Huadong Zheng

High-quality three-dimensional holographic display with use of multiple fractional Fourier transform

In order to realize holographic display of three-dimensional (3D) objects and suppress zero-order light, conjugate image, and speckle noise, a novel method is proposed based on multiple fractional Fourier transform (M-FrFT) for calculating holograms of 3D objects. A series of kinoforms are generated by adding pseudorandom phase factor (PPF) to object planes in calculating each kinoform, and generating the PPF randomly again in the next kinoform calculation. The reconstructed images from kinoform sequence are superposed together in order to suppress the speckle noise of reconstructed image and improve the contrast and detail resolution of the reconstructed images. The qualities of reconstructed images from single amplitude hologram, single kinoform, and kinoform sequence calculated by M-FrFT are compared. The effects of suppressing speckle noise are analyzed by calculating the speckle index of numerical reconstructed images. The analytical results illustrate that, with the proposed method for 3D holographic display, the zero-order light, conjugate image, and speckle noise can be suppressed, and the qualities of reconstructed images can be improved significantly.

Holographic imaging of full-color real-existing three-dimensional objects with computer-generated sequential kinoforms

We propose a computational method for generating sequential kinoforms of real-existing full-color threedimensional (3D) objects and realizing high-quality 3D imaging. The depth map and color information are obtained using non-contact full-color 3D measurement system based on binocular vision. The obtained full-color 3D data are decomposed into multiple slices with RGB channels. Sequential kinoforms of each channel are calculated and reconstructed using a Fresnel-diffraction-based algorithm called the dynamicpseudorandom-phase tomographic computer holography (DPP-TCH). Color dispersion introduced by different wavelengths is well compensated by zero-padding operation in the red and green channels of object slices. Numerical reconstruction results show that the speckle noise and color-dispersion are well suppressed and that high-quality full-color holographic 3D imaging is feasible. The method is useful for improving the 3D image quality in holographic displays with pixelated phase-type spatial light modulators (SLMs).

Full-color holographic display with increased-viewing-angle [Invited]

Among the important features of holographic displays are the wide viewing angles and the full color of the reconstructed images. The present work focuses on achievement of both features. We propose an increased-viewing-angle full-color holographic display using two tiled phase-only spatial light modulators (SLMs), a 4f concave mirrors system, and a temporal-spatial multiplexing method. The 4f optical system consists of two concave mirrors and serves to increase the viewing angle. A temporal-spatial multiplexing synchronization control (TSMSC) method is developed to achieve a full-color image and to remove the color crosstalk of the image. We calculate RGB phase-only holograms of a computer-generated color pyramid by using a slice-based Fresnel diffraction algorithm. The experimental results indicate that the proposed display system is feasible to reconstruct a full-color holographic 3D image with a viewing angle of 12.8°, which is about 3.8 times wider than the viewing angle formed by a single SLM.

Study on permanent holographic recording in trimethylol propane triacrylate-based photopolymer films with high diffraction efficiency

We investigate permanent hologram recording in a photosensitive material with high diffraction efficiency (DE) of ∼90%. We successfully recorded three-dimensional (3D) object information, gratings, and “hogel” images in this photopolymer film without postprocessing. In addition, we study multiplexed hologram storage in this material. Because of its high resolution, high DE, and lack of need for electric field and postprocessing, this photopolymer may be suitable for analog hologram, digital hologram, and big data permanent storage. Our study proposes a potential holographic recording material to apply in large size static 3D holographic displays, including analog hologram storage, digital hologram prints, holographic anticounterfeiting, and big data holographic disks.

Latest development of display technologies

In this review we will focus on recent progress in the field of two-dimensional (2D) and three-dimensional (3D) display technologies. We present the current display materials and their applications, including organic light-emitting diodes (OLEDs), flexible OLEDs quantum dot light emitting diodes (QLEDs), active-matrix organic light emitting diodes (AMOLEDs), electronic paper (E-paper), curved displays, stereoscopic 3D displays, volumetric 3D displays, light field 3D displays, and holographic 3D displays. Conventional 2D display devices, such as liquid crystal devices (LCDs) often result in ambiguity in high-dimensional data images because of lacking true depth information. This review thus provides a detailed description of 3D display technologies.

Method for removing longitudinal chromatism in full color holographic projection system

Hologram, as a type of diffractive optical element, is sensitive to wavelength in the process of optoelectronic reconstruction. Due to the different wavelengths of three prime colors used in full color holographic projections, there are chromatisms which badly spoil the reconstructed image. The chromatisms are composed of transverse and longitudinal chromatisms. For a computer generated hologram, transverse chromatism can be compensated by resampling the object information. However, it becomes more complex for longitudinal chromatism. This paper analyzes how the image is reconstructed from the phase-type hologram in a holographic projection system and the causations of longitudinal chromatism. To remove it, this paper proposes loading a specially designed phase distribution on a phase-type hologram. The advantage of this method is that it can be achieved by computer calculation and without adding any hardware such as achromatic optical element. A time-sharing system for a full-color hologram projection is developed in this paper. Comparisons have been made between the reconstructed images with and without chromatism. The experimental result shows that the method is effective in removing longitudinal chromatism and the quality of the reconstructed image is improved.

Holographic storage of three-dimensional image and data using photopolymer and polymer dispersed liquid crystal films

We present holographic storage of three-dimensional (3D) images and data in a photopolymer film without any applied electric field. Its absorption and diffraction efficiency are measured, and reflective analog hologram of real object and image of digital information are recorded in the films. The photopolymer is compared with polymer dispersed liquid crystals as holographic materials. Besides holographic diffraction efficiency of the former is little lower than that of the latter, this work demonstrates that the photopolymer is more suitable for analog hologram and big data permanent storage because of its high definition and no need of high voltage electric field. Therefore, our study proposes a potential holographic storage material to apply in large size static 3D holographic displays, including analog hologram displays, digital hologram prints, and holographic disks.

Speckle suppression in holographic displays using temporal averaging effect combined with rotating symmetric diffuser

The speckle noise will seriously influence the quality of reconstructed images in holographic displays based on spatial light modulators (SLMs). In order to suppress the speckle noise quickly, we propose a method which combines temporal averaging effect by superposing multi sub-frame images and adding a rotating symmetric diffuser in optical path. The sub-frame images are reconstructed from sequential sub-frame kinoforms. The sequential kinoforms are calculated using Fresnel diffraction based algorithm by adding dynamic pseudorandom initial phase factors. A rapidly rotating symmetric diffuser is replaced the pinhole in optical path to produce illumination light sources with various speckle patterns over a short periods of time. Hence, various holographic images with different speckle patterns can be reconstructed and superposed to reduce the speckle noise. Optical reconstructions with a phase-only SLM show that, with the proposed method, the speckle noises are well suppressed by superposing fewer sub-frame images compared to use temporal averaging method only. The proposed method is useful for improving the quality of reconstructions in holographic displays with pixelated SLMs.

Reduction of speckle noise by multi-kinoforms in holographic three-dimensional display

In order to avoid missing low-frequency information of three-dimensional (3D) object, pseudorandom phase is generally added to object planes in tomographic hologram calculation, but speckle noise is inevitably introduced. A novel method is proposed to improving the quality of image reconstructed from kinoform generated by computational tomographic holography. Multi-kinoforms of 3D object are calculated, and the images of these kinoforms are superposed to suppress the speckle noise of reconstructed image. An invariant pseudorandom phase is added to each object plane in calculating each kinoform, and the pseudorandom phase is generated randomly again in next kinoform calculating. Digital reconstruction results from single kinoform and multi-kinoforms are analyzed by considering the peak signal-to-noise ratio (PSNR) and correlation coefficient (CC) between reconstructed images and original object, which verifies that the speckle noise in reconstructed image can be suppressed by superposing enough images reconstructed from the kinoforms. Electro-optical reconstruction results also confirm that the method is available.

A dynamic three-dimensional display technique based on liquid crystal spatial light modulator

A dynamic three-dimensional (3D) display method based on Liquid Crystal on Silicon (LCoS) spatial light modulator is introduced in this paper. Sixty viewing-angles are set at regular intervals of six degrees along a complete circle in the horizontal plane, and phase holograms of three-dimensional virtual object are calculated under these viewing-angles by use of computational tomographic method as well as spatial coordinate transformation. Multi- kinoforms are calculated for each angle by adding proper pseudorandom phase in each object plane, which can avoid losing spectrum information and be able to reduce the speckle noise of reconstructed image. These kinoforms are written to a 3D electro-holographic display system based on LC-R2500 spatial light modulator (SLM) by a proper loading sequence. A 650 nm diode laser with power of 150 mW is used in the system. A transparent screen is taken as a display media, which could show three-dimensional images reconstructed from holograms loaded on LC-R2500. A pair of Fresnel lenses is used to improve the viewing effect and three-dimensional images floating in space can be viewed by multiple observers.