Silicon photonics has attracted tremendous research interest because it has a huge potential that enables on-chip photonic integrated circuits, and low power consumption. However, the polarization-dependent nature of these devices, e.g. polarization mode dispersion, polarization dependent loss, and polarization dependent wavelength shift, significantly deteriorates the practical performance. How to control of the polarization state of lighthas been becoming an important issue in silicon photonics.
Prof. Lin Chen has been devoted to the research of artificial electromagnetic metamaterials for many years. The response of the anisotropic metamaterial for different polarizations is quite different. Generally, people are mainly focused on the polarization control of light in free space owing to the fact that the coupling between the waveguide and metamaterial is a challenging issue, inducing the utilization of metamaterial for waveguide polarization control unrealistic. Based on the previous research on graphene's optical characteristics, Lin Chen's group have discovered that the graphene metamaterial has different response on different light polarizations, and strong coupling between the graphene metamaterial and waveguide can also be achieved, indicating the graphene metamaterial might play a peculiar role on waveguide polarization control. As the light polarization is parallel to the graphene, a weak light-graphene interaction will lead to a negligible effect on the light transmission. As for the light polarization is vertical to the graphene, graphene/light interaction become very strong. Recently, Prof. Chen, and his student Xiang Yin, cooperated with Prof. Xun Li, propose a graphene based TE-pass waveguide polarizer. In the research, theequivalent permittivity can be flexibly changed by tuning the chemical potential of graphene with gate voltage. As the equivalent permittivity reaches zero, light wave of TM mode will be squeezed into the graphene. The strong light-graphene interaction will lead to a large insertion loss for the TM mode. Meanwhile, graphene has negligible effect on the TE mode, resulting in a low loss for the TE mode. The proposed polarizer has several advantages: 1. Low insertion loss for the TE mode; 2. High extinction ratio; 3. Smaller footprint comparing with those polarizers reported.
This work titled as "Ultra-compact TE-pass polarizer with graphene multilayer embedded in a silicon slot waveguide" has been recently published in Optics Letters (Vol. 23, Iss. 9, pp. 11657-11664, 2015) on 15th, April. This work was supported by the National Natural Science Foundation of China (Grant No. 11474116).