Fibre coupling to SiGe optoelectronic devices

Recent years have seen the rapid evolution of silicon-based optoelectronics . The absorption properties of Si1-xGex alloys make them excellent material s for the realisation of photodetectors operating at the near-infrared wave lengths of 1.3 and 1.55 mum which are important for fibre optic communicati on systems. An important design consideration for such systems is the effic ient coupling of optical fibres to optoelectronic integrated circuits. A Si 1-xGex rib waveguide spot-size transformer is presented that performs two e ssential roles: the transformation of the large spot fibre to a small spot waveguide mode, and subsequently the transfer of the mode from a passive Si waveguiding region to an active Si1-xGex region where optical absorption m ay occur. This transformation is accomplished by the use of a tapered waveg uide structure. An analysis technique based on the spectral index method is used to investigate the local modal behaviour of the structure and experim ental results confirm its successful operation.