Abstract: A phase-modulated fiber optic gyroscope comprises a signal generating a signal generating section, a photoelectric converter section and a signal processing section. The signal generating section includes a light source, an optical path for propagating light from the light source clockwise and counterclockwise, and a phase modulator for modulating the light propagating through the optical path. The photoelectric converter section converts an optical signal received from the signal generating section into an electric signal. The signal processing section derives a direction of rotation and a velocity of rotation from the electric signal received from the photoelectric converter section. The signal processing section includes an analog-to-digital converter for converting the electric signal received from the photoelectric converter section into a digital signal, and a digital signal processor for carrying out angle calculations based on the digital signal received from the analog-to-digital converter.