Prof. Alan H. Greenaway Profile

Prof. Alan H. Greenaway

at Heriot-Watt Univ

SPIE Involvement:

Author

Publications (30)

Proceedings Article | 4 August 2016 Paper

Use of a photonic lantern into an image plane fiber beam combiner

Ettore Pedretti, Alan Greenaway, Robert Thomson, Paul Dalgarno

Proceedings Volume 9907, 990735 (2016) https://doi.org/10.1117/12.2232542

KEYWORDS: Telescopes, Interferometers, Single mode fibers, Atmospheric optics, Spatial frequencies, Signal to noise ratio, Visibility, Collimation, Phase interferometry, Phase measurement

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Proceedings Article | 20 March 2014 Paper

A comparison between temporal and subband minimum variance adaptive beamforming

Konstantinos Diamantis, Iben Holfort-Voxen, Alan Greenaway, Tom Anderson, Jørgen Jensen, Vassilis Sboros

Proceedings Volume 9040, 90400L (2014) https://doi.org/10.1117/12.2043602

KEYWORDS: Phased arrays, Apodization, Sensors, Ultrasonography, Transducers, Signal processing, Image resolution, Fourier transforms, Radar signal processing, Optical simulations

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This paper compares the performance between temporal and subband Minimum Variance (MV) beamformers for medical ultrasound imaging. Both adaptive methods provide an optimized set of apodization weights but are implemented in the time and frequency domains respectively. Their performance is evaluated with simulated synthetic aperture data obtained from Field II and is quantified by the Full-Width-Half-Maximum (FWHM), the Peak-Side-Lobe level (PSL) and the contrast level. From a point phantom, a full sequence of 128 emissions with one transducer element transmitting and all 128 elements receiving each time, provides a FWHM of 0.03 mm (0.14λ) for both implementations at a depth of 40 mm. This value is more than 20 times lower than the one achieved by conventional beamforming. The corresponding values of PSL are -58 dB and -63 dB for time and frequency domain MV beamformers, while a value no lower than -50 dB can be obtained from either Boxcar or Hanning weights. Interestingly, a single emission with central element #64 as the transmitting aperture provides results comparable to the full sequence. The values of FWHM are 0.04 mm and 0.03 mm and those of PSL are -42 dB and -46 dB for temporal and subband approaches. From a cyst phantom and for 128 emissions, the contrast level is calculated at -54 dB and -63 dB respectively at the same depth, with the initial shape of the cyst being preserved in contrast to conventional beamforming. The difference between the two adaptive beamformers is less significant in the case of a single emission, with the contrast level being estimated at -42 dB for the time domain and -43 dB for the frequency domain implementation. For the estimation of a single MV weight of a low resolution image formed by a single emission, 0.44 * 109 calculations per second are required for the temporal approach. The same numbers for the subband approach are 0.62 * 109 for the point and 1.33 * 109 for the cyst phantom. The comparison demonstrates similar resolution but slightly lower side-lobes and higher contrast for the subband approach at the expense of increased computation time.

Proceedings Article | 1 March 2013 Paper

A real-space interactive holographic display based on a large-aperture HOE

Javid Khan, Chi Can, Alan Greenaway, Ian Underwood

Proceedings Volume 8644, 86440M (2013) https://doi.org/10.1117/12.2021633

KEYWORDS: Holographic optical elements, Holography, Displays, Holograms, Sensors, Projection systems, 3D image reconstruction, Computer programming, Optical components, Erbium

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Proceedings Article | 28 July 2010 Paper

Status update of the CANARY on-sky MOAO demonstrator

E. Gendron, T. Morris, Z. Hubert, R. Myers, A. Longmore, G. Rousset, G. Talbot, F. Vidal, N. Dipper, D. Gratadour, N. Looker, M. Brangier, E. Younger, A. Sevin, A. Basden, D. Perret, L. Young, D. Atkinson, F. Chemla, D. Henry, T. Butterley, P. Laporte, D. Guzman, M. Marteaud, D. Geng, N. Vedrenne, M. Harrison, T. Fusco, A. Guesalaga, C. Dunlop, S. Todd, K. Dee, C. Dickson, A. Greenaway, B. Stobie, H. Dalgarno, J. Skvarc

Proceedings Volume 7736, 77360P (2010) https://doi.org/10.1117/12.857668

KEYWORDS: Telescopes, Calibration, Adaptive optics, Tomography, Mirrors, Sensors, Actuators, Device simulation, Cameras, Deformable mirrors

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Proceedings Article | 5 May 2010 Paper

A low-resolution 3D holographic volumetric display

Javid Khan, Ian Underwood, Alan Greenaway, Mikko Halonen

Proceedings Volume 7723, 77231B (2010) https://doi.org/10.1117/12.858596

KEYWORDS: Holography, Holograms, 3D displays, Volume holography, 3D image processing, 3D image reconstruction, Projection systems, Image segmentation, Multiplexing

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Proceedings Article | 10 July 2008 Paper

CANARY: the on-sky NGS/LGS MOAO demonstrator for EAGLE

Richard Myers, Zoltán Hubert, Timothy Morris, Eric Gendron, Nigel Dipper, Aglaé Kellerer, Stephen Goodsell, Gérard Rousset, Eddy Younger, Michel Marteaud, Alastair Basden, Fanny Chemla, C. Dani Guzman, Thierry Fusco, Deli Geng, Brice Le Roux, Mark Harrison, Andrew Longmore, Laura Young, Fabrice Vidal, Alan Greenaway

Proceedings Volume 7015, 70150E (2008) https://doi.org/10.1117/12.789544

KEYWORDS: Adaptive optics, Tomography, Control systems, Wavefront sensors, Sensors, Telescopes, Device simulation, Wavefronts, Calibration, Real-time computing

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Proceedings Article | 14 August 2006 Paper

Wavefront sensing for 3D particle metrology and velocimetry

N. Angarita-Jaimes, E. McGhee, M. Chennaoui, H. Campbell, S. Zhang, C. Towers, A. Greenaway, D. Towers

Proceedings Volume 6292, 62920K (2006) https://doi.org/10.1117/12.681561

KEYWORDS: Particles, Image segmentation, Image processing, Wavefronts, Wavefront sensors, 3D metrology, Metrology, Calibration, Imaging systems, 3D image processing

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Proceedings Article | 13 June 2006 Paper

Decreasing the inner working angle in high-contrast imaging by pupil replication

Frank Spaan, Alan Greenaway

Proceedings Volume 6265, 62651D (2006) https://doi.org/10.1117/12.670248

KEYWORDS: Telescopes, Point spread functions, Planets, Imaging systems, Apodization, Stars, Coronagraphy, Space telescopes, Numerical simulations, Wavefronts

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Imaging for exo-planet detection requires both high contrast and a small inner working angle. We show that, for several of the techniques proposed so far to achieve this, the inner working angle can be reduced by adding pupil replication between the telescope and the high contrast imaging system. Using pupil replication, the on-axis image of the star is decreased to a size smaller than the diffraction limit of the telescope, and off axis the point spread function of the planet undergoes minor changes, contained within the envelope of the point spread function of the telescope; the spectrum remains unchanged. The principle of pupil replication was proven experimentally and can be effected by a small-sized, high throughput optical system added between the telescope and the high contrast imaging system. High contrast imaging systems to which pupil replication has been found to be applicable so far include apodisation techniques like pupil apodisation, aperture masks, image plane masks, coronagraphs and combinations. Mathematical assessment and simulations of the sensitivity of pupil replication to optical errors show that the requirements for this system are the same as those for the primary telescope - pupil replication effectively remaps the output pupil of the telescope to the input pupil of the high contrast imaging system. Our results in this paper aim to show, in a realistic set-up, the feasibility of an improvement of the inner working angle by a factor of 4 using four-fold replication optics while maintaining the contrast performance. We do this through analysis of the pupil replication principle including off axis behavior when applied to high contrast imaging systems using pupil apodisation or a shaped mask. We specifically look at the situations similar to that of the Terrestrial Planet Finder Coronagraph and Darwin. We found that an inner working angle of 30 mas can be achieved with a contrast of 10^-10and a large field of view without increasing the requirements except for the pointing.