Masaya Horino

Fabrication of an optical beam scanning array integrating mirror and lens arrays by passive self-alignment using precisely formed through-holes

An optical beam scanning array (OBSA) integrating two mirror arrays and a collimator-lens array was fabricated. The passive self-alignment inserting a pin into a through-hole was carried out for integration of the mirror arrays and the collimator-lens array. The mirror arrays consist of a mirror substrate with 35 single-axis-rotational mirrors and an electrode substrate for actuating the corresponding mirror by electrostatic force. Each substrate includes two kinds of through-holes: one for passing a collimated-optical beam through, the other for inserting a pin. The conditions for deep-reactive-ion etching (DRIE) of silicon were optimized to form through-holes suitable for passive self-alignment. DRIE from both surfaces of a silicon wafer under the optimized DRIE conditions—a C4F8/SF6 gas-flow ratio of 90% and a bias power in SF6 gas of 110 W—formed precision through-holes with an average undercut of 3.4 µm and an average sidewall angle of 89.9°. The passive self-alignment then yielded an assembly deviation of less than 17.5 µm, which meets the specification of less than 50 µm. This means that passive self-alignment using a through-hole formed under the optimized DRIE conditions can be exploited to make OBSAs without requiring optical alignment of mirrors and lenses.