Electrostatic micro torsion mirrors for an optical switch matrix

We have developed a new type of a compact optical switch by silicon micromachining technique, Torsion mirrors (300 mu m x 600 mu m) supported by thin polysilicon beams (16 mu m wide, 320 mu m long, and 0.4 mu m thick) are arranged in a 2 x 2 matrix (total size 3 mm x 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 (less than or equal to -7.66 dB), considering the length of a light path (greater than or equal to 10 mm), a large switching contrast (greater than or equal to 60 dB), and small crosstalk (less than or equal to -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 (less than or equal to 50 V) was lower than the voltage to attract the mirror (100 similar to 150 V) because of the hysteresis of angle-voltage characteristic of electrostatic operation.