Hierarchical Scalable Photonic Architectures for High-Performance Processor Interconnection

This paper introduces two hierarchical optical structures for processor interconnection and compares their performance through analytic models and discrete-event simulation. Both architectures are based on wavelength division multiplexing (WDM) which enables multiple multi-access channels to be realized on a single optical fiber. The objective of the hierarchical architectures is to achieve scalability yet avoid the requirement of multiple wavelength tunable devices per node. Furthermore, both hierarchical architectures are single-hop: a packet remains in the optical form from source to destination and does not require cross dimensional intermediate routing. The first structure is physically hierarchical but wavelength flat: all nodes share the same wavelength space. The second structure is a wavelength multiplexed hierarchical structure with wavelength channel re-use at each level, allowing it to be scaled to very large system sizes. It employs acousto-optic tunable filters in conjunction with passive couplers to partition the traffic between different levels of the hierarchy without electronic intervention. An advantage of the second structure is its ability to dynamically vary the bandwidth provided to different levels of the hierarchy. The architectures are compared in terms of complexity and performance scalability.