Design and Simulation Analysis on TM–Pass GST-Assisted Asymmetric Directional Coupler-Based Polarizer

In this paper, the performance analysis on phase change material Germanium-antimony-tellurium-Ge2Sb2Te5 (GST) assisted silicon waveguide-based non-volatile polarizer is proposed. The designed structure contains a GST-assisted hybrid silicon waveguide and a regular silicon waveguide. By perfectly selecting the physical parameters of the proposed polarizer, the transverse electric (TE) mode is coupled and shifted to cross port as an output at the amorphous state of GST (aGST), and for the crystalline state of GST (cGST), it is coupled back to the bar port. Similarly, the transverse magnetic (TM) input mode passes through the bar port as an output at both the state of GST. The performance of the polarizer is evaluated by numerical calculations with the help of mode analysis of the 2-D finite element method (FEM) and it is further verified by the 3-D finite difference time domain method (FDTD). At 1550 nm operating wavelength, the calculated insertion loss (IL) is 8.02E-08 dB (negligible) for the TE input at aGST state and it is 0.08743 dB for TM input at the cGST state. And, for the TE input, the calculated cross-talk (CT) and extinction ratio (ER) are −77.3 dB and 77.3 dB, respectively at aGST state and for the TM input at the cGST state; the values of CT and ER are −16.9 dB and 16.8 dB. Finally, optimization of the proposed structure is realized via variations in the wavelength, GST width, GST height and the coupling gap by using the FEM analysis. Hence, a broadband (200 nm) and ultracompact (~6 μm) polarizer is proposed with high ER, low IL, and low CT, which can be suitable for on-chip tunable polarization optical circuits.