Fig. 9: The basic principle of fiber optic gyroscopes.
From: Low-coherence semiconductor light sources: devices and applications
a Schematic of the Sagnac effect. b Schematic of the fiber optic gyroscope (FOG). Light emitted from a broadband light source passes through the fiber optic coupler 1 and enters the polarizer. The linearly polarized light propagates along the polarization-maintaining fiber, and then through the fiber optic coupler 2, forming two beams of light propagation along the clockwise and counterclockwise directions. These two optical signals interfere with each other when they return to fiber coupler 2, and this interference signal is then detected by the photodetector (PD) through coupler 1.
