Optimization of hi-birefringence-fiber-based distributed force sensors

In this paper, we present two new approaches of distributed optical fiber force sensors. The first approach relies on the optical Kerr effect which utilizes two lasers launched into a Hi-Bi fiber from the same end. A He-Ne laser provides a CW probe beam which is launched into fiber to excite two polarization modes with equal intensities. A Nd:YAG laser is used to provide a pulsed pump beam which excites one polarization mode. The polarization state of the CW beam changes when the pump beam propagates through the fiber, or when a force is applied to the fiber. Information regarding the intensity of the force and its position can be obtained using a data acquisition and analysis system. The second approach is based on the FMCW technique. In this case, a frequency modulated laser beam is launched into a Hi-Bi fiber with one polarization mode and reflected from the far end of the fiber by a mirror. When a force is applied to the fiber at any position, mode coupling will occur. By detecting the beat frequency produced by the two coupled mode beams, the intensity and the position of the force can be found. In this paper, the experimental results obtained from the two sensor systems are presented.