Precise automatic alignment of a pinhole integrated with photodiodes

The spatial filter of a Si micromachined pinhole integrated with photodiodes is fabricated. The photodiode cells placed around the center pinhole can detect the relative position between the incident beam spot and the pinhole. In our previous study, the automatic alignment of the pinhole realized the accuracy of 1 micrometers using the feedback control based on the obtained position signal. To increase the alignment accuracy, the suitable design of the pinhole and the photodiode cell is necessary, since it decides the sensitivity to the laser spot position. The sensitivity is examined changing the separation length between the photodiode cells.