Abstract: A fiber optic rotation rate sensor employs two fiber loop interferometers. Two Sagnac fiber optic interferometers are interleaved such that both fibers are contained in each each interferometer. A coherent light beam at one frequency is proprogated in only one of the fibers, and an opticl beam at another frequency is proprogated in the other fiber. The beam emerging from one of the fibers is combined with the beam emerging from the other of the fibers for each of the two ends of each fiber to produce a pair of interference signals each having a frequency equal to the difference between the two light beam frequencies. The relative phase of these two signals is then determined to provide an indication of the rate of angular rotation of the fiber optic loops, and this determination is independent of any temperature-related characteristics that produce offset phase errors.