Bulletin Special Supplement on Prof. Charles K. Kao, Former Vice-Chancellor and Nobel Laureate The Love and Labour of a Laureate

The Nobel Lecture  23 they made very credible progress in considered steps. They searched the literature, talked to experts, and collected material samples from various glass and polymer companies. They also worked on the theories, and developed measurement techniques to carry out a host of experiments. They developed an instrument to measure the spectral loss of very low- loss material, as well as one for scaled simulation experiments to measure fiber loss due to mechanical imperfections. Charles zeroed in on glass as a possible transparent material. Glass is made from silica — sand from centuries past that is plentiful and cheap. The optical loss of transparent material is due to three mechanisms: (a) intrinsic absorption, (b) extrinsic absorption, and (c) Rayleigh scattering. The intrinsic loss is caused by the infrared absorption of the material structure itself, which determines the wavelength of the transparency regions. The extrinsic loss is due to impurity ions left in the material and the Rayleigh loss is due to the scattering of photons by the structural non-uniformity of the material. For most practical applications such as windows, the transparency of glass was entirely adequate, and no one had studied absorption down to such levels. After talking with many people, Charles eventually formed the following conclusions. 1. Impurities, particularly transition elements such as iron, copper, and manganese, have to be reduced to parts per million or even parts per billion. However, can impurity concentrations be reduced to such low levels? 2. High temperature glasses are frozen rapidly and therefore are more homogeneous, leading to a lower scattering loss. The ongoing microwave simulation experiments were also completed. The characteristics of the dielectric waveguide were fully defined in terms of its modes, its dimensional tolerance both for end-to-end mismatch and for its diametre fluctuation along the fiber lengths. Both the theory and the simulated experiments supported the approach. They wrote the paper entitled, ‘Dielectric-Fiber Surface Waveguides for Optical Frequencies’ and submitted it to the Proceedings of Institute of Electrical Engineers . After the usual review and revision, it appeared in July 1966 — the date now regarded as the birthday of optical fiber communication. 4. The paper The paper started with a brief discussion of the mode properties in a fiber of circular cross section. The paper then quickly zeroed in on the material aspects, which were recognized to be the major stumbling block. At the time, the most transparent glass had a loss of 200 dB/km, which would limit transmission to about a few metres — this is very obvious to anyone who has ever peered through a thick piece of glass. Nothing can be seen.