Watt‐level compact green laser for projection display

Abstract— In this paper, a compact efficient diode‐pumped solid‐state (DPSS) green laser based on a periodically poled MgO:LiNbO³ (MgO:PPLN) crystal, which is suitable for low‐cost mass production, was demonstrated. A linearly polarized 532‐nm laser light of 1.02‐W CW output power was obtained by employing a simple parallel‐plane configuration. A numerical method, based on the 1 ‐D coupled‐mode equations, is used in the cavity design and investigation of the intra‐cavity second‐harmonic‐generation process.     

A super‐fine‐pitch screen for rear‐projection TV

Abstract— An advanced screen for use with LCD/LCoS/DMD rear‐projection TV has been developed. A lenticular lens having a pitch of 64 μm has been developed without loss in any other optical property. A 70% black‐stripe ratio was obtained by optimizing the patterning process, which maintains high contrast. As described in this paper, the FC‐Screen manufacturing technology has been further developed.     

Image modification for immersive projection display based on pseudo‐projection models

This paper describes a practical method that enables actual images to be converted so that they can be projected onto an immersive projection display (IPD) screen. IPD screens are particularly unique in that their angle of view is extremely wide; therefore, the images projected onto them need to be taken on a special format. In practice, however, it is generally very difficult to shoot images that completely satisfy the specifications of the targeting IPD environment due to cost, technical problems or other reasons. To overcome these problems, we developed a method to modify the images by abandoning geometrical consistency. We were able to utilize this method by assuming that the given image was shot according to a special projection model. Because this model differed from the actual projection model with which the image was taken, we termed it the pseudo‐projection model. Since our method uses simple geometry, and can easily be expressed by a parametric function, the degree of modification or the time sequence for modification can readily be adjusted according to the features of each type of content. Copyright © 2003 John Wiley & Sons, Ltd.     

Reliability of prototype microcapsule diffuser for speckle noise reduction in laser displays

A microcapsule diffuser of the transparent type is proposed to reduce the speckle noise generated on a laser display. This diffuser has a microcapsule that is secured between two transparent electrodes. The microcapsule contains light diffusion particles that are electrically charged. Because the particles in the microcapsules are moved by the electric field, the proposed device reduces speckle noise. This paper reports the results of one study of the device reliability.     

Full‐parallax autostereoscopic display with scalable lateral resolution using overlaid multiple projection

Abstract— A method to increase the viewing resolution of an autostereoscopic display without increasing the density of microlenses is proposed. Multiple projectors are used for the projection images to be focused and overlaid on a common plane in the air behind the microlens array. The multiple overlaid projection images yield multiple light spots inside the region of each elemental lenslet of the microlens array. This feature provides scalable high‐resolution images by increasing the number of projectors. Based on the proposed method, a prototype display that includes 15 projectors was designed and built. 3‐D images were successfully reproduced on the prototype display with full parallax and a wide viewing angle of 70°.     

Non‐planar projection performance evaluation and projector pose optimization

In projector applications, the actual display effect is primarily dependent on two aspects: projector performance parameters (intrinsic properties), and projector placement (extrinsic properties). Many studies have been conducted on the impact of the original resolution, illumination, and contrast ratio on projection performance. However, few studies have focused on the influence of extrinsic properties, including the position and orientation of the projector on the projection effect. In this paper, three projection performance evaluation criteria—projection resolution, resolution difference, and projection distance difference—are proposed in terms of extrinsic properties. Based on these evaluation criteria, a projection performance evaluation function was constructed. Through this function, as well as optimization employing the multi‐start and Monte Carlo methods, projector pose parameters corresponding to optimal projection effects can be obtained. Evaluations demonstrated that the proposed projection performance evaluation criteria could correctly describe the impacts of projector placement on projection effects. Projection systems arranged according to the projector pose optimization methods achieved good performance on screens in difference shapes with different numbers of projectors, where the resolution and display improved with no change of projector hardware parameters. The optimal projector poses calculated using these optimization methods can provide theoretical guidance for practical projector placement.     

Design of a compact projection display for the visualization of 3‐D images using polarization sensitive eyeglasses

Abstract— A compact optical architecture of a three‐dimensional projection display that simultaneously generates two full‐color images with an orthogonal polarization state is presented. The minimal size of the optical engine was investigated and a compact illumination system using light‐emitting diodes as light sources was designed. The effect of dichroic mirrors in the illumination path on the stereoscopic images was also investigted.     

Invited Paper: Surface‐emitting‐diode lasers and laser arrays for displays

Abstract— High‐power red, green, and blue laser light sources made from vertically emitting arrays of intracavity doubled IR lasers is reported. The emitted infrared light from a monolithic array of large‐aperture vertical cavity lasers is converted into visible light using a PPLN doubling crystal in an external cavity. A volume Bragg grating provides simultaneous feedback for all emitters in the array and sets the laser wavelength. Increased diffraction losses for higher‐order modes result in quasi‐Gaussian beams with excellent conversion efficiency. Green 532‐nm lasers with more than 5.8‐W visible power have been demonstrated at a base temperature of 40°C. Blue 465‐nm lasers with 4.4‐W power at 40°C are unmatched in performance and wavelength when compared to competing GaN‐based edge emitters. Typical wall‐plug efficiencies are higher than 8%. We have measured single‐emitter operating lifetimes to be more than 28,000 hours. Red lasers based on highly strained InGaAs achieve record laser powers of 2.0W at 618 nm in the same form factor as the green and blue lasers. Red single‐emitter lifetimes of more than 10,000 hours have been attained. The technology described in this paper delivers on a full suite of cost efficient and reliable red, green, and blue lasers that meet the demands of the display markets.     

A systematic framework for on‐line calibration of a head‐mounted projection display for augmented‐reality systems

Abstract— Augmented reality (AR) is a technology in which computer‐generated virtual images are dynamically superimposed upon a real‐world scene to enhance a user's perceptions of the physical environment. A successful AR system requires that the overlaid digital information be aligned with the user's real‐world senses — a process known as registration. An accurate registration process requires the knowledge of both the intrinsic and extrinsic parameters of the viewing device and these parameters form the viewing and projection transformations for creating the simulations of virtual images. In our previous work, an easy off‐line calibration method in which an image‐based automatic matching method was used to establish the world‐to‐image correspondences was presented, and it is able to achieve subpixel accuracy. However, this off‐line method yields accurate registration only when a user's eye placements relative to the display device coincides with locations established during the offline calibration process. A likely deviation of eye placements, for instance, due to helmet slippage or user‐dependent factors such as interpupillary distance, will lead to misregistration. In this paper, a systematic on‐line calibration framework to refine the off‐line calibration results and to account for user‐dependent factors is presented. Specifically, based on an equivalent viewing projection model, a six‐parameter on‐line calibration method to refine the user‐dependent parameters in the viewing transformations is presented. Calibration procedures and results as well as evaluation experiments are described in detail. The evaluation experiments demonstrate the improvement of the registration accuracy.     

A high‐contrast front‐projection display system optimizing the projected light‐angle range

Abstract— The problem with front‐projection displays is that the screen contrast ratio decreases under bright‐ambient conditions. To overcome this problem, the design of a special screen, composed of the diffuser whose diffusing property shows top‐hat characteristics and a sawtooth reflector, is proposed. The screen diffuses the incident image light arriving at a projection‐angle range that is a lower‐angle range than the viewing‐angle range, and reflects the ambient light out of the viewing‐angle range. In this paper, the projection‐angle range and the viewing‐angle range was optimized to improve the contrast ratio of a front‐projection display. As a result, a special screen with the above‐mentioned diffusing property was realized, and a high‐quality front‐projection display with a high contrast ratio, even in a bright room, was achieved.     

High‐resolution autostereoscopic 3‐D projection display with a space‐dividing iris‐plane shutter

Abstract— A high‐resolution autostereoscopic 3‐D projection display with a polarization‐control space dividing the iris‐plane liquid‐crystal shutter is proposed. The polarization‐control iris‐plane shutter can control the direction of stereo images without reducing the image quality of the microdis‐play. This autostereoscopic 3‐D projection display is 2‐D/3‐D switchable and has a high resolution and high luminance. In addition, it has no cross‐talk between the left and right viewing zones, a simple structure, and the capability to show multi‐view images.     

SOM‐based projection module for mobile displays

Abstract— The development of a compact, efficient VGA projection module to be embedded in mobile devices is reported. The design incorporates laser/laser diode (LD) light sources, Schlieren optics, and a one‐dimensional diffractive spatial optical modulator (SOM). During development, the optical parameters were determined and the relationships between the parameters to optimize the optical specifications were derived. The resulting optimized specifications enable us to manufacture two types of optical modu les as compact as 13 cc and with as little as 10% speckle contrast ratio.     

Vivid image projection system using e‐Paper active screen

Projected image on a screen is not always vivid enough when it is projected in a bright room. We generally have to choose either vivid image in a dark room or dull image in a bright room. We have suggested a new projection system which can realize high contrast image projection in a bright room. It is consisted of electronic paper screen, projector, and light‐emitting diode room light. The electronic paper (e‐Paper) screen alternates its whole surface white/black with 120 Hz. Room lights are controlled with the same frequency of 120 Hz with the opposite phase as that of the e‐Paper screen. We have confirmed that our new system has achieved higher contrast than the conventional projection system and also enough readability of paper documents in the room simultaneously. We have thus confirmed that our new system can bring an ideal condition, for audience, which can realize a vivid image projection in a bright room.     

GaN‐based high‐output‐power blue laser diodes for display applications

Abstract— We succeeded in fabricating high‐output‐power blue (445 nm) laser diodes (LDs) with an output power of 500 mW. The operating current, voltage, and wall‐plug efficiency of these LDs were 480 mA, 4.8 V, and 21.7%, respectively. The lifetime of these LDs was estimated to be 10,000 hours under continuous‐wave operation at 25°C. From examination of the degradation mode, we found that the operating current seriously affects the lifetime of LDs. In the next stage, we will focuse on the optimization and sophistication of the manufacturing processes to fabricate longer‐lifetime (>30,000 hours) blue LDs.     

Dependency of speckle reduction by wavelength diversity on angular diversity in laser projection system

Speckle is one of the most serious problems in laser projection system. Most speckle reduction methods in a laser projector can be categorized into wavelength diversity, angular diversity, and polarization diversity. In order to reduce speckle to the acceptable level, the combination of some or all of these methods are used. When the speckle reduction by wavelength diversity and angular diversity are used at the same time, the total speckle reduction can be different from the product of each speckle reduction effect when each of them is used separately. Here, the theoretical model of speckle reduction by wavelength diversity and angular diversity when they are used at the same time is derived. The calculation results by the theoretical model are compared with the experimental results. It is shown that theoretical calculation agrees well with the experimental results.     

A 65‐in. slim (255‐mm depth) laser TV with wide‐angle projection optical system

Abstract— A high‐definition laser TV that employs a newly developed laser light source and a super‐wide‐angle projection optical system has been developed. This adoption of a laser light source with three primary colors helped to achieve an extremely wide color gamut, and, in addition, a compact optical engine, which has been optimized to the laser light source and contributed to the achievement of the stylish design of a large screen of 65 in., with the depth being only 255 mm.     

Polarization‐independent modulation for projection displays using small‐period LC polarization gratings

Abstract— Progress in the use of liquid‐crystal polarization grating (LCPG) to modulate unpolarized (and polarized) light with a grating period as small as 6.3 μm is reported. Similar to LCPGs formed at larger periods (11 μm) reported previously, polarization‐independent switching, predominantly three diffraction orders, maximum contrast ratios of ～100:1 for unpolarized broadband light, very low scattering, and diffraction efficiencies >98% continue to be observed. The smaller period led to an expected lower threshold voltage, even though the thickness was greater. Because the smaller grating period enables a brighter result from a Schlieren projection scheme for a microdisplay using the LCPG light valve, the inherent tradeoffs involved with both material and design parameters are discussed, and prospects for a polarization‐independent projection display are commented upon.     

Design of compact projection lenses using double‐layered diffractive optical elements

Abstract— Based on several special properties of diffractive optical elements (DOEs) such as savings in mass and to freely modulate the wavefront of incident light, a new compact projection lens with double‐layered DOEs is presented. It is comprised of five lenses and has nearly half the weight of its original structure. The modulation transfer function (MTF) value on‐axis is 0.7 at a spatial frequency of 33 lp/mm and more than 0.3 for all off‐axis values, which satisfies the requirement of a color‐filter‐type liquid‐crystal‐on‐silicon (LCoS) 0.59‐in. display with a SVGA resolution. The maximum distortion is 0.46%.     

Analysis and reduction of dark zone in ultra‐thin wedge‐plate displays

Abstract— A wedge plate can be used as the screen of a display, and the thickness of the display can be incredibly thin. In this paper, a basic formula for ray tracing in such a wedge plate is deduced. The fundamental limitation on the display quality of a wedge plate is explored, and the formation of a dark zone on the display screen is analyzed and verified numerically. Experimental exploration and confirmation of one 14‐in. acrylic wedge plate with a white‐light‐emitting diode is also provided. Two approaches to eliminate the dark zone are proposed, and the corresponding numerical demonstration of a 52‐in. wedge‐plate display is also shown.     

Resolution enhancement of integral‐imaging three‐dimensional display using directional elemental image projection

Abstract— A new approach to resolution enhancement of an integral‐imaging (II) three‐dimensional display using multi‐directional elemental images is proposed. The proposed method uses a special lens made up of nine pieces of a single Fresnel lens which are collected from different parts of the same lens. This composite lens is placed in front of the lens array such that it generates nine sets of directional elemental images to the lens array. These elemental images are overlapped on the lens array and produce nine point light sources per each elemental lens at different positions in the focal plane of the lens array. Nine sets of elemental images are projected by a high‐speed digital micromirror device and are tilted by a two‐dimensional scanning mirror system, maintaining the time‐multiplexing sequence for nine pieces of the composite lens. In this method, the concentration of the point light sources in the focal plane of the lens array is nine‐times higher, i.e., the distance between two adjacent point light sources is three times smaller than that for a conventional II display; hence, the resolution of three‐dimensional image is enhanced.