CMOS optical centroid processor for an integrated Shack-Hartmann wavefront sensor

A Shack Hartmann wavefront sensor is used to detect the distortion of light in an optical wavefront. It does this by sampling the wavefront with an array of lenslets and measuring the displacement of focused spots from reference positions. These displacements are linearly related to the local wavefront tilts from which the entire wavefront can be reconstructed. In most Shack Hartmann wavefront sensors, a CCD is used to sample the entire wavefront, typically at a rate of 25 to 60 Hz, and a whole frame of light spots is read out before their positions are processed. This results in a data bottleneck. In this design, parallel processing is achieved by incorporating local centroid processing for each focused spot, thereby requiring only reduced bandwidth data to be transferred off-chip at a high rate. To incorporate centroid processing at the sensor level requires high levels of circuit integration not possible with a CCD technology. Instead a standard 0.7J..lmCMOS technology was used but photodetector structures for this technology are not well characterised. As such characterisation of several common photodiode structures was carried out which showed good responsitivity of the order of 0.3 AIW. Prior to fabrication on-chip, a hardware emulation system using a reprogrammable FPGA was built which implemented the centroiding algorithm successfully. Subsequently, the design was implemented as a single-chip CMOS solution. The fabricated optical centroid processor successfully computed and transmitted the centroids at a rate of more than 2.4 kHz, which when integrated as an array of tilt sensors will allow a data rate that is independent of the number of tilt sensors' employed. Besides removing the data bottleneck present in current systems, the design also offers advantages in terms of power consumption, system size and cost. The design was also shown to be extremely scalable to a complete low cost real time adaptive optics system

CMOS optical centroid processor for an integrated Shack-Hartmann wavefront sensor

A Shack Hartmann wavefront sensor is used to detect the distortion of light in an optical wavefront. It does this by sampling the wavefront with an array of lenslets and measuring the displacement of focused spots from reference positions. These displacements are linearly related to the local wavefront tilts from which the entire wavefront can be reconstructed. In most Shack Hartmann wavefront sensors, a CCD is used to sample the entire wavefront, typically at a rate of 25 to 60 Hz, and a whole frame of light spots is read out before their positions are processed. This results in a data bottleneck. In this design, parallel processing is achieved by incorporating local centroid processing for each focused spot, thereby requiring only reduced bandwidth data to be transferred off-chip at a high rate. To incorporate centroid processing at the sensor level requires high levels of circuit integration not possible with a CCD technology. Instead a standard 0.7J..lmCMOS technology was used but photodetector structures for this technology are not well characterised. As such characterisation of several common photodiode structures was carried out which showed good responsitivity of the order of 0.3 AIW. Prior to fabrication on-chip, a hardware emulation system using a reprogrammable FPGA was built which implemented the centroiding algorithm successfully. Subsequently, the design was implemented as a single-chip CMOS solution. The fabricated optical centroid processor successfully computed and transmitted the centroids at a rate of more than 2.4 kHz, which when integrated as an array of tilt sensors will allow a data rate that is independent of the number of tilt sensors' employed. Besides removing the data bottleneck present in current systems, the design also offers advantages in terms of power consumption, system size and cost. The design was also shown to be extremely scalable to a complete low cost real time adaptive optics system

Structural analysis and design of adaptive lightweight mirrors

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1993.Includes bibliographical references (leaves 136-139).by Celia H. Liu.M.S

Optimising the NAOMI adaptive optics real-time control system

This thesis describes the author's research in the field of Real-Time Control (RTC) for Adaptive Optics (AO) instrumentation. The research encompasses experiences and knowledge gained working in the area of RTC on astronomical instrumentation projects whilst at the Optical Science Laboratories (OSL), University College London (UCL), the Isaac Newton Groups of Telescopes (ING) and the Centre for Advanced Instrumentation (СfAI), Durham University. It begins by providing an extensive introduction to the field of Astronomical Adaptive Optics covering Image Correction Theory, Atmospheric Theory, Control Theory and Adaptive Optics Component Theory. The following chapter contains a review of the current state of world wide AO instruments and facilities. The Nasmyth Adaptive Optics Multi-purpose Instrument (NAOMI), the common user AO facility at the 4.2 William Herschel Telescope (WHT), is subsequently described. Results of NAOMI component characterisation experiments are detailed to provide a system understanding of the improvement optimisation could offer. The final chapter investigates how upgrading the RTCS could increase NAOMI'S spatial and temporal performance and examines the RTCS in the context of Extremely Large Telescope (ELT) class telescopes

Robust real-time control of an adaptive optics system

This research contributes to the understanding of the limitations when designing a robust control real-time system for Adaptive Optics (AO). One part of the research is a new method regarding the evaluation of a Shack-Hartmann wavefront sensor (SHWFS) to enhance the overall performance. The method is presented based on the application of a Field Programmable Gate Array (FPGA) using Connected Component Labeling (CCL) for blob detection. The FPGA has been utilized since the resulting delay is crucial for the general AO performance. In this regard, the FPGA may accelerate the evaluation largely by its parallelism. The developed algorithm does not rely on a fixed assignment of the camera sensor area to the lenslet array to maximize the dynamic range. In extension to the SHWFS evaluation, a new rapid control prototyping (RCP) system based on hard real-time RTAI-patched Linux kernel has been developed. This system includes the required hardware e.g.~the analog output cards and FPGA based frame-grabber. Based upon a Simulink model, accelerated C/C++ code is automatically generated which uses the available parallel features of the processor. A continuative contribution is the application of a robust control scheme using H-infinity methods for designing a controller while considering uncertainty of the identified model. For synthesizing the controller, a special optimization technique called non-smooth mu-synthesis is utilized which minimizes the H-infinity norm while coping with pre-specified controller schemes. Depending on the pre-specified controller scheme, the resulting controller can be computationally costly but the RCP approach is designed to cope with the problem. Based on simulations and according to experiments, the validity of the identified models of the AO setup is assured. At the same time, the enhanced performance of the new RCP setup is demonstrated.Die wissenschaftliche Arbeit trägt maßgeblich zum Verständnis der gängigen Limitierungen bei robusten echtzeit-fähigen Regelungssystemen für Adaptiv Optische (AO) Systeme bei. Ein wesentlicher Teil der Arbeit befasst sich mit einer neuartigen Methode der Auswertung eines Shack-Hartmann Wellenfrontsensors (SHWFS). Die Methode basiert auf der Anwendung eines Field Programmable Gate Arrays (FPGA) zur Auswertung des SHWFS. Die zu Grunde liegende Methode ist ein Resultat der Graphentheorie zur Erkennung zusammenhängender Bildbereiche. Der Einsatz eines FPGA ermöglicht hierbei, dass die resultierende Verzögerung durch die Auswertung des SHWFS auf ein Minimum reduziert wird. Hinzu kommt, dass die neuartige Auswertungsmethode den dynamischen Bereich des Wellenfrontsensors gegenüber dem üblichen Verfahren erweitert, da für die Methode keine feste Zuordnung der Spots zu dem Linsenarray notwendig ist. Zusätzlich zu dem neuartigen Verfahren für die Auswertung wurde ein Rapid Control Prototyping (RCP) System entworfen, welches auf einem echtzeitfähigen Linux Kernel basiert. Die Echtzeitfähigkeit wird durch die Verwendung des Real-Time Application Interface for Linux (RTAI) erreicht. Der Entwurf des RCP Systems umfasst die Entwicklung spezieller Hardware wie beispielsweise eine analoge Ausgangskarte und der PCIe FPGA Framegrabber. Aus einem Simulink Modell wird automatisch C/C++ Quellcode generiert. Dieser generierte Code nutzt die vorhandenen parallelen Erweiterungen des Prozessors zur Beschleunigung der vorkommenden Berechnungen. Basierend auf diesem System wurde ein robustes Regelungsverfahren angewendet, welches auf der H_infty Entwurfsmethodik basiert. Das Entwurfverfahren des Reglers (non-smooth mu Synthese) berücksichtigt die vorhandene Unsicherheit der identifizierten Modelle bereits während der Synthese. Das Verfahren ermöglicht die H_infty Norm des geschlossenen Regelkreises zu minimieren, wobei die Regler-Struktur vorgegeben werden kann. Basierend auf verschiedenen Simulationen und experimentellen Versuchen wurde die Gültigkeit der identifizierten Modelle des AO Systems nachgewiesen. Zudem wird gezeigt, dass das entworfene RCP System deutlich leistungsfähiger als vergleichbare Systeme ist und somit eine deutlich verbesserte Performance aufweist

Lunar Ultraviolet Telescope Experiment (LUTE), phase A

The Lunar Ultraviolet Telescope Experiment (LUTE) is a 1-meter telescope for imaging from the lunar surface the ultraviolet spectrum between 1,000 and 3,500 angstroms. There have been several endorsements of the scientific value of a LUTE. In addition to the scientific value of LUTE, its educational value and the information it can provide on the design of operating hardware for long-term exposure in the lunar environment are important considerations. This report provides the results of the LUTE phase A activity begun at the George C. Marshall Space Flight Center in early 1992. It describes the objective of LUTE (science, engineering, and education), a feasible reference design concept that has evolved, and the subsystem trades that were accomplished during the phase A

Large Space Antenna Systems Technology, 1984

Mission applications for large space antenna systems; large space antenna structural systems; materials and structures technology; structural dynamics and control technology, electromagnetics technology, large space antenna systems and the Space Station; and flight test and evaluation were examined