Freeform Optics

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Rolf Wester

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Rolf Wester

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+49 241 8906 401

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Refracting and reflecting surfaces that strongly depart from spherical and aspherical shapes are often referred to as freeform optics. Here, the techniques of classical optics design can no longer be applied and new algorithms need to be developed, focusing on the efficient redistribution of energy to tailor irradiance and intensity distributions. Freeform optics are used in high-efficiency luminaires, to reduce energy consumption and operating costs for a given illumination setup. Additionally, freeform optics achieve a flexible shaping of light distributions.

The Freeform Optics group develops freeform optics tailored to the non-imaging applications of our industrial and research customers. Collaborating with local manufacturers, we provide virtual prototypes with production-ready design as well as the characterization of the finished optical systems.

 
 

Design of highly efficient freeform optics

Compact freeform lens for an automotive fog lamp Fraunhofer ILT Compact freeform lens for an automotive fog lamp

The main focus of our research is the application-oriented design of optical freeform surfaces, specifically surfaces with almost arbitrary boundaries and gaps, the calculation of freeform-optical systems consisting of multiple freeform surfaces, and the treatment of real, extended light sources. In the development of such design algorithms, we benefit from research in the fields of differential geometry, computer graphics as well as nonlinear optics.

The Chair for Technology of Optical Systems (TOS) develops design algorithms for freeform optical surfaces that meet these requirements. Key characteristics include the algorithms’ flexibility when designing two-part freeform optical surfaces, whereby refracting and reflecting surfaces can be combined within a single optical element. By combining two complementary freeform refracting surfaces it is possible to reduce losses caused by Fresnel reflection and, in contrast to freeform optics with only one freeform surface, increase efficiency as closely as possible to its maximum point.

Although in theory freeform tailoring methods can achieve very complex irradiance distributions, this capability is limited to point light sources. As real sources are always extended to a certain degree, approximations are used to describe them. At the Chair TOS, we are developing phase-space-based techniques capable of working out freeform optical surfaces with extended sources, thus removing the need for approximation.

 
 

Prototype development

Injection-moulded freeform lens mounted on LED Fraunhofer ILT Injection-moulded freeform lens mounted on LED

Our years of experience in the realization of freeform optics and our close working relationships with manufacturers guarantee that the virtual prototypes we produce can be used to manufacture finished optics. We assist our customers in developing pioneering technologies that range from optical simulators to designs for functional optical elements with smooth or microstructured freeform surfaces. We also help them optimize the chosen manufacturing process.

A given optics design is first used to create a virtual prototype that is then put through its paces using simulation software. At the Chair TOS we have access to a wide range of software packages – some commercial, others developed in-house – that can be used to verify photometric parameters and determine the influence of production and assembly tolerances.

 
 

Analysis of lighting systems

High-efficiency freeform optics for street lighting Fraunhofer ILT High-efficiency freeform optics for street lighting

The Chair TOS provides the measurement and functional assessment of manufactured optical prototypes. Measurements of light intensity and luminance as well as assessment of the prototypes’ light-intensity distributions ensure that the desired functionality can be precisely carried over into series production.