| The fiber optical gyroscope (FOG) is one of the most important achievements in fiber optic sensor field, through the continuous development of the last years, it has been to establish a "preferred" status in the field of inertial technology. So far, The FOG mainly through three generations which were the interferometer (IFOG), resonant (RFOG) and Brillouin type (BFOG).Among them, the IFOG technology has been matures and successfully applied to various fields, but the temperature and the miniaturization were the obstacle to the development of high accuracy. As the third generation FOG-BFOG, due to the simple structure, simple signal processing, high sensitivity, large dynamic range, small size and other advantages, it was on behalf of the development of high precision and miniaturization. In recent years, with the development of optical communication and related technologies, the appearance of narrowband pump source, specialty optical fiber, new high coupler devices bring a new development opportunity to BFOG, and it is of great significance to study this new FOG. In this research paper, it mainly focuses on several key technologies in the implementation process for BFOG. The main thesis works are as follows:Firstly, the work principle and sensitivity analysis was studied. Optical fiber stimulated Brillouin scattering effect is the physical basis of BFOG, the fiber Brillouin scattering and Brillouin scattering threshold with fiber length and fiber loss were analyzed, the relationship between stimulated Brillouin gain spectrum and pump wave type was studied, the beat frequency formula in theory and considering actual case of BFOG were derived, the potential accuracy and dynamic range of BFOG has been theoretical analyzed and calculated.Then, the output stability of Brillouin fiber ring laser light was studied. The Brillouin fiber ring laser is the core of BFOG and the gyro performance was directly affected by the laser frequency stability. Brillouin fiber ring laser cavity is an active cavity, the stability of laser in resonant cavity was the basis of light intensity analysis. The best conditions for resonance was derived, and it was obtained that the light intensity in resonator cavity was maximum and the emitted light intensity is zero when the resonator cavity is critical coupling state, and then the fineness is the highest. The relationship between the pump light intensity and stokes light intensity was analyzed in Brillouin fiber ring laser, and obtained that the incident pump light intensity should be controlled between the first-order and the second-order threshold intensity. The two major factors were polarization and temperature which affect the output stability of Brillouin fiber ring laser were studied in detail. The relationship between the pump light and stokes light polarization and the Brillouin gain coefficient was theoretical analyzed, the two eigenstates polarization of pump light and Brillouin laser light were resonance in Brillouin resonant cavity at the same time, and the phase difference between the two eigenstates polarization fluctuated due to temperature and other environmental change which resulting in polarization crosstalk. The polarization axis90°rotation and single-polarization single-mode fiber ring resonator to build fiber ring cavity to eliminate the polarization fluctuation were analyzed and verified by experimentally. The temperature on the Brillouin frequency shift, threshold optical power, gain coefficient, the laser mode hopping and optical path length were analyzed and calculated. It can be obtained by calculating that the Brillouin frequency shift by temperature was about1.2MHz/℃, the fiber ring cavity parameters was the mainly factors which affect Brillouin threshold optical power, and the Brillouin threshold optical power temperature coefficient is about-961×10-6/℃, The change of optical path length caused by temperature change will result in scale factor error and gyro bias instability.Thirdly, the mainly optical noise errors in BFOG were studied, the mainly optical noise in BFOG including Rayleigh backscattering, magnetic field Faraday Effect and optical Kerr effect. The backscattering mechanism of pump light and Brillouin laser were studied, the results show that the backscatter light intensity in the fiber ring cavity was resonant enhanced and is about1%of the main light intensity. The backscattering light from pump light will increase the fiber ring loss, and result in the stimulated Brillouin laser threshold increasing. The backscattering light from Brillouin laser light was coupled with the opposite transmitted laser light, and resulting in locking phenomenon. The Faraday Effect in BFOG was analyzed, and the gyro error model was established; and obtained that the error caused by Faraday Effect exists in BFOG was due to the presence of circular birefringence in fiber. There were two ways to reduce the Faraday effect error, one is to use high birefringence fiber, the other is to reduce the twist rate in fiber, the use of polarization maintaining fiber with high birefringence suppress Faraday effect error was theoretical analyzed. The optical Kerr effect error model which considering the light power difference and polarization factors was established, the causes of Kerr effect error in gyroscope was analyzed in detail, then the pump light intensity modulated to eliminate optical Kerr effect was proposed and designed.Finally, the influence of pump light detuning on BFOG was discussed, the pump light frequency stabilization scheme in BFOG was proposed. The expression of the maximum detuning which limited the dynamic range were derived and calculated. Due to the single frequency stabilization can’t solve the influence of pump light detuning on BFOG absolutely, then the dual light path frequency stabilization was proposed and designed. The triangle wave phase modulation was used to achieve square wave frequency modulation in CCW direction of the pump light, and the beat frequency signal of rotation speed is equal to the frequency difference caused by the CW pump laser detuning. The overall system of BFOG was designed, the optical system was analyzed and the main optical devices were analyzed and selected, the signal detection and frequency stabilization circuit were designed, then the system was tested. |
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