The fiber optic gyro (FOG), which is currently one of the most widely used fiber optic sensors, has firmly occupied a considerable market share of inertial sensors and offers the benefits of high stability and easy integration. The resonant FOG, also known as the RFOG, is a sensor that identifies a rotation rate by employing the use of a fiber ring resonator. It possesses a higher application potential in terms of optical stability and system miniaturization because it is an FOG of the second generation. This review begins with an exploration of the RFOG principle and then moves on to concentrate on the two aspects of RFOG optical noises suppression and signal processing in order to examine the progression of RFOG in the most recent years. Several distinct types of RFOG schemes that have a high application potential are dissected individually; these are the types of schemes that are anticipated to become mainstream application schemes in the not-too-distant future. In the end, the prospect and research challenge of RFOG are presented to help researchers clarify research directions. This article presents an in-depth analysis of the current state of research regarding RFOG-related technologies and offers a forecast regarding the path that the inertial sensor will take in the foreseeable future.

In order to suppress Kerr-effect induced error in resonant fiber optic gyro (RFOG), a resonator based on spun fiber (SF) is proposed for the first time. The theory of the Kerr-effect induced error in gyro is analyzed first and the suppression method for this issue is explained, highlighting the advantages of circular state of polarization (CSOP) light and SF. Then the structure design and optimization of the resonator are completed to guide resonator fabrication and meet the better noise suppression requirement. Finally, the gyro experiment indicates that the resonator based on SF can suppress the Kerr-effect induced error by at least 96.6 % without a power compensation structure, which is of great significance for simplifying the system. In addition, the method proposed in this article first confirms the potential of CSOP light in optical noise and error suppression of RFOG.

Resonant fiber optic gyros (RFOGs) generally use fiber ring resonator propagating linearly polarized light, so it is inevitably affected by coherent optical noises between two counterpropagation beams such as nonlinear effect and backscattering noise. So, we propose the incoherent suppression method of optical noises in a RFOG based on the circularly state of polarization (CSOP) light. The spun-fiber is used to fabricate a resonator that can realize the reciprocal transmission of CSOP light for the first time, and the highly reciprocal signal processing scheme is applied in RFOG based on the Faraday effect. We demonstrate that the designed resonator realizes orthogonal separation of backscattered light thereby suppressing the backscattering noise, and we confirm that the reciprocal CSOP light can greatly reduce the nonlinear effect due to incoherence. With the closed-loop method based on the Faraday effect and spun-fiber resonator, whose finesse is 6.6 with a length of 11-meter spun-fiber and 6-meter single-polarization fiber, the long-term stability and short-term stability of a RFOG have been greatly improved. The incoherence method based on a reciprocal CSOP light propagation mechanism has great potential in the suppression of coherence optical noises in a RFOG, which provides a new, to the best of our knowledge, idea to solve the problem.

The practical application of integrated gyroscopes in engineering has not yet been fully realized due to the linear correlation between the Sagnac effect and dimensions. In recent demonstrations, gyroscopes operating near exceptional points (EPs) under parity-time (PT) symmetry have shown significant potential in enhancing their response to rotational rates. However, constructing higher-order EPs with refined physical properties poses a considerable challenge. Additionally, current methods for constructing higher-order EPs with robustness primarily rely on passive cavities, with almost no reports on constructing robust EPs using PT-symmetric systems that encompass both gain and loss. Here, we propose a robust design for a scalable fabrication of higher-order EP gyroscopes with PT-symmetric structure. We investigate the influence of perturbations on the frequency splitting of the higher-order EP gyroscope and demonstrate that it is possible to achieve a resonance splitting eight orders of magnitude higher than that obtained through the classical Sagnac effect. In comparison to the previously proposed PT-symmetric gyroscope, our solution allows a tunable frequency splitting by adjusting the phase shift, making it more measurable at the output power spectrum.

As an important inertial navigation sensor, resonant fiber optic gyro (RFOG) has become a research hotspot in recent years due to its advantages of light weight and high stability. The optical effects in the fiber ring resonator(FRR), such as scattering effects, polarization mode crosstalk, etc., are the bottleneck restricting the development of RFOG, and they are also the key problems that researchers are trying to solve. Aiming at the problem of polarization noise, this paper conducts in-depth theoretical and experimental research on polarization stability using spun fiber resonator for the first time. Compared with a common polarization-maintaining fiber (PMF) resonator of the same length, the results show that the RFOG using the spun fiber resonator has improved temperature stability compared to the conventional resonator structure. This research provides a new idea for the polarization noise suppression method of RFOG, and lays an important foundation for the practical application of spun fiber in RFOG.

High-precision mapping and positioning of urban underground pipelines are the basic requirements of urban digital construction. Aiming at the above problems, a dead reckoning algorithm based on the starting point and ending point correction and forward and reverse solution information reuse is proposed. This paper firstly establishes a dead reckoning system model consisting of a microelectromechanical system (MEMS) inertial measurement unit (IMU) and an odometer and analyzes the propagation mechanism of dead reckoning errors. The algorithm constructs the trajectory correction matrix by using the position information of the starting point and the ending point of the short-distance underground pipeline and then uses the trajectory correction matrix to correct the trajectory position information obtained by forward and reverse dead reckoning. Finally, the corrected forward and reverse trajectory position information is fused and averaged to achieve high-precision mapping and positioning of underground pipelines. The simulation results of the 100 m pipeline show that the maximum positioning error of the proposed algorithm for straight pipelines is within 5 cm, and the maximum positioning error for 90° curved pipelines is within 20 cm. The algorithm effectively solves the problem of a rapid accumulation of errors over time in the process of dead reckoning, which greatly improves the positioning accuracy.