Double-polarization interferometer for digital force sensing by fiber tension bending

A fiber-optic interferometric force sensor with digital readout by fringe counting is investigated. Ambiguity in fringe counting is eliminated by employing the double-polarization method. Force F(t), transverse to the fiber axis, is measured by tension-bending-induced fiber strain. A theoretical strain-force characteristic is derived, yielding an F(t)(2/3) dependence of fiber strain on the transverse force that is verified experimentally.