In recent years optical networks are developing towards high rate and wide bandwidth. Optical networks propagate a great amount of information, and its security issues are drawing more and more attention. Impact of high power signal on optical networks and protection technology has become a hotspot for research in the area of security of optical networks. Gain competition attack, inter-channel crosstalk attack, and intrachannel crosstalk attack caused by high power signal in optical networks are introduced, and attack impact caused by high power signal on legitimate signals in optical networks is also analyzed. Security protection technologies aiming at attack impact of high power signal in optical networks are summarized from the viewpoints of attack detection and location technology, secure routing protection technology and other protection technologies.