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New High Precision Chip-Based Laser Gyroscope Can Measure Earth's Rotation:
Optical gyroscopes are used in applications such as aircraft navigation systems, while MEMS gyroscopes are found in devices like smartphones. For the last few decades, researchers have wondered whether it would be possible to bridge the gap between these two technologies and create a new type of gyroscope that combines the precision of laser gyroscopes with the ease of manufacture of MEMS gyroscopes. Now, Caltech scientists have developed an optical gyroscope that marries some of the best characteristics of each into one device.
In a new paper published in Nature Photonics, Kerry Vahala (BS '80, MS '81, PhD '85), Caltech's Ted and Ginger Jenkins Professor of Information Science and Technology and Applied Physics, describes a laser gyroscope his lab built from a piece of silicon-based material in much the same way that MEMS devices are manufactured. The new type of gyroscope has achieved something considered a benchmark for gyroscopes: the ability to measure the rotation of the earth.
All optical gyroscopes, including the one developed by Vahala, make use of something known as the Sagnac effect to measure rotation. Two light waves traveling in opposite directions around a ring-like path will have equal propagation times. However, when the path rotates, the time to reach a specific point on the rotating path will be different for each wave. This difference provides a measure of the rate of rotation and can be determined very precisely by measuring the interference between the two light waves.
[...] In Vahala's gyroscope, the pathway is a circular silica disk, and the laser light is generated by high frequency vibrations in the disk through a process called stimulated Brillouin scattering.
Although the shorter light path in Vahala's gyroscope helps to keep the device smaller, it could also result in lower sensitivity. To make up for that, the light is "recycled," says Yu-Hung Lai, co-author on the paper. "The light is allowed to circulate around the path again and again, creating a stronger Sagnac effect and greater sensitivity to rotation."
Journal Reference:
Yu-Hung Lai, Myoung-Gyun Suh, Yu-Kun Lu, et al. Earth rotation measured by a chip-scale ring laser gyroscope, Nature Photonics (DOI: 10.1038/s41566-020-0588-y)
(Score: 2) by inertnet on Friday June 05 2020, @10:21PM (5 children)
A long time ago when I was conscripted into the army, my task was to operate a device [prc68.com], based on a gyroscope, for finding true north. This was before GPS was used for aiming nuclear missiles (called 'Honest John'), at least in Europe. I believe the USA already used more modern missiles and GPS at the time. Our missiles were replaced with "Lance" missiles right after I was discharged.
Anyway, that device used a gyroscope to find true north. One measurement took several minutes and for extra accuracy 2 measurements in a row were required, the first based on magnetic north which resulted in a preliminary result. The second based on the first result, which gave a very accurate Earth axis north. The gyroscope hangs on a sort of blade and would swing from left to right and back. I'd write down the angles of the extremes and the their average would be the Earth axis.
I think it was exactly like the one I linked, only with a green tripod and with the cover, shown further down the page.
(Score: 0) by Anonymous Coward on Friday June 05 2020, @10:54PM (1 child)
Interesting. What about Earth wobble? (30 ft in the point at which the axis intersects the Earth's surface and has a period of 433 days)
(Score: 2) by inertnet on Saturday June 06 2020, @12:13AM
We were launching nuclear missiles (only pretending) with a 15 mile range. They didn't need to be *that* accurate. A complete measurement took about 15 minutes, first determine magnetic north, based on that use the gyroscope to determine Earth axis. Next do another measurement based on the first gyroscope result. Report the result to the targeting team. If I remember correctly the result would be well within one degree accuracy.
(Score: 2) by driverless on Sunday June 07 2020, @04:39AM (2 children)
That's probably because dropping a warhead onto Stevens Point when you were aiming for Novokuznetsk could lead to a reduction in rank and accompanying demotion to the next inferior pay grade under some circumstances.
(Score: 2) by inertnet on Sunday June 07 2020, @10:01AM (1 child)
We were told that the Belgians once had managed to find 'true south' instead of true north and shot their rocket, luckily with only a test payload causing a small explosion a kilometre above ground, exactly 180 degrees opposite to where it was supposed to go.
(Score: 0) by Anonymous Coward on Sunday June 07 2020, @03:39PM
Talk about things going south...