Single-mode, single-polarization and dispersion-flattened waveguides based on silicon carbide and diamond

•Low loss, flexible dispersion engineering, and pure single-polarization and single-mode operation are achieved at the same time.•Ultra-low and flat dispersion that varies from −1 to 1 ps/nm/km is obtained over an octave-spanning bandwidth from 1.81 to 3.63 μm, with four zero-dispersion wavelengths (ZDWs).•In comparison with a standard strip waveguide, scattering loss is greatly reduced by 8.6 times.•The proposed waveguides are easier to process without dry etching SiC and diamond and show better fabrication tolerance.