Spinning the Light: The World's Smallest Optical Gyroscope
Gyroscopes are devices that allow vehicles, drones, and portable electronic devices to sense their orientation in three-dimensional space. They are commonplace in almost every technology we rely on every day. Originally, gyroscopes were sets of nested wheels, each turning on a different axis. But open a cell phone today and you'll find a microelectromechanical sensor (MEMS), today's equivalent, that measures changes in forces acting on two identical masses that oscillate and move in opposite directions. These MEMS gyroscopes are limited in their sensitivity so that optical gyroscopes have been developed to perform the same function but with no moving parts and a higher degree of accuracy using a phenomenon called a Sagnac effect.
What is suitable The problem
The smallest available today high performance gyroscopes are larger than a golf ball and are not for many portable applications, the Sagnac effect [1
. As optical gyroscopes become smaller and smaller, the signal also absorbs the Sagnac effect, making it increasingly difficult for the gyroscope to detect motion. So far, this has prevented the miniaturization of optical gyroscopes.
Caltech engineers headed by Ali Hajimiri, Bren Professor of Electrical and Medical Engineering in the Department of Engineering and Applied Science, developed a new optical gyroscope that is 500 times smaller than the current device to date State of the art, but they can detect phase shifts that are 30 times smaller than such systems. The new device is described in a publication in the November issue of Nature Photonics
How It Works
The new gyroscope from Hajimiri's lab achieves this improved performance through the use of a new technique, the "reciprocal sensitivity enhancement". In this case, "reciprocal" means that both beams of light in the gyroscope are affected in the same way. Since the Sagnac effect is based on detecting a difference between the two beams as they move in opposite directions, it is considered non-reciprocal. Within the gyroscope, the light moves through miniaturized optical fibers (small lines that carry light that perform the same function as wires for electricity). Imperfections in the optical path that could affect the beams (for example, thermal fluctuations or light scattering) and any external disturbance affect both beams equally.
Hajimiri's team found a way to eradicate this reciprocal noise, while signals of the Sagnac effect remain intact. The reciprocal sensitivity enhancement thus improves the signal-to-noise ratio in the system and allows integration of the optical gyroscope onto a chip smaller than a grain of rice.