Some applications for distance metrology require absolute distance information with a very high precision. Many optical methods are able to determine an absolute distance but are not precise enough to get an accuracy of a few nanometers. Interferometers are very precise due to the fact that they determine the phase of the light, but they have a very small range of unambiguity. To fit the requirements for a very precise and absolute distance measurement we use interferometry with synthetic wavelengths. Fiber optics introduces two additional advantages: firstly it allows the realisation of an interferometer with a small size sensor. This makes the adjustment of the interferometer convenient. Secondly several sensors can be connected to the main unit for simultaneous measurements at different locations.
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