Fiber optic earth rotation gyro compass

摘要

A fiber-optic rotation sensor particularly adapted to be placed adjacent a drill head to measure the orientation of a drill string with respect to the axis of rotation of the earth during or after drilling for minerals such as oil and gas. The analog sensor is based on a Sagnac interferometer and uses light beams counterrotating in one or more oblong circular shaped coils of optical fiber in which dual phase modulators are used to generate an AC signal to enable detection of a rotation rate output. The sensor also includes means to mechanically or electrically flip the sensitive axis of the rotation sensor to null out bias drift. If one coil is used, the flipping is in 90 DEG segments. When two coils at 90 DEG to each other are used, they are flipped 180 DEG .