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.