Who is the father of fiber optics: Charles Kuen Kao or Narinder Singh Kapany?
It depends on, what they did.
Neither of them found the concept, but both made a lot of inventions/developments to make optical cables working.
Narinder Singh Kapany
He was the founder and chairman K2 Optronics Inc, and
published over 100 scientific papers and four books on opto-electronics and entrepreneurship.
Charles Huen Kao
created various methods to combine glass fibres with lasers in order to transmit digital data, which laid the groundwork for the evolution of the Internet.
Fibre optics was not a single, revolutionary development, instead it was the evolution of many small results. Both of them made many essential steps. This technology seems to have many fathers.
The possibility that it could work, was probably well known about from the development of the LEDs.