An on-fiber tunable coupler and switch for communication systems. Two optical fibers are modified by replacing passive cladding with at least an inner metallic electrode, an electrooptic material layer on the inner electrode, and an outer metallic electrode on the electrooptic material. The optical fibers are positioned close to each other. More layers can be coated between any of these layers to improve the interface properties or reflectivity. The presence of an electric signal, will change the optical properties of the modified cladding, as will the propagation characteristics of the optical signal within one fiber core. This will permit tunable coupling of the signal from the first fiber core to the second fiber core(s). The coupling coefficient between the first and the second fiber(s) is adjustable. Switch-off the signal output from the first fiber to the second fiber is achieved at 100% coupling ratio.