17.1.1. Interferometry
Out-of-plane motion in MEMS is conveniently measured using an interferometer, which is a displacement measuring instrument based on the interference of coherent light beams. A variety of interferometers have been utilized for MEMS characterization, and a number of excellent descriptions of interferometry are available in textbooks [8, 9]. The basic concepts of interferometry are illustrated in Figure 17.3, which shows a Michelson interferometer. Light from a monochromatic or quasi-monochromatic light source is split into a measurement and a reference path, using a beam splitter. The light in the measurement path reflects off the surface of the MEMS device, whereas the light in the reference path is reflected by a flat ...
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