The phase-generated carrier (PGC) algorithm is one of the most commonly employed demodulation schemes in optical fiber sensors. It exhibits high sensitivity in detecting weak signal and is less susceptible to fluctuations in light source intensity. However, the inevitable uneven frequency response of photoelectric detection will lead to distortion in the harmonic amplitudes, subsequently resulting in demodulation errors in the PGC scheme. This significantly jeopardizes the precision and accuracy of optical fiber sensors. This paper analyzes the demodulation errors in the PGC algorithm caused by non-uniform frequency response and proposes a correction method. In this method, only a correction factor is introduced in the final step of the PGC algorithm, without introducing additional complex computations. In comparison to conventional correction algorithms such as linear regression, function fitting, and neural networks, this method is simple, effective, and resource-friendly for DSP systems with limited resources. Experimental validation of this method is conducted using a fiber optic gyroscope prototype. The results demonstrate a remarkable reduction of 33-fold in demodulation error within the measurement range of -6 to +6 radian, reducing it from 610 parts per million (ppm) to a mere 18.3 ppm.
The measurement of rotational components in seismic waves holds significant importance in various fields, including seismic early warning, subsurface structure inversion, and the study of Earth's internal dynamic processes. The interferometric fiber optic gyroscope (IFOG) is a kind of sensor that measures the rotational velocity of an object based on the Sagnac effect. In this study, a synchronous four-state modulation scheme based on a light source sharing configuration is employed to suppress RIN. Moreover, this work extensively investigates the impact of shot noise and Johnson-Nyquist noise. By adjusting the modulation depths of the two minimum configurations, the influence of shot noise and Johnson-Nyquist noise is well-handled while achieving RIN suppression. Furthermore, this scheme avoids introducing any external feedback, thereby preventing a decrease in sensitivity caused by the dead zone issue. In a test on detecting the rotation rate of the Earth, a self-noise level of 55 nrad/s/Hz1/2 and an angular random walk of 1.5 × 10−4 deg/h1/2 are achieved with an enclosed area of only 25.5 m2. Compared to the minimum configuration using the conventional phase generated carrier algorithm, the scheme realizes a 20-fold reduction in self-noise and an 18- fold reduction in angular random walk.
We propose and implement a source-sharing configuration based on fiber-optic gyroscopes for differential-mode and common-mode measurements. By adopting suitable values of the modulation parameters, the effect of relative intensity noise and thermal phase noise can be suppressed. Experimental results show that this configuration can achieve a maximum of 5.78 times self-noise suppression. We also show that the deviation of the modulation frequency from the eigenfrequency or its harmonics leads to an increase of the self-noise level. A deviation of 400 Hz can lead to a degradation of the self-noise level by up to 2.38 times. Finally, we prove the ability of suppression the environmental disturbance through an observation with the effect of natural vibrations.
We propose a structure based on fiber-optic gyroscopes for gravity measurement in accordance with the tilt-coupling effect, where Sagnac effect can remove the coupling between translational and rotational motion in the tilt-coupling effect. A fiber-optic gyroscope with a sensitivity of 2 × 10−11 rad/s2/√ HZ in sub-millihertz frequencies is reported, which can be utilized to measure the rotational motion in gravity measurement. The application of dual-polarization configuration improves the adaptability of exploration environment.
Interferometric fiber optical gyroscopes (IFOGs) have become one of the widely used sensors of inertial technology and rotational seismology, owing to their high precision and stability. In recent years, the dual-polarization IFOG, which allows two orthogonal polarization to work simultaneously, has been proved to achieve better measurement performance than the conventional minimum configuration through mutual compensation. In this work, a prototype of dualpolarization fiber-optic gyroscope is designed and realized. Laboratory tests show the self-noise has reached 9 nrad/s/sqrt(Hz) over the frequency from 0.01 to 125 Hz and the angular random walk has achieved 2.6×10-5 deg/sqrt(hr). For an Open-loop IFOG, which does not need a confiscated feedback control system, it avoids the dead-zone of closedloop IFOG. However, limited by the measurement range, as a result of the periodic and nonlinear response of open-loop demodulation, the scale factor of open-loop IFOG varies around 100~1000 parts per million (ppm) conventionally, which hinders its detection accuracy. In this work, with new measurement extension and linearity compensation methods, the prototype achieves an outstanding precision with scale factor nonlinearity up to 5 ppm within ±10 deg/s, and shows the potential of dual-polarization IFOGs for rotational seismology.
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