Scattering losses in optic fiber materials. I. A new parametrization

Many different nonsilica‐based fiber materials are presently being examined as possible candidates for use in extremely low loss fibers for infrared communications. One useful figure of merit in estimating fiber potential for low absorption is the total intrinsic scattering loss at the minimum dispersion wavelength. In this paper formulae for these losses, which include Rayleigh, Brillouin, and Raman mechanisms, are derived solely in terms of parameters which are either already known, or which can be reliably estimated, for essentially all of the materials in question. The basic techniques for calculating power losses due to intrinsic thermodynamic fluctuations are well established in principle. This paper first extends them for use with arbitrarily complex multicomponent mixtures and for the specific inclusion of Raman loss and then, via the use of the concept of bond polarizabililty, relates the various components (due respectively to density, composition, and lattice vibrational modulations of dielectric constant) in a new parametrization. Finally, using a three‐parameter Sellmeier formalism to locate the wavelength of minimum dielectric dispersion, the various scattering losses at this wavelength are finally given in an explicit form for which all quantities involved are experimentally accessible and are included in their normally quoted experimental units. In the following companion paper these power loss formulae are used directly to obtain actual numerical estimates (in dB/km) for a wide selection of candidate materials.