Caltech engineers have created an optical gyroscope that is 500 times smaller than the current state-of-the-art fiber optic device, yet able to detect phase shifts that are 30 times smaller than existing systems. This is the optical gyroscope developed in Ali Hajimiri’s lab, resting on grains of rice. Courtesy of Ali Hajimiri/Caltech. Gyroscopes — devices that help vehicles, drones, and wearable and handheld electronic devices orient themselves in 3D space — are commonplace in the technology we rely on every day. Optical gyroscopes have been developed to perform the same function as MEMS gyroscopes, but with no moving parts and a greater degree of accuracy. Optical gyroscopes measure the rotation rate using a relativistic phenomenon called the Sagnac effect. The smallest high-performance optical gyroscopes available today are larger than a golf ball and not suitable for many portable applications. The smaller the optical gyroscope, the smaller the signal that captures the Sagnac effect, which makes it more difficult for the gyroscope to detect movement. Up to now, this has hindered the miniaturization of optical gyroscopes. The new nanophotonic gyroscope, developed by an engineering team led by professor Ali Hajimiri, uses a technique called “reciprocal sensitivity enhancement.” It exploits the reciprocity of passive optical networks to significantly reduce thermal fluctuations and mismatch. Inside the gyroscope, which uses twin beams that travel in opposite directions along a circular pathway, light travels through miniaturized optical waveguides. Imperfections in the optical path that could affect the beams (for example, thermal fluctuations or light scattering) and any outside interference affect both beams similarly. Hajimiri’s team found a way to weed out this reciprocal noise while leaving signals from the Sagnac effect intact, thus improving the signal-to-noise ratio in the system and enabling the integration of the optical gyroscope onto a chip smaller than a grain of rice. The researchers say that their approach is capable of enhancing the performance of optical gyroscopes by one to two orders of magnitude. The research was published in Nature Photonics (https://doi.org/10.1038/s41566-018-0266-5).