Noninvasive switchable acousto-optic taps for optical fiber

Two novel tap designs are demonstrated based on phase-matched coupling from the fundamental mode of a fiber to a higher-order core-guided or cladding-guided mode through the acoustooptic effect. The acoustic waves are coupled to the fiber using a Hertzian (deformed surface-to-surface) contact with a grooved transducer substrate. The first tap consists of a two-mode fiber coupler in conjunction with a microbend tap. The coupler converts approximately 5% of the fundamental mode power to the second-order mode. At the microbend tap, the higher-order mode is preferentially radiated from the fiber. The second tap uses a similar mode-coupling mechanism to convert a fraction of the fundamental mode power into a cladding-guided mode in a single-mode fiber