Bending and Strain Sensitivities in a Helicoidal Long-Period Fiber Gratings

In this letter, we report bending and strain sensitivities of helicoidal long-period fiber gratings fabricated by twisting single-mode fibers during CO₂ laser irradiation. Linear spectral shifts of the resonant wavelengths under the bending and tensile strain were observed with the sensitivities of -11.7 nm/m^-1 and -1.1 pm/muepsiv, respectively. The corresponding transmission power variations at the resonance wavelength were 4.1 dB/m^-1 and 2.2 times 10^-4 dB/muepsiv, respectively. Detailed measurement techniques and sensor applications are discussed.