Improved automatic alignment of pinhole integrated with photodiode

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. The automatic alignment of the pinhole was realized using a feedback control based on the position signal obtained from the photodiode cells. In our previous study, the alignment accuracy achieved was ±0.5 μm for a pinhole of 50 μm diameter. In this study, the design is improved by reducing the separation length between the surrounding photodiode cells. An alignment accuracy of ±0.03 μm was demonstrated.