A carrier rod having at least one recess extending along at least part of the length of the rod, in which recess a optical fiber assembly for monitoring strain, temperature and/or other physical parameters is arranged, which optical fiber assembly is along at least part of its length bonded within the recess. The carrier rod can be used in a system or a method of monitoring deformation and other characteristics of a casing or other tubular or cylindrical well equipment in a well traversing an underground formation.