OPTICAL WAVE GUIDE APPLICATION IN ADVANCED WIRELESS CONCEPT...

<font color=#AA0000>OPTICAL WAVEGUIDES IN WIRELESS APPLICATIONS</font>
Optical waveguides are also used in lighting and illumination. Especially light guides prepared from polymeric materials possess a low weight, but high strength-toweight ratio. This was already understood by DuPont in the 1930’s when they proposed poly(methyl methacrylate) as a replacement for quartz illuminators12,29. Furthermore, polymers are easily processed and hence result in a flexible layout design using standard processing techniques as for instance compression moulding, extrusion and injection moulding. The use of polymeric materials in lighting applications opens up a large number of applications in for instance lightweight mobile devices but also in the field of signage and displays as a replacement for high voltage neon devices, which are rigid, fragile and limited in length30. Some of the many examples where fibre optic lighting by polymers is installed are for instance: motorway signalling31, the fountains at Duck Island in St. James Park, London and the Louvre museum in Paris. Furthermore, also the Efteling in Kaatsheuvel and the Euro Tower in Frankfurt are at night illuminated by fibre optic lighting (see Figure 1.2)32,33. Figure 1.2: Examples of actual fibre optic lighting systems in the field; 2 and 4 mm diameter
Optical waveguides in lighting or illumination applications are split up in two distinct categories, the end or point-source lighting and the side or line-lighting. The former involves transmission of light from the proximal to the distal end, analogously to optical fibres in data communication. The latter term is used to describe light guides that combine the properties of light transmission and light emission, in which the desired emission direction of the light is often perpendicular to its propagation direction.
endlight fibres woven into the roof of the main entrance of the Efteling, Kaatsheuvel, The Netherlands (left) and 30 side-emitting optical fibres each 11 mm diameter and 13 m in length at the top of the Euro Tower, Frankfurt, Germany (right) 33. Commercially available step-index polymer optical fibres are suitable for most endlighting applications, since only transmission of the light is required. Total internal reflection of the transmitted light must be overcome to extract light along the length of the waveguide. Techniques to produce laterally emitting waveguides optical fibres are described both in scientific and patent literature34,35. However, these techniques show some limitations with regards to the applied processing techniques and the spatial distribution of the emitted light.