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UBC Theses and Dissertations

Transport and distribution of light energy for illuminating engineering applications Whitehead, Lorne Arthur


This thesis concerns the transport of light along a class of cylindrical hollow optical structures, with an aim to develop practical light transport and distribution systems for illuminating engineering applications. Based on intuition, it is postulated that it may be possible to guide light energy in a hollow cylindrical optical structure, by means of total internal reflection on the external surfaces. Such a development would allow light to be guided with the efficiency of optical fibres, but with reduced material costs. In order to assess this possibility, a new technique is presented for analytic ray tracing in general cylindrical structures. The technique makes it possible to trace ray paths in the cross sectional plane of the structure, with the motion in the dimension out of the cross sectional plane precisely taken into account with a simple correction. This technique greatly simplifies the ray tracing calculations which are necessary to study the light transport properties of the proposed structures. It is then shown with the aid of this technique that a certain class of prismatic structures do indeed have the capability of guiding light, and members of this class are termed prism light guides. In any real prism light guide, light is not conducted perfectly, but is lost as a result of a number of deviations from the ideal model. Of these, the one intrinsic loss mechanism, which distinguishes a prism light guide from optical fibres, is diffraction at the corners of the prismatic surfaces. Fortunately, diffraction effects are significantly smaller than losses from practical imperfections in prism light guides. A detailed study of the other types of loss mechanisms is then presented. These arise from imperfections of the optical material comprising the prism light guide (absorption and scatter), and imperfections in the shape of the prism light guide. The importance of these effects is discussed first in an approximate assessment, and they are then modelled precisely by means of computer ray tracing Monte Carlo techniques. These predictions are compared with experimental measurements of actual prism light guides, with substantial agreement. Consideration is then given to the use of a prism light guide in illuminating engineering applications. In these situations light is distributed along the length of a prism light guide, and is uniformly emitted from the surface. The performance of such a system is modelled with Monte Carlo computer ray tracing, and experimentally tested, with substantial agreement. This study concludes with a measurement of diffraction losses. These losses were enhanced by the use of longer wavelength radiation (3mm wavelength microwaves). The results confirm that diffraction losses are small relative to other loss mechanisms. In general, the results reported in this thesis demonstrate the existence of a useful class of light guidance structures which are particularly well suited to the requirements for distribution and transport of optical radiation for illuminating engineering applications.

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