A Branch-Type TE/TM Wave Splitter Using a Light-Guiding Metal Line

The three-dimensional (3-D) beam-propagation method is applied to the analysis of a novel transverse electric/transverse magnetic (TE/TM) wave splitter using a light-guiding metal (Ag) line with an embedded dielectric (SiO₂) waveguide. Before analyzing the splitter, a mode converter with a tapered metal is designed to smoothly convert the guided mode of an embedded waveguide into the surface plasmon-polariton (SPP) mode, and vice versa. After demonstrating the effectiveness of a converter consisting of a two-step linear taper, the performance of the splitter is evaluated. To obtain a high coupling efficiency, the wavefront mismatch of the SPP mode is compensated for. In addition, a TE-pass polarizer is added to the TE output waveguide, reducing the undesirable TM wave. In contrast to the long device length of a conventional branch-type splitter (>1000 mum), the present splitter is found to have a noticeably short device length of less than 200 mum, although a loss of about 3 dB is observed for the TM wave. The crosstalk and the extinction ratio are, respectively, evaluated to be less than -15 dB and more than 15 dB for a branching angle of 16plusmn2deg at wavelengths of 1.31 and 1.55 mum