Comparison of two approaches for implementing free-space optical interconnection networks

A particular design choice in the implementation of free-space optical interconnection networks (e.g. photonic backplanes) based on cascaded image-relay lenses is investigated. In these systems, a communication link can be implemented either by a single hop between source and destination nodes with the signal remaining in the optical domain through many image-relay stages, or by multiple hops between adjacent nodes with the signal undergoing optical-electrical conversion and vice versa at intermediate nodes (which act as repeaters). These two approaches place different demands on the optical system and the optoelectronic interface. We compare the raw bandwidth-per-link available in two example networks (the mesh and the completely connected network) using a model of the bandwidth and power consumption of an optoelectronic data channel and considerations on the aggregate bandwidth of the optoelectronic interface chip. We find that the single-hop approach provides a higher bandwidth-per-link. For example, the single-hop bandwidth-per-link is three times greater than the multiple-hop value for a mesh network of 49 nodes and for a completely connected network of 13 nodes. The advantage can increase further as the network size grows. The methodology is also applicable to the investigation of other implementation choices in optoelectronic interconnects.