Abstract: An interferometer gyro employing a coiled optical fiber includes a pair of acousto-optic modulators to modulate first and second frequencies onto two components divided from the light of a light source. The light source need not exhibit the high degree of source coherence heretofore required, and can be an incandescent bulb in many applications. The first and second modulated light components are injected in opposite or counter-rotating directions into the optical fiber wherein they experience phase changes due to the apparent change in optical length of the optical fiber upon rotation of the fiber about an axis of sensitivity. The light components are then, after being removed from the fiber, combined and compared with the signals applied at the input. The phase difference therebetween is then established to measure the rate of rotation of the optical fiber about the axis of sensitivity.