Neil Gould schrieb:

I said I *don't understand* that aspect of the design

Don't feel bad about it: Understanding a Fiber Optic Gyroscope is pretty
involved.

As an (incorrect!) starting point, you could think like this: You send a
light flash in both directions through the ring. The light needs some
time to travel through the fiber. If you turn, you will have changed
your position until you receive the light again, so that the light in
one direction has to travel more than 360 degrees, while in the other
direction the path is shorter than 360 degrees. Tiny as the difference
is, you can measure that.

As I said, this approach is *not* correct, but it may help you to
understand how such a thing *might* work. However, you can not
understand the Fiber Optic Gyroscope without understanding the theory of
relativity. So a reasonable approach for a non-physisict is to just
believe that it works.

Stefan