SUMMARYIn this paper, we delve into the distinctive color characteristics resulting from color dispersion in SRG and wavelength degeneracy in VHOE, exploring their application in a diffractive light guide for near-eye glasses. The assessment of color performance involves three gratings that cover red, green, and blue light, respectively. With a laser-like spectrum emanating from the display panel, the color gamut achieves an impressive 194% sRGB. However, this narrow-band spectrum proves unsuitable for a VHOE light guide. In contrast, a broad-band spectrum, such as that generated by an LED, results in a common color gamut of 133% sRGB for an SRG light guide and 130% sRGB for a VHOE light guide in the presence of two multiplexed holograms. This innovative approach elucidates the color performance of diffractive light guides like SRG and VHOE, affirming their suitability for crafting high-quality near-eye glasses.

Proceedings of the International Display Workshops Volume 26 (IDW '19),The Full Color See-through Head Mounted Display Based on Transmission-type Holographic Optical Elements and Parallel Plane Mirrors

In this study, a head-mounted display (HMD) system based on a wedge-shaped holographic waveguide that can present holographic virtual images with tunable distance is achieved. The compact computer-generated-hologram system using a spatial light modulator was employed to offer the dynamic image, where the probe beam for the hologram reconstruction is a convergent wave, and the DC term of the diffraction wave can be blocked by a barrier. The wedge-shaped holographic waveguide element was used as the combiner of the HMD system to generate a compact structure. A wedge with a polished surface was designed for in-coupling the image into the waveguide, and a reflection-type holographic optical element (HOE) was used for out-coupling the image from the waveguide. The astigmatism aberration and deformation of the diffraction images at various distances are analyzed and then are compensated. Finally, the virtual image can be obtained without aberration with experimental verification.

Endoscopic surgery causes less tissue injury compared to open surgical techniques, thus promoting more rapid recuperation and reduced post-operative pain. Endoscopy, however, allows the surgeon to visualise only the anatomical surface of the surgical site, with a relatively narrow field of view. Moreover, the 2D video captured by the conventional endoscope does not provide depth perception of the surgical scene. In this study, these limitations have been addressed with the development of an augmented reality (AR) system with stereoscopic visualisation. A phantom and its 3D CT model were used, respectively, to form the real and virtual parts of the AR. The virtual environment camera pose was tracked using algorithms for image feature detection, feature matching and Perspective-n-Point applied on the endoscopic image and the 3D virtual model-rendered image. The endoscope video frame-and the virtual model-rendered images were superimposed to form the AR composite view. The depth buffer (z-buffer) of the rendering window was further used to make a stereo pair of the AR image. The AR system produced a stereo composite view having well-aligned real and virtual components. The RMS error of the real and virtual image contours registration was 9.6 +/- 6.7 mm. Correlation coefficients between the depth map from z-buffer and a depth camera was between 0.60 and 0.96 (p < 0.05). The AR system requires further improvement to be applicable at a higher frame rate of endoscope image acquisition. It also needs to include motion and deformation models when applied to animals or patients.

In this study, a Fresnel lens, a half-reflecting mirror and a LCD were used to build up a see-through floating image system. A gesture recognition module was employed to achieve the human-computer interaction function. The designed system offers a simple and economic architecture for augmented reality (AR) system.

This paper presented an electrically tunable holographic material fabricated with polymer dispersed liquid crystals for 532nm laser light recording. And we use the polymethylmethacrylate instead of glass substrate to fabricate the liquid crystal films which can be bended. We study the diffraction efficiency of the material and demonstrate the image diffraction of the recorded hologram before and after folding the recording film.

We report the impact of lithium doping to ZnO/InZnO thin film transistors' electrical and optical characteristics. A best device with mobility similar to 0.94 cm(2)/vs, and an on/off current ratio over 10(6) were achieved. Further, the high ionization energy of lithium (5.39eV) led the transistor stabilizer than which without lithium doping.

A projection lens design for a virtual image projector in a helmet is presented. The designed projection lens system shows that optical modulation transfer function (MTF) is 0.55 at the spatial frequency of 40 Ip/mm and field of view (FOV) is 8 degrees. In this system, the imaging location is in the front of exit pupil with Im, and the eye relief in this system is 81 mm.

We have proposed and demonstrated a holographic security storage system that is implemented with a shift multiplexing technique. The security function of this storage system is achieved by using a microdiffuser (MD) for random phase encoding of the reference beams. The apparatus of random phase encoding in this system offers an additional and flexible function during the recording processes. The system can generate holographic security memory or nonsecurity holographic memory via using the MD or not. The storage capacity and the average signal-to-noise value of the security storage system are 16 bits/μm2 and 3.5, respectively. Lateral shifting selectivity in this holographic security storage system is theoretically analyzed and experimentally investigated.

A head up display (HUD) with laser backlight unit has two principle problems; one is laser speckles and the other is distortion. In this study, we propose that a rotating diffuser set at the intermediate image plane of the HUD projection system can simultaneously solve these problems. The conditions of speckle reduction and de-distortion are also estimated in this paper.

A holographic optical element (HOE) simultaneously accompanied with light guiding and beam shaping function is implemented with edge-lit holograms in this study. This holographic optical element is generated in a polymer-dispersed- liquid-crystal (PDLC) film with 20μm thickness. In the holographic reconstruction process of the HOE, the wavefronts emitted from the light source will propagate to the HOE and a quasi collimation diffraction beam can be obtained from this device. We demonstrate two applications of edge-lit HOE in this study. One demonstration is a head-mounted display (HMD) system, and the other is an illumination device for display holograms.

A compact holographic collimator is presented for the reconstruction of display holograms. The diffracted 3D image from a display hologram can be observed through the illumination of the holographic collimator. A compact active holographic display can be achieved by switching the internal light source of the holographic collimator to control the diffraction of the 3D image.

We presented holographic optical elements fabricated with polymer-dispersed-liquid-crystal for head mounted displays. The polymer-dispersed-liquid-crystal consists of E7, APTMS, TMPTA, PI and PS. The thickness of the material used in the experiment is 20 pm, and the diffraction efficiency of the holographic optical element is about 52 %.

A nonvolatile reading of erasable polarization holograms in dye-doped liquid-crystal films using the same writing wavelength is presented. The recorded hologram can be easily erased with the illumination of one p-polarized wave; nevertheless, it becomes nonvolatile when reading the hologram with one s-polarized wave. We have proven the nonvolatile reading property is induced by dye adsorption on the substrate of the sample.

An electrically controllable polarization holographic gratings for switching 3D and 2D image on liquid crystal display (LCD) panel is developed in this study. We use external AC voltage to adjust the diffraction efficiency of polarization gratings generated by two opposite circular polarized writing beams in dye-doped liquid-ctystal films.

Distortion aberration of a virtual image generated by a projection lens system is reduced by a diffuser. This technique is implemented by putting a diffuser on the intermediate image plane in the imaging system. Theoretical simulation and experimental imaging results of the proposed technique are analyzed and demonstrated.