基于非互易耦合腔的纯光学偏频激光陀螺研究

Ring laser gyros (RLGs) have been widely used in areas such as aviation and aerospace due to their advantages such as high dynamic range and accurate scale factor. They can measure angular rates accurately with frequency difference between counter traveling wave modes, but due to energy coupling, the two modes lock their frequencies together yielding none rotation information at low rotation rates. This well-known phenomenon is called lock-in. RLGs are often mechanically dithered to reduce the effects of lock-in. Although the dithered gyros reach size and precision requirement for guidance and navigation applications, the moving parts they used result in many disadvantages such as mechnical disturbance, coning error and sculling error. Four-mode differential laser gyros have attracted great interests from many institutes, companies and universities, since they ideally solve the lock-in problem with purely optical method. However, they are difficult to develop because of intracavity elements which lead to lasing modes unstability. As a result, the technical skill level they need is too high. This research will study a novel laser gyro based on nonreciprocal coupled cavity, which uses electromagnetic dithered biasing but not intracavity elements. Therefore, it has the advantages of both mechanically dithered gyro and four-mode differential laser gyro.First of all, the tranfer function of coupled cavity will be established and then the nonreciprocal biasing and Sagnac beat frequency will be derived using self-reproduction condition. Consequently, influence of parameters of the coupled cavity can be investigated. In addition, the biasing frequency will be modulated from DC to AC so it can be eliminated by low pass filter. In this way, the angular rates is obtained. Finally, the null shift mechanisms will be analysed and measures will be taken to reduce the null shift. Through these studies, the dithered biasing will be realized for laser gyro with coupled cavity and the null shift mechanisms will be made clear, which will provide support for further engineered prototype both theoretically and technically.

激光陀螺具有动态范围大、比例因子准确等优点，在航空航天等领域具有广泛的应用。目前应用最广泛的激光陀螺是机械抖动激光陀螺，但机械抖动装置会导致机械干扰、噪声等问题。四频差动激光陀螺不存在这些问题，但由于使用了腔内元件而对工艺要求很高，增大了研制难度。本项目拟对一种新颖的基于非互易耦合腔偏频的激光陀螺进行系统研究，它采用电磁抖动偏频，又不使用腔内元件，因而兼具机械抖动和四频差动激光陀螺的优点。首先建立耦合腔的传递函数模型，利用激光振荡的自再现条件推导出非互易偏频和Sagnac拍频随耦合腔参量的函数关系，并进行实验验证。接着利用抖动调制技术，将偏频从直流调制成高频交流，再用低通滤波器滤除以得到角速度信息。最后，分析零偏的物理机理，并提出减小零偏的措施。通过上述研究，可以实现耦合腔激光陀螺的抖动偏频，弄清影响其零偏稳定性的物理机制，为进一步工程化样机的研制提供理论和技术支持。

激光陀螺具有动态范围大、比例因子准确等优点，在航空航天等领域具有广泛的应用。目前应用最广泛的激光陀螺是机械抖动激光陀螺，但机械抖动装置会导致机械干扰、带宽窄等问题。四频差动激光陀螺不存在这些问题，但由于使用了腔内元件而对工艺要求很高，增大了研制难度，且对温度和磁场非常敏感。本项目提出了一种基于非互易耦合腔偏频的激光陀螺方案，它采用电磁抖动偏频，又不使用腔内元件，因而兼具机械抖动和四频差动激光陀螺的优点。首先建立了耦合腔的传递函数模型，推导了光场经过耦合腔再出射后幅度和相位的变化，模型参量包括耦合腔中反射镜曲率和反射率、非互易元件的相移和损耗、耦合腔光程等，并将耦合腔等效为一个复合反射镜代入到环形谐振腔，利用激光振荡的自再现条件推导出非互易偏频和Sagnac拍频随耦合腔参量的函数关系，发现在某些参数条件下，耦合腔激光陀螺的比例因子可增强若干数量级，但线性度和测量范围降低。提出了基于法拉第调制器的电磁抖动偏频、基于电光/弹光的抖动偏频方案，并分析比较了它们的优缺点，认为法拉第调制方法能够严格消除偏频导致的零偏，并试制了一套法拉第调制器。为了提高激光陀螺性能，对环形谐振腔的本征光场模式、衍射损耗以及增益管放电特性、合光棱镜串扰等特性进行了研究，为进一步工程化样机的研制提供了理论和技术支持。