MIMO channel for modal multiplexing in highly overmoded optical waveguides

In order to meet the increasing demand for data rate in modern multiprocessor systems optical transmission has become an important technology. Due to cost reasons only highly multimodal waveguides come into question for mass-producible board level interconnects. We present the idea of an optical multiple-input multiple-output (MIMO) channel by having more than one data source at the channel input and a multisegmented photodetector at the channel output. We develop channel models for the optical MIMO channel and show that orthogonality between modes in a highly multimodal waveguide can be exploited to submit independent data streams over different mode groups (modal multiplexing). Our performance results in terms of bit error rates show that the MIMO scheme outperforms the SISO scheme when the data rate is the same. Hence, optical MIMO schemes allows either to increase the data rate by keeping the amount of intersymbol interference (ISI) constant or to reduce the ISI by keeping the data rate constant.