Bart Van Giel

Using a fly’s eye integrator in efficient illumination engines with multiple light-emitting diode light sources

Abstract. High brightness light emitting diodes LEDs become a seri-ous alternative for ultrahigh performance lamps in projection displays.We focus on the illumination part of a LED projection engine. We discussthe problem of using several LED light sources for each primary color. Incritical applications, the use of several light sources for each color hasand makes it possible to design a system that is tolerant for failures ofone of the LEDs. Therefore, we need an optical system that is bothefficient and is able to produce a uniform light beam if one of the LEDsfails. We show that our illumination engine using a fly’s eye integratormeets these requirements, using ray-tracing simulations of the engine.An efficient optimization method based on the simplex method R. J.Koshel, Opt. Lett. 30 , 649–651 2005 was developed to design the LEDcollimation reflective device with collection efficiencies up to 95%. Thelens systems in the engine were designed with the same method. Thisresults in a total system efficiency of 77%.

Low-speckle laser projection with a broad-area vertical-cavity surface-emitting laser in the nonmodal emission regime

We demonstrate low-speckle laser projection using a broad-area vertical-cavity surface-emitting laser (VCSEL) emitting at 840 nm wavelength as the illumination source. By driving the source in a nonmodal emission regime, we were able to achieve speckle contrast values as low as 3.5% in a realistic projection setup. This was done by driving the VCSEL with specific current pulses without using any additional or mechanically moving components to destroy the coherence of the laser beam. We quantitatively model the speckle contrast reduction based on polarization scrambling and the reduced temporal and spatial coherence of the VCSEL.

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.

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.

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.

Two liquid crystal on silicon panel projector with efficient light-emitting diode illumination engine

LED-based projectors have numerous advantages compared to traditional projectors. They are more compact, they exhibit a larger color gamut and a longer lifetime, the supply voltage is lower and they can even operate on batteries. LEDs can switch rapidly (possibility to pulse) and they have a high dimming ratio (contrast considerations). However, they have low optical power per etendue, although this is also improving consistently. With an efficient illumination engine design we can build an LED projector with a moderate light output and with superior properties. We present a relatively compact LED projector with two liquid crystal on silicon (LCOS) light valves (LVs). One of these LVs alternately modulates red and blue information, while the other permanently modulates green information to achieve a good color balance. Additionally, we apply some methods to increase the brightness on the screen. Our two-LCOS approach results in a compact, efficient LED projector that produces 171 lm projected D65 flux.

Efficient and compact illumination in LED projection displays

In this paper we propose an efficient illumination engine for LED based projection systems. Our design had to be both compact and efficient. We designed the projector with two LCOS light panels. We investigate two phenomena that affect the optical efficiency of this projector. We show that a relevant gain of the light output can be obtained by using certain methods.

LED based full color stereoscopic projection system

We present a compact light emitting diode (LED) based projection system with potential for stereoscopic viewing. The optical core consists of four polarizing beam splitters (PBS), positioned in a cross configuration, with wavelength selective half wave plates placed between them. Four liquid crystal on silicon (LCoS) panels are located at the exterior facets of two PBSs in opposite corners of the cuboid. The illumination system combines individual LED sources and ensures telecentric illumination through the optical core. This architecture gives rise to two light paths that independently generate two linear polarized images with orthogonal polarization direction. When the observer wears polarization sensitive eyeglasses and a polarization maintaining screen is used, each eye will see a different projected image such that three-dimensional (3-D) viewing can be perceived. On the other hand, 2-D vision is possible by projecting two identical images.

LED projector with two liquid crystal on silicon light valves and a fly`s eye integrator

Abstract We present a projection system with two liquid crystal on silicon light valves that are illuminated by light-emitting diode light sources (LEDs). The LED illumination system is designed with a fly’s eye integrator. Using this integrator we combine for each primary color two LEDs into one bright source to illuminate the light valve. In the color management system a wire-grid polarizer is used to combine two beams with opposite state of polarization. The contrast behavior of our two LCOS approach is investigated with a basic model and ray tracing. The consequences of using this polarizer are discussed. We present contrast, uniformity and light output measurements of a concept demonstration set-up.

Optical design of a compact illumination system for LED projection displays

In this publication we investigate the optical design of a illumination system with a flys eye integrator for LED projection displays. We compare the performance of CPC-like collimators and tapered light pipes with respect to their optical efficiency. We show that the tapered light pipes with a lens are more efficient and can be used to collimate the light of rectangular LED modules too. Using these tapered light pipes we design an illumination system with tilted collimators. This adapted 2F processor makes a more compact illumination system possible.