Ultra-Broadband Polarization Splitter-Rotator Based on the Mode Evolution in a Dual-Core Adiabatic Taper

A polarization splitter-rotator (PSR) based on the supermode evolution in a dual-core adiabatic taper with multiple segments is designed. For this dual-core adiabatic taper, one core becomes narrow and the other one becomes wide. The gap between them is kept constant except the input/output parts where these dual cores are separated gradually. When choosing some specific widths for the dual cores, mode hybridization between the TM ₀ supermode and the TE ₁ supermode happens. As a result, when light propagates along the dual-core adiabatic taper, the TM ₀ supermode launched from the input port can be efficiently converted to the TE ₁ supermode, which is mainly confined in the core connected to the cross port, and finally one has the TE ₀ mode output from the cross port. On the other hand, the TE ₀ mode launched from the input port is confined tightly in the core connected to the through port and finally outputs from the through port with a very low loss. For the structural design of the adiabatic taper, three operation wavelengths of 1450, 1550, and 1650 nm are considered simultaneously so that the PSR works well in a very broad band from 1450 to 1650 nm. Here, the widths of the multiple segments in the taper section are chosen optimally according to the mode hybridization regions of the dual-core waveguide when operating at the wavelengths of 1450, 1550, and 1650 nm. With this design method, the designed PSR based on silicon-on-insulator nanowires is about 240 μm long. The bandwidth is even as large as 300 nm (1450-1750 nm) for an extinction ratio of >16 dB and an excess loss of <;0.1 dB in theory.