The smallest optical gyroscope in the world

Gyroscopes are devices that help vehicles, drones and portable and portable electronic devices to know their orientation in a three-dimensional space. They are common in almost every technology we rely on every day. Originally, gyroscopes were sets of nested wheels, each rotating on a different axis. But open a cell phone today and you'll find a microelectromechanical sensor (MEMS), the modern equivalent, that measures the variations in forces acting on two identical masses that oscillate and move in opposite directions. The sensitivity of these MEMS gyroscopes being limited, optical gyroscopes have been developed to fulfill the same function but without moving parts and with a higher degree of precision thanks to a phenomenon called Sagnac effect.

What is the Sagnac effect?

The Sagnac effect, named after the French physicist Georges Sagnac, is an optical phenomenon rooted in Einstein's theory of general relativity. To create it, a beam of light is split in two and the double beams move in opposite directions along a circular path, and then join at the same light detector. Light moving at a constant speed, the rotation of the device – and with it the path taken by the light – allows one of the two beams to reach the detector before the camera. other. With a loop on each axis of orientation, this phase shift, called the Sagnac effect, can be used to calculate the orientation.

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 the optical gyroscopes are built smaller and smaller, the signal capturing the Sagnac effect is also, it is increasingly difficult for the gyroscope to detect motion. Until now, this prevented the miniaturization of optical gyroscopes.

L & # 39; invention

The Caltech engineers led by Ali Hajimiri, Professor Bren of Electrical Engineering and Medical Engineering at the Division of Engineering and Applied Sciences, have developed a new optical gyroscope 500 times smaller than the current state-of-the-art device, but they can detect phase shifts that are 30 times smaller than these systems. This new device is described in an article published in the November issue of Nature Photonics.

How it works

The new gyro from the Hajimiri lab gets this improved performance using a new technique called "improving reciprocal sensitivity". In this case, "reciprocal" means that it affects the two beams of light inside the gyroscope in the same way. Since the Sagnac effect relies on the detection of a difference between the two beams when they move in opposite directions, it is considered nonreciprocal. Inside the gyroscope, light travels through miniaturized optical waveguides (small light carrying ducts, which 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 external interference will affect both beams in the same way.

The Hajimiri team has found a way to eliminate this mutual noise while leaving the Sagnac effect signals intact. The improvement of the reciprocal sensitivity thus improves the signal-to-noise ratio in the system and allows the integration of the optical gyroscope on a smaller rice chip.