【作者】 张勇；

【导师】 李绪友；

【作者基本信息】 哈尔滨工程大学 ， 精密仪器及机械， 2009， 博士

【摘要】 光纤陀螺是一种基于Sagnac效应的惯性角速度传感器,它在各种导航及制导系统中起着重要的作用。目前干涉型光纤陀螺已经发展成熟,但它在系统小型化等方面存在困难。与干涉型光纤陀螺相比,布里渊光纤陀螺(BFOG)采用的光纤长度要短很多,信号处理系统大大简化,在实现光纤陀螺高精度和小型化方面的优势明显。因此,开展BFOG的研究具有重要意义。布里渊光纤有源环形腔是BFOG的核心和主体,也是BFOG实现的难点,因此本课题主要针对布里渊光纤环形腔的若干关键问题进行了研究。论文的主要工作如下：首先对布里渊光纤环形腔的光强进行了深入研究。采取由浅入深的方法进行光路分析,在研究了无源腔的基本特性后再进行布里渊有源腔的研究。利用泰勒级数简化了腔特性的描述,并结合递归思想,推导出入射光强、腔内循环光强、各阶斯托克斯光强及出射光强之间的关系。结合BFOG的要求,得出入射光强必须控制在第一窗口,腔体必须处于过耦合态的结论。设计了自由谱线宽度为19.35MHz,精细度为70的环形腔,验证了关于泵浦阈值、斯托克斯光出射功率等方面的理论,并提出一种“过损耗熔接”的方法进行BFOG的腔体设计,测试表明这种腔体能够有效抑制腔内循环光强的流出,符合BFOG的要求。然后针对试验中遇到的谐振峰漂移以及谐振峰振动问题,研究了布里渊光纤环形腔的动态性能,并设计了稳频电路实现腔中的谐振稳定。分析指出光纤双折射产生的偏振波动是导致谐振峰漂移的根本原因,研究了它对于受激布里渊散射及腔内循环光强的影响,得出保持腔内偏振稳定的两种方法,并对其中偏振主轴旋转的方法进行了验证。理论上证明了正弦波调制下谐振峰振动现象的根本原因来自于PZT的调制速率过快,并据此研究了对陀螺输出的影响。分析了实际环境中腔长难以保持谐振稳定的原因,提出了基于PID控制原理的透射腔直流稳频方案,设计了基于FPGA的稳频电路,使得腔内谐振频率的稳定度控制在9.45Hz的范围内。之后开展了BFOG的光路建模及其它相关理论研究,完善了BFOG的理论体系。采取Jones矩阵光学的原理建立了BFOG的光传输模型,根据该模型研究了器件理想与非理想情况下的光路输出,结果表明光源的功率波动及偏振波动对于陀螺输出信号的检测灵敏度影响较大,焊点、耦合器及偏振器的参数对陀螺也有一定的影响。参照RLG频率读出系统,分析了布里渊光纤陀螺的拍频读出方法。探讨了光源及光纤环的选取依据,得出了光源峰值输出光功率应大于4mW,功率波动小于10μW,频率波动小于10KHz,光纤环最佳长度为10m的结论。针对BFOG动态范围和阈值光功率对于光纤环长度要求的矛盾,提出了光纤环“双向缠绕”法,在保证阈值光功率的前提下提高了陀螺的动态范围。最后开展了BFOG克尔效应方面的研究。克尔效应被公认为BFOG的主要误差源,因此这一部分的研究具有重要意义。通过对光纤中非线性光学克尔效应的基础分析,指出交叉相位调制是导致光纤中折射率差的主要原因。理论分析指出克尔效应可产生腔内光强的光学双稳态,实验在输入功率440μW时验证了这一现象,并且指出该双稳态可通过调节耦合器的参数进行抑制。分析得出BFOG克尔效应误差的主要原因来自于稳频过程中产生的谐振偏离,它不仅导致陀螺输出非线性,并且把陀螺的动态范围限制在±22°/s。据此提出双环BFOG工作方案,理论上避免了克尔效应对于陀螺输出的不利影响。对双环方案中存在的参数误差研究表明,该误差导致的陀螺总附加拍频小于10Hz,对陀螺零漂的影响优于0.015°/s,双环BFOG方案能够满足中等精度光纤陀螺的要求。更多还原

【Abstract】 Fiber optic gyro (FOG) is an inertial angular velocity sensor based on the Sagnac effect, which plays an important role in a variety of navigation and guidance system. At present, the interferential fiber-optic gyro (IFOG) has reached a mature state, but it faces some difficulties such as miniaturization. Compared with IFOG, Brillouin fiber optic gyro (BFOG) has great predominance in fiber length and signal processing system. Therefore, the research on BFOG is of great significance. Brillouin fiber ring resonator (BFRR) is the core and main part in BFOG, and it is also the linchpin to achieve BFOG. So a number of key issues in BFRR were studied in this dissertation, detailed as follows:First of all, the optical intensity in BFRR was studied in detail. The easy-to-digest method was taken on optical analysis, in order to analyze the basic characteristics of passive cavity before BFRR. And then the Taylor series was used to simplify the description of characteristics of cavity. Combined with recursive thinking, the relationship among incident light, circuiting light, different order Stokes light and transmitted light were derived. Considering BFOG requirements, the incident light should be controlled in the first window, and the cavity must be over-coupled. At last, the BFRR was designed, in which the FSR is 19.35MHz and the finesse is 70. In our experiments, theory of pump threshold and Stokes optical power was testified, and the over-tear welding method was utilized to design the cavity which suitable for BFOG.In the experiments, the resonance peaks shift and vibration was discovered, so the dynamic performance of BFRR were researched in the dissertation. First the impact of polarization fluctuations that arises from optical birefringence on stimulated Brillouin scattering and cavity effects were studied, and the technique of achieving a stable resonant cavity were analysed. Theoretic analysis showed that, the root causes of resonance peaks vibration came from too fast PZT modulation rate, and then its impact on gyroscope were studied. Analysis showed it is difficult to maintain stable cavity length in actual environment, so the DC frequency stabilization method based on PID control was derived, and FPGA-based frequency stabilization circuit was designed. Results showed that the resonant frequency stability was controlled under 9.45Hz. Then, the research of BFOG modeling and other related theory were carried out to improve BFOG theoretical system. The Jones optics was adopted to establish the optical transmission model of BFOG. According to this model, the optical output under ideal and non-ideal condition was discussed. Results showed that the light source power fluctuations and polarization fluctuations played an important role in the gyro sensitivity, and the parameters of coupler and polarizer also had appreciable effect. How to choose the optical source power and fiber ring length was discussed afterwards, and the conclusion showed that, the peak output optical source power should be larger than 4mW, the power fluctuations should be less than 10μW, the frequency fluctuations should be less than 10KHz, and the best fiber length is 10m. Aimed at the conflict between the threshold power and BFOG dynamic range, the "two-way winding" method was brought forward, which enhanced the gyro dynamic range under the premise of optical power threshold. At last, the BFOG frequency read out system was designed on reference of RLG.Finally, research of Kerr effect in BFOG was carried out. Kerr effect was recognized as the main error sources in BFOG, so the research of this part is of great significance. Through basic analysis of fiber-optic nonlinear optics, the cross-phase modulation had been shown to be the main reason of refractive index change. Though theoretic analysis, Kerr effect may produce optical bistablity. Experiment showed it happened as the input power was 440μW, and the bistablity could be restrained by adjusting the coupling parameters. The main reason for Kerr effect in BFOG was resonant detuning. It brought not only the nonlinear output, but also restricted-the gyro dynamic range. The double-loop BFOG program was proposed for this suit, and the adverse effects of gyro output was avoided theoretically. Then the parameter error of double-loop scheme was discussed, and results showed that total additional frequency was less than 10Hz, which means its impact on gyro zero-drift was less than 0.015°/s. The results could meet moderate FOG requirements.更多还原