Metamaterial-based ultrashort multimode waveguide taper with low intermodal crosstalk

We propose and theoretically demonstrate an ultrashort multimode waveguide taper based on the all-dielectric metamaterial. Attributed to the gradient index distribution of the metamaterial, the spot sizes of the four lowest-order transverse magnetic (TM) modes can be expanded in a short distance of 6 μm with negligible mode conversions. Numerical results prove that the insertion losses of the taper are lower than 1 dB, 1.12 dB, 1.26 dB and 1.66 dB for the TM 0 - TM 3 modes, respectively, and the intermodal crosstalk values are below -15 dB for the four modes, both in the wavelength range of 1.5 μm - 1.6 μm. To the best of our knowledge, this is the first multimode waveguide taper that has low intermodal crosstalk of < -15 dB over a 100-nm bandwidth.