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.     

Invited Paper: LCOS microdisplay technology for advanced applications

Abstract— Some technology aspects of LCOS microdisplays that are important for their deployment in advanced projection applications are discussed. The selection of the liquid‐crystal parameters of the vertically aligned system as a function of the requirements (response speed, contrast, etc.) is addressed; a three‐dimensional simulation engine to evaluate fringe‐field effects between pixels is described, allowing the fine‐tuning of the LCOS design with respect to the optical output. Finally, some observations on the nature of the so‐called Vcom drift inside the asymmetrical LCOS cells are presented.     

A lifetime model for LCOS panels under intense illumination

Abstract— The mechanisms of photochemical reactions occurring during the operation of LCOS panels under intense illumination are analyzed. Regardless of the liquid‐crystal‐mixture formulation, light may generate radicals in the liquid crystal and the polyimide alignment layer. The interaction of these radicals modifies the PI surface and causes alignment degradation. Using kinetic equations for these processes, a lifetime model for the LCOS panels is developed. This new model of lifetime dependence versus light intensity is found to be in agreement with experimental data. This model verifies the TN LCOS panel lifetime to be in excess of 50,000 hours for RPTV applications.     

Microdisplay‐based industrial 3‐D and microstructure measurement systems

Abstract— Microdisplays, whether they are of the liquid‐crystal‐on‐silicon (LCOS) or organic light‐emitting diode (OLED) type, have been, up until now, mainly used in multimedia applications or head‐mounted displays. Due to their interesting possibilities, these displays open more and more alternative applications; for example, in optical metrology. Projection lenses for this application area need to be specially designed because the requirements on these systems differ completely from those for multimedia applications. The lenses must have very low geometrical image distortion and they have to be adapted to small objects and/or image distances. On the other hand, they often work with light sources with small spectral bandwidths; consequently, they do not need to be corrected for chromatic aberrations. In addition, the numerical aperture has to be large enough to collect and transfer as much light as possible, but also the size of the projection lens has to be as small as possible to ensure compact measurement systems. All these requirements lead to a compromise in optical lens design. Three optical system designs and realizations — one with an OLED microdisplay and two with an LCOS microdisplay — are presented.     

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.     

Three‐panel LCOS projection systems

Abstract— Three‐panel liquid‐crystal‐on‐silicon (LCOS) projection systems are presented with an emphasis on the commercially successful shared retarder‐stack‐filter (RSF) polarizing‐beam‐splitter (PBS) architectures. The design and operation of the specific CQ90 projection core is presented in detail, and its contrast and transmission derived. alternative three‐PBS/X‐cube LCOS architectures are briefly introduced and their performance is compared to that of the CQ90.     

基于螺旋相衬成像的棉麻纤维检测

棉麻纤维的微细结构在普通光学显微镜下不易被观察到,针对此问题,分析了螺旋相位滤波增强图像细节的机理,并据此设计出32阶阶梯型螺旋相位模板。利用Matlab创建一个大小为1024×768的螺旋阶梯型灰度矩阵图像,并将其加载到纯相位液晶空间光调制器(LCOS)上,然后建立纤维成像实验系统,经LCOS相位调制后,获得振幅和相位梯度调制后的纤维图像。通过该方法获得的纤维图像纹理结构和边缘信息明显、对比度较高,可显著提高检测准确度和效率。     

Contrast optimization for MacNeille‐PBS‐based LCOS projection systems

Abstract— Contrast limits are investigated for MacNeille‐PBS‐based LCOS projection systems that use retarder stack filters (RSFs). The two contributing factors are considered separately; namely, the color‐management system and the panel port. To enhance performance of the former, skew‐ray‐compensated RSFs are introduced. For the latter, a general three‐step methodology is presented to optimize contrast by compensating the LCOS panel. It is shown that the orientation of the LCOS panel and compensator, relative to the MacNeille PBS, is critical. The significant impact of AR‐coating performance on system contrast is also revealed. Methods to enhance ANSI contrast are proposed. A high‐contrast architecture will be presented by way of example.     

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.     

MUTED: Multi‐user 3‐D display

Abstract— Research described in this paper encompasses the design and building of glasses‐free (autostereoscopic) displays that utilize a direct‐view liquid‐crystal display whose backlight is provided by a projector and novel steering optics. This is controlled by the output of a multi‐user head‐position tracker. As the displays employ spatial multiplexing on a liquid‐crystal‐display screen, they are inherently 2‐D/3‐D switchable with 2‐D being achieved by simply displaying the same image in the left and right channels. Two prototypes are described in this paper; one incorporating a holographic projector and the other a conventional LCOS projector. The LCOS projector version addresses the limitations of brightness, cross‐talk, banding in the images, and laser stability that occur in the holographic projector version. The future development is considered and a comparison between the prototypes and with other 3‐D displays is given.     

Plasma‐beam alignment technique for ferroelectric liquid crystals

Abstract— The plasma‐beam alignment procedure earlier developed for the alignment of nematic liquid crystals is successfully extended to ferroelectric liquid crystals (FLC). The highly uniform alignment of the “chevron” structure (before electrical treatment of FLC cells) and “quasi bookshelf” structure (after the electrical treatment) are realized. The contrast of bistable switching larger than 350:1 is achieved. This makes the non‐contact plasma‐beam alignment procedure especially attractive for high‐contrast bistable LCDs on an LCOS base, particularly used in PDA and e‐books. Fast switching and realization of gray scale in the plasma‐beam aligned FLC cells makes this technique also promising for full‐color displays including color LCD TV.     

Diamond‐like‐carbon LC‐alignment layers for application in LCOS microdisplays

Abstract— To improve the lifetime and yield of LCOS microdisplays, non‐contact LC alignment techniques using inorganic materials are under investigation. This report focuses on oblique ion‐beam treatment of diamond‐like carbon (DLC) layers, and in particular on the influence of the ion dose on the LC alignment on DLC, keeping the ion‐beam angle (40°) and ion‐beam energy (170 eV) the same. LC alignment on ion‐milled DLC layers is uniform if the ion dose is between 3.8 × 10^?4 C/cm² and 5.5 × 10^?3 C/cm². Above and below this ion dose range, non‐uniform alignment is observed. NEXAFS experiments show that this is caused by lack of molecular anisotropy on the surface of the ion‐milled DLC layers. By varying the ion dose between 3.8 × 10^?4 C/cm² and 5.5 × 10^?3 C/cm², LC molecules have an average pre‐tilt between 3° and 5°, which is within the desired range for application in LCOS microdisplays. The lifetime of the LCOS microdisplays with ion‐milled DLC for projection‐TV application is, however, shorter than the lifetime of microdisplays with PI layers. Ion milling probably creates a reactive surface that is unstable under the high light fluxes used in projection TVs. A solution for this problem could be chemical passivation of the ion‐milled alignment layers. Initial experiments with passivation of ion‐milled PI resulted in an increase in lifetime, but the lifetime after passivation was still lower than the lifetime of rubbed PI layers (factor 0.7). Nevertheless, ion‐milling of DLC or PI can be a good alternative LC alignment technique in other LCD applications. LC‐alignment layers based on inorganic layers such as obliquely deposited SiO₂ films would be a better option for application in LCOS microdisplays due to their higher light stability.     

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.     

Development of an 8‐bit VGA LCOS microdisplay with FSC modes using a low‐cost process

Abstract— A VGA‐resolution LCOS microdisplay operated in the field‐sequential color (FSC) mode was fabricated using a low‐cost process. An 8‐bit digital data driver with digital‐to‐analog converters, which can realize a 256‐level gray scale and gamma compensation, has been integrated into a color microdisplay. A top‐to‐bottom approach to the design of an FSC LCOS microdisplay is described. The design of the silicon‐backplane circuits is outlined in detail. Finally, a prototype of this display and its imaging performance are discussed.     

Assembly technology for the manufacture of LCOS panels

Abstract— The technological issues related to the fabrication of high‐performance LCOS displays are described. The considered devices use the vertically aligned nematic liquid‐crystal mode because of its superior performance characteristics. The issues addressed mostly stem from this choice and the ensuing need for inorganic alignment layers. In particular, the compatibility of the inorganic alignment layers with the sealant material are treated in detail.     

A study of electro‐optical characteristics depending on LC pre‐tilt angle and cell gap in a full‐HD LCOS panel

Abstract— The goal of this work is to achieve a better understanding of the electro‐optical characteristics of a VA‐mode full‐HD LCOS panel via simulations and experiments. The optical parameters, such as reflectance, fill factor, and contrast that vary due to the pre‐tilt angle and cell gap, were also studied. Based on the simulations, the optical fill factor was the highest at an angle of 81° and 2.1 μm under the given conditions. The contrast ratio was the highest at an angle of 89° and 2.4 μm. Five different LCOS panels were fabricated; three different angles (85°, 87°, and 89°) at a 2.1‐μm cell gap and two different cell gaps (1.8 and 2.1 μm) at an angle of 87°. The measured reflected light intensity was compared to the calculated reflectance. The simulated and measured contrasts were compared with each other. The simulation results well‐matched the experimental results and the differences were less than a few percentage points. Based on the comparative studies on reflectance and contrast, the test panel under the condition of an 87° angle and 2.1‐μm gap showed the best performance results.     

Compensation of birefringence in lead‐free polarizing beam splitters for LCOS projectors

Abstract— Most optical designs for delivering light to LCOS imagers and then from the imagers to the projection lens use polarizing‐beam‐splitter (PBS) technology. Most of the PBSs used in commercial LCOS projectors contain glass with a significant amount of lead (Pb). Such glasses have inherently low stress birefringence, and therefore maintain the polarization state of light passing through them. However, Pb‐bearing glass is an expensive, difficult to process, and hazardous material with special disposal requirements and is therefore not desirable in consumer‐electronic products. On the other hand, Pb‐free wire‐grid plate PBSs require a longer back focal length than would be optimal. Data and modeling results show that uniform high‐contrast dark states may be obtained from lead‐free‐glass Cartesian PBS prisms when a quarter‐wave compensator is used between the imager and the PBS.     

Fast‐response liquid‐crystal displays using crossed fringe fields

Abstract— A fast‐response and wide‐view liquid‐crystal display (LCD) using the crossed fringe‐field‐switching (CFFS) mode is proposed, where the fringe‐field electrodes exist on both the top and bottom substrates. The bottom fringe field is used to turn on the LC directors and the top fringe field is used to assist in the LC decay process. The decay time is reduced by ～2× compared to that of the conventional FFS mode between the full bright and dark states, and more than a 2× improvement is obtained for other gray‐scale transitions. This CFFS mode also preserves the wide‐view characteristics as the conventional FFS mode. Its applications to LCD TVs and monitors for reducing image blur are addressed.     

An LCOS IC layout verification method that uses a computational model for lithography manufacturing

Abstract— An advanced approach to LCOS IC layout verification is presented. It is based on incorporating the results of optical lithography computational models into the verification process. The first section describes an algorithm for the numerical modeling of optical lithography that uses a source integration method for computation of an aerial image. The second section dwells on an application of this algorithm for layout physical verification. A proposed physical verification method uses modeled contours of the manufactured elements to check whether a given layout will be manufacturable. The proposed verification method also considers deviations of manufactured contours from their modeled shapes due to variation of manufacturing parameters to further improve verification quality. At the same time, the method is conservative in terms of the use of a time‐consuming lithographical modeling.     

Microdisplay‐based optical module for avionic display applications

Abstract— A new optical scheme for a LCOS‐based rear‐projection system utilizing an LED illumination source is presented. The proposed optical module could conveniently replace conventional aircraft panel instrumentation not only because it achieves major standard avionics application requirements, such as the capability to withstand mechanical shocks, high reliability, and weight and power‐consumption minimization, but also as a consequence of the fact that it allows the display image area to be properly matched to the shape of the instrument panel more easily than with conventional displays.