Bent Embedded Optical Waveguide With a Loaded Metal Film for Reducing a Polarization Dependent Loss

The beam-propagation method is applied to the analysis of a bent embedded waveguide with a loaded metal film. As a basic study, coupled bent slab waveguides are treated to discuss their mechanism for reducing the pure bend and transition losses. Based on this study, a metal film is loaded on the bent embedded waveguide. The metal film serves to generate the surface plasmon-polariton mode for the transverse-magnetic (TM) wave, so that the embedded waveguide with the metal film can be regarded as coupled bent waveguides for the TM wave. This leads to reduction in the bend losses for the TM wave. As a result, a low polarization dependent loss (PDL) can be obtained over a wide spectral range, since the pure bend loss of the embedded waveguide for the TM wave is larger than that for the transverse-electric wave. Furthermore, the application to a trench structure with a depressed refractive index contributes not only to a low PDL but also to a low pure bend loss.