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ABSTRACT: The Durham adaptive optics real-time controller is a generic, high
performance real-time control system for astronomical adaptive optics systems.
It has recently had new features added as well as performance improvements, and
here we give details of these, as well as ways in which optimisations can be
made for specific adaptive optics systems and hardware implementations. We also
present new measurements that show how this real-time control system could be
used with any existing adaptive optics system, and also show that when used
with modern hardware, it has high enough performance to be used with most
Extremely Large Telescope adaptive optics systems.
05/2012;
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ABSTRACT: Modern adaptive optics (AO) systems for large telescopes require tomographic techniques to reconstruct the phase aberrations induced by the turbulent atmosphere along a line of sight to a target which is angularly separated from the guide sources that are used to sample the atmosphere. Multi-object adaptive optics (MOAO) is one such technique. Here, we present a method which uses an artificial neural network (ANN) to reconstruct the target phase given off-axis references sources. We compare our ANN method with a standard least squares type matrix multiplication method and to the learn and apply method developed for the CANARY MOAO instrument. The ANN is trained with a large range of possible turbulent layer positions and therefore does not require any input of the optical turbulence profile. It is therefore less susceptible to changing conditions than some existing methods. We also exploit the non-linear response of the ANN to make it more robust to noisy centroid measurements than other linear techniques.
Optics Express 01/2012; 20(3):2420-34. · 3.59 Impact Factor
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ABSTRACT: Astronomical adaptive optics systems with open-loop deformable mirror control
have recently come on-line. In these systems, the deformable mirror surface is
not included in the wavefront sensor paths, and so changes made to the
deformable mirror are not fed back to the wavefront sensors. This gives rise to
all sorts of linearity and control issues mainly centred on one question: Has
the mirror taken the shape requested? Non-linearities in wavefront measurement
and in the deformable mirror shape can lead to significant deviations in mirror
shape from the requested shape. Here, wavefront sensor measurements made using
a brightest pixel selection method are discussed along with the implications
that this has for open-loop AO systems. Discussion includes elongated laser
guide star spots and also computational efficiency.
09/2011;
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ABSTRACT: The Durham adaptive optics (AO) real-time controller was initially a proof of concept design for a generic AO control system. It has since been developed into a modern and powerful central-processing-unit-based real-time control system, capable of using hardware acceleration (including field programmable gate arrays and graphical processing units), based primarily around commercial off-the-shelf hardware. It is powerful enough to be used as the real-time controller for all currently planned 8 m class telescope AO systems. Here we give details of this controller and the concepts behind it, and report on performance, including latency and jitter, which is less than 10 μs for small AO systems.
Applied Optics 11/2010; 49(32):6354-63. · 1.41 Impact Factor
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ABSTRACT: Using non-parametric estimation techniques, we have modeled an area of 126 actuators of a micro-electro-mechanical deformable mirror with 1024 actuators. These techniques produce models applicable to open-loop adaptive optics, where the turbulent wavefront is measured before it hits the deformable mirror. The model's input is the wavefront correction to apply to the mirror and its output is the set of voltages to shape the mirror. Our experiments have achieved positioning errors of 3.1% rms of the peak-to-peak wavefront excursion.
Optics Express 09/2010; 18(20):21356-69. · 3.59 Impact Factor
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ABSTRACT: The EAGLE instrument for the E-ELT is a multi-IFU spectrograph, that uses a MOAO system for wavefront correction of interesting lines of sight. We present a Monte-Carlo AO simulation package that has been used to model the performace of EAGLE, and provide results, including comparisons with an analytical code. These results include an investigation of the performance of compressed reconstructor representations that have the potential to significantly reduce the complexity of a real-time control system when implemented. Comment: 34 pages, 10 figures at end, accepted by Applied Optics
05/2010;
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ABSTRACT: Open-loop adaptive optics is a technique in which the turbulent wavefront is measured before it hits the deformable mirror for correction. We present a technique to model a deformable mirror working in open-loop based on multivariate adaptive regression splines (MARS), a non-parametric regression technique. The model's input is the wavefront correction to apply to the mirror and its output is the set of voltages to shape the mirror. We performed experiments with an electrostrictive deformable mirror, achieving positioning errors of the order of 1.2% RMS of the peak-to-peak wavefront excursion. The technique does not depend on the physical parameters of the device; therefore it may be included in the control scheme of any type of deformable mirror.
Optics Express 03/2010; 18(7):6492-505. · 3.59 Impact Factor
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ABSTRACT: We present a design improvement for a recently proposed type of Shack-Hartmann wavefront sensor that uses a cylindrical (lenticular) lenslet array. The improved sensor design uses optical binning and requires significantly fewer detector pixels than the corresponding conventional or cylindrical Shack-Hartmann sensor, and so detector readout noise causes less signal degradation. Additionally, detector readout time is significantly reduced, which reduces the latency for closed loop systems and data processing requirements. We provide simple analytical noise considerations and Monte Carlo simulations, we show that the optically binned Shack-Hartmann sensor can offer better performance than the conventional counterpart in most practical situations, and our design is particularly suited for use with astronomical adaptive optics systems.
Applied Optics 09/2007; 46(24):6136-41. · 1.41 Impact Factor
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ABSTRACT: Adaptive optics systems are essential on all large telescopes for which image quality is important. These are complex systems with many design parameters requiring optimization before good performance can be achieved. The simulation of adaptive optics systems is therefore necessary to categorize the expected performance. We describe an adaptive optics simulation platform, developed at Durham University, which can be used to simulate adaptive optics systems on the largest proposed future extremely large telescopes as well as on current systems. This platform is modular, object oriented, and has the benefit of hardware application acceleration that can be used to improve the simulation performance, essential for ensuring that the run time of a given simulation is acceptable. The simulation platform described here can be highly parallelized using parallelization techniques suited for adaptive optics simulation, while still offering the user complete control while the simulation is running. The results from the simulation of a ground layer adaptive optics system are provided as an example to demonstrate the flexibility of this simulation platform.
Applied Optics 04/2007; 46(7):1089-98. · 1.41 Impact Factor
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ABSTRACT: Adaptive optics systems are essential on all large telescopes where image quality is important. These are complex systems with many design parameters requiring optimisation before good performance can be achieved. The simulation of adaptive optics systems is therefore necessary to categorise the expected performance. This paper describes an adaptive optics simulation platform, developed at Durham University, which can be used to simulate adaptive optics systems on the largest proposed future extremely large telescopes (ELTs) as well as current systems. This platform is modular, object oriented and has the benefit of hardware application acceleration which can be used to improve the simulation performance, essential for ensuring that the run time of a given simulation is acceptable. The simulation platform described here can be highly parallelised using parallelisation techniques suited for adaptive optics simulation, whilst still offering the user complete control while the simulation is running. Results from the simulation of a ground layer adaptive optics system are provided as an example to demonstrate the flexibility of this simulation platform.
12/2006;
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ABSTRACT: ESO is starting a number of new projects collectively called Second Generation VLT instrumentation. Several of them will use Adaptive Optics (AO). In comparison with today's ESO AO systems, the 2nd Generation VLT AO systems will be much bigger (in terms of degrees of freedom) and faster (in terms of loop frequency). Consequently the Real-Time Computer controlling these AO systems will be significantly bigger and more challenging to build compared with today's AO systems in operation. To support the new requirements ESO started the development of a common flexible platform called SPARTA for Standard Platform for Adaptive optics Real Time Applications. The guidelines along which SPARTA is developed recognize the importance of industry standards over custom development to lower the development costs, ease the maintenance and make the system upgradeable thus delivering the performance required. SPARTA is based on a hybrid architecture that comprises all the major computing architectures available today: the high computational throughput is achieved through the combination of FPGA and DSP usage, where DSP are used as fast coprocessors and FPGA are used as front and as communication infrastructure, thus guaranteeing also the low latency. The flexibility is spread between the usage of both high-end CPUs and again the DSPs. All three technologies are organized in a parallel system interconnected by fast serial fabrics based on standard protocols. External input / output interfaces are also based on industry standard protocols, thus enabling the usage of commercially available tools for development and testing.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
06/2006;
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ABSTRACT: We present a new approach for the control of a deformable mirror (DM), part of a Multi Object Adaptive Optics (MOAO) on-sky demonstrator. The control is based on H synthesis methods, achieving better performance than classical Proportional-Integral methods, while offering other appealing advantages such as an optimized design based on the temporal spectra of the wavefront and vibration rejection capabilities. We describe laboratory results obtained with a 97 actuator Xinetics DM, using a high-resolution Shack-Hartmann wavefront sensor for measuring DM surface. A connection between the turbulence dynamics represented in a Zernike basis and the controller requirements is studied, showing that the controller parameters and structure can be easily optimized for each Zernike mode according to their particular temporal spectra.
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Dani Guzmán,
Andrés Guesalaga, Richard Myers,
Ray Sharples,
Tim Morris,
Alastair Basden,
Christopher Saunter,
Nigel Dipper,
Laura Young,
Luis Rodriguez,
Marcos Reyes,
Yolanda Martin
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ABSTRACT: A Deformable Mirror Controller (DMC) has been devised to overcome the open-loop nature of Multi Object Adaptive Optics (MOAO), in particular for AO systems with update rates of 1 ms or less. The system is based on a figure sensor, which uses a monochromatic illumination source and a Shack-Hartmann (SH) wavefront sensor (WFS) to obtain a fine sampling of DM's 3D surface. The sensor's beam is optically separated from the science path in order to not interfere with science observations. The DMC incorporates a real-time controller in charge of driving the DM. This controller runs in a dedicated Field-Programmable-Gate-Array (FPGA) based processor to keep up with stringent speed requirements. The DMC is being tested in the laboratory and is part of CANARY, an MOAO on-sky demonstrator to be installed at the William Hershel Telescope.
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ABSTRACT: We present a novel technique for the design of DM controllers in high spatial resolution adaptive optics systems, operating in open-loop. It consists of a Shack-Hartmann (SH) figure sensor and multiple overlapping MIMO controllers based on the H ∞ synthesis method. The controller synthesis can be carried out periodically using a linearized representation of a continuously adjusted model that accounts for varying physical or ambient conditions and incorporates the spatial geometry of the SH. The figure sensor uses a bright reference source and a fast CMOS detector to sample the DM surface sequentially with an optical arrangement that does not interfere with the main corrected beam. Taking full advantage of such robust techniques, the controller can successfully handle the dynamics and non-linearity of the DM, allowing one to decouple, from the main AO control loop standpoint, the turbulence estimation errors from those originating in the DM servo-loop. It can also implement noise and vibration rejection without compromising the loop stability, pushing the control bandwidth to the physical limits imposed by hardware and software components. By splitting the control function into several overlapping controllers, implementation complexity is reduced and continuous updating of the controller can be easily achieved. Simulations show its ability to successfully control the DM shape, in spite of partial and non-simultaneous sampling of the SH figure sensor due to detector speed limitations.
