ABSTRACT
A bias control approach is an automatic lock working point algorithm based on variational mode decomposition (VMD) and lock-in amplification (LIA) demodulation for a lithium niobate polarization controller (LNPC). Commonly, the dither voltage applied to the LNPC is much smaller than the bias voltage to avoid the influence of the dither signal on the output light, which reduces the polarization control accuracy of the LNPC. In this paper, we use VMD and LIA, with which the polarization control accuracy of LNPC can be improved, to extract and amplify the dither signal to compensate the drift half-wave of LNPC. The light intensity fluctuations of the output polarized light in vertical or horizontal directions are less than 0.017%.
ABSTRACT
The multifunction integrated optical chip (MIOC) is one of the most critical parts of the interferometric fiber optic gyroscope (IFOG), and research on the halfwave voltage of the MIOC is meaningful for a high-precision IFOG. In this paper, the correlation between the frequency and halfwave voltage, which affects the interference light intensity of IFOG, is presented theoretically. A widespread measurement method for frequency dependence of the halfwave voltage, based on lock-in amplification and sinusoidal modulation, is proposed. Further, the measurement result and the oscillation of interference light intensity in the Sagnac interferometer are presented, which are in great agreement with the theory. This paper proposes the frequency dependence of the halfwave voltage and provides a new error research direction for the improvement of the MIOC in a high-precision IFOG.
ABSTRACT
A wide dynamic range, high precision, non-contact and large bandwidth angular displacement measurement (ADM) is greatly necessary for the applications such as industrial control and military equipment. This paper proposes a simple and effective ADM method based on Doppler Effect, heterodyne detection and diffuse reflection, which can fulfill these requirements simultaneously. Two beams of parallel light generated by a pair of laser Doppler vibrometers are incident upon the surface of rotational target, then data processing unit acquires the velocity of dual laser incident points on the moving target, and resolves the rotational angular displacement and translation displacement of target through the relationship between dual laser beams dynamically. Several major measurement errors that may affect the ADM accuracy are analyzed. A high precision rotary table is used as an angular displacement standard to verify the measurement range and accuracy, the verification experiment shows that the measurement range is not less than ±10° and the measurement accuracy is 0.0362° based on the method. After using a polynomial error compensation, the measurement accuracy can be promoted to 0.0088°, and this compensation method can be applied to real time measurement.
ABSTRACT
Based on the theory of the radial magnetic error (RME) in depolarized interference fiber optic gyroscopes (D-IFOGs) under magnetic field, a new optical method is proposed to decrease the RME by adding a suppressing section fiber (SSF) in D-IFOGs. A related theoretical model is established, and the solutions of the parameters of the SSF are obtained with numerical calculations. Then the results of the suppressed RME are simulated. An experimental system is set up to verify the theory and simulation, and the experimental results prove that the RME can be suppressed effectively with a SSF added in the D-IFOG. The magnitude of the RME can be reduced to one-tenth of the original.
ABSTRACT
A theory for nonreciprocal phase shift caused by cross coupling generated in a polarization maintaining (PM) fiber optic gyroscope (FOG) under the combined action of magnetic and temperature fields is proposed. The magnetic-thermal coupling in the FOG originates from the interaction of the magnetic field, fiber twist, birefringence caused by thermal stress, and the intrinsic and bending birefringence of the fiber. The cross coupling changes with temperature. When the PM fiber has a diameter of 250 µm, beat length of 3 mm, length of 500 m, twist rate of 1 rad/m, and optical source wavelength of 1310 nm, the maximum degree of magnetic-thermal coupling generated by a 1 mT radial magnetic field within the temperature range of -20°C to 60°C is -5.47%.
