A pair of light waves may hold the key to creating the world's smallest gyroscope that is just a fraction of the width of a human hair, according to scientists, including one of Indian-origin.
Gyroscopes are indispensable components in a number of technologies, including inertial guidance systems, which monitor an object's motion and orientation.
Space probes, satellites, and rockets continuously rely on these systems for accurate flight control.
If the size of an optical gyroscope is reduced to just a fraction of a millimetre, as is presented in the new study, it could then be integrated into optical circuit boards, according to Li Ge, a physicist at the Graduate Center and Staten Island College, City University of New York.
This could drastically reduce the equipment cost in space missions, opening the possibility for a new generation of micro-payloads.
In optical gyroscopes, dual light waves race around an optical cavity or fibre, constantly passing each other as they travel in opposite directions.
Traditionally, engineers have used two approaches to make optical gyroscopes, both based on the Sagnac effect which creates a measurable interference pattern when light waves split and then recombine upon leaving a spinning system.
The first one uses an optical cavity - an engineered structure on a crystal - to confine light and the second one uses an optical fibre to guide light.
The second approach has, to date, been most practical because its sensitivity can be easily enhanced by using longer sections of optical fibre (some up to five kilometres long).
These lengths of fibre would then be wrapped around an object about five centimetres in diameter, achieving a more manageable size.
Though this system is sensitive to rotation, there are practical limits to how long the fibre can be and how small it can be wrapped before the fibre itself is damaged.
To go truly small, optical cavities seem to be the preferable option, where the Sagnac effect manifests as a subtle colour change.
The problem, however, has been that the sensitivity of this type of optical gyroscopes degrades as the cavity gets smaller.
The researchers were able to overcome this hurdle by using a very different principle based on far-field emission. Rather than directly measuring the colour change of the light waves, the researchers determined that they could measure the pattern the light produced as it exited the cavity.
"That was our key innovation - finding a new signal with a much improved sensitivity to rotation," said Ge, who conducted the study with physicist Hui Cao and her student Raktim Sarma, both at Yale University in New Haven.
"Optical gyroscopes optimised to produce and detect this new signal, we found, could be about 10 microns across - smaller than the cross section of a human hair," said Ge.
