光谱共焦技术被广泛应用于精密制造、集成电路、生物医学等领域，是精密位移测量的热点技术之一。在光谱共焦位移测量技术研究中，普遍采用最大值归一化策略处理反射光谱，但其波长-位置响应曲线易受光源光谱和待测表面的非线性影响，鲁棒性差。针对上述问题，本论文主要研究色散物镜、归一化策略、聚焦波长提取算法等关键技术，搭建具有高精度、强鲁棒性的光谱共焦位移测量系统，并将其应用于表面轮廓和薄膜厚度测量。为提升光谱共焦系统成像质量，分析了共轭小孔和超分辨光瞳对分辨率和信噪比的影响。由于反射光同时包含聚焦波长及非聚焦波长，其光谱较宽，本文提出基于亚像素插值的阈值质心法，能有效抑制噪声、降低光谱仪分辨率局限性，并从运算效率、求解精度和稳定性等方面优选最佳参数。提出了一种分光路参考策略，并设计了分段式色散物镜。利用X型光纤耦合器连接照明臂、探测臂、参考臂和测量臂，设置可调光阑控制光路开关。分段式色散物镜将白光先准直后色散聚焦，以便利参考光路设计。根据仿真的轴向球差曲线来确定超分辨光瞳结构参数，回光减少但球差降低。动态标定波长-位置响应曲线，1.05 mm色散范围的拟合误差优于±2 μm，静态测量时的聚焦波长稳定性达±0.2 nm，实际位移分辨能力约为1.5 μm左右。为进一步提高测量精度和鲁棒性，提出共轴自参考策略，校正光源光谱及待测表面的非线性影响。整体式色散物镜的放大倍数0.3~0.4，成像质量更佳。动态标定波长-位置响应曲线，400 μm色散范围的拟合误差±0.4 μm，是最大值策略的13%，聚焦波长重复误差优于±0.2 nm。实验表明光源光谱与待测表面颜色对响应曲线的影响小于0.9 nm，均优于最大值归一化策略。经过高精度压电陶瓷检测，该系统的实际位移测量精度为0.25 μm（全量程）。基于上述光谱共焦系统实现了多种位移测量应用。基于共轴自参考的光谱共焦系统的轴向位移测量结果与商业化传感器相当，所得菲涅耳透镜轮廓与探针轮廓仪相似，沟槽周期基本一致，圆度测量结果能够满足国标中对圆度公差等级的评定要求，基于光谱反射率的硅基二氧化硅薄膜厚度的测量精度与商业化膜厚仪相差仅0.8%，重复测量精度约0.065 nm。
Chromatic confocal technology is widely used in precision manufacturing, intereated circuits, and biomedicine and so on. It has been developed as one of the most popular methods in the high-precision displacement measurement. In previous study of chromatic confocal technology, the reflected spectrum was usually normalized with its biggest value. The strategy would not change the curve shape of the reflected spectrum, making it hard to remove the nonlinear modulation of the light source or the sample surface to be measured. Hence, the wavelength-displacement response curve of the chromatic confocal system cannot keep still with different light sources and sample surfaces. To solve the problem, this paper studied the key technologies in the chromatic confocal displacement measurement, such as the dispersion probe, reference strategy, peak extraction algorithm. Based on these studies, two types of chromatic confocal sensors are brought out with high precision and strong robustness. In addition, they show good application feasibility in the measurement of the surface profile and the thin film thichkness.In order to improve the imaging quality of the chromatic confocal system, the paper analysised the effects of the conjugated pinholes and the super-resolution pupil on the resolution and signal-to-noise ratio. As the reflected light contains both the focus wavelength and off-focus wavelengths, its spectrum is usually too wide to extract the accurate focus wavelength. In this paper, a threshold centroid method with subpixel interpolation is proposed, effectively suppressing the noise and reducing the limitation of the spectrometer resolution. What’s more, the main parameter of the proposed method is optimized by analyzing the efficiency, accuracy and stability.A beam-splitting reference strategy and a segmented dispersion probe are proposed at first. An X-type fiber coupler is used to connect the illumination arm, the detection arm, the reference arm and the measurement arm. Two adjustable aperture are set in the reference arm ang the measurement arm to open or shut down the optical switch. The segmented dispersion probe uses several lens to colimate and disperse the incidence light to monochromatic lights, which would focus on different positions along the optical axis. Super-resolution pupil is designed according to the longitudinal aberration curves at different wavelengths in ZEMAX, which decreases the reflected light intencity but corrects the spherical aberration. The wavelength-displacement response curve is achieved by calibration experiment to show a good fitting error of about ±2 μm in the full measurement range of 1.05 mm. In addition, the focuse wavelength fluctuation for a still mirror is about ±0.2 nm. In the last, the chromatic confocal system is compared with a precise linear stage, showing the actual displacement resolution of about 1.5 μm.In order to improve the measurement accuracy and robustness, a coaxial self-reference strategy is proposed to correct the nonlinear influence of the light source spectrum and the ample surface to be measured. The magnification of the integral dispersion probe is about 0.3~0.4, and the imaging quality is much better than the segmented dispersion probe. The wavelength-position response curve from the dynamic calibration shows better fitting error of about ±0.4 μm in the full dispersion range of 400 μm, which is 13% of the tradittional normalization strategy with the biggest vale. Furthermore, the repetition error of the response curve is better than ±0.2 nm in the focus wavelength. The experimental results show that the influence of light source spectrum and surface color on the response curve is less than 0.9 nm. With a high-precision piezoelectric ceramic stage, the actual displacement measuring accuracy of the chromatic confocal system is about 0.25 μm in the full measurement range.Based on the chromatic confocal systems, a variety of displacement measurement applications is carried out to show their accuracy and robustness. The chromatical confocal system with coaxial self-reference strategy and the integral dispersion probe is tested to own similiar accuracy with the commercial sensor. The Fresnel lens profile is achieved by the longitude scanning to show similar shape with the probe profilometer, and the groove period is nearly the same. The roundness of a shaft part is measured with two-probe method, satisfying the evaluationof the roundness in Chinese national standard. Finally, the thickness of the silicon dioxide film on silicon substrate is measured with an accuracy of only 0.8% compared with the commercial film thickness gauge, and a repeatability of about 0.065 nm.
