Method and apparatus for measuring the length of, or distances to

Abstract

A lightwave component measurement system provides modulation measurements and the use of digital signal processing for the resolution of single or multiple optical reflections in optical fiber cable or in open beam at discontinuities attributable to changes in the effective index of refraction in an optical transmission medium. The lightwave component measurement system preferably incorporates a transform capability that converts data measured in the modulation frequency domain to the time or distance domain. The time-domain data are both stable and accurate, since they are calculated from highly-stable, highly-precise frequency-domain information. The time-domain transform capability in the lightwave component measurement system allows a reflection to be located to millimeters, and resolution of multiple discontinuities just centimeters apart. This also enables precise measurement of the magnitude and distance to each discontinuity, as well as the length of an optical transmission medium, such as optical fiber cable. The lightwave component measurement system in accordance with the invention has a broad measurement dynamic range (typically 45 dB) with no measurement dead zones.