Abstract

Two-mode elliptical-core (e-core) fibers have been used as efficient vibration sensors when operated in the linear region.¹ Such ruggedized e-core sensors can perform as vibration-mode filters when placed appropriately along the vibration antinodes of the beam.² We report the development of distributed modal sensors using optical fiber techniques. The variable sensitivity of the fiber sensors has been achieved by utilizing the feature that the differential propagation constant in a two-mode fiber is directly dependent on the normalized frequency (or, V-number). Tapering the fiber changes the V-number and hence can change the sensitivity of the sensor along its length. We show that these sensors are fiber optic analogs of shaped, piezo-electric modal sensors that have emerged recently in the area of structural control³ and demonstrate their applications for clamped-free onedimensional beams.

© 1992 Optical Society of America