Development of grating fiber sensor with asymmetrical cross section detectable the bending direction for prevention of slope failures

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Micro-machined grating fiber was evaluated as a sensor for prevention of slope failures. There is some possibility to detect refractive index of liquid on the fiber tip by the difference of reflected light power between at the center reflection wavelength and at the other wavelengths. Reflected light spectra were measured, when a serial arrangement of two FBGs with two different center reflection wavelengths and similar asymmetrical cross sections with different etching faces was bent. It was found that bend was recognized with accuracy of 5°in bend direction and 3.0 m-1in curvature when the clad thickness was 14μm.