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An Acousto-Optic Gyroscope (AOG) consisting of a photonic integrated device embedded into two inherently matched piezoelectric surface acoustic wave (SAW) resonators sharing the same acoustic cavity is presented. This constitutes the first demonstration of a micromachined strain-based optomechanical gyroscope that uses the effective index of the optical waveguide due to the acousto-optic effect rather than conventional displacement sensing. The theoretical analysis comparing various photonic phase sensing techniques is presented and verified experimentally for the cases based on a Mach-Zehnder interferometer, as well as a racetrack resonator. This first prototype integrates acoustic and photonic components on the same lithium niobate on insulator (LNOI) substrate and constitutes the first proof of concept demonstration of the AOG. This approach enables the development of a new class of micromachined gyroscopes that combines the advantages of both conventional microscale vibrating gyroscopes and optical gyroscopes.

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Slow light photonic crystal waveguides (PCWs) have been the subject of intensive study due to their potential for on-chip applications such as optical buffers and the enhancement of nonlinear phenomenon. 1 However, due to high group velocity mismatch between the strip waveguide and the slow light waveguide efficient coupling of light is challenging. The coupling efficiency is also very sensitive to the truncation at the interface between the two waveguides. 2 This sensitivity can be removed and light can efficiently be coupled from the strip waveguide to the slow light waveguide by adding an intermediate photonic crystal waveguide (or coupler) that operates at a group index of ∼ 5. Several designs have been proposed for couplers to obtain higher coupling efficiency within the desired group index range. 3 We have studied uniaxial stretched couplers in which the lattice constant is stretched in the direction of propagation by 10-50 nm in the coupler region. Using a Finite Difference Time Domain (FDTD) Simulation Method that allows the extraction of the group index, 4 we have observed 8.5 dB improvement in the coupling efficiency at the group index of 30. Efficient coupling is dominantly determined by the band edge position of the coupler region and maximum transmission efficiency is limited by the maximum transmission of the coupler PCW. If the band edge of coupler PCW is sufficiently red shifted relative to the band edge of the slow light PCW then higher coupling efficiency can be achieved.