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Miniaturized optical switches based on piezoelectrically driven microprism arrays

Using the principle of focussing an incoming beam onto a plane with special optical microstructures, novel miniaturized switching elements can be built up for different applications. As switching is achieved by a lateral movement of the microstructures, only small displacements (about 10 micrometers ) are sufficient for efficient beam manipulation. In this paper, we present the results of both theoretical and experimental investigations on a concept of multichannel beam deflection by microprisms located in the focal plane of an incoming beam. This concept is suitable for singlemode fiber switches. It is shown that nearly aberration free operation can be achieved by choosing the right substrate thickness and the axial focal position with respect to the microprisms for the cases of placing them on the front or rear substrate surface. A trade-off must be made between the numerical aperture of the focussed beam, the prism angles and the number of output channels of the deflecting element in order to achieve sufficient angular separation of the deflected beams. Two different techniques have been tested for microprism fabrication: wet anisotropic etching in silicon and a new method of mask projection onto scanned photoresist layers. Microprisms with sufficient optical quality have been fabricated with both methods. In experimental investigations, we showed that for a singlemode fiber 1 X 9-switch low insertion loss (< 1 dB) and low cross-talk between the output channels (-50 dB) can be obtained.