According to a group of scientists led by Dr Li Ge from the CUNY’s College of Staten Island, a pair of light waves may hold the key to creating the world’s smallest gyroscope.
Further studies are needed to take into consideration the possibility that many modes, or light paths, exist simultaneously in the cavity, Dr Ge and his colleagues said. Their far-field emission patterns may change in different ways, which causes a reduction of the sensitivity to rotation. Image credit: Li Ge et al.
Light-powered gyroscopes have revolutionized precision measurement of rotation thanks to their long-term reliability and compact size.
These devices have been widely utilized for both civilian and military aircraft as well as satellites, rockets, and nautical navigation.
Engineers have used two approaches to make optical gyroscopes, both based on the so-called Sagnac effect.
The first one uses an optical cavity – an engineered structure on a crystal – to confine light and the second one uses an optical fiber 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 fiber, some up to 5 km long. These lengths of fiber would then be wrapped around an object about 5 cm in diameter, achieving a more manageable size.
Though this system is sensitive to rotation, there are practical limits to how long the fiber can be and how small it can be wrapped before the fiber itself is damaged.
To go truly small, optical cavities seem to be the preferable option, where the Sagnac effect manifests as a subtle color change.
The problem, however, has been that the sensitivity of this type of optical gyroscopes degrades as the cavity gets smaller.
Dr Ge and his colleagues were able to overcome this issue by using a very different principle based on far-field emission.
Rather than directly measuring the color change of the light waves, they 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 Dr Ge, the first author on the paper published in journal Optica.
“Optical gyroscopes optimized to produce and detect this new signal, we found, could be about 10 microns across – smaller than the cross section of a human hair.”
“Though these optical gyroscopes are not new, our approach is remarkable both in its super-small size and potential sensitivity,” Dr Ge said.
Due to their small footprints and on-chip integration capability, microcavity-based gyroscopes can play an important role in reducing the equipment cost in space missions and open the possibility for a new generation of on-chip optical gyroscopes.
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Li Ge et al. 2015. Rotation-induced evolution of far-field emission patterns of deformed microdisk cavities. Optica, vol. 2, no. 4, pp. 323-328; doi: 10.1364/OPTICA.2.000323
