In the 1960s telecommunication depended on copper wires and radio links whose capacity was reaching its limits. Kao argued that the main cause of fiber loss was not scattering defects but the intrinsic purity of the glass itself, and he set an unprecedented goal of less than 20 dB/km attenuation. Inspired by his vision, Corning produced high-purity silica fiber in 1970, launching a communications revolution. Modern fibers now reach losses as low as 0.2 dB/km, underpinning the Internet, video streaming, and cloud computing. Kao’s foresight fundamentally reshaped infrastructure and economic activity.

Working with Hockham, Kao employed planar waveguide theory and ray-optics models to show that scattering losses are dominated by transition-metal ions such as Fe²⁺ and Cu²⁺. He identified the 1.3–1.55 µm window where pure silica could reach theoretical losses near 0.15 dB/km and argued that controlling the refractive-index difference between core and cladding would suppress modal dispersion, paving the way for single-mode fiber designs. Coupled with the advent of semiconductor lasers, optical fibers later integrated WDM and EDFA technologies to achieve massive, long-haul capacity. Today’s terabit-scale networks would not exist without Kao’s theoretical insight and materials-purification roadmap.

In his 1966 Proc. IEE paper, Kao estimated the fundamental loss floor of SiO₂ fibers to be 0.2 dB/km, separating Rayleigh-scattering (∝1/λ⁴) and OH absorption contributions. Core-modification via SiCl₄-CVD evolved into MCVD/PCVD processes, culminating in ITU-T G.652 fibers typified by SMF-28. Design rules for DWDM channel spacing that avoid four-wave mixing and spin-draw techniques that randomize birefringence to suppress PMD trace back to Kao’s analyses. His work continues to provide theoretical benchmarks for photonic-crystal and hollow-core fiber research.