Freeform optics for innovative illumination solutions

Freeform optical surfaces are based on the same principles as conventional optical elements: incident light is either reflected or refracted. Unlike traditional optical elements, freeform surfaces can assume any shape and do not need to be symmetrical. This means that they can be matched optimally to a particular application, which allows for compact and efficient illumination appliances for both niche and high-volume markets. Additionally, this technology makes it possible to implement tailored solutions for optical measurement schemes, making it possible to produce low-cost optoelectronic sensors. For years, Helbling has been developing new applications that use the advantages of freeform optical surfaces. These have included rain/light sensors for the automotive industry and illumination systems for camera modules.

There are obvious advantages to freeform optical surfaces: light sources themselves usually produce a wide light cone without any significant structure. However, if only a certain region is to be illuminated, then the optical element must deflect light rays and distribute the light intensity accordingly. In such situations, freeform surfaces are well-suited, because often a single element can produce the desired effect. This helps with meeting requirements for a specific intensity distribution and tight space constraints, usually resulting in high optical efficiencies. In addition to homogeneously illuminated surfaces, any intensity distribution can be created.

Helbling uses a combination of two different simulation tools during the development process for freeform optical surfaces: first, «FFOptik» is used to precisely calculate the freeform surface with idealized conditions for a desired intensity distribution. In a second step, realistic simulations are performed with «LightTools», which uses extensive material and LED databases and employs the ray-tracing method. Based on the simulation results, it is possible to iteratively adjust the calculation of the freeform surface where necessary.

Helbling can quickly and easily realize the first functional models of a plastic optic in close cooperation with its partners. The optical elements are manufactured within about ten working days by diamond turning or milling using the latest high-precision machines. Rapid prototyping techniques are used to integrate these into a functional model with the appropriate light source. Subsequently, the intensity distribution can be measured and characterized in Helbling’s optics lab or can be tested by the customer in the desired application.

In series production, freeform optical elements are manufactured by injection molding or glass molding. Importantly, whether it is a traditional, spherical optical element or a freeform surface is irrelevant in terms of production costs. These costs primarily depend on the required tolerances and surface accuracy, but not on the actual shape of the surface.

Freeform optical elements are especially useful for improving the intensity distribution in situations where the optics cannot be attached centrally above the target area but instead must be placed to the side due to space constraints. One concrete example is the illumination optics for a camera application. Here, the freeform optics compensate for the drop in brightness at the edges of the objective lens, which is called vignetting. Other examples are tailored beam shaping for lasers, illumination for HMIs, or applications with light guides.

For illumination applications, a freeform optical surface distributes the optical power to the surroundings. In addition to this, freeform optics can also collect light from the environment and direct it toward a detector. Specific examples of this are light measurements for motion sensors in rooms or rain/light sensors for the automotive industry. This opens up the possibility of developing optoelectronic sensors in the low-cost range.