It is generally accepted that the fringe shift produced in a fiber optic Sagnac interferometer is independent of the refractive index of the fiber. In fact, the waveguide aspect of the fiber is not of any consequence, the counter propagating beams may propagate in any dielectric medium. Does anybody know a physical explanation for this effect, other than the special relativistic (M von Laue: On the Experiment of F. Harress) or general relativistic (Post, E.J: Sagnac Effect) explanations? It has been reported that(Wang, R: Modified Sagnac experiment for measuring travel-time difference between counter-propagating light beams in a uniformly moving fiber) the Sagnac effect is produced even when the moving path is effectively a straight line. This later configuration approximates an inertial frame, and with in an inertial frame one should not be able to measure one's state of motion!
Just wanted to share you with some observations from an amateur's viewpoint.
My understanding about the LAW of conservation of angular momentum is ... it manifests itself that "ROTATION" is an "ABSOLUTE" motion (e.g. the spinning of any fermions) with respect to anyone on the inertial reference frames.
The fringe differences in FOG (Fiber Optic Gyro or Sagnac Interferometer) is indeed dependent of the refractive index of the fiber. A larger refractive index will cause the larger fringe phase shift. While having normalized light speed and wavelength in accordance the refractive index of the media, we shall still get the same and a designated angular (rotation) speed of that particular "encircled" system.
Sagnac effect is produced even when "PART" of the moving path is effectively a straight line along with a "encircled" system. Once considering a "encircled" system, such a "Partial-linear" ROG configuration CANNOT approximate with any inertial frames.
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