Bending sensitivity of long-period fiber gratings written in polarization-maintaining fiber by CO 2 laser

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We demonstrate the unique bending characteristics of the long-period fiber gratings (LPFGs) written in a panda polarization-maintaining (PM) fiber using CO₂ laser. The bending sensitivity of the grating is not only sensitive to the direction of the fiber bending, but also dependent on the irradiation direction of the laser writing beam with respect to the principal axes of the PM fiber. The high sensitivity directional bending effect can be attributed to the asymmetric index distribution of the fiber cladding induced by both stress changes in the stress-applying parts of the PM fiber and high absorption of the CO₂ laser at the exposure side, which may find promising application in fiber grating based bending sensors.