Abstract: An optic rotation sensing apparatus includes a light source emitting light. The light emitted from the light source is transmitted to a sensing loop which provides a phase difference between opposite-direction light waves in response to a rotation. Return light outputted from the sensing loop is transmitted to a photodetector. A device modulates a phase of light propagating in the sensing loop. Another device depolarizes light propagating in the sensing loop. The invention further controls and processes an output signal representing the output of the photodetector at a phase at which a level of an AM noise component of the output signal is minimized.

Abstract: A fiber-optic coil for use as the sensor loop of a fiber-optic gyroscope includes a first optical fiber segment wound as radially successive coiled layers around a coil bobbin in a first region thereof, and a second optical fiber segment wound as radially successive coiled layers around the coil bobbin in an axially adjacent second region thereof. The first and second optical fiber segments are joined to each other through a longitudinal middle portion, which is positioned in the radially innermost coiled layers of the first and second optical fiber segments adjacent to a longitudinal center of said coil bobbin. Each of the first and second optical fiber segments is wound in alternate axial directions in the radially successive coiled layers. The first and second optical fiber segments may be integrally joined to each other by the longitudinal middle portion, or may be separate from, but joined to, each other by a depolarizer across the longitudinal middle portion.