Optics is an important research domain both for its scientific interest and industrial applications. In this paper, we constructed
a citation network of papers and performed topological clustering method to investigate the structure of research and to detect
emerging research domains in optics. We found that optics consists of main five subclusters, optical communication, quantum
optics, optical data processing, optical analysis and lasers. Then, we further investigated the detailed subcluster structures
in it. By doing so, we detected some emerging research domains such as nonlinearity in photonic crystal fiber, broad band
parametric amplifier, and in-vivo imaging techniques. We also discuss the distinction between research front and intellectual
base in optics.