Scattering Losses Caused by the Support Structure of an Uncladded Fiber

A typical optical fiber consists of a core, the refractive index of which is larger than that of the cladding material surrounding the core.1 The cladding serves the purpose of keeping any outside influence, such as dust, at a safe distance from the core. The requirement of a lower refractive index for the cladding makes it difficult to find suitable cladding materials for one of the most promising core materials-fused silica. Fused silica is particularly useful as fiber core material because of its inherently low absorption loss. However, the refractive index of fused silica n = 1.4G, is lower than that of most other glasses. In particular, there are as yet no low-loss materials suitable for fiber claddings, the refractive indices of which are lower than that of fused silica. The few available materials have absorption losses that rule out their use as claddings for low-loss optical fiber waveguides. It appears natural to ask whether a fiber without cladding could not be made. In principle a dielectric fiber waveguide works just as well without a cladding if it could be suspended in air or in vacuum. But since no method of levitating the fused silica fiber without mechanical supports has yet been devised, the necessity exists of holding the uncladded core by some kind of supporting structure. If the supports of 205