We propose and experimentally demonstrate a single-mode fiber length and
dispersion measurement system based on a novel frequency-shifted asymmetric
Sagnac interferometer incorporating an acousto-optic modulator (AOM). By
sweeping the driving frequency of the AOM, which is asymmetrically placed in
the Sagnac loop, the optical length of the fiber can be determined by measuring
the corresponding variation in the phase delay between the two
counter-propagating light beams. Combined with a high-resolution data
processing algorithm, this system yields a dynamic range from a few centimeters
to 60km (limited only by our availability of long fibers) with a resolution
about 1ppm for long fibers.Comment: 3 page
