Correction of backscatter-induced systematic errors in ring laser gyroscopes

In ring laser gyroscopes, backscatter coupling between the counterpropagating beams leads to systematic errors in measured rotation rates. We show the errors can be derived from the nearly independent optical frequency perturbations of the separate beams. In a process of double backscatter each beam is scattered first into the other beam direction, then rescattered back into itself, giving phase and amplitude perturbations. The analysis proceeds from a purely passive ring cavity, through inclusion of a gain medium and gain saturation. The rotation rate errors may be estimated and corrected from the modulations of the counterpropagating beams. The method is demonstrated with real data.