Herbert De Smet

Complete electrical and optical simulation of electronic paper

Abstract A complete model for the internal particle distribution of electrophoretic image displays (EPIDs) is presented. From this model, simulation formulas for electrical and optical properties are calculated. These formulas incorporate both time dependence and voltage dependence. They make it possible to optimize display properties since the model is built up with physical parameters. Results are shown that prove that this model is indeed capable of complete optical and electrical transient simulation. The importance of centrifugation during display manufacturing is proven as a way to improve the switching speed of the display.

Electrical model of a liquid crystal pixel with dynamic, voltage history-dependent capacitance value

The voltage history-dependent nature of a liquid crystal pixel capacitance becomes an important issue in active matrix addressing as large storage capacitors are replaced with more intelligent circuitry such as in-pixel frame buffers. In this paper, a simple but flexible Spice macro model is introduced that allows accurate simulations of the electrical behaviour of a nematic liquid crystal pixel capacitance. The model correctly predicts voltage drops caused by the increasing dielectric constant when liquid crystal molecules align themselves to the electric field. An internal node of the macro model represents the average director orientation and can also be used to predict the optical response. In its basic embodiment, the model uses a first-order, low pass RMS filter to implement the dynamic behaviour of the pixel, which suffices to predict response delays and asymmetric rise and fall times. However, the model also supports more elaborated filters that offer more control over the simulated dynamic behaviour. A number of simulations are performed that illustrate the usefulness of the new model during the design of novel ‘smart’ pixel architectures.

Demonstration of a multiview projection display using decentered microlens arrays

In this work we present a prototype multiview projection display that combines high-spatial and high-angular resolution with low complexity, compact form factor and potentially low-cost design. The system consists of a single projector and an image steering projection screen. It is based on beam steering using decentered microlens arrays in the projection screen and time-sequential rear-projection of the view images. The prototype has a 25 in. screen, a total of 27 viewing zones with XGA resolution and a horizontal field of view of 30°.

Projection display for the generation of two orthogonal polarized images using liquid crystal on silicon panels and light emitting diodes

We present a projection system that is capable of two-dimensional and three-dimensional image display. A novel projection architecture is discussed that can simultaneously generate two linear polarized full-color images with orthogonal states of polarization using only one optical system. Both images are modulated by using two high-resolution liquid crystal on silicon panels that are illuminated with high-power light emitting diodes. The optical core and the illumination system are simulated, characterized, and optimized with nonsequential ray tracing software. A proof-of-concept demonstrator of the entire projection system is built and characterized. Important component specifications are discussed to improve the system performance.

SiGe MEMS technology: a platform technology enabling different demonstrators

In imecs 200mm fab a dedicated poly-SiGe above-IC MEMS (Micro Electro-Mechanical Systems) platform has been set up to integrate MEMS and its readout and driving electronics on one chip. In the Flemish project Gemini the possibilities of this platform have been further explored together with the project partners. Three different demonstrators were realized: mirrors for display applications, grating light valves (GLV) and accelerometers. Whereas the mirrors and GLVs are made with a similar to 300 nm thick SiGe structural layer plus optical coating, the SiGe structural layer thickness for the accelerometers is 4 mu m in order to improve the capacitive readout of in-plane devices. The processing and measurement results of these functional demonstrators are shown in this paper. These new demonstrators reconfirm the generic nature of the SiGe MEMS platform.

Method for measuring the cell gap in liquid-crystal displays

A method for measuring the cell gap of liquid-crystal displays (LCDs) is presented. It is based on analyzing the interference spectrum of white light reflected by the LCD. It can be used before or after filling the LCD. The method is applicable for LCDs whose operation is based on the polarization or the scattering of light. Four methods for the calcu- lation of the cell gap are presented. The first method is based on the wavelengths corresponding with the peaks in the interference spectrum. Two other methods use analog and digital filtering techniques to filter out all the irrelevant information in the interference spectrum; the cell gap is then calculated with fast Fourier transform (FFT) or the inverse FFT. In the fourth method an empirical model is fitted to the measured interfer- ence spectrum.

Comparison of the light output of LCOS projection architectures using LEDs

We investigate the optimal driving conditions of high power light emitting diodes (LED) in a four liquid crystal on silicon (LCOS) micro display projection architecture, taking lifetime issues of the LEDs into account. This architecture is an extension of a two LCOS panel approach. The possible light output is compared with other LCOS architectures as a function of relevant LCOS specifications.

Increased lumens per étendue by combining pulsed light-emitting diodes

LED-based projectors have numerous advantages compared to traditional projectors, such as compactness, larger color gamut, longer lifetime, and lower supply voltage. As LEDs can switch rapidly, there is the possibility to pulse. However, there is also an important disadvantage. The optical power per unit of etendue of an LED is significantly lower than, e.g., an ultra-high-performance (UHP) lamp. This problem can be remedied partly by pulsing the LEDs. If one drives an LED with a pulsed current source, the peak luminance can be higher, albeit the average luminance will not increase. By pulsing two LEDs alternately (50% duty cycle), their increased flux can be added up in time and will generate a higher average flux within the same etendue. We combine the LEDs with a polarizing beam splitter (PBS) and change the polarization of one LED with a switchable retarder. The achieved substantial net gain after all losses is 36%.

New model for the characterization and simulation of TFTs in all operating regions

Abstract— A new, semi-empirical model that describes TFTs in all operating regions with only one dynamic and five static parameters is proposed. This model can easily be implemented in most simulation programs and used to predict TFT circuit behavior. The five static parameters can automatically be extracted from current measurements and form a very compact yet adequate representation of the TFT characteristics. This proves especially useful when storing and statistically processing measurement results for a large number of devices, such as the pixel TFTs in an active matrix.

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

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 investigated.