Otdr method for detecting hollow-core fibers

A method of locating a hollow-core fiber segment amongst silica core segments along an optical fiber link, comprising:

• using an OTDR test instrument, sending test signals along the optical fiber link and receiving returning signals therefrom;
• measuring from said returning signals a Rayleigh backscatter level as a function of distance along the optical fiber link;
• identifying a position of a proximal extremity of the hollow-core optical fiber segment, comprising locating a discrete drop greater than a drop threshold value in the Rayleigh backscatter level;
• and
• identifying a position of a distal extremity of the hollow-core fiber segment, comprising locating one of a discrete step greater than a step threshold value in the Rayleigh backscatter level and end-of-fiber indicator;
• wherein the drop threshold value and the step threshold value are commensurate with a difference between a Rayleigh backscatter level in hollow-core optical fibers and a Rayleigh backscatter level in silica core optical fibers of the type of the silica core fiber segment immediately preceding and immediately following the hollow-core fiber segment, respectively.