An RLG uses two laser beams housed in an optical cavity with a set of highly reflective mirrors. One laser beam travels clockwise around the optical cavity while the other moves counter-clockwise. When the gyroscope is rotated, a small difference in the circulation time for each beam occurs because one beam travels less distance than the other. This difference is used to compute the rate of angular rotation. RLGs are commonly used in commercial and military aviation, land applications, satellites, space launch vehicles and high performance tactical missiles.
FOGs employ optical fiber wound on a spool.
Each FOG has a light source and control electronics to provide two beams of light, one traveling clockwise and the other counter-clockwise, through the wound coil. A detector on the coil output senses phase shifts between the two light beams and converts the phase shift into an angular rate of rotation. FOGs were developed after RLGs and are beginning to be utilized in commercial and military aviation, land applications, satellites, space launch vehicles and high performance tactical missiles. MEMS is a developing technology which produces IMUs using silicon wafers made from semiconductor manufacturing processes and sophisticated micro-machining. MEMS IMUs may permit manufacturers to achieve significant size, cost and weight reductions in the product.