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The basic principle for guiding light by total internal reflection (TIR) in a dielectric media was first demonstrated around 1840 by D. Colladon. Colladon showed very simply that sunlight could be guided by a stream of water flowing out through a hole in a water-filled vessel. Later he applied these ideas to lighting water fountains. In fact, his ideas were responsible for the spectacular lighted and colored fountains at the Universal Exposition in Paris in 1889. In an excellent account on the history of fiber optics, J. Hecht, in the City of Light - The Story of Fiber Optics, discusses the role of Colladon and that of Tyndall, who repeated Colladon's experiments in 1853. Because Tyndall was a well-known scientist at the time, he is often wrongly given credit for the first observation of light guiding in water jets.
The first glass fiber optic was proposed in 1926 by C.W. Hansell. Hansell was a prolific inventor who was trying to transmit an image of an instrument dial to a remote location for viewing around corners and curves. In fact, up until the mid-1950s, the driving force behind fiber optic transmission was the need for a flexible image bundle for industrial and medical applications. In the latter case, it was the wish of several teams of surgeons and engineers to have flexible endoscopes for seeing inside the body. Until then only crude arrangements of rigid tubes and mirrors, the forerunners of today's modern articulated arms used to transmit CO2 laser power, were used for visualization within the body. Also, in the early 1950s, van Heel, O'Brien, and others came onto the idea of a clad fiber as a means of more effectively trapping and confining the light within a single glass fiber. This was important because crosstalk present in the core-only, coherent image bundles distorted the image. These investigators realized that it was necessary to have a lower refractive-index material, i.e., a cladding layer, surround the glass core for TIR. The first cladding materials were oils; most oils have a lower refractive index than glass and they were readily accessible.
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