Orientation-dependent fiber-optic displacement sensor using a fiber Bragg grating inscribed in a side-hole fiber

We propose and experimentally demonstrate an orientation-dependent fiber-optic bending sensor. The sensing probe consists of a fiber Bragg grating inscribed in both the fiber core and the surrounding cladding of a section of a side-hole fiber. We utilized a side-illumination technique using a femtosecond laser to achieve the grating structure formation. The transmission intensities of both resonances are highly sensitive bending of the fiber, and the bending response shows orientation dependence. The surrounding temperature fluctuation causes a wavelength shift, but not an intensity variation. Therefore, the proposed sensor can be employed for simultaneous measurement of bending and temperature.