Vertical coupling and polarization-independent subwavelength grating beam splitter based on silicon-on-insulator

We describe a novel beam splitter with advantages of a single-layer, compact and vertical coupling structure, which is based on Bragg diffraction conditions and phase match equation. FDTD method is used to optimize the design of beam splitter. The result of simulation shows that both polarizations incident light are separated into two beams of nearly equal power (near 43% split and 45% split, respectively), which are coupled into opposite directions in the waveguide. For TE mode, the coupling efficiency of the right direction and the left direction are 42.54% and 43.68, respectively. That of TM mode is 46.03% and 44.07%, respectively. The power difference for two polarizations of two output port is less than 1% and 2%, in addition, 40nm and 65nm bandwidth is achieved.