Light pipes are useful for non conventional illumination problems in cars, for displays, etc. The design of such devices is a challenging problem because of the large number of parameters. Depending on the application, the light pipes have various shapes and dimensions. This paper investigates different design strategies for light pipe illumination devices. A new generation of commercially available non- sequential ray-tracing programs allow the analysis of scattering light pipes. However, the modeling of complex optical systems requires the knowledge of the physical behavior and the related numerical algorithms. For the design optimization, ray-tracing is too cumbersome because of the large number of necessary rays. Therefore, we introduce a finite element approach to describe the power transfer through appropriately chosen volume elements. This method gives a good estimation of the macroscopic behavior of the light pipe. The fine tuning of the different pipe parameters is made easier. In addition, the possibility to simulate the light pipe in its surrounding environment by means of global illumination methods is discussed.
A scattering light pipe has been designed for a non- conventional illumination system. The spatial distribution of the light is controlled by diffusers which are deposited on top of the pipe faces. The first realized samples have used a scattering paint as diffuser which has good optical properties but is unsuited to fabrication. Diffusers based on micro-optics have the potential to replace favorably classical Lambertian diffusers. Micro-optical diffusers (MODs) allow the generation of perfectly defined scattering distributions which are well adapted for the design of an optimized light pipe. A further advantage of such surface relief elements is their potential for cheap mass production. The strengths and limits of micro-prisms, micro- lenses, and gratings are evaluated in view of their use as diffusers. Finally a proposition for an optimized design of the illumination light pipe is presented.
A linear light pipe allowing the transformation of a quasi- point source into an extended lighting device has been developed. The control of the spatial light distribution is of special interest for the uniform illumination of extended surfaces. The distribution of the emitted light is achieved by the combination of scattering and reflective coatings on the light pipe faces. Paint has been used as scattering coating. Paint characterization and introduction of the measured parameters into the ray-tracing program are described. Several light pipe configurations have been simulated and manufactured. The performance of the different configurations are discussed and compared with experimental results.
The potential of diffractive optical elements for advanced laser communication terminals has been investigated. Applications include beam shaping of high- power laser diode arrays, optical filter elements for position detection and hybrid (refractive/diffractive) elements. In addition, we present a design example of a miniaturized terminal including diffractive optics.
Continuous surface-relief phase gratings for two-dimensional (2-D) array generation have been designed and fabricated by laser-beam writing lithography. Separable and non-separable solutions for the design of 2-D fan-out elements are compared. A 9 X 9 fan-out element has been fabricated in photoresist by laser-beam writing. A diffraction efficiency of 94% and an uniformity better than +/- 8% over the whole array were achieved.
Progress in the fabrication of diffractive optical elements (DOEs) as 2-dimensional continuous-relief microstructures is described. The elements are fabricated by laser-beam writing in photoresist and have typical microreliefs up to 5 micrometers and periods down to 10 micrometers . Examples include fan-out elements and Fresnel microlens arrays. The design and fabrication of a 9 X 9 fan-out DOE with a diffraction efficiency of 94% and an overall uniformity of +/- 8% is described. High quality replicas are produced by low-cost embossing and casting techniques.
The recording of the efficient fan-out elements as volume holograms has been studied using coupled wave theory. The authors have found that the efficiency and uniformity of regular fan- out elements depend strongly on the relative phases of the object waves, if the thickness t of the holographic emulsion is smaller than t<(lambda) /(n tan(theta) 0 (Delta) (alpha) ). High efficiency and uniformity can be achieved by optimized phases of the object beams, thereby requiring a low dynamic range of the holographic recording material.
This paper reports the design and fabrication of transmission holographic optical elements (HOEs) for
clock distribution. First, we have studied and fabricated a multi-focus doublet HOE. The aberrations due
to the wavelength shift between recording ( = 488 nm) and reconstruction ( = 780 nm) have been
minimized by an appropriate recording and readout geometry. The diffraction efficiency has been
optimized by a copying technique. Second, we have investigated the near-field internal reflection (TIR)
holographic recording technique to solve the problems of miniaturization. With this method, we have
recorded a lOOxlOO lenlet array with focal lengths of f =400 μm.