Marcel P. C. M. Krijn

2-D/3-D displays based on switchable lenticulars

— An attractive concept for 3-D displays is the one based on LCDs equipped with lenticular lenses. This enables autostereoscopic multiview 3-D displays without a loss in brightness. A general issue in multiview 3-D displays is their relatively low spatial resolution because the pixels are divided among the different views. To overcome this problem, we have developed switchable displays, using liquid-crystal (LC) filled switchable lenticulars. In this way, it is possible to have a high-brightness 3-D display capable of fully exploiting the native 2-D resolution of the underlying LCD. The feasibility of LC-filled switchable lenticulars was shown in several applications. For applications in which it is advantageous to be able to display 3-D and 2-D content simultaneously, a 42-in. locally switchable prototype having a matrix electrode structure was developed. These displays were realized using cylindrically shaped lenticular lenses in contact with LC. An alternative for these are lenticulars based on gradient-index (GRIN) LC lenses. Preliminary results for such switchable GRIN lenses are presented as well.

LED-based mini-projectors

We have built a mini-projector with LED light sources that is sufficiently small for portable applications. The projector has a three-panel architecture with transmissive LCD micro-displays in order to combine a high lumen output with a low cost price. The volume of the light engine is 100 cc.

Ray-tracing simulations of liquid-crystal gradient-index lenses for three-dimensional displays

For the first time, to our knowledge, we report ray-tracing simulations of an advanced liquid-crystal gradientindex lens structure for application in switchable two-dimensional/three-dimensional (3D) autostereoscopic displays. We present ray-tracing simulations of the angular-dependent lens action. From the results we conclude that the lens action of the advanced optical design corresponds to the desired performance for small viewing angles. For oblique viewing angles of approximately 30° and higher, the lens action becomes significantly weaker compromising the 3D performance of an autostereoscopic display. The general approach and the advanced ray-optics analysis procedures presented form a useful tool in the search for improvements for high viewing angles and enable a better understanding of the liquid-crystal technology discussed.

28.1: Invited Paper: Multi-view 3D Displays

In this paper we analyze the performance of multi-view barrier and lenticular based 3D displays in their most important display properties, being resolution, brightness, uniformity and cross-talk. We will show that the barrier display is superior in uniformity and that the lenticular is superior in brightness. We will show that the cross-talk and uniformity of an ideal slanted barrier equal that of an ideal defocused lens. for a realistic barrier we will show that diffraction increases the cross-talk but does not change the uniformity. We will also show that the spherical aberrations of the cylindrical lens limit the uniformity of the display but do not affect the cross-talk.

Electrostatic aberration correction in low-voltage SEM

The resolution of a low-voltage scanning electron microscope is limited by the chromatic and spherical aberration of the objective lens. Any significant improvement of the resolution requires an aberration corrector or monochromator. Recently, correction of both Cc and Cs has been demonstrated in a SEM, using a combination of magnetic and electrostatic quadruples and octuples. This paper presents an alternative and purely electrostatic design which, like most quadrupole-octuple correctors, is based on the concept of creating a stigmatic path and correcting Cc in the two line foci. We propose a combination of strongly oscillating mono- and quadruple fields as dispersive elements. Our arrangement of the mono- and quadruple fields creates a thick non-focusing correcting elements, which corrects for Cc in one plane, while these fields act as a telescope (with magnification M=+/- 1) in the other plane. The telescopic properties of the correcting element in both planes reduce the chromatic magnification aberration of the corrector to acceptable proportions. To model our corrector realistically, the electrostatic potential has been computed for a 3D electron geometry with the EO-3D package from MEBS. From this the electrostatic potential has been computed for a 3D electrode geometry with the EO-3D package from MEBS. From this potential we extracted axial field functions for the monopole up to octuple fields. Ray tracing with these axial fields using MEBSs MULTIPOL package yields all aberrations up to fifth order. The numerical calculations show a resolution enhancement by a factor of 2 with a Cc and Cs corrector that is based on our novel correcting elements.

Injecting light of high-power LEDs into thin light guides

A new method using a thin-film multilayer filter is described to couple light from high-power LEDs into a thin light guide such as an LCD backlight. Light emitted below the critical angle is reflected back to the LED and recycled. Largeangle emitted light passes the filter and is transported by total internal reflection in the light guide. The light guide can be as thin as 0.3mm for an LED of 1x1mm2, and the best coupling efficiency is estimated to be around 80%. With this approach, a backlight system can be greatly simplified but also compact collimators can be realized. In this paper the optical design and testing of the filter is described, and a 1mm thick, 6.5mm diameter collimator is presented that emits in a cone of 2×13°. Measurements on prototypes show good agreement with the designed characteristics.

Large, thin, flexible and low-cost light emitting surfaces

Solid State Lighting is becoming increasingly more advanced, both in terms of lumen output as well as energy efficiency. At the same time, packages emitting enough lumens for lighting applications are decreasing in size. This smaller packaging enables several new applications. In this paper we will discuss one of these new applications: low cost, large, flexible and very thin light emitting surfaces. Our approach consists of using very thin transparent lightguides. Due to their limited thickness, these lightguides are quite flexible. Tiny low power, side-emitting LEDs are used to couple light into these lightguides. A carefully calculated outcoupling structure ensures light is coupled out uniformly. Although this general principle is known, some aspects are new to our approach. The flexibility of our thin lightguides can be very useful for numerous lighting applications; a radius of curvature of just a few centimeters is easily obtained, while still maintaining good outcoupling and uniformity. Furthermore, we show that for several geometries, a perfect homogeneous brightness can only be obtained using a precise pattern and density distribution of outcoupling structures.

Color reproduction for LED-based general lighting

Solid State Lighting is becoming increasingly more advanced, both in terms of lumen output as well as energy efficiency. However, implementation in color consumer lighting products, such as the Philips Ambilight television sets, still requires improvements in both color reproduction as well as intensity uniformity. To build a lighting system capable of correctly reproducing a large color spectrum, 3 primary colored LEDs are required. However, this approach causes problems. In particular, the generation of a white color without color fringes is difficult to implement, as the total amount of light from each primary color should ideally be identical at each position within the light bundle. Our paper focuses on systems using a limited number of high power LEDs. The lumen output of these LEDs is such that even a single red, green and blue LED together can deliver the required lumen output for certain applications. To optimize performance for both luminance and color uniformity we investigated several design options. Ray tracing simulations are compared to the performance of real size prototypes, and recommendations are given for the design of color lighting systems.

Optical design and laser ablation of surface textures: demonstrating total internal reflection

In lighting applications key drivers for optical design of surface textures are integration of optical elements, the disentanglement of optical functionality and appearance and late stage configuration. We investigated excimer laser ablation as a mastering technology for micro textured surfaces, where we targeted an increase in correspondence between surface design and ablated surface for high aspect ratio structures. To achieve this we have improved the photo mask design using a heuristic algorithm that corrects for the angular dependence of the ablation process and the loss of image resolution at ablation depths that exceed the depth of field. Using this approach we have been able to demonstrate close correspondence between designed and ablated facet structures up to 75° inclination at 75 μm depth. These facet design parameters allow for total internal reflection (TIR) as a means of beam deflection which is demonstrated in a range of mono shaped cone arrays in hexagonal tessellation. BSDF analysis was used to characterize the narrow TIR deflection beams that matched the peak positions of the design down to 28° apex. In addition, a single surface TIR-Fresnel lens design with focal distance 5 mm has been manufactured using this photo mask design algorithm and beam collimation up to 12° beam angle and 32° field angle is shown. These outcomes demonstrate that the laser ablation process intrinsically yields sufficient small dispersion in structure and fillet radii for lighting applications.

Enabling eye-contact for home video communication with a multi-view autostereoscopic display

In this paper we present a system for real-time home video communications with multiple users. In order to offer a more natural face-to-face-like communication experience, we have designed a special 3D multi-view display showing different perspectives from different viewing positions. This enables proper directional eye contact and at the same time offers the sense of true physical presence. Our prototype system has clearly shown advantages as compared to existing video communication system for improved naturalness.