High‐efficiency optical system for ultra‐short‐throw‐distance projector based on multi‐laser light source

Abstract— A novel laser‐light‐source projector having the three outstanding features of high brightness, ultra‐short throw distance, and high color reproduction has been developed.These features have recently come to be required in the high‐end projector market. The technologies for the laser‐light‐source projectors fully utilize the advantages of lasers, such as high luminance, small étendue, and high color purity. By integrating a triple‐rod illumination system with a multi‐laser light source and an ultra‐wide‐angle projection system, the developed high‐efficiency optical system has achieved a brightness of 7000 lm and a throw ratio of 0.28 with an image size of 100–150 in. Another new technology, laser color processing (LCP), has offered vivid color reproduction which has a color gamut that is up to 180% wider than the BT.709 standard without appearing unnaturally colored. Furthermore, a speckle suppression effect produced by the multi‐laser light source has been demonstrated. In this paper, an overview of these newly developed technologies that are used in the novel laser‐light‐source projector is presented, and solutions to the issues of speckle noise and safety are presented.     

Eye‐safety analysis of current laser‐based LCOS projection systems

Abstract— A laser safety analysis for liquid‐crystal—on—silicon (LCOS) based imaging projection systems utilizing laser light sources is presented. It is shown that a typical laser‐based imaging projector is capable of providing a D65 white‐balanced luminous flux in excess of 20 lm while remaining Class 1 eye safe. By considering a Class 2 classification, it is shown that the same architecture is capable of providing several hundred lumens, a performance level which could potentially be applicable to a new class of high‐brightness miniature projection systems.     

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.     

Projection‐based head‐tracking 3‐D displays

Abstract— This paper describes the construction and operation of four 3‐D displays in which each display produces two images for each eye and thus fits into the category of projection‐based binocular stereoscopic displays. The four 3‐D displays described are pico‐projector‐based, liquid‐ crystal—on—silicon (LCOS) conventional projector‐based, 120‐Hz digital‐light‐processor (DLP) projector‐ based, and the HELIUM3D system. In the first three displays, images are produced on a direct‐view LCD whose conventional backlight is replaced with a projection illumination source that is controlled by a multi‐user head tracker; novel steering optics direct the projector output to regions referred to as exit pupils located at the viewers' eyes. In the HELIUM3D display, the image information is supplied by a horizontally scanned, fast, light valve whose output is controlled by a spatial light modulator (SLM) to direct images to the appropriate viewers' eyes. The current statu s and the multimodal potential of the HELIUM3D display are described.     

Color‐tuning projection system for adaptive combination of high brightness and wide color gamut

Abstract— The demand for projectors with high brightness and wide color gamut has been increasing; however, UHP lamp projectors cannot deliver those two qualities efficiently and simultaneously because of its color‐separation system. The newly developed projection system — “Color‐Tuning Projection System” — realizes the adaptive combination of high brightness and wide color gamut with one projector. This projector features a fourth liquid‐crystal panel — “Color Tuner” — with a 3LCD optical engine, which controls yellow light separately from the RGB light of a UHP lamp. This color‐tuner‐based optical engine — “Color‐Tuning Optical Engine” — and a new color‐conversion signal‐processing algorithm — “Adaptive Color Conversion Algorithm” — controls the yellow‐light volume and corrects color‐shifted pixels according to the brightness and chromaticity analysis of the input image, key technologies of the Color‐Tuning Projection System. This additional panel system enables the projector to ach ieve up to 115% higher brightness and 120% wider color gamut according to the input image. This paper presents an innovative design concept, a novel technology regarding brightness and a color‐gamut conversion projection system, and the characteristics of the prototype.     

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.     

Super‐short‐focus front projector with aspheric‐mirror projection optical system

Abstract— We have developed a new front projector with a super‐short projection distance of 0.65 m at 100 in. We installed a newly developed reflective‐type projection optical system in this projector, which was composed of only four aspheric mirrors that were free of color aberrations. Using this new system and a single‐chip DMD?, we projected a picture that had excellent sharpness and high contrast from 40 to 100 in. This paper describes the principles, design, and characteristics of the new WT600? front projector.     

Multi‐primary image projector using programmable spectral light source

This paper presents a practical prototype of a multi‐primary image projector system in which light source spectra can be programmable for suiting any purpose. Our multi‐primary projection system is mainly configured with a light source component and an image projection component. The programmable light source can reproduce any spectral curve. Spatial images are then generated using a digital mirror device chip that quickly controls the intensity of the light source spectra in 2D image plane. The multi‐primary images in our projection system are reproduced by multiplexing the time‐sequential images with different primary colors. Our multi‐primary image projector realizes not only wide gamut projection but also spectral projection. To achieve this, we also show how light source spectra of four or six primary colors are designed.     

Laser display with single‐mirror MEMS scanner

Abstract— While arrayed DMD and LCD microdisplays are well‐established approaches for visualization tasks, image‐forming laser scanners are an emerging technology used to build miniaturized projection displays. A directly modulated RGB‐laser module consisting of diode lasers for red and blue and a frequency‐doubled semiconductor laser for green with color combining optics form the light source for the laser scanner have been developed. Subsequent beam‐shaping optics suppresses unwanted stray light and enables optimum illumination of the scanning mirror. The MEMS device features a single scanning mirror oscillating in two directions in resonant mode. This requires appropriate data delivery realized by a custom‐made driving logic, which converts the pixel stream originally arranged in rows and columns to the Lissajous‐like spot trajectory on the screen. Additionally, the increased image brightness at the vertical and horizontal borders of the field of view (FOV) is also compensated by the modulation of laser power. Theoretical investigations of the resulting maximum achievable system transmission are presented. Different systems, such as an extremely miniaturized monochrome projection head with an integrated diode laser and a full‐color projector have been realized. Important problems to be tackled are fast analog modulation of the laser power with high resolution and improved suppression of stray light and speckle.     

Spatial optical modulator (SOM): Samsung's light modulator for next‐generation laser displays

Abstract— A new type of diffractive spatial optical modulators (SOMs) has been developed for projection‐display and other applications such as holographic data storage, programmable lithography, and optical communications. It exhibits the inherent advantages of fast response time and high‐performance light modulation, suitable for high‐quality and high‐resolution projection displays. The ±1st‐order efficiency and contrast ratio of 39% and 1000:1 was achieved for a prototype SOM. The response time can be as fast as 0.7μsec with a 400‐nm displacement, enough to make a full‐HD display, being driven by 10‐V. A laser display in full‐HD format (1920 × 1080) was successfully demonstrated by using prototype projection engines having SOM devices, signal‐processing circuits, and projection optics.     

Eye‐safety analysis of phase‐only holographic projection systems

Abstract— Recently, laser‐safety analyses have been presented for scanned‐beam and LCOS imaging projectors. A third class of projection technology, based on the properties of phase‐only diffraction, is differentiated from scanned‐beam and LCOS counterparts in its ability to provide a significantly higher effective luminous flux for video style images. In this paper, this desirable property is recognized by the definition of the “video lumen” and a detailed design fora hypothetical holographic projector and corresponding laser safety analysis is presented. As in the case of conventional amplitude‐modulating LCOS projectors, a holographic projector is capable of delivering several hundred white lumens in Class 2; an appropriately specified holographic projector can also provide several tens of video lumens while maintaining a Class 1 classification.     

Processes,characterizations, and system applications of color‐filter liquid‐crystal‐on‐silicon microdisplays

Abstract— A color‐filter liquid‐crystal‐on‐silicon (CF‐LCOS) microdisplay that integrates color filters on silicon for color will be presented. The color‐filter process on silicon was optimized to achieve fine resolution and precise alignment of the color filters on the pixel array, good adhesion to the silicon suface, and a flat surface for the liquid‐crystal cell assembly. Important optical and electrical parameters of the color filters were extracted to establish an electro‐optical model of the CF‐LCOS microdisplays for device simulation. Thermal, chemical, and light‐stability characterizations were performed to ensure the stabilty of the color filters and CF‐LCOS microdisplays. With color CF‐LCOS microdisplays already available, the projection or viewing optics is greatly simplified. This CF‐LCOS microdisplay is ideal for near‐to‐eye displays because of its low‐power consumption and compactness. The CF‐LCOS microdisplay could also withstand medium light illumination for medium‐sized projectors. A single‐panel projector based on one CF‐LCOS microdisplay of 1280 × 768 × RGB resolution was demonstrated.     

Bistable FLCOS devices for doubled‐brightness micro‐projectors

Abstract— Optical output is of paramount importance to emerging ultra‐miniature projector products. Experimental bistable ferroelectric liquid‐crystal‐on‐silicon (FLCOS) projection microdisplay devices using newly developed FLC materials aligned on obliquely deposited SiO₂ have been developed. These devices enable the doubling of the illumination duty cycle, and hence doubling of the achievable projector light output, while maintaining a DC‐balanced electrical drive.     

An LCOS‐based digital‐cinema projector

Abstract— A digital cinema projector that utilizes three JVC QXGALCDs, and provides 12,000 lumens, 2000:1 contrast, and 3‐Mpixel resolution was developed. This system, which was described in a prior paper (see Ref. 10), has a novel optical configuration based on the use of intermediate imaging optics and wire‐grid polarizers and is described in greater detail in this paper. The polarization optics, including the polarization compensators, contribute to a system that provides high contrast at a low f/#, with a wide color gamut and minimal color shading at high power.     

Refractive‐reflective optical system for realizing an ultra‐thin rear projector

Abstract— This paper presents a new optical system used in an ultra‐thin rear projector with a 1500‐mm diagonal size and 260‐mm depth. A refractive‐reflective optical system was developed to achieve a large projection angle of 136° with a small optical distortion of 0.1%. The optics consists of a convex aspherical mirror and a refractive lens. In addition, a new Fresnel screen composed of hybrid blades of refractive‐TIR (total internal reflection) elements was developed to attain good uniformity of brightness and color within the image area.     

Invited Paper: The evolution of projection displays: From mechanical scanners to microdisplays

Abstract— The development of electronic projection systems from its earliest days in the 1930s to the present will be reviewed. Early projection systems were dominated by cathode‐ray tubes (CRTs) and mechanical scanners (Scophony). Until the invention of the Eidophor oil‐film light‐valve (LV) projector in the 1940s, there was no all‐electronic alternative to CRTs. Oil‐film LVs and CRTs dominated projection until the introduction of the first liquid‐crystal‐device (LCD) light‐amplifier system by Hughes. Today, the oil‐film LV has vanished and the CRT is vanishing. The light amplifier has morphed into several variations of liquid crystal‐on‐silicon (LCoS). Mechanical scanners are starting to be re‐introduced for laser display systems. However, transmissive LCDs, the digital micromirror device (DMD), and LCoS microdisplays dominate the projection‐display market today. In addition to discussing the projection systems themselves, certain key component technologies that have made modern projection systems possible will be discussed.     

Wire‐grid polarizers in modern LCOS light‐engine configurations

Abstract— Wire‐grid polarizers that have a very high transmission, reflection, polarized‐light optical performance, and opto‐mechanical packaging advantages compared to the older polarization technologies have been developed. The wire‐grid polarizer operation principles and performance data are reviewed. The power of using finite‐difference time‐domain (FDTD) modeling techniques to understand the interaction of the electromagnetic waves with the wires and improve the optical performance of the wire‐grid polarizers and ultimately the light‐engine optical performance is shown. The ability to ray trace through a complete digital projector light engine from light source to the screen, including the wire‐grid polarizers, will be discussed. The main focus is to present the modern LCOS light‐engine architectures that use the wire‐grid polarizers. One‐, two‐, and three‐panel LCOS light engines are covered.     

Multi‐viewer autostereoscopic display with dynamically addressable holographic backlight

Abstract— The Multi‐User 3‐D Television Display (MUTED), designed to provide three‐dimensional television (3‐D TV) by the display of autostereoscopic imagery to multiple viewers, each of whom should enjoy freedom of movement, is described. Such an autostereoscopic display system, which allows multiple viewers simultaneously by the use of head tracking, was previously demonstrated for TV applications in the ATTEST project. However, the requirement for a dynamically addressable, steerable backlight presented several problems for the illumination source. The MUTED system demonstrates significant advances in the realization of a multi‐user autostereoscopic display, partly due to the provision of a dynamic backlight employing a novel holographic laser projector. Such a technology provides significant advantages in terms of brightness, efficiency, laser speckle, and the ability to correct for optical aberrations compared to both imaging and scanned‐beam projection technologies.     

Efficient and compact green laser for micro‐projector applications

Abstract— Efficient and compact green lasers are keystone components for micro‐projector applications in mobile devices. An architecture that consists of an infrared‐producing DBR (distributed Bragg reflector) laser with a frequency‐doubling crystal is used to synthesize a green laser that has high electrical‐to‐optical conversion efficiency and can be modulated at speeds required for scanner‐based projectors. The design and performance of a green‐laser package that uses adaptive optics to overcome the challenge of maintaining alignment between the waveguides of the DBR laser and the frequency‐doubling crystal over temperature and lifetime is described. The adaptive optics technology that is employed uses the piezo‐based smooth impact drive mechanism (SIDM) actuators that offer a very small step size and a range of travel adequate for the alignment operation. The laser is shown to be compact (0.7 cm³ in volume) and capable of a wall‐plug efficiency approaching 10% (at 100‐mW green power). It was demonstrated that the adaptive optics enables operation over a wide temperature range (10–60°C) and provides the capability for low‐cost assembly of the device.     

Laser‐based multi‐user 3‐D display

Abstract— The development of a multi‐user stereoscopic display that does not require the use of special glasses (autostereoscopic), and that enables a large degree of freedom of viewer movement and requires only the minimum amount of information (a stereo pair) for the displays described. The optics comprise an RGB holographic laser projector that is controlled by the output of a multi‐target head‐position head tracker, an optical assembly that converts the projector output into steerable exit pupils, and a screen assembly comprising a single liquid‐crystal display (LCD) and image multiplexing screen. A stereo image pair is produced on the LCD by simultaneously displaying left and right images on alternate rows of pixels. Novel steering optics that replace the conventional backlight are used to direct viewing regions, referred to as exit pupils, to the appropriate viewers' eyes. The results obtained from the first version of the display, where the illumination source consists of several thousand white LEDs, are given and the current status of the latest prototype being constructed on the basis of these results is described. The work indicates that a laser‐based head‐tracking display can provide the basis for the next generation of 3‐D display.