Chao Zhang, Fa-Jie Duan
State Key Lab of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, China.
Rev Sci Instrum. 2011 Nov;82(11):113105. doi: 10.1063/1.3658480.
Closed-loop active homodyne control can be used to make an interferometer steady against phase fluctuating followed by, for example, temperature gradients. This technology is introduced to stabilize π/2 -rad phase steps in a full-field interferometer. Two beams emitted from a fiber-optic coupler are combined to form an interference fringe pattern on a diffusely reflecting object. Fresnel reflections from the distal fiber ends undergo a double pass in the fibers and interference at the fourth port of the coupler which formed a Michelson interferometer. We suggested two means of ac phase tracking (PTAC) and dc phase tracking (PTDC) to maintain the interference intensity at quadrature by feedback control. Stepping between quadrature positions forces a π/2 -rad phase step. A method based on the ratio of harmonic of the interference signal was proposed to estimate phase step accuracy. A root-mean-square phase stability of 1.5 mrad and phase step accuracy of 2.6 mrad were measured with PTAC and a root-mean-square phase stability of 2 mrad and phase step accuracy of 13.8 mrad were measured with PTDC for the fiber-optic projected-fringe digital interferometry following the same condition. It worked well in two hours without resetting the integrator.
闭环有源零差控制可用于使干涉仪在例如温度梯度等相位波动情况下保持稳定。该技术被引入以稳定全场干涉仪中的π/2 弧度相位步长。从光纤耦合器发射的两束光在漫反射物体上合并形成干涉条纹图案。来自光纤远端的菲涅尔反射在光纤中经历双程传播，并在耦合器的第四端口发生干涉，从而形成迈克尔逊干涉仪。我们提出了交流相位跟踪（PTAC）和直流相位跟踪（PTDC）两种方法，通过反馈控制使干涉强度保持在正交状态。在正交位置之间切换会强制产生π/2 弧度的相位步长。提出了一种基于干涉信号谐波比值的方法来估计相位步长精度。在相同条件下，对于光纤投影条纹数字干涉测量，采用PTAC测量得到的均方根相位稳定性为1.5毫弧度，相位步长精度为2.6毫弧度；采用PTDC测量得到的均方根相位稳定性为2毫弧度，相位步长精度为13.8毫弧度。在不重置积分器的情况下，该系统在两小时内运行良好。
