Fibre optic gyroscope
Encyclopedia : F : FI : FIB : Fibre optic gyroscope
-->A fibre optic gyroscope (FOG) contains a coil with a long (up to 5 km) wound optical fiber (3). Two light beams travel along the fiber in opposite directions. An optical system with a beam splitter (2) directs the beams on a photodetector (4).
When the attitude rate is zero, the phase shift between the two beams is 180°; they cancel each other and the output photocurrent is minimized.
FOGs provide extremely precise rotational rate information, in part because of their lack of cross-axis sensitivity to vibration, acceleration, and shock,and are designed both on open-loop and closed-loop technology. The FOG typically shows a higher resolution than a ring laser gyro but also a higher drift and worse scale factor performance. It is used in surveying, stabilization and inertial navigation tasks.
With the attitude rate oriented along the fiber (around the coil's axis), the original phase shift is changed. This change occurs because of the increase in the light path for one beam and decrease in the path for another beam. As a result, the photodetector's current responds to the increased illumination and becomes larger.
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