Mode couplings due to external forces distributed along a polarization-maintaining fiber: An evaluation

A new interferometric scheme for measuring mode conversion distributed locally along a polarizationmaintaining fiber is presented. Using this technique the power coupling coefficient, varying with magnitude and angle of external pressure transversely applied to a fiber, was evaluated both theoretically and experimentally. The coupling point location is determined with ±1.5-cm accuracy and resolution of better than 10cm for a 220-m long fiber having modal birefringence of 4.4 * 10_-4The coupling coefficient was proportional to the external force in the range from 5 * 10_-3to 0.1 kg/mm. The relationships determined experimentally reflected those predicted by theory.