Modified Sagnac experiment for measuring travel-time difference between   counter-propagating light beams in a uniformly moving fiber
  A fiber optic conveyor has been developed for investigating the travel-time difference between two counter-propagating light beams in uniformly moving fiber. Our finding is that there is a travel-time difference Deltat=2vDeltal/c^2 in a fiber segment of length Deltal moving with the source and detector at a speed v, whether the segment is moving uniformly or circularly. 
Ruyong Wang, Yi Zheng, Aiping Yao and Dean Langley