Numerical analysis of systematic errors in an optical encryption system

Author(s): David S. Monaghan, Unnikrishnan Gopinathan, Damien P. Kelly, Thomas J. Naughton, John T. Sheridan

Abstract:

“We consider a double random phase encoding Encryption/Decryption system in which the image encryption/decryption process is performed numerically. In this paper we look at the effect of quantisation in the decryption process due to the discrete values which a spatial light modulator can display. We look at the characterisation of a transmissive spatial light modulator and we present results from simulations of the system.”

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Publication: SPIE Proceedings
Issue/Year: Proc. SPIE, Vol. 6187, 61870X (2006)
DOI: 10.1117/12.663063

Fast digital hologram generation and adaptive force measurement in liquid-crystal-display-based holographic tweezers

Author(s): Marcus Reicherter, Susanne Zwick, Tobias Haist, Christian Kohler, Hans Tiziani, and Wolfgang Osten

Abstract:

“Computer-generated holograms in conjunction with spatial light modulators (SLMs) offer a way to dynamically generate holograms that are adapted to specific tasks. To use the full dynamic capability of the SLM, the hologram computation should be very fast. We present a method that uses the highly parallel architecture of a consumer graphics board to compute analytical holograms in video real time. A precice characterization of the SLM (Holoeye LC-R-2500) and the adaption of its settings to our near-infrared application is necessary to guarantee an efficient hologram reconstruction. The benefits of a fast computation of adapted holograms and the application of an efficient SLM are demonstrated by measuring the trapping forces of holographic tweezers.”

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Publication: Applied Optics
Issue/Year: Applied Optics, Vol. 45, Issue 5, pp. 888-896, 2006
DOI: 10.1364/AO.45.000888

Spiral phase contrast imaging in microscopy

Author(s): Severin Fürhapter, Alexander Jesacher, Stefan Bernet, and Monika Ritsch-Marte

Abstract:

“We demonstrate an optical method for edge contrast enhancement in light microscopy. The method is based on holographic Fourier plane filtering of the microscopic image with a spiral phase element (also called vortex phase or helical phase filter) displayed as an off-axis hologram at a computer controlled high resolution spatial light modulator (SLM) in the optical imaging pathway. The phase hologram imprints a helical phase term of the form exp(i ??) on the diffracted light field in its Fourier plane. In the image plane, this results in a strong and isotropic edge contrast enhancement for both amplitude and phase objects.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 13, Issue 3, pp. 689-694, 2005
DOI: 10.1364/OPEX.13.000689

Optische Verarbeitung von interferometrischen Streifenbildern und die Fehlererkennung durch Wavelet-Filterung (Optical Processing of Interferometric Fringes and Detection of Faults by Wavelet Filtering)

Author(s): F. Kallmeyer, G. Wernicke, S. Krüger, H. Gruber, W. Osten, D. Kayser

Abstract:

“Das Erkennen und Klassifizieren von Fehlern ist eine wichtige Aufgabe der optischen zerstörungsfreien Materialprüfung in der industriellen Qualitätskontrolle. Eine Vielzahl von Daten über Fehler im Material sind in interferometrischen Streifenmustern enthalten. Diese Daten müssen für die weitere Auswertung reduziert werden. Eine Möglichkeit der Datenreduktion ist durch die Wavelet-Transformation gegeben. Fehler in interferometrischen Streifenmustern sollen durch Wavelet-Filter erkannt, lokalisiert und klassifiziert werden. Wavelet-Funktionen sind sowohl im Ortsraum als auch im Frequenzraum lokalisiert und eignen sich deshalb zur Extraktion von Merkmalen ohne Verlust der räumlichen Zuordnung. Eine Klassifizierung der Interferogramme ist möglich, da die Fehlerklassen charakteristische Eigenschaften haben, die mit bestimmten Klassen von Wavelet-Filtern erkannt werden können.

The detection and classification of faults is a major task for optical non-destructive testing in industrial quality control. Interferometric fringes contain a large amount of data with information about possible defect structures. These data must be reduced for further evaluation. One possible way is the filtering of the images by the adaptive wavelet transform. Faults in interferometric fringe patterns should be detected, localised, and classified by wavelet filters. Wavelet functions are localised in the spatial as well as in the frequency domain. Therefore both the extraction and the localisation of faults is possible by the application of wavelet filters. A classification of interferograms can be realised, because the fault classes have characteristics detectable with a given class of wavelet filters.”

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Publication: tm – Technisches Messen
Issue/Year: tm – Technisches Messen, Volume: 70, Issue: 2, Pages 66-70, 2003
DOI: 10.1524/teme.70.2.66.20110

Recognition of Cuneiform Inscription Signs by use of a Hybrid-Optoelectronic Correlator Device

Author(s): Nazif Demoli, Jörn Kamps, Sven Krüger, Hartmut Gruber, and Günther Wernicke

Abstract:

“A hybrid-optoelectronic correlator device and an algorithm are proposed for recognizing cuneiform inscription signs. The device is based on the extended correlator architecture with three liquid-crystal display(s) (LCD)s and three light detectors: one CCD camera for capturing the input image, one LCD for displaying the input image, two LCDs for the complex correlation filter (amplitude and phase parts), and two detectors for measuring the total and peak intensities of the output correlation information. The recognition algorithm is designed to allow automatic as well as real-time processing. The recognition results are given for the cuneiform signs impressed on an original clay tablet. The investigated tablet (VAT 12890 of the Pergamon Museum, Berlin, Germany) was found in Bogazköy (Hattusha) and dates from the 14th century B.C. It is a fragment of the Epic of Gilgamesh in the Akkadian language with a large number of the sign samples.”

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Publication: Applied Optics
Issue/Year: Applied Optics, Vol. 41, Issue 23, pp. 4762-4774, 2002
DOI: 10.1364/AO.41.004762

Anwendung von Wavelet-Filtern in einem optischen Prozessor zur automatischen Fehlererkennung in Interferogrammen

Author(s): G. Wernicke, S. Krüger, F. Kallmeyer, H. Gruber, Wolfgang Osten, D. Kayser, N. Demoli

Abstract:

“Die Wavelet-Transformation hat sich als leistungsfähiges Werkzeug bei der Erkennung von Strukturen mit definierter räumlicher Auflösung erwiesen. Im vorliegenden Aufsatz wird die Filter-Prozedur in der komplexen Ebene nicht nur auf numerische Simulationen erweitert, sondern auch in optischen Experimenten durch einen zweifachen Frequenzebenen-Korrelator angewandt. Hierzu wurden drei räumliche Lichtmodulatoren (SLM) auf der Basis von Twisted-Nematic-Flüssigkristallen verwendet.”

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Publication: tm – Technisches Messen
Issue/Year: tm – Technisches Messen, Volume: 69, Issue: 5, Page 236
DOI: 10.1524/teme.2002.69.5.236

Optical processing for the detection of faults in interferometric patterns

Author(s): Frank Kallmeyer, Sven Krueger, Guenther Wernicke, Hartmut Gruber, Nazif Demoli, Wolfgang Osten, Daniel Kayser

Abstract:

“The detection and classification of faults is a major task for optical nondestructive testing in industrial quality control. Interferometric fringes, obtained by real-time optical measurement methods, contain a large amount of image data with information about possible defect features. This mass of data must be reduced for further evaluation. One possible way is the filtering of these images applying the adaptive wavelet transform. The wavelet transform has been proved to be a capable tool in the detection of structures with definite spatial resolution. In this paper it is shown the extraction and classification of disturbances in interferometric fringe patterns, the application of several wavelet functions with different parameters for the detection of faults, and the combination of wavelet filters for fault classification. Furthermore the implementation of complex valued wavelet filters and correlation filters is shown. We will present an algorithm to classify interferometric fringe patterns. In order to achieve real-time processing a hybrid opto-electronic system with a digital image processing and an optical correlation module is favored. The calculated wavelet filters are implemented into the optical correlator system that is based on liquid-crystal spatial light modulators. So, all discussed items were verified experimentally in the optical setup. ”

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Publication: SPIE Proceedings
Issue/Year: Proc. SPIE, Vol. 4777, 371 (2002)
DOI: 10.1117/12.472237

Optimization in mapping of correlation filters in a liquid crystal display based frequency plane correlator

Author(s): Alexander Hirsch, Sven Krüger, Günther Wernicke, Hartmut Gruber, and Mathias Senoner

Abstract:

“An optimization procedure for the optical implementation of correlation filters (CFs) in an optical-hybrid frequency plane correlator is presented. Our approach is based on mapping of the given calculated CF values to the values constrained by the available spatial light modulator (SLM) device to achieve the maximum intensity of the output correlation peak. The optimization is provided for the implementation of the CFs using a Sanyo liquid crystal display (SLCD). The commercially available SLCDs are characterized by the phase modulation curves that are (1) nonlinear, (2) of a smaller total phase change interval than desired (0,2 pi) interval, and (3) significantly disturbed by the coupled amplitude variations. For such a case, the optimization achieved by varying a phase shift parameter is explained theoretically, demonstrated numerically, and confirmed experimentally.”

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Publication: SPIE Optical Engineering
Issue/Year: Opt. Eng., Vol. 38, 1058 (1999);
DOI: 10.1117/1.602150
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