
The World's Tiniest Optical Gyroscope Is Now Smaller Than a Grain of Rice - NicoJuicy
https://interestingengineering.com/the-worlds-tiniest-optical-gyroscope-is-now-smaller-than-a-grain-of-rice
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kurthr
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...](https://authors.library.caltech.edu/88626/3/41566_2018_266_MOESM1_ESM.pdf)

[http://resolver.caltech.edu/CaltechAUTHORS:20180807-12540532...](http://resolver.caltech.edu/CaltechAUTHORS:20180807-125405326).
- permalink

Or the entire article ois available from Springer:

[https://www.nature.com/articles/s41566-018-0266-5](https://www.nature.com/articles/s41566-018-0266-5)

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

It's not true at all.

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holstvoogd
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!
>_<

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v_lisivka
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.

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

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racnid
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.

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wcoenen
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.

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racnid
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.

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stephengillie
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?

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kurthr
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.

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

