Design of a compact polarization splitter composed of a multiple-slotted waveguide and a silicon nanowire

A polarization splitter (PS) based on a directional coupler (DC) composed of a vertical multiple-slotted waveguide (MSW) and a silicon nanowire is proposed and designed by using a modified three-dimensional full-vectorial beam propagation method (BPM). By utilizing the unique modal properties of the slotted waveguide, the coupling of the DC in quasi-TE modes can be almost neglected, and only that in quasi-TM modes is considered, leading to a compact PS. Moreover, the MSW has the advantages of both strong field confinement and high birefringence, which improve the performance of the device. The numerical results show that a PS with a length of 20.5 mu m in the coupling region is achieved with a bandwidth of up to 22 nm (ranging from 1.540 to 1.562 mu m) with the crosstalk lower than -20 dB. In addition, the fabrication tolerances for the structural parameters are investigated in detail. The evolution of the injected field along the propagation distance through the PS is also demonstrated.