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.
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.
Future large telescopes, such as E-ELT and TMT, will need feedback control of the thousands of actuators underneath their segmented primary mirrors (M1). Differences in actuator dynamics and spatially and temporally changing disturbances make it extremely difficult to formulate classical controllers which are both sufficiently robust and highly performing. Therefore, TNO has developed and tested a control approach, in which the actual system response is quickly measured, disturbances are continuously estimated and the controller is adapted in real-time. The algorithm is tested on an actual M1-relevant setup, in which it converges to a sub-nm optimum within a few minutes, keeps track of changing disturbances and shows its reliability over multiple days.
Described is the M1 segment support, as designed by TNO in the period 2015-2016. The design has significantly changed and improved compared to the earlier designs. During the period 2009-2010 prototypes for the primary mirror support of the E-ELT have been developed. These have been extensively tested by ESO. Design improvement were found to be necessary, especially in the field of manufacturability and maintainability. Furthermore, the technical performance had to improve in specific areas as well. This has evolved into a new specifications which have resulted in a new design for the segment support structure. The design rules that have led to the prototype design have been maintained but the implementation has been much improved. Also considerable improvement has been obtained with respect to the dynamic behavior. Accessibility and visibility on all parts and subsystems has changed such that everything is now clearly visible. Despite the increased performance no mass increase has been recorded meaning that more efficient use has been made of the material.
The active means to influence the segment shape by use of the warping harness has been completely redesigned. A very important quality that has been achieved is simplicity. Hence a minimum amount of components is used. Reliability and safety are other aspects that have been greatly improved compared to the prototypes. The design for the M1 segment support provides a solution that not only performs to specification but one that can be operated in a telescope environment, all 798 of them.
Segmented primary mirror telescopes require dedicated piston-tip-tilt actuators for optimal optical performance. Netherlands Organisation for Applied Scientific Research (TNO) has developed various prototypes of such actuators, in particular for the E-ELT. This paper presents the dynamics analysis and feedback control results for a specific two-stage prototype. First, the dynamics of the actuator in interconnection with the to-be-positioned mass has been analyzed, both using frequency response measurements and first principles modeling, resulting in a detailed understanding of the dynamic behavior of the system. Next, feedback controllers for both the fine and the coarse stage have been designed and implemented. Finally, the feedback-controlled actuator has been subjected to a realistic tracking experiment; the achieved results have demonstrated that the TNO actuator is able to suppress wind force disturbances and ground vibrations with more than a factor 103, down to 1.4 nm root mean square, which is compliant with the requirements.
Segmented primary mirror telescopes require dedicated piston-tip-tilt actuators for optimal optical performance. TNO has developed various prototypes of such actuators, in particular for the E-ELT. In this paper the control results of a specific two-stage prototype will be presented. First, the dynamics of the actuator in interconnection with the to-be-positioned mass has been analyzed, both using frequency response measurements and first principles modeling, resulting in a detailed understanding of the dynamic behavior of the system. Next, feedback controllers for both the fine and the coarse stage have been designed and implemented. Finally, the feedback controlled actuator has been subjected to a realistic tracking experiment; the results have demonstrated that the TNO actuator is able to suppress wind force disturbances and ground vibrations with more than a factor 103, down to 1.4 nm RMS, which is compliant with the requirements.
The European Southern Observatory (ESO) has started technology development for their next generation optical
telescope. Due to its ultra large collecting area, The European Extremely Large Telescope (E-ELT) will require a
paradigm shift in telescope design to keep the overall program cost at an acceptable level. The E-ELT will feature a 42
meter segmented primary mirror and will make extensive use of active and adaptive optics. Each primary mirror segment
will be supported by three actuators that control piston and tilt. TNO has developed a low cost nanopositioning actuator
(PACT) for the primary mirror segments. The actuators will be tested by IAC and ESO, with support from TNO, under
operational conditions in a Wind Evaluation Breadboard (WEB) at the Roque de Los Muchachos observatory in La