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

本研究利用正弦波长扫描干涉仪和双反馈控制系统，对波长以外的距离进行实时测量。SWS干涉仪的干涉信号除了具有传统的相位α外，还具有与光程差和波长扫描幅度B成正比的相位调制幅度Z_B。施加到PZT的电压使参考镜产生位移并使相位α等于恒定值（2π或3π/2），该电压变成具有小于波长的刻度的标尺。施加在波长扫描装置上的电压决定波长扫描的幅度B，并使幅度Z_B等于π或2π，该电压成为标记每个波长的标尺。采用双反馈控制，每隔一个波长改变OPD值，可自动实现每一个波长的标尺标定。这两条规则 ...更多信息 采用液晶法布里-珀罗干涉仪（LC-FPI）作为波长扫描器件，采用双反馈控制，实现了慢波干涉仪的波长扫描。通过引入双正弦相位调制，我们获得了一个更好的干扰信号，我们可以从中产生的反馈信号的频率带宽等于两倍的慢波系统的频率。由于LC-FPI在慢波系统中的高分辨率，我们可以获得测量范围的上限为200 μm。此外，我们用Z_B=2π的锁相代替了Z_B=π的锁相，使测量范围的上限变为300 μm。在100 μm ~ 300 μm范围内获得了所有稳定点，并以纳米量级的高精度测量了270 μm OPD附近的相对距离。此外，声光可调谐波长滤波器（AOTF）也被采用作为波长扫描装置。该干涉仪采用线阵CCD图像传感器对测量点进行电扫描，实时测量一维台阶轮廓。测量了台阶高度分别为1 μm和20 μm的两种不同台阶轮廓，测量误差小于8 nm。一个测量点的测量时间为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