All-fiber magneto-optic isolator based on the nonreciprocal phase shift in asymmetric fiber

A new magneto-optic effect in optical fibers is suggested and observed for the first time to our knowledge. The nonreciprocal phase shift in a perpendicular magnetic field, previously observed for TM modes in planar waveguides, is shown to exist in fibers with asymmetrical cores in which a TM-like mode can be defined. The effect is observed in a special fiber in which one side of the core is doped with holmium. New all-fiber isolators are proposed, both single polarization and polarization independent, based on these special fibers in Mach–Zehnder interferometer configurations. The effect can also be used in circulators and Sagnac effect fiber-optic gyroscopes.