Position measurements of multiple light beams with one position-sensitive detector (PSD)

A method for measurement of the positions of multiple light beams irradiating a single two-dimensional lateral-effect position-sensitive detector (PSD) is reported. The measurement method relies on using light sources each of which is modulated at different frequencies and then demodulated in the sensor signal processing circuit using pulse amplitude modulation (PAM). Experimental results show that the maximum difference between the measured positions of one light beam in the presence and absence of another beam is less than 0.25% of full scale. This difference is repeatable and almost uniform throughout the entire PSD workspace; therefore it does not affect the resolution and accuracy of the measurement if the multiple light beams are always present. The test results also show that no change in the linearity and resolution of the sensor results from using multiple light sources simultaneously. The number of light beams which can be used simultaneously is limited only by the bandwidth of the PSD and signal loss considerations