Numerical study on flat dispersion in a single-layer Si3N4 coupled-waveguides with four zero-dispersion wavelengths for supercontinuum generation

We achieve a flat broadband dispersion profile in a dual-core silicon nitride (Si3N4) waveguide utilizing the mode coupling between the quasi-TE00 mode in a narrow waveguide and the quasi-TE10 mode in a wide waveguide. Mode coupling extends the anomalous dispersion region and flattens the entire dispersion, creating four zero dispersion wavelengths. The generated dispersion profile varies between-10 and 13 ps/(nm center dot km) over an octave bandwidth from 1150 nm to 2425 nm. A two-octave supercontinuum spectrum from 750 nm to 3001 nm can be generated through the 5 mm long Si3N4 waveguide by launching a 50-fs 5-kW hyperbolic secant input pump pulse at anomalous dispersion region. Significant spectral broadening is also observed, by pumping in the normal dispersion region. The proposed Si3N4 waveguide has only a single-layer core structure and is compatible with the photonic Damascus process. Moreover, the obtained dispersion profile is insensitive to the gap distance between the narrow and wide waveguides, making it easier to fabricate than slot-assisted waveguide structures.