Computer-generated Fourier Holograms Research Articles

Computer-Generated Holography Methods for Data Page Reconstruction Using Phase-Only Medium

Achievements in the field of high-speed spatial modulation electrooptic components provide the possibility to create perspective optical-digital diffractive systems for information storage and processing that outperform modern electronic counterparts by utilizing throughput, energy efficiency, and reliability. This work presents a study of computer-generated holography methods that allow the formation of spatially-modulated information signals (data pages) with high accuracy using phase-only spatial light modulators. Computer-generated Fourier hologram fringe patterns were formed using bipolar intensity and double-phase coding. Numerical and experimental results of both methods’ implementation are compared. It was determined that bipolar intensity holograms provide higher data density on the data page if complex digital modulation methods such as multilevel amplitude and phase or quadrature modulation are used to represent data points. Double-phase coding can offer perspective for multilevel amplitude or multilevel intensity modulated data page reconstruction; however, exact control of phase modulation characteristics is required to obtain high reconstruction quality.

Пространственно-спектральная фильтрация светового поля с помощью фазового модулятора света

An improved approach to the synthesis of holographic filters, which are achromatic computer-generated Fourier holograms, is demonstrated, taking into account the spatial and spectral characteristics of the light field. An experimental testing of the obtained filters was carried out based on the use of a holographic wavefront sensor operating on the principles of correlation analysis, using several quasi-monochromatic radiation sources. Using the proposed filters, the longitudinal chromatic aberration was measured, the value of which was λ/3 with an error of λ/50.

Computational Method for Wavefront Sensing Based on Transport-of-Intensity Equation

Recently the transport-of-intensity equation as a phase imaging method turned out as an effective microscopy method that does not require the use of high-resolution optical systems and a priori information about the object. In this paper we propose a mathematical model that adapts the transport-of-intensity equation for the purpose of wavefront sensing of the given light wave. The analysis of the influence of the longitudinal displacement z and the step between intensity distributions measurements on the error in determining the wavefront radius of curvature of a spherical wave is carried out. The proposed method is compared with the traditional Shack–Hartmann method and the method based on computer-generated Fourier holograms. Numerical simulation showed that the proposed method allows measurement of the wavefront radius of curvature with radius of 40 mm and with accuracy of ~200 μm.

The Island CGH, a new coding scheme: concept and demonstration.

Computer generated holograms (CGHs) are powerful optical elements used in many fields, such as wavefront shaping, quality testing of complex optics, and anti-counterfeiting devices. The Lee algorithm is the most used to generate binary amplitude Fourier holograms. Grayscale CGHs are known to give a higher reconstruction quality than binary holograms, but they usually require a cumbersome production process. A very simple and straightforward method of manufacturing rewritable grayscale CGHs is proposed here by taking advantage of two key components: a digital micro-mirror device (DMDs) and a photochromic plate. An innovative algorithm, named Island algorithm, able to generate grayscale amplitude Fourier CGHs, is reported and compared with the standard Lee approach, based on 9 levels. A crucial advantage lies on the fact that the increase or decrease of the quantification does not affect the spatial resolution. In other words, the new coding leads to a higher spatial resolution (for a given CGH size) and a reconstructed image with an order of magnitude higher contrast with respect to the classical Lee-coded hologram. In order to show the huge potential of our approach, a 201 level Island hologram is designed, produced and reconstructed, pushing the contrast to values higher than104. These results reveal the potential of our process as well as our algorithm for generating programmable grayscale CGHs.

Transparency function presentation of computer generated Fourier holograms for complex data page restoration

The present manuscript is dedicated to the development of a holographic data storage (HDS) system based on computer generated Fourier holograms (CGFH). The application of advanced modulation methods such as phase modulation and spatial quadrature amplitude modulation to represent digital data massives as complexly modulated two-dimensional data pages allows one to increase the information capacity of the HDS system. The application of CGFH for storing and reconstructing such data pages is discussed in this article. Particularly, the efficiency of implementation of different light modulation methods that can be used for CGFH transparency function physical realization, such as purely-amplitude, purely phase and combined amplitude and phase, are investigated by means of numeric simulations.

Fast and improved bioimaging via temporal focusing multiphoton excitation microscopy with binary digital-micromirror-device holography.

Conventional temporal focusing-based multiphoton excitation microscopy (TFMPEM) can offer widefield optical sectioning with an axial excitation confinement of a few microns. To improve the axial confinement of TFMPEM, a binary computer-generated Fourier hologram (CGFH) via a digital-micromirror-device (DMD) was implemented to intrinsically improve the axial confinement by filling the back-focal aperture of the objective lens. Experimental results show that the excitation focal volume can be condensed and the axial confinement improved about 24% according to the DMD holography. In addition, pseudouniform MPE can be achieved using two complementary CGFHs with rapid pulse-width modulation switching via the DMD. Furthermore, bioimaging of CV-1 in origin with SV40 genes-7 cells demonstrates that the TFMPEM with binary DMD holography can improve image quality by enhancing axial excitation confinement and rejecting out-of-focus excitation.

Analytical design for computer-generated Fourier holograms of shaded multi-polygonal three-dimensional objects

ABSTRACTWe report here on design and computer simulation of computer-generated holograms for three dimensional (3D) imaging and display. Angular spectrum of general polygon patches was calculated in closed analytical form that includes angular dependence of the intensity and linear gradient of phase at each polygon. Special attention was paid to reduction of the dynamic range in the amplitude transmittance of the hologram by proper random choices of slopes and initial phases of each polygon. Numerical computer simulation results proved that our polygon-patched design demonstrates halftones of object shades and shows expected sharp focusing of different parts of the reconstructed 3D images in their different cross-sections.

Zero Order Correction of Shift-multiplexed Computer Generated Fourier Holograms Recorded in Incoherent Projection Scheme

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Decomposition method for fast computation of gigapixel-sized Fresnel holograms on a graphics processing unit cluster.

A parallel computation method for large-size Fresnel computer-generated hologram (CGH) is reported. The method was introduced by us in an earlier report as a technique for calculating Fourier CGH from 2D object data. In this paper we extend the method to compute Fresnel CGH from 3D object data. The scale of the computation problem is also expanded to 2gigapixels, making it closer to real application requirements. The significant feature of the reported method is its ability to avoid communication overhead and thereby fully utilize the computing power of parallel devices. The method exhibits three layers of parallelism that favor small to large scale parallel computing machines. Simulation and optical experiments were conducted to demonstrate the workability and to evaluate the efficiency of the proposed technique. A two-times improvement in computation speed has been achieved compared to the conventional method, on a 16-node cluster (one GPU per node) utilizing only one layer of parallelism. A 20-times improvement in computation speed has been estimated utilizing two layers of parallelism on a very large-scale parallel machine with 16 nodes, where each node has 16 GPUs.

Optical memory system based on incoherent recorder and coherent reader of multiplexed computer generated one-dimensional Fourier transform holograms

The present article highlights the development results of archive memory holographic system based on application of computer generated Fourier holograms. The proposed idea allows realization of holographic principles of digital data record using simple and compact optical devices. Special interest is paid to synthesis and multiplexed record of one-dimensional Fourier transform holograms. The principal schemes of constructed prototypes of incoherent data recorder and coherent data reader are described in the present paper. The results of experimental implementation of the constructed devices are presented.

Development of projection-type optical scheme for computer-generated Fourier hologram recorder

Projection-type recorders of computer-generated Fourier holograms have potential due to the decreased precision requirements of the optical scheme compared to most known holographic data recorders based on two-beam schemes. In the case of optical memory system development, the reduction factor of the projection scheme requires the application of properly developed optical components. The present report is dedicated to the development of special objectives for the projection scheme of computer-generated Fourier holograms.

Three-dimensional scene encryption and display based on computer-generated holograms.

An optical encryption and display method for a three-dimensional (3D) scene is proposed based on computer-generated holograms (CGHs) using a single phase-only spatial light modulator. The 3D scene is encoded as one complex Fourier CGH. The Fourier CGH is then decomposed into two phase-only CGHs with random distributions by the vector stochastic decomposition algorithm. Two CGHs are interleaved as one final phase-only CGH for optical encryption and reconstruction. The proposed method can support high-level nonlinear optical 3D scene security and complex amplitude modulation of the optical field. The exclusive phase key offers strong resistances of decryption attacks. Experimental results demonstrate the validity of the novel method.

Application of optoelectronic micro-displays for holographic binary data recorder based on computer generated fourier holograms

Present article highlights the researches provided during the development of holographic memory system based on application of computational methods to encode binary data pages as amplitude computer generated Fourier holograms (CGFH). Using electro-optical micro-display and projection optics CGFH can be recorded onto photosensitive medium. The type of display that is used in data recorder determines the specificities of optical scheme architecture with its own limitations and advantages. There are three projection schemes of binary data recorder discussed in the paper. A linear scheme based on transparency-type liquid crystal spatial light modulator (LC SLM), a scheme based on reflection-type liquid crystal on silicon spatial light modulator (LCoS SLM) which uses a beamsplitting cube, and the most compact and simple scheme based on self-emitting OLED-display. The results of experimental implementation of all the three projection schemes for CGFH of binary data pages record onto the holographic carrier and consequent optical reconstruction and analysis of the encoded data are presented.

Wave front sensor based on holographic optical elements

A wavefront sensor (WFS) based on holographic optical elements, namely computer generated Fourier holograms is proposed as a perspective alternative to the Shack-Hartmann sensor. A possibility of single and multimode sensor and the dependence of their characteristics were investigated.

Performance of the 4k phase-only spatial light modulator in image projection by computer-generated holography

We present the experimental results of holographic image projection with the use of the newly available Liquid Crystal on Silicon Spatial Light Modulator with a resolution of 4096 by 2400 pixels and a pixel pitch of 3.74um. This combination of parameters has allowed the highest resolution and throw angle of projected images formed by the reconstruction of computer-generated Fourier holograms. We additionally present the interferometric measurements of the flatness of the panel and evaluation of its diffractive efficiency in the case of displayed binary and saw-tooth diffractive gratings. Full Text: PDF References H. Sasaki, K. Yamamoto, K. Wakunami, Y. Ichihashi, R. Oi, T. Senoh, "Large size three-dimensional video by electronic holography using multiple spatial light modulators", Sci. Rep. 4, 6177 (2014). CrossRef N. Collings, J.L. Christmas, D. Masiyano, W.A. Crossland, "Real-Time Phase-Only Spatial Light Modulators for 2D Holographic Display", J. Disp. Tech. 11, 278 (2015). CrossRef S. Osten, S. Krüger, A. Hermerschmidt, "New HDTV (1920x1080) phase-only SLM", Proc. SPIE 6487, 64870X (2007). CrossRef M. Makowski, "Minimized speckle noise in lens-less holographic projection by pixel separation", Opt. Express 21, 29205 (2013). CrossRef T. Shimobaba, M. Makowski et al., "http://dx.doi.org/10.1016/j.optcom.2014.07.081", Opt. Comm. 333, 274 (2014). CrossRef J. García-Márquez, V. López, A. González-Vega, E. Noé, "Flicker minimization in an LCoS spatial light modulator", Opt. Express 20, 8431 (2012). CrossRef K. Kakarenko et al., "Utilization of the phase flicker of a LCoS Spatial Light Modulator for improved diffractive efficiency", Phot. Lett. Pol. 2, 128 (2010). CrossRef Z. Zhang et al., "Zero-dimensional polariton laser in a subwavelength grating-based vertical microcavity", Light Sci. Appl. 3, 1 (2014). CrossRef

An analysis of the influence of the color rendition of images reconstructed from full-color computer-generated Fourier-transform holograms

The color rendition of an image reconstructed from a color computer-generated Fourier hologram (CCGFH) is both a basic and an important issue in the field of holography. In this study, CCGFHs are encoded with the Burch encoding algorithm and then loaded onto a spatial light modulator for optical reconstruction. The influence of the color rendition of the reconstructed images has been analyzed primarily through experiments. The experimental results show that the individual element size used in encoding the CCGFH is inversely proportional to both the size and the central location of the reconstructed images, whereas the wavelength of the monochromatic light used in optical reconstruction is proportional. Some parameters related to the spectrum, such as different transmittances, half-widths of the three primary color filters and different sensitivity levels to the three primary colors of the complementary metal–oxide–semiconductor (CMOS), affect the color rendition of the reconstructed image. A method for correcting color aberration in reconstructed images is proposed. Using this method, the influence of the wavelength can be corrected by stretching the reconstructed image to an appropriate size and the influence of the spectrum can be corrected by equalizing the spectral sensitivity levels of the CMOS. The color rendition of the reconstruction is improved significantly using the method. The proof-of-principle experiments demonstrate that the method is effective and feasible.

Holographic memory optical system based on computer-generated Fourier holograms

Holography is known to be a prospective tool for storing large amounts of digital information, providing long lasting safety and high speed data access. In this paper, we present a new approach to holographic memory system design. Our method is based on an application of discrete Fourier-transform calculations to encode two-dimensional binary data pages as computer-generated amplitude Fourier holograms (CGFHs). These CGFHs, represented as grayscale raster images, can be displayed with the use of a high resolution amplitude spatial light modulator (SLM) in an optical projection system and exposed on holographic medium with multiple reduction. The optical scheme required for the technical realization of this method appears significantly simpler compared with known holographic memory recording devices; moreover, it can be built using either coherent or incoherent light sources. Coding of data pages by precise pseudorandom phase masks during CGFH synthesis allows us to achieve about 3% of the recorded microholograms diffraction efficiency. The experimental results of CGFH projection recorded with a 20× reduction on photosensitive holographic medium and its reconstruction are presented.

Three random phase encryption technology in the Fresnel diffraction system based on computer-generated hologram

We propose a new method of image encryption using Fourier computer-generated hologram (CGH) in the encryption system of multiple Fresnel diffraction transforms with phase masks. The digital image to be encrypted is modulated by a series of three random-phase masks in Fresnel diffraction system and finally is transformed into a complex-amplitude image which is stationary white noise (in which the information is like stationary-white-noise). Because the complex-amplitude information is not easy to be directly saved, the binary real value Fourier CGH is applied to record it. Compared with the traditional double random-phase image encryption technology, this method adds new keys which enhance the image encryption security and the Fourier CGH greatly improves the antinoise performance.

An ocular wavefront sensor based on binary phase element: design and analysis

A modal wavefront sensor for ocular aberrations exhibits two main advantages compared to a conventional Shack–Hartmann sensor. As the wavefront is detected in the Fourier plane, the method is robust against local loss of information (e.g. local opacity of ocular lens as in the case of cataract), and is not dependent on the spatial distribution of wavefront sampling. We have proposed a novel method of wavefront sensing for ocular aberrations that directly detects the strengths of Zernike aberrations. A multiplexed Fourier computer-generated hologram has been designed as the binary phase element (BPE) for the detection of second-order and higher-order ocular aberrations (HOAs). The BPE design has been validated by comparing the simulated far-field pattern with the experimental results obtained by displaying it on a spatial light modulator. Simulation results have demonstrated the simultaneous wavefront detection with an accuracy better that ∼λ/30 for a measurement range of ±2.1λ with reduced cross-talk. Sensor performance is validated by performing a numerical experiment using the City data set for test waves containing second-order and HOAs and measurement errors of 0.065 µm peak-to-valley (PV) and 0.08 µm (PV) have been obtained, respectively.

Experimental investigation of the closest parallel pulses in holographic femtosecond laser processing

In holographic femtosecond laser processing, diffractive parallel pulses are distorted by phase discontinuities and mutual interference between the neighborhoods in the reconstructed image of a Fourier computer-generated hologram when the interval is smaller than the beam diameter. We investigated holographic fabrication on a glass surface using parallel pulses with different intervals. We found the closest parallel pulses with sufficient separation to avoid mutual interference in holographic femtosecond laser processing. The minimum interval was 2.8 times larger than the diffracted beam diameter. The experimental results were also supported by a computer simulation. Our findings will be very useful in the design of holographic laser processing systems.