为了实现pF量级小电容的精密测量, 建立了基于激光锁定Fabry-Perot干涉仪的精密电容测量系统。对该系统所采用的计算电容原理、激光锁定干涉仪方法及其整数级次确定方法进行了研究。首先, 根据Lampard和Thompson电学基本原理介绍了Fabry-Perot干涉仪的结构与工作方式, 采用一种锁定干涉仪测量位移的方法。其次, 介绍了Fabry-Perot干涉仪的光路设计, 详细分析了干涉仪锁定控制系统的工作状态以及锁定状态下干涉仪腔长的抖动情况。通过分析利用电容值确定干涉仪整数级次变化的可行性, 提出了基于1 pF标准电容器确定Fabry-Perot干涉仪整数级次的实验过程。最后, 介绍了Fabry-Perot锁定干涉仪的台阶式位移过程以及利用该套系统测量电容的重复性。实验结果表明: Fabry-Perot干涉仪在锁定状态下, 腔长抖动峰峰值为0.4 nm, 测量1 pF标准电容器重复性达到5.0×10-9。

In order to realize precise measurement for pF level capacitor, a capacitance measurement system based on laser locking Fabry-Perot interferometer was established and its basic principle, method of interferometer locking and determination of order numbers variation were studied. Firstly, according to the Lampard and Thompson electrical theorem, configurations and operation modes of Fabry-Perot interferometer were presented, and a displacement measurement by locking interferometer was demonstrated.Then the optical layout for Fabry-Perot interferometer was presented, and the operation status of the interferometer locking servo system and the fluctuation of cavity length in close loop were carefully analyzed. After the feasibility of determining the order numbers through the prior value of 1 pF standard capacitor was evaluated, the experiment process for confirming the variation of order numbers was presented. Finally, the character of step moving displacement and measurement repeatability of 1 pF standard capacitor were discussed. Experimental results indicate that the peak to peak fluctuation of the interferometer is 0.4 nm after its locking, and the repeatability of 1 pF standard capacitor measurement is 5.0×10-9. It can satisfy the requirements of precisely measuring the pF level capacitor. However, further study of the displacement measurement will focus on the uncertainty evaluation and optimization for the displacement measurement system.