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The development of optical-fiber cables and communications technology has
undergone a dynamic revolution over the past decade. The most basic design of an optical fiber consists of silica cladding surrounding a silica core doped with germanium (GeO2), which increases the index of refraction by up to 2% above pure silica, allowing light to be guided simply by total internal reflection at the core-cladding interface. Over the years, however, this basic geometry has evolved to substantially alter the
waveguide properties, especially the dispersion in the 1.3
to 1.6 micron wavelength region. Design variations have included shaping the core index profile and adding down-doped and up-doped rings as well as elliptical cores for polarization-preserving fibers. Just recently, significant new developments—specifically, the use of
microstructure air holes around the fiber core—have made possible some incredible new properties, with applications in many fields, from metrology to medicine.