Silicon is the most widely used material in modern electronics industry, both in Taiwan and the world, due to its natural abundance, semiconductor/doping property, mass production, and capability to be densely integrated. It is a long-awaited goal to amalgamate photonics with the advantages of silicon, i.e. silicon photonics. In the field of electronics, the key success relies on nonlinear components, such as transistors, that can control electric signal via voltage or current, i.e. all-electric control. Similarly, in silicon photonics, light-control-light, or equivalently all-optical control, is a highly desirable function. However, the optical nonlinearity of silicon is too weak to achieve efficient all-optical control.
Under the support of MOST “Outstanding young scientist project”, MAGIC program, and regular projects for one decade, as well as long-term support from NTU Molecular Imaging Center, Prof. Shi-Wei Chu of NTU Physics has formed an international and national collaboration team, including Prof. Junichi Takahara and Prof. Katsumasa Fujita of Osaka University, Prof. Xiangping Li of Jinan University, Dr. Kung-Hsuan Lin of Academia Sinica, Dr. Chih-Wei Chang of NTU, and Prof. Kuo-Ping Chen of NCTU. In two recent publications in top journal “Nature Communications”, they jointly revealed that silicon nanostructures, which exhibit special electromagnetic resonance mode that can enhance light interaction, plus thermally isolated nano-environment that enables efficient temperature increase, can provide 3-4 orders of magnitude enhancement of optical nonlinearity over bulk silicon. The underlying mechanism is photothermal interaction between light and silicon nanostructures, but impressively, the response time is a few orders faster than common photothermal responses, reaching nanosecond scale. The giant and fast nonlinearity allows nearly 100% all-optical modulation of scattering light from a single silicon nanoparticle, at GHz speed. Furthermore, we combine the giant nonlinearity and super-resolution techniques to realize 40-nm resolution, featuring not only one order resolution enhancement, but also label-free imaging in silicon nanostructures. These results open up a new avenue in silicon photonics, toward the goal of all-optical circuits with silicon.