Examples include the inner surfaces of micro-drilled holes, narrow gaps or complex free-form surfaces. The optical inspection technique offers a fast, contactless and wear-free way of measuring micro-structures and distances. Including at production speed, if required. Using fibre-optic sensors and miniature measuring probes, the layer position, drill hole depth and surface quality in MICROVIAS on multi-layer boards can be detected. Distance sensors are suitable for the detection, differentiation and measurement of objects using ultrasound. This new method uses tandem low-coherence interferometry and an optical fiber cut at an angle of 45°.
[pdf] Optical fibers can be used as sensors to measure, , and other quantities by modifying a fiber so that the quantity to be measured modulates the,,, or transit time of light in the fiber. Sensors that vary the intensity of light are the simplest, since only a simple source and detector are required. A particularly useful feature of intrinsic fiber-optic sensors is that they can, if required, provide distributed sensing over very large distances.
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