Stability improvement enabled by four-state modulation in dual-polarization fiber optic gyroscopes

A four-state modulation scheme is proposed to improve the stability performance of a dual-polarization fiber optic gyroscope (IFOG) operating under an open-loop configuration, overcoming the dead-zone issue that occurs in a closed-loop configuration and achieving a better signal-to-noise ratio (SNR) than conventional sinusoidal modulation. We prove theoretically and demonstrate experimentally that owing to the cross-coupling between the two orthogonal light polarizations co-existing in the dual-polarization IFOG, the rotation rate is not rigorously solvable under square-wave modulation. Instead, four-state modulation accurately extracts the rotation rate, even when the cross-coupling strength varies in time. An improved angular random walk (ARW) of 2.2x10(-4) degrees /root h and bias instability (BI) of 3.5x10(-4) degrees/h were achieved in detecting the rotation rate of the Earth, verifying the effectiveness of the proposed method.