Optical satellite communication is growing fast and among various applications it requires higher throughput optical feeder links. Optical feeder links for satellite communication necessitate very high data throughput, up to 1 Terabit/s and beyond. Amongst several multiplexing strategies, dense wavelength division holds a key position to enable overall throughput rates above 1 Terabit/s. As a consequence, hardware architectures capable of handling high throughput links must be devised. Complementary to the high throughput requirement, the devices should also cope with the high optical power levels needed in optical ground stations. Combination of spatial aperture multiplexing and free space bulk optics configurations of multiplexers with transmission diffraction gratings are presented as possible concepts. Besides wavelength multiplexing, it is essential to include the beam propagation effects in the performance analysis, since this may affect the overall feeder link properties. A modelling framework is presented that covers the multiplexing behavior as well as the beam propagation of the transmission gratings based concept. The modelling framework based on first principles of optical diffraction is general, and independent of the grating choice. The results suggest that the design of a free space bulk multiplexer for optical feeder link must be approached already at system level. Decisions about telescope sizing, channels distribution and modulation formats may affect the performance of the multiplexer, resulting in severe effects on the link performance. The work discusses the effect of each design parameter and proposes design guidelines for high power satellite communication beam multiplexing.
Optical communications will complement radio frequency (RF) communications in the coming decades to enhance throughput, power efficiency and link security of satellite communication links. To enable optical communications technology for intersatellite links and (bi-directional) ground to satellite links, TNO develops a suite of technologies in collaboration with industry, which comprises of terminals with different aperture sizes, coarse pointing assemblies and fast steering mirrors. This paper presents the current state of the development of TNO technology for optical space communications. It mainly focuses on the development of an optical head with an entrance aperture of 70 mm, an optical bench for CubeSats and coarse pointing assemblies (CPAs). By continuing these steps, world wide web based on satellite communications will come closer.
For the next generation of very high throughput communication satellites, TNO and DLR envision optical free-space communication between ground stations and geostationary telecommunication satellites to replace the traditional RF links. To mitigate atmospheric turbulence, an Adaptive Optics (AO) system will be used to apply uplink pre-correction. OFELIA, an ground terminal breadboard was developed to demonstrate the pre-correction principle over an realistic link. Currently, integration tests have been performed to verify the AO performance. Also a laser link experiment over 10 km distance has already been established, in a scenario relevant to ground-to-satellite links. The paper shows that AO is clearly beneficial for the downlink performance. In addition the first preliminary experimental results of the pre-correction show it is also beneficial for the uplink.
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 high-throughput optical feeder links.
TNO and DLR envision optical free-space communication between ground stations and geostationary telecommunication satellites to replace the traditional RF links for the next generation of Very High Throughput Satellites. To mitigate atmospheric turbulence, an Adaptive Optics (AO) system will be used. TNO and DLR are developing breadboards to validate Terabit/s communication links using an AO system. In this paper the breadboard activities and first results of the sub-systems will be presented. Performance of these subsystems will be evaluated for viability of terabit/s optical feeder links.
In the framework of the ADM-Aeolus satellite mission, successful test campaigns have been performed in ESTEC’s laser laboratory, and the efficiency of several mitigation techniques against Laser-Induced Contamination (LIC) have been demonstrated for the ALADIN laser. These techniques include the standard contamination control methods of materials identification with particular tendency to cause LIC, reduction of the outgassing of organic materials by vacuum bake-out and shielding of optical surfaces from the contamination sources. Also novel mitigation methods such as in-situ cleaning via partial pressures, or the usage of molecular absorbers were demonstrated. In this context, a number of highly sensitive optical measurement techniques have been developed and tested to detect and monitor LIC deposits at nanometre level.
is a well-known detection method which is applied in many different scientific and technology domains including atmospheric physics, environmental control, and biology. It allows contactless and remote detection of sub-micron size particles. However, methods for detecting a single fast moving particle smaller than 100 nm are lacking.
In the present work we report a preliminary design study of an inline large area detector for nanoparticles larger than 50 nm which move with velocities up to 100 m/s. The detector design is based on light scattering using commercially available components.
The presented design takes into account all challenges connected to the inline implementation of the scattering technique in the system: the need for the detector to have a large field of view to cover a volume with a footprint commensurate to an area of 100mm x 100mm, the necessity to sense nanoparticles transported at high velocity, and the requirement of large capture rate with a false detection as low as one false positive per week. The impact of all these stringent requirements on the expected sensitivity and performances of the device is analyzed by mean of a dedicated performance model.
Operation of high fluence pulsed laser systems in space imposes various risks to optical components involved. Volatile
organic components are omnipresent in vacuum vessels housing space-borne laser systems and can be the source for
selective contamination of optics. Laser systems may respond very sensitively to absorption increases of their multiple
optical surfaces leading to inacceptable transmission losses and system degradation. In the recent past, thorough and
long term laser tests, performed at the optics qualification laboratories at DLR and at ESTEC using space relevant and
model substances, have revealed the onset, the built-up, and the later stages of the deposition process. It was found that
these deposits tend to accumulate preferably on the laser footprint area of the optic. Observed thicknesses are on the
order of several tens of nanometers, which can be sufficient to induce noticeable absorption. Sensitive techniques for insitu
and ex-situ monitoring of these molecular contaminative effects under vacuum conditions were developed and are
applied successfully. They are summarized in this paper, along with the phenomena, which are significant for the
appearance of deposits. In addition, adverse conditions, which are favorable for provoking deposits, are communicated.
Finally, mitigative and preventive methods are discussed.
Laser-induced contamination (LIC) is a phenomenon that can lead to the degradation of the properties of optical
components in vacuum due to the formation of deposits in the area irradiated by a laser beam. The deposit growth is
proposed to be the result of photochemical and photothermal mechanisms triggered by the interaction of UV laser
radiation and outgassing species from polymeric materials on the surface of the optics. In the framework of ESA's ADM-Aeolus
satellite mission, a successful test campaign has been performed, which has demonstrated the efficiency of
several mitigation techniques against LIC for the ALADIN laser. These include the standard contamination control
methods of identification of materials with particular propensity to cause LIC, reduction of the outgassing of organic
materials by vacuum bakeout and shielding of optical surfaces from contamination sources as well as novel methods
such as in-situ cleaning. These methods are now being applied at satellite level in order to guarantee the success of the
mission. The subject of this paper is to summarise the various mitigation techniques from the large number of studies
that have been performed and is applicable to any use of high power pulsed lasers in vacuum in the presence of organic
The European Space Agency ESA is running a series of earth observation missions. In order to perform global windprofile
observation based on Doppler-LIDAR, the satellite ADM-Aelolus will be launched in April 2011 and injected
into an orbit 400 km above Earth's surface. ADM-Aeolus will be the first satellite ever that is equipped with a UV-laser
(emitting at 355 nm) and a reflector telescope.
At LLG, a setup was developed that allows monitoring transmission, reflection and fluorescence of laser-irradiated
optical components, in order to assess their possible optical degradation due to radiation-induced contaminant deposition
in orbit. For both a high-reflecting mirror and an anti-reflective coated window long-term irradiation tests (up to 500
million laser pulses) were performed at a base pressure < 10-9 mbar, using a XeF excimer laser (wavelength 351 nm,
repetition rate 1kHz). At this, samples of polymers used inside the satellite (insulators for cabling, adhesives, etc.) were
installed into the chamber, and the interaction of their degassing with the sample surfaces under laser irradiation was
investigated. Various paramters were varied including pulse repetition rate, view factor and coatings. Optical degradation
associated with contaminant adsorption was detected on the irradiated sample sites.
We have investigated the growth mechanisms for laser induced contamination of space optics in vacuum, particularly
during the early stages of the deposit formation. Experiments have been performed in vacuum to study the influence of
the environmental conditions and the condition of the optical surface, using a variety of physical and chemical
techniques. In particular, different methods of conditioning the surface prior to irradiation and cleaning the surface after
irradiation have been tested.
We present the investigation of second harmonic generation in congruent undoped lithium niobate crystal in presence of
strong photorefractive and photovoltaic effect. We show that phase matching condition can be efficiently varied
employing both the temperature and the electric field tuning. We also perform experiments on second harmonic generation with focused light, showing that the photorefractive effect is responsible for a strong distortion of the beam as well as a local modification of the phase matching condition. Finally, we demonstrate that an external bias can be used in order to switch from optical damage and distortion to self-confinement and guidance, reaching higher conversion
efficiency through confinement and good overlap between interacting waves.
We measure electronic and thermal nonlinear refractive indices of periodically nano-patterned and un-patterned siliconon-
insulator (SOI) in comparison with that of bulk silicon, using a fast reflection Z-scan setup with a high-repetition-rate
fs laser (at 800 nm wavelength), and a new procedure for discrimination between electronic and thermal nonlinearities.
The electronic nonlinear response of nano-structured SOI is strongly enhanced in comparison with those of un-patterned
SOI and of bulk Si. These results could be important in silicon photonics for optical devices with nonlinearity controlled
by periodic nano-structuring.
In this paper we study second harmonic generation in Lithium Niobate in presence of photorefractive and photovoltaic
effect. Our investigation reveals that the application of a strong external bias causes a self focusing effect that efficiently
traps both the generated second harmonic and the fundamental beam, resulting in an improved conversion efficiency.
The variation of the second harmonic output power during the build up of the space charge field also testifies that the
phase relation between the interacting waves is affected by the photorefractive effect, and that the phase matching
condition is modified in the part of the crystal shined by the light.
Finally, we introduce a numerical model in order to explain the complex dynamic between the photorefractive effect and
parametric process. The developed theory is in qualitative agreement with the performed experiments.
We present the first investigation of bright screening soliton formation in Erbium doped lithium niobate grown by the Czochrlaski technique (0.7% mol.). We analyse the formation of two-dimensional spatial soliton and study its long term stability. Measurements of photovoltaic current show that presence of erbium in the lattice cause an increase of the current density. Both dynamic of soliton formation and photovoltaic measurements indicates a lower NA content in erbium doped samples compared to undoped samples.