Engineers have designed the world’s smallest version of an optical gyroscope, a device that relies on light rather than moving parts, in a feat that could lead to models with much higher precision than comparable mechanical devices. It is 500 times smaller than regular gyroscopes and is about the size of a grain of rice.
Above – Rice grains dwarf a gyroscope of a type that uses light rather than mechanical components. Credit: Pooya Vahidi
Inside a conventional optical gyroscope, a spooled-up optical fiber carries pulses of laser light, some running clockwise and some running anticlockwise. The device measures the rate of rotation by detecting tiny shifts in the timing of the pulses’ arrival at a sensor. Optical gyros have been difficult to scale down because, as they shrink, the signal from their sensors weakens and is then drowned in noise created in part by scattered light.
Parham Khial and his colleagues at the California Institute of Technology in Pasadena designed a low-noise, photonic gyroscope. The researchers etched light-guiding channels onto a 2-square-millimeter silicon chip to guide the light traveling in each direction around a separate circle, so that scattered light would not confuse the device’s sensors. The new design also periodically reverses the light’s direction, helping to cancel out much of the noise.
Optical gyroscopes measure the rate of rotation by exploiting a relativistic phenomenon known as the Sagnac effect. Such gyroscopes are great candidates for miniaturization onto nanophotonic platforms. However, the signal-to-noise ratio of optical gyroscopes is generally limited by thermal fluctuations, component drift and fabrication mismatch. Due to the comparatively weaker signal strength at the microscale, integrated nanophotonic optical gyroscopes have not been realized so far. Here, they demonstrate an all-integrated nanophotonic optical gyroscope by exploiting the reciprocity of passive optical networks to significantly reduce thermal fluctuations and mismatch. The proof-of-concept device is capable of detecting phase shifts 30 times smaller than state-of-the-art miniature fiber-optic gyroscopes, despite being 500 times smaller in size. The approach is capable of enhancing the performance of optical gyroscopes by one to two orders of magnitude.