We present two concepts to create multiview 3-D displays with high spatial and angular resolution at a reasonable system cost. We investigate a rear projection approach using only one projector with a digital micromirror device as a light modulator. The first concept is based on time sequentially illuminating the entire light modulator from different directions. Each illumination direction corresponds to a different viewing zone. We design an illumination system that generates all distinct illumination beams, and a lens system integrated into the projection screen to enlarge the viewing zones. A second concept is based on a projection screen architecture that steers images into different horizontal directions and does not require a directional illumination of the light modulator. In this way, the entire acceptance étendue of the projection system can be used for every image. This is achieved by horizontally moving a double-sided lenticular sheet with respect to a sheet of microlenses with a square footprint. Both concepts are investigated with advanced optical simulations.
KEYWORDS: Projection systems, Light emitting diodes, Liquid crystal on silicon, Modulation, 3D displays, LED displays, Digital micromirror devices, 3D visualizations, Visualization, 3D image processing
LED-based projection systems have several interesting features: extended color-gamut, long lifetime, robustness
and a fast turn-on time. However, the possibility to develop compact projectors remains the most important
driving force to investigate LED projection. This is related to the limited light output of LED projectors
that is a consequence of the relative low luminance of LEDs, compared to high intensity discharge lamps. We
have investigated several LED projection architectures for the development of new 3D visualization displays.
Polarization-based stereoscopic projection displays are often implemented using two identical projectors with
passive polarizers at the output of their projection lens. We have designed and built a prototype of a stereoscopic
projection system that incorporates the functionality of both projectors. The system uses high-resolution liquidcrystal-
on-silicon light valves and an illumination system with LEDs. The possibility to add an extra LED
illumination channel was also investigated for this optical configuration. Multiview projection displays allow the
visualization of 3D images for multiple viewers without the need to wear special eyeglasses. Systems with large
number of viewing zones have already been demonstrated. Such systems often use multiple projection engines.
We have investigated a projection architecture that uses only one digital micromirror device and a LED-based
illumination system to create multiple viewing zones. The system is based on the time-sequential modulation
of the different images for each viewing zone and a special projection screen with micro-optical features. We
analyzed the limitations of a LED-based illumination for the investigated stereoscopic and multiview projection
systems and discuss the potential of a laser-based illumination.
We present compact illumination engines for DMD projection systems making use of light emitting diodes (LEDs) as light sources. The impact of uniformization optics and color-combining dichroic filters is investigated with respect to the color uniformity on the screen. PhlatLight LEDs are considered as light sources because of their superior luminance levels. Also PhotonVacuum optics are used to collimate and transform the emitted LED light distribution. The optical engines are simulated with advanced non-sequential ray tracing software. They are evaluated on the basis of étendue efficiency, compactness and color uniformity of the projected images. Color plots are used as tools to investigate the simulated color gradients in the image. To validate our simulation models, we have built a compact prototype LED projector. Its color-related specifications are compared with the simulated values.
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.
Disparity estimation can be used for eliminating redundancies between different views of an object or a scene recorded
by an array of cameras which are arranged both horizontally and vertically. However, estimation of the disparity vectors
is a highly time consuming process which takes most of the operation time of the multi-view video coding. Therefore,
either the amount of data that is to be processed or the complexity of the coding method needs to be decreased in order to
encode the multi-view video in a reasonable time. It is proven that the disparities of a point in the scene photographed by
cameras which are spaced equidistantly are equal. Since there is a strong geometrical correlation of the disparity vectors,
the disparity vector of a view can for most blocks be derived from the disparity vector of another view or views. A new
algorithm is presented that reduces the amount of processing time needed for calculating the disparity vectors of each
neighboring view except the principal ones. Different schemes are proposed for 3x3 views and they are applied to
several image sequences taken from a camera-array. The experimental results show that the proposed schemes yield
better results than the reference scheme while preserving the image quality and the amount of encoded data.
In this publication we investigate the optical design of a illumination system with a fly's 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.
We present a single optical system that can simultaneously generate two linear polarized full-color images with
orthogonal state of polarization. The system architecture of the optical core is discussed. Four liquid crystal
on silicon panels are used to modulate both images. We also discuss the design of the illumination system
with light emitting diodes as light sources. The contrast of both images is simulated. A proof-of-concept
demonstrator is built and experimentally characterized. It is capable of two-dimensional and three-dimensional
image display. Three-dimensional images can be perceived, independent of the tilt angle of the viewer's head, by
wearing specific polarization sensitive eyeglasses and placing a quarter-wave retarder at the projector's output.
Important component specifications are overviewed to improve the performance of the demonstrator setup.
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 étendue, 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.
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.
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.
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