  In this paper, we report on new high-precision absolute distance measurements
performed with frequency scanned interferometry using a pair of single-mode
optical fibers. Absolute distances were determined by counting the interference
fringes produced while scanning the frequencies of the two chopped lasers.
High-finesse Fabry-Perot interferometers were used to determine frequency
changes during scanning. Dual lasers with oppositely scanning directions,
combined with a multi-distance-measurement technique previously reported, were
used to cancel drift errors and to suppress vibration effects and interference
fringe uncertainties. Under realistic conditions, a precision about 0.2 microns
was achieved for a distance of 0.41 meters.

Instrumentation and Detectors;Optics