Interferometric device for determining sizes and properties of cylindrical objects based on phase shift measurements

摘要

A system for measuring cross sectional diameters of optical fibers and other elongate cylindrical objects includes a transmitting optics module for generating two collimated laser beams, and causing the beams to intersect and interfere with one another over a measurement region. The optical fiber under inspection is caused to intersect the measurement region with its longitudinal axis perpendicular to a plane defined by the laser beams. Several photodetectors collect light scattered by the optical fiber, and generate signals indicating fiber diameter based on phase differences in the scattered light received by the detectors. The system can determine fiber refractive index by using three detectors to obtain two phase shifts. Differences in Doppler frequencies also are sensed by the detectors, for determining transverse velocity components.