Glass fibers of high silica content, such as common optical lightguides, exhibit a nonlinear elastic response, becoming stiffer with increasing tensile stress. The nonlinear behavior may be of importance in certain sensing application, in particular stress and load monitoring, and in constructing correct models for these optical fiber-based sensor systems. The objectives of the current study is to investigate the nonlinear constitutive behavior of high-silica optical fibers and to determine the implication on mechanical modeling and the likely implications on sensor function. In this study, the nonlinear elastic tensile properties of an optical fiber are studied from an experimental as well as from an analytical standpoint. Critical tensile experiments were carried out on optical fibers. A nonlinear constitutive model based on elasticity theory is introduced to describe the material behavior, and its ramification on the stress analysis is investigated. Macroscopically, the elastic behavior may be accurately modeled using a quadratic function of strain from the onset to failure. However, in the normal operating range of embedded optical fiber sensors, i.e. less than 1% strain, the nonlinear effects small enough that they may in most cases effectively be ignored.