Generation of a ruler marking every wavelength and its application to nano measurement by a wavelength-scanning interferometer with double feedback control

本文研究了利用正弦波长扫描干涉仪和双反馈控制系统实时测量波长以上距离的分析和实验。SWS干涉仪的干涉信号除具有常规相位α外，还具有与波长扫描光程差（OPD）和振幅b成正比的相位调制幅度Z_b。施加到PZT上的电压使参考镜产生位移，使相位α等于恒定值（2π或3π/2），从而成为比波长更小的标尺。施加在波长扫描装置上的电压，决定了波长扫描的振幅b，使振幅Z_b等于π或2π，就成了标记每一个波长的标尺。采用双反馈控制，每隔一个波长左右改变OPD，即可自动标定每一个波长的标尺。这两个规则…更多的er使我们能够实时测量比波长更长的绝对距离。采用双反馈控制的液晶法布里-珀罗干涉仪（LC-FPI）作为SWS干涉仪的波长扫描器件。通过加入双正弦调相，我们得到了一个更好的干扰信号，由此产生的反馈信号的带宽等于SWS频率的两倍。由于LC-FPI在SWS中的高分辨率，我们可以得到测量范围的上限为200 μm。并且我们用Z_b=2π的锁相代替Z_b=π，使测量范围的上限变为300 μm。我们获得了100 ~ 300 μm范围内的所有稳定点，并测量了270 μm OPD周围的相对距离，精度达到纳米数量级。此外，还采用声光可调谐波长滤波器（AOTF）作为波长扫描器件。在这种情况下，稳定点的重复性高于LC-FPI。该干涉仪采用线阵CCD图像传感器对测量点进行电扫描，实时测量一维阶跃轮廓。测量了台阶高度分别为1 μm和20 μm的两种不同的台阶轮廓，测量误差小于8 nm。一个测点的测量时间为0.04 s。少

This research deals analyses and experiments about real-time measurement of a distance longer than a wavelength using sinusoidal wavelength-scanning (SWS) interferometer and double feedback control system. In addition to a conventional phase α an interference signal of SWS interferometer has phase-modulation amplitude Z_b that is proportional to the optical path difference (OPD) and amplitude b of the wavelength-scanning. Voltage applied to the PZT which gives a displacement to a reference mirror and makes the phase α equal to a constant value (2π or 3π/2) becomes a ruler with scales smaller than a wavelength. Voltage applied to a wavelength-scanning device that determines the amplitude b of the wavelength-scanning and makes the amplitude Z_b equal to π or 2π becomes a ruler marking every a wavelength. The calibration of the ruler marking every a wavelength could be made automatically with the double feedback control by changing the OPD at intervals of about a wavelength. These two rul … More ers enabled us to measure an absolute distance longer than a wavelength in real-time.A liquid-crystal Fabry-Perot interferometer (LC-FPI) was adopted as a wavelength-scanning device in the SWS interferometer with double feedback control. By incorporating double sinusoidal phase-modulation we obtained a better interference signal from which we could generate the feedback signal whose frequency bandwidth was equal to twice the frequency of the SWS. Because of the high resolution of the LC-FPI in the SWS we could obtained the upper limit of the measurement range to 200 μm. Moreover we used the phase lock of Z_b=2π instead of Z_b=π, so that the upper limit of the measurement range became 300 μm. We obtained all of stable points from 100 μm to 300 μm, and we measured the relative distance around the OPD of 270 μm with a high accuracy of the order of nanometer. Moreover, an acousto-optical tunable wavelength filter (AOTF) was also adopted as a wavelength-scanning device. In this case the repeatability of the stable points was higher that in the case of the LC-FPI.A linear CCD image sensor was used to electrically scan a measuring point and measure one-dimensional step-profiles in real-time with this interferometer. Two different step profiles with a step height of 1 μm and 20 μm, respectively, were measured with the measurement error less than 8 nm. Measuring time for one measuring point was 0.04 s. Less