Zuchen Zhang

In recent years, the rapid development of integrated optics provides a novel approach to realize miniaturized and lightweight fiber optic gyroscope (FOG). This paper proposes a TE-pass polarizer based on the silicon nitride on insulator (SNOI) platform operating at 850nm, whose insertion loss is lower than 1.02dB with the polarization extinction ratio (PER) larger than 47dB. The proposed polarizer could directly edge-couple to the thin film lithium niobate (TFLN) modulator with a negligible loss (<0.19dB) to form a combined hybrid modulator, which integrates the function of modulating, splitting, and polarizing. Compared with the traditional bulk lithium niobate modulator, the utilization of the hybrid modulator in FOGs could increase the optical power entering the fiber coil by 68% at 850nm, which greatly facilitates the improvement of FOG precision. Furthermore, the undesired residual intensity modulation effect in the bulk lithium niobate modulator is also theoretically avoided by employing the hybrid modulator.

Improving the coupling efficiency of the optical transceiver module in fiber optic gyroscopes (FOGs) benefits both the working efficiency of the module and the signal-to-noise ratio of the FOG system. In this work, a single-mode fiber (SMF) with an elliptical mode field distribution is proposed as the coupling fiber for the FOG transceiver module. The coupling efficiency of the transceiver module using fibers with different mode field distributions at the endface is analyzed. Two structure schemes of the transceiver module are compared: one focuses the beam directly onto the endface of the fiber, and the other collimates the beam and then converge it. The optimal coupling efficiency can reach above 91.5% when the horizontal and vertical mode field radii of the fiber endface are approximately 4.05 μm and 3.37 μm respectively. The influence of the axial and angular alignment errors of the pigtail on the coupling efficiency is also investigated. The maximum tolerance of the axial alignment reaches approximately ±40.10 μm and ±30.08 μm for the two structure schemes. The maximum tolerance of the angular alignment reaches approximately ±4.4° and ±5.2° in the horizontal direction, and approximately ±3.5° and ±3.6° in the vertical direction, respectively. These tolerances are favorable for practical applications.

Chip-scale interferometric fiber optic gyroscope (IFOG) has caught growing attention for its huge application potential in the low-cost consumer electronics market. In this paper, a novel three-axis IFOG is proposed and assembled with an integrated coupler chip (ICC) fabricated on the silica platform. The ICC realizes bidirectionally multichannel optical interconnection without waveguide crossings. The test results indicate the weak wavelength dependence and comparatively low insertion loss at 0.85μm of the ICC. With ~900m polarization-maintaining fiber coils, the three-axis IFOG exhibits a long-term stability of <0.16 °/h, which satisfies the requirements of the tactical grade systems. The novel IFOG scheme with ICC paves the way for the research on chip-scale multi-axis IFOGs.

As one of the most successful applications in optical fiber sensing, interferometric fiber optic gyroscope (IFOG) has become the ideal choice for inertial navigation systems, and has been widely used in the fields of aviation, aerospace, navigation, and land. Exploring the theoretical noise limit and improving the practical precision are the objectives of FOG investigations, and the advanced photonic crystal fibers offer powerful approaches and potential to achieve these goals. In this review, the progress of photonic crystal fibers in FOGs research and applications for angular velocity measurement have been reviewed, together with the advanced technologies for improving the FOG's precision and reducing its volume.

Radiation-induced magneto-optic fluctuations (RI-MOF) is a kind of environmental compounding effect of fiber optic gyroscope (FOG) in space application. Here, we suggested a model of RI-MOF and experimentally tested it in irradiated polarization-maintaining fibers (PMFs) and polarization-maintaining photonic crystal fibers (PM-PCFs). The test results reveal that the main sources of RI-MOF are the radiation-induced change of the Verdet constant and the modal birefringence. In a spacecraft with good thermal control conditions, an evaluation method based on the RI-MOF model can be summarized and implemented to suppress the environmental disturbance on the performance of FOG.

A temperature correlation effect of transverse magneto-optic error (TMOE) in miniaturized fiber optic gyroscopes (FOGs) is proposed. The theoretical model based on mode perturbation and temperature correlation terms is established. The temperature dependence of the Verdet constant is measured by the thermo-controlled Verdet constant measurement system based on the phase-sensitive detection, and the temperature dependence of the refractive index is analyzed by the multiphysics finite element method. The experiment based on the miniaturized FOG prototype with two kinds of fibers is carried out. Experimental result shows that the average temperature correlation coefficients of TMOE with polarization-maintaining fibers and photonic-crystal fibers are $5.335\times 10^{-4}$ and $2.377\times 10^{-4}\,\,^{\circ }$ /h/Gs/°C, which are in good agreement with the analysis results.

The residual intensity modulation (RIM) of the multifunction integrated optic circuit (MIOC) can be classified into the linear term and the nonlinear term, which can impact the performance of the fiber-optic gyroscope (FOG). According to the generation mechanism of the RIM and the demodulation principle of the FOG, a model is established to analyze the influence of RIM on the FOG performance. Simulation shows that both the linear and the nonlinear RIM can lead to a large and sudden change in the FOG output at reset points of the feedback step wave, as well as fluctuations within the reset period. The magnitude of the sudden change at the reset point is proportional to the difference between the linear RIMs of two branches in the MIOC, and the fluctuation within the period of the feedback step wave is more dependent on the nonlinear RIM. The relationship between the FOG output and the linear and nonlinear RIMs are verified by experiments. The RIM-induced output can result in the increase of the bias error and the scale factor error of the FOG, especially at small input angular velocity. Furthermore, the application of FOG for the real-time high-speed position tracking to stabilize the attitude control platform can be limited.

Micrometeoroid and orbital debris (MMOD) can cause serious impact damage to long-term on-orbit spacecraft. MMOD impact detection and location are essential to improve the safety and reliability of the on-orbit spacecraft. In this article, a combined artificial neural network (ANN) and Mahalanobis distance method for MMOD impact detection and location based on fiber Bragg grating (FBG) sensor network is proposed. The inputs of the proposed ANN are the Mahalanobis distances determined by the wavelength changes of the FBG sensors at impact points and reference points. A finite element model is developed to explore the relationship between the Mahalanobis distance and the actual distance, which proved to be nonlinear based on the finite element simulation results of MMOD impacts. Four FBG sensors were installed on the back of the test board and sampled at a frequency of 100 Hz using a four-channel FBG demodulator. A total of 360 impact experiments were carried out on this experiment system. The average location error of the proposed method is 0.89 cm, which is 39% and 31% lower compared with the Mahalanobis distance discriminant analysis method and the ANN method, respectively. The combined ANN and Mahalanobis distance method reduces the location errors and has higher accuracy of position prediction.

The modulation asymmetry of a multifunction integrated optic circuit (MIOC) indicates the difference in the phase response to modulation electric fields with the same magnitude but different directions, and is partly caused by the vertical component of the modulation signal. This introduces a nonlinear phase error that is difficult to compensate in fiber optic gyroscopes (FOGs), which needs to be suppressed. In this paper, a sinking-electrode MIOC design to suppress the modulation asymmetry is proposed and verified through numerical simulations. Optimal parameters of the gap, height, side-wall angle, and center position error of the sinking electrodes are obtained on the basis of the simulation results. With the proposed method, the modulation asymmetry of MIOC can be reduced from 5×10-4 rad to 1×10-6 rad, thus facilitating the development of high-performance FOGs. Furthermore, compared with the traditional electrode design, the sinking-electrode design can increase the tolerance for the manufacturing process, and the design configuration can be obtained through the general process method.