Multi-parameter Sensor Based on Long Period Grating in Polarization-maintaining Panda Fiber

In this work, we have combined the potentialities of polarization-maintaining Panda fiber with the versatility of Long Period Grating (LPG), in order to develop a multi-parameter sensor for the simultaneous measurement of three stimuli such as temperature, strain and surrounding refractive index. The sensor consists of a single LPG written in a Panda fiber by using a simple method based on the electric arc discharge technique. The sensing principle is based on the simultaneous monitoring of the resonance wavelength shift of three rejection bands, where each one is associated to the coupling between the core mode and a different cladding mode. The acquisition of these spectral resonances is performed by considering two orthogonal polarizations of the input light, i.e. aligned to the fast and slow axis of the fiber. The key aspect enabling a three-parameter sensing relies in the fact that these attenuation bands have different responses to the three measurands, moreover the sensitivities change their magnitude and polarity when the input light polarization is switched. This kind of sensors can be applied in structural health monitoring and material science, where the measurement of these three parameters is vital.