Driven by an ever-increasing number of new services and applications, transport networks have been undergoing significant changes. In this paper, we describe several exciting technology directions associated with future optical transport networks. We review the status of 100G, which is now commercially available and entering volume deployments, and its applications in China. Beyond 100G is considered as the primary technology for the expansion of both channel and fiber capacity in the near term, and several enabling techniques are introduced. Then, key technologies, products, and future evolutionary options of Optical Transport Networks (OTNs) are extensively discussed. Compared to fixed bandwidth and coarse granularity of current WDM network, a flexible grid architecture is a desirable evolution trend, and key technologies and challenges are described. Finally, we illustrate the multi-dimension convergences in terms of IP and optical, Packet OTN (P-OTN), as well as Electronic Integrated Circuits (EICs) and Photonic Integrated Circuits (PICs). Transport networks are therefore in the process of becoming more broadband, robust, flexible, cost-effective and lower-power-consumptive.