Gyroscopes are multi-functional devices used today to help orient everything from vehicles to drones. Although we never think about them, they are present in nearly every bit of technology we use daily.
It goes without saying that to empower their near ubiquitous implementation, modern-day engineers have had to make them quite small. These smaller advanced gyroscope versions are called microelectromechanical sensor (MEMS) and to find one you need look no further than your cell phone.
The Sagnac effect in effect!
However, MEMs are limited in their sensitivity, so engineers have also developed superior optical gyroscopes that perform with better accuracy and with the omission of moving parts. To do this these devices rely on a phenomenon referred to as the Sagnac effect.
Named after French physicist Georges Sagnac, this optical effect rooted in Einstein’s theory of general relativity works by seeing the optical gyroscope split a beam of light into two and then rotate to manipulate the arrival of the now separate beams at its detector.
This creates two twin beams traveling in opposite directions along a circular pathway which then meet at the same light detector at different times since the rotation move has delayed one of the beam’s journey. The resulting phase shift is what is known as the Sagnac effect and what is used to calculate orientation so precisely by optical gyroscopes.
Although very useful, so far even the best high-performance optical gyroscopes have been bigger than a golf ball and therefore incompatible with most of today’s portable electronics. Previous attempts to build smaller versions of these high-precision devices, unfortunately, have always resulted in a reduced Sagnac effect signal and therefore reduced reliability and accuracy.
Now, a team of Caltech engineers led by Ali Hajimiri, Bren Professor of Electrical Engineering and Medical Engineering in the Division of Engineering and Applied Science, have found a way to shrink these devices while at the same time improving their accuracy. The discovery is bound to forever change the use of optical gyroscopes, likely making them even more popular and ever-present than MEMS.
Reciprocal sensitivity enhancement
Caltech’s novel optical gyroscope is 500 times smaller than the best devices currently available, making it smaller than a grain of rice, yet it can detect phase shifts 30 times smaller than even the most precise models out there. To do this, the tiny device uses something called “reciprocal sensitivity enhancement.”
This technique is a novel intelligent method for weeding out the reciprocal noise of optical gyroscopes without affecting the signals derived from the Sagnac effect. In this way, the signal-to-noise ratio in the system is this improved without the requirement of a large device. The result is tiny optical gyroscopes with impressively better accuracy.
Caltech’s invention is described in detail in a study titled “Nanophotonic optical gyroscope with reciprocal sensitivity enhancement” published in the November issue of Nature Photonics.
The research was funded by the Rothenberg Innovation Initiative.