Dual-axis torsional mirror Lucent lambda router optical switch

3 Dual-axis torsional mirror Lucent lambda router optical switch 

Two different types of optical switches have been developed. One is called 3-d, for three-dimensional switching, where optical signals are directed through a 3-d space. The other is called 2-d, because the optical signals are directed in the two-dimensional space above a wafer surface. For performance reasons, 3-d switches are used in larger arrays ( 32), 

To obtain flat mirrors, with a radius of curvature more than 250 mm, the processing conditions for the polysilicon and mirror metallization had to be controlled to minimize residual stresses and stress-gradients. The thickness of the polysilicon mirror membrane was 3.5 pm, a thickness that can be obtained by stacking Polyl (2 pm) and Poly2 (1.5 pm) in the PolyMUMPS process. 

To lift the reflector out of plane after it had been released, a special high-stress metallization layer was deposited on top of 1.5 pm thick, 100 pm wide polysilicon assembly arms. The composition of this high-stress layer (tensile) causes the arms to curl upward after release, lifting the mirror frame and locking it into place. When the assembly arms are released, they curl up into arcs with a radius of curvature R that is dependent on the thin-film stress. The height at a distance x from the anchor of the arm is given by 

If the end of the arm is acted on by a force F, the arm will be deflected downward by a distance given by 

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