Absolute distance measuring fiber-coupled interferometer for surface topography measurement

带有光纤耦合探头的干涉式距离传感器在生产测量技术中有着广泛的应用。原则上，这些传感器可以替代触觉触控笔尖系统。与触觉系统相比，干涉式传感器提供了更好的距离分辨率。由于非接触式原理，可以加快测量过程。如果使用微型光学探头，可以实现灵活性和难以接近的表面积。要在实践中利用这些优势，高数据速率、关于测量和接近过程的良好自动化能力以及低成本是重要的先决条件。电流传感器在这些点上失效的事实表明，需要进一步的研究。为了进行干涉距离测量，仅记录单个光强值是不够的。事实上，测量通常需要对干扰信号进行时间或空间相位调制。在自己以前工作的基础上，本项目研究了不同的时间相位调制方法，对它们进行了比较，并就测量精度和相关的不确定度影响进行了研究。该项目首先假设，在三个步骤的过程中，光纤耦合双波长干涉仪将能够以快速、稳健和精确的方式执行接近和测量过程。首先，两个激光二极管发出的光将通过二极管注入电流进行波长调制，以便使用适当的数字信号处理算法实现绝对距离测量，不确定度在10微米范围内。在干涉仪的参考臂上附加光程长度的正弦调制和双波长相位分析，有望实现由合成波长产生的约19微米的无模糊范围，最大测量偏差小于0.5微米。这些方法的结合提供了一种新的测量系统。在以往的研究中，对于1550 nm的单一波长，通过相位分析可以获得小于1 nm的标准偏差。因此，这种组合代表了一种非常有前途的方法，可以实现测量偏差在纳米范围内的绝对距离测量。

Interferometric distance sensors with fiber-coupled probe heads open a wide range of application in production measuring technology. In principle, these sensors may substitute tactile stylus tip systems. Compared to tactile systems interferometric sensors provide a better distance resolution. Due to the contactless principle, measurement processes can be accelerated. Flexibility can e achieved and surface areas, which are difficult to access, can be reached, if micro-optical probe heads are used.To utilize these benefits in practice, high data rates, good automation capabilities with respect to measurement and approaching processes as well as low costs are important prerequisites. The fact that current sensors fail with respect to these points shows that there is a need for further research.In order to perform interferometric distance measurements it is not enough to record a single intensity value. In fact, the measurement commonly requires temporal or spatial phase modulation of the interference signal. Based on own previous work the present project studies different methods of temporal phase modulation in comparison with each other and with respect to measurement accuracy and relevant uncertainty effects. The project starts with the hypothesis that in a three-step process a fiber-coupled dual-wavelength interferometer will be able to carry out approaching and measuring processes in a fast, robust, and precise manner. First, the light emitted by the two laser diodes will be wavelength-modulated via the diode injection current in order to reach absolute distance measurements with an uncertainty in the range of 10 µm by use of appropriate digital signal processing algorithms. An additional sinusoidal modulation of the optical path length in the reference arm of the interferometer and dual-wavelength phase analysis are expected to achieve an unambiguity range of approximately 19 µm, which results from the synthetic wavelength, and a maximum measuring deviation below 0.5 µm. The combination of these methods provides a novel measurement system. In previous studies a standard deviation of less than 1 nm could be obtained via phase analysis for a single wavelength of 1550 nm. Thus, this combination represents a very promising approach to achieve absolute distance measurements with a measurement deviation in the nanometer range.