On-chip microwave interferometry using phononic integrated circuits

Piezoelectric phononic integrated circuits (PnICs), chip-scale platforms in which GHz frequency acoustic fields are routed in µm-scale waveguide geometries, have steadily advanced in performance and complexity, providing new degrees of freedom for manipulating microwave signals. Here, we consider the use of PnICs for implementing on-chip microwave interferometers ( f = 3.4 GHz ) using a gallium nitride ( Ga N ) on silicon carbide ( Si C ) PnIC platform. We demonstrate controlled mode amplitude splitting, differential control (local phase shift), and mode recombination in an unbalanced ( Δ L = 1.6 mm ) phononic Mach-Zehnder interferometer (MZI), achieving a maximum fringe visibility > 0.985 . The high visibility does not imply high sensitivity due to the presence of parasitic acoustic modes in the MZI. We quantify the effect of these parasitic guided modes in the interferometer, and discuss potential design improvements for achieving quasi-single-mode operation in PnICs, with a view toward enabling applications in microwave and acoustic signal processing and sensing.