An optical add/drop multiplexer includes a mode converter. A first mode coupler is coupled to an input of the mode converter. A second mode coupler is coupled to an output of the mode converter. The mode converter includes an optical fiber with multiple cladding modes and a single core mode guided along a core. An acoustic wave propagation member is coupled to the optical fiber. The acoustic wave propagation member propagates an acoustic wave from its proximal to its distal end. At least one acoustic wave generator is coupled to the proximal end of the acoustic wave propagation member.