A Interrupt Immune Two-Mode Single-Ended Localized Fiber Optic Sensor

Fiber optic sensors, as an alternative sensing technology with much to offer over conventional means, have been extensively investigated over the past decade. Modal Domain interferometric technique is one of many sensing topologies which has received considerable attention especially from the Smart Structures research community. Two-mode sensors have been fabricated with both regular single-mode weakly guiding fiber and elliptical core fiber. The two -mode strain-induced modulation pattern is well behaved in the elliptical core fiber, but not the other. In this dissertation, mode pattern stability is considered from a waveguide point of view. The implications of this analysis are used to examine a number of commercially available fibers and thus establish a set of prerequisites for optimum sensor performance. Since interrupt immunity must be achieved before successful integration of fiber optic sensors into practical systems can be realized, a novel absolute sensing technique for the two-mode sensor is developed and demonstrated. As a spin-off of this investigation a novel technique for accurate determination of the effective cut-off wavelength has been developed and tested. Results indicate improved measurements by one order of magnitude. Finally, system requirements for successful sensor performance have been addressed and a new multiplexing approach has been proposed.