Grating-based optical fiber sensors for structural analysis

Long-period gratings are versatile optical fiber sensing elements that are simple and economical to fabricate and demodulate. Long-period gratings are periodic photoinduced structures in fiber cores that couple light from guided to cladding modes. This paper discusses the applications of these devices to strain measurements in highperformance materials and structures. Experimental results from a preliminary loading test carried out on rebar commonly used to reinforce civil structures are presented. The cross-sensitivity of long-period grating-based strain sensors to temperature is analyzed and two methods to overcome this limitation are presented. Furthermore, the application of such gratings to temperature measurements in the presence of actively varying axial strain is discussed. Preliminary results indicate that long-period gratings hold tremendous potential for health monitoring of advanced materials and structures.