Highly sensitive, wide dynamic range displacement sensor combining chromatic confocal system and phase-sensitive spectral optical coherence tomography.

A displacement sensor with nanometer-sensitivity and a submillimeter dynamic range is proposed. It integrates a chromatic confocal system and phase-sensitive spectral optical coherence tomography (PhS-SOCT) into the fiber-based Michelson interferometer and codes interference and confocal signals with spectral multiplexing. A displacement is evaluated using depth-resolved phase information decoded from the interference signal, which is unwrapped based on the position information decoded from the confocal signal. A sensor system with a 0.102mm dynamic range was built to validate the method. The temperature induced sample surface displacement was measured with a root mean square error of 3.9nm.