Vertical mirrors fabricated by reactive ion etching for fiber optical switching applications

We report on vertical mirrors fabricated by deep reactive ion etching of silicon. In view of their application in fiber optical switches the mirror height is 75 mu m. So the mirror covers well the fiber core of a single mode fiber, when the fiber is placed in a groove of the same depth and etched at the same time as the mirror. A minimal mirror thickness of 2.3 mu m was achieved, resulting in an aspect ratio over thirty. The verticality was better than 89.3 degrees. The surface roughness of the etched surface is 36 nm rms. For an increased reflectivity the silicon mirrors are coated with aluminium. Their reflectivity was measured to be 76 %. To obtain an uniform etch depth, etching is stopped on a buried oxide layer. This allows to integrate at the same time mirrors with suspension and actuation structures as well as fiber-alignment grooves in one processing step. Using this technology we have fabricated a fiber optical switch with promising performance: The coupling loss in the OFF position is 2.5dB and 4dB in the ON position. The switching time is below 0.2 ms.