  We consider an all in-fiber optical modulator based on a ring resonator
configuration. The case of adiabatic to nonadiabatic transition is considered,
where the geometrical (Berry) phase acquired in a round trip along the ring
changes abruptly by pi. Degradation of the responsivity of the modulator due to
finite linewidth of the optical input is discussed. We show that the
responsivity of the proposed modulator can be significantly enhanced with
optimum design and compare with other configurations.
