RESUMO
We show that linearly polarized light launched at different angles with respect to the major axis of a two-mode, elliptical-core fiber results in an amplitude-modulated beat-length pattern in the far field. The variation of the output pattern is explained theoretically and confirmed experimentally. A polarizer placed at the output of the fiber is shown to eliminate the amplitude modulation in the output signal. A simple theoretical model, based on the weakly guiding assumption, is shown to be helpful in determining few-mode fiber sensor parameters in practical systems.
RESUMO
Photoinduced refractive-index changes in two-mode, elliptical-core optical fibers affect the beat length and the sensor sensitivity. Chirped gratings are written by attaching such fibers to cantilever beams positioned in a strained state. We show that fibers with in-line chirped gratings, with the chirp being shaped in the form of a vibration-mode shape, can be used as spatially weighted fiber sensors for vibration analysis. We demonstrate enhanced detection of the first and second modes of vibration of a cantilever beam using this process; vibration mode suppression of the order of 10 dB is obtained.
