A symmetric dielectric-slab wave guide with a passive core and an active cladding is considered. A bound mode of the structure is assumed to propagate in the guide with the objective of optically pumping the cladding region adjacent to the core to induce an optical gain condition there. A signal beam whose frequency differs from that of the pump mode is simultaneously allowed to propagate as a bound mode of the structure. It is shown theoretically that the signal mode is amplified through the interaction of its evanescent field with the active region of the cladding. The advantages of evanescent-wave active devices are illustrated and discussed. A noteworthy effect is that of gain enhancement obtained by means of evanescent-wave pumping over that gain obtainable by conventional means.
Development of Sensors Using Evanescent Wave Interactions in Sapphire Optical Fibers