All-optical tunable plasmon-induced transparency (PIT) finds great applications in the fields of ultrahigh-speed quantum information processing and integrated photonic circuits. Owing to the small third-order optical nonlinearity of conventional materials, the achieved operating pump intensity was as high as GW/cm2 order. Moreover, it is very difficult to obtain a material with a large nonlinearity and ultrafast response simultaneously at the optical communication range. This has seriously restricted the practical applications of PIT.

Gong’s group proposed a new strategy to achieve an ultrafast and large third-order optical nonlinearity at optical communication range. They fabricated a novel polycrystalline ITO/gold metamaterial. A large third-order nonlinear susceptibility was achieved by using quantum confinement provided by nanoscale crystal grains of polycrystalline ITO, the hot-electron injection from gold nanostructure to polycrystalline ITO, and the field reinforcement provided by plasmonic resonances. The threshold pump power was reduced by four orders of magnitude. The threshold pump intensity was reduced to 0.1 MW/cm2 order. An ultrafast response time of picoseconds order was maintained by using the fast recombination process of carriers in ITO crystal grains.

This work was published in Scientific Reports (Yu Zhu, Xiaoyong Hu, Yulan Fu, Hong Yang, and Qihuang Gong, “Ultralow-power and ultrafast all-optical tunable plasmon-induced transparency in metamaterials at optical communication range”, Scientific Reports 3, 2338 (2013)). This work was highly appraised by the reviewers “The authors succeeded to get a huge third-order nonlinear susceptibility and tune the resonant wavelength of PIT using low pump intensities between 0.1 and 1.0 MW/cm2. For conventional semiconductor materials, such studies are quite difficult.” “This work is of great fundamental interest in the field of plasmonics and metamaterial, and also has important potential for ultrafast integrated photonic devices”

The work was supported by the Creative Research Group Project of the National Natural Science Foundation of China, and the National Basic Research Program of China.