Optimal optical density of the absorbing holographic materials

The theoretical and experimental estimations of optimal optical density of absorbing holographic photopolymer materials for different schemes of holograms recording are carried out. The estimations are based on analytical equations for dependence of the rate photoinduced change of refractive index and effective thickness of the volume holograms on the initial optical density of the photopolymer. Good accordance of theoretical curves and experimental data is observed. The optimal optical density for material with direct chromophore phototransformation is discussed. The text was submitted by the authors in English.     

A framework for holographic scene representation and image synthesis

We present a framework for the holographic representation and display of graphics objects. As opposed to traditional graphics representations, our approach reconstructs the light wave reflected or emitted by the original object directly from the underlying digital hologram. Our novel holographic graphics pipeline consists of several stages including the digital recording of a full-parallax hologram, the reconstruction and propagation of its wavefront, and rendering of the final image onto conventional, framebuffer-based displays. The required view-dependent depth image is computed from the phase information inherently represented in the complex-valued wavefront. Our model also comprises a correct physical modeling of the camera taking into account optical elements, such as lens and aperture. It thus allows for a variety of effects including depth of field, diffraction, interference, and features built-in anti-aliasing. A central feature of our framework is its seamless integration into conventional rendering and display technology which enables us to elegantly combine traditional 3D object or scene representations with holograms. The presented work includes the theoretical foundations and allows for high quality rendering of objects consisting of large numbers of elementary waves while keeping the hologram at a reasonable size     

Eosin Y spirit soluble/Triethanolamine doped poly (methyl methacrylate-co-hydroxyethyl methacrylate) photopolymer for holographic data storage

Volume holographic recording characteristics of a new bulk photopolymer, in which a bimolecular photoinitiator system, Eosin Y spirit soluble (EYss)/Triethanolamine (TEA) was doped in poly (hydroxyethyl methacrylate-co-methyl methacrylate) copolymer matrix have been investigated and reported in this paper. Experimental results show that, by introducing bimolecular photoinitiator into the polymer system, the material sensitivity of holographic recording has been improved. The text was submitted by the authors in English.     

Low cost transparent SU-8 membrane mask for deep X-ray lithography

Deep X-ray lithography masks require good transparency and mechanical resistance to the intense synchrotron X-ray beam, large active areas (cm)² and compatibility with the standard fabrication processes (optical lithography and gold electroforming). Moreover higher resolution can be achieved with low roughness flat membrane. Furthermore multiple aligned exposures require an optically transparent material. Diamond like Carbon membranes fulfill those requirements but have a prohibitive cost. Our approach consists in using an SU-8 epoxy resin layer as membrane material. In this communication the different steps of the fabrication process will be presented, as well as the results obtained using the mask for particular applications.     

Dual-side see-through integral imaging 3D display system based on lens array holographic optical element

We propose a dual-side see-through integral imaging 3D display based on a lens array holographic optical element (LAHOE). The display system consists of two projectors and a LAHOE. The LAHOE is fabricated according to the theory of reflective volume holograms. An interference pattern is formed by a plane-wave beam and a spherical-wave array beam, and the interference pattern is recorded into a photopolymer material. Thus, the LAHOE is formed. When a reference beam is projected into the LAHOE, the wavefront of a convex micro-lens array is reconstructed. When a phase conjugation reference beam is projected into the LAHOE, the wavefront of a concave micro-lens array is reconstructed. So, the LAHOE possesses the optical properties of a convex micro-lens array and a concave micro-lens array. The proposed display is developed using integral imaging principle and it realizes dual-side see-through integral imaging 3D display.     

Comparative analysis of optical arrangements intended for recording of holograms with optically encoded and concealed images

In the paper we analyze some optical arrangements intended for recording of holograms with optical encoding of the image. In the first section on the basis of the Opto-electronic systems theory we are considering the processes of hologram recording and reconstruction with optically encoded images for Fourier and Fresnel hologram recording schemes with encoding mask in reference and subject branches. In the second section the detailed analysis of these schemes with encoding mask consisting of a set of secondary point sources placed in reference branch is made. The results of influence of optical elements installing inaccuracy in the arrangement of image retrieval on a quality of this image are obtained. The hologram recording arrangement for the further studies on the base of the analysis is chosen. In the third section we estimate a signal to noise ratio in the image plane for the arrangements selected. Analysis of multiplexing holograms using possibility with image optical encoding is made. The article is published in the original.     

Specificities of data page representation in projection type optical holographic memory system

The matter of the present article covers the results obtained during the development of holographic memory record system based on projection of computer-generated amplitude Fourier holograms. The basic issue is the investigation of representation specificities of binary data pages, which were choose to be encoded on computer-generated amplitude Fourier hologram and then recorded on photosensitive medium as microhologram using simple projection optics and spatial light modulator. Limitations of data page resolution caused by limited resolution of SLM that is used to display the digitally synthesized holograms are discussed. Also the results of random phase coding of data page during the holograms synthesis research are presented.     

Multiplane full-color phase-only holograms generation based on iterative algorithm with a modified amplitude constraint

Depth-division multiplexing (DDM) is distinguished for generating full-color holograms. However, this method is confronted with such issues as poor quality and severe crosstalk when reconstructing multiplane color images. In this paper, we propose an improved iterative method based on Gerchberg-Saxton (GS) algorithm to generate multiplane full-color phase-only holograms (POHs), and the information of red (R), green (G), and blue (B) channels of images is recorded in three POHs, respectively. In the iterative process, we introduce an improved hologram plane constraint that consists of modified amplitudes given a static weighting factor, and display the reconstruction results for three-layer images, which ultimately improve the quality of the reconstructed images and effectively avoid the crosstalk among different color channels. And compared with GS algorithm, our method can effectively balance the reconstruction quality of three-color channels of each image. The feasibility of the method is verified by numerical simulations and optical experiments.     

A method of chromatic aberration compensation in holographic projection display based on a single spatial light modulator

In this paper, we propose a method of chromatic aberration compensation in holographic projection display based on a single spatial light modulator (SLM). By combining the hologram of the object with that of the digital lens, three color holograms with different focal lengths can be generated. Then, the SLM is divided into three parts, input three color holograms with different focal lengths to the SLM, and each occupies one‐third area of the SLM. We verify our method, and the results show its feasibility.     

A full‐color eyewear display using planar waveguides with reflection volume holograms

Abstract— A full‐color eyewear display with over 85% see‐through transmittance with a 16° horizontal field of view was developed. Very low color crosstalk, less than 0.008 Δu′v′ uniformity, and 120% NTSC color gamut were achieved. Waveguides with two in‐ and out‐coupling reflection volume hologram elements enabled a simple configuration that has an optical engine beside the user's temples. The reflection volume hologram elements used on the waveguides realized a small thickness of 1.4 mm for each waveguide, and an out‐coupling reflection volume hologram used as an optical combiner contributed a high see‐through transmittance of 85% due to its wavelength selectivity. However, there are technical challenges in achieving a reasonable screen size and quality color images with optics that utilize holographic waveguides because holograms have large chromatic dispersions compared to conventional optical elements such as lenses and mirrors. Approaches to overcome these issues are described.     

一种新的傅立叶变换全息图的计算机生成方法

首先以模拟退火方法计算了二元傅立叶变换全息图和四相位傅立叶变换全息图,然后以傅立叶变换性质为基础,提出了一种逆向求解全息图方法。在该方法中,将被显示的图象作为全息图的傅立叶变换面,图象的每个象素由全息面中特定空间频率的正弦光栅的傅立叶变换形成,各正弦光栅的空间频率由象素坐标决定,全息图则为一系列正弦光栅的线性迭加。该方法是一种计算机生成全息图的新方法。     

菲涅耳全息图的CCD记录及重现

为了更好地进行菲涅耳全息图的CCD记录及重现,设计了一种CCD同轴全息图的重构算法,该方法首先用CCD代替传统干版直接记录菲涅耳同轴全息图,并以位图形式存储到计算机中;然后利用数值计算代替光学衍射过程来再现物体的像;最后通过实验验证了该算法及数字全息图的不可撕毁性。     

Self-conjugation heteroassociative memories using thin static nonlinearly recorded holograms

The problem of all-optical holographic associative memory is elaborated with account of recording nonlinearity of thin static off-axis holograms. It is shown that the recording nonlinearity results in reconstruction of angularly separated diffraction orders, in one of which (minus 2nd) the complex congugate associative response is reconstructed as such a hologram is read out by incomplete version of the stored pattern. Being angularly separated from the readout beam, the phase conjugate response occurs be error-corrected. Moreover, recording nonlinearity provides unique feasibilities for associative coupling and reconstruction of heteroassociations beteween complex patternts accumulated at one carrier without interference. This feasibility obliged just to natural recording nonlinearity (‘nonidealness’) of registration medium leads to limit generalization of the concept of holographic associative memory.     

Viewing‐angle enhancement in holographic reflective displays by nanoscale holographic patterning

Abstract— This work presents a method to increase the viewing angle of holographic polymer‐dispersed liquid‐crystal (H‐PDLC) reflective displays. One of the drawbacks to H‐PDLC technology is the existence of a narrow viewing angle. We present a way to alleviate this problem by structuring the phase front of the recording beams to increase the viewing cone of the display. Analysis of the diffractive properties of these holograms shows that the macroscopic and the nanoscale morphologies both play a role in the optical properties of the films.     

High-resolution long-array thermal ink jet printhead fabricated by anisotropic wet etching and deep Si RIE

This paper describes the fabrication and characterization of a thermal ink jet (TIJ) printhead suitable for high speed and high-quality printing. The printhead has been fabricated by dicing the bonded wafer, which consists of a bubble generating heater plate and a Si channel plate. The Si channel plate consists of an ink chamber and an ink inlet formed by KOH etching, and a nozzle formed by inductively couple plasma reactive ion etching (ICP RIE). The nozzle formed by RIE has squeezed structures, which contribute to high-energy efficiency of drop ejector and, therefore, successful ejection of small ink drop. The nozzle also has a dome-like structure called channel pit, which contributes to high jetting frequency and high-energy efficiency. These two wafers are directly bonded using electrostatic bonding of full-cured polyimide to Si. The adhesive-less bonding provided an ideal shaped small nozzle orifice. Use of the same material (Si substrate) in heater plate and channel plate enables the fabrication of high precision long printhead because no displacement and delamination occur, which are caused by the difference in thermal expansion coefficient between the plates. With these technologies, we have fabricated a 1" long printhead with 832 nozzles having 800 dots per inch (dpi) resolution and a 4 pl. ink drop volume.     

Special-purpose computer for holography HORN-4 with recurrence algorithm

We designed and built a special-purpose computer for holography, HORN-4 (HOlographic ReconstructioN) using PLD (Programmable Logic Device) technology. HORN computers have a pipeline architecture. We use HORN-4 as an attached processor to enhance the performance of a general-purpose computer when it is used to generate holograms using a “recurrence formulas” algorithm developed by our previous paper. In the HORN-4 system, we designed the pipeline by adopting our “recurrence formulas” algorithm which can calculate the phase on a hologram. As the result, we could integrate the pipeline composed of 21 units into one PLD chip. The units in the pipeline consists of one BPU (Basic Phase Unit) unit and twenty CU (Cascade Unit) units. These CU units can compute twenty light intensities on a hologram plane at one time. By mounting two of the PLD chips on a PCI (Peripheral Component Interconnect) universal board, HORN-4 can calculate holograms at high speed of about 42 Gflops equivalent. The cost of HORN-4 board is about 1700 US dollar. We could obtain 800×600 grids hologram from a 3D-image composed of 415 points in about 0.45 sec with the HORN-4 system.     

Laser scanning path generation considering photopolymer solidification in micro-stereolithography

It is essential to automate the scanning path generation process to effectively implement the micro-stereolithography. However, a scanning path that is generated based only on a 3D CAD model introduces dimensional inaccuracies. In micro-stereolithography, the photopolymer solidification is affected by fabrication conditions, such as the optical properties (laser power, laser scanning speed, laser scanning pitch focusing condition, etc.) and material properties of the photopolymer. Thus, the photopolymer solidification phenomena must be considered when generating a laser scanning path. In this paper, a scanning path generation algorithm that uses 3D CAD data and considers the photopolymer solidification phenomena is proposed to improve the dimensional accuracy in micro-stereolithography. Multi-line photopolymer solidification experiments were performed for various laser scanning conditions to examine the photopolymer solidification phenomena. From these experiments, linear relations between the solidification length (width) and scanning length (width) were acquired and stored in a database. Subsequently, these data were utilized to compensate the scanning path of the laser beam. In addition, experiments for determining the layer thickness in the z-direction were performed and these results were also used in the scanning path generation algorithm.This research was supported by the Highly Advanced National Project (http://www.most.go.kr), which performs some of the National R&D Program, and sponsored by the Korean Ministry of Science and Technology under the contract project code M10214000116-02B1500-02010.     

“Red Tweezers”: Fast,customisable hologram generation for optical tweezers

Holographic Optical Tweezers (HOT) are a versatile way of manipulating microscopic particles in 3D. However, their ease of use has been hampered by the computational load of calculating the holograms, resulting in an unresponsive system. We present a program for generating these holograms on a consumer Graphics Processing Unit (GPU), coupled to an easy-to-use interface in LabVIEW (National Instruments). This enables a HOT system to be set up without writing any additional code, as well as providing a platform enabling the fast generation of other holograms. The GPU engine calculates holograms over 300 times faster than the same algorithm running on a quad core CPU. The hologram algorithm can be altered on-the-fly without recompiling the program, allowing it to be used to control Spatial Light Modulators in any situation where the hologram can be calculated in a single pass. The interface has also been rewritten to take advantage of new features in LabVIEW 2010. It is designed to be easily modified and extended to integrate with hardware other than our own.     

Discrete Representation of Holograms of Halftone Objects

A comparative analysis of methods for calculating digital holograms based on discrete transformations for various types of objects is presented. Qualitative results of synthesis and reconstruction of holograms are obtained, as well as examples of the realization of some of the types of holograms considered. The quality of digital hologram recovery is estimated by calculation of signal-tonoise ratio (SNR) and root-mean-square error (RMSE).