Position and velocity sensing measurements using an integrated VCSEL and pin photodetector assembly

A position sensing optical microsystem that is low-power, non-contact and long-range was characterized. A vertical-cavity surface-emitting laser monolithically integrated with a photodetector packaged in a low profile assembly was used in conjunction with a metallic optical grating. By observing the modulated reflection of laser light off the grating collected by the detector, we can determine the speed and/or the relative position of the grating. The capability of the assembly as a sensor was investigated using a motorized stage and an air gantry motion system. On the air gantry system, the position sensing assembly measured the distance traveled to within 0.875 microns and the velocity to within 3% of the speed measured by conventional means. With the linear actuator, due to the discrete steps of operation, the measured distance was within 3.5 microns and the velocity to within 60%