What do vehicles, drones and wearable/handheld devices have in common? They all utilize gyroscopes in determining their orientation in three-dimensional space.
Gyroscopes used to be “sets of nested wheels” with each wheel spinning on a different axis. Now, opening up a cell phone and you will find the modern-day equivalent: a microelectromechanical sensor (MEMS). These MEMS gyroscopes measure the differences in the forces exerted on two oscillating identical masses moving in opposite directions. Because they are limited in their sensitivity, optical gyroscopes were developed to perform the same function but have a greater degree of accuracy by a phenomenon called the Sagnac effect.
Named after the French physicist Georges Sagnac, the Sagnac effect is an optical phenomenon based on Einstein's theory of general relativity. To the Sagnac effect, a beam of light is split into two with the twin beams traveling in opposite directions along a circular pathway where the meet at the same light detector.
Presently, the smallest high-efficacy optical gyroscopes available today are larger than a golf ball which makes them unsuitable for many portable applications. If optical gyroscopes are built smaller, then the signal that captures the Sagnac effect will also decrease, making it altogether a challenge for the gyroscope to detect movement--preventing the miniaturization of optical gyroscopes.
Worlds Smallest Gyroscope. Image Credit: Ali Hajimiri via CalTech.edu
However, engineers at Caltech have sought to develop a newly optimized gyroscope that is 500 times smaller than the current high-applicative device and can detect phase shifts that are 30 times smaller. Funded by the Rothenberg Innovation Initiative, the research study, which was led by Ali Hajimiri, Bren Professor of Electrical Engineering and Medical Engineering in the Division of Engineering and Applied Science, was published in the November issue of Nature Photonics.
In the paper “Nanophotonic optical gyroscope with reciprocal sensitivity enhancement”, authors describe a new technique called "reciprocal sensitivity enhancement” that has improved the efficiency of the developed gyroscope. In this case, "reciprocal" means that it affects both beams of the light inside the gyroscope in the same way. Since the Sagnac effect relies on detecting a difference between the two beams as they travel in opposite directions, it is considered nonreciprocal.
Inside the gyroscope, the light travel through tiny conduits that transfer light; miniaturized optical waveguides. The researchers have found a way to “take-out” that reciprocal noise while only leaving the signals deriving from the Sagnac effect. The process of enhancing reciprocal sensitivity has greatly improved the signal-to-noise ratio and enabled the optical gyro to integrate onto a chip that smaller than a grain of rice.