Polarization Rotators in Add-Drop Filter Systems With Double-Ring Resonators

A design of highly integrated polarization rotators (PRs) with double-ring resonators in add-drop filter systems is demonstrated theoretically. Based on mode-evolution theory and 3D finite-difference time-domain simulation, two vertically stacked microrings with dislocation are designed and optimized, which efficiently decreases the size of PR to a double-ring structure with a radius of <;3.5 μm for the wavelength of 1.55 μm in a silicon-on-isolator system. Numerical simulations obtain an extinction ratio (ER) of -22 dB and an insertion loss of 0.07 dB with practical material parameters. This PR combines the advantages of the periodic spectrum of ring resonators and add-drop filtering functionality. The method and result presented here can be valuable for applications in polarization-diversity circuits.