Dr. Yuan-Mu Yang from Tsinghua University, China, visited C-UFO on 30th May, 2018 and gave the public talk on " Efficient active optical material ". Prof. Qi-Dai Chen hosted the talk.Combined with his own work, Yuan-Mu Yang  introduced  the potential value of metamaterials' application in the field of optics, described how to improve the efficiency of active optical materials, and shared his research and exploration work in this respect. After the report, the speaker also discussed with teachers and students, and the site interaction was warm, and the report achieved good results.