We develop a method to determine volumetric scattering model parameter values based on measured BSDF characteristics. Example models often use Mie or Gegenbauer particles. The accuracy and flexibility of this approach are illustrated.
Automatic optimization algorithms can be used when designing illumination systems. For systems with many design variables, optimization using an adjustable set of variables at different steps of the process can provide different local minima. We present a few examples of implementing a multi-step optimization method. We have found that this approach can sometimes lead to more efficient solutions. In this paper we illustrate the effectiveness of using a commercially available optimization algorithm with a slightly modified procedure.
A hollow backlight unit (HBLU) preserves all the benefits of a conventional backlight unit based on a solid light guide but has a lower weight and cost. We study the performance of a unique HBLU architecture vs. various parameters of the backlight assembly.
The field of illumination optics has a number of applications where using free-form reflective surfaces to create a required light distribution can be beneficial. Oliker’s concept of combining elliptical surfaces is the foundation of forming a reflector for an arbitrary illuminance distribution. The algorithm for fast implementation of this concept is discussed in detail. It is based on an analytical computation of a 3D cloud of points in order to map the reflector shape with the required flux distribution. Flux delivered to chosen zones across the target can be calculated based on the number of associated cloud points and its locations. This allows optimized ellipse parameters to achieve the required flux distribution without raytracing through the reflector geometry. Such a strictly analytical optimization is much faster than building reflector geometry and raytracing each step of the optimization. A generated 3D cloud of points can be used with a standard SolidWorks feature to build the loft surface. This surface consists of adjacent elliptical facets and should be smooth to maintain continuous irradiance across the target. A secondary operation to smooth the surface profile between elliptical facets is discussed. Examples of proposed algorithm implementations are presented.
An illumination system for a microdisplay projector with a two-step imaging system is described here. In the first step,
an imaging condenser creates an image of the LED at the color combiner entrance window. In the second step, we relay
the image of the integrator exit window onto the micro-display. The illuminator demonstrates high collection efficiency,
small footprint, and efficient mixing of light from RGB LEDs that provides required uniformity. A variety of approaches
to collecting light emitted from LEDs of various types are compared, leading to the two-step design. A design example
using a 0.55” diagonal DLP-based optical engine is presented with the following characteristics:
Footprint: 3.9”x3.3”x2.0” (25.7 cubic inches)
Light output: 338 white lumens
Efficiency: 4.7 lm/watt
General lighting applications often require a light patch with a specific shape and distribution. This work presents
examples and details of a practical implementation of Oliker's ellipsoidal faceted reflector algorithm. We present
example designs for various shapes of light patches. Uniformity and limitations of this technique are discussed.
Analytical solution can be used to obtain a starting point for optimization. A technique to generate a smooth best fitting
surface to meet manufacturing requirements is also presented.
3M Polarization Beam Splitter (PBS) technology has been shown to be the most light efficient solution to the needs of
LCOS projection. It also provides very high contrast and extremely uniform dark states without the use of lead in the
glass prisms. We report on recent improvements in contrast performance, increased understanding of the effects of pupil
shape and size on contrast, effects of temperature on optical performance, and improved photostability. We also suggest
new light-engine architectures employing the 3M PBSs with associated light budget analyses.
We consider the problem of enhanced analyses to predict/visualize the level of color correction in projection lenses. Modern optical science describes all aspects of chromatic aberrations; however on the projection screen we can see not individual aberrations, but the cumulative effect of light propagation through the system. For example, a combination of spherochromatism and lateral color can create a result that is difficult to visualize. The purpose of this work is to fill the gap between aberration theory and image quality as it can be observed on the screen. One of the important parameters of image quality in the projection industry is the coloration of the border between wide black and white areas on the screen. We developed a computer model for full color image analyses. The output of such modeling is the edge function for individual (up to five) wavelengths or superposition of monochromatic edge functions with chosen waiting factors. It can be presented in graphical and color-coded formats. Basically, the computed superimposed edge function corresponds to what can be seen on the screen. The software supports calculations for a nominal system and for a disturbed system when any possible mechanical error is introduced. Nominal system analysis is useful at the stage of optical design evaluation. Analysis of a disturbed system is a very important instrument for the study of opto-mechanical sensitivity and optimization of the mechanical structure of the lens assembly.
One of the well-known layouts of illumination systems for projection displays consists of an elliptical lamp reflector, an integrator and an optical relay. The presented analysis of the system is based on the paraxial properties of the relay and on the computer simulation of the source of light. This analysis allows system optimization, thus maximizing the geometrical collection efficiency for chosen lamp and for given etendue (target size and effective system F-number) of the optical system. Results of experimental tests are presented.
Optomechanical sensitivity is the amount of image quality degradation in response to a certain deviation of any primary parameter of an optomechanical system. The sensitivity depends not only on the optical system but also on the mechanical layout. A technique for calculation of optomechanical sensitivity is presented. Only mechanical parameters are used as primary parameters. It is shown that airspaces or element tilts and decentrations cannot be used as primary parameters. The tolerances of an optomechanical system can be determined based on the computed sensitivity. Edge Function is used to evaluate the image quality for projection lenses. Software for realization of this technique has been developed. Examples of optimization of the optomechanical system of a projection lens using the developed technique are presented.
This paper describes both an analytical method and an autocollimation microscope for enhanced measuring the position of the center of curvature for a single optical surface in a lens assembly. Because the test is done in a non-destructive manner, it is possible to measure the position of the image of the center of curvature, but not the position of the center of curvature. The developed mathematical model determines the position of the centers of curvature in the lens assembly on the basis of measuring results. It takes into consideration the real position of all surfaces placed between test surface and microscope. When the measurement is complete for all surfaces, the optical axis of the assembly is determined as an average line through all of these measured centers. The decentration and tip of the optical elements can then be controlled with regard to this optical axis. Experiments verify the developed analytical model and software. The accuracy of the measurement is better than 10 microns.