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California Institute of Technology (Caltech) engineers have created the world's smallest optical gyroscope, a sensor that can be used in smartphones and drones.
The tiny device, smaller than a grain of rice, determines its position in a three-dimensional space using what is called the Sagnac effect. Based on the principles of general relativity, the Sagnac effect occurs when a beam of light is split and the two resulting beams move in opposite directions in a circle, arriving at the same light detector. Despite the fact that the speed of light is constant, the rotation of the plain in which these beams move causes the arrival of one beam earlier than the other. When these loops are placed on each axis of orientation, the Sagnac effect can be used to determine the spatial position.
As the optical gyroscopes are built smaller and smaller, the signal capturing the Sagnac effect is also, which makes it more and more difficult to detect movements by the device. Until now, this has prevented the miniaturization of optical gyroscopes, the smallest and most powerful devices exceeding the golf balls.
The Caltech team overcame this problem by developing a new technique called "reciprocal enhancement of sensitivity". Imperfections in the optical paths taken by the beams can cause thermal fluctuations or scattering of light, which can lead to reciprocal signal noise. Under the direction of Professor Ali Hajimiri, Caltech engineers were able to suppress this mutual noise while leaving intact the signals of the Sagnac effect. It's this breakthrough that has finally allowed them to dramatically miniaturize the technology.
According to the Caltech team, the device is 500 times smaller than the state-of-the-art optical gyroscope, but it can detect phase shifts that are 30 times smaller than these systems. The book is described in an article published in the November issue of Photonic Nature.
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