KEYWORDS: Bidirectional reflectance transmission function, Reflectivity, Data modeling, Ray tracing, Laser induced damage, Near field optics, Light sources, Light emitting diodes, Prototyping, Near field
The reliability of ray tracing simulations is strongly dependent on the accuracy of the input data such as the bidirectional reflectance distribution function (BRDF). Software developers offer the possibility to implement BRDF data in different ways, ranging from simple predefined functions to detailed tabulated data. The impact of the accuracy of the implemented reflectance model on ray tracing simulations has been investigated. A light-emitting diode device including a frequently employed diffuse reflector [microcellular polyethylene terephthalate (MCPET)] was constructed. The luminous intensity distribution (LID) and luminance distribution from a specific viewpoint were measured with a near-field goniophotometer. Both distributions were also simulated by use of ray tracing software. Three different reflection models of MCPET were introduced, varying in complexity: a diffuse model, a diffuse/specular model, and a model containing tabulated BRDF data. A good agreement between the measured and simulated LID was found irrespective of the applied model. However, the luminance distributions only corresponded when the most accurate BRDF model was applied. This proves that even for diffuse reflective materials, a simple BRDF model may only be employed for simulations of the LID; for evaluation of luminance distributions, more complex models are needed.
We present an enhanced out-of-plane coupling component for Printed Circuit Board-level optical interconnections.
Rather than using a standard 45° micro-mirror to turn the light path over 90° we introduce a curvature in the
mirror profile and incorporate an extra cylindrical micro-lens for beam collimation. Both modifications enable
an increase in coupling efficiency and are extensively investigated using non-sequential ray tracing simulations in
combination with Matlab optimization algorithms. The resulting design is fabricated using Deep Proton Writing
and experimental characterization of the geometrical properties and measured coupling efficiencies are presented.
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.
High brightness light emitting diodes (LEDs) become a serious alternative for ultrahigh performance lamps in projection displays. We focus on the illumination part of a LED projection engine. We discuss the problem of using several LED light sources for each primary color. In critical applications, the use of several light sources for each color has important benefits. It increases the possible light output to the screen and makes it possible to design a system that is tolerant for failures of one of the LEDs. Therefore, we need an optical system that is both efficient and is able to produce a uniform light beam if one of the LEDs fails. We show that our illumination engine using a fly's eye integrator meets 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 LED collimation reflective device with collection efficiencies up to 95%. The lens systems in the engine were designed with the same method. This results in a total system efficiency of 77%.
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.
In our contribution we present a solution to an important question in the design of a LED-based illumination engine for projection systems: the collimation of the LED light. We tested the principle in the modification of a common device in non-imaging optics, the compound Parabolic Concentrator. This CPC-like achieves a collection of 72% (ideal reflective coating presumed). This CPC-like was tailored by numerically solving an differential equation. This approach has some serious drawbacks. For a compact collection device with high collimation, an other approach is required. A more elegant design strategy will rely fully on geometrical principles. The result of our work is a compound collection lens that achieves a collection efficiency of 87%, assuming an ideal reflective coating and neglecting Fresnel losses. We study the performance of this device in detail. Further enhancements are suggested.
Illumination systems with lens array integrators for LED-based projection systems are thoroughly investigated. The aim is to develop compact and efficient projection systems with a high image-quality. Different possible illumination configurations for single-panel LCOS projection architectures, are critically evaluated with the use of advanced optical simulations. LED-light collectors which are to be used in combination with the lenslet integrators are also investigated.
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