Those papers are interesting. I think it may well be a more general form of the Sagnac effect.
However it doesn't appear to contradict the equation proportional to enclosed area. The Fiber Optic Conveyor (FOC) is not rotating as a whole, so the traditional Sagnac equation cannot be applied. They have found a new equation to describe this new type of motion.
There is a very simple way to analyse the FOC, FOG and China-Japan. It is this:
Note the location where the signal was transmitted from. Note the location it was received at. Use simple geometry to calculate the path length l. Assume constant light speed. Calculate travel time as t=l/c.
If you do this for a traditional circular loop, you find the transmission occured at a _different location_ to the reception, so l <> circumference.
If you do this for Wang's FOC, you also find that the light was transmitted at a _different location_ to where it was received. So again the path length l <> 50m length of fiber.
If you do this for a signal from Japan to China and back. You find the transmission and reception occured at the _same location_. So l = 2*distance between China and Japan.
Do you see this fundamental difference between FOC/FOG and China-Japan?
Notice that Wang has not shown that his results are in any way affected by the overall linear speed of the system, which you are suggesting. This is clearly stated by Wang/etc in the 2nd paper:
"Just as a FOG detects the rotational motion of an
object, a FOLMS can detect the relative linear motion
between two objects"
They did not suggest it could be used to measure linear velocity relative to the Sun!!
