Sub-wavelength grating assisted mode order converter on the SOI substrate.

We have designed three mode order converters using the sub-wavelength grating on the silicon-on-insulator substrate. The proposed mode order converters can separately realize the mode order conversion from the fundamental transverse electric mode to the first-order transverse electric mode (TE0-to-TE1), the second-order transverse electric mode (TE0-to-TE2) and the third-order transverse electric mode (TE0-to-TE3) with compact device sizes and good performances. The simulation results show that the mode order conversion efficiencies of TE0-to-TE1, TE0-to-TE2 and TE0-to-TE3 are larger than 94.4%, 95.7% and 83.7% in the wavelength ranging from 1.5 µm to 1.6 µm, the corresponding device length are 8.72 µm, 4.98 µm and 14.54 µm. In addition, the mode order converter can be fabricated with only once etching which will be advantage to the device fabrication.