Centre for Sensors, Instruments and Systems Development

Universitat Politècnica de Catalunya

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2D strategy to design reflectors using freeform facets

Next November 11th, Núria Tomàs will defend her doctoral thesis entitled "2D strategy to design reflectors using freeform facets." The thesis has been directed by Dr. Josep Arasa.

Date: November 11, 2015
Time: 12:30
Location: Passeig 22 de Juliol 660, Terrassa
website: http://foot.upc.edu/es/lescola-es/nuestras-instalaciones/auditorio-joan-salvado


This work can be framed in the field of computer-aided optical systems design and it is a part of a larger project in which automated processes are studied and implemented aiming to reduce the time span that stands between the idea and the functional device. One of the problems in optical systems optimization is the need for a predesign good enough to start, so that the automatic system is effective and leads to a quality optical system. To define a general criteria for initial conditions that are valid to start a process of automatic design in the specific field of non-imaging optics, is an objective which contributes to the capacity of the industry responding to market demands.

A strategy is defined to design reflectors as non-imaging optical systems in two stages: the first stage performs the design of a single reflective freeform surface providing a predetermined light distribution. The second stage defines the method that can generate valid initial configurations for the overall design of non- imaging optical systems.
In order to design a one surface freeform reflector, a 2D strategy to build 3D solutions is defined which can describe the geometry of the freeform reflector using Bezier surfaces through a simplified calculation process in 2D. The process of choosing 2D planes where to apply the strategy is based on expanding the criteria on what is accepted as a solution to transport light between two points. The basis and appropriate approaches have been defined in order to go from an exact solution to a plausible solution. An alternative method is presented, which is approximate and computationally simpler, but allows plausible solutions in the general case that the source is not placed in the plane defined by the direction normal to the facet. In this case, the projection of the source in this plane provides an acceptable solution if you choose the right working conditions. The error has been delimited when using such a projection instead of finding the exact point that corresponds to one of the ellipse’s focus contained in the plane. It is found that the error is acceptable within the purposes of the present study.

Applying the formulation of Snell’s law in Bezier curves placed on strategic planes, a method for calculating the control points that defines the solution as a Bezier surface is provided. For that purpose, enhancement functions responding  to various purposes, such as concentrate or distribute light around the chosen target points, are used .
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