POSITION DETECTION OF MULTIPLE LIGHT-BEAMS USING PHASE DETECTION

Earlier work on lateral-effect position-sensitive detectors (PSD) has used an amplitude detection signal-processing scheme to determine the position of the centroid of the incident light beam on the PSD surface . In this work we introduce a phase detection method of position measu rement which is based on detecting the phase difference between the si nusoidal currents flowing through the metal electrodes. A distributed transmission line model for the PSD and a one-pole model for the trans impedance preamplifier are used in the analysis of the sensor. Experim ental results are presented and are found to be in close agreement wit h simulation results. It is seen that the spatial resolution is propor tional to the modulation frequency. With a light modulation frequency of 50 kHz and the introduction of frequency multiplication (x 8) after the transimpedance preamplifier, a spatial resolution of 2 mum is dem onstrated. For application in multi-degree-of-freedom position sensors , we demonstrate the simultaneous detection of centroids of multiple l ight beams using frequency division multiplexing. Application of the p hase method of position detection to a two-dimensional PSD shows a max imum deviation from linearity of 1% over the working range of the PSD.