An optical standing-wave interferometer for displacement measurements

Laser interferometers have become an important instrument for the measurement of displacement. In future, there is likely to be ever greater importance set on those measuring tasks which use sensors taking up very little space. One solution, proposed here, is a standing-wave interferometer, with a novel photoelectric detector. The latter is 'partially transparent and photoelectrically active', and scans the intensity profile of an optical standing-wave pattern. Arranging two of these transparent photoelectric detectors on the optical axis of the standing wave with the phase shifted permits bidirectional fringe counting. The transparent photoelectric detectors are basically pin-photodiodes with transparent contacts. Two sets of measurements were obtained, the first on a single transparent photoelectric detector and the second on a pair of transparent photoelectric detectors in the standing-wave pattern, and the results are discussed. It is shown that two phase-shifted photoelectric signals (sine and cosine) from two transparent photodetectors in different spatial positions on the optical axis of the standing wave can be received, and that the phase relation between the signals is a function of the distance.