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.
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. Throughout these developments there is a particular aim for high levels of system integration, compactness and low recurring cost in order to meet the overall requirements related to market viability. TNO develops terminals with aperture sizes of 70 and 17 mm, coarse pointing assemblies and fast steering mirrors. This paper discusses the state of development of these different technologies and provides and outlook towards the future.
ESO is building the Phase Referenced Imaging and Microarcsecond Astronomy (PRIMA) facility for the Very Large
Telescope Interferometer (VLTI) in Chile. PRIMA will enable interferometric imaging of very faint objects and high
precision astrometry with both Unit (UT) and Auxiliary (AT) telescopes. The PRIMA facility consists of four major
sub systems: Star Separators, Differential Delay Lines, Metrology and Fringe Sensor Units. TNO has developed the
PRIMA Star Separator (STS) subsystems for both the UT and AT telescopes. The STS separates the light of two
astronomical objects and feeds it into the long stroke delay line. The STS compensates for field rotation, stabilizes the
beam tip tilt and adjust the lateral and axial alignment of the pupil. Chopping and/or counter-chopping on the science
object or the guide star has also been implemented.
In the framework of the Phase-Referenced Imaging and Micro-arcsecond Astrometry facility (PRIMA) developed for the Very Large Telescope Interferometer (VLTI), a sophisticated opto-mechanical system has been developed by TNO-TPD. It will be placed at the Coudé focus of the telescopes and will allow picking up two stars anywhere in a 2 arcmin field-of-view and collimating their light into two beams that will propagate through the rest of the interferometer toward the instrument. These Star Separator systems have a very high optical quality, fast and accurate pointing and chopping, independent high speed remote control of the beam tip-tilt and of the pupil position. They are very rigid, accurate mechanical systems non-sensitive to temperature variations The Star Separator systems are described in this paper.
At TNO TPD we have realized an Adaptive Optics test bench. The bench has an in-house built turbulent atmosphere simulator. For the wavefront sensors there is the possibility to choose between a Shack-Hartmann sensor and a pyramid sensor. Compensation of the wavefront error is performed by a separate tip-tilt mirror and a deformable mirror. Both are off the shelf products.
The AO system is controlled by a Multi-Input-Multi-Output control system with 40 actuator channels and 50 sensor channels. The proposed control strategy corresponds to a Linear Quadratic approach, in which the sum of the mean squared wavefront error over the sensor points and the weighted control effort is minimized. In the optimization process the dynamic properties (spatial-temporal correlation) of both the turbulence-induced wavefront error and the mirror/sensor combination are taken into account. Furthermore, important issues like closed-loop stability and robustness are included in the control design. An adaptive control algorithm has been derived, which converges to the LQ-solution and also enables tracking of changes in the characteristics of the turbulent wavefront.
This paper presents the first results achieved with the Adaptive optics test bench. It shows that a simplified version of the adaptive feedback control strategy already gives promising results, both implemented in a commonly used AO simulation software package and in real-time on the AO test bench.