phase and shot noise. The phenomenon of cycle slips is statistically investigated as well as the impact of Doppler shift on the signal frequency due to the relative velocity between the satellites. Finally, a possible extension for the homodyne concept of QPSK modulation will be discussed which allows even higher data rates.

We present a comparison of homodyne and intradyne detection schemes for high-order modulation formats in optical inter-satellite communication systems. The homodyne detection based on optical PLL techniques is numerically investigated for BPSK and QPSK transmission. We compare this scheme with intradyne detection based on digital frequency offset and phase noise compensation as an approach for future flexible software defined systems. We explain the applied algorithms and present numerical simulations in terms of receiver sensitivity in order to show that digital frequency offset compensation is a promising solution in OISL for increasing the data rate and lowering the system complexity.

This study demonstrates that phosphorus-related radiation-induced absorption (RIA) bands such as P-OHC and P1 in erbium/ytterbium-doped optical fibers (EYDFs) are effectively decreased by germanium (Ge) co-doping. The suppression of the generation of both P-OHC during X-ray irradiation of glass preforms and P1 during gamma-ray irradiation of optical fibers was measured for Ge concentrations between 0 wt% and 6.7 wt%. For the 10 krad X-ray irradiation of glass preforms, it was found that the RIA decreased from 5.6 dB/cm to 1.3 dB/cm when the Ge concentration was increased from 0.79 wt% to more than 4.4 wt%. Furthermore, in multimode optical fibers (MMFs) exposed to 100 krad of gamma-ray irradiation, the RIA decreased from 3.7 dB/m to 0.90 dB/m when the Ge concentration was increased from 0.0 wt% to 4.0 wt%, whereas it was 0.35 dB/m for a single-mode optical fiber (SMF) with a Ge concentration of 6.7 wt%. These results demonstrate that Ge concentrations up to 4.4 wt% are strongly correlated with improved radiation tolerance for both glass preforms and optical fibers. This effect was more prominent for SMFs than MMFs and became saturated with excess co-doping in both cases. Therefore, Ge co-doping may represent a good solution for reducing P-related RIA in EYDFs for space applications.

This paper reviews key characteristics and requirements for Two-Way Satellite Time and Frequency Transfer (TWSTFT) links. The outline and perspective of two concepts are described: 1. The classical bend-pipe transponder, without special equipment on board, with the potential of 10-17/day frequency transfer uncertainty; 2. The ACES-MWL (Atomic Clock Ensemble in Space Microwave Link) like active on-board equipment, with the potential down to few 10-19/day, using both high-rate modulation and carrier-phase. An outlook to advanced links is given. The aim of these proposed links is to provide a unique platform for the demanding requirements in the field of time and frequency metrology and to support improved orbit determination and relativistic geodesy for the next decades.

This paper presents the activities performed by TNO in the field of Space Laser Communication Terminals for high-volume low cost applications, and its plans for the further development of the required technologies for space terminals with particular emphasis on highly reliable, high performance, cost effective terminals.

The paper details the approach, sequence, and results of the in-orbit campaign for E/O data relay using the Tesat Laser Communication Terminals from a LEO spacecraft - Sentinel 1A - a part of the EU Copernicus program, to the TDP1 payload of Alphasat, Europe's largest telecommunication satellite. After configuring the LCT́s on both spacecrafts to a standard operating mode in the first 2 month of the campaign, the next few months have been used for testing the capabilities of the systems. Links with transmit powers as low as 100mW over 42000km and links probing the upper atmosphere are examples of this test campaign. In addition, far field laser beam profile and tracking performance measurements have been performed, using the unique capability of the LCT on board of Alphasat to deliver 25kHz sampled data for all internal sensors (tracking and acquisition).

The high-speed satellite-terrestrial network (STN) is an indispensable alternative in future mobile communication systems. In this article, we first introduce the architecture and application scenarios of STNs, and then investigate possible ways to implement mobile edge computing (MEC) technique for QoS improvement in STNs. We propose satellite MEC (SMEC), in which a user equipment without a proximal MEC server can also enjoy MEC services via satellite links. We propose a dynamic network virtualization technique to integrate the network resources, and furtherly design a cooperative computation offloading (CCO) model to achieve parallel computation in STNs. Task scheduling models in SMEC are discussed in detail, and an elemental simulation is conducted to evaluate the performance of the proposed CCO model in SMEC.

The application of free space optical communications technology between unmanned airborne vehicles (UAVs) can significantly improve its communications rate and capacity. However, it will produce strong disturbance due to the change of external conditions when the UAV is flying, which will affect the acquisition probability of a light beacon. The wide beacon can generally increase the acquisition range and acquisition probability, but there are disadvantages of increased weight and energy consumption. We report on an advanced method to improve the performance of narrow beacon spatial acquisition under the condition of UAV drift. The acquisition probability model has been established to study narrow beacon spatial acquisition considering UAV drift. A multiscanning method is proposed to improve the acquisition probability instead of simply increasing the scanning area to overcome severe UAV drift, which is also proven by experimental validation. Moreover, through the control method of active disturbance rejection control (ADRC), the pointing accuracy of multifield fast scanning is improved under the condition of external interference. This technique is extremely useful to develop a smaller, lighter terminal for UAV optical communications in the future.

The Integrated Laser Communication/Ranging System, which uses coded signal as the ranging information carrier, is of great importance to the next large-capacity inter-satellite information network. In this paper, the parallel FFT estimation is applied to improve the speed and range of tracking wavelength drift caused by both the trajectory estimation error and laser instability, it can handle dynamic wavelength drift up to 2.4 pm/s (300 MHz/s). Meanwhile, for clock sources with subtle dynamic frequency offset and sufficient stability, the proposed fractional symbol ranging method based on the timing offset compensation in the receiver is proven to achieve millimeter-level measurement accuracy. The Integrated Laser Communication/Ranging Link with high-sensitivity feedback-homodyne detection and fractional symbol ranging is demonstrated with real-time FPGA implementation and is shown to perform well in terms of both laser linewidth tolerance and noise resistance.

The European Data Relay System (EDRS) relies on optical communication links between Low Earth Orbit (LEO) and geostationary (GEO) spacecrafts. Data transmission at 1.8 Gbps between the S/Cs will be applied. EDRS is foreseen to go into operation in 2015. As a precursor to the EDRS GEO Laser Communication Terminals (LCT), an LCT is embarked on the Alphasat GEO S/C. Sentinel 1A is a LEO earth observation satellite as part of ESAs Copernicus program and carries an LCT on board. Both the Alphasat and the Sentinel 1A LCT have completed their individual in orbit commissioning and a joint link commissioning phase, with first LEO to GEO optical communication links in 2014. In this presentation, the design principle of the LCT applied for EDRS will be investigated. The most recent results of the in-orbit link commissioning phase of the LCTs on board of Alphasat and Sentinel 1A will be presented.

The European Data Relay System (EDRS) relies on optical communication links between Low Earth Orbit (LEO) and geostationary (GEO) spacecrafts. Data transmission at 1,8 Gbps between the S/Cs will be applied for link distances up to 45000 km. EDRS is foreseen to go into operation in 2015. As a precursor to the EDRS GEO Laser Communication Terminals (LCT), a LCT is embarked on the Alphasat GEO S/C, which was launched in July 2013. Sentinel 1A is a LEO earth observation satellite as part of ESAs Copernicus program. Sentinel 1A also has a LCT on board. In November 2014, the first optical communication link between a LEO and a GEO Laser Communication Terminal at gigabit data rates has been performed successfully [1]. Data generated by the Sentinel 1A instrument were optically transferred to Alphasat. From Alphasat, the data were transmitted via Kaband to a ground station. In the ground station, the original data were recovered successfully. So the whole chain from LEO to ground was verified. Since then, many optical communication links between the Alphasat LCT and the Sentinel 1A LCT were performed. During these tests, the acquisition and tracking performance was investigated. The first communication links showed a very robust link acquisition capability and tracking errors in the sub-μrad range. The communication link budget was verified and compared to the predictions, showing excellent overall system behavior with sufficient margin to support future GEO GEO link applications.

TDP-1 is a quasi-operational technology demonstration payload, designed to prove the concept of data transfer between low-orbit observation satellites and earth via a geostationary relay satellite in between the communication chain. This detour allows to significantly increase transferable data volume at reduced latency time, and is performed with the help of Laser Communication Terminals (LCTs) on board the low-orbit as well as the geostationary satellite, from which the data is immediately downlinked via Ka-Band. In this framework, TDP-1 is the successful precursor mission for the forthcoming European Data Relay Satellite System (EDRS).

Satellite constellations are used for navigation purposes since long. Connecting the satellites in a constellation by intersatellite links (ISLs) offers a full range of new possibilities. Ranging and time synchronization information can be exchanged between the satellites to improve the in orbit SC positioning knowledge. Besides ranging and time synchronization, ISLs can be used for service channel purposes or to distribute SW updates for the spacecrafts in a short period of time. ISLs improve the navigation constellations autonomy properties being less vulnerable to ground station unavailabilities. For ISLs, radio frequency (RF) and optical technologies have been investigated. Due to the shorter wavelength, a better ranging resolution can be achieved with optical than with RF ISL solutions. Optical ISLs (OISLs) offer a very attractive solution for intersatellite links in terms of size, weight and power while providing multi gigabit per second data rate capabilities. In addition, optical communication links offer high operational security and immunity to interference sources while benefitting from a non-regulated optical frequency spectrum. For those reasons, optical intersatellite links for navigation constellations have been investigated in several studies supported by DLR and ESA. TESAT with partners have investigated the benefit of OISLs for navigation systems and on the Galileo OISL Terminal design. In this paper, the results of these studies will be presented. Various OISL connection schemes in a navigation constellation are compared. The key design parameters of a Laser Communication Terminal for navigation systems will be given. Furthermore, the results of a lab demonstration showing the parallel distribution of ranging and communication data will be summarized. The focus of the investigation is on the Galileo navigation constellation.

Pumping solid state lasers in LCTs requires the application of highly reliable, low-noise semiconductor lasers. Two design variants of pump lasers have been developed and tested. The first design consists of broad area laser arrays, spectrally stabilized by an external Bragg grating. Those lasers exhibit decent reliability and thus they are utilized in various space missions. The drawback of that design is due to hardly controllable intensity noise at certain operating conditions induced by optical feedback. To overcome this drawback, DBR RW arrays with monolithically integrated Bragg grating have been optimized aimed at low noise performance and high reliability over an extended operating time. Life test results indicate that the reliability goal can be achieved by careful preselection of the devices and eventually by increasing the number of active emitters.

Publisher’s Note: This paper, originally published on 4/1/2016, was replaced with a corrected/revised version on 4/14/2016. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance. We describe the performance of versatile high-performance multi-rate WDM laser transmitters using next-generation compact high-extinction-ratio power-efficient (CHERPe) transmitter designs. These leverage periodic time-frequency windowing of directly modulated laser signals to efficiently generate nearly ideal WDM waveforms with only mW-class drive power. facilitating WDM-channelization and providing straightforward access to many THz of available optical spectrum with low-bandwidth electronics. Furthermore, this approach can support scalable multi-rate operation with good power- and photon-efficiency and enable new architectural options. This approach is attractive for numerous applications and systems ranging from small airborne or CubeSAT-sized communication payloads to larger interplanetary lasercom platforms.

Over the past years, we have successfully applied adaptive optics (AO) in optical ground stations to improve the quality of satellite-to-ground laser communication links. In this paper, we present a design overview of the adaptive optics add-on to the ESA optical ground station (1 m telescope), including optics, components, and the reconstruction scheme. The system is suited to be operated with laser communication systems at 1064 nm or with one in the 1550 nm region. The wave-front sensor is a Shack-Hartmann-sensor (21 sub-apertures across the pupil), matched to a 24×24 actuator deformable mirror. The system is able to remove a large part of the turbulence-induced and static wave-front errors by using more than 90 degrees of freedom (“modes”). Due to a special high-speed infrared camera, the AO control loop is optimized for an update rate of 4 kHz in excess.

Over the past years we have successfully applied adaptive optics (AO) in some optical ground stations (OGS) to improve the signal-to-noise ratio of satellite to ground laser communications.

Optical intersatellite communication is an attractive alternative to current RF satellite communication in order to increase the data rate and lower the power consumption. By using coherent detection, full signal recovery is achieved at the receiver which allows modulating both, amplitude and phase. However, the needed local oscillator requires a complex carrier recovery system. In order to achieve homodyne detection an optical phase-locked loop is used which is characterised by a nonlinear behaviour that influences the data transmission performance. We present a nonlinear characteristic investigation of this Costas-loop based carrier recovery system for optical high-speed intersatellite data transmission. We combine the fundamentals of future optical intersatellite communication with analyses of an optical phase-locked loop based carrier control system. The corresponding nonlinear differential equation system is derived and finally investigated by phase plane diagrams. The impact of noise as well as the cycle slip phenomena will be discussed.