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Micromachined polysilicon torsion mirrors for an electrostatic optical switch in a free space

We have developed a new type of compact optical cross- connector by silicon micromachining technique. Torsion mirrors (300 micrometers X 600 micrometers ) supported by thin poly silicon beams (16 micrometers wide, 320 micrometers long, 0.4 micrometers thick) are arranged in a 2 X 2 matrix (3 mm X 5 mm) and independently operated by electrostatic force to reflect the incident light in a free-space. Using collimated-beam optical fibers for optical coupling, we obtained small insertion loss (-7.6 dB), a large attenuation ratio (>=60 dB), and small crosstalk (<EQ60 dB). The fabrication yield was higher than 80% thanks to the newly developed releasing technique using a silicon oxide diaphragm as an etch-stop layer and as a mechanical support in the process. Holding voltage (50 V) was reduced lower than the voltage to attract the mirror (100 approximately 150 V) using the large hysteresis of the angle-voltage characteristic of electrostatic operation.