Common-path interferometry with one-dimensional periodic filters

Author(s): Victor Arrizón and David Sánchez-de-la-Llave

Abstract:

“We discuss a spatial filtering interferometry setup that employs a periodic spatial filter with either cosine transmittance or binary phase modulation. The setup’s input plane is formed by two separate windows, one of which supports a phase object and the other, a reference beam. Using the appropriate frequency and orientation of the filter produces an interference pattern of the two input fields at the output plane of the system. The main attributes and advantages of the setup are discussed and experimentally illustrated with the example of a binary phase periodic filter implemented with a spatial light modulator.”

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Publication: Optics Letters (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 29, Issue 2, pp. 141-143 (2004)
doi:10.1364/OL.29.000141

Complex modulation with a twisted-nematic liquid-crystal spatial light modulator: double-pixel approach

Author(s): Victor Arrizón

Abstract:

“I modify the double-phase holographic code to implement complex modulation with a transmission twisted-nematic liquid-crystal display. This device is employed in the mostly phase configuration, for which the phase modulation is coupled with a nonconstant amplitude modulation. The modified double-phase code implements arbitrary complex modulation employing the constrained complex modulation of the display.”

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Publication: Optics Letters (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 28, Issue 15, pp. 1359-1361
doi:10.1364/OL.28.001359

Amplitude, Phase, and Hybrid Ternary Modulation Modes of a Twisted-Nematic Liquid-Crystal Display at ~400 nm

Author(s): Judit Reményi, Péter Várhegyi, László Domján, Pál Koppa, and Emõke Lõrincz

Abstract:

“Applicability of a commercial twisted-nematic liquid-crystal display is examined at ~400 nm. Different modulation modes predicted by Jones-matrix calculus are experimentally tested. High contrast amplitude modulation with negligible loss, high contrast and low loss hybrid ternary modulation, and 1.5π continuous phase delay without intensity modulation and with low loss are presented. Simulation results of a 4f holographic system prove the usefulness of the high contrast for amplitude modulation, and the importance of π phase difference between high transmission white levels in a hybrid ternary modulation.”

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Publication: Applied Optics, (subscription required)

Issue/Year/DOI: Applied Optics, Vol. 42, Issue 17, pp. 3428-3434 (2003)
doi:10.1364/AO.42.003428

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 Digital Library, (subscription required)

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

Das digital-optische Lasersystem. Eine neue Generation optischer Komponenten.

Author(s): Günther Wernicke, Sven Krüger, Marcel Rogalla, Stephan Teiwes

Abstract:

“Zwei innovative Bereiche der Optik, die diffraktive Optik und die adaptive Optik, finden ihre gemeinsame Umsetzung in einer sehr jungen Technologie, den räumlichen Lichtmodulatoren. Mikrodisplays, die Lichtwellenfronten hochauflösend in Amplitude und/oder Phase beeinflussen können, fungieren als schaltbare optische Komponenten, die als digital-analoge Schnittstelle optische Transmissionsfunktionen direkt aus dem Optik-Design auf reale Wellenfronten anwenden können. Optische Komponenten also, die sowohl als Linsen, Prismen, Gitter oder auch Hologramme agieren können.”

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Publication: Humboldt-Spektrum, (free download)

Issue/Year/DOI: Humboldt-Spektrum, Issue 1/2003

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, (subscription required)

Issue/Year/DOI: tm – Technisches Messen, Volume: 70 | Issue: 2, Pages 66-70
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 (subscription required)

Issue/Year/DOI: Applied Optics, Vol. 41, Issue 23, pp. 4762-4774
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, (subscription required)

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

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, (subscription required)

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

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