  Here, we theoretically investigate the nonreciprocal response of an
electrically biased graphene-coated dielectric fiber. By electrically biasing
the graphene coating along the fiber axis, the dynamic conductivity of graphene
exhibits a nonsymmetric response with respect to the longitudinal component of
guided-mode wave vectors. Consequently, the guided waves propagating in two
opposite directions may encounter distinct propagation features. In this work,
the electromagnetic properties, such as modal dispersion and some field
distributions are presented, and the strength of nonreciprocity is discussed
for different parameters of graphene, such as its chemical potential and
material loss. Furthermore, the influence of the radius of the fiber on the
nonreciprocal response is investigated. We envision that such nonreciprocal
optical fibers may find various potential applications in THz, microwave, and
optical technologies.
