Upgrading multimode channels in board-level optical interconnects

Abstract

Board-level optical interconnects are currently the most promising alternative to overcome the capacity limitations inherent to copper-based electronic data transmission in high-end systems such as servers, switch-routers and supercomputers. Even if these short-range optical interconnects are to be confined «inside the box» the underlying planar waveguides are still facing transmission distances that may scale up to several meters. Obviously both the extra-large sample size and the industrial production environment associated to state-of-the-art multilayer PCBs are in conflict with the clean-room processing usually involved for single- mode optical waveguides. Eligible waveguide technologies, however, will always adhere to large waveguide cross-sections up to 100 μm x 100 μm and, hence, to highly-multimode optical transmission channels supporting up to several thousand waveguide modes. In order to counteract the detrimental impact of intermodal dispersion we have proposed novel transmission schemes relying on modal multiplexing, where the mode diversity is exploited either in the spatial domain or in the reciprocal space (associated to the mode’s transversal wave vector). In the presentation we shall discuss a comprehensive dynamical physical channel model that allows us to advocate an «upgrading» towards an optical (IM/DD-) MIMO system for aggregated data rates accessing the multiple 10 Gb/s range.