An optical backplane for high bit rate data transmission between processor boards is presented. The backplane consists of lowloss polymer multimode waveguides, integrated micromirrors and lenses for focusing/collimation. Free space transmission is used for the coupling between processor boards and the backplane. Due to an expanded beam, high alignment tolerances between the boards and the backplane are obtained. Backplanes are realized for a 55 cm (21 in.) interconnection length, for a ring network and for a 4ϫ4 star network. For each backplane, data transmission with a bit rate Ͼ1 Gbit/s is demonstrated and first environmental tests are successfully passed.

Optical links are expected to overcome the limitations imposed by electrical links even for short transmission distances as they have done in telecommunications trunk networks. For board-to-board and board-to-multiboard communication we have developed an optical backplane for applications in mobile systems. Compared to fiber based realizations it is compact, rugged and has the potential to be fabricated at low cost. The main features of the optical backplane in planar technology are free space expanded beam transmission between boards and backplane and guided wave transmission within the backplane. No optical connectors are required. Due to the expanded beams and highly multimode waveguides large coupling tolerances of several 100 tm are achieved. Low loss polymer backplane waveguides (3dB/rn) allow transmission lengths of more than 19". Demonstrators for board-to-board interconnections and star networks have been realized. Transmission experiments at lGBitJs have been successfully performed. Environmental tests prove the thermal stability ofthe polymer waveguides.

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