Optical data center networks (DCNs) are becoming increasingly attractive due to their technological strengths compared with the traditional electrical networks. However, existing optical DCNs are either hard to scale, vulnerable to single point of failure, or provide limited network bisection bandwidth for many practical data center workloads. To this end, we present WaveCube, a scalable, fault-tolerant, high-performance optical DCN architecture. To scale, WaveCube removes MEMS,¹ a potential bottleneck, from its design. WaveCube is fault-tolerant, since it does not have single point of failure and there are multiple node-disjoint parallel paths between any pair of top-of-rack switches. WaveCube delivers high performance by exploiting multi-pathing and dynamic link bandwidth along the path. For example, our evaluation results show that, in terms of network bisection bandwidth, WaveCube outperforms prior optical DCNs by up to 400% and is 70%-85% of the ideal non-blocking network (ı.e., theoretical upper bound) under both realistic and synthetic traffic patterns. WaveCube's performance degrades gracefully under failures-it drops 20% even with 20% links cut. WaveCube also holds promise in practice-its wiring complexity is orders of magnitude lower than Fattree, BCube, and c-Through at scale, and its power consumption is 35% of them.