Novel optical fiber Bragg grating designs for vector bending measurement

Two novel fiber Bragg grating (FBG) based sensing schemes are proposed and experimentally demonstrated for directional bending measurement: One of which is based on two weakly titled Bragg gratings spliced together with tilt planes at nearly 90 degree, followed by a cleaved end mirror; the other one is based on an off-axis printed FBG, which both exhibit large amount of cladding modes in transmission spectrum in contrast with that of a normal FBG. Well-chosen cladding resonances in these two structure are demonstrated respectively for ultra-sensitive bending measurement via power detection. Meanwhile the surrounding temperature is proven independent to fiber bent.