All-silicon interferometric optical probe for non-contact dimensional measurements in confined environments

We developed an interferometric optical micro-probe, for the purpose of non-contact measurement of distance-to-surface for samples in confined environments, such as holes and trenches whose lateral dimensions are in the order of hundreds of microns (typically fuel injection nozzles). A Michelson interferometer was integrated at the end of a 4mm-long, 390μm-thick, 550μm-wide cantilever, which incorporates grooves for input-output optical fibers. The whole system is a monolithic silicon block obtained by DRIE. The fabricated probe demonstrates simultaneous measurements of distance and thickness for silicon wafer used as a test surface. Data are obtained from Fast Fourier Transform of the spectral interferogram.