We present a high precision fiber roughness sensor based on annular core optical fiber (ACF). The ACF has a cone-frustum-shaped tip to enable the annular core to generate a focused ring light. When the incident light passing from the ACF is focused on the rough surface to be measured, the specular light will also be collected by using the ACF, which realizes the integration of the incident optical path and collecting optical path about optical roughness detection. Because the focused ring light has a smaller spot radius than that of the emergent light of a single-mode fiber, the proposed sensor has a higher spatial resolution. Moreover, the ACF with a cone-frustum tip can reduce the diffuse light coupling into the sensor; in this way, we improve the measurement precision. The experimental results show that for the surface roughness of 10 nanoscales, the error between the measured value and the theoretical value is about 5% and the spatial resolution reaches 6 µm. Thus, our sensor can be widely used in high precision nondestructive surface roughness measurements.

中文翻译：

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基于环形纤芯光纤的高精度粗糙度传感器

我们提出了一种基于环形纤芯光纤 (ACF) 的高精度光纤粗糙度传感器。ACF 有一个圆锥台状的尖端，使环形核心能够产生聚焦的环形光。当来自ACF的入射光聚焦在待测粗糙表面上时，ACF也会收集镜面光，实现了光粗糙度检测的入射光路和收集光路的一体化。由于聚焦环形光的光斑半径小于单模光纤出射光的光斑半径，因此所提出的传感器具有更高的空间分辨率。此外，带有锥台尖端的 ACF 可以减少进入传感器的漫射光；通过这种方式，我们提高了测量精度。实验结果表明，对于10纳米级的表面粗糙度，实测值与理论值的误差约为5%，空间分辨率达到6 μm。因此，我们的传感器可广泛用于高精度无损表面粗糙度测量。