The laser is an important component of the resonator fiber-optic gyroscope (RFOG) and the optical noise of the laser severely limits the performance of the RFOG system. The mathematical model which presents the effect of the intensity noise on the RFOG is established. In order to verify the correctness of the model, an acousto-optic modulator is innovatively used to generate the intensity noise of the laser, through which the intensity noise could be quantitatively changed without introducing unexpected noises of the laser. The experimental results indicate the intensity noise results in the deterioration of the scale factor nonlinearity and the increase of detected rotation rate error. In addition, a scheme based on the second harmonic demodulation of the intensity-modulated signal is proposed to compensate the light intensity fluctuation of the laser in the RFOG. The test results show the drift of the gyro introduced by the light intensity fluctuation could be reduced >8 dB through this method.
Hollow-core photonic crystal fiber (HCPCF) resonator optic gyroscope is an important direction of high accuracy fiber optic gyroscope. The development and application of HCPCF has provided broad prospect for the research of resonator fiber optic gyroscope (RFOG). The HCPCF can restrict light to propagate in the fiber core filled with air/vacuum based on photonic band-gap effect. Compared with conventional polarization maintaining fiber based RFOG (PM-RFOG), the HCPCF based RFOG (HC-RFOG) has great potential to achieve lower nonreciprocal bias and better environment adaptability. The polarization noise, which is one of the main noise sources in the RFOG, is modeled and simulated in this paper. The resonance curves of RFOG with two polarization modes excited are presented, and the polarization noises caused by fiber parameters are calculated. The comparison of polarization noises between HCPCF resonator and polarization maintaining optical fiber (PMF) resonator are carried out by numerical simulation. The polarization features of the HCPCF resonator and conventional PMF resonator are experimentally characterized. The analysis result shows that the polarization stability of HCPCF resonator can be two orders of magnitude lower than that of the conventional PMF resonator. Therefore, the HCPCF resonator has evidently superiority in reducing polarization noise and improving gyro performance. The captive tests based on the HCPCF RFOG system are realized, and a bias stability in the range of 2.5°/s is successfully demonstrated.
A feasible program of single-polarization active resonator using hollow-core photonic crystal fiber is proposed in this paper. The basic structure of HCPCF active resonator is designed, and the influence of polarization mode dispersion on the detection accuracy is analyzed with a solution being put forward using single-polarization HCPCF. Then the cross structure of photonic crystal fiber is designed, modeled and simulated by finite element method (FEM) at the wavelength of 632.8nm, and the mode field distribution in the cross-section is obtained. By designing the core size of photonic crystal fiber properly, a polarization extinction ratio of 8.4dB is achieved; therefore single-polarization propagation can be realized in the HCPCF, resulting in suppression of polarization mode dispersion of resonator and improving the theoretical gyroscope detection limit. This research is of great guiding significance to the development of HCPCF RLG.
The drift of birefringence difference can be caused by the ambient temperature variety of the fiber, which will lead to the change of lightwave polarization mode in the fiber. In the resonator fiber optic gyro systems, the change of lightwave polarization mode of the light transmission in the fiber can bring about the measurement error of the system. The hollowcore photonic crystal fiber (HCPCF) resonator is designed to reduce the drift of birefringence difference caused by the temperature variety. It is verified experimentally that the temperature coefficient of the HCPCF birefringence difference is decreased about two orders of magnitude which is lower than that of the normal polarization maintaining fiber (PMF).