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Spinning the Light: The World's Smallest Optical Gyroscope
Gyroscopes are devices that help vehicles, drones, and wearable devices in three-dimensional space. They are commonplace in just about every bit of technology we rely on every day. Originally, gyroscopes were set of nested wheels, each spinning on a different axis. The goal is to open up a cell phone today, and you will find a microelectromechanical sensor (MEMS), the modern-day equivalent, which measures changes in the forces acting on two identical mbades that are oscillating and moving in opposite directions. These MEMS gyroscopes are limited in their sensitivity, so optical gyroscopes have been developed to perform the same function with a greater degree of accuracy than Sagnac effect.
What is the Sagnac Effect? [19659004TheSagnaceffectnamedafterFrenchphysicistGeorgesSagnacisanopticalphenomenonrootedinEinstein'stheoryofgeneralrelativityTocreateitabeamoflightissplitintotwoandthetwindirectionsofacircularpathwaythenmeetthesamelightdetectorLighttravelsataconstantspeedwiththelighttravels-causesoneofthetwobeamstoarriveatthedetectorbeforetheotherWithalooponeachaxisoforientationthisphaseshiftknownastheSagnaceffectcanbeusedtocalculateorientation
The Problem
The smallest high-performance optical gyroscopes available today are bigger than a golf ball and are not suitable for many portable applications. As optical gyroscopes are built smaller and smaller, so is the signal that the Sagnac effect, which makes it more difficult for the gyroscope to detect movement. Up to now, this has prevented the miniaturization of optical gyroscopes
The Invention
Caltech engineers led by Ali Hajimiri, Bren Professor of Electrical Engineering and Medical Engineering in the Division of Engineering and Applied Science, developed a new optical gyroscope that is 500 times smaller than the current state-of-the-art device, yet they can detect phase shifts that are 30 times smaller than those systems. The new device is described in a paper published in the November issue of Nature Photonics.
How it Works
The new gyroscope from Hajimiri's lab achieves this performance by using a new technique called "reciprocal sensitivity enhancement." In this case, "reciprocal" means that it affects both beams of light inside the gyroscope in the same way. Since the Sagnac effect is related to detecting a difference between the two beams, it is considered nonreciprocal. Inside the gyroscope, light travels through miniaturized optical waveguides (small conduits that carry light, that perform the same function as wires for electricity). Imperfections in the optical path that may affect the beams (for example, thermal fluctuations or light scattering) and any other interference will affect both beams similarly.
Hajimiri's team found a way to weed out this reciprocal noise while leaving signals from the Sagnac effect intact.Reciprocal sensitivity enhancement improves the signal-to-noise ratio in the system and enables the integration of the optical gyro onto a smaller chip than a grain of rice.
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