Transversal force sensor using polarization-maintaining fiber independent of direction of applied force: proposal and experiment

Distributed or multiplexed fiber-optic stress sensors have been gaining interest in the fields of integrity monitoring and security maintenance of civil structures. It has been proposed that mode-couplings within a polarization-maintaining fiber induced by an external force could be used to measure stress on the fiber. Several systems using this principle have demonstrated distributed or multiplexed stress sensing capabilities. In this paper, we propose a novel method of uniformly twisting the fiber at a pitch of T/sub p/=2b/sub l/n and perturbing the fiber at a pitch of P/sub p/=b/sub l/n/4 to overcome the angular and perturbation length dependence of the sensor, where b/sub l/ is the beat length of the fiber and n is an arbitrary odd integer. Experimental results obtained were in good agreement with theoretical prediction.