Due to the fast growth of internet services, datacenter related traffic has become the major part of the global network traffic. As a main technology for high-speed data transmission, optical communication technologies have been widely used in today's datacenter networks, from a few meter server-to-server interconnects to transoceanic datacenter-to-datacenter optical networks. Here the optical communication technologies for datacenters were reviewed, including technologies connecting datacenters in wider-area networks and metro-area networks as well as optical interconnect technologies within datacenters, and the advantages and disadvantages of some technologies in the networks were discussed.