The Sagnac interferometer consists of optical components which first split light into two beams and then route each of these beams in opposite directions around a common optical path. After propagating around the optical path, both beams are recombined on a detector or screen where the resulting interference pattern can be observed The construction of fiber optic interferometers i s similar to the construction of classic optical interferometers with open light flux. They are designed for measurements of phase shift caused by an interaction between external fields and optical fiber. The value of characteristic frequency fr depends on the disturbance position. Exactly, it depends on the difference ?D Between times of reaching the interference place by wave fronts of two counter running waves with distributed phase. We can see that if the sensing loop length is increased, the characteristic frequency is decreased.