Silicon-based electro-optical gyroscope overcomes SNR deficiencies

January 21, 2019 //By Bill Schweber
Silicon-based electro-optical gyroscope overcomes SNR deficiencies
A 2mm-square silicon-based optical gyroscope devised at Caltech overcomes the major source of error in these tiny units thanks to the use of a self-cancellation technique. Those tiny gyroscopes—along with accelerometers, the foundation of inertial guidance—keep getting better.

The mechanical spinning-wheel and laser-based optical gyro have been supplanted in most applications by fiber-optic and MEMS gyros, but the latter pair have difficulties reaching the precision performance of the former. Attempts to miniaturize the fiber gyro have fallen short due to second- and third-order errors that result from thermal fluctuations, component drift, and fabrication mismatch brought on signal-to-noise ratio (SNR) degradation as size and optical-path length shrinks.

Engineers know that intrinsic errors in systems can be reduced by using techniques such as upfront or ongoing calibration. They minimize the sources of the errors through ever-better components and materials, and—perhaps the best technique where feasible—devise an architecture that causes the errors to self-cancel. Applying that last principle, a team at Caltech funded by the Rothenberg Innovation Initiative has devised, built, and tested a new approach to tiny, silicon-based electro-optical gyros that provides precision performance with little cost or other negatives (see figure 1).

1. This electro-optical nano-gyroscope devised at Caltech measures just 2 mm on each side, yet provides excellent performance due to a technique that enables cancellation of a major source of errors. (Source: Ali Hajimiri/Caltech)

Their solution leverages what they denote as the “reciprocity” of passive optical networks to greatly reduce thermal fluctuations and mismatch, and thus yield superior results compared to previous approaches. Their demonstration device is capable of detecting phase shifts—a primary figure of merit for these units—that are 30 times smaller than state-of-the-art, miniature fiber-optic gyroscopes, even though the unit itself is 500 times smaller. The overall improvement in performance of optical gyroscopes is one to two orders of magnitude.

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