Frequency-multiplexed multiple-beam optical position detector using phase detection

TL;DR: In this article, the authors demonstrate a technique to make an optical position sensitive detector (PSD) smarter, in this case capable of reading centroid positions of multiple light intensity distributions which are modulated at different frequencies.

Abstract: The `smartness' of the optical position sensitive detector (PSD) lies in its capability to read the centroid position of the incident optical intensity distribution, independent of total intensity. Most measurands of interest to the smart structures community can be made to appear as changes in spatial distributions of optical intensity, such as interference pattern shifts, motion of reflected spots from moving or deforming objects, or changes in relative intensity among two or more light sources. In this work we demonstrate a technique to make a PSD smarter, in this case capable of reading centroid positions of multiple light intensity distributions which are modulated at different frequencies. This capability can be exploited in multi-degree-of- freedom position sensors as well as for multiplexing outputs from sensors distributed over a smart structure or skin. In this novel operating mode, the PSD behaves as a transmission line with detectors at either end and a current source at the centroid. Measurements of phase difference versus spot position for different modulation frequencies show good agreement with a superposition-based numerical model. Multiple light distributions incident on the same PSD can be frequency multiplexed. Spatial resolution increases with modulation frequency for positions near the center of the working range.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.