Oscillating microoptical fiber sensor for precision production measurement

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During the first phase of the project optical sensors with different oscillating fiber optical microprobes were built, analyzed, and optimized with respect to the used components and signal processing algorithms. A result is a two wavelength interferometer which reaches a standard deviation of repeatability measurements below 1 nanometer. The system measures on plane, tilted, and curved specularly reflecting surfaces. Based on existing components and systems in the second phase of the project more advanced research topics shall be studied in order to be able to assess the capabilities of the novel technology. Crucial aspects are related to an enhancement of the data rate of the sensor, roughness measurement on engineered surfaces, extension of the measurement range until an absolute distance measurement is reached, improvement of the microoptical probes, and finally the measurement of 3D-topography via dynamic probe tracking. An extended analysis of the measured phase-modulated interference signals based on the Hilbert transformation aims at an enhanced data rate of the sensor of several 100 kHz. Preliminary investigations show that the use of infrared light of the wavelength range from 1300 nm to 1550 nm enables surface roughness measurements on engineered surfaces characterized by Ra values of several 100 nanometers. Therefore, the applicability of the new sensor to surface roughness measurement shall be studied in detail. Approaches known from literature allow an extension of the measurement range of a two wavelength interferometer beyond the limitation of half the synthetic wavelength. These approaches shall be used in context with the new sensor considering the uncertainty of phase measurement. In order to demonstrate the capabilities of the sensor a demonstration system comprising two lateral scan axes and a precise contour tracking mechanism shall be built. This requires an electronic synchronization of the actuator signal and the measured signals in order to achieve as good as possible measurement accuracy.