Showing papers by "Malgorzata Kujawinska published in 2012"

Extended viewing angle holographic display system with tilted SLMs in a circular configuration.

Abstract: This paper presents an extended viewing angle holographic display for reconstruction of real world objects in which the capture and display systems are decoupled. This is achieved by employing multiple tilted spatial light modulators (SLMs) arranged in a circular configuration. In order to prove the proper reconstruction and visual perception of holographic images the Wigner distribution function is employed. We describe both the capture system using a single static camera with a rotating object and a holographic display utilizing six tilted SLMs. The experimental results based on the reconstruction of computer generated and real world scenes are presented. The coherent noise removal procedure is described and implemented. The experiments prove the possibility to view images reconstructed in the display binocularly and with good quality.

Wide angle holographic display system with spatiotemporal multiplexing.

Abstract: This paper presents a wide angle holographic display system with extended viewing angle in both horizontal and vertical directions. The display is constructed from six spatial light modulators (SLM) arranged on a circle and an additional SLM used for spatiotemporal multiplexing and a viewing angle extension in two perpendicular directions. The additional SLM, that is synchronized with the SLMs on the circle is placed in the image space. This method increases effective space bandwidth product of display system data from 12.4 to 50 megapixels. The software solution based on three Nvidia graphic cards is developed and implemented in order to achieve fast and synchronized displaying. The experiments presented for both synthetic and real 3D data prove the possibility to view binocularly having good quality images reconstructed in full FoV of the display.

Computation of diffracted fields for the case of high numerical aperture using the angular spectrum method

Abstract: The angular spectrum (AS) method is a popular solution to the Helmholtz Equation without the use of approximations. In this work, new criteria on sampling requirements are derived using the Wigner distribution (WD). It is shown that for the case of high numerical aperture the conventional AS method requires a very large amount of zero-padding, making it impractical due to requirements on memory and computational effort. This work proposes the use of a modified AS algorithm that evaluates only non-zero components of the field. The results obtained from the WD combined with the modified AS algorithm enable an accurate and efficient field computation for cases where the conventional AS method cannot be implemented.

Holographic Capture and Display Systems in Circular Configurations

Abstract: This paper presents a novel method of multi-spatial light modulator (SLM) holographic image display that enables wide angle reconstruction of images of real world objects. The image data are delivered by means of digital holography. The capture and display systems are arranged in a circular configuration. In order to support the proper information flow between the multi-sensor capture and multi-SLM display systems we perform analysis using the Wigner distribution function. We also consider a mismatch of the capture and display configurations as well as the visual perception of the displayed image. Experimental results based on the reconstruction of real world scenes are presented that demonstrate the validity of the theoretical solutions. A single camera is used to record the digital holograms, where the object is rotated between captures, and these holograms are then displayed on a circular configuration of SLMs. The results show the limitation of multi-SLM holographic displays in terms of visual perception. These problems arise from the limited angular distribution of the SLMs on a display circle and the presence of gaps between the SLMs.

Application of Hybrid FEM-DIC Method for Assessment of Low Cost Building Structures

Abstract: In this work pre-operating tests of low-cost building structures have been presented. A hybrid experimental-numerical methodology has been used to determine the influence of an external, environmental load on the overall endurance of a hangar made of self-supporting metal-plates. Numerical simulations carried out on a FEM model have been consequently verified by measurements of the structure performed with the 3D Digital Image Correlation method and as a result, a detailed, calibrated FEM model of the structure has been developed.

LCoS SPATIAL LIGHT MODULATORS AS ACTIVE PHASE ELEMENTS OF FULL-FIELD MEASUREMENT SYSTEMS AND SENSORS

Abstract: Spatial light modulators (SLM) are devices used to modulate amplitude, phase or polarization of a light wave in space and time. Current SLMs are based either on MEMS (micro-electro-mechanical system) or LCD (liquid crystal display) technology. Here we report on the parameters, trends in development and applications of phase SLMs based on liquid crystal on silicon (LCoS) technology. LCoS technology was developed for front and rear projection systems competing with AMLCD (active matrix LCD) and DMD (Digital Mirror Device) SLM. The reflective arrangement due to silicon backplane allows to put a high number of pixels in a small panel, keeping the fill-factor ratio high even for micron-sized pixels. For coherent photonics applications the most important type of LCoS SLM is a phase modulator . In the paper at first we describe the typical parameters of this device and the methods for its calibration. Later we pres ent a review of applications of phase LCoS SLMs in imaging, metrology and beam manipulation, developed by th e authors as well as known from the literature. These include active and adaptive interferometers, a smart holographic camera and holographic display, microscopy modified in illuminating and imaging paths and active sensors.

Interferometric and tomographic investigations of polymer microtips fabricated at the extremity of optical fibers

Abstract: In this paper we present a simple method of manufacturing micrometer-sized polymer elements at the extremity of both single mode and multimode optical fibers and its possible modifications in order to provide requested functionalities. We show that the knowledge about 3D distribution of refractive index and birefringence in these elements is required and that interferometric and elastooptics tomography are the methods which provide these data. Exemplary polymer microtips manufactured from the polymeric material with different concentration of heptafluorobutyric acid are investigated in tomographic systems and the obtained results are discussed in reference to the theoretically expected refractive index distributions.

Modified two-dimensional digital image correlation method with capability of merging of data distributed in time

Abstract: In this article an analysis of two-dimensional (2D) digital image correlation (DIC) data captured over a long period of time is presented, where the case of a 2D DIC setup is not fixed in the same position between consecutive measurements. An implementation of the data merging procedure is described and a proof of concept is provided using example measurements for both: a numerical model and a physical model. An evaluation of the accuracy of the method and main sources of errors are also presented. The developed method can be used for long-term monitoring of different kinds of objects, which is particularly important for the use of DIC technique in application, e.g., building engineering, building control, or power engineering.

Application of Image Based Methods for Monitoring and Measurements of Structures in Power Stations

Abstract: The implementation of selected full-field optical methods for monitoring and measurements of displacements, strains and shape of structures in power plants are reported. Digital Image Correlation, Fringe Projection and integrated thermovision-DIC method have been utilized for monitoring and control of repair processes of selected elements during general overhauls in power plants, including control of welds annealing process in boiler drum and steam pipes and measurements of geometry changes of steam pipes in “hot” and “cold” states. The experience gathered during the measurement sessions in power plants has been used for enhancement and adaptation of typical architecture of measurement systems to demanding and difficult industrial environment conditions. The measurements had been carried out in different power plants located in Poland. The possible future application of full-field optical measurement methods as the alternative to standard techniques (ultrasound, X-ray, strain gauges) and their advantages and disadvantages are discussed.

Twyman–Green-type integrated laser interferometer array for parallel MEMS testing

Abstract: In this paper the concept, design and realization of an integrated laser interferometer are presented. The integrated Twyman?Green-type interferometer is based on micro-optical diffraction gratings in the resonance domain. The fabrication process of these gratings and their assembly in the functional interferometer will be discussed in detail. The interferometer, available in array configuration of 5???5 channels, is part of a test set-up for a fast characterization of M(O)EMS devices at a wafer level. The first results of the interferometric measurements on an MEMS object are presented.

Holographic Television: Status and Future

Abstract: Recent history of visual multimedia is given by a rapid development of three-dimensional imaging, visualization and display. This includes stereoscopic and autostereoscopic systems, head mounted displays, integral photography and digital holography [1,2,3]. Although almost all currently available 3D displays used in 3D TV are stereoscopic, a viewer still suffers a certain discomfort due to physical duplication of 2D light distribution which reaches his eyes. The technology which could potentially offer more comfortable and realistic 3D capture and display is holography. It has been recognized by Lieth and Upatnieks already in 1962 [4], however due to several limitations connected with an analog versus digital data capture and limited bandwidth of hologram transmission systems the real implementation of optical holography in television had not been realized. The dormancy of the research works on the holographic television lasted until 1990 when high resolution CCD cameras, fast image processing computers and spatial light modulators become available [5]. The advances in these electro-optics products speed up works at both electro-holographic video and displays as well as the full concept of 3D holographic television. Below we report on history, present works, limitations and prediction for future development of the research on these topics.

Accurate and quantitative phase retrieval methods for a series of defocused images with application to in-line Gabor microscopy

Abstract: In 1948, Gabor proposed a lens-less in-line holographic microscope where the recorded hologram is a result of interference of both reference wave and the wave diffracted from the object. In this work, an analysis of the hologram formation and sampling issues are presented using the local-spatial frequency distribution at the camera plane. Techniques are presented that enable the reconstruction of the complex object wave at the camera plane from a series of defocused images. It is suggested to use the band-limited angular spectrum method for the back-propagation of the field components, so that an accurate and quantitative estimate of the object-wave at the object plane is obtained. The reconstruction procedure does not rely on the paraxial approximation and is therefore applicable to the case of high NA beams.

Wide angle digital holographic interferometry with real-time optical reconstruction

Abstract: In the paper we will discuss the wide angle capture and display systems applied for digital holographic interferometry (DHI). The static capture system is based on a single camera and an object located at a rotational stage. The holograms are captured sequentially in time during object loading and the phases at a hologram plane are calculated by phase shifting method. The dynamic capture system employs several cameras located around an object and simultaneous capture of several holograms is performed with the frequency of impulse laser applied. For both DHI capture systems the holographic display configuration is proposed. Multiple spatial light modulators aligned in circular configuration are put to work together. In the paper the main requirements for optical reconstruction of resultant interferograms originated from both capture systems are discussed. The results of experiments are presented and analyzed.

Low Cost Laser Triangulation System for Rail and Guide Wear Evaluation

Abstract: Periodic rail and guide wear evaluation is essential for their reliability and safety. By regular measurement it is possible to determine whether certain rail or guide fragments need urgent replacement reducing the risk of accidents. In the paper at first we present the measurement system, which is intended to operate in small rail systems such as trams, light rail, narrow gauge rail, mine rail. It can be adopted to operate in two modes: manual pulled along the rail or guide or automatic attached to a measurement car. The measuring system is flexible enabling the measurement of different features of rail or guide geometry depending on the needs. By simplifying the design, the system can be operated by an unqualified personnel, however final wear evaluation has to be done by a qualified engineer. Finally we present the exemplary results of measurements performed on a selected rail section and the full data processing path. The method of relative calibration and synchronizing data from several measurement modules is also reported.

Micromachined array-type Mirau interferometer for MEMS metrology

Abstract: We present the development of an array-type micromachined Mirau interferometers, operating in the regime of low coherence interferometry (LCI) and adapted for massively parallel inspection of MEMS. The system is a combination of free-space microoptical technologies and silicon micromachining, based on the vertical assembly of two glass wafers. The probing wafer is carrying an array of refractive microlenses, diffractive gratings to correct chromatic and spherical aberrations and reference micro-mirrors. The semitransparent beam splitter plate is based on the deposition of a dielectric multilayer, sandwiched between two glass wafers. The interferometer matrix is the key element of a novel inspection system aimed to perform parallel inspection of MEMS. The fabricated demonstrator, including 5x5 channels, allows consequently decreasing the measurement time by a factor of 25. In the following, the details of fabrication processes of the micro-optical components and their assembly are described. The feasibility of the LCI is demonstrated for the measurement of a wafer of MEMS sensors.

Status and Issues of Digital Holographic Display

Abstract: Holography is believed as one of the most prospective three-dimensional display technologies. Recently, many remarkable successes have been reported to solve practical issues in holographic display. We review and discuss candidate solutions and current status of holographic technology.