Specialty Optical Fibers Handbook

produce wave guiding or because of optical attenuation, which would be exces-

sive in a fiber device that has a path length of meters. The dominant host has

been silica, but the range of compositions is small because of glass-forming

limitations. Even use of modest dopant levels is problematic because most

elements cause excess optical attenuation and must be avoided, whereas the

remaining few have only modest influence. Some, such as phosphorus as a co-

dopant for Er, cause undesirable changes in the spectrum, such as spectral

narrowing.

More radical modification requires use of other hosts, such as phosphates,

borates, tellurites, and fluorophosphates, as well as nonoxygen hosts such as

fluorides, sulfides, and other chalcogenides. For these, there ...