Application of a communication signal, RF (radio frequency) or microwave signal to a modified optical fiber for modulating or switching-off the optical signal propagating within the optical fiber. The passive cladding material of an ordinary optical fiber is removed from a small region and replaced with active multilayer materials including at least three layers of cladding surrounding the core. These layers are the inner metallic electrode coated on the surface of the optical fiber core, the electrooptic active material layer placed on the top of the inner electrode, and the outer metallic electrode coated on the top of the electrooptic material. A communication signal applied to the electrodes will result in optical modulation so that the modulated intensity and phase of the optical signal at the receiving end of the fiber can be detected, and demodulation of the signal can be achieved.