Multiplexing interferometers using range-resolved interferometry

Optical interferometry is widely used for high-precision displacement measurements in many areas of science and technology. Multiplexing interferometers to obtain interferometric phase measurements at multiple locations along a single beam is, however, a relatively new idea. This is possible using laser wavelength-modulated interferometric signal processing approaches such as the range-resolved interferometry (RRI) technique that can separately demodulate phase signals with sub-nanometer resolution from multiple interferometers with differing optical path lengths. Novel capabilities provided by RRI, include, for example, position or angular encoders with multiple degrees-of-freedoms that are multiplexed onto a single fiber-coupled access port. Also, the tomographic view of all signal sources present in an interferometric setup can be very useful for diagnostic purposes and allows additional absolute distance measurements. Furthermore, the ability to cleanly suppress multiple reflections allows for highly linear phase measurements. Therefore, range-resolved signal processing techniques open up novel solutions to existing measurement problems in precision engineering and advanced dimensional metrology.