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

The Nobel Lecture  21 Charles joined the long-haul waveguide group led by Dr. Karbowiak at STL. He was excited to see an actual circular waveguide. He was assigned to look for new transmission methods for microwave and optical transmission. He used both ray optics and wave theory to gain a better understanding of waveguide problems — then a novel idea. Later, his boss encouraged him to pursue a doctorate while working at STL. So Charles registered at University College London and completed the dissertation ‘Quasi-Optical Waveguides’ in two years. The invention of the laser in 1959 gave the telecom community a great dose of optimism that optical communication could be just around the corner. The coherent light was to be the new information carrier with capacity a hundred thousand times higher than point-to- point microwaves — based on the simple comparison of frequencies: 300 terahertz for light versus 3 gigahertz for microwaves. The race between circular microwave waveguides and optical communication was on, with the odds heavily in favor of the former. In 1960, optical lasers were in their infancy, demonstrated at only a few research laboratories, and performing much below the needed specs. Optical systems seemed a non-starter. But Charles still thought the laser had potential. He said to himself: ‘How can we dismiss the laser so readily?’ ‘Optical communication is too good to be left on the theoretical shelf.’ He asked himself the obvious questions: 1. Is the ruby laser a suitable source for optical communication? 2. What material has sufficiently high transparency at such wavelengths? At that time only two groups in the world were starting to look at the transmission aspect of optical communication, while several other groups were working on solid state and semiconductor lasers. Lasers emit coherent radiation at optical frequencies, but using such radiation for communication appeared to be very difficult, if not impossible. For optical communication to fulfill its promises, many serious problems remained to be solved. 3. The key discovery In 1963 Charles was already involved in free space propagation experiments: The rapid progress of semiconductor and laser technology had opened up a broader scope to explore optical communication realistically. With a helium-neon laser beam directed to a spot some distance away, the STL team quickly discovered that distant laser light flickered. The beam danced around several beam diametres because of atmospheric fluctuations. The team also tried to repeat experiments done by other research laboratories around the world. For example, they set up con-focal lens experiments similar to those at Bell Labs: a series of convex lenses were lined up at intervals equal to the focal length. But even at the