One-way optical power transmission in silicon-on-insulator (SOI) waveguide with broad passband and high efficiency

We propose a novel strategy to realize the broadband unidirectional optical power transmission in a silicon-on-insulator (SOI) waveguide. It is obtained by cascading a waveguide-mode converter and a mode filter along the SOI waveguide. Without violating the reciprocity, the unidirectional propagation works as a one-way mode conversion. By designing one section of partly etched waveguide as a mode converter and another section of 1D photonic crystal waveguide as a mode filter, we theoretically demonstrate that within the wavelength interval between 1.42 µm and 1.62 µm, the TE₀-like mode of the SOI waveguide can only pass through the cascaded structure in the forward direction and be converted into TM₀-like mode with a transmittance larger than 0.9. Meanwhile, the backward transmittance of TE₀-like mode is less than 0.01. At the wavelength 1.50 µm, the maximum ratio between the forward and backward transmittance reaches 35 dB. The broadband unidirectional propagation with large ratio and high transmittance origins from the independent designs of the mode converter and the mode filter in the proposed structure, which may provide a new way to control the modes of on-chip waveguides. (paper)