Simultaneous Measurement of Bending and Temperature Using Long-Period Fiber Grating Inscribed on Polarization-Maintaining Fiber with CO2 Laser

Here we report on the simultaneous measurement of bending and temperature, carried out using a long-period fiber grating (LPFG) inscribed on polarization-maintaining fiber (PMF) with a CO2 laser at similar to 10.6 mu m. An LPFG written on PMF, referred to as a PM-LPFG, has an input-polarization-dependent resonance dip, and two separated resonance dips, designated as Dips A and B, are obtained with respect to orthogonal input polarization. At the resonance wavelengths of Dips A and B, the core mode is coupled into two different cladding modes that have different bending and temperature sensitivities. The fabricated PM-LPFG whose grating period and length are similar to 505 mu m and similar to 14.65 mm, respectively, has two resonance wavelengths, i.e., lambda(A) = similar to 1479.98 nm and lambda(B) = similar to 1568.78 nm, measured with respect to two orthogonal input polarization states. The bending sensitivities of this PM-LPFG were measured as similar to 22.23 and similar to 33.38 nm/m(-1) (adjusted R-2 values: similar to 0.9916 and similar to 0.9810) at lambda(A) and lambda(B), respectively, in a curvature range of 1.41-2.30 m(-1). The temperature sensitivities of the PM-LPFG were measured as similar to 0.132 and similar to 0.039 nm/degrees C (adjusted R-2 values: similar to 0.9929 and similar to 0.9980) at lambda(A) and lambda(B), respectively, in a temperature range of 30-90 degrees C. These linear bending and temperature responses of the PM-LPFG at two different resonance wavelengths enable simultaneous measurement of bending and temperature variations applied to the PM-LPFG.