Compact polarization beam splitter for silicon-based slot waveguides based on an asymmetrical multimode interference coupler

Abstract

A compact polarization beam splitter (PBS) for silicon-based slot waveguides is proposed based on a multimode interference coupler, where an asymmetrical multimode waveguide (AMW), cut by a right angle at one corner, is employed to efficiently separate the TE and TM modes. With the unique modal properties of the slot waveguides and corresponding optimized designs, the input TE mode can almost pass through the AMW and then enter into the bar port, while a mirror image is formed at the cross port for the input TM mode due to the self-imaging effect. Meanwhile, tapered waveguide structures and S-bend are incorporated into the designed PBS for further enhancing the performance. According to the numerical results, a PBS with an AMW of 2.3 μm in length is achieved, where the extinction ratios are 16.6 and 20.9 dB, respectively, for TE and TM modes, and the insertion losses are 1.37 and 0.81 dB, respectively, at the wavelength of 1.55 μm. For keeping extinction ratios over 15 and 20 dB for TE and TM modes, the bandwidths are around 59 and 73 nm, respectively, both covering the entire C-band. In addition, field evolution along the propagation distance through the PBS is also demonstrated.