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    Photoinduced, refractive-index gratings in germanium-doped two-mode, elliptical-core optical fibers

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    LD5655.V855_1991.G733.pdf (17.15Mb)
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    Date
    1991-11-15
    Author
    Greene, Jonathan Andrew
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    Abstract

    Permanent, photoinduced refractive-index gratings written along the longitudinal axis of germanium-doped, two-mode, elliptical-core fibers are found to affect the differential phase modulation between the co-propagating LP 0l and LP 11 even modes. The modal beat length of a two-mode fiber grating is found to vary inversely with strain induced to the fiber and leads to a new type of weighted optical fiber sensor whose sensitivity varies as a function of length along the structure to which it is attached or embedded. A weighting function is imparted to the fiber sensor by way of a chirped, two-mode grating written into the core, the chirp adopting the shape of a specific vibration-mode amplitude. This novel type of spatially-weighted, distributed fiber sensor is shown experimentally to function as an efficient vibration-mode filter by enhancing either the first or second mode of a thin, one dimensional cantilever beam. These results support future applications of spatially-weighted/ distributed optical fiber sensors for the evaluation and control of vibrating structures.

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    http://hdl.handle.net/10919/44380
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    • Masters Theses [19662]

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