When the ring laser is hardly rotating, the frequencies of the counter-propagating laser modes become almost identical. RLGs, while more accurate than mechanical gyroscopes, suffer from an effect known as "lock-in" at very slow rotation rates. Therefore, the net shift of that interference pattern follows the rotation of the unit in the plane of the ring. This introduces a tiny separation between the frequencies of the counter-propagating beams, a motion of the standing wave pattern within the ring, and thus a beat pattern when those two beams are interfered outside the ring. Principle of operation Ī certain rate of rotation induces a small difference between the time it takes light to traverse the ring in the two directions according to the Sagnac effect. Where ultra accuracy is needed however, spin gyro based INSs are still in use today. These hybrid INS/GPS units have replaced their mechanical counterparts in most applications. Unlike a mechanical gyroscope, the device does not resist changes to its orientation.Ĭontemporary applications of the Ring Laser Gyroscope (RLG) include an embedded GPS capability to further enhance accuracy of RLG Inertial Navigation Systems (INS)s on military aircraft, commercial airliners, ships and spacecraft. Additionally, the entire unit is compact, lightweight and highly durable, making it suitable for use in mobile systems such as aircraft, missiles, and satellites. This means there is no friction, which in turn eliminates a significant source of drift.
The advantage of using an RLG is that there are no moving parts (apart from the dither motor assembly, see further description below and laser-lock), compared to the conventional spinning gyroscope. Ring laser gyroscopes can be used as the stable elements (for one degree of freedom each) in an inertial reference system. At the beam sampling location, a fraction of each of the counterpropagating beams exits the laser cavity.
Schematic representation of a ring laser setup.