Corrugated long-period fiber gratings as strain, torsion, andbending sensors

We present a novel corrugated long-period fiber grating whose transmission spectra are highly sensitive to the applied tensile strain, torsion, and bending due to the periodical index modulation created and changed by these mechanic forces. The induced index modulation can also be experimentally characterized by using a built-in fiber Bragg grating (FBG). The long period fiber gratings possess the following unique properties when used as sensors. As a tensile strain sensor, its resonance loss varies but resonance wavelength remains stable. As a torsion sensor, the wavelength varies with the applied twist rate. As a bending sensor, the cladding-mode resonance grows with the bending curvature