Two dimensional automatic alignment of pinhole integrated with photodiode

The authors use apparatus in which a Si micromachined pinhole surrounded by photodiode cells is used for automatic alignment. When the laser beam is apart from the pinhole and incident on the photodiode cells placed around it, the relative position of the laser spot from the pinhole can be found by comparing the photocurrents obtained from four photodiode cells. Using this signal as the input of the feedback control, actuators move the pinhole so that the laser beam can pass through the pinhole. In our previous study (1998), a one dimensional version of the automatic alignment was achieved using a Si micromachined pinhole and shape memory alloy actuators. In this study, two dimensional automatic alignment is described.