In a Ring Laser Gyro (RLG), because of coupling of the clockwise and counterclockwise rotating beams of light, at low input rotation rate, the frequencies of the two lock together causing the lock-in phenomenon. Both theory and experiments-have explained this lock-in phenomenon as due to mirror backscattering. Mirror backscattering comes mainly from mirror surface and coating imperfections. In RLG application, lock-in, characterized by SQL, the rotation rate below which the gyro output is locked, affects performance in several ways. First of all, it creates a dead band where the gyro does not operate, secondly, it affects scale factor linearity and stability; and thirdly, in a mechanically dithered RLG, it contributes directly to the increase in angular random walk noise in gyro output. The understanding and reduction of SQL is therefore very important in RLG technology.
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