Lawrence Bogaert

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.

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.

Single projector multiview displays: directional illumination compared to beam steering

We present two multiview rear projection concepts that use only one projector with a digital micromirror device light modulator. The first concept is based on time sequentially illuminating the light modulator from different directions. Each illumination direction reflects on the light modulator toward a different viewing zone. We designed an illumination system that generates all distinct illumination beams and a lens system integrated into the projection screen to enlarge the viewing angles. The latter is crucial since the viewing extent of the viewing zones decreases inversely proportional to the size of the projected image. A second concept is based on a specific projection screen architecture that steers images into different horizontal directions. In this way, the entire acceptance ´etendue of the projection system can be used for every image. This is achieved by moving a double-sided lenticular sheet horizontally with respect to a sheet of microlenses with a square footprint. Both concepts are investigated with advanced optical simulations.

Prototyping micro-optical components with integrated out-of-plane coupling structures using deep lithography with protons

We present Deep Lithography with Protons (DLP) as a rapid prototyping technology to fabricate waveguide-based micro-optical components with monolithically integrated 45° micro-mirrors acting as out-of-plane couplers, splitting the optical signal in 3 separated paths. For the first time, two different proton beam sizes are used during one irradiation and a 20μm collimating aperture is chosen to accurately define the out-of-plane coupling structures. We fully optimized the DLP process for this 20μm proton beam and we measured the surface roughness (Rq=27.5nm) and the flatness (Rt=3.17μm) of the realized components. Finally, we experimentally measured the optical transmission efficiency of the micro-optical splitter component. The results are in excellent agreement with non-sequential ray-tracing simulations performed for the design. Above that, we present a pluggable out-of-plane coupler incorporating a single micro-mirror for the 90° coupling of light to or from polymer multimode waveguides integrated on a printed circuit board (PCB). This millimeter-sized mass-reproducible component can then be readily inserted into laser ablated cavities. Nonsequential ray-tracing simulations are performed to predict the optical performance of the component, showing coupling efficiencies up to 78%. These results are then experimentally verified using piezo-motorized positioning equipment with submicron accuracy in a multimode fiber-to-fiber coupling scheme, showing coupling efficiencies up to 56%. The fabricated coupling components are suitable for low-cost mass production since our micro-optical prototyping technology is compatible with standard replication techniques, such as hot embossing and injection molding, has been shown before.

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.

Efficient disparity vector prediction schemes with modified P frame for 2D camera arrays

An efficient disparity estimation algorithm for multi-view video sequences, recorded by a two-dimensional camera array in which the cameras are spaced equidistantly, is presented. Because of the strong geometrical relationship among views, the disparity vectors of a certain view can for most blocks be derived from the disparity vectors of other views. A frame constructed using that idea is called a D frame in this work. Three new prediction schemes which contain D frames are proposed for encoding 5x3 multi-view video sequences. The schemes are applied to several multi-view image sequences taken from a camera-array and they are compared in terms of quality, bit-rate and complexity. The experimental results show that the proposed prediction schemes significantly decrease the complexity of the encoder at a very low cost of quality and/or bit-rate.