Zero crosstalk in asymmetric multimode waveguides for higher-order mode crosstalk suppression via subwavelength...

We present a generalized zero-crosstalk design method for asymmetric multimode waveguides using anisotropic subwavelength grating (SWG) claddings. Based on non-orthogonal coupled-mode theory, we show that optical power transfer in asymmetric systems is governed by the effective coupling coefficient κ_eff, and the zero-crosstalk condition is achieved when κ_eff = 0. By engineering the anisotropic dielectric perturbation of the SWG cladding, the longitudinal field component contributing to κ_eff can be counterbalanced, enabling complete suppression of coupling between dissimilar waveguides and different orders of transverse-electric (TE) modes. Geometric parameter spaces achieving zero-crosstalk trajectories are identified, and the concept is validated with a manufacturable discrete SWG structure with strong tolerance to parameter deviations. This approach provides a scalable solution for higher-order mode crosstalk suppression in dense multimode photonic integrated circuits.