Optical fiber-based key for remote authentication of users and optical fiber line

We have shown the opportunity to use the unique inhomogeneities of the internal structure of an optical fiber waveguide for remote authentication of users or an optic fiber line. Optical Time Domain Reflectometry (OTDR) is demonstrated to be applicable to observing unclonable backscattered signal patterns at distances of tens of kilometers. The physical nature of the detected patterns was explained, and their characteristic spatial periods were investigated. The patterns are due to the refractive index fluctuations of a standard telecommunication fiber. We have experimentally verified that the patterns are an example of a Physically Unclonable Function (PUF). The uniqueness and reproducibility of the patterns have been demonstrated and an authentication protocol has been provided.