Advances in elliptical-core two-mode optical fiber sensors

Methods designed to improve the practicality of the elliptical-core two-mode optical fiber sensors for use in real-life applications are presented. The improvements include the development of insensitive lead fibers and an optical device which allows fringe counting at the output of the sensor. The insensitive leads eliminate extraneous perturbations and effectively isolate the sensing region. The fringe counting optics are designed to generate quadrature-phase shifted signals, thereby allowing the determination of whether the strain is increasing or decreasing.

Work performed to advance the understanding of the effect of sensor placement within a composite specimen is also presented. Optical fiber sensors are embedded between different laminae of a graphite-epoxy composite panel, and the outputs of the sensors are shown to be proportional to the distance of the sensor from the neutral axis.