You may not realize it, but gyroscopes can be found in pretty much any modern electronic gadget. With applications ranging from cell phones to vehicles, drones, and wearables, the humble gyroscope sensor is also one of the most versatile. These days, the gyroscopes that you can find in your phone will likely be MEMS-based. Now, however, researchers from Caltech have successfully built another type of gyroscope that is 500 times smaller and 30 times more sensitive than the MEMS version.
Traditional MEMS-based gyroscopes work by measuring the forces of two identical masses that are oscillating and moving in opposite directions. By contrast, the optical gyroscope that the Caltech team developed employs lasers rather than MEMS to achieve the same result. Although optical gyroscopes are effective in theory, in practice they have been hard to miniaturize, as the noise-to-signal ratio is inversely proportional to the optical gyroscope’s size.
To understand the optical gyroscope, one must first begin with the Sagnac Effect. Discovered by French physicist Georges Sagnac, the effect uses Einstein’s principle of general relativity to detect changes in angular velocity. Essentially, a laser is broken into two beams, and each beam is shot along one side of a disk. Because light travels at a constant speed, the two beams reach the end of the disk at the same time so long as the disk is not in motion. If the disk is spinning, the laser beams will arrive at the end-point out of sync. This difference in synchronization is what the gyroscope measures, as the end-point beam has minute changes in its properties that can reveal, for instance, whether or not you’ve just dropped your smartphone.
Unfortunately, the Sagnac Effect is often prohibitively sensitive to noise in the signal. Everything from small thermal fluctuations, to vibrations from nearby construction or loud noises, can disrupt the beams as they travel. To make matters worse, the smaller the gyroscope is, the more easily it is disrupted. The smallest high-performance optical gyroscopes today are around the size of a golf ball—not very suited to being stuffed inside a smartwatch.
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