Zhenxiang Zeng

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.

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.

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.

Full-color holographic 3D display using slice-based fractional Fourier transform combined with free-space Fresnel diffraction

The fractional Fourier transform (FRT) has been used for computing holograms in holographic displays due to its continuity of describing wave diffraction in the near field and far field. In this study, we propose a method to realize a full-color holographic 3D display with combined use of the FRT and the free-space Fresnel diffraction. A slice-based optical configuration and the calculation algorithm of the FRT are proposed for generating phase-only holograms of full-color 3D objects. Sequential phase-only holograms are generated for reducing the speckle noise of reconstructed images by the time-averaging effect. Free-space Fresnel diffraction is used for 3D image reconstruction from the generated holograms. The relationship between the fractional orders of different color channels and the free-space Fresnel diffraction distance is analyzed. Chromatic aberrations caused by different wavelengths of RGB lasers are also compensated. A full-color holographic display system using a reflective phase-only spatial light modulator (SLM) is established. Both the numerical and optical reconstruction results demonstrate the feasibility of the proposed method.

Improved real-time holographic video display using super-fast-refresh liquid crystal films

We have achieved real-time dynamic holographic display with holographic response time under an order of a microsecond using super-fast-response liquid crystal films. The hologram formation time and self-erasable time can both reach ~ 1 ms in this film. Holographic video display was realized using it without any cross talk between the holograms. However, the holographic display videos we obtained before need to be improved in image quality. This paper presents improvement of holographic video display of the films, and our achievement may be useful for its potential applications in a large-size, high-definition, and color holographic three-dimensional video display.

Imaging quality analysis of computer generated holograms in 3D holographic display using different Fresnel zone plates in look-up table

Hologram calculation of 3D object with look-up-table (LUT) method using Fresnel zone plate (FZP) is a typical and commonly used approach. However, the types of Fresnel zone plate (FZP) significantly affect the holographic imaging quality of 3D objects. This paper mainly analyzes the relationships between imaging quality and the modulation types of FZP. Simulation reconstruction and optoelectronic reconstruction results with amplitude-modulation type and phase-only modulation type of FZP show that, conjugate image exists in the imaging plane using amplitude-type FZP in LUT method. However, no conjugate image exists in the imaging plane using phase-type FZP in LUT method. The experimental results show that, compared to the amplitude-type FZP, the phase-type FZP is more suitable for improving the imaging quality of holographic 3D display.

Full-Parallax Colorful 3D Imaging Using Orthogonal-Stacked Lenticular Sheets and Computer-Generated Stereogram

This paper proposes a full-parallax colorful three-dimensional (3D) imaging method based on orthogonal-stacked lenticular sheets (OLSs) and computer-generated stereogram. Colorful 3D image with full-parallax is observed by matching the printed stereogram with the OLS.

Method for image quality improvement of full-color holographic projection system

In the optoelectronic reconstruction of full-color hologram, transverse and longitudinal chromatisms are introduced due to the hologram is sensitive to wavelength, which makes the colorful image fuzzy. The image quality is also affected by the characteristic of the spatial light modulator used in optoelectronic projection system. Multi-order diffraction images occurred due to the ratio of active area and dead area (fill rate). In the colorful holographic projection system, three lasers with red, green, and blue color are applied as the light sources, color crosstalk due to the switching of the different lasers also impairs the image quality. In order to improving the image quality of full color holographic projection system, this paper analyzes the effect of the fill rate and the color crosstalk on the reconstruction image quality. Transverse and longitudinal chromatisms are removed by resampling the object information and loading a specially designed virtual phase distribution in the computer hologram respectively. We proposed time sequence updating chart of RGB laser to solve the problem of color crosstalk. Experimental results are also provided to verify the improvement of the image quality.