It is widely argued that optical communication and networking technologies will play a significant role in future data centers. Although the optical technologies have made a significant advancements over the last few years towards providing a very high data transmission rate as well as increased flexibility and efficiency, an additional effort is needed to investigate suitable architectures and technologies for optical network within (intra) and outside (inter) data centers. This paper presents a brief overview on optical networks for data centers. Furthermore, the paper provides a qualitative categorization of the proposed schemes based on the type of optical switches. In the end, future research direction and opportunities of optical interconnect for data centers are discussed.