Materials Effects on the Radiation Sensitivity of Single Mode Optical Fibers
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MATERIALS EFFECTS ON THE RADIATION SENSITIVITY OF SINGLE MODE OPTICAL FIBERS E.J. FRIEBELE,* C.G. ASKINS,* SCHMIDT*** *Naval Research Laboratory, "**Alfred University, Alfred, ***Michigan State University,
M.E. GINGERICH,* C.M. SHAW,** AND W.H. Washington, DC 20375 NY 14802 E. Lansing, MI 48824
ABSTRACT Statistically significant correlations have been established between certain fabrication parameters of matched clad single mode fiber waveguides and the induced attenuation and recovery kinetics following exposure to an ionizing radiation dose. INTRODUCTION The incremental loss induced in optical fiber waveguides by ionizing radiation exposure is affected by parameters such as the type and concentration of core and clad dopants, impurities such as OH in the guiding region, glass deposition conditions, and fiber draw conditions.[1] The dopants have been varied in previous studies of multimode[2,3] and single mode[4,5] fibers, primarily in an effort to understand the origin of the radiation-induced loss and to increase radiation hardness. In general, these studies have reported qualitative associations of incremental loss with fabrication parameters although the dependence of radiation damage on [P] in the clad of single mode fibers was quantitatively determined by Mies and Soto[5] in a one-dimensional study. The goals of this study were two-fold: 1) to experimentally quantify the relationship between a wide variety of factors associated with the fabrication of matched clad single mode fibers and radiation response parameters, and 2) to determine which, if any, experimental correlations have statistical significance. It should then be possible to develop the capability for predicting single mode fiber radiation response from analysis of the core and clad dopant levels and from knowledge of fabrication variables such as oxygen ratios used during deposition and fiber draw parameters. In addition, significant improvements in the radiation resistance of these fibers should be forthcoming. EXPERIMENTAL Fibers for the study were fabricated by the MCVD method with variations in core and clad [Ge], oxygen-to-reagent ratio during core and clad deposition, fiber draw speed, and draw tension. The levels of these factor§ are shown in Table I. If this study were conducted one factor at a time, 3• X 23 = 216 preforms would have to be made and fibers drawn and irradiated, all with levels of the factors equal to the targets of Table I. On the other hand, the absolute minimum number of fibers needed to determine all one-way interactions is equal to the degrees of freedom (contrasts between levels) + 1 = 10. This minimal case provides only one degree of freedom for the error term in the analysis and precludes evaluation of any higher order interactions. As a compromise, an experimental design of 16 fibers was developed (Table II) to provide a potential for 7 degrees of freedom for the error and the derivation of some selected interaction terms.[6] Although this is a considerably smaller study than one-factor-at-a-time, the yield of p
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