Manufacturing and measurement of freeform optics

A feedback modification method based on variable separation mapping is proposed in the design of free-form optical system with uniform illuminance for LED source. In this method, the non-negligible size of LED source is taken into account, and a smooth optical system is established with single freeform surface regenerated by adding feedback to the lens design for a point light source. More rounds of feedback can improve the lens performance. As an example, a smooth free-form lens with rectangular illuminance distribution is designed, and the illuminance uniformity is improved from 18.75% to 81.08% after eight times feedback.

Design of compact and smooth free-form optical system with uniform illuminance for LED source.

In order to achieve competitive system costs in mass-production, it is essential that CPV concentrators incorporate sufficient manufacturing tolerances. This paper presents an advanced concentrator optic comprising a Fresnel lens and a refractive secondary element, both with broken rotational symmetry, an optic producing both the desired light concentration with high tolerance (high acceptance angle) as well as an excellent light homogenization by Kohler integration. This concentrator compares well with conventional Fresnel-based CPV concentrators.

High performance Fresnel-based photovoltaic concentrator

For the problem of point source forming prescribed irradiance, a new, to the best of our knowledge, method-variable separation mapping method is presented, which establishes separately the correspondence between variables on the light source and the target plane. The role played by the optical surfaces is then to redirect the light rays to their corresponding target points. The surface of the lens is determined by first calculating the surface points and then their normal vectors. Considering that normal deviations are produced in the surface construction process, a normal deviation control method is also presented to restrict the deviation. With this normal deviation control method, discontinuities are introduced onto the lens surface. From these mapping and normal control methods, a fast and efficient algorithm has been developed for several prescribed irradiance problems with simple nonrotational shape of the illuminated region.

Discontinuous free-form lens design for prescribed irradiance

Application specific LED packaging (ASLP) is an emerging technology for high performance LED lighting. We introduced a practical design method of compact freeform lens for extended sources used in ASLP. A new ASLP for road lighting was successfully obtained by integrating a polycarbonate compact freeform lens of small form factor with traditional LED packaging. Optical performance of the ASLP was investigated by both numerical simulation based on Monte Carlo ray tracing method and experiments. Results demonstrated that, comparing with traditional LED module integrated with secondary optics, the ASLP had advantages of much smaller size in volume (approximately 1/8), higher system lumen efficiency (approximately 8.1%), lower cost and more convenience for customers to design and assembly, enabling possible much wider applications of LED for general road lighting. Tolerance analyses were also conducted. Installation errors of horizontal and vertical deviations had more effects on the shape and uniformity of radiation pattern compared with rotational deviation. The tolerances of horizontal, vertical and rotational deviations of this lens were 0.11 mm, 0.14 mm and 2.4 degrees respectively, which were acceptable in engineering.

http://mitros.sweb.cz/fyzika/Desing%20of%20compact%20freeform%20lens%20for%20application%20specific%20light-emitting%20diode%20packaging,%20Wang%20Kai.pdf

Design of compact freeform lens for application specific light-emitting diode packaging

The simultaneous multiple surface (SMS) method in 3-D geometry is presented. Given two orthotomic input ray bundles and another two orthotomic output ray bundles, the method provides an optical system with two free-form surfaces that deflects the rays of the input bundles into the rays of the corresponding output bundles and vice versa. In nonimaging applications, the method enables controlling the light emitted by an extended light source much better than single free-form-surface designs, and also enables the optics contour to be shaped without efficiency losses. The method is also expected to find applications in imaging optics.

Simultaneous multiple surface optical design method in three dimensions

The simultaneous multiple surface (SMS) method is used to design air-gap RXI-type lenses, which efficiently produce a very narrow beam from high-powered LEDs. These designs are compact, with both front surface and reflecting back surface calculated simultaneously from periphery inward, as profiles of circular symmetry, via applying the edge-ray principle to the chip geometry. The light source is a Lambertian-glowing cube 1.2 mm square and 0.15 mm high, as viewed through its clear (n = 1.54) package dome, with emission down to 95 deg from the symmetry axis. A given exit-aperture diameter defines a minimum, etendue-limited collimation angle, = arc sin (chip-width/diameter). At the center of the back surface there is a cavity surrounding the source. The front surface reflects that source flux to the back surface, which reflects it back forward again, accomplishing the optical folding thereby. The back surface is shaped so that the light it reflects forward will be refracted out the front surface to become the collimated output beam.

Pablo Gimenez-Benitez

Papers

Simultaneous multiple surface optical design method in three dimensions

Simultaneous multiple surface design of compact air-gap collimators for light-emitting diodes