Silicon-on-insulator waveguide attracts intensive attention due to its high-refractive index contrast among various waveguide structures and compatibility with mature CMOS-compatible technologies. However, the strong modal birefringence of SOI waveguides usually makes the control of light polarization extremely challenging.

Recently, under the guidance of Prof. Lin Chen from Wuhan National Laboratory for Optoelectronics (WNLO), his PhD student Tian Zhang, cooperating with Xiang Yin and Prof. Xun Li from McMaster University, has proposed an ultra-compact polarization beam splitter, utilizing an asymmetrical directional coupler. The asymmetrical directional coupler is composed of a silicon waveguide and a graphene multilayer embedded silicon waveguide. The modal characteristics for the TM mode varies significantly, whereas that for the TE mode changes slightly for the graphene multilayer embedded silicon waveguide. Consequently, the launched TM mode can efficiently pass through the silicon waveguide with little influence from the graphene multilayer embedded silicon waveguide. Meanwhile, originating from a well-satisfied phase-matching condition for the TE mode, the launched TE mode experiences a strong coupling and finally outputs from the graphene multilayer embedded silicon waveguide. The proposed polarizer has several advantages: ultra-compact footprint, large extinction ratio, low insertion loss and tunable splitting-ratio power for TM mode.    

This work titled as "Ultra-compact polarization beam splitter utilizing a graphene-based asymmetrical directional coupler" has been recently published in Optics Letters (Vol. 41, Iss. 2, pp. 356-359, 2016) on 22th, January. This work was supported by the National Natural Science Foundation of China (Nos. 11104093 and 11474116).

Fig. 1 The schematic configuration of the proposed polarization beam splitter.

Fig. 2 Wavelength dependence of the designed polarization beam splitter.