Elliptical-core two-mode optical-fiber sensor implementation methods

We present experimental methods for the practical implementation of few-mode elliptical-core sensors. Techniques for desensitizing the lead-in and lead-out fibers are discussed and results of a vibration sensor embedded in a graphite-epoxy composite are presented. A scheme using a single-mode elliptical-core fiber as the lead-in fiber and an offset circular-core single-mode fiber as the lead-out fiber is successfully implemented. Detection techniques for few-mode fiber sensors are reviewed and a novel fringe-counting method to unambiguously detect the amplitude and direction of dynamic strain is reported for the first time.