Trace Analysis and Ultrapurification of Materials for Optical Waveguide Technology

In the telecommunications industry techniques for purifying and characterizing materials, and analytical methods for solving chemical problems have been vitally important for technological progress. The application of reliable analytical methods to determine optimum conditions for pre— paring materials in controlled states of purity continues to be essential. In fact, the production of materials with unique properties, determined by doping precisely with impurities on the one hand or by insuring the absence of other detrimental ones, continues to be a key to technological advancement. The most recent critical need in the industry for pure materials and ultratrace analysis resulted from the initiation of applied research and development of optical wave— guide systems, where tolerance limits for waveguide materials were projected to be in the 2 to 100 ng/g range for commonly found transition metal impurities Fe, Co, Cr, Cu, Mn, Ni, and V. Applications of neutron activation, X—ray fluorescence, atomic absorption,and laser intracavity absorption spectro— scopy in support of optical waveguide programs will be discussed. Examples will be provided to demonstrate the use of these techniques for screening commercially available glass—making raw materials and chemical vapor deposition reagents, for unequivocally identifying impurities in glasses and fibers, and for detecting sources of contamination during glass—making and fiberdrawing. In the absence of materials of sufficient purity from available commercial sources, specialized preparations have been performed under controlled executions of solvent extraction, ion exchange, mercury cathode electrolysis, and low temperature sublimation. The advantages and pitfalls of these methods will be compared. It will be demonstrated that radioisotope techniques and activation analysis are the most powerful and reliable tools for establishing optimum conditions for executing these procedures and for pinpointing specific deficiencies of each purification process. Factors limiting the ultimate state of purity achievable for analytical reagents for trace analysis will be discussed.