We present a miniature freeform lightguide for sensing applications, designed according to the principles of the flow-line method from Nonimaging Optics. The optic is obtained by combining two 2D flow-line concentrators in a curved monolithic piece, achieving 45° half-acceptance angle and 40° beam steering in a very compact volume (about 1.3 x 2.0 x 20 mm3). We show how the initial design has been adjusted after a thorough tolerance analysis and describe its fabrication through plastic injection molding. The design of the mold involves a non-standard 3D-puzzle approach, which allows uniform high optical quality and minimizes the fillet radius on the optic.
One of the most interesting problems in the illumination research community is the design of optics able to generate prescribed intensity patterns with extended input sources. Such optics would be ideally applied to the current generation of extended, high-brightness, high-CRI LEDs used in general illumination, allowing reduced size of luminaires and improved efficiency. But in 3D, for non-symmetric configurations, how to design optics for prescribed intensity using extended sources remains an open question. We present an alternative approach to this problem, for the case of extended Lambertian sources, in which the design strategy is based on the definition of selected “edge wavefronts” of an illumination system. The extended emitter is represented by input wavefronts originating from selected points belonging to its edge; the prescribed intensity pattern, instead, is put in relationship with specific output edge wavefronts. The optic is calculated by requiring that it transforms the input edge wavefronts exactly into the output ones. This wavefront-matching procedure can be achieved, for example, with the Simultaneous Multiple Surfaces method (SMS). We show examples of freeform optics calculated according to the above procedure, which create non-rotationally symmetric irradiance patterns out of extended sources. A fine tuning of the output design wavefronts allows accurate control over the uniformity and extension of the output patterns, as well as on the definition of cut-offs and intensity gradients.
The Freeform RXI collimator is a remarkable example of advanced nonimaging device designed with the 3D Simultaneous Multiple Surface (SMS) Method. In the original design, two (the front refracting surface and the back mirror) of the three optical surfaces of the RXI are calculated simultaneously and one (the cavity surrounding the source) is fixed by the designer. As a result, the RXI perfectly couples two input wavefronts (coming from the edges of the extended LED source) with two output wavefronts (defining the output beam). This allows for LED lamps able to produce controlled intensity distributions, which can and have been successfully applied to demanding applications like high- and low-beams for Automotive Lighting.
Nevertheless, current trends in this field are moving towards smaller headlamps with more shape constraints driven by car design. We present an improved version of the 3D RXI in which also the cavity surface is computed during the design, so that there are three freeform surfaces calculated simultaneously and an additional degree of freedom for controlling the light emission: now the RXI can perfectly couple three input wavefronts with three output wavefronts. The enhanced control over ray beams allows for improved light homogeneity and better pattern definition.
There is currently a desire to produce thinner LED backlights and frontlights so that the devices which use these components can be as thin and lightweight as possible. This is particularly true for smartphones and tablets both of which make extensive use of such components. The push for thinner devices may lead to situations in which the backlights are thinner than the height of the LED emitting area. This paper deals with the coupling of LEDs and thin light guides, describing some possible ways to efficiently inject light from a relatively large LED into a thinner backlight. These solutions use étendue-squeezing optics, and linear edges which allow high-efficiency light injection.
Today’s SSL illumination market shows a clear trend towards high flux packages with higher efficiency and higher CRI,
realized by means of multiple color chips and phosphors. Such light sources require the optics to provide both near- and
far-field color mixing. This design problem is particularly challenging for collimated luminaries, since traditional
diffusers cannot be employed without enlarging the exit aperture and reducing brightness (so increasing étendue).
Furthermore, diffusers compromise the light output ratio (efficiency) of the lamps to which they are applied.
A solution, based on Köhler integration, consisting of a spherical cap comprising spherical microlenses on both its
interior and exterior sides was presented in 2012. When placed on top of an inhomogeneous multichip Lambertian LED,
this so-called Shell-Mixer creates a homogeneous (both spatially and angularly) virtual source, also Lambertian, where
the images of the chips merge. The virtual source is located at the same position with essentially the same size of the
original source. The diameter of this optics was 3 times that of the chip-array footprint.
In this work, we present a new version of the Shell-Mixer, based on the Edge Ray Principle, where neither the overall
shape of the cap nor the surfaces of the lenses are constrained to spheres or rotational Cartesian ovals. This new Shell-
Mixer is freeform, only twice as large as the original chip-array and equals the original model in terms of brightness,
color uniformity and efficiency.
Today’s SSL illumination market shows a clear trend to high flux packages with higher efficiency and higher CRI, realized by means of multiple color chips and phosphors. Such light sources require the optics to provide both near- and far-field color mixing. This design problem is particularly challenging for collimated luminaries, since traditional diffusers cannot be employed without enlarging the exit aperture and reducing brightness. Furthermore, diffusers compromise the light output ratio (efficiency) of the lamps to which they are applied. A solution, based on Köhler integration, consisting of a spherical cap comprising spherical microlenses on both its interior and exterior sides was presented in 2012. The diameter of this so-called Shell-Mixer was 3 times that of the chip array footprint. A new version of the Shell-Mixer, based on the Edge Ray Principle and conservation of etendue, where neither the outer shape of the cap nor the surfaces of the lenses are constrained to spheres or 2D Cartesian ovals will be shown in this work. The new shell is freeform, only twice as large as the original chip-array and equals the original model in terms of color uniformity, brightness and efficiency.
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