In article hhNbg.22391$ZW3.1565@dukeread04,
"Jim Macklin" wrote:

They all depend on frequency phase shift, it is the
principle, not the medium that determines the function.

The ring in a ring laser gyro is an oscillating laser. The laser gain
medium is inside the ring. The ring itself is lasing independently in
the two opposite directions around the ring, so it's essentially two
lasers. The measured output signal is a *frequency* (the "beat
frequency" between these two lasers) and this beat frequency is (error
and "lock-up" effects aside) directly proportional to the rotation rate
of the gyro. The ring is a single loop ring: winding the ring around in
multiple loops would do no good -- would not increase the sensitivity or
scale factor of the device.

The ring in a fiber optical gyro has laser light traveling through it,
sent in from outside, but the ring is not itself a laser, and is not
lasing. The laser gain medium -- indeed the entire laser in the system
-- is outside the ring, and there is only one external laser in the
system which generates the light going in both directions around the
ring. The output signal is a (very small!!) phase shift (NOT a
frequency shift) between the optical phase delay in the two directions
around the ring, which is proportional to the rotation rate of the ring.
The ring is wound with many, many loops, and the sensitivity or scale
factor of the device goes up directly as the number of loops.

So, a lot of similar physics in the two devices, but they're still
distinctly different.