Strip-slot waveguide mode converter based on symmetric multimode interference

Optical mode mismatch makes coupling between strip and slot waveguides a tough issue in integrated photonics. This Letter presents both numerical and experimental results of a strip-slot mode converter based on symmetric multimode interference (MMI). Distinct from previous reported converters which gradually convert the mode through sharp tips, the proposed solution makes full use of the symmetry of the two-fold image of MMI, and its field distribution similarity with a slot waveguide to convert the mode. A converter based on this mechanism is able to convert light from a TE-polarized fundamental mode of a strip waveguide to that of a slot waveguide, and vice versa. Strip-slot waveguide coupling though this mode converter has a measured efficiency of 97% (-0.13 dB), and the dimensions are as small as 1.24 x 6 mu m. Further analysis shows that the proposed converter is highly tolerant to fabrication imperfections, and is wavelength-insensitive. (C) 2014 Optical Society of AmericaOpticsSCI(E)EI0ARTICLEzjzhou@pku.edu.cn195665-56683