Thanks to the widespread use of optical fibers in telecommunication, they, and their accompanying equipment have become cost-effective and easily accessible. We have proved that the changed attenuation of a monomodal optical fiber built into a polymer composite can indicate the elongation of the structure compared to its original, unloaded state, before the optical fiber breaks. We also proved that the location of deformation in polymer composite structures can be found with OTDR equipment (used for checking the coupling of optical fibers).