Completed her master studies in Electrical Engineering and Information technology, Annie Shalom Isaac is currently working towards her doctoral thesis at the Light Technology Institute at the Karlsruhe Institute of Technology (KIT), Germany. Her research focusses on novel optimization technologies and manufactural tolerances for the optical simulations in the LED illumination design. She is working towards developing a complete automated software tool for the design and optimization of free-form optics which in future could eliminate the need for an optics designer’s expertise. She is a member as well a winner of the best paper award from SPIE and a fellow of the Karlsruhe School of Optics and Photonics (KSOP).
Optimization of Free-Form Optics Using T-Splines in LED Illumination Design
Free-form optics is the game changer in the illumination industry in terms of its ability to redirect the light into the target area. The design of free-form optics relies heavily on one of the methods: tailoring based on point source assumption, SMS design, and many others to create an initial optical surface. As these mathematical methods are not guaranteed to provide accurate results for extended LED sources and as well do not provide generalized solutions, an optical designer still relies on any optimization tool to improve the results.
In free-form optics, Non-Uniform Rational B-Splines (NURBS) is used to represent free-form curves and surfaces. The free-form shape can be varied flexibly by changing the control points or their weights. So an optimization of free-form optics basically means transformation or displacement of the control points present in the NURBS to create a new surface, evaluate it using a defined merit function, iterate until the target functionality is attained. This method works great for global transformation or modification of optical surfaces.
But there are certain optical design tasks that require modification only at certain regions in the surface. In such specific cases, NURBS does not provide a local modification to the optical surface and even optimization routine fails to provide improvement no matter how long it runs. This is mainly due to the underlying mathematical representation of the NURBS making it infeasible for local refinement. On the other hand, a new mathematical representation called T-Splines make this possible by inserting more control points in the desired region. But this has not been implemented so far in any optimization routine and evaluated although its potentialities are very well described.
So this work takes the advantage of the local refinement ability of the T-Splines by implementing it in the optimization routine and evaluation is made. In our method, we add more control points to the region locally where deformation is required which is impossible in NURBS. Results show that more uniform and homogeneous light distribution is attained as compared to NURBS. Moreover, optimization results are also faster with T-Splines than with NURBS when a local modification is necessary. As it is just a different mathematical representation of the same optical surface, it can be used irrespective of the optimization algorithms ranging from Nelder-Mead simplex to complex evolutionary optimization algorithms which have been too verified as a part of this work. This makes optical design or optimization using T-Splines, an intuitive approach for future free-form optical designs.