There are two kinds of gyroscopes in widespread use for navigation and control: optical ones, which are extremely sensitive but also expensive, and microelectromechanical (MEMS) ones, which are inexpensive and easy to manufacture but aren’t as accurate. For years, engineers have wondered if they could “borrow” a bit of technology from each to create a new type of gyroscope with the precision of laser gyroscopes—one that would be as easy and inexpensive to make as MEMS gyroscopes. Engineers at California Technical Institute did just, developing an gyroscope that combines some of the best characteristics of each into one device (while throwing in some new technology as well).
The new gyro is at its heart an optical device, and like all optical gyroscopes, it uses the Sagnac effect to measure rotation, in turn converting that data into direction, speed and location. In the effect, two light waves traveling in opposite directions around a ring-like path will have equal propagation times. However, when the path rotates, the time to reach a specific point on the rotating path will be different for each wave. This difference provides a measure of the rate of rotation and can be precisely determined by measuring the interference between the two light waves.
There are two versions of optical gyroscope. In laser gyroscopes, the ring-shaped path consists of a series of discrete mirrors that light bounces off of. Fiber optical gyroscopes, on the other hand, use a spool of fiber optic cable that can be hundreds or even thousands of meters long to form the path.
In the new gyroscope, the pathway is a circular silica disk. A laser beam is generated by high frequency vibrations in the disk through a process called stimulated Brillouin scattering.
Although the short light path in the new gyro keeps the device small, it could also result in lower sensitivity. To make up for that, the light is “recycled,” and allowed to repeatedly circle, creating a stronger Sagnac effect and greater sensitivity to rotation. The Brillouin laser action is said to magnify this sensitivity by compensating for optical losses in the disk.
In addition to the new gyroscope’s potential for improved sensitivity relative to MEMS gyroscopes, such a system would have no moving parts and would be more immune to vibrations and shocks. That resiliency is one reason researchers are interested in chip-sized optical gyroscopes, as they will be larger than MEMS gyros.
The Caltech team will continue studying these devices. Preliminary experimental evidence suggests they can be made considerably more sensitive by a factor somewhere between 10 and 100. If so, the new gyros would be many orders of magnitude more precise than MEMS versions.
Funding for the research was provided by the Defense Advanced Research Projects Agency (DARPA).