Determining the twist in an optical fiber

We determine the twist in a birefringent optical fiber from measurements, atone end of the fiber, of the fiber response to an impulsive source at the sameend. This is the inverse problem of determining a non-constant coefficient, of afirst order hyperbolic system in one space dimension with two speeds ofpropagation, from measurements at one end of an interval, of the solution ofthis system corresponding to an impulsive source at the same end. We prove astability result for this inverse problem and give a provable reconstructionalgorithm for this inverse problem.