Acousto-optic phase modulation properties of coaxially-deposited ZnO transducers on single-mode fibers

Abstract

The acoustooptic (AO) phase modulation properties of coaxially deposited zinc oxide (ZnO) transducers on single mode optical fibers have been experimentally and theoretically investigated at several laboratories over the past 15 years. Maximum phase shifts are observed at distinct frequencies, corresponding to bulk acoustic waves in the fiber, over the transducer operating range of 200 MHz to 1.0 GHz. Phase shift values have been measured with both cw and pulsed signal inputs to the transducers from milliwatts to above 1 Watt. Transducer lengths have been varied from 30 mm to 2 mm to determine the effects of AO phase shift on the length of the interaction. Modulation efficiencies in the range of 0.2 to 0.3 radians per square root of input power (in mW) per centimeter, for 2 to 6 mm interaction lengths, have been observed at frequencies in the 200 to 400 MHz region corresponding to acoustic wavelengths on the order of the core dimensions of the optical fiber. The characteristics and capabilities of AO modulation in optical fibers with deposited coaxial ZnO transducers is discussed using examples from experimental work.