【作者】 汪之国；

【导师】 龙兴武；

【作者基本信息】 国防科学技术大学 ， 光学工程， 2010， 博士

【摘要】 异面腔四频差动激光陀螺（FMDLG）具有比例因子精度高、不存在机械噪声、信号延迟小等优点,在工业和国防领域具有重要的应用。为了提高异面腔FMDLG的性能,对其零偏的物理机制和变化特性进行了理论和实验研究,并从电子系统设计的角度讨论了减小零漂的方法,主要内容如下:分析了环形激光中的非互易效应对异面腔FMDLG输出差频的影响,将总零偏分解为7项子零偏的贡献之和,分别称为主零偏、偏振差损零偏、方向差损零偏、磁圆二向色性差损零偏、散射零偏、色散零偏、朗缪尔流零偏,并讨论了各项子零偏的变化特性,为课题研究提供了理论依据。设计了一套灵活的实验系统,包括数字信号处理、模数转换、数模转换、温度测量、压电陶瓷驱动、光电转换和放大、磁场发生、高压稳流电源、射频放大和幅度检波等电路模块。在此基础上,实现了基于电子信号处理的读出系统,并采用了分辨率增强技术,使FMDLG的分辨率提高到0.001（″）以上。利用该系统,只需设置各电路模块的连线,然后编写相应的代码即可实现扫模、计数、程长控制等功能,为课题研究奠定了实验基础。结合理论分析,通过改变纵模阶数、失谐频率（工作点）、工作方式、磁场、放电电流和温度,对零偏的主要特性进行了实验研究。结果表明:由于不同阶纵模对应的光路稍有差别,导致零偏有0.01 Hz数量级的差异,因此应使FMDLG工作在同一阶纵模上;在增益介质上施加特定的纵向磁场,可使零偏对工作点变化的敏感性大大降低;通过使FMDLG工作在最佳工作点上可基本消除零偏对磁场的敏感性;磁圆二向色性差损零偏随温度变化较大,是实验用FMDLG温度灵敏度的主要来源。讨论了光强差稳频的缺点,通过调整左、右旋光强的比例系数改变工作点,证明工作点对零偏、开机漂移和温度灵敏度系数都有数量级的影响。由于光强差稳频使用的两路信号在光电转换和放大过程中很难做到完全一致,导致工作点与合光和稳频电路的参量有关。利用顺（逆）时针拍频幅度存在极值的原理设计了小抖动稳频系统,稳频精度为1.9×10^-10,且电路增益和偏置的变化不会影响工作点,实现了抗干扰的稳频。在程长控制程序中增加了智能选模功能,使异面腔FMDLG在任何温度下启动都工作在确定的最优纵模上,不仅消除了开机时初始纵模选择随机性导致的零漂,还可避免大温度范围工作时出现跳模,理论分析了仅根据光强信号进行稳频的缺点,指出由于Ne双同位素合成增益曲线的不对称,即使光电转换过程完全理想,光强差稳频或小抖动稳频所确定的工作点与最佳工作点一致的可能性也极小,因此无法克服增益、腔损、磁场等参量变化导致的零漂。为了解决这个问题,设计了广义程长控制系统,使FMDLG工作在最佳工作点和色散平衡状态下。对比实验表明,将异面腔FMDLG控制在左、右旋光强相等的工作点时,磁灵敏度为62.63（°）/（h·mT）,控制在最佳工作点时,磁灵敏度减小到0.88（°）/（h·mT）,因此广义程长控制系统可有效降低磁灵敏度。通过温度循环实验,利用逐步回归法建立了温度补偿的数学模型,不仅可补偿外界温度变化导致的零漂,而且对开机过程中自发热导致的零漂也有良好的补偿效果。温度补偿后的结果为:在（-40⁶0）°C范围内,开机75 min的零偏稳定性为0.005（°）/h,2 h间隔的零偏重复性为0.005（°）/h,静态补偿零偏极差为0.03（°）/h,均方差为0.009（°）/h,温度变化率1°C/min时零偏极差为0.115（°）/h,均方差为0.015（°）/h,温度以（1⁵）°C/min的变化率随机变化时零偏极差为0.153（°）/h,均方差为0.028（°）/h,随机游走为3.9×10^-4（°）/h^1/2。测试结果表明,在温度变化缓慢的实验室条件下异面腔FMDLG已基本达到了惯性级水平,但为了在剧烈变温、强磁场干扰、振动和冲击等恶劣条件下实现惯性级精度,还需要做很多工作。更多还原

【Abstract】 The nonplanar four-mode differential laser gyro （FMDLG） has important potential applications in the field of industry and national defense due to its advantages such as excellent scale factor precision, absence of mechanical noise and small data delay. In order to improve the performance of nonplanar FMDLG, physical mechanisms and characterics of its bias are investigated both theorctially and experimentally. Moreover, the methods to reduce zero drift in aspect of electronic system design are discussed.The influence of nonreciprocal effects in ring lasers on the difference frequency of nonplanar FMDLG is analyzed. It is shown that the total bias can be resolved into seven sub-biases, which are called main bias, differential polarization loss bias, differential direction loss bias, magnetic circular dichroism loss bias, scattering bias, Verdet constant dispersion bias and Langmuir flow bias respectively. In addition, the characteristics of each sub-bias are discussed.A convient experimental system is designed, including electronic circuit modules such as digital signal processing, analog to digital converter, digital to analog converter, temperature mesasurement, piezoelectric transducer driver, magnetic field generator, current stabilized high voltage power supply, radio frequency amplifier and amplitude detector. With the experimental system, an readout system based on electronic signal processing is realized. Furthermore, the resolution is improved to better than 0.001（″） with resolution enhancement technique. Through configuring the circuit modules accompanied with corresponding codes, the experimental system can realize functions such as mode scanning, countering and path length control.Based on theoretical analysis, main characteristics of the bias are investigated through variation of longtitudal mode order, detuning frequency （operating point）, operating style, magnetic field, discharge current and temperature. Minor difference of optical circuit among different orders of longitudal mode can lead to bias difference on the order of 0.01 Hz. Therefore, it is desirable that the FMDLG maintains the same longitudal mode throughout its mission. Bias sensitivity to operating point variation will be reduced greatly when a longitudinal magnetic field is applied to the gain media with specific amount. Bias sensitivity to magnetic field variation can be eliminated when the FMDLG is operated at the optimal operating point. Magnetic circular dichroism loss bias varies greatly with temperature, which is the major cuase of bias temperature sensitivity in the experimental FMDLG..Disadvantages of the path length control system using the difference between the left and right circularly polarized intensities are disscussed. Experimental results indicate that operating point affect bias, turn-on drift and temperature sensitivity greatly. When the difference between the left and right circularly polarized intensities is used to control path length, operating point will be related to parameters of beam combining and path length control circuit due to asymmetry in the process of opto-electronic convertion and amplification. A path length control system with maximizing clockwise （or anticlockwise） beat wave amplitude is designed, which obtains a frequency stability of 1.9×10-10. Moreover, it is immune to variations of gain and offset in the electronic circuit. In order to eliminate randomness in acquiring initial longitudinal mode at power up and mode jump at large range of operating temperature, smart modes acquisition program is added into the path length control system which makes the FMDLG maintain the same mode all the while.Shortcomings of path length control systems only using beam intensities are analyzed theoretically. Because of the asymmetry of gain curve composed of two isotropes, even with ideal opto-electronic conversion process, it is nearly impossible for the operating points determined by these path length control systems to be consistent with the optimal one. As a result, zero drift caused by variations of parameters such as gain curve, cavity loss and magnetic field can not be cancelled out. In order to solve this problem, a generalized path length control system is designed to make sure the FMDLG working with dispersion equalized and at the optimal operating point. Comparative exeripment showed that the magnetic sensitivity of one FMDLG is 62.63（°）/（h·mT） when controlled with equal intensity, while the magnetic sensitivity is only 0.88（°）/（h·mT） when controlled at the optimal operating point.With temperature cycling experiments, thermal compensation model is established by using stepwise regression method. Zero drift caused by both environmental temperature variation and self heating can be compenstated effectively. Test results of one experimental FMDLG give the following data: at （-40⁶0）°C, bias stability within 75 min after turn-on is 0.005（°）/h; bias repeatability is 0.005（°）/h with 2 hour off time; max bias error （MBE） and root mean square （RMS） are 0.03（°）/h and 0.009（°）/h respectively in static temperature compensation; MBE and RMS are 0.115（°）/h and 0.015（°）/h respectively with temperature varying at 1oC/min; MBE and RMS are 0.153（°）/h and 0.028（°）/h respectively with temperature varying randomly at （1⁵）oC/min; random walk is 3.9×10^-4（°）/h^-1/2.The nonplanar FMDLG has obtained inertial navigation capability in benign environment with slow temperature variation. However, more work should be done so as to realize inertial navigation capability in severe environment such as violent temperature variation, intense magnetic field disturbance, vibration and shock.更多还原