Quadrature demodulation with synchronous difference for interferometric fiber-optic gyroscopes

Abstract

We propose a novel method of quadrature demodulation with synchronous difference for suppressing noise in interferometric fiber-optic gyroscopes (IFOGs). For an IFOG with sine wave phase modulation, an in-phase result and a quadrature result are obtained simultaneously by coherent detection. Eigenfrequency modulation is used and a phase shift of 45° is set between the modulation signal and the reference signal, so that two results have the same expectation of amplitude but with opposite signs. A synchronous difference procedure is carried out for output, in which signals are added up and common noise between two results is eliminated. Theoretical analysis and experimental results show that both short term noise and long term instability of the IFOG are reduced by this method. In experimental comparison with the traditional demodulation method on the same IFOG with a 1982 m fiber coil, this method reduces the bias drift from 0.040°/h to 0.004°/h.

Signal subspace analysis for decoherent processes during interferometric fiber-optic gyroscopes using synchronous adaptive filters

“…We could extract the Sagnac phase through the correlation calculation with orthogonal local signals (LOs). We chose sinnωt and cosnωt as LOs, based on the balance quadrature demodulation [9], it is easy to get the correlation results as…”

“…2, where the two orthogonal channels Ω I m and Ω Q m are the input signal xm. And the measurement value Ω T t derived from the conventional demodulation method [9] is input as the desired signal dm. Based on the gradient descent approach, the update equation of filter coefficient wm is …”

“…Numerous optimization methods have been deployed, such as the light source control in gyrolevel and Kalman filters in system level [6,7]. These methods, however, are processed after having obtained the total rotation velocity value Ω T , which is derived from the orthogonal I Q channels, and thus are short of coherent analysis for decorrelation processes in the coupling noise inhibitions [8,9].…”

“…First, through balance quadrature by local oscillators, we obtained two synchronous orthogonal channels that contained the same rotation information of IFOGs [9]. Hereafter, we made an alignment of these two quadrature channels with two adaptive filters obtaining two independent pairs of signal channels, one are the error signals for the instantaneous response to the measured object, the other are the filter response signals for the long-term steadystate prediction [7,10].…”

Mode-assisted Silicon Integrated Interferometric Optical Gyroscope

“…The phase modulator (PM), which is used to adjust the optimal sensitive operation bias of the gyroscope, is an indispensable part for conventional interferometric rotation sensing. The circulator, which is used to separate the input and output beams 12 , is difficult to fabricate in the integrated scheme actually. Hence, the circulator was normally replaced by a 3 dB coupler, which led to extra loss and reflection light to light source, in the integrated scheme 13 .…”