Broadband TE-pass slot waveguide polarizer using an asymmetrical directional coupler.

A compact TE-pass polarizer for silicon-based slot waveguides is numerically proposed based on a directional coupler where an asymmetrical slot waveguide (ASW) and hybrid plasmonic waveguide (HPW) are involved. The input section is linearly tapered to an ASW to markedly enlarge the modal birefringence. Beneficially, only the TM mode can be coupled into the adjacent HPW and attenuated while the injected TE mode just passes through the slot waveguide without coupling by properly choosing the dimensions. As a consequence, an efficient TE-pass polarizer can be implemented. From the simulation results, the proposed polarizer has an extinction ratio (ER) of 45 dB and insertion loss (IL) of 0.44 dB at 1.55 μm, and its bandwidth exceeds 130 nm with the ER>30  dB and IL<1  dB. In addition, fabrication tolerances to the key structural parameters are analyzed and field evolution along the propagation distance is also demonstrated.