  The use of Passive Optical Networks (PONs) in modern and future data centers
can provide energy efficiency, high capacity, low cost, scalability, and
elasticity. This paper introduces a passive optical network design with 2-tier
cascaded Arrayed Waveguide Grating Routers (AWGRs) to connect groups of racks
(i.e. cells) within a data center. This design employs a Software-Defined
Networking (SDN) controller to manage the routing and assignment of the
networking resource while introducing multiple paths between any two cells to
improve routing, load balancing and resilience. We provide benchmarking results
for the power consumption to compare the energy efficiency of this design to
state-of-the-art data centers. The results indicate that the cascaded AWGRs
architecture can achieve up to 43% saving in the networking power consumption
compared to Fat-Tree data center architecture.
