Abstract: In a closed loop fiber optic gyroscope, the counter-propagating lightwaves are phase modulated by a triangular wave modulation with the triangular wave skewed to lock the phase difference between the counter-propagating waves alternately to specific values of phase difference which are greater than and less than the phase difference due to rotation. The difference in elapsed time between the up-slope and down-slope portions of the triangular wave modulation yields a measure of rotation angle, whereas such difference in elapsed time divided by total elapsed time yields a measure of rotation rate. The phase difference is further modulated about the locked values at a higher frequency, such higher frequency phase difference modulation being synchronously detected to produce a rotation rate signal component employed to generate the skewed triangular wave. Various other features are employed to light polarization errors.