We show that two modes counterpropagating in a single-mode fiber in the presence of random coupling due to refractive-index fluctuations can interfere constructively and give rise to a coherent backscattering process analogous to that associated with backscattering from a disordered medium. Both strong- and weak-localization limits are studied and the interplay between localization and radiation losses is analyzed.

• Received 10 September 1990

DOI:https://doi.org/10.1103/PhysRevA.43.3168