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.     

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.     

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.     

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.     

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.     

Invited Paper: Detailed optical characteristics of multi‐layer optical film polarization beam splitter

Abstract— 3M polarization beam splitter (PBS) technology has been shown to be the most light‐efficient solution currently available for use in LCOS projection. It also provides short back focal length, very high contrast, and extremely uniform dark states without the use of lead‐glass prisms. Recent improvements in contrast performance, increased understanding of the effects of pupil shape and size on contrast, effects of temperature on optical performance, and improved photostability are reported. New light‐engine architectures employing the 3M PBSs with associated light budget analyses are suggested.     

Contrast behavior of a field lens with a wire‐grid PBS

Abstract— In an LCOS projection system, a wire‐grid PBS may be used to improve contrast and a field lens may be employed to simplify the projection lens. However, the combination of the two leads to a reduced contrast, which decreases with increasing field angle in one direction. In a representative arrangement, measured contrast with a mirror varied from over 10,000 in the center to 450 at the left and right edges. Contrast loss can be improved with a weaker field lens. The problem arises due to a phase delay between polarization states introduced by the wire grid. Polarization measurements show a +53‐nm phase delay with an axis parallel to the wire‐grid surface normal. Various compensation schemes are proposed in order to reduce the aforementioned loss of contrast.     

Contrast improvements for scrolling‐color LCoS

Abstract— A scrolling‐color LCoS (liquid‐crystal‐on‐silicon) display must exhibit both fast speed and high contrast. These requirements drive design choices for the liquid crystal and optics of the image kernel. The input director was aligned to the incoming polarization and a compensated 45TN0 effect was choosen. Contrast demands place tight requirements on interfacial reflections. A wire‐grid PBS can achieve high contrast and can simplify the system construction. With attention to the above, we report a sequential contrast of 800:1 at the viewing screen. With a 90TN0 effect, the contrast can be increased even further, but with some penalty in light efficiency. With this effect, sequential contrast of 2000:1 was measured.     

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.     

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.     

General methodology for LCoS panel compensation

Abstract— A general three‐step methodology is presented to optimize contrast when compensating LCoS panels. The first step acts to compensate the in‐plane residual retardation, while the second one improves the field of view (FOV) using either MacNeille‐type or wire‐grid polarizing beamsplitters (PBS). The orientation of the LCoS panel and compensator, relative to the MacNeille PBS, are very critical to achieve good system contrast. The final step is to account for reflections from anisotropic material, which appear as on‐state light, limiting contrast.     

Analysis,simulation, and evaluation of scrolling illumination as a method for reducing motion blur in LCOS projectors

Abstract— A high‐fidelity simulation of motion blurring in an LCOS projector was developed by using the measured temporal response of the projector. The simulation was validated for continuous and scanning illumination by comparison with results of motion‐blur measurements by using a pursuit camera. The simulation was then used to analyze and optimize duty cycle and phase parameters for scrolling illumination in the general case.     

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.     

Contrast‐enhanced wide‐angle high‐speed polarization modulator for active‐retarder 3‐D displays

Abstract— A contrast‐enhanced wide‐angle high‐speed polarization modulator for active‐retarder 3‐D displays is proposed. By using a double liquid‐crystal‐cell structure together with a dedicated driving scheme and an external quarter‐wave retarder, a high‐performance modulator can be realized, resulting in minimized brightness loss and low cross‐talk levels in fast‐refresh time‐multiplexed 3‐D displays.     

Reduction of defects and improvement in the performance of blue phosphor for thick‐dielectric electroluminescent displays using Color‐by‐Blue

Abstract— Defect‐free large‐area inorganic thick‐dielectric EL (TDEL) displays using Color by Blue (CBB) technology have been successfully developed. We have achieved the world's highest blue‐phosphor luminance of 900 cd/m² for a single‐pixel device by using CBB and by optimizing the e‐beam gun configuration and the flow rate of H₂S in the vacuum chamber. By analyzing the defects on panels with triple‐pattern phosphors and CBB panels, we also found that the number of defects on CBB panels can be drastically reduced compared with those on triple‐pattern panels. The defect‐free 17‐in. VGA CBB panels show better characteristics, a high peak luminance of 600 cd/m² and a high contrast ratio of 1000:1, compared with those of triple‐pattern panels.     

Multidimensional Taylor network adaptive control for MIMO time‐varying uncertain nonlinear systems with noises

In this paper, an adaptive control approach based on the multidimensional Taylor network (MTN) is proposed here for the real‐time tracking control of multiple‐input–multiple‐output (MIMO) time‐varying uncertain nonlinear systems with noises. Two MTNs are used to formulate the optimum control and adaptive filtering approaches. The feed‐forward MTN controller (MTNC) is developed to realize the precise tracking control. The closed‐loop errors between the filtered outputs and expected values are directly chosen as the MTNC's inputs. A valid initial value selection scheme for the weights of the MTNC, which can ensure the initial stability of adaptive process, is introduced. The proposed MTNC can update its weights online according to errors caused by system's uncertain factors, based on stable learning rate. The resilient backpropagation algorithm and the adaptive variable step size algorithm via linear reinforcement are utilized to update the MTNC's weights. The MTN filter (MTNF) is developed to eliminate measurement noises and other stochastic factors. The proposed adaptive MTN filtering system possesses the distinctive properties of the Lyapunov theory–based adaptive filtering system and MTN. Lyapunov function of the filtering errors between the measured values and MTNF's outputs is defined. By properly choosing the weights update law in the Lyapunov sense, the MTNF's outputs can asymptotically converge to the desired signals. The design is independent of the stochastic properties of the input disturbances. Simulation of the MTN‐based control is conducted to test the effectiveness of the presented results.     

Electrical models of TFT‐LCD panels for circuit simulations

Abstract— As thin‐film‐transistor liquid‐crystal‐display (TFT‐LCD) panels become larger and provide higher resolution, the propagation delay of the row and column lines, the voltage modulation of Vcom, and the response time of the liquid crystal affect the display images now more than in the past. It is more important to understand the electrical characteristics of TFT‐LCD panels these days. There are several commercial products that simulate the electrical and optical performance of TFT‐LCDs. Most of the simulators are made for panel designers. However, this research is for circuit, system, and panel designers. It is made in a SPICE and Cadence environment as a commercial circuit‐design tool. For circuit and system designers, it will help to design the circuit around a new driving method. Also, it can be easily modified for every situation. It also gives panel designers design concepts. This paper describes the electrical model of a 15‐in. XGA (1024 × 768) TFT‐LCD panel. The parasitic resistance and capacitance of the panel are obtained by 3‐D simulation of a subpixel. The accuracy of these data is verified by the measured values of an actual panel. The developed panel simulation platform, the equivalent circuit of a 1 5‐in. XGA panel, is simulated by HSPICE. The results of simulation are compared with those of experiment, according to changing the width of the OE signal. The proposed simulation platform for modeling TFT‐LCD panels can be especially applied to large‐sized LCD TVs. It can help panel and circuit designers to verify their ideas without making actual panels and circuits.     

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.     

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.     

基于多维泰勒网的多入多出非线性时滞系统辨识

针对多入多出 （multiple input multiple output,MIMO） 非线性时滞系统辨识的准确性与实时性问题,提出基于多维泰勒网（multi-dimensional taylor network,MTN） 的辨识方案。MTN作为辨识模型,综合利用权剪枝 （weight-elimination,WE） 算法和共轭梯度（conjugate gradient,CG）算法,即WE-CG算法作为MTN辨识模型的学习算法;WE算法可以有效精简MTN辨识模型结构,从而降低计算复杂度、提高模型实时性能。最后,引入一个数值仿真例子和一个工程实例来验证所提辨识方案的有效性,同时与传统的MTN辨识方案作对比,给出了两者的准确性与复杂度分析,突出所提辨识方案的准确性与实时性。实验结果表明,所提方案够准确地对MIMO非线性时滞系统进行辨识。同时,相比传统的MTN辨识方案,所提辨识方案结构更精简,具有更低的算法复杂度。