Fiber polarimetric stress sensors.

Simple polarimetric force sensors based on high birefringence fibers are investigated theoretically and experimentally. The sensor consists of a linearly polarized light source, a birefringent fiber, an analyzer or polarizing prism and two photo detectors. At the input, one of the polarization modes is excited. At the output, power in the orthogonal polarization mode is detected. In the theoretical investigation, the sensor is modeled as a concatenation of three birefringent fiber sections with the short middle section as the stress sensing element. The high birefringent fibers are treated as anisotropic media and the effects of stress on the fiber birefringence and the rotation of birefringence axes are studied. In particular, the presence of protective jackets is taken into account in the theoretical consideration. The sensor response is expressed as a function of the applied force, the interaction length, and the direction of force relative to the birefringence axes of the fiber. Experimental results based on high birefringent fibers agree very well with the theoretical predicted behavior.