Design of passive polarization beam splitter in silicon-on-insulator waveguides

Abstract

A passive polarization beam splitter in silicon-on-insulator (SOI) waveguides, which consists of two 3-dB multimode interference (MMI) couplers and two Mach-Zehnder interferometer (MZI) arms with the same length but different rib widths, has been proposed recently and a numerical method of design is needed because the analytical solution for this 3-dimensional (3D) SOI waveguides is difficult to achieve. The scalar finite difference beam propagation method (FD-BPM) is used to design the 3-dB MMI couplers and the positions of the input or output waveguides and the length of multimode waveguide are determined. In our design, the length of MMI couplers is 1228 micron when the width of rib is 36 micron. The propagation constants of TE-polarized and TM-polarized mode supported by 3D rib waveguides on SOI are calculated by the Semi-vector FD-BPM which is polarization related. From these data obtained for different rib widths (from 2.0 micron to 4.0 micron), the appropriate length of MZI arms is selected. In our example, the widths of two arms are 3.4 micron and 2.0 micron respectively and the length of arms is 1506 micron. The TE-polarized light and TM-polarized light are input to the splitter separately and the Semi-vector FD-BPM is used to check the design.