For in-line surface inspection of microfluidic devices, optical measurement techniques with sub-micrometer resolution and a long working distance (W.D.) objective lens are needed. Structured illumination microscopy (SIM) is a good candidate to achieve high resolution. In micro-structured surface inspection, however, measurement needs to be carried out through coherent imaging, and thus conventional incoherent SIM cannot be applied directly due to interference of light from a sample. In this study, equations are reformulated by considering amplitude and phase of light waves. As a result, we found that higher spatial frequencies of samples can be derived even through coherent imaging by using multiple interference images. Based on this proposed coherent SIM, an optical measurement method with a long W.D. objective lens and sub-micrometer resolution for in-line surface inspection of sub-micro- and micro-structured surfaces is proposed. We analyzed resolution and performance of the proposed method from a theoretical and numerical perspective based on Fourier optics and imaging theory. The results verified that even with a long W.D. objective lens, the concept of the proposed method allows us to achieve sub-micrometer resolution in spite of non-fluorescence observation. This cannot be achieved by standard microscopy and the conventional incoherent SIM. We also conducted numerical analysis considering external disturbance that can occur in practical in-line inspection. The results revealed that the proposed method is capable to resolve two points with a distance less than half a micrometer with the maximum measurement error of no larger than 5%, under the condition where a maximal phase error of reference light is 2π/20 i.e., 20 nm error in length. These values are practical in in-line inspection.

对于微流体设备的在线表面检查，需要具有亚微米分辨率和长工作距离（WD）物镜的光学测量技术。结构照明显微镜（SIM）是实现高分辨率的理想选择。然而，在微结构表面检查中，需要通过相干成像进行测量，因此由于来自样品的光的干扰，常规的不相干SIM无法直接应用。在这项研究中，方程是通过考虑光波的幅度和相位来重新制定的。结果，我们发现，即使通过使用多个干涉图像通过相干成像，也可以导出更高的样本空间频率。基于此拟议的相干SIM，采用长WD的光学测量方法 提出了用于亚微米和微结构化表面的在线表面检查的物镜和亚微米分辨率。我们基于傅立叶光学和成像理论从理论和数值角度分析了该方法的分辨率和性能。结果证明，即使使用较长的WD物镜，该方法的概念也使我们能够实现亚微米分辨率，尽管无荧光观察。这无法通过标准显微镜和传统的非相干SIM来实现。我们还进行了数值分析，考虑了实际在线检查中可能发生的外部干扰。结果表明，该方法能够分辨距离小于半微米的两个点，最大测量误差不超过5％，在参考光的最大相位误差为2π/ 20（即长度误差为20 nm）的条件下。这些值在在线检查中很实用。