Malgorzata Kujawinska

Digital fringe projection system for large-volume 360-deg shape measurement

We present a system for 3-D shape measurement in large volumes based on combined digital-fringe-Gray-code projection. With the help of a new calibration procedure, the system provides accurate results despite its crossed-axis configuration and unknown aberrations of the digital light projector and CCD camera. Also, the separate clouds of points captured from different directions are automatically merged into the main cloud. The system delivers results in the form of (x,y,z) coordinates of the object points with additional (R,G,B) color information about their texture. Applicability of the system is proven by presenting sample results of measurements performed on complex objects. The uncertainty of the system was estimated at 10 4 of the measurement volume.

Tomographic phase microscopy of living three-dimensional cell cultures

Abstract. A successful application of self-interference digital holographic microscopy in combination with a sample-rotation-based tomography module for three-dimensional (3-D) label-free quantitative live cell imaging with subcellular resolution is demonstrated. By means of implementation of a hollow optical fiber as the sample cuvette, the observation of living cells in different 3-D matrices is enabled. The fiber delivers a stable and accurate rotation of a cell or cell cluster, providing quantitative phase data for tomographic reconstruction of the 3-D refractive index distribution with an isotropic spatial resolution. We demonstrate that it is possible to clearly distinguish and quantitatively analyze several cells grouped in a “3-D cluster” as well as subcellular organelles like the nucleoli and local internal refractive index changes.

High accuracy Fourier transform fringe pattern analysis

Abstract The principle of the Fourier transform method of fringe pattern analysis is described with emphasis on the refinements for high accuracy measurements. Characteristics of the main sources of errors of the retrieved phase in respect to the interferogram features and the modified software procedure are given. The quantitative results of the analysis of computer-generated and real interferograms are presented. The possibility of obtaining the overall accuracy of λ/100 is proved.

Wide angle holographic display system with spatiotemporal multiplexing.

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.

Application of liquid crystal (LC) devices for optoelectronic reconstruction of digitally stored holograms

Abstract Recent advances in high-resolution CCD detectors allow the development of the concept of digital holography that relies on the capture of 2D microinterferograms and their further numerical reconstruction. This approach is valid for optical metrology applications as it gives direct access to the phase and intensity of an object at the selected distance “ d ”. However, it is not convienient for direct 3D-display purposes. This is the reason why the authors propose the optoelectronic reconstruction of a hologram that is digitally recorded and transferred to another optoelectronic medium. The application of LCD matrices and optically addressed liquid crystal cells as reconstruction media is discussed. Their applicability for computer-generated and optical holograms is tested by means of simple experiments. The problems connected with limited resolution of the recording (CCD) and reconstruction (LCD, DMD) devices are considered. The comparison of the results obtained by numerical and optoelectronic means is presented, together with a discussion of the limitations and further possibilities of these techniques.

Spatial-carrier phase-shifting technique of fringe pattern analysis

The spatial-carrier phase shifting (SCPS) technique that is related to both Fourier transform and phase-shifting methods of calculating the phase is analyzed. In this technique, a large amount of tilt is introduced into an interferogram, so that the phase difference between successive pixels equals (pi) /2. Three successive pixels are used to recover the phase using the adequate standard phase shifting formula. The detailed error analysis is presented. Examples of application of this method in conventional and moire interferometry, as well as in optical triangulation, are shown. As the SCPS technique requires a single frame only for phase calculation, it is capable of making high-speed measurements or performing testing in adverse environments.

Reconstruction of refractive-index distribution in off-axis digital holography optical diffraction tomographic system

In the paper the optical diffraction tomographic system for reconstruction of the internal refractive index distribution in optical fiber utilizing grating Mach-Zehnder interferometer configuration is explored. The setup applies afocal imaging. Conventional grating application gives, however, highly aberrated object beam producing incorrect refractive-index reconstructions. The grating inherent aberrations are characterized, its influence on both image projections and refractive index reconstructions is presented. To remove aberrations and enable tomographic reconstruction a novel digital holographic algorithm, correcting optical system imaging, is developed. The algorithm uses plane wave spectrum decomposition of optical field for solving diffraction problem between parallel and tilted planes and enabling correction of imaging system aberrations. The algorithm concept was successfully proved in simulations and the experiment.

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

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.

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

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.

Digital Holographic Capture and Optoelectronic Reconstruction for 3D Displays

The application of digital holography as a viable solution to 3D capture and display technology is examined. A review of the current state of the field is presented in which some of the major challenges involved in a digital holographic solution are highlighted. These challenges include (i) the removal of the DC and conjugate image terms, which are features of the holographic recording process, (ii) the reduction of speckle noise, a characteristic of a coherent imaging process, (iii) increasing the angular range of perspective of digital holograms (iv) and replaying captured and/or processed digital holograms using spatial light modulators. Each of these challenges are examined theoretically and several solutions are put forward. Experimental results are presented that demonstrate the validity of the theoretical solutions.