To cope with the ever-increasing traffic growth of cloud computing and big-volume data services, a high-throughput, low-latency and energy-efficient data center network (DCN) architecture is desired. Recent advances in photonics make it feasible to exploit advantages of optical networking in designing data centers. In this paper we propose a novel optical DCN architecture that leverages already-available microsecond switching time optical components, together with an efficient traffic scheduler, which features a centralized control plane. Our architecture provides highly flexible connections between racks and has low reconfiguration time. Packet-level simulation results show that, with suitable choices of network dimensioning parameters, the proposed architecture can achieve low latency even with high offered load.