Waveguide Bends for Suppressed Mode Coupling

Waveguide bends are key components of photonic integrated circuits, enabling complex layouts and high packing densities. Often waveguides at bends are wide and consequently multi-mode for lower loss propagation. Higher order modes, which are excited by the bend curvature, may degrade performance for devices downstream, such as extinction ratio in modulators. It is demonstrated that bend curvature functions inspired by window functions used in digital signal processing can greatly suppress the undesirable generation of higher order modes. The proposed curvature functions include sine to the power of n, and Dolph-Chebyshev window. Coupled mode theory provides the insight that the suppression of higher order modes in a bend is related to the side-lobe suppression of the bend curvature Fourier transform. A particular application for the proposed bend geometries is mode division multiplexing, where inter-mode crosstalk may be significantly reduced.