Macro-bend optical fiber linear displacement sensor

Based on the macro-bend induced losses in an optical fiber a linear displacement sensor is developed. The oscillatory bend radius dependent loss is suppressed by coating the bent section with an absorption layer. The sensor is designed as an open-ended fiber probe for easy practical application, where the Fresnel reflection at the cleaved end is utilized. Mechanical modelling is given to optimize the fiber lead length to avoid buckling of the fiber. Resolutions of 30 μm and 0.1 μm, with coefficient of determination of 0.97 and 0.96, respectively over a total measurable displacement of 0 to 30 mm are achieved by utilizing a ratio-metric measurement of the bend loss. Finally a sensor with a smaller footprint is also demonstrated by utilizing a reduced clad fiber with a cladding diameter of 80 μm.

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