Electrostatic micro torsion mirrors for an optical switch matrix

We have developed a new type of compact optical switch using silicon micromachining technique. Torsion mirrors (300 μm×600 μm) supported by thin polysilicon beams (16 μm wide, 320 μm long, and 0.4 μm thick) are arranged in a 2×2 matrix (total size 3 mm×5 mm, t 0.3 mm). The mirrors are independently attracted by electrostatic force of applied bias voltage to redirect the incident light in a free space. Using collimated beam fibers for optical coupling, we obtained small insertion loss (⩽-7.66 dB), considering the length of a light path (⩾10 mm), a large switching contrast (⩾60 dB), and small crosstalk (⩽-60 dB). The fabrication yield was higher than 80% thanks to the newly developed releasing technique that used a silicon oxide diaphragm as an etch-stop layer and as a mechanical support in the process. Holding voltage (⩽50 V) was lower than the voltage to attract the mirror (100~150 V) because of the hysteresis of angle-voltage characteristic of electrostatic operation