Polarimetric and Bragg Optical Fiber Sensors for Stress Distribution and Temperature Measurements in Composite Materials

Composite structures are made from two or more constituent materials with significantly different physical or chemical properties and they remain separate and distinct in a macroscopic level within the finished structure. This feature allows us for introducing an optical fiber sensors matrix into the composite material. These sensors can demonstrate stress distribution inside a tested material influenced by external tensions. Two types of the optical fiber sensors, placed into one fiber simultaneously, are used as s matrix structure. One of them is based on application of the Bragg grating structure written inside the core of the fiber. Longitudinal stress modifies changes parameters of the Bragg grating and in the same, spectral characteristics of the light transmitted through the fiber. The second one is based on application of highly birefringent fibers which under external stress introduce polarization changes in the output light. These sensors placed into one fiber give a possibility to the measure two external tensions separately.