The characteristics of coaxial ZnO thin-film BAW transducers on optical fibers

ZnO thin-film bulk acoustic wave (BAW) transducers, deposited in a coaxial configuration in an optical fiber, have been used to produce acoustooptic phase shifts of single mode guided optical waves. The thin-film transducers and associated electrodes are fabricated by rotating the fiber during the deposition process. Depending on the ZnO deposition parameters and the rotation rate of the fiber, longitudinal or shear bulk acoustic wave generation into the fiber was dominant. The combination of ZnO film and optical fiber forms a resonant structure in which standing-wave conditions periodically occur for the longitudinal and shear waves. Acoustic parameters of the ZnO film and the optical fiber were calculated by measuring the electrical properties of the transducer and its resonant modes. These parameters were examined over the frequency range from 100 MHz to 1.0 GHz for 80- and 125-μm-diameter fibers