The World's Tiniest Optical Gyroscope Is Now Smaller Than a Grain of Rice | Hacker News Reader

The World's Tiniest Optical Gyroscope Is Now Smaller Than a Grain of Rice

interestingengineering.com

43 pointsNicoJuicy15 comments

They use phase detecting photodiodes and thermal effects to measure and tune a miniaturized ring gyro (single turn) to measure rotation in a MEMS device. Their ratiometric compensation makes it much better than you might expect, but not (as is implied by the article above) better than larger gyros.

The supplemental derivations and discussions/figures for this paper are available (in pdf) from the Caltech Library.

https://authors.library.caltech.edu/88626/3/41566_2018_266_M...

http://resolver.caltech.edu/CaltechAUTHORS:20180807-12540532.... - permalink

Or the entire article ois available from Springer:

https://www.nature.com/articles/s41566-018-0266-5

> Named after French physicist Georges Sagnac, this optical effect rooted in Einstein's theory of general relativity works

It's not true at all.

Yeah, maybe special relativity...

Linear Sagnac effect (light grabbed by linear uniform motion) contradicts Special Relativity too.

https://arxiv.org/abs/physics/0609235

The first paragraph of the wikipedia article on the Sagnac effect has the word relative in it, soo, must be relativity or something. Besides, it sounds cool! >_<

Quote from Wikipedia:

> Georges Sagnac set up this experiment to prove the existence of the aether that Einstein's theory of special relativity had discarded

Yes, world "relativity" is present here.

How do optical gyroscopes compare to the Hubble gyroscopes that have been in the news recently?

Not exactly the same thing. The Hubble gyroscopes are largeish flywheels that are on gimbaling platforms. They spin and maintain a constant orientation just like your toy gyroscope. By changing the platform's angle to the satellite with motors the whole satellite can be orientated since it's floating in space. The gyroscopes they're talking about here are used for sensing. There's several types but the simplest conceptually work in the opposite manner. The platform moves and the gyro stays fixed, a resolving device is used to sense the angle. Ring laser gyros (what they're describing here) and other mems gyros work differently still. But basically the idea is that something doesn't move when everything else does.

Could these be used in spacecraft? With no moving parts would they be more reliable?

I believe you are thinking about reaction wheels. Hubble has 4 of those but it also has 6 gyroscope sensors, which is what was in the news recently.

I just don't know how the specs and intended use cases of those Hubble gyros compare to these optical gyros, hence my question.

Honestly I was thinking about the reaction wheels when I wrote my comment because I only skimmed the Hubble articles and didn't realize they were talking about the attitude sensing gyroscopes having to be reset.

How small can we make a gyroscope and still have it respond to gravity? Maybe a few molecules? Could this be a path to unify Quantum Mechanics and General Relativity - through experimentation, since theory seems to have failed?

The gyroscope responds to rotation and not gravity. It requires a ring (or two) for the light to circulate in so I don't think they will be molecular sized for reasonable wavelengths of light.

You're right, I believe I'm thinking of accelerometers.

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