Propagation of fundamental mode in regularly bending multi-mode waveguides.

Transmission of the fundamental mode in multi-mode waveguides is an effective scheme for a silicon-based platform to reduce scattering loss. However, the application of the scheme is usually limited to straight waveguides and restricted in multi-mode bending waveguides. This is because the fundamental mode of a straight waveguide is seriously disordered after passing the bend. In this work, we have presented a "matched bending radius" approach, by which an ultra-low loss and negligible modal disorder have been demonstrated in the Si and Si3N4 multi-mode waveguides. The estimated TE0 mode transmission factor is almost 0 dB at the matched bending radius, indicating that the fundamental mode can be re-generated after passing the multi-mode bending waveguide. The proposed approach will contribute to applying the low loss scheme in large-scale photonic integrated circuits. [ABSTRACT FROM AUTHOR]