Suppose a backlight designer wants to use hemispherical bumps on a light-guide to uniformly illuminate an LCD panel. The odds are that when the light-guide is
mass-produced, bumps that were perfectly hemispherical in the design will now have a flat top and something less than a sharp edge at the base.
Such discrepancies can cause differences between the simulated data and the measured distribution on a real part.
With the release of version 5.4, LightTools enhances its micro-optic design capabilities by allowing any solid geometry to be used as a texture feature. This user-defined texture enhancement allows a designer to create a nearly limitless variety of texture shapes for backlight and micro-lens design, as well as to accurately model the slightly deformed shapes of textures created in the manufacturing process.
With LightTools user-defined textures, a designer can use the simple or complex ideal shapes for the initial design, and then switch to the deformed shape when trying to simulate the performance of the actual part. The ability to model as-manufactured textures increases confidence in the simulation’s accuracy, reduces the need for costly prototypes, and, consequently, reduces the time to market.
To understand how user-defined textures can be applied, consider the example of a corner-cube retro-reflector, as shown in Fig.1. In this system, the user-defined texture element is a single corner-cube primitive, which was arrayed with hexagonal placement in a texture across the face of a solid.
LightTools’ texture placement capabilities have been enhanced with the addition of a new mesh placement control: minimum texture separation. With mesh placement, the surface upon which the texture sits is divided into a rectangular array of bins in which the density of the texture coverage can be controlled. LightTools controls the placement of individual textures in the bin and supports dithering, or randomisation, of the placement of textures in the bin. The minimum separation control allows the designer to specify the minimum allowable distance between two adjacent texture elements, preventing LightTools from specifying a density pattern that violates manufacturing constraints.
Version5.4 also introduces several improvements to the LightTools Optimization module, including two new Monte Carlo-based merit functions: collimate and focus. These two merit functions enhance a designer’s ability to perform two of the most common tasks in illumination design: collimating and focusing light from an extended source. The merit functions are easy to set up, and they converge quickly and robustly.
For the collimate merit function, the designer specifies the direction cosines for the desired collimation direction at a receiver surface. For the focus merit function, the designer specifies the X and Y location on a receiver surface for the desired focal point. It is also possible to allow these merit functions to forgo the definition of a spot location or direction and let the optimiser find the system that produces the smallest spot or best collimation, wherever they may occur, depending on the merit function type used. A wizard is provided to simplify the specification of the merit function parameters. These merit functions also report useful information at each iteration, from RMS spot size to the position and orientation of individual rays. Encircled energy data can also be reported per iteration.
Also added in the LightTools5.4 release are the new CATIAV5 data exchange modules, available to users as Beta features. The import module allows LightTools to open native CATIAV5 part and assembly files and modify them; the export module allows designers to save the modified geometry in CATIAV5 part file format. The new modules are available in addition to the existing suite of data exchange modules that include STEP, IGES, SAT, and CATIAV4. u
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Michael Zollers is a Senior Optical Engineer at Optical Research Associates, Pasadena, CA, USA. www.opticalres.com
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