Fig. 1. (a) Schematic view of the waveguide section; (b) SEM view of spiral waveguide; (c) and (d) TE mode profile at 1200 nm wavelength for a 700 nm-wide waveguide and a 1200 nm-wide waveguide, respectively; (e) schematic view of the final design for the straight waveguide (top view).

Fig. 2. (a) Refractive index of N-rich SiNx measured by ellipsometry compared to Si3N4; (b) calculated dispersion parameter in an N-rich SiNx waveguide for different widths.

Fig. 3. Schematic view of the experimental setup. HWP, half-wave plate; PBS, polarization beam splitter; 60× and 20×, objectives.

Fig. 4. (a) Experimental spectra for the 8.6 mm-long, 1200 nm-wide waveguide (blue dotted line) and the threefold 3 mm-long waveguide (black line) for an input peak power of 3.8 kW; (b) and (c) optical images of the 3 mm-long straight waveguide and the 8.6 mm-long spiral, respectively, from above, showing green and blue scattered light; (d) experimental (black lines) and simulated (green lines) spectra for different input peak powers; from bottom to top: 250 W, 950 W, 3.8 kW. Curves are arbitrarily shifted for better understanding. (e) Spectral evolution along the propagation direction for the simulated SCG 3.8 kW peak power.

Fig. 5. Integrated dispersion for the two sections of the waveguide.

Fig. 6. (a) First-order degree of coherence plotted as a function of wavelength and propagation distance; (b) and (c) individual simulated spectra (blue lines), average of all the spectra (black line), and degree of mutual coherence (orange line) for a 3 mm-long and a 1.7 mm-long waveguide, respectively.